Hemp cellulose nanocrystals for functional chitosan/polyvinyl alcohol-based films for food packaging applications

Abstract

Hemp is known for its swift growth and remarkable sustainability, requiring significantly less water, an adaptable cultivation to a wide range of climates when compared to other fibers sources, making it a practical and environmentally friendly choice for packaging materials. The current research seeks to extract cellulose nanocrystals (CNCs) from hemp fibers using alkali treatment followed by acid hydrolysis and assess their reinforcing capacity in polyvinyl alcohol (PVA) and chitosan (CS) films. AFM analysis confirmed the existence of elongated, uniquely nanosized CNC fibers. The length of the isolated CNCs was approximately 277.76 ± 61 nm, diameter was 6.38 ± 1.27 nm and its aspect ratio was 44.69 ± 11.08. The FTIR and SEM analysis indicated the successful removal of non-cellulosic compounds. Furthermore, the study explored the impact of adding CNCs at varying weight percentages (0, 0.5, 1, 2.5, and 5 wt%) as a strengthening agent on the chemical composition, structure, tensile characteristics, transparency, and water solubility of the bionanocomposite films. Adding CNCs to the CS/PVA film, up to 5 wt%, resulted in an improvement in both the Young's modulus and tensile strength of the bionanocomposite film, which are measured at (412.46 ± 10.49 MPa) and (18.60 ± 3.42 MPa), respectively, in contrast to the control films with values of (202.32 ± 22.50 MPa) and (13.72 ± 2.61 MPa), respectively. The scanning electron microscopy (SEM) images reveal the creation of a CS/PVA/CNC film that appears smooth, with no signs of clumping or clustering. The blending and introduction of CNCs have yielded transparent and biodegradable CS/PVA films. This incorporation has led to a reduction in the gas transmission rate (from 7.013 to 4.159 cm³ (m² day·0.1 MPa))⁻¹, a decrease in transparency (from 90.23% to 82.47%), and a lowered water solubility (from 48% to 33%). This study is the inaugural effort to propose the utilization of hemp-derived CNC as a strengthening component in the development of mechanically robust and transparent CS/PVA-CNC bio-nanocomposite films, holding substantial potential for application in the field of food packaging.