Liquid Crystalline Behaviors of Chitin Nanocrystals and Their Reinforcing Effect on Natural Rubber

Abstract

Chitin nanocrystals (CNCs), rod-like crystalline nanoparticles from natural sources, show high aspect ratio, high modulus, and excellent reinforcing ability toward polymers. In this study, CNCs aqueous dispersions were first prepared by acid hydrolysis of raw chitin. The resulting dispersion was investigated by polarized optical microscopy and rheometry at different CNCs concentrations. A nematic liquid crystals phenomenon with increasing solid concentration is found in the CNCs dispersion. When the concentration of CNCs dispersion is beyond 5 wt %, the dispersion forms liquid crystal phase. CNCs dispersions were then compounded with natural rubber (NR) latex to prepare NR/CNCs composites. CNCs are evenly dispersed in NR matrix, which can effectively enhance the mechanical properties and thermal stability of rubber. The tensile strength of NR/CNCs composite containing 10 wt % CNCs is 5.75 MPa, which is 6.25 multiples of pure NR. Also, the tear strength, storage modulus, and thermal decomposition temperature of the composites increase with increasing CNCs loading. The improvement of NR properties is caused by the uniformly dispersed CNCs and the good interfacial interactions between CNCs and rubber molecular chains. NR/CNCs composites show many advantages such as light color, lightweight, and high performance over the traditional carbon black-filled rubber.