Fabrication of novel antimicrobial nanocomposite films based on polyvinyl alcohol, bacterial cellulose nanocrystals, and boric acid for food packaging

In this study, an environmentally friendly antimicrobial nanocomposite films were made using polyvinyl alcohol (PVOH) reinforced with glycerol, bacterial cellulose nanocrystals (BCNCs), and boric acid. Response surface methodology (RSM) and central composite design (CCD) were engaged to model and optimize the independent variables and water resistance of films. The quadratic models were significant for the water vapor permeability (WVP) and water vapor transmission rate (WVTR), while the linear models were significant for water solubility and moisture content. The findings indicated that 2.81% w/w BCNCs, 14.63% w/w boric acid, and 1.15% w/w glycerol provided the PVOH films with the best water resistance. The corresponding response values for moisture content, water solubility, WVTR and WVP predicted under the optimum condition were 10.25%, 6.23%, 210.89 g/h m² and 6.18 g mm/h m² kPa, respectively. The findings suggest that when comparing the blank glycerol and BCNCs films with the optimal film, it is evident that the addition of glycerol and BCNCs in the optimal film led to an increase and decrease in antibacterial activity against the microorganisms tested, respectively. The optimum film sample exhibited varying degrees of resistance to Bacillus subtilis and Candida albicans, with B. subtilis displaying the highest resistance and C. albicans showing relatively lower resistance. The enhanced biodegradability observed in the optimum film, compared to the neat PVOH film used as a control, can potentially be attributed to two factors: the increased moisture sensitivity of the films resulting from the addition of glycerol, and the biodegradability of glycerol itself by microorganisms. The addition of other ingredients to neat PVOH film led to a reduction in the height of the characteristic crystalline peak, thereby causing a loss in the film's stability. The findings indicated that the optimized film exhibited a higher glass transition temperature of 91 °C compared to the neat PVOH film (78 °C), BCNCs (71 °C), and boric acid (69 °C) blank films. This suggests that the incorporation of BCNCs and boric acid into the film led to an enhancement in its thermal stability. Crosslinked PVOH reinforced with BCNCs showed great potential to produce biodegradable films with modified barrier, thermal, and antibacterial properties for applications in food packaging. Graphical abstract: (Figure presented.)