Comparison of Mechanical and Thermal Properties of Poly(vinyl alcohol)- Bionanocomposite Films Reinforced with Various Modified Cellulose Nanofibrils and Biologically Active Silver Fir Knotwood Extract

Unmodified cellulose nanofibrils (CNFs), TEMPO cellulose nanofibrils (TCNFs) and lignocellulose nanofibrils (LCNFs) were used to reinforce a poly(vinyl alcohol) (PVA) matrix. The aim of the study was to compare the performance of these nanofillers with respect to the properties of PVA-based biocomposites. XRD and thermal analyses showed that CNFs were the most crystalline and thermally stable, followed by LCNFs and TCNFs. All nanofillers improved the mechanical properties of PVA, with TCNFs providing the greatest reinforcement. The PVA biocomposite with 6% TCNF showed a 55% higher modulus of elasticity and 58% higher tensile strength than the reference film. The most thermally stable bionanocomposite among the PVA-nanocellulose biocomposites was PVA with 6 % CNF; thermal degradation (Tonset) started at a temperature 4 °C higher than the reference. A hydrophilic extract of silver fir knotwood was added to the PVA/nanocellulose system to produce biologically active biocomposites, and its effects on mechanical and thermal properties were evaluated. The extract shifted the Tonset to higher temperatures, with the higher content having an even greater effect. While the extract slightly decreased the tensile strength of the biocomposite, the addition of 4% extract to the LCNF-reinforced biocomposite increased the tensile strength by 10% compared to the PVA-LCNF biocomposite.