Hydrolyzed wheat protein as a self-assembled reinforcing filler in synthetic isoprene rubber vulcanizates

Trypsin hydrolyzed gliadin (THGd) from wheat protein is utilized as a reinforcing filler in synthetic rubber. THGd self-assembles into a reinforcing filler phase during sulfur vulcanization of synthetic cis-1,4-polyisoprene rubber (IR), as observed by an increase in the β-sheet aggregation absorbance in Fourier transform infrared (FTIR) spectroscopy. The curing process is studied using differential scanning calorimetry (DSC). THGd filler interferes with the curing process resulting in more incomplete cure and a reduced induction time. Young’s modulus (E) increases with protein concentration, curing time, and silane coupling agent concentration. Moduli comparable to or greater than the IR Control are achieved at all tested protein loadings of 4–16 parts per hundred rubber (phr). Hysteresis decreases with curing time showing the formation of a more elastic network and increases with filler and silane concentration showing energy dissipation through filler re-arrangement and rubber molecule-filler particle detachment, respectively. Reduced swelling is observed with the addition of silane coupling agent as there are more protein-rubber interactions. The results suggest that quantities of THGd greater than 4 phr reinforce the rubber phase through continued aggregation into protein β-sheet nanostructures.