Owing to their superior mechanical performance, strong adhesion, thermal resistance, and insulating properties, epoxy resins are commonly employed as protective coatings, electronic encapsulants, adhesives, and matrices in composites. The selection of the epoxy system components—the base resin and curing agent—along with the chosen curing protocol, directly determines the properties of the final cross-linked polymer. This study compares the influence of halogen substituents in 4,4′-methylenebis(2,6-diethylaniline) (MDEA), 4,4′-methylenebis(3-chloro-2,6-diethylaniline) (MCDEA) and 4,4′-methylenebis(3-bromo-2,6-diethylaniline) (MBDEA). The results of mechanical tests on plastics and composites demonstrated an increase in the strength properties and elastic modulus of the matrix, improved adhesive interactions with carbon fiber, and showed a reduction in moisture saturation across the series MDEA → MCDEA → MBDEA. Notably, the improvement in properties exceeded the increase in the density of the compositions, indicating an enhancement in the specific characteristics of the matrix.

The impact of introducing a nonwoven polyamide PA 12-E material on the mechanical properties of polymer composite materials based on epoxy autoclave prepreg T107 has been investigated. This study demonstrates that the incorporation of nonwoven fabric does not lead to a decrease in the mechanical properties of the composites. A significant advantage of composites reinforced with nonwoven fabric is their enhanced impact resistance. During a free impact with an energy of 6.67 J per 1 mm of the sample, complete breakdown with fiber destruction occurs in samples without nonwoven material. In contrast, samples containing nonwoven material exhibit damage characterized by stratification without compromising the fibers. The compressive strength after impact increased from 260 to 320 MPa with the addition of nonwoven material. Consequently, the proposed modification of the commercial prepreg will expand the material’s range of applications and enhance safety, particularly in aircraft structures.

исследовано влияние введения нетканого материала из полиамида ПА 12-Э на механические свойства полимерных композиционных материалов на основе эпоксидного автоклавного препрега Т107. Наличие нетканого материала незначительно снижает температуру стеклования до 171 ℃, что не влияет возможность применения материала до максимальной эксплуатационной температуры в 120 ℃. Исследование срезов композитов электронной микроскопией выявило равномерное распределение термопластичной фазы между слоями углеродной ткани, а также высокую адгезию полиамида к эпоксидной матрице. Показано, что введение нетканого материала не приводит к снижению механических свойств композитов. Основным преимуществом композитов на основе нетканого материала является повышенное сопротивление к ударным нагрузкам. При свободном ударе с энергией 6,67 Дж на 1 мм образца у образца без нетканого материала наблюдается сквозной пробой с разрушением волокон, в то время как у образца с нетканым материалом разрушение носит характер расслоения без повреждения волокон. Предел прочности при сжатии после удара вырос с 257 до 326 МПа при введении нетканого материала. В итоге, предложенная модификация коммерческого препрега позволит расширить область применения материала и повысить безопасность, в первую очередь, в конструкциях летательных аппаратов. the effect of introducing nonwoven material based on polyamide PA 12-E on the mechanical properties of polymer composite materials based on the epoxy autoclave prepreg T107 was investigated. The presence of the nonwoven material slightly lowers the glass transition temperature to 171 ℃, which does not affect the feasibility of using the material up to the maximum operating temperature of 120 ℃. Electron microscopy studies of the composite's cross-sections revealed uniform distribution of the thermoplastic phase between the layers of carbon fabric as well as high adhesion of polyamide to the epoxy matrix. It was demonstrated that introducing nonwoven material does not lead to a reduction in the mechanical properties of the composites. The main advantage of composites based on nonwoven material is their enhanced resistance to impact loads. Under a free impact with energy of 6.67 J per 1 mm of the specimen, a through penetration with fiber destruction was observed in the sample without the nonwoven material, while for the sample with nonwoven material, the damage was characterized by delamination without fiber damage. The compressive strength after impact increased from 257 to 326 MPa with the introduction of nonwoven material. As a result, the proposed modification of commercial prepreg could expand the range of applications for the material and improve safety, particularly in aircraft structures.

Dicyandiamide (DCDA) is an attractive precursor for triazine-rich phthalonitrile networks but suffers from fundamental incompatibility with hydrophobic phthalonitrile monomers, leading to heterogeneous suspensions, explosive exotherms, and filtration issues during composite fabrication. Herein, we overcome this limitation by pre-reacting DCDA with phthalonitriles to form soluble oligomeric adducts (PTA and CPTA) that retain curing activity. We demonstrate that DCDA reacts selectively with the phthalonitrile moiety, leaving the isolated benzonitrile group intact. This latent functionality provides a wide processing window at 190 °C (gel time > 1 h) and dramatically reduces the polymerization exotherm from ~400 to 20–30 J/g. During post-curing at 330 °C, the isolated nitrile groups participate in additional crosslinking, enabling the composites to achieve a glass transition temperature (Tg) exceeding 320 °C without exposure to the harsh thermal conditions (350–375 °C) typically required for conventional phthalonitrile systems, thereby minimizing thermo-oxidative degradation. The resulting carbon fiber reinforced composites exhibit outstanding properties: interlaminar shear strength (ILSS) > 50 MPa with 94% retention at 300 °C, flexural strength > 880 MPa, and compressive strength > 570 MPa. The hybrid network architecture-containing both pre-formed melamine-like triazines and post-curing-generated s-triazines-represents a new class of phthalonitrile matrices combining excellent processability with high thermo-mechanical performance.

The application of high-temperature bismaleimide resins in structural composites is inherently limited by the trade-off between thermal performance and processability. Here, we report a targeted molecular design strategy to overcome this operational bottleneck. By introducing bulky ortho-ethyl substituents into a monomeric architecture, premature homopolymerization was selectively suppressed up to 300 °C while maintaining the rigidity of the aromatic backbone. The resulting resin system provides an optimized processing profile for vacuum-assisted resin transfer molding (VARTM), characterized by low melt viscosity (<400 mPa·s) across a 120–140 °C range and isothermal stability exceeding 8 h. The fabricated carbon fiber reinforced polymer (CFRP) exhibits a high glass transition temperature (up to 277 °C) and retains 92.5% of its room-temperature flexural modulus at 250 °C (49 GPa). This strategy serves as a technological basis for the autoclave-free manufacturing of heat-resistant structural materials.