Modification mechanism of modified diatomite with flexible amine‐based structure as a filler of epoxy resin and mechanical properties and curing kinetic of composites

Abstract In this study, the binding of amine‐based hyperbranched macromolecular polyethyleneimine (PEI) to diatomite (DE) was carried out by using the silane coupling agent KH560 (PEI‐KH560‐DE). Fourier infrared spectroscopy, scanning electron microscopy were used to characterize the structure of the modified DE. Then, the composites were prepared using PEI‐KH560‐DE as the filler in the epoxy resin matrix and then cured with dimethylimidazole. The cured composites were tested for impact resistance, flexural properties, and tensile properties, and then subjected to DSC. The experimental results showed that when different proportions of diatomite or modified diatomite were added to the epoxy resin matrix, the strength and toughness of the composites could be significantly enhanced. When the content of PEI‐KH560‐DE was 15 wt%, the impact strength of the composites reached the maximum value of 5.39 kJ/m 2 , which was 156.67% higher than that of the pure epoxy resin (2.10 kJ/m 2 ). The tensile strength was also improved from 16.38 MPa of the pure epoxy resin to 26.55 MPa, corresponding to an increase of 62.09%. With the addition of modified diatomite, the T dmax and char yield of the composites were significantly enhanced, indicating that the addition of diatomite can enhance the heat resistance and thermal stability of the composites. The curing kinetics study showed that the addition of PEI‐KH560‐DE can significantly reduce the apparent activation energy required for the curing reaction of epoxy resin probably due to the presence of amine group in PEI, which plays a role in promoting the curing behavior. Highlights Amine groups and flexible chain segments were introduced into diatomite. Mechanism of polyethyleneimine‐modified diatomite was investigated. Improved mechanical and thermal properties of PEI‐KH560‐DE/EP composites. Curing kinetics showed that amine groups reduce apparent activation energy.