Advances in Polyolefin Foaming Technology

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

Colin Li Pi Shan, Brian Yu, Kyle Kummer Dow Packaging & Specialty Plastics

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

➢ Light Weight ➢ Soft and Flexible

➢ Easy to Process Comfort Shoes Performance Footwear ➢ Good Foamability ➢ Low Temperature Use ➢ Recyclable/Sustainable ➢ Safety Protective Mats Safety Equipment

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 3 EVA POE OBC

Ethylene vinyl-acetate Polyolefin Elastomer Olefin Block Copolymer

m

Soft blocks

Hard blocks - High pressure process - Solution process - Solution process, - Free radical catalyst - Molecular catalyst chain shuttling catalysts - Polar functionality (VA) - Non-polar functionality - Non-polar functionality - High melt strength - Linear, high strength - Segmented blocks - High density - Low density - Low density, high Tm

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 4 1.4 DSC Crystallinity Polymer Xc Tg (˚C) Density 1.2 (%) (g/cc) EVA 25 -30 0.941 EVA POE 18 -52 0.870 EVA has higher crystallinity 1 and higher density (due to VA) OBC 20 -62 0.877

POE has low crystallinity POE 0.8 and low Tg

OBC has low crystallinity, Heat Flow(W/g) low Tg, and a high melting 0.6 OBC point

0.4

0.2 -100 -75 -50 -25 0 25 50 75 100 125 150

*Exo down Temperature (˚C)

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 5 Crystallinity Distribution using Enthalpy Corrected DSC

EVA

POE Random Copolymer Olefin Block Copolymer Flexibility and Toughness Elasticity and Heat Resistance

OBC

-30 -10 10 30 50 70 90 110 130 Temperature (°C)

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10000 100

90

s) -

80

) ° 70 1000 60

EVA (2.5MI) EVA (2.5MI) Phase ( Phase Angle 50

Complex Viscosity Complex Viscosity (Pa POE (5MI) POE (5MI) 40 OBC (5MI) OBC (5MI) 100 30 0.1 1 10 100 100 1000 10000 100000 Frequency (rad/s) G* (Pa)

*DMS Rheology measured at 190˚C

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Foam Properties Under-Crosslinked - Foam Density - Closed cell Over-Crosslinked - Cell size, distribution Balance of Foaming and Curing • Melt Strength • Nucleation and Crystallization Good foam cell structure Poor foam cell structure • Crosslinking agent – peroxides, sulphur • Solubility and diffusivity of blowing agent

Chemical Blowing Agents – organic and inorganic blowing agents - azodicarbonamide, OBSH, sodium bicarbonate, citric acid

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Ingredients pre-compounded and mixed Foam together in 1.5L Banbury mixer EVA POE OBC* Ingredients - Polymer EVA 100 - CaCO3 + Filler POE 100 - Blowing agent + Curatives OBC 100 Luperox 40DC SP2 0.9 0.9 0.99 Compression Molding Luperox - 110˚C pre-molding, 4 min 40DC 1.35 1.35 1.485 - 180˚C foaming/Curing, 8 min AC9000 X Y Z ZnO* 0.1X 0.1Y 0.1Z ZnSt* 0.1X 0.1Y 0.1Z Property Testing of Foams CaCO3 5 5 5 - Oven aged shrinkage *Based on prior experiments, POx level was increased by 10% - Tensile, tear, compression set, resilience for the OBC.

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 9 Foam Expansion

Expansion Ratio

Higher and similar expansion ratio observed for EVA and OBC

POE had the lowest expansion ratio

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 10 Degree of Curing MDR Torque (dN.m) 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

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 11 Foam Density and Hardness

Density (g/cc) Shore A Hardness 0.35 60 55 EVA EVA 0.30 50 POE POE 45 OBC 0.25 OBC 40 35 0.20 30 0.15 25 20 0.10 15 1.35 1.50 1.65 1.80 1.95 1.35 1.50 1.65 1.80 1.95 Expansion Ratio Expansion Ratio

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 12 Foam Strength

Tear Strength (N/mm) TensileTensile StrengthStrength ((MPaMpa) 25 5 EVA 20 4 POE 15 OBC 3

10 2 EVA 5 1 POE OBC 0 0 1.35 1.5 1.65 1.8 1.95 MPa Strength, Tensile 1.35 1.5 1.65 1.8 1.95 Expansion Ratio Expansion Ratio

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Resiliency (%) Compression Set (%) 64 70% EVA 62 EVA 60% POE POE OBC 60 OBC 50% 58 40% 56

54 30%

52 20% 1.35 1.50 1.65 1.80 1.95 1.35 1.50 1.65 1.80 1.95 Expansion Ratio Expansion Ratio

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Before Oven Aging

EVA POE OBC

After Oven Aging (70˚C)

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Ionomer can be added to introduce secondary ionic crosslinking

Optimizing foaming behavior: Melt Strength of Foam Compounds (165 C) ▪ Enhancing melt strength 2.5 ▪ Stabilizing bubble growth EVA

2 EVA/Ionomer (10phr) inch)

▪ Controlling the nucleation inch)

- -

lb 1.5

Under-Crosslinked 1

Torgue (lb Torgue 0.5 Torque ( Torque Over-Crosslinked 0.3 0.4 0.5 0.6 0.7 0.8 Peroxide (pph)

Enhanced melt strength with ionomer

*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 16 Ultra Low Density POE/OBC Foam

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

Avg 175µm Foam Properties Avg 52 µm

With POE/OBC Foam Properties 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

® ™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow 17 Polyolefin polymers can be used to make soft, light weight, and resilient foams

Formulation adjustments are needed to account for differences in curing and Summary of Foam Properties 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

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