Mechanochemistry promoted in-situ compatibilization for highly toughened elastomer and super elastic foam

Elastic materials based on biomass fiber reinforced natural rubber (NR) composites featured by renewability, environmental friendliness, and outstanding toughness have attracted intensive attention. However, the improvement in tensile strength via natural fiber reinforcement is always accompanied by the compromise in toughness, which is rooted in the notoriously weak interfacial bonding originating from the significant mismatch in surface energies between constituent materials. In this work, we for the first time present a facile route to realize the interfacial activation of keratin fibers (KFs) derived from leather solid waste as well as the preparation of NR/KF composite with dual excellence in tensile strength and toughness via mechanochemistry. The activated thiol groups generated by mechanochemical pulverization promote the dispersion and in-situ compatibilization of KFs in rubber matrix, thereby facilitating effective interfacial stress transfer and enhancing the mechanical performance of the composites. As a result, the tensile strength, elongation, and toughness at break of composite elastomer reach 19.4 MPa, 781.0%, and 48.8 MJ/m3, respectively, outperforming the state-of-the-art natural fiber reinforced NR composites. Moreover, the incorporation of mechanochemical-pulverized KFs into NR matrix offers heterogeneous nucleation locales, facilitating the foaming of NR in supercritical carbon dioxide (ScCO2). The cell wall of the composite is in turn reinforced, and the resultant foam manages to deliver an excellent compressive recovery rate of 99.4% even after 200 cycles that outstrips those of reported foams. This work highlights a facile and green route to turn waste bovine hair in leather industry into high-performance bio-based elastomer and super-elastic foam.

Automated summary

This study presents a facile method to prepare NR/KF composite with dual excellence in tensile strength and toughness by activating keratin fibers derived from leather waste via mechanochemistry. The mechanochemical process improves the interfacial bonding between KFs and rubber matrix, leading to enhanced mechanical performance of the composites. The incorporation of mechanochemical-pulverized KFs into NR matrix also promotes the foaming of NR and enhances the compressive recovery rate of the resultant foam.