Evaluating the reinforcing potential of enzymatic cellulose nanocrystals in polypropylene nanocomposite

Cellulose nanocrystals (CNCs) produced through enzymatic hydrolysis exhibit physicochemical properties that make them attractive as eco-friendly reinforcing agents in polymer composites. However, the extent of their efficacy within a polymeric matrix is yet to be fully established. This study investigated the reinforcing capabilities of enzymatic CNC (approximately 3 nm in diameter) isolated from bleached eucalyptus Kraft pulp (BEKP), focusing on its application in polypropylene (PP) nanocomposites produced by injection molding. The study compared the performance of this enzymatic CNC (1-5 % wt) with PP composites reinforced with micro-sized cellulose fibers (BEKP at 10-30 % wt, approximately 13 μm) and additionally with commercial CNC produced by sulfuric acid hydrolysis. Despite enzymatic CNC experiencing agglomeration during spray-drying, leading to an average diameter increase to 3 μm, it still significantly increased the crystallization and glass transition temperature of the PP matrix. However, this agglomeration likely hindered the improvement of the mechanical properties within the nanocomposites. The results also showed that enzymatic CNC provided higher thermal stability at lower reinforcement levels compared to BEKP, but this came with a reduction in stiffness, posing a significant consideration in composite design. The addition of a coupling agent greatly enhanced the dispersion of reinforcements and the interfacial adhesion within the matrix, contributing to the enhanced performance of the composite properties. Additionally, enzymatic CNC demonstrated potential for superior reinforcement efficacy compared to commercially available CNC produced by sulfuric acid hydrolysis. In conclusion, enzymatic CNC exhibited a promising role as nano-reinforcement for thermoplastic polymer nanocomposites, exhibiting higher thermal properties at lower reinforcing loads than traditional micro-sized fiber reinforcements. The absence of sulfur, coupled with its higher thermal stability and sustainable potential, positions enzymatic CNC as a particularly favorable choice for applications involving direct contact with food, cosmetics, pharmaceuticals, and biomedical materials.