I 3D P MATERIAL EXTRUSION UL 94 UL 746A MATERIAL P · extrusion and do not distinguish the reported results from material properties measured for 3D printed test specimens. UL investigated

TECHNICAL RESEARCH REPORT

INFLUENCE OF 3D PRINTING BY MATERIAL EXTRUSION ON UL 94 AND UL 746A MATERIAL PROPERTIES

Thomas Fabian, PhD Priyansu Panda Research & Development George Fechtmann Shaun Kubik Amanda Griffin Performance Materials Melissa Albrecht Khalid Rafi, PhD Additive Manufacturing

Issue date: December 13, 2018

Material Extrusion 3D Printing Influence on UL 94 and UL 746A Material Properties P. ii

All rights reserved. This document may not be reproduced or distributed without permission of UL LLC

Copyright © 2018 UL LLC

EXECUTIVE SUMMARY

Mechanical properties of 3D printed materials have repeatedly been demonstrated to significantly vary based on how test specimens were printed. These variations are substantially greater than for conventional injection molded samples. There is a lack of knowledge, however, on the influence of 3D printing on ignition, flammability and electrical material properties associated with UL safety standards. These material properties and performance characteristics when listed on UL’s QMFZ2 – Plastics category (a.k.a. Yellow Card) are relied upon by product developers and UL engineers. Yet the data on Yellow Cards are primarily representative of test specimens formed through conventional manufacturing processes like injection molding and film extrusion and do not distinguish the reported results from material properties measured for 3D printed test specimens. UL investigated the influence of different combinations of material extrusion print parameters and build strategies on ignition, flammability, and electrical properties. Dielectric strength, volume resistivity, hot wire ignition (HWI), comparative tracking index (CTI), high-current arc ignition (HAI), and UL 94 V flammability were assessed for a flame retardant poly(acrylonitrile-butadiene-styrene) (frABS) and a polyetherimide (PEI). The frABS polymer was printed on a popular desktop 3D printer anticipated to be on the low cost end of 3D printers used to make products submitted to UL for certification whereas the PEI was printed on a common industrial-grade 3D printer. Respective materials were also evaluated as injection molded specimens for comparison of material properties measured for test specimens made by 3D printing. While this investigation was by no means all encompassing, particularly with regards to the limited number of investigated materials, print parameters, and build strategies, several important findings expected to translate to other polymers and possibly other printing technologies were made: 1. Material performance properties determined for traditional molding processes are not

representative of properties expected for 3D printed parts.

2. Print quality was more consistent with the industrial-grade printer than the desktop printer.

3. Print parameters and build strategies influenced results such that the same material on the same printer yielded critically different performance.

4. No 3D printed build outperformed (e.g., greater dielectric strength / resistance, better flame rating, shorter burning time) injection molded test specimens except for comparative tracking index (CTI).

5. Comparative tracking index (CTI) measurements of 3D printed specimens appeared to yield misleading results because of a test method artifact.

Based on the work report herein, the following recommendations are made:

Material Extrusion 3D Printing Influence on UL 94 and UL 746A Material Properties P. iii



1. Material performance properties used to assess compliance of 3D printed components and products should be based on test specimens printed same way as the 3D printed component / product and not on traditionally molded test specimens.

2. Guidelines for assessing the “true” CTI of materials used in 3D printed components and parts should be developed.

3. The influence of inherent material characteristics and physical characteristics of printed specimens on performance properties should be investigated.

4. Investigation on the influence of 3D printing should be expanded to include long-term thermal aging effects as described in UL 746C

5. Investigation on the influence of 3D printing should be expanded to other 3D printing technologies

Keywords 3D printing, ABS, additive manufacturing, air gap, build orientation, dielectric strength, fused deposition modelling (FDM), fused filament fabrication (FFF), electrical properties, flammability, ignition, material extrusion, PEI, polyetherimide, raster angle, tip size, UL 94, volume resistivity.

Material Extrusion 3D Printing Influence on UL 94 and UL 746A Material Properties P. iv



TABLE OF CONTENTS EXECUTIVE SUMMARY ............................................................................................................ ii INTRODUCTION .......................................................................................................................... 1 OBJECTIVE AND SCOPE ............................................................................................................ 3

Objectives ................................................................................................................................. 3 Limitations in Scope ................................................................................................................. 3

SAMPLES....................................................................................................................................... 4 Injection Molding...................................................................................................................... 4 3D Printed frABS ...................................................................................................................... 4 3D Printed PEI .......................................................................................................................... 5

EXPERIMENTAL .......................................................................................................................... 7 Volume Resistivity (VR) Tests ................................................................................................. 7 Dielectric Breakdown Voltage (BV) and Strength (DS) Tests ................................................. 7 Comparative Tracking Index (CTI) Tests ................................................................................. 7 Hot Wire Ignition (HWI) Tests ................................................................................................. 8 High-Current Arc Ignition (HAI) Tests .................................................................................... 8 UL 94 Flammability Tests – Vertical ....................................................................................... 9 UL 94 Flammability Tests – 5VB ............................................................................................. 9

RESULTS ..................................................................................................................................... 10 Print Quality ............................................................................................................................ 10 Volume Resistivity (VR) Tests ............................................................................................... 11 Dielectric Breakdown Voltage (BV) and Strength (DS) Tests ............................................... 14 Comparative Tracking Index (CTI) Tests ............................................................................... 19 Hot Wire Ignition (HWI) Tests ............................................................................................... 21 High-Current Arc Ignition (HAI) Tests .................................................................................. 24 UL 94 Flammability Tests – Vertical ..................................................................................... 26 UL 94 Flammability Tests – 5VB ........................................................................................... 36

ANALYSIS ................................................................................................................................... 38 Effect of Sample Conditioning ............................................................................................... 38 Effect of Sample Surface on Comparative Tracking Index (CTI) Tests ................................ 41 3D Printed vs Injection Molded .............................................................................................. 43 Influence of 3D Printing Parameters ....................................................................................... 50

FINDINGS .................................................................................................................................... 59 RECOMMENDATIONS .............................................................................................................. 60

Material Extrusion 3D Printing Influence on UL 94 and UL 746A Material Properties P. 1



INTRODUCTION

Product developers rely on the electrical, flammability, mechanical, and thermal properties listed for polymer materials certified by UL under category QMFZ2 – Plastics (a.k.a. Yellow Card) to select polymers that comply with their product’s functional and safety requirements. Likewise, UL engineers and project handlers rely on Yellow Card listed material properties to verify the suitability of materials used in products submitted for evaluation to a UL standard. The material properties and performance characteristics listed on UL’s 46,000+ Yellow Cards are primarily representative of test specimens formed through conventional manufacturing processes like injection molding and film extrusion and do not distinguish the reported results from material properties measured for 3D printed test specimens. Mechanical properties of materials when 3D printed (including those listed on Yellow Cards) have repeatedly been demonstrated to significantly vary based on how test specimens were printed as well as from the properties measured for the same material when injection molded. Research published in the 2002 Rapid Prototyping Journal demonstrated that the tensile strength of an ABS polymer 3D printed by material extrusion could vary by more than five-fold depending upon the orientation of the printed raster (axial versus transverse) and be as much as an order of magnitude less than a dimensionally equivalent injection molded specimen.1 These variations in tensile strength for 3D printed and conventional injection molded specimens can be readily explained by polymer entanglement theory. Polymer molecules in a well-mixed state are physically tangled together connecting in all unconfined directions and it is this entangled molecular structural conformation that allows mechanical stresses to be transferred from one molecule to another. Polymer molecules that are not entangled cannot transfer stresses efficiently and therefore result in structurally weak areas. Thus, properly injection molded samples are comprised of well-mixed polymer forced into the mold cavity and then cooled to “lock” the entangled molecular structure. In contrast, samples 3D printed by material extrusion are formed by extruding well-mixed, molten polymer into a bead that is deposited alongside other beads. The polymer molecules within the bead are entangled like in the injection molded samples and can transfer stress along the bead (i.e. the raster direction), however, the polymer molecules at the interface between the adjacent beads may or may not be entangled depending upon molecular mobility and diffusion time. If the sample was printed such that the molecules at the bead interfaces had sufficient time to diffuse and entangle across the interface (typically crossing the interface three times), then mechanical integrity at the interface would be comparable to within the bead. If there was insufficient time / energy for the molecules to entangle across the interface, then the interface would be structurally weak relative to the well-mixed molecules along the bead and therefore prone to mechanical failure. Hence mechanical stress transfer in the 3D printed test specimens is more efficient along the axial direction of the bead than the transverse direction as reported by Ahn et al.

1 Ahn SH, Montero M, Odell D, Roundy S, Wright PK. Anisotropic material properties of fused deposition modeling ABS. Rapid Prototyping Journal. 2002; 8(4): 248-257.




Despite ample evidence of the influence of 3D printing on printed part mechanical properties2, there is a lack of knowledge on the influence of 3D printing on safety-critical performance properties such as ignition, flammability, and electrical response associated with UL safety standards. Yet the same polymer entanglement theory in combination with the sample geometry would be expected to yield differing performance characteristics. For example, injection molded specimens are solid throughout with minimal local density variations and smooth sides whereas specimens 3D printed by material extrusion can have gaps and voids between adjacent deposited beads and a non-smooth surface stemming from the exposed bead edges. The air in the gaps and voids created by the 3D printing process have a different dielectric property than the polymer and could therefore act as an insulator to electric current. Likewise, the gaps and voids could act as thermal insulation to heat exposure thereby effectively reducing the thermal mass of the exposed surface and increasing ignitability as compared to a solid injection molded sample. The greater surface area density of the 3D printed sample would also accelerate flame propagation and potentially lower the flame rating of a 3D printed sample relative to an injection molded sample. Finally, vertically oriented voids could act like chimneys to redistribute heat along the inside of the printed specimen and introduce fresh air to further accelerate sample flammability. UL investigated the influence of the four material extrusion user-controllable printer parameters and specimen build variations expected to most influence printed part performance. Two polymers commonly used in the electronics and electrical appliance market, a black color flame retardant poly(acrylonitrile-butadiene-styrene) (frABS) and a natural color polyetherimide (PEI), were printed using systematically different build orientation, build strategy (i.e., raster direction in successively printed layers), layer thickness (via printer tip size), and air gap. The printed specimens were assessed for dielectric strength, volume resistivity, hot wire ignition (HWI), comparative tracking index (CTI), high-current arc ignition (HAI), and UL 94 V flammability performance. The frABS polymer specimens were printed on a popular desktop 3D printer anticipated to be on the low cost end of 3D printers used to make products submitted to UL for certification whereas the PEI specimens were printed on a common industrial-grade 3D printer. Respective materials were also evaluated as injection molded specimens for comparison of material properties measured for test specimens made by 3D printed. Results of the investigation reported herein provide the preliminary knowledge necessary to develop guidelines for certifying polymer materials intended for 3D printing and guidance for drafting requirements to address the gap in performance between 3D printed parts and conventional injection molded and extruded parts.

2 Ahn SH, Montero M, Odell D, Roundy S, Wright PK. Anisotropic material properties of fused deposition modeling ABS. Rapid Prototyping Journal. 2002; 8(4): 248-257. Es-Said OS, Foyos J, Noorani R, Mendelson M, Marloth R. Effect of layer orientation on mechanical properties of rapid prototyped samples. Materials and Manufacturing Processes. 2000; 15(1); 107-122. Galantucci LM, Lavecchia F, Percoco G. Study of compression properties of topologically optimized FDM made structured parts. Manufacturing Technology. 2008; 57; 243-246. Sood AK, Ohdar RK, Mahapatra SS. Parametric appraisal of mechanical property of fused deposition modeling processed parts. Materials and Design. 2010; 31; 287-295. Bagsik A, Schoeppner V, Klemp E. FDM part quality manufactured with Ultem*9085. 14th International Scientific Conference on Polymeric Materials. September 15-17 2010; Halle (Saale).




OBJECTIVE AND SCOPE

The investigation focused on understanding the impact of 3D printing, also referred to as additive manufacturing (AM), by material extrusion on printed polymer material properties. OBJECTIVES The objectives of this study were to explore the influence of various 3D printing and build parameters on UL 94 and 746A material properties and compare results to properties obtained from conventional injection molding. LIMITATIONS IN SCOPE This investigation was focused on ignition, flammability, electrical, and thermal distortion properties for two materials respectively printed by material extrusion on a desktop 3D printer and an industrial-grade 3D printer as well as injection molded specimens of the respective materials. The investigation did not cover: • Assessment of the physical characteristics of printed or molded specimens • Influence of injection molding parameters • Influence of other identified and unidentified printer and build parameters • Influence of material extrusion 3D printing parameters on other performance properties or

the physical characteristics of the printed specimens • Influence of material extrusion 3D printing parameters and materials on the performance of

finished parts and components • Consistency of results for different material extrusion 3D printer models • Consistency of results for printers using other 3D printing technologies • Consistency of results for other polymer materials, metals, or ceramics • User-safety of printers and materials




SAMPLES

Two commercially available polymeric materials were purchased for this investigation: 1. frABS: black color flame retardant poly(acrylonitrile-butadiene-styrene) filament with a 2.85

mm diameter; UL 94 V-0 rating claimed 2. PEI: natural color polyetherimide filament with a 2.85 mm diameter. Test specimens of the two sample materials were made by conventional injection molding and 3D printing as described below. INJECTION MOLDING Injection molded test specimens of the frABS and PEI sample materials were made by UL’s Performance Materials lab in Krefeld, Germany. frABS filament was chopped and dried in circulating air at 80 °C (175 °F) for 2 hours prior to molding and PEI filament was chopped and dried in vacuum at 150 °C (300 °F) for 6 hours prior to molding. Two basic sample shapes were molded using an Arburg 370S-800-150 injection molding machine (25 mm screw diameter): 1. UL 94 flame bars: 125 × 13 × 3.0 mm thick 2. Plaques: 60 × 60 × 3.0 mm thick Flame bars were molded using 2-cavity, end-gate molds at a barrel temperature of 280 °C (540 °F) and a mold temperature of 70 °C (158 °F). Plaques were molded using 2-cavity, fan-gate molds respectively at a barrel temperature of 380 °C (716 °F) and a mold temperature of 150 °C (300 °F). No mold release agent was used during the formation of any samples. 3D PRINTED frABS Three basic frABS test specimen shapes were printed using a popular desktop 3D printer: 1. UL 94 flame bars: 125 × 13 × 3.0 mm thick 2. CTI Plaques: 60 × 60 × 3.0 mm thick 3. Plaques: 120 × 80 × 3.0 mm thick Test specimens were printed starting with an outer contour and then infilled using different combinations of build orientation, air gap, raster angle, and tip size depending on the physical limitations of printing the test specimens. The twenty-seven combinations of build parameter were defined using a full factorial design of experiment with center point as laid out in Table 1. Note that CTI plaque specimens printed in the Y-orientation (builds 10-18) were simply 90° rotations of CTI plaque specimens printed in the X-orientation (builds 1-9). The build plate (print surface) was cleaned of all traces of oil, grease and fingerprints and then coated with a layer of adhesive prior to printing. Test specimens were printed directly on the adhesive layer as illustrated in Figure 3. Printed test specimens were manually separated from the adhesive layer by knife; supporting material was removed using diagonal cut pliers.




Table 1: 3D build parameter combinations for frABS test specimens.

UL 94 Flame Bar, CTI Plaque and Plaque Specimens Build No.

Build Orientation

Tip Size (mm)

Raster Angle Air Gap

1 X 0.21 0/90 -15% 2 X 0.21 0/90 0% 3 X 0.21 45/45 -15% 4 X 0.21 45/45 0% 5 X 0.28 30/60 -8% 6 X 0.33 0/90 -15% 7 X 0.33 0/90 0% 8 X 0.33 45/45 -15% 9 X 0.33 45/45 0%

10 Y 0.21 0/90 -15% 11 Y 0.21 0/90 0% 12 Y 0.21 45/45 -15% 13 Y 0.21 45/45 0% 14 Y 0.28 30/60 -8% 15 Y 0.33 0/90 -15% 16 Y 0.33 0/90 0% 17 Y 0.33 45/45 -15% 18 Y 0.33 45/45 0% 19 Z 0.21 0/90 -15% 20 Z 0.21 0/90 0% 21 Z 0.21 45/45 -15% 22 Z 0.21 45/45 0% 23 Z 0.28 30/60 -8% 24 Z 0.33 0/90 -15% 25 Z 0.33 0/90 0% 26 Z 0.33 45/45 -15% 27 Z 0.33 45/45 0%

Figure 1: Illustration of test specimen printing arrangement.

3D PRINTED PEI Three basic PEI test specimen shapes were printed using a common industrial-grade 3D printer: 1. UL 94 flame bars: 125 × 13 × 3.0 mm thick 2. CTI Plaques: 60 × 60 × 3.0 mm thick 3. Plaques: 100 × 100 × 1.0 mm thick Test specimens were printed starting with an outer contour and then infilled using different combinations of build orientation, air gap, raster angle, and tip size depending on the physical limitations of printing the test specimens. The 26 to 30 combinations of build parameter were defined using full factorial designs of experiment with center point as laid out in Table 2 for the respective sample shapes. Note that plaques printed in the Y-orientation (builds 11-20) were simply 90° rotations of plaques printed in the X-orientation (builds 1-10).

ABS Specimen

Glue Adhesive Layer




Table 2: 3D build parameter combinations for PEI test specimens.

UL 94 Flame Bar and CTI Plaque Specimens Plaque Specimens Build No.

Build Orientation

Tip Size (mm)

Raster Angle

Air Gap (mm)

Build No.

Build Orientation

Tip Size (mm)

Raster Angle

Air Gap (mm)

1 X 0.254 0/90 -0.127 1 X 0.254 0/90 -0.127 2 X 0.254 0/90 0.127 2 X 0.254 0/90 0.127 3 X 0.254 +45/-45 -0.127 3 X 0.254 +45/-45 -0.127 4 X 0.254 +45/-45 0.127 4 X 0.254 +45/-45 0.127 5 X 0.254 +60/-30 0 5 X 0.254 +60/-30 0 6 X 0.33 0/90 -0.127 6 X 0.33 0/90 -0.127 7 X 0.33 0/90 0.127 7 X 0.33 0/90 0.127 8 X 0.33 +45/-45 -0.127 8 X 0.33 +45/-45 -0.127 9 X 0.33 +45/-45 0.127 9 X 0.33 +45/-45 0.127 10 X 0.33 +60/-30 0 10 X 0.33 +60/-30 0 11 Y 0.254 0/90 -0.127 11 Y 0.254 0/90 -0.127 12 Y 0.254 0/90 0.127 12 Y 0.254 0/90 0.127 13 Y 0.254 +45/-45 -0.127 13 Y 0.254 +45/-45 -0.127 14 Y 0.254 +45/-45 0.127 14 Y 0.254 +45/-45 0.127 15 Y 0.254 +60/-30 0 15 Y 0.254 +60/-30 0 16 Y 0.33 0/90 -0.127 16 Y 0.33 0/90 -0.127 17 Y 0.33 0/90 0.127 17 Y 0.33 0/90 0.127 18 Y 0.33 +45/-45 -0.127 18 Y 0.33 +45/-45 -0.127 19 Y 0.33 +45/-45 0.127 19 Y 0.33 +45/-45 0.127 20 Y 0.33 +60/-30 0 20 Y 0.33 +60/-30 0 21 Z 0.254 0/90 -0.127 21 Z 0.254 0 0.127 22 Z 0.254 0/90 0.127 22 Z 0.254 0 0 23 Z 0.254 +45/-45 -0.127 23 Z 0.254 0 -0.127 24 Z 0.254 +45/-45 0.127 24 Z 0.33 0 0.127 25 Z 0.254 +60/-30 0 25 Z 0.33 0 0 26 Z 0.33 0/90 -0.127 26 Z 0.33 0 -0.127 27 Z 0.33 0/90 0.127 28 Z 0.33 +45/-45 -0.127 29 Z 0.33 +45/-45 0.127 30 Z 0.33 +60/-30 0

Test specimens were printed directly on a polyethersulfone (PES) build sheet adhered to the build table via vacuum. A base layer of the PEI material was initially printed on the polymer build sheet followed by a layer of polyethersulfone (PES) support material. The test specimens were then printed on the PES support material layer. The arrangement of build materials is illustrated in Figure 3. Printed test specimens were manually separated from the PES support material layer by knife; PEI supporting material and excess PEI material were removed using an ultrasonic cutter.

Figure 2: Illustration of test specimen printing arrangement.

PEI Specimen

PES Support PEI Base Layer

PES Build Sheet




EXPERIMENTAL

VOLUME RESISTIVITY (VR) TESTS 3D printed and molded plaque specimens were evaluated for volume resistivity in accordance with ASTM D 257 (IEC 60167) as referenced in UL 746A Section 22. For each build set, five specimens were tested following conditioning of at least 48 hours at 23.0 ±2.0 °C (73.4 ±3.6 °F) and 50 ±5% relative humidity (“as-received”) and five specimens were tested following conditioning of 96 hours at 35.0 ±1.0 °C (95.0 ±1.8 °F) and 90 ±2% relative humidity (“oven-aged”). DIELECTRIC BREAKDOWN VOLTAGE (BV) AND STRENGTH (DS) TESTS The 3D printed and molded plaque specimens used for volume resistivity assessment were subsequently evaluated for dielectric breakdown voltage and strength in accordance with ASTM D 149 (IEC 60243) as referenced in UL 746A Section 21. For each build set, five specimens were tested following conditioning of at least 48 hours at 23.0 ±2.0 °C (73.4 ±3.6 °F) and 50 ±5% relative humidity (“as-received”) and five specimens were tested following conditioning of 96 hours at 35.0 ±1.0 °C (95.0 ±1.8 °F) and 90 ±2% relative humidity (“oven-aged”). COMPARATIVE TRACKING INDEX (CTI) TESTS 3D printed and molded CTI plaque specimens were evaluated for comparative tracking index ratings in accordance with IEC 60112 as referenced in UL 746A Section 24. Five specimens were tested for each build set. Specimens were typically evaluated at 300 V and then voltage was increased or decreased at 25 V increments, as appropriate, to identify the highest voltages at which all five specimens survived 50 and 100 drops respectively. 3D printed samples were oriented such that the raster angle of the surface to be tested was oriented relative to the long axis of the electrode cross section (i.e. the 5 mm long side) as depicted in Figure 4. Typically, the top of the printed sample was tested however in certain cases the bottom of the printed sample was tested. The tested surfaces and the relative angles between the electrodes and rasters are indicated in Table 3 for the different frABS and PEI samples.

Figure 3: Example of relative angle between printed raster and electrodes (electrode cross-section depicted in

blue).




Table 3: CTI test sample orientation details for frABS and PEI samples.

frABS Build No. Tested Surface

Relative Angle of Raster to Electrodes

PEI Build No. Tested Surface

Relative Angle of Raster to Electrodes

1 Top 0 ° 1 Top 90 ° 2 Top 0 ° 2 Top 90 ° 3 Top 45 ° 3 Top 45 ° 4 Top 45 ° 4 Top 45 ° 5 Top 60 ° 5 Top 30 ° 6 Top 0 ° 6 Top 90 ° 7 Top 0 ° 7 Top 90 ° 8 Top 45 ° 8 Top 45 ° 9 Top 45 ° 9 Top 45 °

10 Top 90 ° 10 Top 30 ° 11 Top 90 ° 11 Top 0 ° 12 Bottom 45 ° 12 Top 0 ° 13 Bottom 45 ° 13 Bottom 45 ° 14 Top 30 ° 14 Bottom 45 ° 15 Top 90 ° 15 Top 60 ° 16 Top 90 ° 16 Top 0 ° 17 Bottom 45 ° 17 Top 0 ° 18 Bottom 45 ° 18 Bottom 45 ° 19 Top 0 ° 19 Bottom 45 ° 20 Top 0 ° 20 Top 60 ° 21 Top 45 ° 21 Top 0 ° 22 Top 45 ° 22 Top 90 ° 23 Top 30 ° 23 Top 45 ° 24 Top 0 ° 24 Top 45 ° 25 Top 90 ° 25 Top 30 ° 26 Top 45 ° 26 Top 0 ° 27 Top 45 ° 27 Top 90 °

Inj. Mold. na na 28 Top 45 ° na = not applicable 29 Top 45 °

30 Top 30 ° Inj. Mold. na na na = not applicable

HOT WIRE IGNITION (HWI) TESTS 3D printed and molded UL 94 flame bar specimens were evaluated for resistance to ignition from an electrically heated wire in accordance with ASTM D 3874 (IEC 60695-2-20) as referenced in UL 746A Section 32. Five specimens were tested for each build set. HIGH-CURRENT ARC IGNITION (HAI) TESTS 3D printed and molded UL 94 flame bar specimens were evaluated for resistance to ignition from high-current arcing in accordance with UL 746A Section 33. Five specimens were tested for each build set.




UL 94 FLAMMABILITY TESTS – VERTICAL 3D printed and molded UL 94 flame bar specimens were evaluated for UL 94 flammability ratings in accordance with UL 94 Section 8, 50W (20 mm) Vertical Burning Test. For each build set, ten specimens were tested following conditioning of at least 48 hours at 23.0 ±2.0 °C (73.4 ±3.6 °F) and 50 ±5% relative humidity (“as-received”) and ten specimens were tested following conditioning in an air-circulating oven for 168 ±2 hours at 70.0 ±2.0 °C and then cooled for at least 4 hours in a desiccator at 23.0 ±2.0 °C and <20 % relative humidity (“oven-aged”). One end of a vertically oriented test specimen was exposed to a nominally 20 mm high blue (methane) flame for 10 seconds. The flame was removed and the time for any flame (afterflame) to cease, t1, was measured. The flame was then reapplied for an additional 10 seconds and removed. The time for the second afterflame to cease, t2, and the time for afterglow to cease, t3, was measured. The test was conducted 300 mm above absorbent cotton. UL 94 FLAMMABILITY TESTS – 5VB 3D printed and molded PEI UL 94 flame bar specimens were evaluated for UL 94 5VB flammability ratings in accordance with UL 94 Section 9, 500 W (125 mm) Vertical Burning Test; 5VA or 5VB. For each build set, ten specimens were tested following conditioning of at least 48 hours at 23.0 ±2.0 °C (73.4 ±3.6 °F) and 50 ±5% relative humidity (“as-received”) and ten specimens were tested following conditioning in an air-circulating oven for 168 ±2 hours at 70.0 ±2.0 °C and then cooled for at least 4 hours in a desiccator at 23.0 ±2.0 °C and <20 % relative humidity (“oven-aged”). One end of a vertically oriented test specimen was exposed to a nominally 125 mm high blue (methane) flame for 5 seconds and then removed for 5 seconds. This flame application and removal sequence was repeated four additional times. After the fifth flame application, the time for the flame (afterflame) to cease was measured. The test was conducted 300 mm above absorbent cotton.




RESULTS

PRINT QUALITY 3D printed frABS and PEI test specimens were qualitatively assessed to gauge the difference in print quality between the two 3D printer models. In general, the print quality of the frABS test specimens printed on the desktop 3D printer was less than that of equivalent PEI test specimens printed on the industrial-grade 3D printer as defined by visual consistency of the surface rasters. Examples of test specimens printed on the two printer models are shown in Figure 5. The frABS test specimen surface (Figure 5 left image) exhibited uneven light reflection along the raster direction and the cross-raster direction indicating inconsistent surface quality. In contrast, the PEI test specimen surface (Figure 5 right image) did not exhibit either inconsistency observed for the frABS printed test specimens. It did however exhibit a “tiger-banding” pattern parallel to one set of edges.

Figure 4: Examples of (left) frABS 3D printed on the desktop printer and (right) PEI 3D printed on the

industrial-grade printer.

Roughness of the top and bottom surfaces of the 3D printed specimens was also visually distinct, Figure 6. The bottom surface, i.e. the surface in contact with the support or adhesive laver during printing, was not as smooth as the top surface.

Figure 5: Examples of top and bottom surfaces of PEI flame bars printed in horizontal orientation.




VOLUME RESISTIVITY (VR) TESTS Volume resistivity tests were completed at UL’s Performance Materials lab in Krefeld, Germany. Results for the sets of five replicates at each condition are listed in Table 4 and Table 5 and plotted in Figure 7 and Figure 8 respectively for the two materials.

Table 4: Mean and s.d. volume resistivity test results for frABS samples.

Build No. “As-Received” “Oven-Aged”

Thickness (mm)

Volume Resistivity (Ohm·cm)

Thickness (mm)


1 2.982 ±0.046 (7.18 ±3.94) ×1016 3.041 ±0.035 (8.00 ±9.87) ×1016 2 3.102 ±0.049 (2.89 ±3.75) ×1017 3.090 ±0.052 (8.51 ±14.5) ×1016 3 3.011 ±0.070 (8.25 ±4.16) ×1016 3.010 ±0.030 (6.34 ±4.59) ×1016 4 3.040 ±0.074 (10.6 ±1.96) ×1016 2.969 ±0.046 (1.45 ±1.88) ×1017 5 3.126 ±0.086 (10.1 ±4.19) ×1016 3.164 ±0.051 (5.00 ±4.23) ×1016 6 3.141 ±0.062 (8.33 ±3.52) ×1016 3.164 ±0.086 (3.05 ±2.91) ×1016 7 3.133 ±0.062 (11.9 ±9.47) ×1016 3.149 ±0.062 (7.06 ±6.27) ×1016 8 3.122 ±0.044 (5.10 ±5.87) ×1016 3.120 ±0.037 (4.37 ±5.73) ×1016 9 3.196 ±0.054 (4.66 ±5.80) ×1017 3.215 ±0.033 (4.68 ±6.37) ×1016 10 3.053 ±0.079 (8.03 ±7.26) ×1016 3.012 ±0.092 (4.45 ±2.84) ×1016 11 3.040 ±0.075 (1.02 ±1.10) ×1017 3.060 ±0.067 (3.21 ±2.78) ×1016 12 2.967 ±0.075 (5.59 ±2.17) ×1016 3.006 ±0.072 (3.05 ±3.10) ×1016 13 2.989 ±0.075 (1.41 ±1.03) ×1017 3.052 ±0.033 (5.68 ±4.74) ×1016 14 3.072 ±0.080 (1.74 ±1.54) ×1017 3.131 ±0.050 (9.29 ±7.98) ×1015 15 3.159 ±0.057 (15.0 ±4.70) ×1016 3.210 ±0.037 (2.86 ±2.56) ×1016 16 3.188 ±0.025 (1.56 ±2.15) ×1017 3.240 ±0.046 (1.56 ±1.21) ×1016 17 3.153 ±0.010 (1.57 ±1.50) ×1017 3.123 ±0.045 (11.4 ±6.38) ×1014 18 3.201 ±0.046 (2.06 ±2.40) ×1017 3.237 ±0.058 (1.70 ±3.47) ×1016 19 3.047 ±0.103 (6.48 ±2.79) ×1016 3.009 ±0.036 (10.4 ±2.18) ×1014 20 3.065 ±0.051 (7.92 ±3.43) ×1016 3.028 ±0.060 (8.20 ±3.15) ×1016 21 2.977 ±0.022 (5.23 ±2.44) ×1016 2.983 ±0.038 (8.58 ±1.89) ×1016 22 2.949 ±0.015 (5.76 ±4.59) ×1016 2.967 ±0.040 (4.02 ±3.71) ×1016 23 2.961 ±0.050 (10.1 ±2.89) ×1016 2.962 ±0.019 (6.66 ±2.74) ×1016 24 3.023 ±0.049 (9.18 ±5.04) ×1016 3.079 ±0.034 (2.96 ±5.68) ×1017 25 3.083 ±0.037 (6.21 ±4.46) ×1016 3.087 ±0.026 (5.02 ±2.03) ×1016 26 3.004 ±0.010 (5.24 ±4.21) ×1016 3.041 ±0.035 (4.34 ±2.68) ×1016 27 3.068 ±0.056 (3.18 ±2.45) ×1016 3.026 ±0.025 (7.49 ±6.85) ×1016

Inj. Mold. 3.004 ±0.002 (1.96 ±2.14) ×1017 3.017 ±0.005 (11.5 ±5.58) ×1016




Table 5: Mean and s.d. volume resistivity test results for PEI samples.

Build No. “As-Received” “Oven-Aged”

Thickness (mm)


Thickness (mm)


1 1.073 ±0.007 (16.6 ±8.25) ×1016 1.069 ±0.003 (13.8 ±6.32) ×1016 2 1.028 ±0.021 (5.19 ±5.85) ×1016 1.028 ±0.012 (2.88 ±2.65) ×1016 3 1.063 ±0.024 (9.57 ±3.56) ×1016 1.054 ±0.021 (8.52 ±7.12) ×1016 4 1.071 ±0.010 (2.94 ±1.80) ×1016 1.070 ±0.017 (2.95 ±4.35) ×1016 5 1.039 ±0.013 (12.5 ±8.24) ×1016 1.040 ±0.014 (6.13 ±11.9) ×1017 6 1.059 ±0.008 (2.15 ±1.14) ×1017 1.050 ±0.025 (15.8 ±6.62) ×1016 7 1.029 ±0.010 (1.06 ±1.89) ×1016 1.027 ±0.021 (1.30 ±2.60) ×1016 8 1.075 ±0.023 (15.4 ±5.58) ×1016 1.058 ±0.017 (7.34 ±3.84) ×1016 9 1.027 ±0.050 (2.86 ±5.56) ×1016 1.043 ±0.038 (7.86 ±14.1) ×1015 10 1.034 ±0.016 (11.9 ±9.82) ×1016 1.033 ±0.021 (8.00 ±4.27) ×1016 11 1.047 ±0.033 (16.6 ±4.29) ×1016 1.049 ±0.034 (9.54 ±2.11) ×1016 12 1.067 ±0.008 (4.76 ±4.07) ×1016 1.066 ±0.011 (5.17 ±6.26) ×1015 13 1.048 ±0.016 (13.1 ±8.78) ×1016 1.042 ±0.016 (2.98 ±4.40) ×1017 14 1.017 ±0.013 (8.10 ±7.75) ×1016 1.025 ±0.012 (11.1 ±8.22) ×1015 15 1.050 ±0.021 (13.1 ±8.78) ×1016 1.044 ±0.042 (12.1 ±6.39) ×1016 16 1.036 ±0.018 (12.2 ±5.46) ×1016 1.056 ±0.013 (1.95 ±1.17) ×1017 17 1.043 ±0.006 (1.10 ±1.06) ×1017 1.037 ±0.021 (1.52 ±2.49) ×1015 18 1.025 ±0.012 (2.32 ±2.33) ×1017 1.027 ±0.010 (14.8 ±7.74) ×1016 19 1.043 ±0.025 (5.24 ±7.42) ×1016 1.062 ±0.066 (2.17 ±2.35) ×1016 20 1.036 ±0.027 (2.11 ±1.31) ×1017 1.031 ±0.022 (1.68 ±1.47) ×1017 21 1.085 ±0.009 (2.72 ±3.53) ×1017 1.081 ±0.012 (14.3 ±8.68) ×1016 22 1.063 ±0.008 (1.77 ±1.48) ×1017 1.075 ±0.021 (7.44 ±7.20) ×1016 23 1.083 ±0.029 (8.84 ±5.63) ×1016 1.109 ±0.039 (2.43 ±2.80) ×1016 24 1.289 ±0.018 (2.07 ±4.07) ×1017 1.300 ±0.016 (3.98 ±3.40) ×1016 25 1.292 ±0.014 (2.56 ±3.63) ×1017 1.302 ±0.011 (6.37 ±4.19) ×1016 26 1.299 ±0.018 (1.56 ±1.70) ×1016 1.303 ±0.008 (1.80 ±2.88) ×1017

Inj. Mold. 1.013 ±0.002 (4.78 ±1.13) ×1017 1.016 ±0.002 (6.02 ±11.3) ×1017




Figure 6: Volume resistivity test results for frABS samples. Error bars are s.d.

Figure 7: Volume resistivity test results for PEI samples. Error bars are s.d.




DIELECTRIC BREAKDOWN VOLTAGE (BV) AND STRENGTH (DS) TESTS Dielectric breakdown voltage and strength tests were completed at UL’s Performance Materials lab in Krefeld, Germany. “Oven-aged” 3D printed PEI build nos. 9 through 26 and the “oven-aged” injection molded PEI specimens were tested on a different high voltage tester than the other PEI specimens and the frABS specimens. This high voltage tester had a maximum voltage limit of 15.0 kV which was lower than the high voltage tester used for the frABS, “as-received” PEI, and “oven-aged” PEI build nos. 1 through 8. Results for the sets of five replicates at each condition are listed in Table 6 and Table 7 and plotted in Figure 9 through Figure 12 respectively for the two materials. Specimens that did not breakdown or flashover within the capability limits of the utilized high voltage tester were assigned the maximum voltage of 15.0 kV for the purposes of determining a minimum mean breakdown voltage and for calculation of dielectric strength (mean breakdown voltages and dielectric strengths including such specimens are identified as a minimum with a “>”). Dielectric breakdown occurred at the edge of the electrode for all specimens except the following which did not breakdown or flashover within the capability limits of the utilized test instrument:

• Two “oven-aged” PEI specimens from Build No. 11 • Four “oven-aged” PEI specimens from Build No. 13 • One “oven-aged” PEI specimen from Build No. 16 • Four “oven-aged” PEI specimens from Build No. 18 • All five “oven-aged” PEI specimens from Build Nos. 21-26 • All five “oven-aged” injection molded PEI specimens




Table 6: Mean and s.d. dielectric breakdown voltage and strength test results for frABS samples.

Build No.

“As-Received” “Oven-Aged”

Thickness (mm)

Breakdown Voltage

(kV)

Dielectric Strength (kV/mm)

Thickness (mm)

Breakdown Voltage

(kV)


1 2.982 ±0.050 49.7 ±4.2 16.7 ±1.4 3.010 ±0.037 46.7 ±4.4 15.3 ±1.5 2 3.100 ±0.045 39.4 ±8.9 12.7 ±2.8 3.068 ±0.041 43.7 ±4.5 14.2 ±1.6 3 2.994 ±0.057 46.5 ±5.2 15.6 ±1.8 2.988 ±0.049 46.2 ±4.3 15.4 ±1.7 4 3.018 ±0.089 44.2 ±2.4 14.7 ±1.1 2.968 ±0.057 47.0 ±2.5 15.8 ±1.1 5 3.102 ±0.083 49.8 ±5.5 16.2 ±2.1 3.156 ±0.044 45.5 ±3.2 14.4 ±1.0 6 3.146 ±0.065 43.4 ±5.5 13.8 ±1.6 3.144 ±0.069 44.4 ±4.6 14.0 ±1.1 7 3.114 ±0.061 44.8 ±7.0 14.4 ±2.2 3.134 ±0.054 47.1 ±5.1 14.8 ±1.3 8 3.116 ±0.039 42.5 ±4.6 13.7 ±1.6 3.108 ±0.031 39.1 ±2.9 12.6 ±1.0 9 3.182 ±0.057 43.8 ±8.1 13.7 ±2.5 3.202 ±0.030 44.1 ±6.0 13.8 ±1.9

10 3.042 ±0.077 54.7 ±7.6 18.0 ±2.9 2.992 ±0.083 50.2 ±3.4 16.8 ±1.2 11 3.032 ±0.080 46.5 ±12.5 15.4 ±4.3 3.056 ±0.076 46.8 ±7.6 15.3 ±2.6 12 2.948 ±0.073 36.8 ±10.7 12.6 ±3.9 2.988 ±0.070 43.9 ±3.8 14.7 ±1.2 13 2.980 ±0.067 39.1 ±8.1 13.1 ±2.8 3.024 ±0.027 43.4 ±5.8 14.3 ±1.9 14 3.040 ±0.073 48.1 ±1.8 15.8 ±0.8 3.116 ±0.049 44.7 ±3.8 14.5 ±1.0 15 3.148 ±0.081 45.7 ±5.0 14.5 ±1.8 3.182 ±0.048 49.9 ±3.6 15.7 ±1.1 16 3.180 ±0.024 40.5 ±4.1 12.8 ±1.3 3.210 ±0.035 47.9 ±3.0 14.9 ±1.0 17 3.116 ±0.011 42.9 ±5.5 13.8 ±1.8 3.102 ±0.054 43.7 ±4.3 14.1 ±1.3 18 3.184 ±0.060 38.9 ±3.5 12.2 ±1.3 3.222 ±0.054 41.2 ±3.9 12.8 ±1.2 19 3.018 ±0.070 49.1 ±2.6 16.2 ±0.7 2.982 ±0.033 48.2 ±1.0 16.2 ±0.4 20 3.026 ±0.068 48.0 ±2.2 15.9 ±0.7 2.980 ±0.058 49.5 ±2.1 16.6 ±0.4 21 2.898 ±0.100 49.7 ±1.6 16.8 ±0.5 2.948 ±0.044 49.7 ±2.3 16.8 ±0.6 22 2.940 ±0.023 48.0 ±1.2 16.3 ±0.2 2.930 ±0.028 44.9 ±13.3 15.3 ±4.5 23 2.950 ±0.039 42.6 ±2.5 14.4 ±0.8 2.918 ±0.016 42.7 ±6.8 14.6 ±2.3 24 3.008 ±0.046 40.0 ±7.3 13.3 ±2.4 3.034 ±0.029 43.7 ±2.2 14.4 ±0.7 25 3.062 ±0.036 41.3 ±11.2 13.5 ±3.6 3.042 ±0.022 46.9 ±2.5 15.0 ±0.7 26 2.998 ±0.024 35.1 ±11.6 11.7 ±3.8 3.014 ±0.026 42.6 ±4.5 14.1 ±1.5 27 3.044 ±0.034 42.1 ±11.0 13.5 ±3.4 3.010 ±0.037 39.4 ±13.6 13.1 ±4.5

Inj. Mold. 2.994 ±0.005 55.4 ±2.2 18.5 ±0.7 3.048 ±0.008 56.0 ±2.1 18.4 ±0.7




Table 7: Mean and s.d. dielectric breakdown voltage and strength test results for PEI samples.

Build No.

“As-Received” “Oven-Aged”

Thickness (mm)

Breakdown Voltage

(kV)


Thickness (mm)

Breakdown Voltage

(kV)


1 1.066 ±0.005 12.7 ±1.4 12.0 ±1.1 1.066 ±0.005 11.2 ±3.4 10.5 ±3.2 2 1.022 ±0.016 6.6 ±2.4 6.5 ±2.3 1.010 ±0.019 7.1 ±2.3 7.0 ±2.3 3 1.054 ±0.019 15.1 ±7.9 14.4 ±7.9 1.052 ±0.013 11.1 ±2.3 10.6 ±2.4 4 1.062 ±0.011 8.6 ±3.7 8.1 ±3.5 1.050 ±0.007 9.9 ±2.1 9.4 ±2.0 5 1.032 ±0.013 13.9 ±3.1 13.4 ±3.1 1.028 ±0.016 11.9 ±1.7 11.6 ±1.8 6 1.044 ±0.011 10.2 ±1.9 9.8 ±1.7 1.040 ±0.014 12.6 ±2.1 12.2 ±2.2 7 1.008 ±0.008 5.3 ±0.9 5.0 ±0.7 1.004 ±0.017 8.7 ±1.5 8.4 ±1.4 8 1.054 ±0.015 8.7 ±1.8 8.3 ±1.8 1.060 ±0.030 9.8 ±1.5 9.3 ±1.5 9 1.028 ±0.028 6.9 ±1.7 6.8 ±1.6 1.008 ±0.018 9.7 ±3.4 11.0 ±3.9

10 1.028 ±0.004 8.7 ±0.9 8.4 ±0.8 1.022 ±0.008 9.9 ±1.3 9.7 ±1.3 11 1.042 ±0.043 24.2 ±11.8 23.6 ±12.2 1.038 ±0.044 > 12.5 > 12.1 12 1.048 ±0.004 8.0 ±1.1 7.6 ±1.0 1.038 ±0.013 9.0 ±2.6 8.7 ±2.5 13 1.042 ±0.022 21.2 ±4.4 20.3 ±4.5 1.026 ±0.030 > 14.3 > 13.9 14 1.008 ±0.008 6.3 ±1.0 6.2 ±1.0 1.010 ±0.019 6.5 ±0.9 6.4 ±0.8 15 1.050 ±0.023 9.8 ±2.7 9.4 ±2.9 1.028 ±0.040 10.7 ±2.0 10.5 ±2.2 16 1.050 ±0.016 16.3 ±4.2 15.5 ±4.2 1.026 ±0.011 > 13.3 > 13.0 17 1.010 ±0.007 5.9 ±1.8 5.9 ±1.8 1.012 ±0.029 8.3 ±1.6 8.2 ±1.6 18 1.018 ±0.004 21.9 ±5.1 21.5 ±5.0 1.016 ±0.015 > 14.3 > 14.1 19 1.024 ±0.032 5.4 ±1.4 5.2 ±1.3 1.024 ±0.063 9.3 ±2.9 9.0 ±2.5 20 1.010 ±0.019 10.1 ±3.3 10.0 ±3.4 1.028 ±0.022 11.1 ±2.3 10.8 ±2.4 21 1.076 ±0.011 32.6 ±1.0 30.3 ±1.2 1.068 ±0.013 > 15.0 > 14.1 22 1.062 ±0.008 32.7 ±0.9 30.7 ±0.8 1.061 ±0.118 > 15.0 > 14.1 23 1.078 ±0.030 32.3 ±2.2 30.0 ±2.3 1.090 ±0.025 > 15.0 > 13.8 24 1.302 ±0.023 35.4 ±3.1 27.3 ±2.7 1.276 ±0.015 > 15.0 > 11.7 25 1.288 ±0.008 36.7 ±1.3 28.5 ±1.0 1.284 ±0.005 > 15.0 > 11.7 26 1.292 ±0.013 36.7 ±0.8 28.4 ±0.8 1.284 ±0.011 > 15.0 > 11.7

Inj. Mold. 1.012 ±0.004 38.9 ±1.6 38.4 ±1.6 1.014 ±0.005 > 15.0 > 14.8 Note: Results with a “>” symbol include specimens that did not breakdown or flashover within test instrument limits.




Figure 8: Dielectric breakdown voltage test results for frABS samples. Error bars are s.d.

Figure 9: Dielectric strength test results for frABS samples. Error bars are s.d.




Figure 10: Dielectric breakdown voltage test results for PEI samples. Error bars are s.d. Note that “oven-

aged” build numbers 11, 13, 16, 18, 21-26 and IM include test instrument limited data.

Figure 11: Dielectric strength test results for PEI samples. Error bars are s.d. Note that “oven-aged” build

numbers 11, 13, 16, 18, 21-26 and IM include test instrument limited data.




COMPARATIVE TRACKING INDEX (CTI) TESTS Comparative tracking index tests were completed at UL’s Performance Materials lab in Krefeld, Germany. Results for CTI voltages for 50 and 100 drops are listed in Table 8 and plotted in Figure 13 and Figure 14 respectively for the two materials. All of the 3D printed and injection molded frABS specimens flamed, melted and eroded (< 1 mm depth) at failure. The injection molded PEI specimens also flamed, melted and eroded (< 1 mm depth) at failure; however, the 3D printed PEI specimens only melted and eroded (< 1 mm depth) at failure.

Table 8: CTI test sample orientation details for frABS and PEI samples.

frABS Build No.

CTI Voltage at 50 Drops

CTI Voltage at 100 Drops PEI Build

No. CTI Voltage at

50 Drops CTI Voltage at

100 Drops

1 200 150 1 175 150 2 200 175 2 175 150 3 225 175 3 200 175 4 275 250 4 300 200 5 200 175 5 200 175 6 225 150 6 250 225 7 200 175 7 175 150 8 225 175 8 200 150 9 200 175 9 225 200

10 200 175 10 225 200 11 225 150 11 150 125 12 200 175 12 250 200 13 200 175 13 200 150 14 175 125 14 225 200 15 225 175 15 300 225 16 175 150 16 150 125 17 225 150 17 250 225 18 225 200 18 275 225 19 225 150 19 225 200 20 200 175 20 250 200 21 225 200 21 175 150 22 175 150 22 175 150 23 275 225 23 125 100 24 375 250 24 175 150 25 400 275 25 150 125 26 300 250 26 125 100 27 300 250 27 175 150

Inj. Mold.28 250 200 28 175 150 29 175 150 30 150 125 Inj. Mold. 150 125




Figure 12: Comparative tracking index test results for frABS samples.

Figure 13: Comparative tracking index test results for PEI samples.




HOT WIRE IGNITION (HWI) TESTS Hot wire ignition tests were completed at UL’s Performance Materials lab in Krefeld, Germany. HWI Performance Level Category (PLC) were assigned based on the determined mean time for ignition in accordance with the ranges specified in UL 746A Table 32.1, reprinted in Table 9. Specimens that did not ignite within the maximum test duration of 120 s were assigned a value of 120 s for the purposes of determining a minimum mean ignition time and PLC rating (mean ignition times including such specimens are identified as a minimum with a “>”). All 140 tested frABS specimens melted away from the nichrome wire without igniting resulting in a PLC rating of 0 for each build. The test durations at which the specimens melted through, leaving no material in contact with the wire, i.e. melt times, were used to determine an “Effective” PLC based on the ignition time ranges specified in UL 746A Table 32.1 (Table 9). None of the 155 tested PEI specimens ignited within the maximum 120 s test duration except the following nine specimens:

• One specimen from PEI Build No. 12 ignited at 107 s • Two specimens from PEI Build No. 24 ignited at 117 and 118 s • One specimen from PEI Build No. 25 ignited at 115 s • Two specimens from PEI Build No. 26 ignited at 85 and 101 s • Two specimens from PEI Build No. 27 ignited at 88 and 99 s • One specimen from PEI Build No. 30 ignited at 99 s

Effective PLC and mean hot wire ignition test melt times for the sets of five frABS replicates are listed in Table 10 and plotted in Figure 15. Hot wire ignition PLC and mean hot wire ignition times for the sets of five PEI replicates are listed in Table 11.

Table 9: Hot wire ignition performance level categories (UL 746A Table 32.1).

Assigned PLC Mean Ignition Time, IT (s)

0 IT ≥ 120 1 60 ≤ IT < 120 2 30 ≤ IT < 60 3 15 ≤ IT < 30 4 7 ≤ IT < 15 5 0 ≤ IT < 7




Table 10: Mean and s.d. hot wire ignition test results for frABS samples.

Build No. Thickness (mm)

Melt Time (s) Effective PLC

1 2.98 ±0.02 53 ±5 2 2 2.98 ±0.03 56 ±10 2 3 3.21 ±0.02 61 ±6 1 4 3.03 ±0.05 60 ±7 1 5 3.13 ±0.08 55 ±11 2 6 3.17 ±0.05 56 ±6 2 7 3.17 ±0.05 55 ±10 2 8 3.17 ±0.05 61 ±7 1 9 3.21 ±0.05 59 ±5 2

10 3.28 ±0.01 63 ±7 1 11 3.22 ±0.03 60 ±9 1 12 3.23 ±0.04 59 ±2 2 13 3.07 ±0.03 58 ±2 2 14 3.46 ±0.03 72 ±8 1 15 3.38 ±0.02 59 ±2 2 16 3.23 ±0.05 58 ±8 2 17 3.19 ±0.02 59 ±2 2 18 3.17 ±0.01 55 ±5 2 19 3.53 ±0.04 65 ±4 1 20 3.51 ±0.02 67 ±6 1 21 3.41 ±0.14 63 ±3 1 22 3.48 ±0.03 71 ±8 1 23 3.56 ±0.02 70 ±11 1 24 3.60 ±0.03 66 ±9 1 25 3.55 ±0.02 72 ±12 1 26 3.60 ±0.02 66 ±9 1 27 3.55 ±0.03 68 ±14 1

Inj. Mold. 2.97 ±0.00 57 ±4 2 Note: Actual PLC for all builds would have been 0 as none of the

specimens ignited.




Table 11: Mean and s.d. hot wire ignition test results for PEI samples.


Ignition Time (s) PLC

1 2.846 ±0.030 DNI 0 2 2.832 ±0.004 DNI 0 3 2.902 ±0.045 DNI 0 4 2.828 ±0.016 DNI 0 5 2.806 ±0.019 DNI 0 6 3.016 ±0.015 DNI 0 7 3.000 ±0.016 DNI 0 8 3.026 ±0.005 DNI 0 9 3.018 ±0.008 DNI 0

10 3.036 ±0.009 DNI 0 11 3.028 ±0.008 DNI 0 12 3.038 ±0.015 > 117 1 13 3.028 ±0.008 DNI 0 14 3.034 ±0.009 DNI 0 15 3.062 ±0.004 DNI 0 16 3.036 ±0.009 DNI 0 17 3.034 ±0.009 DNI 0 18 3.040 ±0.000 DNI 0 19 3.018 ±0.008 DNI 0 20 3.042 ±0.011 DNI 0 21 3.146 ±0.031 DNI 0 22 3.122 ±0.022 DNI 0 23 3.282 ±0.081 DNI 0 24 3.102 ±0.016 > 119 1 25 3.210 ±0.075 > 119 1 26 3.082 ±0.023 > 109 1 27 3.052 ±0.013 > 109 1 28 3.094 ±0.044 DNI 0 29 3.064 ±0.011 DNI 0 30 3.076 ±0.027 > 116 1

Inj. Mold. 2.976 ±0.005 DNI 0 Notes: ‘DNI’ indicates none of the test specimensignited. Results with a “>” symbol are minimum values that include a mixture of specimens that

ignited and did not ignite




Figure 14: frABS melt times from hot wire ignition tests. Error bars are s.d.

HIGH-CURRENT ARC IGNITION (HAI) TESTS High-current arc ignition tests were completed at UL’s Performance Materials lab in Taipei, Taiwan. HAI Performance Level Category (PLC) were assigned based on the number of arcs required for ignition in accordance with the ranges specified in UL 746A Table 33.1, reprinted in Table 12. Specimens that did not ignite within the maximum test duration of 150 arcs were assigned a value of 150 arcs for the purposes of determining a minimum mean number of arcs required for ignition and PLC rating (mean number of arcs required for ignition including such specimens are identified with a “>”). All frABS specimens carbonized and melted but none ignited within the maximum 150 arcs. All PEI specimens carbonized and melted except the following three specimens:

• One specimen from PEI Build No. 6 ignited at 146 arcs • One specimen from PEI Build No. 8 ignited at 137 arcs • One specimen from PEI Build No. 22 ignited at 145 arcs

Results for the sets of five replicates of each material are listed in Table 13 and Table 14 respectively.




Table 12: High-current arc ignition performance level categories (UL 746A Table 33.1).

Assigned PLC Mean number of arcs to cause ignition, NA

0 NA ≥ 120 1 60 ≤ NA < 120 2 30 ≤ NA < 60 3 15 ≤ NA < 30 4 0 ≤ NA < 15

Table 13: Mean and s.d. hgh-current arc ignition test results for frABS samples.


No. of Arcs to Ignite PLC

1 3.030 ±0.030 DNI 0 2 3.064 ±0.038 DNI 0 3 3.171 ±0.069 DNI 0 4 3.113 ±0.074 DNI 0 5 3.178 ±0.058 DNI 0 6 3.206 ±0.027 DNI 0 7 3.242 ±0.036 DNI 0 8 3.382 ±0.097 DNI 0 9 3.392 ±0.080 DNI 0

10 3.291 ±0.018 DNI 0 11 3.268 ±0.033 DNI 0 12 3.231 ±0.033 DNI 0 13 3.185 ±0.080 DNI 0 14 3.257 ±0.025 DNI 0 15 3.294 ±0.014 DNI 0 16 3.242 ±0.033 DNI 0 17 3.238 ±0.036 DNI 0 18 3.199 ±0.025 DNI 0 19 3.364 ±0.034 DNI 0 20 3.355 ±0.040 DNI 0 21 3.334 ±0.035 DNI 0 22 3.336 ±0.042 DNI 0 23 3.379 ±0.053 DNI 0 24 3.423 ±0.050 DNI 0 25 3.396 ±0.067 DNI 0 26 3.353 ±0.040 DNI 0 27 3.345 ±0.045 DNI 0

Inj. Mold. 3.003 ±0.008 DNI 0 Note: ‘DNI’ indicates none of the test specimens ignited.




Table 14: Mean and s.d. hgh-current arc ignition test results for PEI samples.


No. of Arcs to Ignite PLC

1 2.872 ±0.026 DNI 0 2 2.866 ±0.004 DNI 0 3 2.907 ±0.021 DNI 0 4 2.837 ±0.022 DNI 0 5 2.843 ±0.030 DNI 0 6 3.029 ±0.005 > 149 0 7 3.034 ±0.011 DNI 0 8 3.055 ±0.023 > 147 0 9 3.036 ±0.009 DNI 0

10 3.067 ±0.018 DNI 0 11 3.053 ±0.010 DNI 0 12 3.056 ±0.008 DNI 0 13 3.054 ±0.003 DNI 0 14 3.038 ±0.007 DNI 0 15 3.053 ±0.011 DNI 0 16 3.046 ±0.008 DNI 0 17 3.038 ±0.005 DNI 0 18 3.042 ±0.008 DNI 0 19 3.037 ±0.012 DNI 0 20 3.026 ±0.009 DNI 0 21 3.230 ±0.016 DNI 0 22 3.125 ±0.007 > 149 0 23 3.383 ±0.132 DNI 0 24 3.140 ±0.019 DNI 0 25 3.177 ±0.019 DNI 0 26 3.111 ±0.025 DNI 0 27 3.099 ±0.043 DNI 0 28 3.144 ±0.060 DNI 0 29 3.124 ±0.036 DNI 0 30 3.102 ±0.043 DNI 0

Inj. Mold. 2.976 ±0.002 DNI 0 Notes: ‘DNI’ indicates none of the test specimens ignited . Results with a “>” symbol are minimum values that include a mixture of specimens that

ignited and did not ignite UL 94 FLAMMABILITY TESTS – VERTICAL UL 94 50W Vertical Burning Tests were completed at UL’s Performance Materials lab in Taipei, Taiwan. UL 94 flame ratings based on UL 94 Table 8.1, reprinted in Table 15, are summarized in Table 16 for the two materials. Mean afterflame burn times for complete sets of ten frABS replicates at each condition are listed in Table 17 and Table 18 respectively and plotted in Figure 16 through Figure 19; mean afterflame burn times for complete sets of ten PEI replicates at each condition are listed in Table 19 and Table 20 respectively and plotted in Figure 20 through Figure 23.




Table 15: UL 94 50W Vertical Burning Test material classifications (UL 94 Table 8.1).

Criteria conditions V-0 V-1 V-2

Afterflame time for each individual specimen t1 or t2 ≤10s ≤30s ≤30s Total afterflame time for any condition set (t1 plus t2 for the 5 specimens) ≤50s ≤250s ≤250s

Afterflame plus afterglow time for each individual specimen after the second flame application (t2+t3) ≤30s ≤60s ≤60s

Afterflame or afterglow of any specimen up to the holding clamp No No No

Cotton indicator ignited by flaming particles or drops No No Yes

Note: Total afterflame times for the second criteria were doubled to accommodate the 10 specimen sample size.

Table 16: UL 94 50W Vertical flame ratings for frABS and PEI samples.

frABS Build No.

UL 94 Flame Rating

PEI Build No.

UL 94 Flame Rating

1 V-2 1 V-0 2 Fail 2 V-0 3 V-2 3 V-0 4 Fail 4 V-0 5 V-2 5 V-0 6 Fail 6 V-0 7 V-2 7 V-0 8 Fail 8 V-0 9 Fail 9 V-0

10 V-2 10 V-0 11 V-2 11 V-0 12 V-2 12 V-0 13 V-2 13 V-0 14 V-2 14 V-0 15 V-2 15 V-0 16 V-2 16 V-0 17 V-2 17 V-0 18 V-2 18 V-0 19 Fail 19 V-0 20 V-2 20 V-0 21 Fail 21 V-0 22 V-2 22 V-0 23 V-2 23 V-0 24 V-2 24 V-0 25 V-2 25 V-0 26 V-2 26 V-0 27 V-2 27 V-0

Inj. Mold.28 V-2 28 V-0 29 V-0 30 V-0 Inj. Mold. V-0




Table 17: Mean and s.d. UL 94 50W Vertical afterflame burn times for “As-Received” frABS samples.


t1 (s)

t2 (s)

t1 + t2 (s)

t2 + t3 (s)

1 3.034 ±0.090 20.4 ±7.8 5.1 ±4.5 25.5 ±8.1 5.1 ±4.5 2 3.098 ±0.021 25.8 ±5.4 3.8 ±5.2 29.6 ±8.9 3.8 ±5.2 3 3.157 ±0.053 14.5 ±8.5 5.0 ±5.0 19.5 ±7.2 5.0 ±5.0 4 3.115 ±0.071 21.3 ±9.3 5.5 ±3.5 26.8 ±8.3 5.5 ±3.5 5 3.121 ±0.136 20.7 ±8.5 6.6 ±6.3 27.3 ±12.9 6.6 ±6.3 6 3.307 ±0.098 22.1 ±9.8 5.5 ±5.9 27.6 ±14.0 5.5 ±5.9 7 3.260 ±0.109 15.7 ±7.9 4.5 ±4.1 20.2 ±9.7 4.5 ±4.1 8 3.286 ±0.159 24.6 ±8.3 2.5 ±2.8 27.1 ±9.5 2.5 ±2.8 9 3.281 ±0.143 24.2 ±10.2 6.7 ±4.5 30.9 ±12.3 6.7 ±4.5

10 3.319 ±0.072 12.8 ±8.6 6.3 ±4.9 19.1 ±8.6 6.3 ±4.9 11 3.211 ±0.058 14.5 ±8.0 4.8 ±4.5 19.3 ±7.8 4.8 ±4.5 12 3.134 ±0.077 6.8 ±6.6 5.5 ±2.8 12.3 ±7.1 5.5 ±2.8 13 3.193 ±0.045 17.6 ±11.2 5.4 ±3.3 23.0 ±9.7 5.4 ±3.3 14 3.250 ±0.036 17.2 ±11.6 4.6 ±2.5 21.8 ±10.8 4.6 ±2.5 15 3.271 ±0.092 8.3 ±5.4 6.8 ±3.3 15.1 ±5.0 6.8 ±3.3 16 3.236 ±0.075 9.5 ±9.9 8.1 ±4.1 17.6 ±7.7 8.1 ±4.1 17 3.269 ±0.053 15.8 ±12.3 5.7 ±5.4 21.5 ±14.2 5.7 ±5.4 18 3.172 ±0.070 10.5 ±12.1 7.7 ±1.6 18.2 ±11.3 7.7 ±1.6 19 3.556 ±0.034 20.3 ±10.3 4.5 ±5.5 24.8 ±14.6 4.5 ±5.5 20 3.518 ±0.048 19.4 ±3.5 1.4 ±2.0 20.8 ±3.1 1.4 ±2.0 21 3.566 ±0.027 20.9 ±8.8 2.2 ±1.7 23.1 ±9.0 2.2 ±1.7 22 3.464 ±0.034 18.0 ±7.4 2.1 ±1.8 20.1 ±8.3 2.1 ±1.8 23 3.632 ±0.033 15.6 ±10.2 2.0 ±2.3 17.6 ±10.8 2.0 ±2.3 24 3.599 ±0.031 22.1 ±7.4 4.9 ±6.3 27.0 ±12.7 4.9 ±6.3 25 3.543 ±0.046 17.7 ±7.3 2.1 ±2.5 19.8 ±7.9 2.1 ±2.5 26 3.582 ±0.037 23.2 ±9.4 1.4 ±1.4 24.6 ±10.0 1.4 ±1.4 27 3.565 ±0.027 17.8 ±9.4 2.8 ±2.7 20.6 ±10.1 2.8 ±2.7

Inj. Mold. 2.977 ±0.005 6.0 ±5.4 2.8 ±2.7 8.8 ±6.8 2.8 ±2.7




Table 18: Mean and s.d. UL 94 50W Vertical afterflame burn times for “Oven-Aged” frABS samples.


t1 (s)

t2 (s)

t1 + t2 (s)

t2 + t3 (s)

1 3.010 ±0.101 23.6 ±9.2 6.4 ±6.0 30.0 ±10.5 6.4 ±6.0 2 2.985 ±0.068 18.7 ±10.0 3.6 ±2.5 22.3 ±9.0 3.6 ±2.5 3 3.205 ±0.039 16.6 ±10.0 5.9 ±7.4 22.5 ±9.6 5.9 ±7.4 4 3.031 ±0.080 20.1 ±7.9 3.9 ±4.3 24.0 ±9.6 2.9 ±2.9 5 3.198 ±0.132 22.7 ±6.0 2.6 ±1.4 25.3 ±6.9 2.6 ±1.4 6 3.337 ±0.077 19.8 ±8.0 6.4 ±5.3 26.2 ±10.5 6.4 ±5.3 7 3.193 ±0.139 17.2 ±9.2 3.2 ±3.4 20.4 ±7.8 3.2 ±3.4 8 3.268 ±0.158 17.5 ±9.8 6.4 ±5.1 23.9 ±6.8 6.4 ±5.1 9 3.232 ±0.107 23.7 ±9.4 4.9 ±6.5 28.6 ±9.9 4.9 ±6.5

10 3.316 ±0.057 6.6 ±7.9 14.5 ±9.4 21.1 ±9.8 14.5 ±9.4 11 3.245 ±0.040 12.2 ±14.2 9.8 ±6.8 22.0 ±9.8 9.8 ±6.8 12 3.213 ±0.071 11.1 ±13.0 7.8 ±5.1 18.9 ±10.8 7.8 ±5.1 13 3.167 ±0.043 11.0 ±9.9 7.3 ±1.6 18.3 ±9.6 7.3 ±1.6 14 3.258 ±0.016 11.6 ±10.3 7.9 ±3.4 19.5 ±9.2 7.9 ±3.4 15 3.320 ±0.063 20.4 ±6.3 6.3 ±4.2 26.7 ±8.4 6.3 ±4.2 16 3.252 ±0.036 9.4 ±10.9 9.8 ±7.1 19.2 ±6.4 9.8 ±7.1 17 3.267 ±0.071 11.6 ±5.8 5.2 ±3.4 16.8 ±5.5 5.2 ±3.4 18 3.105 ±0.073 10.1 ±6.1 4.7 ±2.7 14.8 ±5.1 4.7 ±2.7 19 3.556 ±0.023 20.6 ±6.7 5.2 ±6.3 25.8 ±11.8 5.2 ±6.3 20 3.521 ±0.028 18.7 ±7.2 2.7 ±4.1 21.4 ±8.0 2.7 ±4.1 21 3.564 ±0.032 19.9 ±6.1 1.7 ±1.3 21.6 ±6.5 1.7 ±1.3 22 3.491 ±0.042 23.5 ±6.7 4.4 ±5.6 27.9 ±8.6 4.4 ±5.6 23 3.642 ±0.032 14.6 ±6.8 3.7 ±3.7 18.3 ±6.7 3.7 ±3.7 24 3.594 ±0.047 21.1 ±7.5 3.6 ±4.2 24.7 ±7.6 3.6 ±4.2 25 3.549 ±0.046 13.0 ±7.7 2.7 ±1.9 15.7 ±8.1 2.7 ±1.9 26 3.584 ±0.034 17.9 ±10.9 3.5 ±5.1 21.4 ±11.3 3.5 ±5.1 27 3.573 ±0.037 20.6 ±7.1 2.2 ±2.5 22.8 ±7.5 2.2 ±2.5

Inj. Mold. 2.979 ±0.007 18.0 ±10.8 7.4 ±6.3 25.4 ±10.8 7.4 ±6.3




Table 19: Mean and s.d. UL 94 50W Vertical afterflame burn times for “As-Received” PEI samples.


t1 (s)

t2 (s)

t1 + t2 (s)

t2 + t3 (s)

1 2.853 ±0.019 0.3 ±0.5 0.9 ±0.6 1.2 ±0.6 1.1 ±0.3 2 2.822 ±0.015 0.8 ±0.4 1.3 ±0.7 2.1 ±0.7 1.4 ±0.5 3 2.867 ±0.018 0.4 ±0.5 0.9 ±0.6 1.3 ±0.8 1.1 ±0.3 4 2.827 ±0.010 0.7 ±0.5 1.6 ±0.7 2.3 ±0.9 1.6 ±0.7 5 2.834 ±0.029 0.5 ±0.5 0.9 ±0.6 1.4 ±1.0 1.0 ±0.5 6 3.052 ±0.010 0.5 ±0.5 1.3 ±0.5 1.8 ±0.8 1.3 ±0.5 7 3.028 ±0.021 0.9 ±0.3 1.2 ±0.6 2.1 ±0.7 1.3 ±0.5 8 3.081 ±0.010 0.5 ±0.5 1.6 ±0.7 2.1 ±1.0 1.6 ±0.7 9 3.035 ±0.012 0.6 ±0.5 1.3 ±0.7 1.9 ±0.7 1.4 ±0.5

10 3.054 ±0.013 0.8 ±0.4 1.5 ±0.7 2.3 ±0.7 1.5 ±0.7 11 3.051 ±0.014 0.6 ±0.5 1.1 ±0.6 1.7 ±0.7 1.2 ±0.4 12 3.047 ±0.014 0.5 ±0.5 1.1 ±0.7 1.6 ±1.1 1.3 ±0.5 13 3.045 ±0.004 0.8 ±0.4 1.3 ±0.5 2.1 ±0.7 1.3 ±0.5 14 3.046 ±0.016 0.6 ±0.5 1.0 ±0.7 1.6 ±1.0 1.2 ±0.4 15 3.045 ±0.010 0.5 ±0.5 1.1 ±0.7 1.6 ±1.1 1.3 ±0.5 16 3.042 ±0.011 0.9 ±0.6 0.7 ±0.9 1.6 ±1.0 1.2 ±0.6 17 3.033 ±0.011 1.0 ±0.0 0.9 ±0.6 1.9 ±0.6 1.1 ±0.3 18 3.048 ±0.011 0.9 ±0.3 1.2 ±0.9 2.1 ±0.9 1.5 ±0.5 19 3.025 ±0.012 0.6 ±0.5 0.9 ±0.6 1.5 ±0.7 1.1 ±0.3 20 3.035 ±0.018 0.4 ±0.5 1.0 ±0.5 1.4 ±0.8 1.1 ±0.3 21 3.173 ±0.060 0.3 ±0.5 0.9 ±0.6 1.2 ±0.9 1.1 ±0.3 22 3.106 ±0.034 0.7 ±0.5 1.1 ±0.7 1.8 ±0.8 1.3 ±0.5 23 3.307 ±0.098 0.2 ±0.4 0.7 ±0.5 0.9 ±0.6 1.0 ±0.0 24 3.115 ±0.034 0.4 ±0.5 1.1 ±0.6 1.5 ±0.7 1.2 ±0.4 25 3.205 ±0.026 0.5 ±0.5 0.7 ±0.7 1.2 ±0.9 0.8 ±0.6 26 3.065 ±0.021 0.9 ±0.3 1.9 ±1.0 2.8 ±1.1 1.9 ±1.0 27 3.057 ±0.020 0.6 ±0.5 1.5 ±0.8 2.1 ±1.1 1.6 ±0.7 28 3.128 ±0.050 0.8 ±0.4 1.3 ±0.7 2.1 ±0.7 1.4 ±0.5 29 3.083 ±0.028 0.5 ±0.5 1.1 ±0.9 1.6 ±1.1 1.4 ±0.5 30 3.080 ±0.032 0.8 ±0.4 1.3 ±0.7 2.1 ±0.9 1.4 ±0.5

Inj. Mold. 2.977 ±0.008 1.0 ±0.0 1.9 ±1.1 2.9 ±1.1 1.9 ±1.1




Table 20: Mean and s.d. UL 94 50W Vertical afterflame burn times for “Oven-Aged” PEI samples.


t1 (s)

t2 (s)

t1 + t2 (s)

t2 + t3 (s)

1 2.864 ±0.024 0.4 ±0.5 1.1 ±0.3 1.5 ±0.7 1.1 ±0.3 2 2.812 ±0.007 0.8 ±0.4 1.6 ±0.7 2.4 ±0.8 1.6 ±0.7 3 2.854 ±0.036 0.3 ±0.5 1.2 ±0.6 1.5 ±0.8 1.3 ±0.5 4 2.817 ±0.007 0.7 ±0.5 1.5 ±0.5 2.2 ±0.8 1.5 ±0.5 5 2.815 ±0.010 0.7 ±0.5 1.1 ±0.6 1.8 ±0.8 1.2 ±0.4 6 3.046 ±0.011 0.2 ±0.4 0.8 ±0.4 1.0 ±0.7 0.9 ±0.3 7 3.026 ±0.014 0.8 ±0.4 1.4 ±0.7 2.2 ±0.9 1.5 ±0.5 8 3.075 ±0.020 0.7 ±0.5 1.2 ±0.6 1.9 ±0.9 1.3 ±0.5 9 3.050 ±0.021 0.9 ±0.3 1.6 ±1.1 2.5 ±1.2 1.7 ±0.9

10 3.059 ±0.018 0.8 ±0.4 1.0 ±0.5 1.8 ±0.8 1.1 ±0.3 11 3.048 ±0.009 0.4 ±0.5 0.9 ±0.7 1.3 ±1.1 1.2 ±0.4 12 3.050 ±0.010 0.8 ±0.4 0.9 ±0.6 1.7 ±0.8 1.1 ±0.3 13 3.046 ±0.014 0.5 ±0.5 0.8 ±0.4 1.3 ±0.8 1.0 ±0.0 14 3.043 ±0.005 0.4 ±0.5 0.8 ±0.4 1.2 ±0.6 1.0 ±0.0 15 3.049 ±0.008 0.6 ±0.5 0.8 ±0.6 1.4 ±0.8 1.1 ±0.3 16 3.035 ±0.011 0.7 ±0.5 1.0 ±0.7 1.7 ±0.8 1.2 ±0.4 17 3.034 ±0.011 1.0 ±0.0 1.3 ±0.7 2.3 ±0.7 1.4 ±0.5 18 3.054 ±0.006 0.6 ±0.5 0.7 ±0.5 1.3 ±0.7 1.0 ±0.0 19 3.022 ±0.010 0.6 ±0.5 1.0 ±0.7 1.6 ±0.8 1.2 ±0.4 20 3.046 ±0.013 0.9 ±0.3 1.1 ±0.6 2.0 ±0.7 1.2 ±0.4 21 3.174 ±0.044 0.6 ±0.5 0.8 ±0.6 1.4 ±1.0 1.1 ±0.3 22 3.114 ±0.025 0.9 ±0.3 0.7 ±0.7 1.6 ±0.8 1.1 ±0.3 23 3.321 ±0.122 0.9 ±0.3 0.8 ±0.9 1.7 ±0.9 1.2 ±0.6 24 3.107 ±0.021 0.8 ±0.4 0.7 ±0.7 1.5 ±0.7 1.0 ±0.5 25 3.178 ±0.034 0.6 ±0.5 0.8 ±0.8 1.4 ±0.8 1.2 ±0.4 26 3.073 ±0.010 0.9 ±0.3 1.5 ±0.7 2.4 ±0.8 1.6 ±0.5 27 3.081 ±0.060 0.9 ±0.3 0.9 ±1.0 1.8 ±1.1 1.3 ±0.7 28 3.112 ±0.045 0.8 ±0.4 1.4 ±0.5 2.2 ±0.6 1.4 ±0.5 29 3.061 ±0.016 0.7 ±0.5 1.7 ±0.7 2.4 ±1.1 1.7 ±0.7 30 3.087 ±0.029 0.9 ±0.3 1.5 ±0.5 2.4 ±0.7 1.5 ±0.5

Inj. Mold. 2.979 ±0.008 1.0 ±0.0 2.8 ±0.8 3.8 ±0.8 2.8 ±0.8




Figure 15: Mean UL 94 50W Vertical t1 afterflame burn times for frABS samples. Error bars are s.d.

Figure 16: Mean UL 94 50W Vertical t2 afterflame burn times for frABS samples. Error bars are s.d.




Figure 17: Mean UL 94 50W Vertical t1 + t2 afterflame burn times for frABS samples. Error bars are s.d.

Figure 18: Mean UL 94 50W Vertical t2 + t3 afterflame burn times for frABS samples. Error bars are s.d.




Figure 19: Mean UL 94 50W Vertical t1 afterflame burn times for PEI samples. Error bars are s.d.

Figure 20: Mean UL 94 50W Vertical t2 afterflame burn times for PEI samples. Error bars are s.d.




Figure 21: Mean UL 94 50W Vertical t1 + t2 afterflame burn times for PEI samples. Error bars are s.d.

Figure 22: Mean UL 94 50W Vertical t2 + t3 afterflame burn times for PEI samples. Error bars are s.d.




UL 94 FLAMMABILITY TESTS – 5VB UL 94 500W Vertical Burning Tests were completed at UL’s Performance Materials lab in Taipei, Taiwan. Note that plaques were not tested for 5VA classification. Mean afterflame burn times and compliance to UL 94 5VB flame ratings based on UL 94 Table 9.1, reprinted in Table 21, are summarized in Table 22 and plotted in Figure 24.

Table 21: UL 94 500W Vertical Burning Test material classifications (UL 94 Table 9.1).

Criteria conditions 5VA 5VB Afterflame time plus afterglow time after fifth flame application for each individual specimen ≤60s ≤60s

Cotton indicator ignited by flaming particles or drops from any bar specimen No No

Burn-through (hole) of any plaque specimen No Yes

Table 22: UL 94 5VB flame ratings, mean and s.d. afterflame times PEI samples.

Build No.

“As-Received” “Oven-Aged” UL 94 5VB

Flame Rating Thickness (mm)

Afterflame Time (s)

Thickness (mm)

Afterflame Time

(s) 1 2.935 ±0.024 2.2 ±1.4 2.904 ±0.013 2.3 ±1.3 5VB 2 2.851 ±0.027 2.6 ±1.6 2.856 ±0.012 1.7 ±1.4 5VB 3 2.978 ±0.024 1.6 ±0.5 2.984 ±0.019 2.2 ±1.3 5VB 4 2.921 ±0.022 2.4 ±1.4 2.932 ±0.017 2.4 ±1.2 5VB 5 2.929 ±0.022 2.4 ±1.3 2.925 ±0.013 2.1 ±1.4 5VB 6 3.100 ±0.010 1.6 ±1.1 3.086 ±0.015 2.1 ±1.0 5VB 7 3.073 ±0.021 2.8 ±1.8 3.040 ±0.012 3.2 ±1.8 5VB 8 3.090 ±0.014 2.4 ±1.4 3.094 ±0.009 2.4 ±1.4 5VB 9 3.055 ±0.008 2.9 ±1.4 3.043 ±0.021 3.4 ±1.1 5VB

10 3.042 ±0.024 2.5 ±1.4 3.055 ±0.021 2.8 ±1.4 5VB 11 3.045 ±0.006 2.3 ±1.1 3.050 ±0.010 2.2 ±0.9 5VB 12 3.042 ±0.007 3.4 ±1.4 3.047 ±0.008 2.9 ±1.2 5VB 13 3.066 ±0.008 2.1 ±1.3 3.049 ±0.007 2.5 ±1.9 5VB 14 3.045 ±0.008 2.3 ±0.9 3.035 ±0.005 2.3 ±1.5 5VB 15 3.035 ±0.006 2.0 ±0.9 3.030 ±0.007 2.2 ±1.0 5VB 16 3.042 ±0.010 2.8 ±1.2 3.045 ±0.010 3.2 ±1.2 5VB 17 3.031 ±0.010 2.1 ±1.0 3.032 ±0.010 2.4 ±1.2 5VB 18 3.023 ±0.005 2.5 ±1.3 3.024 ±0.006 2.4 ±1.3 5VB 19 3.019 ±0.010 3.1 ±1.4 3.026 ±0.006 2.8 ±1.1 5VB 20 3.020 ±0.007 2.5 ±0.8 3.017 ±0.007 1.6 ±1.0 5VB 21 3.171 ±0.018 1.1 ±0.7 3.174 ±0.019 1.8 ±1.3 5VB 22 3.133 ±0.026 1.5 ±1.1 3.131 ±0.015 2.0 ±1.2 5VB 23 3.331 ±0.056 1.9 ±1.4 3.371 ±0.077 2.1 ±1.4 5VB 24 3.113 ±0.024 1.9 ±0.9 3.142 ±0.022 2.6 ±1.3 5VB 25 3.200 ±0.019 2.1 ±1.2 3.186 ±0.034 1.6 ±0.8 5VB 26 3.082 ±0.009 2.2 ±1.1 3.085 ±0.010 2.4 ±1.2 5VB 27 3.071 ±0.014 2.2 ±1.2 3.073 ±0.012 1.6 ±1.0 5VB 28 3.102 ±0.029 1.7 ±1.2 3.093 ±0.036 1.7 ±0.8 5VB 29 3.083 ±0.014 1.4 ±1.4 3.083 ±0.010 1.9 ±1.1 5VB 30 3.068 ±0.012 1.6 ±1.0 3.073 ±0.011 1.8 ±1.1 5VB

Inj. Mold. 2.970 ±0.003 3.9 ±1.4 2.977 ±0.007 3.0 ±1.6 5VB




Figure 23: Mean UL 94 5VB afterflame times for PEI samples. Error bars are s.d.




ANALYSIS

Test results were analyzed to investigate the influence of sample conditioning, surface quality, and 3D printing parameters on test results as well as to compare safety performance properties for 3D printed specimens versus injection molded specimens. EFFECT OF SAMPLE CONDITIONING Volume resistivity, dielectric breakdown voltage and strength, and the two UL 94 flammability tests were conducted on specimens conditioned at least 48 hours at 23.0 ±2.0 °C (73.4 ±3.6 °F) and 50 ±5% relative humidity (“as-received”) and a second, more severe condition, referred to as “oven-aged”. For the electrical property tests, the “oven-aged” condition is a high humidity exposure intended to increase moisture absorption that could reduce the material’s electrical resistance by virtue of water’s greater conductivity. In contrast to the oven-aging conditions for the electrical tests, the oven-aging conditions for the flammability tests are intended to drive moisture from the material, thereby reducing any potential cooling by evaporation of absorbed water. ABS and PEI materials equilibrate at approximately 1 and 0.3 wt% moisture respectively. Consequently, the change in specimen conditioning would be expected to impact the frABS performance more than the PEI performance. “As-Received” and “Oven-Aged” test results for the respective sample builds of the two materials were compared by Student’s t-tests (two-tailed, homoscedastic, α of 0.05) to determine the fraction of builds for each material per test that were different at a statistically significant level. Results for the 3D printed samples were further broken down by the four investigated parameters – build orientation, tip size, raster angle, and air gap – to determine which parameter was the most significant. Results for the volume resistivity tests are captured in Table 23, dielectric breakdown voltage and strength tests in Table 24, UL 94 50W Vertical Burning tests on frABS in Table 25 and PEI in Table 26, and UL 94 5VB tests on PEI in Table 27. Volume Resistivity (VR) Tests Consistent with the premise of ABS having greater water absorption than PEI, the influence of conditioning was more significant on the volume resistivity behavior of frABS than PEI. Six of the twenty-eight frABS builds had different volume resistivity after exposure to the high humidity conditions versus two of twenty-seven PEI builds. In most cases the volume resistivity of the “oven-aged” specimens were lower than the respective “as-received” specimens (Figure 7 for frABS and Figure 8 for PEI) consistent with the water uptake hypothesis. Amongst the 3D printed samples, air gap was the most significant print parameter such that smaller air gaps tended to result in greater volume resistivity differences (Table 23).




Table 23: Fraction of frABS and PEI builds that exhibited statistically significant differences in volume resistivity behavior after conditioning.

Parameter Value Fraction of Different Builds frABS PEI

ALL BUILDS -- 6 / 28 2 / 27 Injection Molded -- 0 / 1 0 / 1

3D Printed -- 6 / 27 2 / 26

Build Orientation X 1 / 9 1 / 10 Y 3 / 9 1 / 10 Z 2 / 9 0 / 6

Tip Size L 2 / 12 1 / 13 M 1 / 3 -- H 3 / 12 1 / 13

Raster Angle L 3 / 12 1 / 14 M 1 / 3 0 / 8 H 2 / 12 1 / 4

Air Gap L 5 / 12 2 / 10 M 1 / 3 0 / 6 H 0 / 12 0 / 10

Dielectric Breakdown Voltage and Strength (DS) Tests Specimen conditioning was not found to significantly influence dielectric breakdown voltage and strength behavior. Only one of the twenty-eight frABS build variations and two of the sixteen PEI build variations (the eleven PEI build results that were test instrument limited were not included in this analysis) exhibited differences at a statistically significant level, Table 24. For the most part, the “as-received” specimens outperformed the “oven-aged” specimens with greater dielectric breakdown voltages and strengths (Figure 9 and Figure 10 for frABS and Figure 11 and Figure 12 for PEI).

Table 24: Fraction of frABS and PEI builds that exhibited statistically significant differences in dielectric breakdown voltage and strength behavior after conditioning. Results for PEI builds that were test instrument

limited are excluded.

Parameter Value Fraction of Different Builds Fraction of Different Builds frABS BV PEI BV frABS DS PEI DS

ALL BUILDS -- 1 / 28 2 / 16 1 / 28 2 / 16 Injection Molded -- 0 /1 -- 0 / 1 --

3D Printed -- 1 / 27 2 / 16 1 / 27 2 / 16

Build Orientation X 0 / 9 1 / 10 0 / 9 1 / 10 Y 1 / 9 1 / 6 1 / 9 1 / 6 Z 0 / 9 -- 0 / 9 --

Tip Size L 0 / 12 0 / 8 0 / 12 0 / 8 M 0 / 3 -- 0 / 3 -- H 1 / 12 2 / 8 1 / 12 2 / 8

Raster Angle L 1 / 12 1 / 6 1 / 12 1 / 6 M 0 / 3 1 / 6 0 / 3 1 / 6 H 0 / 12 0 / 4 0 / 12 0 / 4

Air Gap L 0 / 12 0 / 4 0 / 12 0 / 4 M 1 / 3 0 / 4 1 / 3 0 / 4 H 0 / 12 2 / 8 0 / 12 2 / 8




UL 94 Flammability Tests – Vertical and 5VB Comparison of UL 94 afterflame burn times for the “as-received” and “oven-aged” 3D printed builds generally did not indicate statistically significant differences for the two materials, Table 25 through Table 27, though for different reasons. For the frABS this was most likely due to relatively large variation in observed test results (COV typically ranged from 15 to 50 %) whereas the PEI generally did not burn for longer than two seconds due to its chemical structure being inherently fire resistant. It was not possible to identify which 3D printing parameter was more influential due to the low number of 3D printed builds that were significantly different. Interestingly, UL 94 Vertical afterflame burn times of the “oven-aged” injection molded specimens were significantly longer than the afterflame burn times of the “as-received” injection molded specimens for both materials.

Table 25: Fraction of frABS builds that exhibited statistically significant differences in UL 94 50W Vertical afterflame burn behavior after conditioning.

Parameter Value Fraction of Different frABS Builds t1 t2 t1+t2 t2+t3

ALL BUILDS -- 2 / 28 5 / 28 2 / 28 5 / 28 Injection Molded -- 1 / 1 1 / 1 1 / 1 1 / 1

3D Printed -- 1 / 27 4 / 27 1 / 27 4 / 27

Build Orientation X 0 / 9 1 / 9 0 / 9 1 / 9 Y 1 / 9 3 / 9 1 / 9 3 / 9 Z 0 / 9 0 / 9 0 / 9 0 / 9

Tip Size L 0 / 12 1 / 12 0 / 12 1 / 12 M 0 / 3 1 / 3 0 / 3 1 / 3 H 1 / 12 2 / 12 1 / 12 2 / 12

Raster Angle L 1 / 12 1 / 12 1 / 12 1 / 12 M 0 / 3 1 / 3 0 / 3 1 / 3 H 0 / 12 2 / 12 0 / 12 2 / 12

Air Gap L 1 / 12 2 / 12 1 / 12 2 / 12 M 0 / 3 1 / 3 0 / 3 1 / 3 H 0 / 12 1 / 12 0 / 12 1 / 12

Table 26: Fraction of PEI builds that exhibited statistically significant differences in UL 94 50W Vertical

afterflame burn behavior after conditioning.

Parameter Value Fraction of Different PEI Builds t1 t2 t1+t2 t2+t3

ALL BUILDS -- 2 / 31 3 / 31 5 / 31 3 / 31 Injection Molded -- 0 / 1 1 / 1 1 / 1 1 / 1

3D Printed -- 2 / 30 2 / 30 4 / 30 2 / 30


Tip Size L 1 / 15 1 / 15 2 / 15 0 / 15 M -- -- -- -- H 1 / 15 1 / 15 2 / 15 2 / 15

Raster Angle L 0 / 12 1 / 12 1 / 12 1 / 12 M 1 / 12 1 / 12 3 / 12 1 / 12 H 1 / 6 0 / 6 0 / 6 0 / 6

Air Gap L 1 / 12 2 / 12 4 / 12 2 / 12 M 1 / 6 0 / 6 0 / 6 0 / 6 H 0 / 12 0 / 12 0 / 12 0 / 12




Table 27: Fraction of PEI builds that exhibited statistically significant differences in UL 94 5VB afterflame burn behavior after conditioning.

Parameter Value Fraction of Different PEI Builds

ALL BUILDS -- 1 / 31 Injection Molded -- 0 / 1

3D Printed -- 1 / 30

Build Orientation X 0 / 10 Y 1 / 10 Z 0 / 10

Tip Size L 0 / 15 M -- H 1 / 15

Raster Angle L 0 / 12 M 0 / 12 H 1 / 6

Air Gap L 0 / 12 M 1 / 6 H 0 / 12

EFFECT OF SAMPLE SURFACE ON COMPARATIVE TRACKING INDEX (CTI) TESTS Quality of the test specimen surface has been acknowledged to influence comparative tracking index test results. In fact, Section 5 of the IEC 60112 test standard specifies that:

“Test specimens shall have nominally smooth and untextured surfaces which are free from surface imperfections such as scratches, blemishes, impurities, etc, unless otherwise stated in the product standard. If this is impossible, the results shall be reported together with a statement describing the surface of the specimen because certain characteristics on the surface of the specimen could add to the dispersion of the results.”

This is because surface imperfections can alter the pooling characteristics of the electrolyte liquid being dripped between the electrodes. With regards to the test specimens evaluated herein, the injection molded samples had smooth, untextured surfaces whereas the 3D printed test specimens had a distinct surface pattern inherent to 3D printing by material extrusion (Figure 5). The channels formed by adjacent raster lines could cause the electrolyte liquid to wick along the raster direction away from the electrodes. Furthermore, the layer-by-layer build could form vertical channels that could wick the electrolyte liquid away from the surface to the interior of the sample. Vertical channels that wick the electrolyte liquid away from the test surface invalidate the test; however, surface channels that impart a preferential surface wicking direction can also influence test results depending upon the wicking direction relative to the electrode orientation. This potential phenomenon is also addressed in Section 5 of the test standard as:




“Where the direction of the electrodes relative to any feature of the material is significant, measurements shall be made in the direction of the feature and orthogonal to it. The direction giving the lower CTI shall be reported, unless otherwise specified.”

In the absence of published studies on CTI measured for 3D printed samples, the 3D printed samples were used to investigate the influence of surface roughness and surface raster angle-electrode orientation. The bottom surface of the 3D printed frABS specimens was qualitatively smoother than the top surface due to being printed directly on the build plate. The PEI material, however, was printed on a support layer of polyethersulfone and manually removed with an ultrasonic cutter. Consequently, the raster pattern of the bottom surface of the PEI specimens were not as defined as the unconstrained top surface and appeared to have been rougher as evidenced by the images in Figure 6. Analysis of this limited data set (eight comparisons), Table 28, indicated a slight tendency of the smoother surface to yield lower CTI results than the rougher surface (six occurrences versus four) consistent with the hypothesis of wicking along the channels. Neither tip size nor air gap were clearly more influential than the other on CTI results.

Table 28: Test specimen surface roughness influence on CTI results.

Material Top v Bottom Build Nos.

Tip Size (mm) Air Gap Surface with higher CTI value

50 drops 100 drops

frABS

3 v 12 0.21 -15% top (rougher) = 4 v 13 0.21 0% top (rougher) top (rougher) 8 v 17 0.33 -15% = top (rougher) 9 v 18 0.33 0% bottom (smoother) bottom (smoother)

PEI

3 v 13 0.254 -0.127 mm = top (smoother) 4 v 14 0.254 0.127 mm top (smoother) = 8 v 18 0.33 -0.127 mm bottom (rougher) bottom (rougher) 9 v 19 0.33 0.127 mm = =

Comparison of specimens tested with the electrodes parallel to the surface rasters versus orthogonal to the surface raster indicated the orthogonal arrangement tended to result in higher CTI for specimens printed with the smaller air gap (two of four builds at 50 drops and all four builds at 100 drops) whereas specimens printed with larger air gaps tended to result in higher CTI when measured parallel to the surface raster (three of four builds at 50 drops and all four builds at 100 drops), Table 29. In contrast to the surface roughness results, tip size was not an influencing factor.

Table 29: Influence of raster angle relative to electrode direction on CTI results.

Material Parallel v

Orthogonal Build Nos.

Tip Size (mm) Air Gap

Orientation with higher CTI value

50 drops 100 drops

frABS

1 v 10 0.21 -15% = orthogonal 2 v 11 0.21 0% orthogonal parallel 6 v 15 0.33 -15% = orthogonal 7 v 16 0.33 0% parallel parallel

PEI

1 v 11 0.254 -0.127 mm orthogonal orthogonal 2 v 12 0.254 0.127 mm parallel parallel 6 v 16 0.33 -0.127 mm orthogonal orthogonal 7 v 17 0.33 0.127 mm parallel parallel




3D PRINTED VS INJECTION MOLDED Voids, channels and the “rough” surface of 3D printed specimens were anticipated to result in different performance properties than equivalent injection molded specimens of the same material. Test results for each of the 3D printed builds were compared to the test results of the appropriate injection molded specimens using Student’s t-tests (two-tailed, homoscedastic, α of 0.05) to ascertain the fraction of builds for each material per test that were different at a statistically significant level. Results for the 3D printed samples were further broken down by the four investigated parameters – build orientation, tip size, raster angle, and air gap – to determine which parameter was the most significant. Results for the volume resistivity tests are captured in Table 30, dielectric breakdown voltage and strength tests in Table 31 and Table 32 respectively, comparative tracking index in Table 33, hot wire ignition in Table 34, UL 94 50W Vertical Burning tests in Table 35 through Table 39, and UL 94 5VB tests on PEI in Table 40. Volume Resistivity (VR) Tests None of the 3D printed “as-received” frABS builds resulted in significantly different volume resistivity than the injection molded frABS; however, many “oven-aged” builds did (thirteen of twenty-seven). Conversely, none of the 3D printed “oven-aged” PEI builds resulted in significantly different volume resistivity than the injection molded PEI yet most of the “as-received” builds did (twenty-two of twenty-six). Despite these different trends, none of the 3D printed builds, frABS or PEI, exhibited significantly greater volume resistivity than the corresponding injection molded specimens (Figure 7 for frABS and Figure 8 for PEI).

Table 30: Fraction of 3D printed frABS and PEI builds that exhibited different volume resistivity behavior than injection molded samples at a statistically significant level.

Parameter Value Fraction of Different frABS

Builds Fraction of Different PEI Builds

As-Received Oven-Aged As-Received Oven-Aged ALL 3D BUILDS -- 0 / 27 13 / 27 22 / 26 0 / 26


Tip Size L 0 / 12 5 / 12 12 / 13 0 / 13 M 0 / 3 1 / 3 -- -- H 0 / 12 7 / 12 10 / 13 0 / 13

Raster Angle L 0 / 12 7 / 12 11 / 14 0 / 14 M 0 / 3 1 / 3 7 / 8 0 / 8 H 0 / 12 5 / 12 4 / 4 0 / 4

Air Gap L 0 / 12 7 / 12 9 / 10 0 / 10 M 0 / 3 1 / 3 5 / 5 0 / 6 H 0 / 12 5 / 12 8 / 10 0 / 10

Dielectric Breakdown Voltage and Strength (DS) Tests Almost all the 3D printed frABS and PEI builds had significantly different dielectric breakdown voltages and strengths than the corresponding injection molded specimens (“oven-aged” PEI specimens could not be compared because results for the injection molded samples were limited by the utilized test instrument). As a result, it was not possible to identify which of the four printing parameters was most significant. However, none of the 3D printed builds, frABS or PEI, in the “as-received” or “oven-aged” condition, had a dielectric breakdown voltage or strength




that was greater than that of the corresponding injection molded specimens (Figure 9 and Figure 10 for frABS and Figure 11 and Figure 12 for PEI). Table 31: Fraction of 3D printed frABS and PEI builds that exhibited different dielectric breakdown voltage behavior than injection molded samples at a statistically significant level. Results for test instrument limited

“oven-aged” PEI builds are excluded.



As-Received Oven-Aged As-Received Oven-Aged ALL 3D BUILDS -- 24 / 27 26 / 27 25 / 26 --

Build Orientation X 8 / 9 9 / 9 10 / 10 -- Y 7 / 9 9 / 9 10 / 10 -- Z 9 / 9 8 / 9 5 / 6 --

Tip Size L 10 / 12 11 / 12 13 / 13 -- M 2 / 3 2 / 3 -- -- H 12 / 12 12 / 12 12 / 13 --

Raster Angle L 10 / 12 12 / 12 13 / 14 -- M 2 / 3 3 / 3 8 / 8 -- H 12 / 12 11 / 12 4 / 4 --

Air Gap L 11 / 12 12 / 12 10 / 10 -- M 2 / 3 3 / 3 6 / 6 -- H 11 / 12 11 / 12 9 / 10 --

Table 32: Fraction of 3D printed frABS and PEI builds that exhibited different dielectric strength behavior than injection molded samples at a statistically significant level. Results for test instrument limited “oven-

aged” PEI builds are excluded.



As-Received Oven-Aged As-Received Oven-Aged ALL 3D BUILDS -- 24 / 27 26 / 27 26 / 26 21 / 26


Tip Size L 10 / 12 11 / 12 13 / 13 11 / 13 M 2 / 3 2 / 3 -- -- H 12 / 12 12 / 12 13 / 13 10 / 13

Raster Angle L 10 / 12 12 / 12 14 / 14 12 / 14 M 2 / 3 3 / 3 8 / 8 5 / 8 H 12 / 12 11 / 12 4 / 4 4 / 4

Air Gap L 11 / 12 12 / 12 10 / 10 6 / 10 M 2 / 3 3 / 3 6 / 6 6 / 6 H 11 / 12 11 / 12 10 / 10 9 / 10

Comparative Tracking Index (CTI) Tests Comparative tracking index results were not possible to statistically compare due to the testing methodology. In lieu of statistical significance, comparisons were based on voltage differences greater than the minimum 25 V step size. Thus, 3D printed builds exhibiting comparative tracking index voltages less than the injection molded sample minus 25 V were considered different as were the 3D printed builds exhibiting comparative tracking index voltages more than 25 V greater than the corresponding injection molded sample, i.e.

|CTI3𝐷𝐷 − CTI𝐼𝐼𝐼𝐼| > 25 V




Approximately half of the 3D printed builds exhibited comparative tracking indices differing from the corresponding injection molded sample by more than 25 V, Table 33. Analysis of the frABS results indicated that most significant differences (more than 25 V difference) were for 3D printed builds with lower comparative tracking indices than the injection molded frABS with the exception of Z-orientation builds which tended to result in greater voltages than the injection molded frABS. In contrast to the frABS samples, none of the 3D printed PEI builds exhibited comparative tracking indices significantly less (more than 25 V) than the injection molded PEI. Build orientation also appeared to be influential on the PEI builds, however, the Z-orientation PEI builds were comparable (within 25 V) to injection molded PEI instead of greater as observed for the Z-orientation frABS builds. In addition to the build orientation effect, air gap seemed to have an influence on the comparative tracking indices of the 3D printed frABS such that greater air gaps yielded greater fractions of significantly different (more than 25 V) 3D printed frABS builds. This effect was not observed for the 3D printed PEI.

Table 33: Fraction of 3D printed frABS and PEI builds that exhibited comparative tracking index behavior differing by more than 25V from injection molded samples.



50 Drops 100 Drops 50 Drops 100 Drops Top Surface -- 14 / 23 12 / 23 11 / 26 10 / 26 Bottom Surface -- 2 / 4 1 / 4 4 / 4 3 / 4

Build Orientation (top surface)

X 5 / 9 3 / 9 7 / 10 6 / 10 Y 3 / 5 3 / 5 4 / 6 4 / 6 Z 6 / 9 6 / 9 0 / 10 0 / 10

Tip Size (top surface)

L 5 / 10 5 / 10 5 / 13 5 / 13 M 2 / 3 1 / 3 -- -- H 7 / 10 6 / 10 6 / 13 5 / 13

Raster Angle (top surface)

L 8 / 12 7 / 12 3 / 12 3 / 12 M 2 / 3 1 / 3 4 / 8 3 / 8 H 4 / 8 4 / 8 4 / 6 4 / 6

Air Gap (top surface)

L 4 / 10 5 / 10 3 / 10 2 / 10 M 2 / 3 1 / 3 4 / 6 4 / 6 H 8 / 10 6 / 10 4 / 10 4 / 10

Hot Wire Ignition (HWI) Tests Although all the frABS builds, 3D printed and injection molded, yielded PLC ratings of 0 by strict interpretation of UL 746A (specimens melted away from the nichrome heating wire without igniting), the melt times for more than one-half of the 3D printed frABS builds (fifteen of twenty-seven) were different from the injection molded frABS at a statistically significant level, Table 34. The melt times of the fifteen significantly different 3D printed frABS builds were longer than the injection molded specimens, consistent with the hypothesis that the irregular surface and the voids and gaps within the specimens acted as thermal insulators. Analysis of the distribution of the different builds indicated that build orientation was the most significant printing parameter, with the Z-direction having the greatest effect on melt times. Six of the thirty 3D printed PEI builds exhibited different hot wire ignition performance from the injection molded PEI, Table 34. However, only one or two of the five test specimens for each of the six builds ignited within the maximum test duration suggesting the performance difference of




those builds may not have been significant. Nonetheless, build orientation, particularly the Z-direction, was also found to be the most influential printing parameter for the PEI builds.

Table 34: Fraction of 3D printed frABS and PEI builds that exhibited different hot wire ignition behavior than injection molded samples at a statistically significant level.

Parameter Value Fraction of Different Builds frABS 1 PEI 2

3D Printed -- 15 / 27 6 / 30


Tip Size L 8 / 12 3 / 15 M 2 / 3 -- H 5 / 12 3 / 15

Raster Angle L 6 / 12 3 / 12 M 2 / 3 1 / 12 H 7 / 12 2 / 6

Air Gap L 7 / 12 1 / 12 M 2 / 3 2 / 6 H 6 / 12 3 / 12

Notes: 1 frABS fractions are based on melt times 2 PEI fractions are based on PLC results

High-Current Arc Ignition (HAI) Tests All of the 3D printed frABS and PEI builds had equivalent high-current arc ignition resistance performance as the corresponding injection molded specimens. UL 94 Flammability Tests – Vertical Twenty of twenty-seven 3D printed frABS builds yielded the same UL 94 V-2 vertical flame rating as the injection molded frABS whereas the other seven 3D printed frABS builds did not meet the requirements for any UL 94 vertical flame rating, Table 35. Build orientation was the most influential of the four investigated printing parameters and the other three print parameters had similar levels of influence to each other. All the 3D printed PEI builds yielded the same UL 94 V-0 vertical flame rating as the injection molded PEI, Table 35. This was not a complete surprise given (a) the inherent fire resistance of the polymer molecular structure, and (b) most PEI materials yielding 5VA ratings when evaluated by UL.




Table 35: Fraction of 3D printed frABS and PEI builds that resulted in different UL 94 Vertical Burn ratings than injection molded samples.

Parameter Value Fraction of Different Builds frABS PEI

3D Printed -- 7 / 27 0 / 30


Tip Size L 4 / 12 0 / 15 M 0 / 3 -- H 3 / 12 0 / 15

Raster Angle L 3 / 12 0 / 12 M 0 / 3 0 / 12 H 4 / 12 0 / 6

Air Gap L 4 / 12 0 / 12 M 0 / 3 0 / 6 H 3 / 12 0 / 12

Analysis of the afterflame burn times for the 3D printed frABS builds versus the injection molded frABS indicated that almost all “as-received” 3D printed builds had significantly different t1 afterflame burn times but only five builds had significantly different t2 afterflame burn times, Table 36. Every significantly different 3D printed build yielded a longer afterflame burn time than the corresponding injection molded frABS afterflame burn time thus supporting the hypothesis that the irregular surface and the voids and gaps within the specimens promoted fire growth. In the “oven-aged” condition”, only one 3D printed frABS build had a significantly different t1 afterflame burn time and four builds had significantly different t2 afterflame burn times, Table 37. Interestingly, in each significant case, the afterflame burn time of the 3D printed build was shorter than that of the injection molded frABS suggesting that the injection molded frABS was more impacted by the aging condition than the 3D printed builds. These observed differences were attributed to the manufacturing process used to make the test specimens because the same lot of material was used for 3D printing and injection molding. Specifically, the difference is hypothesized to originate from the duration required to manufacture the test specimens. Injection molded specimens took less than a minute to manufacture while the 3D printed specimens were on the order of an hour. Consequently, the 3D printed test specimens were at temperatures greater than the conditioning temperature for a significantly longer period than the injection molded test specimens. This in turn resulted in the 3D printed test specimens to perform more like the “oven-aged” injection molded specimens.




Table 36: Fraction of 3D printed frABS builds that exhibited different As-Recived UL 94 50W Vertical afterflame burn behavior than injection molded samples at a statistically significant level.

Parameter Value Fraction of Different Builds t1 t2 t1+t2 t2+t3

3D Printed -- 23 / 27 5 / 27 25 / 27 5 / 27


Tip Size L 11 / 12 1 / 12 11 / 12 1 / 12 M 3 / 3 0 / 3 3 / 3 0 / 3 H 9 / 12 4 / 12 11 / 12 4 / 12

Raster Angle L 10 / 12 2 / 12 12 / 12 2 / 12 M 3 / 3 0 / 3 3 / 3 0 / 3 H 10 / 12 3 / 12 10 / 12 3 / 12

Air Gap L 10 / 12 2 / 12 10 / 12 2 / 12 M 3 / 3 0 / 3 3 / 3 0 / 3 H 10 / 12 3 / 12 12 / 12 3 / 12

Table 37: Fraction of 3D printed frABS builds that exhibited different Oven-Aged UL 94 50W Vertical

afterflame burn behavior than injection molded samples at a statistically significant level.


3D Printed -- 1 / 27 4 / 27 3 / 27 4 / 27


Tip Size L 1 / 12 1 / 12 0 / 12 1 / 12 M 0 / 3 1 / 3 0 / 3 1 / 3 H 0 / 12 2 / 12 3 / 12 2 / 12

Raster Angle L 1 / 12 1 / 12 1 / 12 1 / 12 M 0 / 3 1 / 3 0 / 3 1 / 3 H 0 / 12 2 / 12 2 / 12 2 / 12

Air Gap L 1 / 12 1 / 12 1 / 12 1 / 12 M 0 / 3 1 / 3 0 / 3 1 / 3 H 0 / 12 2 / 12 2 / 12 2 / 12

Analysis of the afterflame burn times for the 3D printed PEI builds versus the injection molded PEI revealed eighteen “as-received” 3D printed builds had significantly different t1 afterflame burn times and eleven builds had significantly different t2 afterflame burn times, Table 38. In the “oven-aged” condition”, eleven 3D printed builds had significantly different t1 afterflame burn times and all the builds had significantly different t2 afterflame burn times, Table 39. The afterflame burn times of 3D printed builds were shorter than that of the corresponding injection molded PEI in every significant difference. Build orientation and tip size were more influential than raster angle or air gap on the fraction of significantly different builds.




Table 38: Fraction of 3D printed PEI builds that exhibited different As-Recived UL 94 50W Vertical afterflame burn behavior than injection molded samples at a statistically significant level.


3D Printed -- 18 / 30 11 / 30 19 / 30 9 / 30


Tip Size L 11 / 15 7 / 15 12 / 15 6 / 15 M -- -- -- -- H 7 / 15 4 / 15 7 / 15 3 / 15

Raster Angle L 6 / 12 4 / 12 8 / 12 3 / 12 M 8 / 12 4 / 12 7 / 12 3 / 12 H 4 / 6 3 / 6 4 / 6 3 / 6

Air Gap L 7 / 12 5 / 12 7 / 12 4 / 12 M 4 / 6 3 / 6 4 / 6 3 / 6 H 7 / 12 3 / 12 8 / 12 2 / 12

Table 39: Fraction of 3D printed PEI builds that exhibited different Oven-Aged UL 94 50W Vertical

afterflame burn behavior than injection molded samples at a statistically significant level.


3D Printed -- 11 / 30 30 / 30 30 / 30 30 / 30


Tip Size L 8 / 15 15 / 15 15 / 15 15 / 15 M -- -- -- -- H 3 / 15 15 / 15 15 / 15 15 / 15

Raster Angle L 4 / 12 12 / 12 12 / 12 12 / 12 M 5 / 12 12 / 12 12 / 12 12 / 12 H 2 / 6 6 / 6 6 / 6 6 / 6

Air Gap L 7 / 12 12 / 12 12 / 12 12 / 12 M 2 / 6 6 / 6 6 / 6 6 / 6 H 2 / 12 12 / 12 12 / 12 12 / 12

UL 94 Flammability Tests – 5VB All the 3D printed PEI builds yielded the same UL 94 5VB flame rating as the injection molded PEI. Afterflame burn times, however, differed such that twenty-four of the “as-received” 3D printed builds had significantly different afterflame burn times while only four “oven-aged” builds had significantly different afterflame burn times, Table 40. As with the UL 94 vertical test, the afterflame burn times of 3D printed builds were shorter than that of the corresponding injection molded PEI in every significant difference. Of the four investigated printing parameters, build orientation appeared to be the most influential.




Table 40: Fraction of 3D printed PEI builds that exhibited different UL 94 5VB afterflame burn behavior than injection molded samples at a statistically significant level.

Parameter Value Fraction of Different Builds AR t1 OA t1

3D Printed -- 24 / 30 4 / 30


Tip Size L 13 / 15 1 / 15 M -- -- H 11 / 15 3 / 15

Raster Angle L 8 / 12 1 / 12 M 10 / 12 1 / 12 H 6 / 6 2 / 6

Air Gap L 11 / 12 1 / 12 M 6 / 6 2 / 6 H 7 / 12 1 / 12

INFLUENCE OF 3D PRINTING PARAMETERS The influence of the four investigated 3D printing parameters on the resulting safety performance properties was analyzed using a Machine Learning-based model building process. The process included evaluation of multiple models against the experimental data to select a final model, tuning the model hyper parameters, and finally assessment of the model accuracy. The Decision Tree model was selected in response to the small experimental data size, the non-linear relationships of the 3D printing parameter values (X-, Y-, and Z-orientations), and better performance than many other models. The model hyper parameters were then tuned using K-Fold cross validation in a grid search for each material and test.3 The results of the modeling are expected to change for different polymers and printer parameters, yet the gross trends observed for the investigated frABS and PEI materials should translate to other polymers. Hence, only the gross trends are reported herein. Volume Resistivity (VR) Tests Volume resistivity of the frABS and PEI in the “as-received” and “oven-aged” conditions were independently modeled to assess the relative influence of the four investigated build parameters for each respective case. The four derived models had relatively large errors with normalized RMSE ranging roughly 43 to 95% and r-squared error ranging from 8.3 to 37%, Table 41. Although these errors are relatively large, they are not uncommon for data spanning two orders of magnitude.

3 A description of the K-fold cross validation process can be found at https://en.wikipedia.org/wiki/Cross-validation_(statistics).




Table 41: Quality of model fit results for volume resistivity measurements on 3D printed frABS and PEI.

Polymer Specimen Condition Normalized RMSE 1 Model Accuracy, r2

frABS as-received 0.714 8.29% oven-aged 0.863 19.45%

PEI as-received 0.428 36.72% oven-aged 0.951 31.38%

NOTE: Normalized RMSE = root mean square error / Mean Interpretation of the models indicated the frABS in the “as-received” condition was nominally equally influenced by tip size and build orientation; however, the “oven-aged” specimens were predominantly influenced only by build orientation, Figure 25. In the “as-received” condition builds printed with larger tip size exhibited greater volume resistivity and Y-orientation builds printed using the largest tip size tended to have the largest volume resistivity of all builds. Contrasting the “as-received” build results, the “oven-aged” Y-orientation builds tended to exhibit lower volume resistivity than either X- or Z-orientation builds. PEI builds in the “as-received” condition were predominantly influenced by air gap such that larger air gaps yielded lower volume resistivity; conversely air gap had the opposite effect on the “oven-aged” PEI samples such that larger air gaps yielded greater volume resistivity, Figure 26.

Figure 24: Pareto chart for parameters influential to volume resistivity measurements on 3D printed frABS

in (left) “as-received” condition and (right) “oven-aged” condition.




Figure 25: Pareto chart for parameters influential to volume resistivity measurements on 3D printed PEI in

(left) “as-received” condition and (right) “oven-aged” condition.

Dielectric Breakdown Voltage and Strength (DS) Tests Dielectric strength of the frABS in the “as-received” and “oven-aged” conditions and PEI in the “as-received” condition (results for PEI in the “oven-aged” condition were test instrument limited) were independently modeled to assess the relative influence of the four investigated build parameters for each respective case. The three derived models had modest errors indicating appropriate model fitting with normalized RMSE ranging roughly 4.5 to 26% and r-squared error ranging from 37 to 81%, Table 42.

Table 42: Quality of model fit results for dielectric strength measurements on 3D printed frABS and PEI.



PEI as-received 0.259 81.49% NOTE: Normalized RMSE = root mean square error / Mean

Interpretation of the models indicated the frABS in the “as-received” condition was only significantly influenced by tip size such that builds printed with the smaller tip size exhibited larger dielectric strengths, Figure 27. Oven-aged frABS samples were similarly influenced by tip size, however, raster angle and air gap were also influential depending upon the tip size used to print the specimens. Raster angle was influential for builds printed with the larger tip size such that the +45° / -45° build strategy yielded larger dielectric strengths than the other two angle combinations. Air gap was influential for builds printed with the smaller tip size such that a negative air gap yielded larger dielectric strengths than a positive air gap. Dielectric strengths of PEI builds in the “as-received” condition were influenced by the four investigated print parameters similarly to the frABS builds (builds printed with the smaller tip size exhibited larger dielectric strengths, air gap had a more significant effect on builds printed with the larger tip size such that larger dielectric strengths were observed for a negative air gap than a positive air gap, Figure 28).




Figure 26: Pareto chart for parameters influential to dielectric strength measurements on 3D printed frABS

in (left) “as-received” condition and (right) “oven-aged” condition.

Figure 27: Pareto chart for parameters influential to dielectric strength measurements on 3D printed PEI in

“as-received” condition.

Dielectric breakdown voltage of the frABS in the “as-received” and “oven-aged” conditions and PEI in the “as-received” condition (results for PEI in the “oven-aged” condition were test instrument limited) were independently modeled to assess the relative influence of the four investigated build parameters for each respective case. The three derived models had modest errors indicating appropriate model fitting with normalized RMSE ranging roughly 4.0 to 12% and r-squared error ranging from 23 to 96%, Table 43.

Table 43: Quality of model fit results for dielectric breakdown voltage measurements on 3D printed frABS and PEI.



PEI as-received 0.119 96.72% NOTE: Normalized RMSE = root mean square error / Mean




Dielectric breakdown voltage models for the frABS in the “as-received” condition demonstrated similar trends as observed for the dielectric strength – breakdown voltage was only significantly influenced by tip size such that builds printed with smaller tip size exhibited larger dielectric strengths, Figure 29. Oven-aged frABS samples were influenced by raster angle such that the 0/90° build strategy yielded larger dielectric breakdown voltages than the other two angle combinations. Build orientation was important for 0/90° builds such that X-orientation builds yielded the lowest dielectric breakdown voltages and Y-orientation builds yielded the largest. Tip size, however, was important for other raster angle build strategies such that builds printed with smaller tip size exhibited larger dielectric breakdown voltages than builds printed with larger tip size. Dielectric breakdown voltages for PEI builds in the “as-received” condition were predominantly influenced by build orientation such that Z-orientation builds yielded larger dielectric breakdown voltages than the other two orientations. Air gap had a smaller influence on dielectric breakdown voltage and the influence depended upon the build orientation. For the Z-orientation builds, negative air gaps yielded lower dielectric breakdown voltages than positive air gaps whereas negative air gaps yielded larger dielectric breakdown voltages for X- and Y-orientation builds than positive air gaps.

Figure 28: Pareto chart for parameters influential to dielectric breakdown voltage measurements on 3D

printed frABS in (left) “as-received” condition and (right) “oven-aged” condition.




Figure 29: Pareto chart for parameters influential to dielectric breakdown voltage measurements on 3D

printed PEI in (left) “as-received” condition.

Comparative Tracking Index (CTI) Tests As previously stated, the test methodology utilized to assess comparative tracking index barred statistically rigorous analysis of CTI results for determining the relative influences of the four investigated print parameters. In lieu of statistical significance, CTI results were analyzed for trends by simple comparison rather than the Machine Learning-based approach used to analyze other performance properties. Only build orientation suggested a clear influence on CTI for both materials, however, the impact differed for the two materials. Z-orientation builds exhibited the highest CTI result for frABS specimens yet the lowest for PEI specimens. Tip size also appeared to be influential for frABS such that specimens printed with the bigger tip size exhibited greater CTI results. None of the other three investigated parameters (tip size, raster angle, air gap) were clearly influential for PEI. Hot Wire Ignition (HWI) Tests Average melt times observed for the hot wire ignition tests on 3D printed frABS was modeled to assess the relative influence of the four investigated build parameters. The derived model had modest errors with a normalized RMSE of 17% and a r-squared error of 65%. Interpretation of the model indicated the frABS was predominantly influenced by build orientation, Figure 31, such that Z-orientation builds took longer to melt through than X- and Y-orientation builds.




Figure 30: Pareto chart for parameters influential to hot wire ignition measurements on 3D printed frABS.

Because only nine of one hundred fifty 3D printed PEI build specimens ignited within the maximum hot wire ignition test duration, test results for the 3D printed PEI builds were not significantly distinguishable to determine the relative influence of the four investigated printing parameters beyond a gross trend of build orientation. In this case it was the Z-orientation build that accounted for all but one of the specimens that ignited. High-Current Arc Ignition (HAI) Tests None of the investigated 3D printing parameters had a measurable influence on high-current arc ignition resistance performance as evidenced by equivalent performance of all the 3D printed builds. UL 94 Flammability Tests – Vertical UL 94 Vertical test afterflame burn times observed for the frABS in the “as-received” and “oven-aged” conditions were independently modeled to assess the relative influence of the four investigated build parameters. The six derived models (t1, t2, and t1+t2 for the “as-received” and “oven-aged” conditions) had relatively large errors with normalized RMSE ranging roughly 18 to 57% and r-squared error ranging from 55 to 73%, Table 44. Although these errors are relatively large, they are not atypical for data with large CoV as observed for UL 94 Vertical tests.

Table 44: Quality of model fit results for UL 94 Vertical flammability test measurements on 3D printed frABS.

Polymer Specimen Condition

t1 afterflame burn t2 afterflame burn t1+t2 afterflame burn Normalized

RMSE 1 Model

Accuracy, r2 Normalized

RMSE 1 Model

Accuracy, r2 Normalized

RMSE 1 Model

Accuracy, r2

frABS as-received 0.570 58.58% 0.219 71.94% 0.264 70.05% oven-aged 0.490 65.06% 0.201 85.99% 0.178 73.06%

NOTE: Normalized RMSE = root mean square error / Mean Interpretation of the six frABS afterflame burn time models indicated build orientation as the most influential build parameter on afterflame burn times, Figure 32 through Figure 34. In general, Y-orientation builds yielded the shortest t1 afterflame burn times and X-orientation builds yielded the longest afterflame burn times. Build orientation had a different influence on t2




afterflame burn times with Y-orientation builds exhibiting the longest burn times and Z-orientation builds exhibiting the shortest burn times. Despite these different relative influences, the combined t1+t2 afterflame burn times were impacted by build orientation in the same relative manner as the t1 afterflame burn times – Y-orientation builds yielded the shortest burn times and X-orientation builds yielded the longest. These trends were observed for both the “as-received” and “oven-aged” specimens. The other three investigated print parameters (air gap, tip size, and raster angle) were secondary or tertiary influencers. In general, smaller air gaps and tip sizes yielded shorter afterflame burn times whereas the influence of raster angle depended upon the other print parameters. It is hypothesized that the same physical phenomenon was responsible for the observed influences of air gap and tip size, namely specimen density. Denser specimens, i.e. greater occupied volume, have fewer and / or smaller voids and therefore less surface area for flame attachment.4 Smaller air gaps would result in rasters in the same plane being printed closer together and thus smaller voids between adjacent rasters; likewise, smaller tip sizes would result in thinner layers and thus smaller voids between adjacently stacked layers.

Figure 31: Pareto chart for parameters influential to UL 94 Vertical t1 afterflame burn time measurements

on 3D printed frABS in (left) “as-received” condition and (right) “oven-aged” condition.

Differences in UL 94 Vertical test afterflame burn times observed for the PEI specimens were within a standard deviation thereby barring assessment of the influence of four investigated build parameters on afterflame burn times.

4 Voids and surface irregularities in injection molded specimens have long been known to adversely influence UL 94 Vertical test afterflame burn times and ratings.




Figure 32: Pareto chart for parameters influential to UL 94 Vertical t2 afterflame burn time measurements


Figure 33: Pareto chart for parameters influential to UL 94 Vertical t1+t2 afterflame burn time measurements


UL 94 Flammability Tests – 5VB As previously stated, all the 3D printed PEI specimens exhibited the same UL 94 5VB flame rating and comparable t1 afterflame burn times thus preventing statistical analysis of results to determine the relative influences of the four investigated print parameters. In lieu of statistical significance, results were analyzed for trends by simple comparison of averages t1 afterflame burn times rather than the Machine Learning-based approach used for other performance properties. Non-statistical analysis suggested tip size and air gap had similar influences on the PEI in 5VB tests as observed for 3D printed frABS in the UL 94 Vertical tests (smaller air gaps and tip sizes yielded shorter afterflame burn times). Build orientation, however, differed for the PEI specimens versus the frABS specimens. Z-orientation builds had the shortest afterflame burn times and Y-orientation builds had the longest afterflame burn times for the PEI specimens whereas frABS specimens printed in the Y-orientation exhibited the shortest afterflame burn times.




FINDINGS

The influence of different combinations of material extrusion 3D printing print parameters and build strategies on material ignition, flammability, and electrical properties was systematically investigated using two commercially-available polymers, a black color flame retardant poly(acrylonitrile-butadiene-styrene) (frABS) and a natural color polyetherimide (PEI). The frABS polymer was printed on a popular desktop 3D printer anticipated to be on the low cost end of 3D printers used to make polymer products submitted to UL for certification whereas the PEI was printed on a common industrial-grade 3D printer. Respective materials were also evaluated as injection molded specimens for comparison of material properties measured for test specimens made by 3D printed. While this investigation was by no means all encompassing, particularly with regards to the limited number of investigated materials, printer models, print parameters, and build strategies, several important findings expected to translate to other polymers and possibly other printing technologies were made: 1. Print quality was more consistent with the industrial-grade printer than the desktop printer

presumably because of the industrial-grade printer’s superior motors, actuators, and measurement system and its enclosed, temperature controlled build chamber.

2. Print parameters and build strategies influenced results such that the same material on same printer did yield critically different performance. a) Build orientation was the most influential of the four investigated print parameters and

build strategies for most of the investigated performance properties. b) Air gap and tip size tended to have an interactive influence on performance properties,

possibly by affecting void size and printed part density. 3. Dimensionally comparable 3D printed and injection molded test specimens did not yield the

same performance results. 3D printed specimens yielded comparable or inferior performance (e.g. lower dielectric strength / resistance, worse flame rating, longer burning time) to injection molded specimens except for comparative tracking index (CTI) (see point 4 below).

4. Comparative tracking index (CTI) measurements of the grooved surface of 3D printed specimens appeared to yield misleading results because of a test method artifact. The surface grooves, and any voids emanating downward from the test surface, can wick the electrolyte test liquid away from the electrodes to artificially reduce the amount of electrolyte at the electrodes and promulgate higher CTI ratings than for a smooth, non-wicking surface.

5. Contrasting UL 94 flammability test behavior for the frABS and PEI materials (3D printed frABS performed worse than injection molded frABS whereas 3D printed PEI was comparable or slightly better than injection molded PEI) suggest that the UL 94 flammability test response of 3D printed specimens is influenced by the print parameters and build strategy (presumably via influence on the physical characteristics of the test specimen) in combination with inherent material properties.




RECOMMENDATIONS

Based on the work report herein, the following recommendations are made: 1. Material performance properties used to assess compliance of 3D printed components and

products should be based on test specimens printed same way as the 3D printed component / product and not on traditionally molded test specimens.

2. Guidelines for assessing the “true” CTI of materials used in 3D printed components and parts should be developed.

3. The influence of inherent material characteristics and physical characteristics of printed specimens on performance properties should be investigated.

4. Investigation on the influence of 3D printing should be expanded to include long-term thermal aging effects as described in UL 746C

5. Investigation on the influence of 3D printing should be expanded to 3D printing technologies beyond material extrusion

Documents

I 3D P MATERIAL EXTRUSION UL 94 UL 746A MATERIAL P · extrusion and do not distinguish the reported results from material properties measured for 3D printed test specimens. UL investigated