Comparative analysis of sisal fiber treatments, <scp>CMC</scp> degree of substitution and nanoclay in corn thermoplastic starch

Abstract Thermoplastic starch (TPS) is a biodegradable and cost‐effective alternative to single‐use plastic packaging; however, its poor mechanical strength and water resistance limit its commercial applications. This study investigated the incorporation of bio‐based materials—sisal fibers (untreated and alkali‐treated), sodium carboxymethyl cellulose (CMC) with different substitution levels (0.7 and 1.2) and nanoclay—into TPS to enhance its properties. Neat TPS and TPS/bio‐based material films were prepared using a casting method and evaluated through tensile testing, SEM, water absorption, thermal analysis and XRD. CMC0.7 exhibited the most balanced performance, increasing the tensile modulus from 52.52 MPa (neat TPS) to 114.04 MPa and the tensile strength from 4.17 to 5.52 MPa, while reducing water absorption from 14.94% to as low as 6.70% depending on CMC0.7 content and maintaining comparable elongation at break. Untreated sisal fiber at 15 wt% provided the greatest reduction in water absorption from 14.94% (neat TPS) to 4.25%, but caused a pronounced decrease in elongation at break from 51.10% to 7.79%, while alkali treatment enhanced tensile properties, thermal stability and crystallinity. CMC1.2 increased the elongation at break up to 133.95% and enhanced crystallinity due to improved chain mobility. Nanoclay contributed to improved moisture resistance by reducing water absorption but offered limited mechanical reinforcement due to dispersion issues. Overall, CMC0.7 emerged as the most effective additive, offering a combination of mechanical enhancement and water resistance suitable for TPS‐based biodegradable films with potential applications in non‐barrier packaging. © 2026 Society of Chemical Industry.