Poly(vinyl alcohol) (PVA) biocomposite films reinforced with cellulose nanofibrils (CNF) and biologically active tannic acid (TA) were prepared. The influence of different concentrations of CNF and TA in the PVA polymer matrix was investigated in terms of mechanical properties, thermal properties and hydrophobicity improvement of the prepared films. The results showed that in all cases the addition of CNF and TA improved the values of tensile strength and elastic modulus. The PVA film with 10 % CNF exhibited a 30 % higher tensile strength, and the three-component PVA film with 2 % CNF and 10 % TA (P2C10T) exhibited a 40 % higher tensile strength compared to the neat PVA film. The thermal properties (T_g, T_onset) of the PVA biocomposite films were greatly improved, with a significant effect observed for the three-component PVA films. The T_g of the PVA film with 10 % CNF and 10 % TA was 87 °C, 12 °C higher than that of the neat PVA film. For three-component PVA biocomposites with 4 % and 6 % CNF and with all weight percentages of TA, the T_onset shifted to a higher temperature range by about 30 °C compared to the neat PVA film. The PVA film with 2 % CNF and 10 % TA exhibited about a 20° higher contact angle than the neat PVA film. Moreover, the addition of both fillers to the PVA matrix resulted in PVA biocomposites with lower water absorption. PVA film with 10 % TA absorbed about 90 % less water and PVA film with 10 % CNF and 10 % TA absorbed about 80 % less water than the neat PVA film after the films were soaked in water for one hour. The better properties of the composite films produced are due to hydrogen and ester bonds between the components of the composite, which was confirmed by FT-IR spectroscopy. Antioxidant effective films were also obtained due to the biologically active TA to the PVA and PVA/CNF systems.

This study compared the use of cellulose nanofibrils (CNF) and lignocellulose nanofibrils (LCNF) in different concentrations to reinforce the poly(vinyl alcohol) (PVA) matrix. Both nanofillers significantly improved the elastic modulus and tensile strength of PVA biocomposite films. The optimum concentration of CNF and LCNF was 6% relative to PVA, which improved the tensile strength of the final PVA biocomposite with CNF and LCNF by 53% and 39%, respectively, compared to the neat PVA film. The addition of LCNF resulted in more elastic films than the addition of CNF to the PVA matrix. The elongation at break of the PVA biocomposite with 2% of LCNF was more than 100% higher than that of the neat PVA film. The integration of tannic acid (TA) into the PVA-LCNF system resulted in antioxidant-active and more water-resistant PVA biocomposites. The three-component biocomposite films with 2 and 6% LCNF and 10% TA exhibited a more than 20° higher contact angle of the water droplet on the surfaces of the biocomposite films and absorbed more than 50% less water than the neat PVA film. New formulations of biocomposite films have been developed with the addition of LCNF and TA in a polymeric PVA matrix.

The aim of the study was to produce biologically active biocomposite films with improved mechanical properties compared to pure poly(vinyl alcohol) (PVA) film. In a first step, two-component films were produced, namely PVA with the addition of nanocellulose. Unmodified cellulose nanofibrils (CNFs), TEMPO cellulose nanofibrils (TCNFs), and lignocellulose nanofibrils (LCNFs) were used as reinforcement, and the performance of these nanofillers with respect to the properties of PVA-based biocomposites was compared. 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 (T_onset) started at a temperature 4 °C higher than the reference. In order to achieve antibacterial activity of the produced three-component films, a hydrophilic extract of silver fir knotwood was added to the PVA/nanocellulose system. In addition to the antibacterial properties, the effects of the hydrophilic extract on the mechanical and thermal properties of the three-component films were also investigated. The extract led to a shift in the T_onset towards higher temperatures, with the higher content having an even greater effect. The addition of 4% extract to the LCNF-reinforced biocomposite increased the tensile strength by 10% compared to the PVA-LCNF biocomposite. Graphical abstract

Water solutions of poly(vinyl alcohol) (PVA) at concentrations of 10%, 15%, and 20% were tested as alternatives to traditional wood coatings, with cellulose nanofibrils (CNFs) added to improve their mechanical and physical properties. The indentation hardness of PVA films decreased with higher PVA concentrations but was enhanced by the addition of CNFs. The coatings showed good wood wetting, with contact angles between 51° and 93°. Scanning electron microscopy revealed that the coatings penetrated 100–200 µm into the European beech (Fagus sylvatica L.) wood, anchoring well within its cellular structure. The coatings reduced wood surface roughness and altered its color (ΔE* ≤ 11.9), while remaining transparent (pure PVA) or semi-transparent (PVA + CNFs). Pure PVA coatings increased the wood gloss by 16 times. All PVA-based coatings made the wood surface more hydrophobic, although hydrolysis of the films was observed. The coatings' elasticity enhanced the resistance to micro-scratching. Photostability tests showed that most color changes were due to chemical alterations in the wood surface. CNFs also exhibited ultraviolet light-blocking properties. The coatings demonstrated excellent adhesion to the wood surface, with pull-off strengths greater than 5 MPa. These results suggest that PVA + CNFs coatings are promising for use as protective treatments for wood, offering improvements in both appearance and durability. Graphical abstract

This study compared the use of different nanofillers CNF and LCNF in different concentrations to reinforce the PVA matrix. Both nanofillers significantly improved the elastic modulus and tensile strength of PVA biocomposite films. The optimum concentration of CNF and LCNF was 6% relative to PVA, which improved the tensile strength of the final P6CNF biocomposite by 53% compared to the neat PVA film and the tensile strength of the final P6LCNF film by 39% compared to the neat PVA film. CNF and LCNF had different effects on the elasticity of the biocomposite. The addition of LCNF resulted in more elastic films than the addition of CNF to the PVA matrix. The elongation at break of the P2LCNF film was more than 100 % higher than that of the neat PVA film. The integration of TA into the PVA-LCNF system resulted in antioxidant active and more water resistant PVA biocomposites. The three-component biocomposite films P2LCNF10T and P6LCNF10T exhibited a more than 20° higher contact angle of the water droplet on the surfaces of the biocomposite films compared to the neat PVA film. The PVA-LCNF-TA biocomposite films also absorbed more than 50 % less water than the neat PVA film.

This article presents the key results and scientific findings from two national postdoctoral research projects supported by the Ministry of Education, Science and Sport of the Republic of Slovenia (MIZŠ) and the Slovenian Research and Innovation Agency (ARIS). We analyzed the biorefinery potential of low-value Scots pine (Pinus sylvestris L.) and black locust (Robinia pseudoacacia L.) wood for the extraction of natural bioactive compounds. Knotwood and heartwood were used as biomass for extracting polyphenolic compounds, which were subsequently applied in bio-based wood preservatives. The results showed that hydrophilic extractives from Scots pine knotwood and black locust heartwood inhibit fungal decay and demonstrate strong potential as biocidal components and antioxidants in natural wood protection formulations. Further research on the antioxidant and antifungal properties of wood and bark extractives is ongoing.