Functionalized Cellulose Nanocrystals for Improving the Mechanical Properties of Poly(Lactic Acid)

Abstract

Biopolymers are emerging materials with numerous capabilities of minimizing the environmental hazards caused by synthetic materials. The competitive mechanical properties of bio-based poly(lactic acid) (PLA) reinforced with cellulose nanocrystals (CNCs) have attracted a huge interest in improving the mechanical properties of the corresponding nanocomposites. To obtain optimal properties of PLA-CNC nanocomposites, the compatibility between PLA and CNCs needs to be improved through uniform dispersion of CNCs into PLA. The application of chemical surface functionalization technique is an essential step to improve the interaction between hydrophobic PLA and hydrophilic CNCs. In this study, a combination of a time-efficient esterification technique and masterbatch approach was used to improve the CNCs dispersibility in PLA. Nanocomposites reinforced by 1, 3, and 5 wt% functionalized CNCs were prepared using twin screw extrusion followed by injection molding process. The mechanical and dynamic mechanical properties of pure PLA and nanocomposites were studied through tensile, impact and dynamic mechanical analysis. The impact fractured surfaces were characterized using scanning electron microscopy. The mechanical test results exhibited that tensile strength and modulus of elasticity of nanocomposites improved by 70% and 11% upon addition of functionalized CNCs into pure PLA. The elongation at break and impact strength of nanocomposites exhibited 43% and 35% increase as compared to pure PLA. The rough and irregular fracture surface in nanocomposites confirmed the higher ductility in PLA nanocomposites as compared to pure PLA. The incorporation of functionalized CNCs into PLA resulted in an increase in storage modulus and a decrease in tan δ intensity which was more profound in nanocomposites reinforced with 3 wt% functionalized CNCs.