Comparative investigation of fillers loading effect on morphological, micromechanical, and thermal properties of polyvinyl alcohol/ biofillers-based composites

Polyvinyl alcohol (PVA)-based biocomposites were fabricated by the incorporation of chitosan (Ch), cellulose fibers (CS), and their mixture (1:1 ratio). Fillers with various loading (2, 4, 8, and 10 wt.-%) were incorporated into PVA employing the solution casting method. The fillers and biocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), brightfield microscopy, tensile and microindentation tests, contact angle measurement and thermogravimetric analysis (TGA). FTIR spectra revealed the removal of lignin, and intermolecular H-bonding between PVA and fillers promoting their filler-matrix interfacial interactions. Crystallographic results showed varied crystallite sizes and crystallinity of composites. Microscopic techniques revealed a uniform filler distribution, attributed to their compatibility with PVA. Tensile and microindentation tests demonstrated a decreased tensile strength (3.3-8.2 MPa of the composites compared to 15.7 MPa of the matrix) and Martens hardness (HM) of biocomposites. However, their value was increased with higher filler concentration, signifying the mechanical reinforcement. Contact angle analysis confirms the decreased wettability (hydrophilicity) of biocomposites, attributed to higher compatibility of fillers with PVA and intermolecular H-bonding between them. A slightly decreased thermal stability of biocomposites with filler incorporation is implied by TGA results despite their uniform distribution and strong matrix-filler interfacial interactions.