Nano cellulose-crystals: Isolation and their promising application as reinforcement in vulcanized natural rubber compounds

Cellulose nanocrystal (CNC) fillers have gained attention in research and industrial applications owing to their excellent properties and environmental bias. They can be added to natural rubber (NR) compounds to enhance properties such as the modulus of elasticity. CNCs can be extracted by different acid methods that promote singular features in interfacial adhesion, according to the type of acid used. This study addresses the feasibility of using cellulose nanoparticles in vulcanized NR composites. For this purpose, two different hydrolysis procedures using sulfuric acid and the less aggressive phosphoric acid were performed. These nanoparticles were then added to different amounts of NR compound. The effects of the CNCs on the vulcanization of the NR compound were evidenced by the formation of a zinc-cellulose-rubber complex, which reduced the optimal vulcanization time and increased the NR compound cure rate, particularly for the samples treated with phosphoric acid. In addition, the formation of this complex structure affected the morphology and mechanical properties of the composites. In particular, the tensile strength, elongation at break, and modulus at 300 % of the composites with nanocellulose treated with phosphoric acid increased by 90 %, 16 %, and 51 %, respectively, compared to the NR compound. Furthermore, the higher aspect ratio of the nanocellulose particles, mainly treated with phosphoric acid, favored the filler-matrix adhesion, making them a promising alternative to enhance the mechanical properties of NR compounds.