Recycled rubber powder in flexible polyurethane foams: chemical and morphological study

Abstract In this work, the effects of adding micronized rubber powder (MRP) as a filler in medium density flexible polyurethane foams were studied, with the aim of expanding the possibilities for using these abundant recycled materials to improve performance and reduce the environmental impacts of polyurethane production chains. A comparative study of foams with MRP particles at 10 parts per hundred of polyol and without rubber addition is described. Results reveal that MRP has no negative impact on foam expansion or final shape parameters, and shows good dispersion of filler particles. Optical microscopy and SEM analysis enabled a deeper understanding of the effect of rubber particles on polyurethane chains. Together with the thermal and Fourier transform infrared (FTIR) analysis results, these findings shed light on the molecular interactions between rubber and polyurethane during materials formation. Micrometric rubber particles are dispersed into the cells, while the smallest particles are on the chain surfaces. The chemical interactions are explored using FTIR and thermal results, and it is concluded that rubber particles interact with polyurethane molecules through rubber styrene or carbon black molecules. The impact of these interactions on the materials is discussed finally in terms of foam parameters such as indentation hardness, resilience, tensile strength, tear resistance and ultimate elongation. Good density control, optimized properties and compatible costs confirm the good potential of these environmentally friendly materials in industry. © 2026 Society of Chemical Industry.