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).

Chemical and Physical Modification of Lignin for Green Polymeric Composite Materials

“…Amination of lignin via the Mannich reaction mechanism employs the reaction of lignin with amine compounds in the presence of formaldehyde. Different amines were employed in such processes, such as dimethylamine [73], methylamine [74], poly(ethylene imine) [75], diethylenetriamine [76][77][78], isophorone diamine [79], urea [80], and glycine [81].…”

“…-Imparting hydrophilicity [73], -Better adsorption capacity of metal ions [74,75], -Better thermal stability [77,79,80], -Enhanced mechanical properties [77,78], -Anti-aging properties of polymeric composites [78].…”

Lignocellulosic Materials for the Production of Biofuels, Biochemicals and Biomaterials and Applications of Lignocellulose-Based Polyurethanes: A Review

“…Another significant process that is intended to enhance hydroxyl value is phenolation. Since diisocyanates also possess a great affinity to amine groups, lignin amination and nitration have likewise been focused on [ 241 , 242 , 243 ]. Nonetheless, the high molecular weight and structure stand for a too-high viscosity and difficulties with reactivity; thus, depolymerisation is often targeted as well.…”

High-Strength and Shape-Memory Epoxy Cellular Material with Wood-Like Architecture

“…However, it remains a great challenge to realize unique porous structures through these conventional production processes . Particularly, the isotropic porous structure of epoxy cellular plastics manufactured by conventional methods yields only moderate compressive strength commonly below ∼25 MPa, − which greatly limits its potential applications. Therefore, there is still an urgent demand to develop techniques to prepare epoxy cellular plastics with well-defined architectures and excellent multifunctional performances.…”