Mechanical Reinforcement of Natural Rubber Latex with Cellulose Nanofibers from Triodia Pungens

This study investigates the effect of residual hemicellulose, lignin and surface modification of cellulose nanofibers (CNFs) in order to strengthen natural rubber (NR) without compromising its compliance. In this study, commercial pre-vulcanized NR latex was combined with high aspect ratio CNFs isolated from Australian spinifex arid grass (Triodia pungens), at 0.1-2 wt.% loadings. The CNFs were prepared by various isolation and chemical treatment approaches, namely; (i) sodium hydroxide treatment (NaOH-CNF), (ii) bleaching with NaClO₂ (B-CNF) and (iii) choline chloride-urea treatment (CCU-CNF) and then were combined with NR latex. The resulting NR-spinifex CNF nanocomposites were benchmarked against NR nanocomposites incorporating commercial CNFs from Maine University, USA (M-CNF).

The results showed that the incorporation of NaOH-CNF and CCU-CNF into NR latex at loadings in the range of 0.1-0.5 wt.% demonstrated enhancement in tensile strength compared to the blank NR, without compromising compliance or elasticity. The tensile strength of nanocomposites reinforced with 0.5 wt.% NaOH-CNF, which had a high content of lignin, and 0.1 wt.% CCU-CNF were enhanced 11% (27 MPa) and 17% (28.4 MPa), respectively. The glass transition temperature and storage modulus of these nanocomposites also remained unchanged, as determined by DSC and DMA. A further study using B-CNF showed a decrease in nanocomposite tensile strength, however; these formulations demonstrated less stiffness and better mechanical properties compared to NR/M-CNF, which is thought to be associated with a higher hemicellulose content (43 wt.%) in B-CNF. The outcomes of this study reveal that the presence of lignin and hemicellulose in CNFs, in combination with further chemical surface modification, can positively influence adhesion and dispersion of CNFs in NR host polymers leading to attractive property profiles.