Flame-retardant, transparent, mechanically-strong and tough epoxy resin enabled by high-efficiency multifunctional boron-based polyphosphonamide

Facile and green fabrication of flame-retardant Ti3C2Tx MXene networks for ultrafast, reusable and weather-resistant fire warning

Flame-retardant epoxy resins (EPs) with superior optical, mechanical and dielectric properties are highly desired in high-tech industries. In this work, a multifunctional hyperbranched additive (BDHDP) was synthesized for EPs. Our results showed that BDHDP catalyzed the curing of epoxy resin because of its tertiary amine and hydroxyl groups. At a low addition level (<3.0 wt%), BDHDP increased the glass-transition temperature and maintained the optical transmittance of epoxy thermoset. Meanwhile, BDHDP improved the mechanical strength and toughness, and reduced the dielectric constant and loss of EP because of the rigid phosphaphenanthrene groups and intra-molecular cavities. Moreover, BDHDP reduced the heat release and smoke generation during the EP combustion. Adding 1.5 wt% of BDHDP led to a UL-94 V-0 rating, and reduced the total smoke production by 16.4%. Hence, this study offers an effective method to create transparent EP thermosets with outstanding mechanical, dielectric and fire-retardant properties via incorporating a P/N/B-containing hyperbranched oligomer. 

A hyperbranched P/N/B-containing oligomer as multifunctional flame retardant for epoxy resins

The design of highly fire-safe and smoke-suppressive single-component epoxy (EP) resins combining modest curing temperature and fast curing rate has been desirable yet very challenging in both academia and industry. Herein, we report a facile design of a phosphorus/imidazole-containing single-component EP system via incorporating 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and a flame-retardant curing agent cyclotriphosphazene-modified benzimidazole (BICP) into EP. Our results show that EP/DOPO/BICP exhibits a rapid modest-temperature curing feature because DOPO serves as a switch that triggers BICP to release benzimidazole (BIM) via substitution reaction in the initial curing stage. Moreover, as-prepared EP/DOPO/BICP shows outstanding fire retardancy, reflected by the high limited oxygen index (LOI) of 38.3% and UL-94 V-0 rating. Compared to the control EP system, the peak of heat release rate (PHRR) and total smoke production (TSP) of EP/DOPO/BICP remarkably decrease by ~74.5% and ~50.6%, respectively, which is superior to previously-reported flame-retardant P-containing epoxy counterparts. The significant enhancements in flame retardancy and smoke suppression are mainly due to the formation of a highly intumescent char layer and the reduced burning degree of pyrolysis fragments. This work offers a facile and scalable strategy for creating fast-curing, modest-temperature curable, highly fire-resistant and smoke-suppressive one-component epoxy systems applicable to large-scale industrial production.

A highly fire-safe and smoke-suppressive single-component epoxy resin with switchable curing temperature and rapid curing rate

With the increasing demand of industry, the fabrication of single-component epoxy (EP) systems with satisfactory flame retardancy and thermal stability is of great significance. Herein, a novel phosphorus/nitrogen-containing single-component EP (EP/DOPO/BDM/BICP) system was synthesized via incorporating N,N′-bismaleimide-4,4′-diphenylmethane (BDM), benzimidazolyl-substituted cyclotriphosphazene (BICP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) into EP. In our previous work, we found that DOPO could promote the decomposition of BICP to produce dissociative benzimidazoles under heating, which endowed the as-fabricated epoxy thermoset with rapid curing speed. However, the addition of DOPO reduced the glass transition temperature (Tg) of epoxy thermosets. To deal with this problem, bismaleimide with superior heat resistance was added. The results indicated that the addition of BDM improved the thermal stability, flame retardancy and smoke suppression of EP/DOPO/BDM/BICP. The obtained thermoset exhibited UL94 V-0 rating, limiting oxygen index (LOI) of 40.5% and low total smoke production (TSP) of 10.4 m2 due to the synergetic flame-retardant effect of phosphaphenanthrene, polybismaleimide and cyclotriphosphazene. This research offers a viable approach to develop single-component EPs with improved flame retardancy, thermal stability and rapid-curing ability.

Jingsheng Wang

Papers

A highly fire-safe and smoke-suppressive single-component epoxy resin with switchable curing temperature and rapid curing rate

Facile fabrication of single-component flame-retardant epoxy resin with rapid curing capacity and satisfied thermal resistance

Preparation and properties of aniline chain-extended thermoplastic epoxy resin using triphenylphosphine as catalyst