SBS, the major raw material for SBS-based TPR footwear, provides strength, elasticity and other performance for footwear. SBS grade YH-815, SBS T171 are frequently used for production of SBS-based TPR footwear. However, the specific grades should be selected based on manufacturers’ requirements for footwear, including costs, performance, sole type, etc.
Softening oil is mainly used for improving the flowability, reducing costs in the production of SBS granules for shoe soles. The flowability of SBS granules for shoe soles is generally measured by melt flow rate (MFR). The hardness of SBS granules for shoe soles can be reduced by adding softening oil.
The softening oil can be chosen based on two cases: a. The selected softening oil has good compatibility with polystyrene, the rigid phase in SBS; b. The selected softening oil has good compatibility with polybutadiene, the soft phase in SBS. The former one is not recommended.
Resin plays the role of improving performance and filling in the production of SBS granules for shoe soles. The selection of resin should consider the compatibility with SBS first, generally following the principle of "SBS is compatible with resin when their solubility parameters are approximate.” General-purpose polystyrene (GPPS) is the most common organic filler, which can enhance hardness and elasticity modulus of SBS granules for shoe soles with slight reduction of abrasion and tear resistance. The commonly used resins also include ethylene vinyl acetate copolymer (EVA) and polyethylene (PE). EVA can enhance weatherability, ozone resistance, aging resistance and solvent resistance.
The addition of fillers in the production of SBS granules for shoe soles is to reduce costs. The commonly used fillers are white carbon black, calcium carbonate, talcum powder, etc.