Influence of hydroxypropyl cellulose on molecular relaxations of epoxy-amine networks

Abstract

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 (α) and secondary (β,γ) relaxations originating from the epoxy and HPC components were well detected. Two primary relaxations of neat epoxy and epoxy/HPC systems, referred to as α epoxy and α epoxy, could be detected, showing a particular glassy behavior for the systems studied in comparison with systems cured in bulk. The main relaxation temperature Tα (at the peak of α epoxy relaxation) of the epoxy systems increased slightly with the addition of HPC. The activation energy for this transition (Tα) of the epoxy-amine networks was determined both from tan δ and the peak temperatures for the loss modulus measured at various frequencies. The activation energy of the α epoxy relaxation determined from the loss modulus was more reliable than that based on tan δ. The addition of HPC lowered the activation energy of this α epoxy relaxation.