Sago starch and esterified sago starch as eco-friendly fillers for rigid polyurethane foams

Novel fillers from sago starch and esterified sago starch were employed as natural fillers for rigid polyurethane foams (RPUFs). Sago starch was esterified by maleic anhydride, resulting in the presence of ester groups on the starch structure. Filled RPUFs were prepared with 0.5-7.0 wt% of starch fillers in the polyol component. The influence of filler type and content on the cell morphology and properties of the RPUFs was analyzed. The results revealed that the esterified sago starch showed better compatibility with polyurethane matrix than the sago starch, which in turn impacted the cellular morphology and physico-mechanical properties of the resulting RPUFs. The density and compressive strength of the RPUFs filled with esterified sago starch were higher than those filled with unmodified sago starch, while their water absorption, and volume shrinkage were lower. The findings also suggested that the compressive strength and density of filled RPUFs increased with starch filler content up to the optimal point and then decreased. This was due to the impact of filler content on cell size, with smaller cell size at low filler content leading to increased strength and density, whereas larger cell size and more open cells at higher filler content reducing strength and density. The best properties were obtained with 1.0 wt% of unmodified sago starch and 0.5 wt% of esterified sago starch in the polyol component.