Post‐Additional Proteins into Rubber Matrices Behave as Filler to Reinforce Rubber

ABSTRACT The effect of post‐additional protein on strain‐induced crystallization (SIC) was investigated in natural rubber, guayule rubber, and synthetic polyisoprene rubber. In this study, we employed bovine serum albumin (BSA) as a model protein for the rubber matrices, and BSA was dispersed in the rubber matrices as the lyophilized powder. Mechanical properties were assessed through uniaxial tensile tests, revealing that all rubber samples exhibited reinforcement with post‐protein addition, regardless of the origin of the rubbers. Additional tests, including swelling, thermal analysis, and dynamic mechanical analysis, indicated that the BSA powder mixed with rubber matrices behaves as a filler. In situ wide‐angle X‐ray diffraction measurements further explained the role of BSA powder as a filler, showing that the onset strain of SIC decreased with the addition of the BSA powder. Our results suggest that post‐additional protein can function as an environmentally friendly filler, depending on the rubber preparation process, regardless of the origin of the polyisoprene rubber.