Biodegradable planting bags composed of a biocomposite film using cassava starch and soy protein isolate: Design, production, and application

Biodegradable packaging materials were produced using blends of cassava starch (CS) and soy protein isolate (SPI) in varying proportions (20%, 30%, and 40% SPI by weight) through an extrusion process, utilizing a regulated heating system to maintain uniform thermomechanical processing of the biopolymer mixtures. XRD and SEM were used to evaluate polymer characteristics and interactions. The mechanical and physicochemical parameters, including tensile strength (TS), elongation at break (EB), contact angle, film solubility, and film thickness, were examined. The XRD analysis indicated that incorporating protein improved crosslinking between starch and protein chains and increased crystallinity. SEM images revealed a rise in surface roughness corresponding to the increase in SPI %. The tensile strength of the CS-SPI film with 30% SPI increased to 27.4 MPa, whereas the inclusion of 40% SPI reduced tensile strength to 19.5 MPa. Conversely, the incorporation of 20% SPI resulted in a higher EB of 117.9%. The water solubility of 30% SPI exceeded that of 20% SPI by 38.5%. All film samples were hydrophilic when measured by contact angle with water; however, 30% SPI was the least hydrophilic. Through protein dispersion, SPI increased film opacity and decreased yellowness. Planting treatments on commercial bags and CS-SPI films were compared. Statistics showed no difference (p > 0.05) in plant height and growth. The CS-SPI film showed that a higher SPI content increased planting bag durability under identical conditions without affecting plant development compared to a commercial nursery bag. However, the film's physical properties should be optimized. • Biodegradable films made from biopolymer blends of cassava starch (CS) and 20%, 30%, and 40% soy protein isolate (SPI) were produced using extrusion. • A higher protein content enhanced crystallinity and starch-protein chain crosslinking, leading to increased film strength. • Increasing SPI content extended the biodegradable planting bag longevity without affecting plant development, comparably to a commercial nursery bag.