Dual-function liquid epoxidized natural rubber polyol: a sustainable macromolecular crosslinker and co-polyol for bio-based polyurethane

Abstract This work reports the potential of natural rubber (NR) and its derivatives as bio-based alternatives for producing polyurethane (PU). Natural rubber latex was first epoxidized and then subjected to oxidative degradation to yield liquid epoxidized natural rubber (LENR). The resulting liquid rubber was further hydrolyzed under acidic condition to yield a rubber-based polyol (LENRX), where its epoxide groups were converted into secondary hydroxyl groups. Unlike conventional linear polyols used in PU synthesis, this study introduces LENRX as both a co-polyol and a crosslinking agent in PU coatings for the first time. A series of PU samples were formulated with varying LENRX-to-polyethylene glycol (PEG) ratios, using isophorone diisocyanate (IPDI) as the curing agent, to systematically tailor the film properties. Spectroscopic analyses, including FTIR and 1 H-NMR, were performed to confirm the products at each synthesis stage, culminating in the formation of PU. In addition, comprehensive characterization inclusive of physicochemical, mechanical, and thermal properties was carried out. Increasing LENRX content improved surface hardness (up to 8H), tensile strength (up to 63.08 MPa), and chemical resistance, while higher PEG content imparted softness and flexibility (elongation at break > 300%). Thermal analysis (DSC and TGA) further supported the structural differences between formulations and demonstrated good thermal stability of the PU films. Overall, this work highlights the potential of LENR derivatives as a sustainable, bio-based platform for PU synthesis, enabling the development of high-performance PU with reduced environmental impact. The findings establish LENR as a promising renewable alternative to conventional polyols.