A combined extrusion, retrogradation, and cross-linking strategy for preparing starch-based straws with desirable mechanical properties

This work developed a novel strategy for producing starch straws with desirable mechanical properties by a combination of extrusion, retrogradation, and sodium trimetaphosphate (STMP) cross-linking. The straws were prepared by first extruding starch, glycerin, and water (10:1:1) with a double screw extruder, then retrograding the resulting straws at 4 °C for 6 h, and finally cross-linking the straws. Rapid visco-analyzer profiles showed decreases in the viscosity of milled straws with increases in the cross-linking duration, perhaps reflecting a higher degree of crosslinking. Fourier transform infrared spectroscopy showed evidence of more hydrogen bonds in the straws with a longer cross-linking duration, while thermogravimetric analysis indicated higher thermal stability for the cross-linked straws than for the controls. The straw cross-linked for 3 h showed 1.52 times higher stiffness after soaking in room-temperature water for 30 min (4967.56 g/s), and 1.88 times higher stiffness after soaking in 60 °C hot water for 5 min (5371.89 g/s) than the original straw. STMP cross-linking also improved the starch straw mechanical properties after soaking in common soft drinks. These findings identify a potential new way to produce biodegradable straws with desirable properties from starch, an affordable biomaterial, while also addressing the problem of petroleum-based plastic pollution.