Influence of PCL on the epoxy workability, insights from thermal and spectroscopic analyses

Abstract

Epoxy compound based on diglycidyl ether of bisphenol A (DGEBA), methyl tetrahydrophthalic anhydride (MTHPA) as hardener and 2,4,6-tris (dimethylaminomethyl) phenol (DEH 35) as catalyzer, at 100/87/5 as fixed concentration was successfully processed. Aiming workable thermoset, thermoplastic Polycaprolactone (PCL) was added at 10, 20 and 30 phr contents to the epoxy compound. Analyses of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and optical microscopy (OM) were conducted in order to obtain evidences from chemical interactions, curing kinetics and phase separation. From FTIR spectra partially miscibility between Epoxy and PCL can be assumed, mainly due to the hydrogen bonding between PCL carbonyl and epoxy hydroxyl, whereas after reaching epoxy's solubility limit PCL segregates and it is suggested separated phases take place through spinodal decomposition (Kinloch et al., 1994) [1] and nucleation and growth (NG) mechanisms which depend on temperature and raw material concentrations, as illustrated in OM images. Curing kinetics followed through released heat during DSC scans, indicated decreased crosslinking density upon PCL addition, as also lower Tg related to neat epoxy. Overcoming epoxy brittle fracture, rough surface fracture images with toughening character were captured from epoxy/PCL. Evidences of workable epoxy/PCL compounds are provided and related results presented in this work offer reliable tools to determine the exact aimed degree of crosslinking widening processing window to desired application.