The trend toward bio-derived and biodegradable packaging materials has led to both consumers and manufacturers to alternative materials. The use poly(lactic acid) (PLA) has shown promise as a bio-derived and biodegradable packaging material but does not have good barrier properties. The addition of cellulose nanocrystals (CNCs) can improve barrier properties while maintaining film transparency. Therefore PLA-CNC composites are a sustainable alternative to reduce the environmental impact of packaging. One of the major challenges is the difficulty in dispersing dried CNCs in the polymer matrix. Poor dispersion can lead to film defects, lack of transparency, and decreased mechanical performance while not fully exploiting the improvements CNCs can impart. Our objective is to advance our understanding of the influence of the morphology of dried CNCs to the properties of the resulting PLA-CNC nanocomposites. In this study, CNC aqueous suspension was diluted from 10.7% to 1% with aid of sonication and followed by freeze drying (slow and flash). The particle size and morphology of the CNCs before and after freeze drying were determined by Atomic Force Microscopy and scanning electron microscopy, respectively. Nanomposites were tested for thermal and mechanical properties. Before freeze drying CNCs were in nano-scale, while agglomerations were formed after freeze-drying process. The sizes of particles/aggregates were reduced with increased sonication treatment time. By incorporating CNCs that were flash-frozen in liquid N<sub>2</sub> from 1 wt% suspension, the mechanical properties of nanocomposites were increased as compared to neat PLA. CNCs dried from diluted suspension showed higher cold-crystallization temperature and lower cold-crystallization enthalpy than neat PLA and nanocomposites from CNCs dried from 10.7% suspension. This indicated delayed cold crystallization kinetics when compounding small aggregates of CNCs. This could be contributed to better dispersion of CNCs with smaller particle sizes which was dried from 1% suspension. The nanocomposites from CNCs with smaller sizes also showed higher degree of crystallinity as determined by differential scanning calorimetry analysis. This demonstrated that smaller aggregates of CNCs would facilitate the crystallization of PLA polymer as a role of nucleation agents. By varying the morphology of dried CNCs the properties of nanocomposites can be tunable for packaging applications.<br/>

Effect of dilution-freezing-drying process on Cellulose Nanocrystals (CNCs) for Polylactic Acid (PLA)-CNC composite packaging

253rd National Meeting (2017)

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