Reinforcement of surface-modified cellulose nanofibrils extracted from Napier grass stem in natural rubber composites

Abstract

Cellulose nanofibrils (CNFs) were prepared from Napier grass stems via alkalization, bleaching and sulfuric acid hydrolysis treatments and subsequently characterized by various techniques. Transmission electron microscopy (TEM) confirmed that CNFs with average diameter of 15 nm were successfully obtained in the diluted suspension. However, after freeze drying, CNFs aggregated and formed large fibrillar bundles. X-ray diffraction (XRD) results revealed that CNFs exhibited Cellulose I structure with crystallinity index of 74 %. Results from Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) confirmed the complete removal of noncellulosic compounds after the alkali and bleaching treatments. Surface treatment of CNFs by Bis-(triethoxysilyl-propyl) tetrasulfide (TESPT) was also carried out. Both untreated and TESPT-treated CNFs were added into natural rubber (NR) at various loadings (0–10 phr) to investigate their reinforcements. Regardless of the filler type, modulus and hardness of the NR composites increased continuously with increasing filler loading. Tensile strength increased with increasing filler loading up to 5 phr before leveling off. At any given filler loading, TESPT-treated CNFs exhibited greater reinforcement than untreated CNFs due to the improved rubber-filler interaction and the enhanced crosslink density. The results show the potential use of the TESPT-treated CNFs in rubber reinforcement.