Percolation Threshold of Bacterial Nanocrystals in Biopolymeric Matrices to Build Up Strengthened Biobased Food Packaging

Bacterial cellulose nanocrystals (BCNCs) extracted from cellulose residues, resulting from film-cutting operations used for the commercial production of dressings, were studied as reinforcement for films based on gelatin, pectin, and hydroxypropylmethyl cellulose (HPMC). The biopolymer matrices differ in their monomer and functional group (gelatin: -COOH and -NH; pectin: -COOH and HPMC -OH). The addition of BCNCs into a polymer matrix for biopolymeric nanocomposite formulation was based on values around the theoretical percolation threshold. The results of this study showed that the BCNCs had a diameter and mean length range of (27 ± 1) nm and (180 ± 10) nm, respectively, producing films reaching 120.13 MPa of tensile strength, 10.9 GPa of Young's modulus, and a toughness of 335.17 × 10⁶ J/m³. All films showed good transparency and a smooth surface. Surface micrographs (SEM) revealed homogeneous, compact, smooth regions, and no macropores. The crystallinity index of the BCNCs produced was 68.69%. The crystallinity of the gelatin, pectin, and HPMC films improved from 10.25 to 44.61%, from 29.79 to 53.04%, and from 18.81 to 39.88%, respectively. These results show the possibility of using films for freeze-dried food packaging.