Concurrently enhancing the flame retardancy and toughness without sacrificing strength, thermal decomposition temperature, and glass transition temperature (Tg) of epoxy thermosets is still challenging. Herein, a new phosphorus/nitrogen-containing hyperbranched epoxy resin (HPITT) was synthesized from itaconic anhydride, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, piperazine, and triglycidyl isocyanurate by a facile method. The HPITT was then utilized for synergistic flame retarding and toughening modification of epoxy thermosets. Upon the introduction of 10 wt% HPITT, the epoxy thermosets reached a limiting oxygen index (LOI) of 31.5 % and UL-94 V-0 rating. Meanwhile, the peak heat release rate (PHRR) and total smoke production (TSP) decreased by 32.3 % and 27.7 % when compared to neat epoxy thermosets, respectively. Moreover, the synergistic flame retarding functions of phosphaphenanthrene, piperazine and isocyanurate segments in HPITT were demonstrated by combined gas and char phase residue analyses. Compared to neat epoxy, features such as the impact strength, tension strength, and flexural strength of the modified epoxy thermosets increased by respectively 53.9 %, 29.2 %, and 58 % owing to intramolecular cavities, rigid segments, and high crosslinking density supplied by HPITT. Moreover, the modified epoxy thermosets still maintained excellent Tg and thermal decomposition temperature. In sum, an attractive strategy for concurrently enhancing flame retardancy and toughness of epoxy thermosets was proposed, useful for future advanced applications in adhesives, coatings, and composite materials. 

Facile synthesis of hyperbranched epoxy resin for combined flame retarding and toughening modification of epoxy thermosets

Recent Develpoments and Applications of Hyperbranched Polymers as Flame Retardants

Cyclotriphosphazene-based epoxy resins with excellent mechanical and flame retardant properties

Improvement of mechanical properties and flame retardancy of epoxy resin by phosphorylated cyclotriphosphazene hyperbranched polymeric flame retardants

Usually, the incorporation of traditional linear molecule flame retardant will bring negative impact on the thermal stability of bismaleimide (BMI), which limited the application of BMI in high-end fields. Based on this problem, a synergistic hyperbranched polymer (HPTDM) containing phosphorus/nitrogen/silicon was used as a novel flame retardant for cured BMI system. Due to the specific hyperbranched structure, the HPTDM itself had high thermal stability. And the elements of nitrogen, silicon and phosphorus can significantly improve the efficiency of flame retardants through synergistic effects. Surprisingly, the addition of flame retardants did not greatly affect the thermal stability of pure BMI, and the BMI/HPTDM-0.5 with the phosphorus content of as low as 0.05 wt% could achieve a maximum reduction of 34.4% in total heat release (THR). Furthermore, the modified BMI resin demonstrated superior toughness owing to the novel hyperbranched structure, and the impact strength of BMI/HPTDM-1.0 was 90.2% higher than the pure BMI. This article provided a novel strategy for designing hyperbranched flame retardant and promoted the BMI in the field of high temperature. 

Bismaleimide with high thermal stability, toughness and flame retardancy modified by synergistic hyperbranched flame retardant

Hexakis(4-hydroxyphenoxy) cyclotriphosphazene (PN-OH) was synthesized by a nucleophilic substitution and aldehyde reduction reaction of hexachlorocyclotriphosphazene with p-hydroxybenzaldehyde, and then cyclophosphazene nucleated hyperbranched polyesters (HBP) were prepared via a one-pot esterification reaction of PN-OH and dimethylolpropionic acid. The chemical structure and molecular weight distribution of HBP were confirmed by 1H-NMR, FTIR, and GPC. The HBP was applied to epoxy resin (EP) to improve its mechanical properties and flame retardancy. The cone calorimeter test revealed that the maximum heat release rate, total heat release and total smoke release of HBP/EP composites were reduced by 35.9%, 21.6%, and 27.3%, respectively, when 7 wt% HBP was added to the EP matrix compared with pure EP. Meanwhile, when 7 wt% HBP was added to EP composites, the limiting oxygen index value was increased from 24.6% to 27.7% and the UL-94 test reached a V-1 rating. More importantly, the thermal stability and mechanical properties of the HBP/EP composites were enhanced. The flame retardant mechanism analysis showed that HBP primarily acted as a flame retardant in the condensed phase. These results indicate that the HBP/EP composites have exceptional overall performance and a broad range of applications in critical fields. 

Effect of cyclophosphazene nucleated hyperbranched polyester on flame retardancy and mechanical properties of epoxy resins

A functionalized cross-linked polyphosphazenes microsphere (Salen-PZN-Ni@DHPP-PTS) was prepared by wrapping Salen-Ni basis polyphosphazenes (Salen-PZN-Ni) with a kind of hybrid flame retardant (DHPP-PTS) to improve the flame retardancy and smoke suppression properties of epoxy (EP) composites. Thermogravimetric analysis showed that the addition of Salen-PZN-Ni@DHPP-PTS greatly improved the thermal stability of the EP composites. The addition of 5 wt% Salen-PZN-Ni@DHPP-PTS remarkably improved the fire safety of EP, which was illustrated by the results of the cone calorimeter. For example, the peak heat release rate and total heat release rate of the EP composites were reduced by 44.2% and 33.1%, respectively. The limiting oxygen index value of 5% Salen-PZN-Ni@DHPP-PTS/EP composite reached 29.8% and UL-94 achieved V-1 rating. In addition, the introduction of Salen-PZN-Ni@DHPP-PTS effectively suppressed the production of toxic CO and other volatiles. Meantime, the synergistic effect between Salen-PZN-Ni and DHPP-PTS was found. The potential flame retardant mechanism of Salen-PZN-Ni@DHPP-PTS is regarded as the synergistic catalytic carbonization effect and the extremely thermally stable components forming. Enhanced fire safety of EP composites by synergistic interaction of various components (nickel and DHPP-PTS) with polyphosphazenes microspheres.

A novel flame retardant consisting of functionalized Salen-Ni based polyphosphazene microspheres

Tribological Properties of Oil-Containing Polyimide Aerogels as a New Type of Porous Self-Lubricating Material

The utilization of epoxy resin (EP) is widespread across various industries. Nevertheless, its combustibility restricts its broader utilization. Additive flame retardants have proven effective in enhancing EP flame retardancy in recent decades. However, poor weather and aging resistance have always been the defects of added flame retardants. A reactive flame retardant (VPD) was synthesized from 3, 5‐diamino‐1, 2, 4‐triazole and phenylphosphonic dichloride, and was used to prepare VPD/EP flame retardant epoxy thermosets. The mechanical properties of the VPD/EP flame retardant epoxy thermosets are lower than those of pure epoxy, because the distance between molecules of VPD is increased compared with that of DDM, the cross‐linking density of the polymer after curing is decreased, and the intermolecular force is reduced. The VPD/EP flame retardant epoxy thermosets have a 40% reduction in total heat release compared to pure EP, an increase in limiting oxygen index value from 24.7% (pure EP) to 29.4%, and a V‐1 rating in UL‐94 testing. The obtained EP has not only good flame retardancy but also better weather resistance and aging resistance than additive flame retardants.

Molecular design and properties of a P‐N synergistic flame retardant epoxy resin curing agent

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