Insights into the curing kinetics of epoxy/PLA: Implications of the networking structure

Abstract

The curing kinetics of thermoset-thermoplastic compounds based on diglycidyl ether of bisphenol A (DGEBA), methyl tetrahydrophthalic anhydride (MTHPA) as the hardener, 2,4,6-tris(dimethylaminomethyl)phenol (DEH 35) as a catalyzer, and poly(lactic acid) (PLA) as workable (i.e., with repairable bonds) phase was investigated using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Hydrogen bonding between PLA carbonyl and epoxy hydroxyl and oxirane groups is the main influent interaction taking place, which acts as changing providers (i.e. hydrogen bonded groups able to move) of curing rate and degree of curing as evaluated from the vibration bands and exothermal released heat. With increasing PLA content, the real crosslink density decreases as also the curing rate is delayed. Partially miscibility between epoxy and PLA is proposed, whereas after reaching epoxy’s solubility limit PLA precipitates, hence the microstructure is suggested to be composed by the epoxy network, interacted Epoxy/PLA and precipitated PLA. Reported data offer reliable tools to reach the aimed degree of crosslinking, controlling of epoxy microstructure overcoming the brittle fracture providing a wider window of processing and applications.

Keywords

• polymer blends and alloys
• epoxy
• pla
• curing kinetics
• workable microstructure