Cha-Cheol Park

Effects of hardness and thickness of polyurethane foam midsoles on bending properties of the footwear

In sports shoe design to achieve better athletics performance, the bending stiffness of a footwear is an important parameter. Its bending stiffness is mostly dependent on its midsole material. Specifically, hardness and thickness of the midsole material are the major factors on its bending stiffness. Hence, this study focuses on studying the effect of hardness and thickness on bending stiffness of sports shoes by using polyurethane(PU) foam midsole. The results from the experiments show that the bending moment increases as the bending angle increases. Increased hardness and increased thickness of midsole also cause a greater bending moment of the sports shoe, respectively. Moreover, the effect of hardness and thickness of midsole on bending moment measured with assembled shoes is much greater than the one measured with midsoles alone. Therefore, low bending stiffness of the midsole material can not be ignored in shoe design because it could result in high bending stiffness of an assembled shoe.

Preparation and properties of emulsifier-/solvent-free slightly crosslinked waterborne polyurethane-acrylic hybrid emulsions for footwear adhesives (III)–effect of trimethylol propane (TMP)/ethylene diamine (EDA) content

Abstract Stable emulsions of emulsifier-/solvent-free slightly crosslinked waterborne polyurethane-acrylic hybrids (WPU/AC-Ts) with a fixed acrylic monomer content (20 wt.%) and different trimethylol propane (TMP)/ethylene diamine (EDA) (0/0.20, 0.02/0.17, 0.04/0.14, 0.06/0.11, 0.08/0.08, the number indicated the mole% of TMP/EDA) for footwear adhesive materials were successfully prepared in this study. The as-polymerized hybrid emulsion containing 0.10/0.05 mole% of TMP/EDA content was found to be unstable, indicating that near 0.10/0.05 mole% of TMP/EDA content was beyond the limit value of crosslinkable TMP component for self-emulsifing. This study examined the effect of mole% of TMP/EDA on the stability and viscosity of hybrid emulsions, the tensile properties and dynamic mechanical thermal properties of hybrid film samples, and the adhesive strengths of formulated adhesives for footwear at both dry and wet states. As TMP content increased, the tensile strength/modulus/storage modulus/hardness of WPU/AC-Ts film samples increased, however, their elongation at break and water swelling% decreased significantly. The adhesive strength (peel strength) of formulated adhesives was found to be dependent upon the degree of drying, but almost not upon the TMP content in WPU/AC-Ts. The adhesive strength of footwear (EVA/leather) dried at room temperature for 24 h was higher than that of footwear dried for 30 min. However, the adhesive strength at wet state increased significantly with increasing TMP content. The optimum TMP/EDA contents were found to be 0.06/0.11 and 0.08/0.08 mole% to achieve the desired high performance adhesive properties such as high strength in wet state.

The effect of the Knead Processing of the Precured CIIR on the Physical Properties of the BR/PCIIR Composites

Rubber composites were prepared by kneading the precured CIIR with BR in order to analyze the effects of the dispersed phase on the BR/PCIIR composites. The particle size of domain in BR/CIIR composites was decreased and homogeneously dispersed by kneading process the precured CIIR used as dispersed phase in kneader once again. In case of BR/PCIIR40, the kneading time of precured CIIR with BR did not have any effect on the rebound resilience and the hardness of the composite. The tensile strength of the composite prepared by kneading precured CIIR particles and then mixing them with BR increased significantly more than 10% when compared to that of the composite which was not kneaded. The composite maintained the surface friction property while increasing anti-abrasion and mechanical properties significantly by kneading the precured CIIR used as dispersed phase.