Improved properties of polyvinyl alcohol films blended with aligned nanocellulose particles induced by a magnetic field

Abstract

In this study, polyvinyl alcohol (PVA) films filled with nanocellulose particles were developed for food packaging. In particular, the effect of the weak magnetic field-induced alignment of the nanocellulose filler in PVA blended with rod-shaped cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) on the physicochemical properties of the respective blends was investigated. For the alignment of the nanocellulose particles (6% with respect to PVA), a film-forming solution of each blend was cast and a homogeneous magnetic field of the order of milli Tesla was applied during drying. Microscopic investigations were conducted to analyze the dispersion of the CNCs and CNFs in the PVA matrix. The influence of particle alignment was examined in terms of the microstructure, intermolecular interactions, crystallinity, and hydration state of the film, as well as water migration. The applied magnetic field induced the orientation of the nanocellulose fillers, leading to their improved dispersion in the PVA matrix. The uniform structure formed owing to the magnetically induced alignment of nanocellulose led to enhanced mechanical, barrier, and hydrophobic properties, as well as thermal stability of the two blends. The improvement was more evident for the CNC/PVA blend compared to the CNF/PVA one. The applied magnetic field decreased the fluidity of the film and increased the number of water molecules bound to PVA. When applied in the preservation of strawberries, the films exposed to a magnetic field facilitated better protection and firmness of the fruit.