An optimized set of processing parameters was determined for trypsin hydrolyzed gliadin protein (THGd, from wheat) and unvulcanized synthetic isoprene rubber (IR) composite compounds. The compounding temperature, time, and shear dependency of the THGd:IR compounds were investigated with rheology, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Individual protein aggregates measuring ∼64 × 280 nm, with a length-to-width aspect ratio of ∼4.3, were agglomerated within the IR matrix, as measured in SEM-EDX micrographs. A higher compounding temperature (T = 150 °C) was favorable for good protein aggregate dispersion and deagglomeration, which resulted in IR reinforcement, as demonstrated by up to a 65% increase in storage modulus (G′). The tan δ was lowered by the addition of the THGd protein to IR, indicating less mechanical energy was lost as heat in the composites. As the compounding speed, that is, shear rate, was increased from 30 to 60 rpm at constant temperature (T = 150 °C), the average agglomerate size and G′ were minimally affected, but the loss tangent (tan δ) was increased, indicating an increase in IR degradation with shear rate. By drying the THGd hydrolysate at a slower rate or to a greater solids content, the composite G′ was increased and tan δ was decreased. In the slow-dried THGd hydrolysate, protein aggregates were less resistant to breakup during processing, indicating that the protein preparation was an important processing parameter.

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