Development of a Novel Curing Accelerator-Blowing Agent for Formulating Epoxy Rigid Foam Containing Aminated-Lignin

Abstract

Rapid curing of epoxy foams at room temperature is critical to reducing energy consumption and processing time at the manufacturing sites. In this work, a novel ultra-accelerator was developed by mixing calcium carbonate with nitric acid, which acted as a blowing agent and remarkably stimulated foam hardening. Softwood kraft lignin was aminated via Mannich reaction and utilized as a cohardener to cure commercial diglycidyl ether of bisphenol A (DGEBA) to formulate a series of epoxy foams. The foams prepared with this novel accelerator-blowing agent were cured in 1 min at room temperature, which is significantly lower than the time (usually several hours at low temperatures) that takes for an epoxy foam to cure using currently available hardeners in the market, that is, primary amine (m-phenylenediamine) or anhydride (methyltetrahydrophthalic anhydride). Also, use of this novel blowing agent provided opportunities to prepare an epoxy foam at room temperature without the need to postcure. On the other hand, epoxy foams cured by aminated-lignin (EFAL) displayed comparable thermal stability to epoxy foams cured with a pure petroleum-based hardener [isophorone diamine (IPDA)]. Benefiting from the rigidity of the aromatic skeleton of lignin, the epoxy foam EFAL-15, which was prepared by using 15 wt % (based on the epoxy resin) of aminated-lignin as a cohardener, showed much higher compressive strength (6466 kPa) than the foam cured using commercial hardener IPDA (3437 kPa).