Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Schematic of crumb rubber hydroxylation and reactive incorporation of modified particles into polyurethane (PU) resin, as well as tensile stress-strain curves of PU composites showing improved tensile modulus from hydroxylation.

ABSTRACT
This study examines the mechanical recycling of crumb rubber derived from waste footwear soles, focusing on addressing compatibility issues with polymer matrices through surface modification. Crumb rubber particles were treated with hydrogen peroxide and acetic acid to introduce reactive hydroxyl groups via epoxidation and hydrolysis of residual surface unsaturation. The hydroxylation was confirmed by intensified ν(OH) band in FTIR spectrum, appearance of new α-carbon resonances in 13C SSNMR spectrum, and increased oxygen content as determined by elemental and EDS analyses. These hydroxylated crumb rubber particles were incorporated as a reactive filler into polyurethane resin before polymerization, forming a homogeneous, well-dispersed composite. Compared to PU resin filled with unmodified crumb rubber, the modified crumb rubber increased the tensile modulus by ~116%, without compromising tensile strength or elongation at break. Improvements in compressive strength and abrasion resistance were also observed. These enhancements arise from strong interfacial adhesion due to urethane bond formation, as validated through control reactions between the hydroxylated crumb rubber and diisocyanate. Compared to other recycling methods, the hydroxylation and reactive filling of polydiene-based crumb rubber is simple, cost-effective (adding only ~6% to material cost), scalable, and has an immediate relevance to the footwear, automotive, and packaging sectors.