An essential work of fracture study of the toughness of thermoset polyester coatings

Abstract

Abstract The fracture toughness of a range of thermoset polyester paints with different cross-link densities has been studied, using the essential work of fracture (EWF) method. The glass transition temperature, Tg, of each of the materials was measured using differential scanning calorimetry, and found to lie between 8 and 46 °C. EWF tests were performed on the paint films at a range of temperatures around the measured glass transition temperature of each material. The essential work of fracture, we, at Tg was found to decrease with increasing cross-link density from around 20 kJ/m2 at a cross-link density of 0.4 × 10−3 mol/cm3 to around 5 kJ/m2 for cross-link densities of approximately 1 × 10−3 mol/cm3 or higher. A maximum in the essential work of fracture was observed at around Tg when we was plotted versus temperature, which could be attributed to the effect of an α-relaxation at a molecular level. The polyesters were found to be visco-elastic, and the applicability of the EWF test to the study of these visco-elastic thermoset materials is discussed.