Effects of coupling agents on dynamic mechanical properties of aged and wet multi-functional epoxy resins cured with acid anhydrides and filled with pitch based carbon short fibers treated with coupling agents

Pitch-based carbon short fibers (PCF) as functional fillers were treated with five types of coupling agents (CA) and were filled with multi-functional epoxy resin (EP) cured with three types of acid anhydrides at 22.2 wt%. The influence of aging and wetting on the dynamic mechanical properties was studied by use of a non-resonant forced-vibration method. The samples were aged at 130°C for 5000 h or wetted in distilled water at 21 °C for 5000 h. The longer the aging time, the larger the weight reduction of the aged specimens: the maximum value was 3.6 wt% for 5000 h. The glass transition temperature (Tg) for the CA-treated specimens dropped more compared with the untreated specimens (UA). Although CA on the surfaces of PCF was lost by aging, the storage modulus (E') increased at a lower temperature -140°C and decreased at higher temperatures (over 200°C). The maximum water absorption rate for the wetted specimens was 2.3 wt% and the decrease of Tg was similar to that for the UA specimens. The value of E' increased at lower temperatures but decreased at higher temperatures. The influence by both aging and wetting on the mechanical dynamic properties was similar even though the mechanism for each is different.