Improving water resistance property of starch straw by synergistic effects of chemical crosslinking, physical barrier, and surface modifications

Starch straws are developed by focusing on improving the critical weakness of all starch-based materials: moisture sensitivity. Various technologies including blending (with hydrogel carrageen), chemical crosslinking (using citric and boric acids, and furfural), physical barrier (using talc), and surface modifications (by adding stearic acid, or hot oxalic acids) are evaluated, and then synergized in this study. The materials and products are characterized by Fourier transform infrared spectroscopy, contact angle, mechanical properties, water solubility and water absorption. All the trends of individual modification are similar to previous work but it was found that the influence of some modifications on the extruded straws was significantly different from that of the casting films reported previously since extrusion with high shear stress can destroy chemical and physical crosslinking or network formed. It was found that there was a maximum acid content to improve the water sensitivity since the excessive amount of acid could degrade starch and have more damage to the cross linking during extrusion, resulting in decreasing mechanical properties and increasing solubility. On the other hand, some synergic functions, like cross linked by additional citric acid and surface treatment by hot oxalic acid, were observed. The promising starch straws are developed based on synergic methodologies, in which typical samples were prepared by crosslinking using citric (1 w%), boric (2 w%), talc (3 w%), and stearic acids (1 w%) and treated with hot oxalic acids for 2 s. The optimized straw can be smoothly processed, reduced water absorption significantly (55.3%), and mechanical properties (modulus) increased about 54% compared with neat starch one after being immersed in water at room temperature (25 degrees C) for 20 min. This synergic strategy provides a useful guideline for developing starch-based materials with low moisture sensitivity.