This study aims to investigate the toughening effects of rubber and thermoplastic particles on epoxy resin (EP), and to understand the mechanism underlying their synergistic effect. For this purpose, three EP systems were prepared using diglycidyl ether of bisphenol-A (DGEBA) epoxy resin (E-54) and 4,4-Diamino diphenyl methane (Ag-80) as matrix resin, 4,4-diaminodiphenyl sulfone (DDS) as a curing agent, and phenolphthalein poly (aryl ether ketone) particles (PEK-C) and carboxyl-terminated butyl liquid rubber (CTBN) as toughening agents. These systems are classified as an EP/PEK-C toughening system, EP/CTBN toughening system, and EP/PEK-C/CTBN synergistic toughening system. The curing behavior, thermal properties, mechanical properties, and phase structure of the synergistic-toughened EP systems were comprehensively investigated. The results showed that PEK-C did not react with EP, while CTBN reacted with EP to form a flexible block polymer. The impact toughness of EP toughened by PEK-C/CTBN was improved obviously without significantly increasing viscosity or decreasing thermal stability, flexural strength, and modulus, and the synergistic toughening effect was significantly higher than that of the single toughening system. The notable improvement in toughness is believed to be due to the synergistic energy dissipation effect of PEK-C/CTBN.

Structural damping composites exhibit considerable potential in aerospace and other fields due to their excellent damping and vibration reduction performance, as well as their structural carrying capacity. However, conventional structural damping composite materials generally do not combine excellent mechanical and damping properties at the same time, which makes it difficult for them to meet the practical demand in engineering. In this paper, polyetherimide (PEI) non-woven fabric interlayer materials loaded with quantified polydopamine (PDA) and carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were used to prepare carbon fiber-reinforced bismaleimide composites through the co-curing process. The mechanical and damping properties of the composites were systematically studied. The results demonstrate that PEI non-woven fabric interlayers loaded with PDA and MWCNTs-COOH can synchronously improve the mechanical and damping properties of the co-cured composites. The incorporation of carbon nanotubes and polydopamine during the co-curing process synergistically improves the flexural strength, flexural modulus, interlaminar shear strength, and impact fracture toughness of the composites. Most importantly, damping properties show an increase of 45.0% in the loss factor of the co-cured composites. Moreover, the reinforcement mechanism was investigated using the optical microscopy and scanning electron microscopy, which indicated that the PEI interlayers loaded with carbon nanotubes and polydopamine form a rich resin area between the layers of the composites.

Thermosetting polymers and composites are a class of high-performance materials with significant industrial applications. However, the widespread use of thermosets and their composites generates large quantities of waste and leads to serious economic and environmental problems, there is a critical need in the elaboration of sustainable composite materials. Here, we propose a method to prepare sustainable carbon fiber reinforced composites with different degrees of greenness by blending environmentally friendly EIA with DGEBA in different ratios, and the properties compared with a well-known commercial petroleum-based epoxy resin. The prepared carbon fiber reinforced polymer (CFRP) composites with different degrees of greenness had excellent dimensional stability under extreme hygrothermal aging. After aging, the green CFRP composite T700/EIA-30 has higher strength and performance retention than that of petroleum-based CFRP composites. The higher hygrothermal stability and durability of EIA-based epoxy resins as compared with BPA-based epoxy resins demonstrated significant evidence to design and develop a novel bio-based epoxy resin with high performance to substitute the petroleum-based epoxy resin.

Metal–organic frameworks (MOFs) have been previously shown as an emerging modified class of epoxy resin. In this work, we report a simple strategy for preventing zeolitic imidazolate framework (ZIF-8) nanoparticles from agglomerating in epoxy resin (EP). Branched polyethylenimine grafted ZIF-8 in ionic liquid (BPEI-ZIF-8) nanofluid with good dispersion was prepared successfully using an ionic liquid as both the dispersant and curing agent. Results indicated that the thermogravimetric curve of the composite material had no noticeable change with increasing BPEI-ZIF-8/IL content. The glass transition temperature (T_g) of the epoxy composite was reduced with the addition of BPEI-ZIF-8/IL. The addition of 2 wt% BPEI-ZIF-8/IL into EP effectively improved the flexural strength to about 21.7%, and the inclusion of 0.5 wt% of BPEI-ZIF-8/IL EP composites increased the impact strength by about 83% compared to pure EP. The effect of adding BPEI-ZIF-8/IL on the T_g of epoxy resin was explored, and its toughening mechanism was analyzed in combination with SEM images showing fractures in the EP composites. Moreover, the damping and dielectric properties of the composites were improved by adding BPEI-ZIF-8/IL.