Properties of Polyvinyl alcohol composite film reinforced with nanocellulose isolated from coconut husks fiber

Coconut husks is an agro-industrial waste available in large quantities in several countries, including Malaysia. This research utilizes the waste of coconut husks as a source of cellulose to obtain cellulose nanocrystals (CNCs) via acid hydrolysis process. The box-behnken design (BBD) based on the response surface methodology (RSM) was applied to study the effects of sulphuric acid concentration, reaction temperature and reaction time on the yield of CNCs and the regression model was established between the yield and three factors. The results showed that the yield of the CNCs was 44.84%, under the optimum conditions of 64.61% of sulphuric acid concentration, 44.6 °C of reaction temperature and 58.54 min of reaction time. The CNCs presented a needle-shaped morphology, high crystallinity (63.5%), average length (L) of 92.84 nm, diameter (D) of 7.90 nm, and high aspect ratio (L/D) of 12. The effect of incorporating CNCs from coconut husks into the tensile strength, thermal and weight loss of polyvinyl alcohol (PVOH) to form biodegradable nanocomposites film were evaluated. PVOH/CNCs nanocomposite films with different CNCs contents (1, 3, 5, 7 and 9% by wt) were prepared by solution casting method. The crystallinity index, tensile strength, thermal stability (TS), of the nanocomposites were measured. When compared to PVOH (0) film, the tensile strength of the nanocomposites improved significantly, by 35.7%. Based on the thermogravimetric analysis, the incorporation of CNCs into PVOH had improved the thermal stability of nanocomposite films. The biodegradability of PVOH/CNCs nanocomposites film was also measured after the films were introduced to the soil burial method for 10 weeks. The addition of CNCs into PVOH matrix had enhanced the weight loss of nanocomposite films and PVOH (9) showed the highest weight loss (23.1%) compared to the other contents of CNCs. The soil obtained on the surface of PVOH/CNCs were isolated using serial dilution technique. Then, the potential microorganisms of degrading plastic were investigated by solid state fermentation (SSF) and liquid state fermentation (LSF). The isolates bacterial (D1, D2, D3, D4 and D5) were cultured in mineral salt medium broth containing PVOH/CNCs film powder. The bacterial D1 showed the highest growth response (0.254) in broth media. The fungal S1 had contributed to the weight reduction weight of PVOH/CNCs nanocomposite film by 3.13% after 14 days of cultivation. The molecular analysis through polymerase chain reaction and DNA sequencing indicated that the bacterial D1 is Citrobacter freundii sp. and fungal S1 is Aspergillus japonicas sp. with 99% and 100% similarities, respectively. The novelty of the study found Aspergillus japonicas sp. and Citrobacter freundii sp. were the first reported as fungal and bacterial strain of PVOH/CNCs degrader found in the soil. Therefore, the fungi and bacteria isolated from soil have the capability in degrading PVOH/CNCs nanocomposite films.