Phosphorus-containing flame retardant epoxy thermosets: Recent advances and future perspectives

A liquid phosphorus-containing imidazole derivative as flame-retardant curing agent for epoxy resin with enhanced thermal latency, mechanical, and flame-retardant performances.

Novel phosphorus-containing halogen-free ionic liquid toward fire safety epoxy resin with well-balanced comprehensive performance

Single component phosphamide-based intumescent flame retardant with potential reactivity towards low flammability and smoke epoxy resins.

A DOPO-based phosphorus-nitrogen flame retardant bio-based epoxy resin from diphenolic acid: Synthesis, flame-retardant behavior and mechanism

Flame-retarding epoxy resin with an efficient P/N/S-containing flame retardant: Preparation, thermal stability, and flame retardance

Flame retardancy and corrosion resistance required by high-performance epoxy resins (EP), especially in the field of composites and coating, are difficult to achieve simultaneously. In this study, a facile method was put forward to impart both flame-retardant and anti-corrosive properties to epoxy resins, via chemically introducing bifunctional phosphorus-containing triazole derivatives (D-ATA). In the resultant epoxy thermosets, the phosphorylated triazole structure directly contributed to flame retardancy, while the triazole structure can effectively suppress the electrochemical corrosion. With only 5 wt% loading of D–ATA, the epoxy thermoset showed excellent flame retardancy with a high limiting oxygen index of 33.2%, V-0 rating in UL-94 tests and significant suppression of heat and smoke release in cone calorimetry tests. Meanwhile, the electrochemical corrosion tests confirmed that the corrosion protection efficiency of EP/5 wt% D-ATA increased by 95.3% in comparison to neat EP. Due to hydrogen bonding and π-π interactions caused by the introduction of D-ATA, the versatile epoxy thermoset also had enhanced mechanical properties with the improved tensile and flexural strength. Moreover, the anti-corrosion and flame-retardant mechanisms were also discussed in detail. This work provides a facial strategy for preparing versatile high-performance epoxy thermoset with fire safety and corrosion resistance for various applications.

Mechanically strong and flame-retardant epoxy resins with anti-corrosion performance

In this work, calcium gluconate (CaG) as an eco-friendly additive was subtly incorporated into intumescent flame-retardant epoxy resin (EP) aiming to increase the flame-retardant efficiency. As expected, CaG exhibited synergistic effect in combination with APP, which could further decrease the heat release of epoxy thermosets including peak of heat release rate (PHRR), as well as the smoke production covering smoke production rate (SPR) and total smoke production (TSP). Typically, EP81 with 10 wt% flame retardants (8:1, the mass ratio of APP and CaG) easily passed a UL-94 V-0 rating, and got the highest LOI value of 31.8%; besides, during combustion it displayed PHRR value at 336 kW/m2 with a reduction of 39.7% compared to EP/10 wt% APP. In addition, its TSP value was further reduced to 9.2 m2 from 18.1 m2 of EP/10 wt% APP. According to the analyses of char residues, it indicated that the presence of APP-CaG was beneficial for EP to form more continuous and compact char which was more effective to insulate the transfer of heat and the diffusion of fuels. Besides, despite the introduction of CaG the tensile strength of EP/APP material was well maintained.

Influence of eco-friendly calcium gluconate on the intumescent flame-retardant epoxy resin: Flame retardancy, smoke suppression and mechanical properties

In order to solve the contradiction between the flammability and mechanical properties of epoxy resins, a novel organophosphorus heteroaromatic compound (DMBT) was designed and synthesized derived from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 2-mercaptobenzothiazole (MBT). In the existence of DMBT, the properties of the resultant epoxy thermosets (EP) were improved obviously in the aspect of flame retardancy and mechanical properties. Benefitting from the design of strong intermolecular action between DMBT and EP, the tensile strength, flexural strength and modulus of EP/10 wt% DMBT largely increased to 82.2 ± 4.0 MPa, 122.2 ± 1.7 MPa and 3426 ± 81 MPa from 70.2 ± 5.9, 94.0 ± 2.0 and 2654 ± 139 MPa of EP, respectively. Meanwhile, under the action of DMBT, EP/10 wt% DMBT passed UL-94 V-1 rating and possessed a LOI value of 33.5%. The results of calorimeter tests confirmed that the incorporation of DMBT could effectively reduce the heat release rates (HRR) and total heat release (THR) of materials during combustion. Furthermore, the analysis of the char residue after burning and the volatile products in pyrolysis revealed that the flame-retardant mechanism of DMBT was attributed to improving the charring ability and releasing phosphorus-containing free radicals. This work provides a new strategy to prepare the mechanically-strong and flame-retardant epoxy resins.

Yuan-Fang Ai

Papers

Single component phosphamide-based intumescent flame retardant with potential reactivity towards low flammability and smoke epoxy resins.

Flame-retarding epoxy resin with an efficient P/N/S-containing flame retardant: Preparation, thermal stability, and flame retardance

Mechanically strong and flame-retardant epoxy resins with anti-corrosion performance

Influence of eco-friendly calcium gluconate on the intumescent flame-retardant epoxy resin: Flame retardancy, smoke suppression and mechanical properties

Organophosphorus heteroaromatic compound towards mechanically reinforced and low-flammability epoxy resin