Fabrication of untreated and silane-treated carboxylated cellulose nanocrystals and their reinforcement in natural rubber biocomposites

Abstract

In this study cellulose nanocrystal (CNC) was extracted from Napier grass stems and subsequently functionalized to carboxylated cellulose nanocrystal (XCNC) by using an environmentally friendly method namely the KMnO4/oxalic acid redox reaction. The XCNC was subsequently modified with triethoxyvinylsilane (TEVS) called VCNC by using ultrasound irradiation. The characterization of the prepared XCNC and VCNC was performed. The needle-like shape of XCNC was observed with an average diameter and length of 11.5 and 156爊m respectively. XCNC had a carboxyl content of about 1.21爉mol爂?1. The silane treatment showed no significant effects on the diameter and length of XCNC. When incorporated into natural rubber (NR) both XCNC and VCNC showed very high reinforcement as evidenced by the substantial increases in modulus and hardness of the biocomposites even at very low filler loadings. However due to the high polarity of XCNC tensile strength was not significantly improved with increasing XCNC loading up to 2 phr above which it decreased rapidly due to the filler agglomeration. For VCNC the silane treatment reduced hydrophilicity and improved compatibility with NR. The highly reactive vinyl group on the VCNC抯 surface also takes part in sulfur vulcanization leading to the strong covalent linkages between rubber and VCNC. Consequently VCNC showed better reinforcement than XCNC as evidenced by the markedly higher tensile strength and modulus when compared at an equal filler loading. This study demonstrates the achievement in the preparation of a highly reinforcing bio-filler (VCNC) for NR from Napier grass using an environmentally friendly method and followed by a quick and simple sonochemical method. ? 2023 The Author(s).