A Cross-Linking/Percolating-Integrated Strategy to Enhance Crystallizable Rubber Using Rod-Like Reactive Biobased Nanocrystals

Cross-link-based and percolation-based methods have been separately applied to develop highly elastic crystallizable materials. However, cross-linking may exert a trade-off effect between the strength and the stretchability, and the heterogeneous nucleation of percolation fillers may change the crystalline behavior in an undesirable way and may decrease the toughness. We thus focused on exploring a method to increase the elastic properties of crystallizable polymers with no strength decrease. Using cellulose nanocrystals (CNCs) with high percolation properties due to their high aspect ratio, we integrated the two strategies of cross-link and percolation to improve the full mechanical properties of eucommia ulmoide gum (EUG), a sustainable polymer, for developing green composite materials. The crystallinity of EUG could decrease to 22% with thiol-functionalized CNCs (mCNCs), solving the urgent problem of EUG on its inevitably high crystallinity from its trans-double bonds. The thiol-functionalization was to offer CNC chemical activity to cross-link with EUG, which limited the segment movement of the EUG around CNC and decrease the heterogeneous nucleating ability of CNC. Then, the strength and elongation at break of EUG-based nanocomposite maximally increased to 16.2 MPa and 498%, respectively. Such an EUG-based material was prepared with biomass resources and was a qualified candidate for sustainable elastomers, which was of high industrial potential in packing materials.