1

Ultra High Molecular Weight FunctionalSiloxane Additives in Polymers:

Effects on Processing and Properties

by Kevin J. RyanKevin E. Lupton

Peter G. PapeVivian B. John

Dow Corning Corporation

2

©1999 Dow Corning Corporation. All rights reserved.

Abstract

Two new types of solid siloxane additives for plastics, which give improvedbenefits compared with previous silicone additives, are described in this paper.Ultra high molecular weight (UHMW) siloxanes are used in the new additives;traditional silicone plastic additives have used much lower molecular weightsilicones. The siloxane is converted into solid forms, either masterbatchpellets or powders, which are easy to feed, or mix, into plastics during com-pounding, extrusion or injection molding.

UHMW siloxanes can be compounded into masterbatch pellets at highersiloxane concentrations than previously possible, e.g., up to 50 percent. Theyimpart improved processing and release, lower coefficient of friction, andbroader performance latitude compared with conventional lower molecularweight silicones. These benefits can be delivered at reduced siloxane levelswith increased concentration at the surface interface with a new, functionalizedUHMW siloxane, which provides unique surface segregation characteristics.

UHMW siloxanes have been formulated into powders that can also act asprocessing aids and mechanical property modifiers for highly filled polymerssuch as fire retardant systems.

This paper will use polyolefins as a model. However, many of the effects shownin polyolefins have also been seen in other resin systems.

3

INTRODUCTIONSilicon-based monomers and polymers are finding increasing use in theplastics industry from polymer synthesis to compounding, fabrication andimproving performance of plastic materials1. They are unique materials with awide variety of structural types and a broad range of chemical and physicalproperties.

Polydimethylsiloxanes, the most common silicone polymers, consist of apolymeric backbone of alternating silicon and oxygen atoms (siloxane struc-ture) with methyl groups attached to silicon. Methyl groups can be substitutedwith functional groups to influence compatibility and mobility within thethermoplastic matrix. The number of repeating units can range from one toseveral thousand to give rise to silicone materials with molecular weightsranging from 236 to as much as one million. Even at ultra high molecularweights (UHMWs) approaching one million, the flexibility and free volume ofthe siloxane chain allow silicone polymers to exist as transparent fluids withviscosities increasing as molecular weight increases. UHMW polydimethyl-siloxanes are not crosslinked, will flow like molten polymer, and have viscosi-ties in the 10 million mm2/sec to 50 million mm2/sec (centistoke, or cSt)range. Typical properties of UHMW siloxanes are shown in Table 1.

Lower molecular weight silicone polymers, with viscosities of less than 1000mm2/sec, are used extensively by the plastics industry as external releaseagents on the mold surface. For the past 25 years, higher molecular weightsilicones, with viscosities ranging from 10,000 mm2/sec to 60,000 mm2/sec,have been used as internal additives in thermoplastic polymers to give process-ing advantages and surface property improvements, such as reduced coeffi-cient of friction, improved abrasion resistance, lower wear rates, mold release,easier processing, faster mold cycles and other benefits2,3.

UHMW siloxanes impart expected silicone benefits to plastics, often moreefficiently and more effectively than lower molecular weight silicones, but aredifficult to handle4. This paper will describe UHMW siloxanes that have beenconverted into solid plastic additives that are easy to use and possess function-ality designed to enhance surface effects and processability. Two productforms — pelletized concentrates and powdered additives — have beendeveloped. Some unique benefits have been discovered, compared withprevious technology. The nature of these additives, and their effect on pro-cessing and physical properties of plastics, will be discussed.

Table 1. Properties of Polydimethylsiloxanes

Pour Point -40/-50°C

Glass Transition Temperature -123°C

Density (25°C) 0.977 kg/m3

Refractive Index (25°C) 1.4035

Surface Tension (25°C) 21 mN/m

Dielectric Constant (1000 Hz) 2.76

Solubility Parameter (δ) 7.4

4

EXPERIMENTAL bar pressure, injection and hold Surface roughness samples wereLaboratory compounding was done times of 25 sec and 40 sec, and mold prepared with 5 percent siloxaneon twin-screw extruders such as a temperature of 55°C. A Brabender masterbatches and octene (C8)Leistritz® Micro 18. Siloxane PL2000 Plasticorder and a Rosand LLDPE (MI=2.7 dg/min). Profilesmasterbatches were prepared on Capillary Rheometer were used for were produced on a 1-mm by 25.4-laboratory or production twin-screw other rheometry measurements. The mm ribbon die with a 10-mm landextruders with special screw configu- Rotational Disc Friction Test was and a continuous land made from P-rations to maximize dispersions. developed by Dow Corning Toray 20 alloy steel attached to a 50-mmSiloxane powders were compounded Silicone Co., Ltd., to give COF vs. 24:1 L/D screw (3:1 compressionin proprietary compounding equip- pressure-velocity data. Mold release ratio) with a Maddock mixingment to maximize intimate mixing data was obtained with LDPE on a section and screen pack (40 meshof silica and siloxane components. 35-ton Arburg unit. Screw slippage and 100 mesh). The extruder was

data was obtained with 5.0-MI hoPP not flooded with process aid for theStandard ASTM testing for physicalon a 30-ton Newbury unit. Extrusion practice of preconditioning the dieproperties were carried out for theoutput, amperage and barrel surface. Mean height (R ) measure-data in Table 2. Amoco® 4018 a

pressure data was obtained with ments (micro-cm) of the surfacepolypropylene homopolymer® Linear Low Denisty Polyethylene profile were made with a Mitutoyo(MI = 12) and Petromont film

(LLDPE) on a 2-inch Davis-Standard Surftest 402 (series 178).grade HDPE (MI = 0.1) were used assingle-screw extruder. Paintabilitybase resins and blended with the PP- Coefficient of friction (COF) wasand printability were evaluated withand LDPE-based masterbatches, measured for film made from butenePP in compliance with ASTM Drespectively, to obtain the siloxane- (C3359. Paintability testing used a Red 4) LLDPE blended with 10 percent

modified samples. BASF Novolen® polyolefin plastomer (POP) usingSpot lacquer-based paint system.1160L, a polypropylene homopoly- ASTM D 1894. Contact angle wasPrintability testing used a solvent-mer (hoPP), was used for the rheol- measured on injection-moldedbased two-part ink system andogy data (MI = 7.5). Spiral flow data polypropylene (12 MFR) plaquesTampo pad printer.was obtained on a Battenfeld unit, 40 using ASTM D 724 and a goniometer.

Table 2. Polypropylene and High Density Polyethylene ModifiedWith UHMW Siloxane Masterbatches

Physical Properties With 1 percent and 5 percent Siloxane

Test HDPEHDPE/1percent

HDPE/5percent PP

PP/1percent

PP/5percent

Tensile, MPa 25 25 22 39 37 33

Elongation, percent 76 79 105 36 70 220

Modulus, MPa 1364 1632 908 1751 1884 1646

Izod, Notch, J/m 957 811 721 15 21 29

Melt Flow, g/10 min. 0.1 0.1 0.1 13.3 13.6 13.7

Vicat Softening, °C 128 125 119 157 155 153

Taber Abrasion, mg loss 3.9 7.1 6.3 16.2 14.4 12.0

Coefficient of FrictionStatic 0.21 0.13 0.07 0.25 0.24 0.15Kinetic 0.12 0.07 0.05 0.17 0.14 0.10

5

DISCUSSIONUHMW Siloxane/ThermoplasticResin MasterbatchesHigh viscosity (12,500 mm2/sec to60,000 mm2/sec) silicone additiveshave been supplied as concentrates,usually 20 percent silicone in athermoplastic matrix, or metereddirectly into the process duringinjection molding or extrusion5.Silicone fluid with a minimumviscosity of 10,000 mm2/sec at 25°Cis necessary to give a combination ofexcellent dispersion in the thermo-plastic matrix and excellent surfaceproperties (lubricity, release) to thesilicone-modified thermoplastic.

With proper dispersion of a suffi-ciently high molecular weightsiloxane polymer in a thermoplasticpolymer, the siloxane will form astable dispersion in the polymermatrix even though it is incompat-ible with the organic polymer. Thesiloxane does not migrate to thepolymer surface during processingeven at temperatures above the glasstransition temperature6. Paintabilitytests have shown that if the high-viscosity siloxane is dispersed in therigid resin matrix at a level of lessthan 2 percent and at a fine particlesize (2-4 microns), the siloxaneadditive does not interfere withadhesion of paints, metallics, labelsor decoration7.

Even though UHMW siloxanes aredifficult to handle, siloxanes withviscosities of 15 million mm2/sec to30 million mm2/sec can be com-pounded into common thermoplas-tics such as olefinics, styrenics,polyoxymethylene, nylon andthermoplastic polyesters to makemasterbatches. The siloxane isdispersed in the thermoplasticmatrix at particle sizes of less than 10microns. A photomicrograph ofUHMW siloxane in polypropylene isshown in Figure 1. The UHMWsiloxane masterbatches are dry,conventionally shaped pellets thatcan be used in the same manner asother types of additive concentrates.With previous silicone concentrates,a maximum of 20 percent silicone in

a thermoplastic resin could beobtained. UHMW siloxane concen-trates containing 50 percent siloxanecan be prepared. A list of concen-trates in carrier resins is shown inTable 3.

Table 3. Commercial UHMW Siloxane Masterbatches

SiloxaneMasterbatch Masterbatch Carrier Resin Application

Standard UHMW

MB50-001 PP (Polypropylene) PP, PP/PE Copolymer

MB50-002 LDPE (Low Density Polyethylene) PP, PE/PP Copolymer

MB50-004 HIPS (High Impact PS) GPPS, HIPS

MB40-006 Polyoxymethylene (acetal) copolymer Acetal

MB50-008 SAN (Styrene Acrylonitrile) SAN, ABS, Polycarbonate

MB50-010 HYTREL® (Thermoplastic Polyester) HYTREL®, TP Polyester

MB50-011 Polyamide 6 Polyamide 6, -6,6, -6,12

Functionalized UHMW

MB25-302 LDPE (Low Density Polyethylene) PE, PP

MB50-313 LLDPE (Linear Low Density Polyethylene) LLDPE

MB50-314 HDPE (High Density Polyethylene) HDPE

Functionalized LMW1

MB25-501 PP (Polypropylene) PP, PE

MB50-504 HIPS (High Impact PS) GPPS, HIPS, ABS, SAN

MB25-513 LLDPE (Linear Low Density Polyethylene) PE

1Functionalized LMW Siloxane Masterbatches are currently developmental products.

Figure 1. Photomicrograph of 50 percent UHMW SiloxaneDispersed in Polypropylene (MB50-001)

6

Siloxane additives in plastics, if usedat levels of 5 percent or less siloxane,have little adverse effect on tensileproperties. In Table 2, variousproperties of polypropylene andhigh-density polyethylene, modifiedwith 1 percent and 5 percent UHMWsiloxane (from MB50-001 and MB50-002 masterbatches), are shown.There is a slight decrease in tensilestrength and little effect on melt-flow rate or vicat softening. Somesiloxane-modified thermoplasticsshow no effect on elongation.

UHMW siloxane improves moldrelease. For example, the ease ofrelease of low-density polyethylenefrom a mold surface with UHMWsiloxane (from MB50-002) at a 1percent siloxane level is shown inFigure 2. With virgin LDPE using adeeply cut mold, only 64 percent ofthe part cycles released using a semi-automatic mode. With the additionof 1 percent UHMW siloxane, 100percent of the part cycles released.Evaluations in other resins show thatUHMW siloxane additive impartssignificantly improved releasecharacteristics with lower releaseforce and less siloxane required.

Agglomerated silicone in a thermo-plastic can over-lubricate the screwand cause screw slippage during theextrusion or injection-moldingprocess. Reactive extrusion to forminterpenetrating polymer networksof a silicone and thermoplastic hasbeen suggested to prevent screwslippage8. But properly dispersedhigh-viscosity siloxane gives littlescrew slippage and UHMW siloxaneadditive gives even less screw slippage.

ts R

elea

sed

% P

ar

1009080706050403020100

0

Figure 2. Mold Release of LDPE

1% UHMW Siloxane

7

In Figure 3, MB50-001 masterbatchin polypropylene at siloxane levelsup to 5 percent is compared with30,000 mm2/sec viscosity PDMS,erucamide, and N,N'-ethylenebisstearamide. Results show that theUHMW siloxane in MB50-001 givesless effect on screw return time vs.the other materials in the injection-molding process. Reducing “screwslippage” can be an importantfeature in reducing overall processcycle time.

Figure 4 illustrates the effect ofUHMW siloxane at levels up to 3percent on output in a single-screwextruder in LLDPE. Results show noevidence of decreased output due toscrew slippage and actually indicateslightly increased output using theUHMW siloxane vs. virgin resin.

Figure 4. Output Effect in Single Screw Extrusion

Out

put (

m/m

in)

14

12

10

8

6

4

2

00.2

% UHMW Siloxane in DOWLEX1 2047 LLDPE1 30

20 RPMs

40 RPMs

1DOWLEX is a registered trademark of The Dow Chemical Company.

Scre

w R

etur

n T

ime

(sec

)

55

50

45

40

35

30

25

20

152

% Additive3 4 51

Note: Screw Return Time at 5 percent additive for 30,000 cSt 200fl, Erucamide, andN, N' Ethylene Bisstearamide was >50 seconds.

Figure 3. Injection Molding Screw Slippage

UHMW Si

200 fl. (30,000 cSt)

Lonza Acrawax C

Croda Erucamide ER

8

Other features observed when usingthe UHMW siloxane in the single-screw extrusion process have beenevident when evaluating barrelpressure and amperage draw. Bothare significantly reduced as shown inFigure 5 and 6 at up to 3 percentsiloxane in LLDPE.

A collaborative project with U.K.-based Manchester MetropolitanUniversity9 produced rheology datato show that the siloxane master-batches have profound effects on theflow of polypropylene melts. Fourtechniques were used: torquerheometry to measure the torque onthe melt during and after fusion;capillary rheometry to measure theeffect on elongation viscosity; spiralflow measurement; and the moldingof hair combs at marginal conditionsas a practical measure of the effects.

Figure 5. Barrel Pressure Effect in Single Screw Extrusion

Bar

rel P

ress

ure

(psi

)

3500

3000

2500

2000

1500

1000

500

00.2

% UHMW Siloxane in DOWLEX 2047 LLDPE1 30

20 RPMs

40 RPMs

Figure 6. Amperage Effect in Single Screw Extrusion

DC

Am

pere

s

30

25

20

15

10

5

00.2

% UHMW Siloxane in DOWLEX 2047 LLDPE1 30

20 RPMs

40 RPMs

9

Figure 7 illustrates the result oftorque rheometry using a BrabenderPlasticorder. As can be seen, theaddition of 0.2 percent UHMWsiloxane (as 0.4 percent of MB50-001siloxane masterbatch) reduces thepeak torque produced during meltingof the polymer by 25 percent and theequilibrium torque by 40 percent.

The second technique, capillaryrheometry (using a Rosand instru-ment), illustrates the effect onelongation viscosity of PP. See Figure8. Again, 0.2 percent UHMWsiloxane gives a dramatic effect withelongation viscosity reduced by afactor of four. The beneficial effecton mold filling, for example, can beimagined.

Figure 9 shows the results of spiralflow tests and again illustrates theeffect of 0.2 percent UHMW silox-ane. The benefit can be obtained intwo ways: 1) at various temperaturesthe siloxane offers an increase in theflow of about 30 percent, or 2) thesame flow can be achieved with a50°C reduction in operatingtemperature.

The effect of these rheology differ-ences could be seen when two haircombs were molded from the samepolypropylene. The one moldedwithout siloxane masterbatch (at190°C) gave roughly a similar level ofshort shot in every case over a seriesof 200 moldings. A series of mold-ings under the same conditions butwith 0.4 percent of MB50-001incorporated, i.e., 0.2 percentUHMW siloxane, gave 200 perfectmoldings.

Figure 7. Brabender Rheometry

Tor

que

(Nm

)

35

30

25

20

15

10

5

01000

0% Si

0.2% Si

200 300 400 500Time (seconds)

Figure 8. Rosand Capillary Rheometry

Elo

ngat

ion

Vis

cosi

ty (

kPa

s)

20

18

16

14

12

10

8

6

4

2

00.00E+00

0% Si

0.2% Si

Apparent Shear Rate (/s)

1.00E+03 2.00E+03 3.00E+03 4.00E+03 5.00E+03

Figure 9. Spiral Mold Flow

Flow

(cm

)

60

50

40

30

20

10

0160

0% Si

0.2% Si

Melt Temperature (°C)

180 200 220 240 260

10

An evaluation of the effect ofUHMW siloxane additive on weldline strength of a thermoplasticpolyolefin resulted in the data inFigure 10, which shows that theaddition of UHMW siloxane in-creased the energy to break. Withthe addition of only 0.2 percentUHMW siloxane the energy to breakincreased by 27 percent over virginTPO.

The printability of a polypropylenesubstrate was evaluated at FerrisState University via ASTM D 3359.Virgin PP was compared to PP withthe additions of UHMW siloxane,polydimethylsiloxane (30,000 cSt.),erucamide, and a commercialorganic blend additive at levels up to3 percent. It is well known thatpolypropylene is difficult to print onwithout surface treatment. However,for this study the injection-moldedplaques were tested without surfacetreatment. Figure 11 shows that theuse of the UHMW siloxane did notsignificantly reduce the printabilityof the PP, whereas the other internallubricants reduced print adhesion toa greater degree, by this test method.

The paintability of a polypropylenesubstrate was evaluated at an outsidelaboratory via ASTM D 3359. VirginPP was evaluated and compared withPP with additions of UHMW siloxaneand PDMS (60,000 cSt) at up to 5percent. Table 4 shows that the useof the siloxane materials in thissystem did not decrease paintadhesion with this test method andpaint system.

Figure 10. Weld Line Strength

2.5

2

1.5

1

0.5

0VirginTPO

0.2% PDMS(30,000 cSt)

1% PDMS(30,000 cSt)

0.2%UHMW Si

1%UHMW Si

En

ergy

to B

reak

(Jo

ules

)

Additive % Change

Virgin TPO 0

0.2% PDMS (30,000 cSt) 7.67

1% PDMS (30,000 cSt) 19.82

0.2% UHMW Si 27.38

1% UHMW Si 3.07

Figure 11. Printability of PP

100

90

80

70

60

50

40

30

20

10

00.2

% Additive1 3 50

UHMW Si

PDMS (30,000 cSt)

Erucamide

Commercial OrganicBlend Additive

Note:Tested as moldedTape: 3M No. 250

% P

rin

t Rem

ain

ing

ID

1-11-22-32-43-53-64-74-85-95-106-116-127-137-14

Material Type

100 percent Polypropylene

99.5 percent PP/0.5 percent PDMS (60,000 cSt)

97 percent PP/3 percent PDMS (60,000 cSt)

Adhesion RatingMethod A Method B

2A2A

3B

2A3A4A4A4A4A3A2A4A4A4A4A

95 percent PP/5 percent PDMS (60,000 cSt)95 percent PP/5 percent PDMS (60,000 cSt)99.5 percent PP/0.5 percent UHMW siloxane99.5 percent PP/0.5 percent UHMW siloxane97 percent PP/3 percent UHMW siloxane97 percent PP/3 percent UHMW siloxane95 percent PP/5 percent UHMW siloxane95 percent PP/5 percent UHMW siloxane

100 percent Polypropylene

99.5 percent PP/0.5 percent PDMS (60,000 cSt)

97 percent PP/3 percent PDMS (60,000 cSt)

3B4B4B4B4B5B5B4B3B4B4B4B5B

Notes:1. Testing performed by outside test facility – ACT Laboratories Inc.2. Topcoat was Red Spot AE267 Blue (interior primerless PP lacquer) after powerwash.

Relevant specifications:Ford: WSB-M15J7-A; General Motors: GM4350N class C/O; Chrysler: MS PP9-6

3. Testing per ASTM D 3359.

Table 4. Paintability Testing

11

Lowering the COF of surfaces ofplastics is enhanced with UHMWsiloxane additives. Figure 12 showsthe effect on COF of 3 percentUHMW siloxane (from MB50-001masterbatch) in polypropylene. TheCOF was determined by rotating acylinder of PP containing 3 percentsiloxane against unmodified PP at avarying velocity and constant 2-kilogram force. PP without additivefused because of higher COF andexcessive heat generation; PP withUHMW siloxane shows excellentreduction in COF and fuses at muchhigher velocities.

Recently, a new, functionalizedUHMW siloxane masterbatch hasbeen developed that provides uniquecharacteristics. The functional groupon the siloxane chain is such that ithas an affinity for the metallurgyduring the processing of the poly-mer. Figure 13 illustrates lowersurface roughness of polyethylenewith functional siloxane than withequal levels of other process aids thatall rely on coating the extrusionmetallurgy. The functional siloxaneoutperforms commercial extrusionprocess aids, e.g., fluoropolymers, aswell as nonfunctional UHMWsiloxane.

Figure 12. Friction Testing. Pressure-Velocity Plot for Silicone Masterbatch in PP

0.5

0.4

0.3

0.2

0.1

0

Velocity (m/s)0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

No Silicone

Silicone Masterbatch

P

AA

A: PP withUHMWadditive

)v

Coe

ffic

ient

of

Fric

tion (3% Si)

Figure 13. Surface Roughness

3M FX 5920

Dupont FFTA

Union CarbideUCARSIL PA-1

UHMW siloxane

UHMWfunctional siloxane

0

440 ppm Process Aids in C8 LLDPE

50 100 150 200 250 300 350 400

Avg. Surface Roughness (micro-inches)

257.13

5.6

18

106.9

20.5

158.2

240.2

379.1

40 RPM

20 RPM

12

The new masterbatch demonstratessuperior slip performance inpolyolefin films. Immediate slipmeasurement is made possible asillustrated in Figure 14, which showsthe stability of COF over timerelative to erucamide, which requiresa migration period to achievetargeted COF levels. Figure 15 showsthe consistency of COF at high linespeeds and hot packaging applica-tions that generate high film surfacetemperatures on form fill sealequipment. Erucamide’s slip perfor-mance becomes less effective at thehigher temperatures.

Figure 14. COF Stability Over Time (C4 LLDPE/C8 LLDPE/LDPE blown coex film)

CO

F

1.4

1.2

1

0.8

0.6

0.4

0.2

00%

Film: Film 0 days

Film: Film 8 days

Si Additive Level

0.50% 1% 1% +1000 ppm

AB

Figure 15. COF as a Function of Surface Temperature(C4 LLDPE/C4 LLDPE/LDPE + 10 percent mPE)

CO

F

0.8

0.6

0.4

0.2

0Ambient

NonmigratorySlip Film: Film

Erucamide reference

Temperature

50°C 60°C

13

Figure 16. Coefficient of Friction (COF)

Coe

ffic

ient

of

Fric

tion

(C

OF)

0.3

0.25

0.2

0.15

0.1

0.05

0Erucamide reference UHMW siloxane

Nonmigratory Slip Type (4% addition)

UHMW functional siloxane

0.17

0.26 0.27 0.26 0.270.24

Film: Film

Film: Metal

Figure 17. Contact Angle

LDPE

1% UHMW Siloxane

2.5%UHMW Siloxane

1% Functional UHMWSiloxane (MB25-302)

2.5% Functional UHMWSiloxane (MB25-302)

PP

92

Contact Angle

94 96 98 100 102 104 106 108

100

102

103

100

110 112 114

113

111

The surface segregation featurefacilitates a higher concentration ofthe siloxane toward the surface of afabricated part, thus impartingimproved surface benefits. Siloxaneselectively moves to the surface onlywhen the thermoplastic is in themelt phase. In solidified thermoplas-tic, UHMW siloxane remains indiscrete domains, unlike low molecu-lar weight silicone fluids that mi-grate. Figure 16 illustrates improvedfilm-to-film COF and Figure 17demonstrates increased hydropho-bicity associated with increasedcontact angle of the functionalUHMW siloxane. Also, use levels ofthe additive required for surfacemodification can be less becausemore is being utilized at the surfacethrough surface segregation, ratherthan being trapped in the bulk.Lower molecular weight versions arealso in the development stage.

The improvement in performance ofUHMW siloxane over lower-viscositysilicones as a plastic additive canresult from greater chain entangle-ment and greater mechanicalintegrity of the siloxane whilefunctioning as an additive10. Sincesiloxanes are not compatible withorganic polymers, they entangle withthe polymer and reside at theinterface between polymer mol-ecules, or between polymer mol-ecules and a surface. The highermolecular weight of the siloxaneadditive with its low surface tensionand high free volume exerts its effectmore efficiently and permanentlythan does a lower molecular weightsilicone.

14

SILOXANE POWDERADDITIVESA second series of solid siloxaneadditives for plastics is in the form ofa powder. UHMW siloxane is con-verted into a free-flowing powderwith a particle size range of 6 micronsto 600 microns (average = 90 mi-crons) by compounding UHMWpolydimethylsiloxane with a silicafiller and other additives. Thesepowders can be further modified toattach organo-reactive sites, such asepoxy and methacrylate, to helpmake the powders compatible inorganic resins. A list of powder typesand the suggested resin compatibilityof each are shown in Table 5.

The siloxane powders, when com-pounded into an organic resin usingconventional equipment such as asingle screw or, preferably, a twin-screwextruder, break down their particlesize to a range of 0.5 microns to 5microns. The powders will functionin a manner similar to the UHMWsiloxane masterbatches to improveprocessing, lower COF and give otherbenefits. But a surprising discovery isthe effect on the manner in whichthe modified plastic burns: the rateof heat release, generation of smokeand evolution of toxic carbon mon-oxide gas are significantly reducedrelative to unmodified resin. Fire-related data is discussed in separatepapers11,12.

The effect of a siloxane powder as aprocessing aid in polypropylene isdemonstrated by extrusion torqueshown in Figure 18. Polypropylene,when compounded with typical fireretardants, is very difficult to process.Because of the high filler content andnon-lubricious nature of the additives,high torque and machine wear areproblems during processing. With theaddition of 1 percent siloxane powderC, extrusion torque is reduced over50 percent in the fire-retardantsystem. The siloxane-modified resinalso exhibits improved mechanical

SiloxanePowder

A

B

C

Product Code

4-7105 Resin Modifier

4-7051 Resin Modifier

4-7081 Resin Modifier

Organic Reactivity

None

Epoxy

Methacrylate

Application

PP, PE, vinyl, PS, HIPS,engineering resins

PC, PPO, PBT, PET,thermoplastic elastomers

PP, PE, vinyl, PS, HIPS

Table 5. Siloxane Powders, Functionality and Recommended Resins

Figure 18. Extrusion Torque (% vs. Control)

1009080706050403020100

70% PP/30% FR1(Control)

69% PP/30% FR1/1% Powder C

85% PP/15% FR1 70% PP/30% FR2(Control)

80% PP/15% FR2/5% Powder C

Per

cent

age

Figure 19. Notched Izod Impact Strength

40

35

30

25

20

15

10

5

070% PP/30% FR1

(Control)69% PP/30% FR1/

1% Powder C85% PP/15% FR1 70% PP/30% FR2

(Control)80% PP/15% FR2/

5% Powder C

Joul

es/m

eter

properties as illustrated in Figure 19.The addition of 1 percent siloxanepowder C increased the impactstrength by approximately 100percent over the fire-retardant system,restoring mechanical properties lostfrom the fire-retardant additives.

15

CONCLUSIONSTwo types of solid siloxane additivesfor thermoplastics have beendeveloped that give improved andunique benefits over previoussilicone additives. UHMW siloxanesimpart improved processing, moldrelease, reduction of COF, andscratch and mar resistance.

The addition of UHMW siloxane canexhibit a unique combination ofprocessing and property improve-ments that previously has beendifficult to achieve. Furthermore,with the newly developed,functionalized UHMW siloxanemasterbatch, the technology hasbeen further advanced providingsurface segregation characteristicsfor more efficient delivery of im-proved performance.

An example of the benefit chain canbe envisioned by the followingexample. An OEM would like a

better olefin-based material for theirautomotive interior application toprovide better scratch and marresistance, a surface property thatthe UHMW siloxane has been foundto improve. The injection moldershould see better mold release anddecreased cycle time due to theability to use lower processingtemperatures, thus less cooling timeand less screw return time. Thecompounder should see increasedoutput while decreasing amperageand barrel pressure, providingincreased capacity on a line, espe-cially in compounds with high fillerloadings.

Other valued benefits of usingsiloxane masterbatch technologyinstead of conventional silicone fluidadditives include: 1) materialshandling, in which dirt has anaffinity to silicone fluid (potentialquality issue); 2) spills that are notan issue with the masterbatches

(potential safety issue); 3) additionalequipment, which is not needed(pumps, flow meters, etc.); 4) loss of10 percent to 20 percent fluid due tohigh viscosity and sticking to sides ofdrums; 5) and recycling of drums,among others.

The UHMW siloxane additives areavailable as pelletized masterbatches,with as high as 50 percent siloxane invarious thermoplastic carrier resins,or as a series of powdered siloxaneadditives.

The solid, easy-to-use form of thesesolid siloxane additives is in contrastto the viscous silicone fluids that areoften used in the plastics industry.

16

REFERENCES1. P.G. Pape, “Applications of Silicon Based Chemicals in the Plastics Indus-

try,” Proc. Chemspec USA ’90 Symposium, Cherry Hill, NJ (Oct. 1990).

2. P.J. Clark in: Polymer Surfaces (D.T. Clark and W.J. Feast, eds.),“Modification of Polymer Surfaces by Silicone Technology,” Chapter 11,235-247, John Wiley, New York (1978).

3. R.F. Smith, “Friction and Wear Characteristics of Silicone-ModifiedThermoplastics,” Paper 760371, Soc. Auto. Engineers (Feb. 1976).

4. J.W. White, P.G. Pape, D.J. Romenesko, T. Imai, and Y. Morita, “NewSilicone Modifiers for Improved Physical Properties and Processing ofThermoplastics and Thermosets,” Proc. Ann. Tech. Conf., Soc. Plast.Engineers, 1904–1906 (May 1991).

5. R.F. Smith, “Silicone Fluids as Internal Processing Aids for Thermoplastics,”Paper 780357, Soc. Auto. Engineers (Feb. 1978).

6. M.P.L. Hill, P.L. Millard and M.J. Owen, “Migration Phenomena inSilicone Modified Polystyrene,” Polym. Sci. Technol. 5B, 469 (1974).

7. R.F. Smith, “Silicone Additives Permit Decorating Plastic Parts Right Outof the Mold,” Plast. Des. Process. 17 (8), 53-56 (1977).

8. M. Zolotnitsky, “Modification of Polypropylene with Silicone IPNs,” Proc.Ann. Tech. Conf., Soc. Plast. Engineers, 3576-3580 (May 1995).

9. V. John and D. Puckett, “New Solid Silicone Additives for Plastics Applica-tions,” PE ’97 Conference, Milan, Italy (May 1997).

10. F. W. Fearon and R.F. Smith, “Wear Characteristics of Silicone ModifiedPolystyrene,” Polym. Sci. Technol, 5B, 481 (1974).

11. R. Buch, W. Page and D. Romenesko, “Silicone-Based Additives forThermoplastic Resins Providing Improved Mechanical, Processing, andFire Properties,” Proc. Fire Retardants Chem. Assoc. Symp., 1-16, Tucson,AZ (Oct. 1993).

12. D.J. Romenesko and R.R. Buch, “Method of Imparting Fire Retardancy toOrganic Resins,” U.S. Patent 5,391,594 (to Dow Corning) (Feb. 21, 1995).

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