Enhancing Sustainability in Unsaturated Polyester Resin: A Way to Use Biobased Curing Agents for Reduced Styrene Content and Improved Recyclability Properties

Unsaturated polyester resin (UPR) is a commercially thermosetting material renowned for its favorable thermomechanical properties and exceptional chemical resistance. These characteristics are typically attributed to the use of styrene as a curing agent. However, the undiscussed toxicity and potential carcinogenicity of styrene have inspired research and industry to investigate more sustainable and environmentally friendly alternatives, such as vegetable oils, polyphenols, and carbohydrates. In this study, unsaturated polyester (UP) was synthesized and cured with a blend of acrylated epoxidized soybean oil (AESO), 2-hydroxyethyl methacrylate (HEMA), and styrene in low content. Notably, styrene was reduced from 40% to 26%. Zinc(II) acetyl acetonate was introduced into the blend to promote transesterification processes, potentially enhancing both dissolution and recycling capabilities. Following comprehensive characterization, the resulting resins were employed in composite manufacturing, with subsequent comparison to available counterparts made of commercial UP with a content of styrene at 40%. Remarkably, the mechanical properties, glass transition temperature, and thermal stability of the polyester were effectively preserved, despite the incorporation of biobased curing agents.