Microwave-assisted phosphorylation of organosolv lignin: new bio-additives for improvement of epoxy resins performance

Abstract

The search for bio-additives for enhancing the thermal and optical performance of epoxy resins has been increasing constantly. Lignin represents an interesting alternative for such purposes. Therefore, the aim of this work was promote the valorization of acetosolv coconut shell lignin (ACSL) and phosphorylated acetosolv coconut shell lignin (P-ACSL) as bio-additives in epoxy resins, evaluating their effects on the thermal and UV-blocking properties of the thermosetting materials. The phosphorylation of ACSL was carried out at 60 °C during 5, 10, and 20 min under microwave irradiation. ACSL and P-ACSL were characterized by TGA, DSC, GPC, and 1H and 31P NMR analyses. ACSL and P-ACSL were added to diglycidyl ether of bisphenol A (DGEBA) and isophoronediamine (IPDA) at 0, 0.5, 1.0, 2.5, 5.0, and 10 wt%, being cured at room temperature during 24 h. The neat and additivated epoxy resins were characterized by TGA, DSC, and UV-Vis analyses. It was observed a notorious enhancement of the thermal (≈ 9 °C for ACSL and P-ACSL) and thermo-oxidative (≈ 8.5 and 15 °C for ACSL and P-ACSL, respectively) stabilities of the thermosetting materials using both lignins, as well as for their glass transition temperatures (Tg), which presented a slight increase of 2.1 and 3.5 °C for ACSL and P-ACSL, respectively. Furthermore, ACSL and P-ACSL exhibited UV stabilizer properties through the complete absorption of UV light in the UV-A and UV-B regions. It can be concluded that P-ACSL could represent an alternative bio-additive that can be easily produced through a clean and fast methodology, capable of improving the thermal, optical, and chemical resistance properties of epoxy resins.