Advances in Polyolefin Foaming Technology...Foaming Technology Foam Properties-Foam Density-Closed cell-Cell size, distribution 8 Balance of Foaming and Curing • Melt Strength •

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow

The Dow Chemical Company

Advances in Polyolefin Foaming Technology

Colin Li Pi Shan, Brian Yu, Kyle Kummer

Dow Packaging & Specialty Plastics

Xian Jiang

E.I. du Pont de Nemours and Company, Inc

Advances in Polyolefin Foaming Technology

▪ Influence of polymer structure on crystallinity and rheology

▪ Chemical foaming – polymer-property relationships

▪ Ionomer addition for ultra low density foams

2


Features of Polyolefin Foams

3

➢ Light Weight

➢ Soft and Flexible

➢ Easy to Process

➢ Good Foamability

➢ Low Temperature Use

➢ Recyclable/Sustainable

➢ Safety

Performance FootwearComfort Shoes

Safety EquipmentProtective Mats


OBC

Soft blocks

Hard blocks

- High pressure process

- Free radical catalyst

- Polar functionality (VA)

- High melt strength

- High density

- Solution process

- Molecular catalyst

- Non-polar functionality

- Linear, high strength

- Low density

- Solution process,

chain shuttling catalysts

- Non-polar functionality

- Segmented blocks

- Low density, high Tm

EVA POE

Ethylene vinyl-acetate Polyolefin Elastomer Olefin Block Copolymer

4

m


0.2

0.4

0.6

0.8

1

1.2

1.4

-100 -75 -50 -25 0 25 50 75 100 125 150

Heat

Flo

w (

W/g

)

Temperature (˚C)

EVA

POE

OBC

Polymer Xc

(%)

Tg (˚C) Density

(g/cc)

EVA 25 -30 0.941

POE 18 -52 0.870

OBC 20 -62 0.877

EVA has higher crystallinity

and higher density (due to VA)

POE has low crystallinity

and low Tg

OBC has low crystallinity,

low Tg, and a high melting

point

*Exo down

DSC Crystallinity

5


Crystallinity Distribution using Enthalpy Corrected DSC

-30 -10 10 30 50 70 90 110 130

Temperature (°C)

EVA

POE

OBC

Random Copolymer

Flexibility and ToughnessOlefin Block Copolymer

Elasticity and Heat Resistance

6


Rheology Comparison

*DMS Rheology measured at 190˚C

7

100

1000

10000

0.1 1 10 100

Co

mp

lex

Vis

cosi

ty (

Pa-

s)

Frequency (rad/s)

EVA (2.5MI)

POE (5MI)

OBC (5MI)

30

40

50

60

70

80

90

100

100 1000 10000 100000

Ph

ase

An

gle

(°)

G* (Pa)

EVA (2.5MI)

POE (5MI)

OBC (5MI)


Foaming Technology

Foam Properties

- Foam Density

- Closed cell

- Cell size, distribution

8

Balance of Foaming and Curing

• Melt Strength

• Nucleation and Crystallization

• Crosslinking agent – peroxides, sulphur

• Solubility and diffusivity of blowing agent

Chemical Blowing Agents

– organic and inorganic blowing agents

- azodicarbonamide, OBSH, sodium bicarbonate,

citric acid

Under-Crosslinked

Over-Crosslinked

Good foam cell structure Poor foam cell structure

8


Experimental

Foam Ingredients

EVA POE OBC*

EVA 100POE 100OBC 100

Luperox 40DC SP2 0.9 0.9 0.99Luperox

40DC 1.35 1.35 1.485AC9000 X Y Z

ZnO* 0.1X 0.1Y 0.1ZZnSt* 0.1X 0.1Y 0.1ZCaCO3 5 5 5

Ingredients pre-compounded and mixed

together in 1.5L Banbury mixer

- Polymer

- CaCO3 + Filler

- Blowing agent + Curatives

Compression Molding

- 110˚C pre-molding, 4 min

- 180˚C foaming/Curing, 8 min

Property Testing of Foams

- Oven aged shrinkage

- Tensile, tear, compression set, resilience*Based on prior experiments, POx level was increased by 10%

for the OBC.

9


Foam Expansion

10

Higher and similar

expansion ratio observed

for EVA and OBC

POE had the lowest

expansion ratio

Expansion Ratio


Degree of Curing

11

POE cured the fastest and

had the highest degree of cure

OBC cured the slowest and

showed the lowest degree of

cure

EVA showed an intermediate

degree of cure

MDR Torque (dN.m)


Foam Density and Hardness

12

0.10

0.15

0.20

0.25

0.30

0.35

1.35 1.50 1.65 1.80 1.95

Expansion Ratio

EVA

POE

OBC

Density (g/cc)

15

20

25

30

35

40

45

50

55

60

1.35 1.50 1.65 1.80 1.95

Expansion Ratio

EVA

POE

OBC

Shore A Hardness


Foam Strength

13

0

5

10

15

20

25

1.35 1.5 1.65 1.8 1.95

Expansion Ratio

EVA

POE

OBC

Tear Strength (N/mm)

0

1

2

3

4

5

1.35 1.5 1.65 1.8 1.95

Ten

sile

Str

en

gth

, MP

a

Expansion Ratio

EVA

POE

OBC

Tensile Strength (Mpa)Tensile Strength (MPa)


Foam Resiliency

14

52

54

56

58

60

62

64

1.35 1.50 1.65 1.80 1.95

Expansion Ratio

EVA

POE

OBC

Resiliency (%)

20%

30%

40%

50%

60%

70%

1.35 1.50 1.65 1.80 1.95

Expansion Ratio

EVA

POE

OBC

Compression Set (%)


Foam Shrinkage

Before

Oven

Aging

After

Oven

Aging

(70˚C)

EVA POE OBC

15


Ionomer Addition for Foaming Control*

Ionomer can be added to introduce secondary ionic crosslinking

Optimizing foaming behavior:

▪ Enhancing melt strength

▪ Stabilizing bubble growth

▪ Controlling the nucleation

Under-Crosslinked

Over-Crosslinked

Enhanced melt strength with ionomer

16

0.5

1

1.5

2

2.5

0.3 0.4 0.5 0.6 0.7 0.8

To

rgu

e (lb

-in

ch

)

Peroxide (pph)

Melt Strength of Foam Compounds (165 C)

EVA

EVA/Ionomer (10phr)

To

rqu

e (

lb-i

nch

)

*C.F. Hsu, R. Chou, W. Whelchel, Y.T. Ou, U.S. Patent 6,528,550 (1999).

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 17

Avg 175µm Avg 52 µm

POE/OBC Foam PropertiesWith 1 phr

ionomer

1.74 Expansion Ratio 1.69

0.14 Av Density, g/cc 0.16

27.5 Shore A 31

60 Rebound, % 61

53 CSET 50%, 50C/6h 53

353 Avg-Strain at Break 383

2.1 Avg-Stress at Break 3.1

11.4 Type C Tear, N/mm 15.5

Ultra Low Density POE/OBC Foam

Foam Properties

Low levels of ionomer significantly reduces cell size and improves foam strength.


Polyolefin polymers can be used to make soft, light weight, and resilient foams

Formulation adjustments are needed to

account for differences in curing and

rheology

▪ EVA - higher foam tear strength

▪ POE, OBC - lower density, softer foams

▪ OBC – excellent dimensional stability and resiliency

▪ Ionomers – cell size reduction, improved foam strength

18

Summary of Foam Properties


The Dow Chemical Company

Thank You

19

Advances in Polyolefin Foaming Technology...Foaming Technology Foam Properties-Foam Density-Closed cell-Cell size, distribution 8 Balance of Foaming and Curing • Melt Strength •

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