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Natural rubber/cellulose nanocrystals (NR/CNCs) form true biocomposites from renewable resources and are demonstrated to show significantly improved thermo-mechanical properties and reduced stress-softening. The nanocomposites were prepared from chemically functionalized CNCs bearing thiols. CNCs served as both reinforcing and cross-linking agents in the NR matrix, and the study was designed to prove the cross-linking function of modified CNCs. CNCs were prepared from cotton, and the cross-linkable mercapto-groups were introduced onto the surface of CNCs by esterification. Nanocomposite films were prepared by dispersing the modified CNCs (m-CNCs) in NR matrix by solution casting. The cross-links at the filler-matrix (m-CNCs-NR) interface were generated by photochemically initiated thiol-ene reactions as monitored by real-time FTIR analysis. The synergistic effects of reinforcement and chemical cross-linking at the m-CNCs-NR interface on structure, thermo-mechanical, and stress-softening behavior were investigated. Methods included field emission scanning electron microscopy (FE-SEM), swelling tests, dynamic mechanical analysis, and tensile tests. Compared to biocomposites from NR with unmodified CNCs, the NR/m-CNCs nanocomposites showed 2.4-fold increase in tensile strength, 1.6-fold increase in strain-to-failure, and 2.9-fold increase in work-of-fracture at 10 wt % of m-CNCs in NR.

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Microfibers were prepared from coir, an important lignocellulosic fiber, by chemico‐mechanical treatment. The microfibers with a diameter of 8–13 μm were incorporated in natural rubber and the resultant biocomposites were evaluated for the reinforcing effect of microfibers. Latex stage processing employed for composite preparation reduces fiber agglomeration and provide uniform dispersion of microfibers in the elastomer matrix. Microfiber/natural rubber composites were found to exhibit significant improvement in mechanical properties compared with unfilled and macrofiber filled composites. Microfibers showed higher thermal stability compared with untreated coir. However, degradation resistance of microfiber composites remain lower with respect to vulcanized natural rubber. POLYM. COMPOS., 40:414–423, 2019. © 2017 Society of Plastics Engineers