Smoke emission and smoke toxicity have drawn more attention to improving the fire safety of polymers. In this work, a polyoxometalates (POMs)‐based hybrids flame retardant (P‐AlMo6) epoxy resin (EP) is prepared with toxicity‐reduction and smoke‐suppression properties via a peptide coupling reaction between POMs and organic molecules with double DOPO (bisDOPA). It combines the good compatibility of the organic molecule and the superior catalytic performance of POMs. Compared to pure EP, the glass transition temperature and flexural modulus of EP composite with 5 wt.% P‐AlMo6 (EP/P‐AlMo6‐5) are raised by 12.3 °C and 57.75%, respectively. Notably, at low flame‐retardant addition, the average CO to CO2 ratio (Av‐COY/Av‐CO2Y) is reduced by 33.75%. Total heat release (THR) and total smoke production (TSP) are lowered by 44.4% and 53.7%, respectively. The Limited Oxygen Index (LOI) value achieved 31.7% and obtained UL‐94 V‐0 rating. SEM, Raman, X‐ray photoelectron spectroscopy, and TG‐FTIR are applied to analyze the flame‐retardant mechanism in condensed and gas phase. Outstanding flame retardant, low smoke toxicity properties are attained due to the catalytic carbonization ability of metal oxides Al2O3 and MoO3 produced from the breakdown of POMs. This work advances the development of POMs‐based hybrids flame retardants with low smoke toxicity properties.
As a promising nanofiller, layered double hydroxides (LDHs) can advance the fire safety of epoxy resin (EP), but so far, due to the problems of dispersion and low efficiency, it has still been a challenge to incorporate the flame retardancy and mechanical properties of EP nanocomposites effectively under the circumstance of a low additive amount. In this work, we take LDHs as the template, via the adsorption of a catechol group and the condensation polymerization between catechol groups and phenylboric acid groups, to prepare a core–shell structured nanoparticle LDH@BP, which contains rich flame-retardant elements. EP/LDH@BP nanocomposites were prepared by introducing LDH@BP into EP. The experimental results indicate that, compared with the original LDH, LDH@BP disperses uniformly in the EP matrix, and the flame retardancy and mechanical properties of EP/LDH@BP are significantly improved. At a relatively low content (5 wt%), EP/LDH@BP reached the rating of V-0 in the UL-94 test, LOI was increased to 29.1%, and peak heat release rate (PHRR) was reduced by 35.9% in cone calorimeter tests, which effectively inhibited the release of heat and toxic smoke during the combustion process of EP. Simultaneously, the mechanical properties of EP/LDH@BP have been improved satisfactorily. The above results derive from the reasonable architectural design of organic–inorganic nano-hybrid flame retardants and provide a novel method for the construction of efficient and balanced EP nanocomposite system with LDHs.
Currently, because of the depletion of petroleum resources and pollution problems associated with the use of petrochemicals, bio-based epoxy thermosets have received wide attention. However, epoxy thermosets derived entirely from bio-based raw materials combining high performances in mechanical properties, fire resistance, and degradation are less reported. In this work, a fully bio-based Schiff base epoxy resin named VA-FA-EP is prepared from vanillin (VA) and 2-furfurylamine (FA). The curing kinetics and behavior of the imine exchange reaction are explored systematically. After being cured by 4,4′-diaminodiphenylmethane (DDM), VA-FA-EP/DDM exhibits excellent mechanical properties with a glass transition temperature of 200.1 °C. VA-FA-EP/DDM has also been proven to have good fire resistance. There are significant reductions of 66.73% and 81.72% in total heat release (THR) and total smoke production (TSP), respectively. The intrinsic flame-retardant mechanism is systematically illustrated. In addition, the VA-FA-EP/DDM has also shown a good degradation property. In summary, this study offers a viable approach for producing eco-friendly fire-safe Schiff base epoxy thermosets utilizing entirely sustainable raw materials.
It is still extremely challenging to endow epoxy resins (EPs) with excellent flame retardancy and high toughness. In this work, we propose a facile strategy of combining rigid–flexible groups, promoting groups and polar phosphorus groups with the vanillin compound, which implements a dual functional modification for EPs. With only 0.22% phosphorus loading, the modified EPs obtain a limiting oxygen index (LOI) value of 31.5% and reach V-0 grade in UL-94 vertical burning tests. Particularly, the introduction of P/N/Si-containing vanillin-based flame retardant (DPBSi) improves the mechanical properties of EPs, including toughness and strength. Compared with EPs, the storage modulus and impact strength of EP composites can increase by 61.1% and 240%, respectively. Therefore, this work introduces a novel molecular design strategy for constructing an epoxy system with high-efficiency fire safety and excellent mechanical properties, giving it immense potential for broadening the application fields of EPs.
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