Effective surface alkylation of cellulose nanocrystals (CNCs) was developed using a nucleophilic substitution reaction with an alkyl bromide to convert hydrophilic groups on the CNCs into alkyl groups and the degree of substitution was quantitatively determined. The resultant alkylated CNCs exhibited improved dispersion in a nonpolar environment and increased hydrophobicity, compared with unmodified and acetylated CNCs. Polylactide (PLA) nanocomposites reinforced with unmodified and modified CNCs were prepared by a solution casting method and the effects of reinforcement on the thermal stability, mechanical properties, morphology, and barrier properties were investigated. In addition, modeling of the mechanical properties was evaluated to simulate the modulus of the PLA nanocomposites and results were compared with the experimental values. PLA nanocomposites reinforced with alkylated CNCs exhibited superior properties in terms of thermal stability, tensile strength, Young's modulus, and barrier properties because of the uniform dispersion and strong interfacial adhesion between filler and matrix. This high performance and fully return-to-nature nanocomposite is expected to expand the utilization of CNCs from sustainable bioresources and the practical application of biodegradable plastics.
Keywords: cellulose nanocrystals; nanocomposites; polylactide; surface modification.