Oil Sorption Capacity of Recycled Polyurethane Foams and Their Mechanically Milled Powders

Polyurethane (PU) is widely recognized for its efficient oil sorption properties. However, this capacity is highly dependent on its intrinsic chemical composition and morphological structure, which can be altered by mechanical or chemical treatments commonly applied before using it as a sorbent. In this study, we present a comprehensive investigation of the oil sorption behavior of both soft and rigid PU foams, and their blade-milled ground (BMG) counterparts obtained by mechanical treatment of several recycled PU-based products, including seats, mattresses, side panels of cars, packaging components, and insulating panels of refrigerators and freezers. We found that blade milling the soft PU foams leads to a significant reduction in oil sorption capacity proportional to the extent of grinding. Pristine soft PU foams and BMG-PUs with intermediate particle size (-250 μm-1 mm) exhibited the highest oil uptake (20-30 g/g), whereas the finest fraction (5 μm-250 μm) showed a lower capacity (3-7 g/g). In contrast, rigid PU foams showed consistently low oil sorption (~5 g/g), with negligible differences between the original and ground materials. At the macroscopic level, optical and morphological analyses revealed the collapse of the 3D porous network and a reduction in surface area. On the microscopic scale, spectroscopic, structural, and thermal analyses confirmed phase separation and rearrangement of hard and soft segmented domains within the polymer matrix, suggesting a different mechanism for oil sorption in BMG-PU. Despite reduced performance compared to pristine foams, BMG-PU powders, especially those with intermediate dimensions and originating from soft PU foams, present a viable, low-cost, and sustainable alternative for oil sorption applications, including oil spill remediation, while offering an effective strategy for effective recycling of PU foam wastes.