Nacre-like toughening of photopolymers - TU Wien · 2017. 11. 23. · Nacre-like toughening of photopolymers Dipl.-Ing. Sonja Baumgartner Christian Doppler Laboratory ... 4 5 7 6

Nacre-like toughening of photopolymers

Dipl.-Ing. Sonja Baumgartner

Christian Doppler Laboratory

„Photopolymers for Digital and Restorative Dentistry“

19.10.2017

Motivation I

• Commercial resins for Additive Manufacturing (AM) and casting

2RADTECH EUROPE 2017

SLA FDM SLA SLS Casting

Ch

arp

y Im

pac

t St

ren

gth

[kJ

/m²]

Source: T. Swetly, Capabilities of additive manufacturing technologies (AMT) in the validation at BMW, Rapid. Tech, Mai 2014

19.10.2017

• Natural toughening mechanisms

Motivation II


Naleway et.al. (2016). Structure and mechanical properties of selected protective systems in marine organisms. Materials Science and Engineering: C. 59. 1143-1167.

High toughness High strength

19.10.2017

• Toughness: Resistance against crack growth

• Strengthening: important for large deformation volume

Toughening + Strengthening

RADTECH EUROPE 2017 4

𝑊 = න

𝑉

න

𝜀𝑏

𝜎 ∙ 𝑑𝜀 ∙ 𝑑𝑉Dissipated energy:

W …. Deformed volume V

W …. Flow stress s

W …. Strain at break eb

Crack

Force F

Plastic zone

19.10.2017

Tough photopolymers

• Large internal friction

• Physical bonds (hydrogen bonds)

• Reduce crosslink-density (e.g. chain transfer agent )

• Heterogeneity

• Phase separation

• Core-shell-particles

• “Digital materials”

• Strengthening

• High-MW additives or crosslinkers


19.10.2017

ABS

• Matrix/ continuous phase: Acrylonitrile/styrene copolymers (SAN)

• Dispersed phase: based on polybutadiene (PB)


brittle, hard

soft, tough

tough & strong

Figure: Motoki, S.; Kaneko, T.; Aoyama, Y.; Nishioka, H.; Okura, Y.; Kondo, Y.; Jinnai, H. Journal of Electron Microscopy 2010, 59, S45.

phase separation

internal frictionhigh molecular weight

19.10.2017

• Matrix: Urethanemethacrylate

• Toughener: Core-shell particles

Heterogeneity


Source: Alexandre Megret, Master thesis TU Wien (2017)

CSPs amount (wt%)

Ch

arp

yIm

pac

t St

ren

gth

(kJ/

m²)

soft core

rigid shell

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Stereolithographic Manufacturing

• DLP – Digital Light Processing

1 Light Source (LED 460nm)2 DMD Chip (dynamic mask)3 Optics4 Coating system 5 Tiltable vat6 Building platform7 Back light8 Manufactured part

12

3

4

5

67

8

Dynamic mask approach Resolution: ~25 µmBuilding size: 80 mm x 45mmWavelenght: 405 nm - 460nm


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Printing system


1 Coating system 2 Tiltable vat3 Rotating building platform4 Inkjet printhead

1 2

3

4

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Inkjet strategies

• Drop-on-Demand

• Selective placement of inkjet droplets

• Resolution 100 dpi

• Nozzle size 52 µm


5V TTLInk flowUSB/RS232

1

2

6

745

3

1 Drop-Tuner2 Host PC3 Camera4 Flash controller5 High power LED6 Ink delivery system7 Print head

19.10.2017

• Stereolithography/ Matrix:

• Inkjet/ jetted parts:

Inkjet strategies


1920 x 1080 px

image for 3D printing

302 x 256 px

1920 x 1080 px

image after slicing pips

image for inkjet

slicing

converting

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• Boundary conditions:

• Nozzle size: 52 µm

particles < 2 µm

• Viscosity: 8 – 20 mPas

• Surface tension: 24 – 36 mN/m

• Heating of printhead

• Reactivity

• Additives

• Rheology

• Thixotropy

• Sedimentation

Ink development


reactive ink based on PPGDA

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Results: Printing


droplets on glass slide droplets inside 3D-printed part

100 dpi

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• Specimens:

• Without Inkjet (“Reference“)

• Every 2nd layer („50%“)

• Each layer („100%“)

Results: DMA


XYZ

0

0,05

0,1

0,15

0,2

0,25

0

1000

2000

3000

4000

-50 0 50 100 150

Tan

Del

ta

Sto

rage

Mo

du

lus

[MPa

]

Temperature [°C]

Reference 50% Inkjet 100% Inkjet

Nearly constant Tg

Decreasing storage modulus

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• With higher ink content:

• Decreasing tensile strength

• But significantly higher elongation at break

Results: Tensile Test


0

2

4

6

8

10

12

14

16


Elo

nga

tio

n a

t b

reak

[%

]

9,5%

12,4%

14,7%+ 55%

0

10

20

30

40

50

60

70

0 5 10 15

Ten

sile

str

ess

[N/m

m²]

Elongation [%]

58,8 MPa53,1 MPa

49,5 MPa

- 15%

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Results: Impact Test


0

2

4

6

8

10

12

Reference 100% Inkjet

DYN

STAT

Imp

act

stre

ngt

h (

kJ/m

²)

XZY XYZ ZXY

• Dynstat: 10 specimens for each direction

and ink content

Increasing toughness for all building directions by 25 - 45%

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• creep (cold flow)

• 3-point-bending

• at 37°C for 3h

• 2% deformation

• in H2O

• Relaxation

Results: DMA (RSA)


0

15

30

0 50 100 150 200

Stre

ss [

MPa

]

Time [min]


Stress [MPa] 0 min 60 min Relative drop

Reference 24,6 5,8 76,4%

50% Inkjet 28,3 5,7 79,9%

100% Inkjet 24,5 6,3 74,3%

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Summary



Storage Modulus at RT [MPa] 2650 2750 2450 ↓ (-)

Tan Delta/ Tg 0,24/ 99°C 0,23/ 101°C 0,24/ 98°C ↔

Tensile strength [MPa] 59 53 49 ↓ (-)

Strain at break [%] 9,5 12,4 14,7 ↑ (+)

Dynstat Impact Strength [kJ/m²] 7,7 - 10,3 ↑ (+)

Relaxation in 1h [%] 76,4 76,4 76,4 ↔

19.10.2017

Outlook

• Material development

• Matrix material

Tougher matrix for overall improvement of mechanical properties

• Jetting material (“Ink”)

Elastomers

Fillers: Core-shell particles, ceramics, metal oxides…

• Hot Lithography

• “Printability” of high viscous materials

• The other way round:

• Strengthening tough material instead of toughening brittle material

(“Backbone”)


19.10.2017

• Aesthetic applications

• bio-inspired aesthetics

coloring of teeth, prostheses, …

• Selective coloring of parts

• Conductive inks

• Direct printing of electronic components

• Multimaterial

• Combination of e.g. ceramic filled inks and tough photopolymers for

stereolithography

Surface modification (tribological properties, wear resistance,…)

Future Possibilities


Thank you for

your attention!

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Nacre-like toughening of photopolymers - TU Wien · 2017. 11. 23. · Nacre-like toughening of photopolymers Dipl.-Ing. Sonja Baumgartner Christian Doppler Laboratory ... 4 5 7 6