A Novel Anderson-Type POMs-Based Hybrids Flame Retardant for Reducing Smoke Release and Toxicity of Epoxy Resins.

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-CO2 Y) 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 Al2 O3 and MoO3 produced from the breakdown of POMs. This work advances the development of POMs-based hybrids flame retardants with low smoke toxicity properties.

Asymmetric Hydrophosphonylation of Imines to Construct Highly Stable Covalent Organic Frameworks with Efficient Intrinsic Proton Conductivity.

Imine-linked covalent organic frameworks (COFs) have received widespread attention because of their structure features such as high crystallinity and tunable pores. However, the intrinsic reversibility of the imine bond leads to the poor stability of imine-linked COFs under strong acid conditions. Also, their thermal stability is significantly lower than that of many other COFs. Herein, we report for the first time that the reversible imine bonds in the skeleton of COFs can be locked through the asymmetric hydrophosphonylation reaction of phosphite. The functionalized COFs not only retain the crystallinity and porous structure but also exhibit evidently improved chemical and thermal stabilities. In addition, the phosphorous acid groups generated by acidic hydrolysis attached to the skeleton endow the COFs with good intrinsic proton conductivity. Due to the diversity of phosphite derivatives and imine-linked COFs, this work may provide an avenue for extending the COF structures and functions through the asymmetric hydrophosphonylation reaction.

A Novel P/N/Si-Containing Vanillin-Based Compound for a Flame-Retardant, Tough Yet Strong Epoxy Thermoset.

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.

LDH@Boronate Polymer Core-Shell Nanoparticles: Nanostructure Design for Synergistically Enhancing the Flame Retardancy of Epoxy Resin.

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.