Latent Curing, Chemorheological, Kinetic, and Thermal Behaviors of Epoxy Resin Matrix for Prepregs

Abstract

Epoxy prepregs are extensively exploited in a myriad of applications. Thermal, rheological, and curing behaviors of epoxy resins are important for the impregnation of carbon fibers into the resin. The demand for latent curing properties in the field of epoxy prepregs is more intense than in the field of epoxy resins owing to the impregnation process at high temperature. In this study, we examined the thermal, rheological, kinetic, and curing properties of a latent curable epoxy resin matrix for prepregs by tailoring the material composition and deactivators (latent curing additives). Four organic and inorganic deactivators were found for the epoxy/amine/tertiary amine system. The incorporation of fumed silica, boric acid, benzoic acid, and triethyl borate (TEB) induced latent curing behaviors of the epoxy resin matrix. TEB was found to be an excellent deactivator, showing no reaction at 60 °C for 1 day and increasing the exothermic reaction peak temperature. The systematically investigated epoxy matrix for prepregs with optimum composition can be used for aerospace and automotive applications.

Catalysis of Silver and Bismuth in Various Epoxy Resins

“…Their utility is grounded in a combination of remarkable qualities, including excellent adhesion, facile formulation and fabrication, cost-effectiveness, lightweight nature, and commendable mechanical and thermal characteristics [6][7][8][9][10]. Nonetheless, these benefits coexist with certain drawbacks, such as brittleness, susceptibility to ultraviolet (UV) degradation, and the prolonged curing process [11][12][13]. These distinctive traits stem from the intricate molecular architecture that incorporates oxirane groups, thus contributing to reactivity and hydroxyl moieties that influence adhesion as a pivotal factor and reactivity as a secondary consideration [14].…”

“…Over the preceding decades, extensive efforts have been devoted to expanding the range of properties exhibited by epoxy resin, thus widening their range of application [1,2]. A paramount avenue for manipulating these properties involves the deliberate adjustment of composition through the integration of diverse additives [13,15]. These additives include fillers, reinforcement, plasticizers, elastomers, antifoaming agents, leveling agents, thixotropic agents, thickeners, UV and heat stabilizers, flow control agents, colorants, pigments, adhesion promoters, flame retardants, accelerators, and catalysts.…”

“…Diverse catalysts, ranging from highly efficient to less efficient options, find applications in epoxy systems. These include Lewis acids (e.g., boron trifluoride and its complexes), imidazoles (e.g., 1-methyl imidazole), and ureas (e.g., 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU)) [13,16,20,21]. Notably, the optimal catalysts vary among different epoxy systems, encompassing epoxy-amine, epoxy-anhydride, and epoxy-diacid subclasses [15,16].…”

Controlled Triphenylphosphine Reactivity for Epoxy Resin Cure by Transition-Metal β-Diketonates

“…The resin monomers or prepolymers typically soften and thin with initial thermal input when gaining molecular chain mobility, while once polymerization initiates, the molecular weight buildup will drastically reduce the ability of the resin to flow. The allowed processing and application window, concerning both temperature and time, are essential to composite, molding, and adhesive films such as no-flow underfill (or nonconductive film, NCF) applications, especially seeing the increase in composite filler loading level, and stage temperature or on-stage time in thermal compression bonding (TCB) assembly. After these processes, a rapid cure to achieve a fully cured resin is further preferred, although in certain cases, too violent a heat release may cause reliability issues related to thermal runaway or void formation.…”