Pyrolysis mechanism and kinetics of high-performance modified lignin-based epoxy resins

Lignin used was extracted from the bio-ethanol production residue by enzymatic hydrolysis method. In this study, a novel lignin-based flame retardant agent (Lig-F) was synthesized by modification using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and piperazine (PA) as grafting reactants, and characterized by thermogravimetric analysis coupled with Fourier transformation infrared spectroscopy (TG-FTIR). Three degradation stages were observed by TG analysis. FTIR results showed that significant variations in functional groups such as the presence of C-N at 3060 cm(-1), CaromaticP at 1478 cm(-1), PO at 1203 cm(-1), PN at 866 cm(-1), and C-aromatic-O-P at 749 cm(-1) had been detected after grafting reaction. Epoxy resin (EP) composites with different amounts of Lig-F (2-10 %) were prepared through a curing agent, 4,4'-diaminodiphenylmethane (DDM). The investigation on thermal stability of EP composites demonstrated that more char residue with high thermal stability was obtained after pyrolysis as compared to EP, which was due to the highly efficient charring performance derived from PA-based DOPO compound. Furthermore, the content of char residue increased with the increase of Lig-F addition. The flame retardancy determined by limiting oxygen index (LOI) presented that EP composite containing 10 % Lig-F exhibited the highest LOI value of 34.8 %. Finally, the activation energy of LigF, an important component in the polymeric system of lignin and EP, was investigated, and significant effects of PA-based DOPO were mainly reflected in the early and final stages of decomposition as compared to general lignocellulosic biomass materials.