A Comparative Study on the Thermal Resistance, Flammability and Mechanical Properties of Unsaturated Polyester and Epoxy Resins

Thermal properties, flammability and mechanical properties of three different kinds of unsaturated polyester resins, ortho, iso and vinyl ester and an epoxy resin based on diglycidyl ether of bisphenol-A were investigated. Since these resins are widely used in the composite industry it is vital to recognize their properties. For this purpose, viscosity, burning rate, limiting oxygen index (LOI) and flexural properties were measured. Fourier transform infrared (FTIR) spectroscopy and thermal gravimetric analysis were also performed. The viscosity of unsaturated polyester resins which was in the range of 300 to 450 cp showed an advantage compared to the viscosity of epoxy resin which was in the range of 600 to 1000 cp. The low viscosity property which is usually seen in unsaturated polyester resins is very important from the processing point of view, which in turn helps to ensure a simple processing. The ortho resin showed the highest conversion and conversion rate among the three unsaturated polyester resins. The vinyl ester resin showed a higher conversion than the iso resin. The results showed that the vinyl ester resin had the highest thermal resistance, flammability and mechanical properties among the unsaturated polyester resins used in this work. On the other hand, although the epoxy resin showed the highest burning rate but it had the highest carbon residue or char yield (12.4%) and LOI (20.2%), and consequently the highest thermal resistance. The results of flexural test showed that the epoxy resin had the highest flexural strength (116 MPa) and modulus (4.1 GPa) and the lowest deflection-at-break (2.8%) and toughness in comparison with the unsaturated polyester resins used in this work.