Novel application of Zn-containing Zeolitic Imidazolate Frameworks in promoting the vulcanization and mechanical properties of natural rubber composites

Three kinds of Zn-containing Zeolitic Imidazolate Frameworks (Zn-ZIFs, including ZIF-8, ZIF-11 and ZIF-14) based on the zinc ions coordinating with different imidazolate ligands were added into the natural rubber (NR) using the DM and TMTD binary accelerators system, respectively. The influences of Zn-ZIFs on the sulfur vulcanization behaviors and mechanical properties of NR matrix were evaluated. The results indicated that the addition of ZIF-8 or ZIF-14 could realize the fast vulcanization of NR at 130°C (the ordinary vulcanization temperature of NR is above 150°C), while ZIF-11 did not show the obvious accelerating performance. Amongst the three Zn-ZIFs, ZIF-8 benefited NR matrix for the acquirement of the highest tensile strength and the largest crosslinking density. As an optimal additive, ZIF-8 with 0.6 phr distinctly improved the physical-mechanical, thermo-oxidative aging resistance and dynamic mechanical properties of NR composites. It proved that Zn atom and its coordination porous network in Zn-ZIFs played synergistic effects in accelerating vulcanization and enhancing mechanical properties of NR matrix besides its role of reinforcement filler. Then the above ZIF-8/DM/TMTD vulcanization system was used to prepare the UHMWPE fibers/NR composites. The mechanical properties of the UHMWPE/NR composites were significantly improved in contrast to the pure NR matrix.