Agricultural proteins as multifunctional additives in ZnO‐free synthetic isoprene rubber vulcanizates

Abstract

Corn zein and wheat gliadin protein are compounded into synthetic cis-1,4-polyisoprene rubber (IR) and sulfur-cured in a zinc oxide (ZnO)-free system. The curing kinetics and mechanical and morphological properties are compared to a ZnO-activated or carbon black (CB)-reinforced cure system. The proteins provide reversion resistance and reinforcement to IR at filler loadings as low as 1 part per hundred rubber (phr). The zein-IR composites exhibit higher moduli, better filler-matrix adhesion, and less filler agglomeration/migration than gliadin-IR because zein is more chemically compatible with IR. The gliadin-IR composites have a lower percent set and hysteresis, indicating the formation of an elastic restoring gliadin network. Optimal properties are achieved at 2-phr gliadin and 4-phr zein. At gliadin loading >2 phr and zein loading >4 phr, the protein domain size increases and mechanical properties deteriorate. At equal filler loading, property improvements over CB-IR are observed for one or both proteins.

Bioresourced fillers for rubber composite sustainability: current development and future opportunities

“…The developed LDH was able to deliver Zn ions during the curing process to complete the vulcanization process and hence, ZnO-free rubber compound. Recently, plant proteins (i.e., wheat gliadin and corn zein) have been used to improve the properties of ZnO-free synthetic isoprene rubber 338 . These efforts demonstrate that there are a number of chemistries and technologies under development that can potentially replace or complement ZnO, which will reduce the current concerns associated with the leaching of Zn species from rubber goods after being disposed in the environment.…”

Highly Stretchable, Ultratough, and Multifunctional Poly(vinyl chloride)-Based Plastics via a Green, Star-Shaped Macromolecular Additive

“…Developing elastomers with improved mechanical performance, low cost, high stability, and preferred functionalities is highly demanded for current industrial applications such as in sealants, medical devices, automotives, and other emerging areas including flexible strain sensors, stretchable batteries, roll-up displays and communication devices. − Currently, most of the elastomers are derived from polymers with low glass transition temperature ( T g ) far below the ambient temperature, such as poly­(isoprene), and poly­(butyl acrylate), poly­(dimethylsiloxane), and poly­(butadiene) . With liquid-like behavior and weak mechanical performance for these intrinsic elastic polymers, chemical/physical cross-linking or copolymerization with another type of glassy polymer ( T g > ambient temperature) is usually applied to achieve elastomers with improved modulus and high toughness. − Mays and co-workers have reviewed different types of living polymerization techniques, including anionic polymerization, that have been utilized for the synthesis of hard blocks and soft blocks containing copolymeric elastomers with different architectures, such as triblock linear polymers, star copolymers, and bottlebrush copolymers .…”