Thermal Treatments of Composites: Thermal Analysis, Flexural Strength and Conversion

Objectives: The aim of this study was to perform the thermal characterization of two composites, a nanofilled (Filtek Supreme XT: FT) and a microhybrid (Esthet X: ET, shade A2, submitted to different thermal treatments. Methods: The experimental groups were: G1: no treatment; G2: pre-heated at 68°C with Calset device; G3: post-heated in a MP-130 (EDG) oven, 10°C/min up to reach 140°C for 20min and G4: pre and post-heated. After curing, thermogravimetric analysis and differential scanning calorimetry (DSC) were carried to determine thermal stability of the composites, glass transition temperature (Tg), exothermic peak and heat releasing after photoactivation. Results: Analysis of variance and Tukey's test (P<0.05) showed that FT and ET composites have 25.8% and 23.7% of organic matrix in weight respectively and thermal stability at 200°C. The G2 group release more heat (9.9J/g) than G1 (7.3J/g). Exothermic peak of G2 group (63.5°C) is higher than G1 (60.9°C). G3 and G4 groups did not show exothermic peak and heat releasing. ET composite of G2 group presented the highest exothermic peak (65.2°C) of all groups. The glass transition temperature is nearly 160.5°C to FT and 161.4°C to ET.

Conclusion: Pre-heating at non-isothermal conditions does not promote higher conversion for DSC technique. Heat treatment after cure can be carried through 160°C without mass loss.