Studying the Effect of an Htpb Rubbery Modifier on Thermal Properties of Some Selected Dgeba Based Epoxy Resin

摘要

Epoxy resin (ER) based on diglycidyl ether of bisphenol A (DGEBA) and varying contents of hydroxyl terminated polybutadiene (HTPB) as a toughening (modifying) agent were cured using a (Versamid-l25) as a polyamide hardener. Polyamide cured epoxies provide improved flexibility, moisture resistance, and adhesion. Moreover, Versamid could provide lower viscosity, better compatibility, and better cure profiles under adverse conditions. Due to its high compatibility with HTPB and DGEBA, ethylene propylene diene terpolymer (EPDM) as a rubbery thermal insulation, is used to evaluate and compare the thermal conductivity via the adhesion interface. Thus, the use of (Versamid-I25) as a polyamide curing agent for an epoxy resin modified with HTPB together with EPDM gave this study an importance in formulating adhesives to be used in high temperature applications. A systematic study has been conducted to investigate the matrix properties by introducing HTPB in different proportions (2.5, 5, 10 and l5 phr) into an epoxy resin. A sequential mechanical mixing process is performed in order to guarantee an evenly good dispersion for the HTPB particles throughout the entire volume of the resin, and then the wholly homogenized system is subjected to vacuum in order to get rid of any air bubbles. Thermal conductivity (k) of the neat, modified epoxy, EPDM and some selected EPDM-modified epoxy bonded sheets have been measured. The results show that the values of (k) for the modified epoxy samples suffer a very slight increase with increasing the HTPB content, whereas, the average conductivity values of the bonded sheets was found smaller than that of the single EPDM sheets. Effect of HTPB addition to the epoxy resin on the glass transition temperature was evaluated using a differential scanning calorimeter (DSC). The presence of HTPB inside the network resulted only in a slight displacement of the T g value towards lower temperatures. This may be attributed to the reduction in cross-linking density of the thermoset upon modification. Thermal stabilities and degradation of the neat (unmodified) and toughened (modified) epoxies were studied and compared via the thermogravimetry analysis (TGA & DTGA). The obtained TGA values show that the neat cured resins are thermally stable up to about 300 °C and that this stability was preserved or evenly slightly improved by addition of the HTPB to the resin. About 2.5phr of HTPB was quite enough to enhance the resin thermal properties. These findings were found to be in agreement with what has been already investigated by the authors for the corresponding mechanical properties.