Preparation And Properties Of Modified Epoxy Resin And Polycarbonate

Modifications of two widely used materials, polycarbonate (PC) and epoxy, were reported. In order to ensure long-term performance, effects of annealing (or physical aging) on mechanical properties as well as long-term creep behaviors were investigated. The results of the two modified systems are outlined in detail below.Although PC has excellent room temperature toughness, its low temperature toughness is low and more importantly, its toughness decreases dramatically after annealing. In order to address those issues, silicon-rubber containing core-shell particle (MSiA) was added into PC. Effects of MSiA loading, annealing, temperature and geometry (size) on mechanical properties were studied, and effects of MSiA loading on thermal properties were also reported. The main conclusions are as follows.(1) Although the room temperature mechanical properties (tensile strength and toughness) of PC/MSiA are slightly lower, the low temperature toughness is much higher than that of PC. In addition, after long time annealing, PC/MSiA can still keep high enough toughness.(2) By studying the enthalpy relaxation behaviors during physical aging, the following conclusions are drawn. For PC and PC/MSiA, the peak temperature and peak area of enthalpy relaxation peak both increase with aging time, which agree with the normal trend; addition of MSiA can increase the aging rate. However, for PC-silicon rubber block copolymer (PC-PDMS), the peak temperature decreases with aging time, which is unexpected. If external forces are applied during physical aging of PC-PDMS, the peak temperature becomes higher with aging time, which is normal. The different trends in peak temperature may be related to the changes in compatibility and residual stress during physical aging.(3) Addition of MSiA particle can increase the magnitude of creep. Long-term creep master curve can be constructed using short-time creep curves at high stress through time-stress superposition principle. Residual stresses have important effects on creep curves and lead to a "three-step" curve.In the second part, three hyperbranched epoxy materials were used to toughen E51/anhydride curing system, which can improve toughness without sacrificing tensile strength and Tg. Due to the higher fractional free volume, the toughness after physical aging and long-term creep behaviors were studied in order to ensure long-term performance. The main conclusions are as follows.(1) Addition of 5wt% hyperbranched epoxy (HBPE) can simultaneously improve Tg, tensile strength, toughness and fractional free volume.(2) Addition of proper amount of HBPE can improve the creep resistance at both room temperature and high temperatures.(3) Addition of HBPE accelerates the enthalpy relaxation during physical aging. Although high magnitude of drop in toughness is observed in modified hybrid epoxy, its toughness is still higher than unmodified epoxy.