Preparation, characterization, and performance evaluation of composite films of polyvinyl alcohol/ cellulose nanofiber extracted from Imperata cylindrica

Abstract

In recent years, production of cellulose nanofiber (CNF) from waste materials has achieved great interest owing to their renewable nature, biodegradability, high mechanical properties, economic value, and low density. Because Polyvinyl alcohol (PVA) is a synthetic biopolymer with good water solubility and biocompatibility, the composite material formed of CNF and PVA, is a sustainable way of monetizing to address environmental and economic issues. In this work pure PVA, PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5, and PVA/CNF2.0 nanocomposite films were produced using the solvent casting approach with the addition of 0, 0.5, 1.0, 1.5, and 2.0 wt% of CNF concentrations respectively. The strongest water absorption behaviour was found as 25.82% for pure PVA membrane, followed by PVA/CNF0.5 (20.71%), PVA/CNF1.0 (10.26%), PVA/CNF1.5 (9.63%), and PVA/CNF2.0 (4.35%). The water contact angle of 53.1°, 47.8°, 43.4°, 37.7°, and 32.3° was formed between water droplet and the solid-liquid interface of pure PVA, PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5, PVA/CNF2.0 composite films respectively. The SEM image clearly shows that a network structure like a tree form at the PVA/CNF0.5 composite film, where the sizes and number of pores are apparent. XRD analysis suggested that unique peaks found at 2θ = 17.5°, 28.1°, 33.4°, and 38° for nanocomposites indicating new crystal plane generated upon cross-linking in presence of malic acid. The maximum loss rate temperature (Td,max) for PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5 was determined by TG analysis to be around 273.4 °C. FTIR studies suggested that PVA/CNF0.5 composite film showed the highest peak at 1428 cm−1 as compared to other PVA/CNF composite films representing the presence of higher crystalline band in the composite film matrix. PVA/CNF0.5 composite film was found to have a surface porosity and mean pore size of 27.35% and 0.19 μm respectively, classifying it in the MF membrane category. The maximum tensile strength (TS) of 5.27 MPa was found for PVA/CNF0.5, followed by PVA/CNF1.0, PVA/CNF1.5, pure PVA, and PVA/CNF2.0. The maximum young's modulus (111 MPa) was found for PVA/CNF1.0, followed by PVA/CNF0.5, PVA/CNF2.0, PVA/CNF1.5, and pure PVA, which could be attributed to the cyclization of the molecular structures by cross-linking. PVA/CNF0.5 exhibits greater elongation at break (21.7) than the other polymers, indicating a material's ability to undergo significant deformation before failure. Performance evaluation of the PVA/CNF0.5 composite film showed that 46.3% and 92.8% yield were found in the retentate for 200 mg/L of BSA, and 5 × 107 CFU/mL respectively. However, more than 90% E. coli was retained by PVA/CNF0.5 composite film, therefore absolute rating of this membrane is 0.22 μm. The size of this composite film may be therefore considered in the range of MF.