Spin coating method improved the performance characteristics of films obtained from poly(lactic acid) and cellulose nanocrystals

Abstract

For the last few decades, the application of biopolymers such as poly(lactic acid, PLA) as an alternative to synthetic polymers in the packaging industry is in great demand. However, to rival the traditional polymers, the barrier properties and antimicrobial activities of PLA need to be adapted to the food packaging requirements. The purpose of this research was to compare the impact of thin-film fabrication techniques in combination with different contents of cellulose nanocrystals (CNCs) (1–5 wt%) on the barrier and antimicrobial properties of PLA films. The nanocomposite thin films were manufactured via solvent casting and spin-coating techniques. The spin-coating method has been employed for the first time in this work to prepare nanocomposite thin films with a thickness of ˂ 0.2 mm. The nanocomposite films were tested for surface morphology, degree of crystallinity, water vapor permeability, contact angle, and antimicrobial properties. Scanning electron microscopy (SEM) micrographs revealed the strong tendency of CNCs to establish microscale aggregates, however, a high drying rate in the spin-coating method decreases the self-assembly in CNCs. Thus, a significantly higher degree of crystallinity and glass transition temperature were observed in spin-coated films due to a more uniform dispersion of CNCs in PLA. Higher contact angle and lower water vapor transfer rate in spin-coated samples confirmed the lower hydrophilicity character of spin-coated thin films. Two separate assays were employed for evaluating the anti-microbial activity of PLA on the foodborne pathogens. The results showed that the film manufacturing technique and CNC concentration have a strong influence on microbial reduction.