Thermal degradation of extractive-based bio-epoxy monomer and network: Kinetics and mechanism

• Based on the results of TGA, FTIR and Py-GC/MS, we proposed a new thermal degradation mechanism for bio-based epoxy resin.
• The backbone structure of bio-based epoxy resin was successfully identified using Py-GC/MS.
• The activation energy of model compound confirmed one of the major components is methyl abieta-8,11,13-trien-18-oate.

In order to broaden the applications of bio-epoxy resins in high performance sector, an understanding of thermal behavior of these environmentally-friendly biopolymers is essential. This study investigates the thermal degradation mechanism of a bio-epoxy resin (E-epoxy) derived from bark extractives in comparison with a petroleum-based epoxy resin. The thermogravimetric analysis (TGA) results show that the activation energy of E-epoxy varied significantly with the extent of degradation indicating a multistage degradation mechanism involving a variety of compounds. According to Fourier transform infrared spectroscopy (FTIR) analysis, the dehydration and crosslinking reactions occurred at low temperatures, while the Claisen chain rearrangement and chain–scission reactions dominated at high temperatures. The pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) results show that a significant amount of methyl abieta-8,11,13-trien-18-oate, diethyl phthalate, 2,2′-isopropylidenebis(3,5-dimethylbenzofuran), and epimanool were detected in the bio-epoxy resins. The newly proposed degradation mechanism of bio-epoxy resins based on structural illustration through FTIR and Py-GC/MS can provide guidance for design of high performance bio-based epoxies.