Improved dimensional stability of water-blown polyurethane foam with aluminum hydroxide and magnesium hydroxide

Water is eco-friendly and safe; thus, it used as a blowing agent in the fabrication of water-blown polyurethane (PU) foam. However, water-blown PU foam may experience dimensional instability due to shrinkage of the cells inside the foam. In order to reduce cell shrinkage due to the loss of CO₂ gas, vacuum formation is prevented in the closed-cell foam and the maximum reaction temperature must be raised to increase the degree of curing of the PU foam. In this study, two flame retardants, aluminum trihydrate (ATH) and magnesium dihydrate (MDH), were selected as additives to partially open the cells and increase the maximum reaction temperature. ATH and MDH were both effective for increasing the maximum foam reaction temperature and decreasing dimensional change. Notably, PU foams with 7.5 wt% ATH were the most dimensionally stable at both room temperature and high temperature. Moreover, the compressive strength and flexural strength of such foams were also improved compared to those of the foams without any additive.