Influence of Hydroxypropyl Cellulose on Molecular Relaxations of Epoxy-amine Networks

A dynamic mechanical analysis (DMTA) study was conducted on epoxy-amine networks crosslinked in the presence of low contents of hydroxypropyl cellulose (HPC). The epoxy resin chosen was diglycidylether of bisphenol-A (DGEBA) and the crosslinker was 4,4'-diaminodiphenylmethane (DDM). In the glassy region, primary (alpha) and secondary (beta, gamma) relaxations originating from the epoxy and HPC components were well detected. Two primary relaxations of neat epoxy and epoxy/HPC systems, referred to as alpha(epoxy) and alpha'(epoxy), could be detected, showing a particular glassy behavior for the systems studied in comparison with systems cured in bulk. The main relaxation temperature T-alpha (at the peak of alpha(epoxy) relaxation) of the epoxy systems increased slightly with the addition of HPC. The activation energy for this transition (T-alpha) of the epoxy-amine networks was determined both from tan delta and the peak temperatures for the loss modulus measured at various frequencies. The activation energy of the alpha(epoxy) relaxation determined from the loss modulus was more reliable than that based on tan delta. The addition of HPC lowered the activation energy of this alpha(epoxy) relaxation.