Morphology-Engineered Polyurethane Foams via Water Content Adjustment: A Strategy for Energy-Efficient Dye Adsorbents

Abstract

This study investigates the influence of water content (0, 2.5, and 5 wt%) on the morphology and methylene blue (MB) dye adsorption performance of polyurethane foams (PUFs). The foams were synthesized using a polyester polyol and methylene diphenyl diisocyanate (MDI), with water acting as a chemical blowing agent. Characterisation results demonstrated that increasing the water content accelerated the CO₂ production rate, decreasing the cream and rise times. Consequently, foams with higher water content exhibited larger average cell sizes, broader cell size distributions, increased open-cell content, higher surface roughness on cell walls, and lower bulk density. The adsorption experiments revealed a direct correlation between water content and dye removal efficiency, with the PUF containing 5% water achieving the highest removal rate (57%) for a 500 mg/L MB solution. The enhanced performance is attributed to the increased open-cell content and surface roughness, which provide a greater accessible surface area for adsorption. These findings present a straightforward and effective strategy for engineering the microstructure of PUFs via water content adjustment to develop efficient, low-cost adsorbents for wastewater treatment.