Improving the Flame Retardancy and Mechanical Properties of Vinyl Ester Resins through Maleated Epoxidized Corn Oil/Epoxy Resin Additives for Sustainable Thermoset Composites

Thermoset polymers serve a significant role in modern industrial applications, and with a global annual output of over 65 million tons to meet this growing demand for sustainable materials, scientists and engineers need to go beyond what makes a material best for a certain use. Vinyl ester (VE) is a thermosetting polymer derived from polyester and epoxy resin. Its mixing properties distinguish it from its competitors, offering advantages in terms of curing efficiency, wettability, corrosion resistance, and low cost, which are crucial for modern industrial applications. Researchers have continuously explored the modifications of the intrinsic properties of VE using additives to enhance its flame retardancy and mechanical characteristics for more cost-effective and environmentally friendly materials applicable across various industries. In this study, we developed an easy-to-process eco-thermoset blend additive (50% v/v), known as maleated epoxidized corn oil/epoxy resin (MEPECO). Adding an optimal amount of MEPECO (5%) to the VE resin significantly improved its flame retardancy properties, as assessed by pyrolysis-combustion flow calorimetry, contact angle measurements, and thermogravimetric analysis. The mechanical properties, specifically strength, also showed substantial enhancement with the same optimal amount of MEPECO, as determined by flexural testing and spectral analysis. However, during the digestion of the eco-thermoset resin, the modulus and impact energy were notably lower owing to shear-yielding localization, as evidenced by the morphological analysis. This paper presents a novel in situ and straightforward technique for the easy and effective blending of eco-thermoset additives into petroleum-based epoxy resins, thereby facilitating their potential application in the development of sustainable green composite materials.