Effects of Multiple Recycling on the Structure and Morphology of SEBS/PP Composites

A study of the chemical, mechanical, rheological, and morphological properties of recycled styrene–ethylene–butylene–styrene/polypropylene ( SEBS / PP ) composites was performed to investigate the viability of the application of these materials as recyclable halogen‐free alternatives to plasticized poly(vinyl chloride). The SEBS and PP were initially compounded in a ratio of 3:7 and repeatedly recycled. After over ten rounds of recycling, the SEBS / PP composites exhibited no significant changes either in tensile strength or in tensile elongation. However, a reduction in hardness, decrease in the temperature of the onset of thermal decomposition, and significant increase in their melt flow index ( MFI ) values were observed. Notably, X‐ray scattering measurement and transmission electron microscopy experiments of the SEBS / PP composites indicated that these changes in hardness and MFI originated from morphological changes of the SEBS / PP composites resulting from thermal degradation of the SEBS triblock copolymers that occurred over multiple rounds of recycling.