Development of Low Viscosity Itaconic Acid-Based Epoxy Resins for Cationic-Radical Hybrid Uv-Curable Coatings with Superior Properties

Abstract

Bio-based UV-curable coatings are receiving increasing attention due to their eco-friendly, renewable, and energy-efficient nature. However, the conventional bio-based UV-curable coatings tend to exhibit high viscosity and rely on a single crosslinking mechanism, often leading to the cured products with insufficient crosslinking, inferior thermal and mechanical properties, and excessive shrinkage. In this study, a bio-based epoxy resin (EIA) was synthesized from itaconic acid via esterification, which contains both epoxy groups and C=C bonds, along with a low viscosity of 235.8 mPa·s. These unique characteristics enabled the development of a solvent-free, cationic-radical hybrid UV-curable coating system with exceptional properties. The results showed that the UV-cured film with glycidyl methacrylate as the comonomer achieved 98.01% epoxy conversion, 78.70% C=C bond conversion, and a crosslinking density of 979.89 mol·m−3. Meanwhile, the UV-cured films exhibited outstanding mechanical thermal, and physical properties, including a tensile strength of 26.5 MPa, a glass transition temperature (Tg) of 54.5°C, minimal shrinkage (2.3%), and high gloss (92.3°). Additionally, all UV-cured coatings showed excellent pencil hardness, adhesion, and hydrophobicity. These hybrid UV-curable systems represent a novel and effective approach for producing high-performance UV-curable coatings with enhanced environmental sustainability and exceptional properties.

Keywords: itaconic acid, UV-curable epoxy coatings, low viscosity, cationic