Dual enhancement of dispersion of cellulose nanocrystals, crystallization performance, flexibility and barrier properties through polyethylene glycol coating in melt-processed poly(L-lactide)-based nanocomposites

Poor barrier properties of cellulose nanocrystal (CNC) filled poly(L-lactide) (PLA) caused by inferior dispersions have limited its widespread use in food packaging applications. In this work, polyethylene glycol (PEG) was employed as a coating agent for CNC to fabricate ternary PLA-based system via a continuous extrusion method. Our research strategy is to ultimately achieve enhanced gas barrier properties of the system, through generating/enhancing the dispersion of CNC and crystallization performance of PLA, which depend on the composition of PEG (PEG/CNC ratio). With the increase of PEG/CNC ratio, the dispersion of CNC, flexibility, and the synergistic effect of crystallization performance on PLA between them were gradually improved. Consequently, the oxygen barrier properties of the system were improved due to the increased overall crystallinity and the enhanced dispersion of CNCs. The PEG/CNC ratio of 5/1 simultaneously achieved excellent CNC dispersion with a mean length of approximately 200 nm, a very fast crystallization rate, a high degree of crystallinity of 23 %, an elongation at break of 180 %, and a 60 % reduction in oxygen transmission rate. To the best of our knowledge, no melt-processed CNC-filled PLA materials with such CNC dispersion, crystallinity, barrier properties and flexibility have been reported in the open literature. The obtained results provided valuable insights and practical guidance for the large-scale production of PLA/CNC-based materials for food packaging applications. • Ternary PLA/CNC/PEG biocomposites with enhanced dispersion of CNC and physical properties were prepared by melt processing. • The dispersion of CNC in the system was gradually improved by increasing PEG/CNC ratio. • The synergistic effect between PEG and CNC on crystallization of PLA was verified from multiscale analysis. • PEG at appropriate molar mass as an excellent CNC carrier could also enhance the toughness and barrier properties.