Development of Epoxy Foaming with CO2 as Latent Blowing Agent and Principle in Selection of Amine Curing Agent

Some commercially available amines used as curing agents for epoxy resins can capture CO2 to form ammonium carbamates, which represent a novel type of latent blowing and curing agent for epoxy foaming. The principles in the selection of suitable amines are critical for final applications. This work aimed to reveal these principles by screening and comparing the preparation, chemical structure and composition, and curing and foaming performance of several types of ammonium carbamates from typical amine curing agents. It is found that amines with pK a >9 are eligible to react with CO2 to form ammonium carbamates with a high yield. Furthermore, the amines should have rigid cyclic groups in their structures to form a solid ammonium carbamate powder, which can be easily mixed with epoxy resins. The curing rate of the amine should not be much faster than the decomposition of the carbamate to obtain epoxy foams with good pore morphology and mechanical performance.