Facile fabrication of chrome-tanned leather wastes/natural rubber composite: Mechanochemical de-crosslinking effect on collagen fibers and chrome complexation enabled in-situ compatibilization

With the growth of leather industry, plenty of leather solid wastes (LSW) have been generated annually but economic and ecological solution to utilize LSW is lacking because the crosslinked structure inhibits the reprocessing at macromolecular level to attain high performance materials. Herein, we present a facile route to realize physically de-bundling and de-crosslinking of chrome tanned collagen fibers as well as the preparation of LSW/natural rubber (NR) composite featuring remarkable tensile properties via mechanochemistry effect exerted by solid-state shear milling (S 3 M) equipment. It is found that original coordination between chrome and carboxylic group can be cleaved and the released chrome enables the in-situ compatibilization between LSW and natural rubber via the complexation between chrome and sulfur, which enables dual excellence in toughness and tensile strength compared with non-chromium containing composite. The improved dispersion and interfacial interaction enable the incorporation of 40 wt% LSW to afford respective NR composites with exceptional stress at 100 % strain (S100) and modulus, which are 5.07 MPa and 27.33 MPa, respectively, as well as superior tear strength and thermal stability. The S 3 M technology not only highlights a facile and green route to turn chrome containing LSW into high performance bio-based NR material, but also spurs the devising of innovative materials comprising leather collagen fibers.