Effect of cellulose nanocrystals (CNC) as reinforcement on polyvinyl alcohol/CNC nanocomposite

The non-biodegradable nature of petroleum-derived plastic films pollutes the environment in various ways, including food, drinks, soil, water, and even the air (after burning). Hence, many countries are pushing to replace fossil fuel-based synthetic polymers with bio-based and eco-friendly materials via the Sustainable Development Goals (SDG) initiative. This study investigated the effect of different concentrations of cellulose nanocrystals (CNC) as reinforcement on PVA/CNC nanocomposite and characterised the morphology, physiochemical, and thermal properties of the nanocomposite. Three samples were prepared with different CNC concentrations (2 wt.% PVA/CNC, 4 wt.% PVA/CNC, and 6 wt.% PVA/CNC) to study the properties of the nanocomposite. The samples obtained were characterised using transparency tests, Optical Microscopy (OM), Field Emission Scanning Electron Microscope (FE-SEM), X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy Total Reflectance (FTIR-ATR), Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC). Then, 17 different samples (based on RSM parameters) were used in the tensile strength and elongation at break experiments, which were later optimised using Response Surface Methodology (RSM). Higher CNC loading did not affect the optical transparency of the nanocomposite films. FESEM micrographs of the nanocomposite with lower CNC concentration showed an even distribution of CNC on the PVA membrane surface. However, an increase in the concentration of CNC in the matrix of PVA causes cluster formation. Optical microscopy showed that anisotropy increased with increasing CNC content, and the CNCs appeared to be largely well distributed through the thin films at this size scale due to the presence of a rainbow-like polarised colour scheme as opposed to the CNC aggregates. A common functional group was detected in the samples by observing the FTIR-ATR results. An XRD study shows that the incorporation of CNC in PVA increased the crystallinity of the nanocomposites by as much as 54% for a 6 wt.% PVA/CNC nanocomposite. The thermal decomposition temperature of PVA/CNC nanocomposites was slightly reduced at higher CNC contents, and the residual weight was highest at 6 wt.% PVA/CNC nanocomposite (25%). The optimum conditions of a PVA/CNC nanocomposite with 4.07 wt.% CNC loading, a mixing temperature of 55.12 °C, and 45.21 minutes of mixing time can provide optimum tensile strength and elongation at break (8.65 MPa and 17.9 %). As a result, incorporating CNC as a natural filler in PVA nanocomposite membranes could be a promising way to create a biodegradable and environmentally friendly nanocomposite membrane with good mechanical, physio-chemical, and thermal properties.