Thermal degradation and combustion behavior of flame-retardant epoxy resins with novel phosphorus-based flame retardants and silicon particles

An Organometallic Flame Retardant Containing P/N/S-Cu2+ for Epoxy Resins with Reduced Fire Hazard and Smoke Toxicity

Epoxy resins (EPs) have superior physical and chemical features and are used in a wide range of applications in everyday life and engineering. However, its poor flame-retardant performance has hindered its wide application. Over the past decades of extensive research, metal ions have received increasing attention for their highly effective smoke suppression properties. In this work, we used an "aldol-ammonia condensation" reaction to structure the Schiff base structure, together with grafting using the reactive group on 9,10-dihydro-9-oxa-10-phospha-10-oxide (DOPO). Then, Cu²⁺ was used to replace Na⁺ to obtain DCSA-Cu flame retardant with smoke suppression properties. Attractively, DOPO and Cu²⁺ can collaborate, thus effectively improving EP fire safety. At the same time, the addition of a double-bond initiator at low temperatures allows small molecules to form in situ macromolecular chains through the EP network, enhancing the tightness of the EP matrix. With the addition of 5 wt % flame retardant, the EP shows well-defined fire resistance, and the limiting oxygen index (LOI) reaches 36% with a significant reduction in the values of peak heat release (29.72%). In addition, the glass-transition temperature (T_g) of the samples with in situ formations of macromolecular chains was improved, and the physical properties of EP materials are also retained.

Discotic Liquid Crystal Epoxy Resins Integrating Intrinsic High Thermal Conductivity and Intrinsic Flame Retardancy

The integration of intrinsic thermal conductivity and intrinsic flame retardancy of epoxy resins shows wider application prospects in electricals and electronics. Discotic liquid crystal epoxy (D-LCE) is synthesized from pyrocatechol, 2-allyloxyethanol, and 3-chloroperoxybenzoic acid. P/Si synergistic flame-retardant co-curing agent (DOPO-POSS, DP) is synthesized from p-hydroxybenzaldehyde, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO), and amino terminated polysilsesquioxane (POSS). Finally, D-LCE is cured within liquid crystal range with 4, 4'-diaminodiphenyl methane (DDM) and DP, to obtain intrinsic highly thermal conductive/flame-retardant epoxy resins (D-LCER_DP ). D-LCER_DP-10.0 (10.0 wt% DP) synchronously possesses excellent intrinsic thermal conductivity and intrinsic flame retardancy, with thermal conductivity coefficient in vertical and parallel direction (λ_⊥ and λ_∥ ) of 0.34 and 1.30 W m^-1 K^-1 , much higher than that of general bisphenol A epoxy resin (E-51, λ_⊥ of 0.19 W m^-1 K^-1 , λ_∥ of 0.65 W m^-1 K^-1 ). The limiting oxygen index (LOI) value of D-LCER_DP-10.0 reaches 31.1, also better than those of E-51 (19.8) and D-LCER (21.3).

Recent Developments in the Flame-Retardant System of Epoxy Resin

With the increasing emphasis on environmental protection, the development of flame retardants for epoxy resin (EP) has tended to be non-toxic, efficient, multifunctional and systematic. Currently reported flame retardants have been capable of providing flame retardancy, heat resistance and thermal stability to EP. However, many aspects still need to be further improved. This paper reviews the development of EPs in halogen-free flame retardants, focusing on phosphorus flame retardants, carbon-based materials, silicon flame retardants, inorganic nanofillers, and metal-containing compounds. These flame retardants can be used on their own or in combination to achieve the desired results. The effects of these flame retardants on the thermal stability and flame retardancy of EPs were discussed. Despite the great progress on flame retardants for EP in recent years, further improvement of EP is needed to obtain numerous eco-friendly high-performance materials.