Synergistic effect of an aromatic boronic acid derivative and magnesium hydroxide on the flame retardancy of epoxy resin

A Simple and Efficient Magnesium Hydroxide Modification Strategy for Flame-Retardancy Epoxy Resin

Magnesium hydroxide, as a green inorganic flame-retardancy additive, has been widely used in polymer flame retardancy. However, magnesium hydroxide is difficult to disperse with epoxy resin (EP), and its flame-retardancy performance is poor, so it is difficult to use in flame-retardant epoxy resin. In this study, an efficient magnesium hydroxide-based flame retardant (MH@PPAC) was prepared by surface modification of 2-(diphenyl phosphine) benzoic acid (PPAC) using a simple method. The effect of MH@PPAC on the flame-retardancy properties for epoxy resins was investigated, and the flame-retardancy mechanism was studied. The results show that 5 wt% MH@PPAC can increase the limiting oxygen index for EP from 24.1% to 38.9%, achieving a V-0 rating. At the same time, compared to EP, the peak heat release rate, peak smoke production rate, total smoke production rate, and peak CO generation rate for EP/5 wt% MH@PPAC composite material decreased by 53%, 45%, 51.85%, and 53.13% respectively. The cooperative effect for PPAC and MH promotes the formation of a continuous and dense char layer during the combustion process for the EP-blend material, significantly reducing the exchange for heat and combustible gases, and effectively hindering the combustion process. Additionally, the surface modification of PPAC enhances the dispersion of MH in the EP matrix, endowing EP with superior mechanical properties that meet practical application requirements, thereby expanding the application scope for flame-retardant EP-blend materials.

Advances in the Chemistry of 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine

Heterocyclic systems are now considered to be an integral part of material chemistry. Thiophene, selenophene, furan, pyrrole, carbazole, triazine and others are some such examples worth mentioning. 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine is a C3h -symmetric system with thiophene as the donor unit and s-triazine as the acceptor unit. This review gives an insight into the advances made in the thienyl-triazine chemistry over the past two to three decades. The synthetic pathways for arriving at this system and all its important derivatives are provided. The major focus is on the materials synthesized using the thienyl-triazine system, including star molecules, linear and hyperbranched polymers, porous materials and their diverse applications. This review will play a catalytic role for new dimensions to be explored in thienyl-triazine chemistry.

Synthesis of a highly efficient flame retardant containing triazine and pentaerythritol phosphate groups and its intumescent flame retardancy on epoxy resin

A novel phosphorus-nitrogen-containing flame retardant (DOPT) has been successfully synthesized via the substitution reaction of cyanuric chloride, pentaerythritol phosphate and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. The chemical structure of DOPT was confirmed by 1H, 31P and 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy and elemental analysis. Then, flame retardants were added to epoxy resin to prepare epoxy resin composites by pouring method. Thermal properties, flame retardancy, and combustion behavior of epoxy resin composites were evaluated by thermogravimetric analysis, vertical burning, limiting oxygen index and cone calorimeter test. Thermogravimetric analysis test showed that the carbon residue rate of DOPT at 800°C reached 52.53%, which indicated that the introduction of high-efficiency char-forming agent triazine and pentaerythritol phosphate groups could significantly improve its char-forming performance and thermal stability. The epoxy resin composite achieved vertical burning V-0 grade and the limiting oxygen index value reached 35.5% when 7 wt% DOPT was incorporated. Furthermore, the cone calorimeter test results manifested that the addition of DOPT stimulated degradation of the epoxy resin matrix during the combustion process and accelerated the formation of an expanded and dense carbon layer. Additionally, the incombustible gas produced during the decomposition of DOPT had played a flame-retardant effect in the gas phase. Hence, compared with neat epoxy resin, the total heat release and total smoke production of the EP-7 wt% DOPT composite decreased by 14.0% and 25.3%, respectively. Moreover, owing to the excellent compatibility and the strong interface effect between DOPT and epoxy resin, the addition of DOPT also enhanced the mechanical and fire resistance properties of the epoxy resin composite. Therefore, it is proposed that DOPT could be exploited as an economical and high-efficiency flame retardant, and it has considerable prospects in flame retardant epoxy resin composites.

Transparent low-flammability epoxy resins using a benzoguanamine-based DOPO derivative

We successfully prepared a highly effective flame-retardant additive called hsalbenzoguanamine phosphaphenanthrene (HDPD) through salicylaldehyde and nitrogen-rich benzoguanamine. The introduction of HDPD into epoxy resin (EP) sharply enhanced the flame retardancy of EP/HDPD thermosets. The introduction of 6 wt% HDPD into EP succeeded in reaching the V-0 rating. Limited oxygen index results revealed the high flame-retarding performance of HDPD. Cone calorimeter test data revealed that heat and smoke released from EP/6 wt% HDPD thermoset were significantly restrained. In addition, EP/6 wt% HDPD thermoset demonstrated excellent transmittance and mechanical strength. The transmittance of EP/6 wt% HDPD was assessed from 520 to 800 nm. The results showed that transmittance of EP/6 wt% HDPD were nearly 90% of the control group.

A transparent and intumescent phosphaphenanthrene/phenylpyrazole-containing epoxy resin system and its flame retardancy

A novel intumescent flame retardant, PPMD, was designed from phosphaphenanthrene and nitrogen heterocycles through the two-step gut reactions of 1,4-phthalaldehyde and 3-methyl-1-phe-nylpyrazol-5-ylamine. After determination of its structure by nuclear magnetic resonance and Fourier-transform infrared analyses, PPMD was added to an epoxy resin (EP) to facilitate a curing process. Thus, EP/PPMD samples with excellent transparency and flame retardancy were acquired. For example, the EP sample satisfied the UL-94 V-0 standard and achieved a limiting oxygen index value of 30.5% because of the incorporation of 5 wt% PPMD. The cone calorimeter test of the EP/5% PPMD sample revealed that its total smoke production (TSP) and total heat release (THR) values of EP/5% PPMD was only 22.5% and 56.4% of the control group, respectively. Moreover, the average effective heat of combustion (av-EHC) value of EP/5% PPMD was reduced by 34.1%, indicating that PPMD possessed high flame-inhibition activity and smoke suppression efficiency. The flame-retardant mechanisms of PPMD were also investigated in gas phase by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and in condensed phase by XPS and IR.

Magnesium Hydroxide Nanoparticles Kill Exponentially Growing and Persister Escherichia coli Cells by Causing Physical Damage

Magnesium hydroxide nanoparticles are widely used in medicinal and hygiene products because of their low toxicity, environment-friendliness, and low cost. Here, we studied the effects of three different sizes of magnesium hydroxide nanoparticles on antibacterial activity: NM80, NM300, and NM700. NM80 (D₅₀ = 75.2 nm) showed a higher bactericidal effect against Escherichia coli than larger nanoparticles (D₅₀ = 328 nm (NM300) or 726 nm (NM700)). Moreover, NM80 showed a high bactericidal effect against not only exponential cells but also persister cells, which are difficult to eliminate owing to their high tolerance to antibiotics. NM80 eliminated strains in which magnesium-transport genes were knocked out and exhibited a bactericidal effect similar to that observed in the wild-type strain. The bactericidal action involved physical cell damage, as confirmed using scanning electron microscopy, which showed that E. coli cells treated with NM80 were directly injured.

Recent Developments in the Flame-Retardant System of Epoxy Resin

With the increasing emphasis on environmental protection, the development of flame retardants for epoxy resin (EP) has tended to be non-toxic, efficient, multifunctional and systematic. Currently reported flame retardants have been capable of providing flame retardancy, heat resistance and thermal stability to EP. However, many aspects still need to be further improved. This paper reviews the development of EPs in halogen-free flame retardants, focusing on phosphorus flame retardants, carbon-based materials, silicon flame retardants, inorganic nanofillers, and metal-containing compounds. These flame retardants can be used on their own or in combination to achieve the desired results. The effects of these flame retardants on the thermal stability and flame retardancy of EPs were discussed. Despite the great progress on flame retardants for EP in recent years, further improvement of EP is needed to obtain numerous eco-friendly high-performance materials.

Synergistic Flame Retardant Effect of an Intumescent Flame Retardant Containing Boron and Magnesium Hydroxide

In this study, to develop an organic/inorganic synergistic flame retardant and to reduce the dosage and cost of flame retardants, organic/inorganic synergistic flame retardants, hexakis(4-boronic acid-phenoxy)-cyclophosphazene (CP-6B), and magnesium hydroxide (MH) were chosen. The flame retardant properties of CP-6B/MH in epoxy resin (EP) were discussed. EP/CP-6B/MH had better flame retardancy and heat resistance compared with EP/CP-6B and EP/MH. A limiting oxygen index of EP/3.0%CP-6B/0.5%MH of 31.9% was achieved, and vertical burning V-0 rating was achieved. Compared with EP, the cone calorimeter dates of EP/CP-6B/MH decreased. CP-6B/MH inhibited combustion and did little to damage mechanical properties. Besides, the flame retardant mechanism was studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and pyrolysis-gas chromatography-mass spectrometry. CP-6B/MH exerted good synergistic effects.

Bi2Se3 decorated recyclable liquid-exfoliated MoS2 nanosheets: Towards suppress smoke emission and improve mechanical properties of epoxy resin

Bimetallic compounds have been proved superior suppression effect on smoke emission during combustion of polymers. In this work, MoS₂/Bi₂Se₃ (MB) hybrids were prepared by a facile wet chemical method and showed superior performance on smoke suppression of EP matrix during combustion. N-vinyl pyrrolidone (NVP) was employed to exfoliate molybdenum disulfide (MoS₂) nanosheets in a recyclable method, which showed high efficiency and was recyclable. Exfoliated MoS₂ exhibited large surface area and used as carriers to synthesize MB hybrids. Considering the catalytic effect of bismuth and molybdenum, the hybrids had a great influence on the smoke emission behaviors of EP composites. The smoke production was obviously suppressed during the flaming combustion (more than 22% and 23% decrease obtained from cone calorimeter and steady state tube furnace, respectively) or smolder processes (more than 23% decrease obtained from smoke chamber) at only 1 wt% content of MB hybrids. What's more, due to superior dispersion state, the addition of MB hybrids also enhanced the mechanical properties of EP matrix, including wear resistance and tensile property. This work provided a safe and green exfoliation method of MoS₂ to prepare polymers/MoS₂ composites and also constructed a novel binary hybrids for enhancing combination performances of polymers.

Enhanced flame retardancy of polyethylene/magnesium hydroxide with polycarbosilane

Polycarbosilane (PCS) was used for surface modification of magnesium hydroxide (MNH) to enhance the flame retardant effectiveness by forming cohesive binding between MgO particles with ceramic adhesive. Chemical interaction and ceramic reaction were revealed between PCS and MNH, which made for a compact, thermal stable and ceramic-like barrier during the combustion of polyethylene (PE). The flame retardancy of PE/MNH/PCS composites was greatly enhanced and a limiting oxygen index (LOI) of 35.0 was achieved at the PCS/MNH ratio of 4/26 in the composite with 30 wt.% PCS modified MNH. Such results were superior in terms of high LOI value at low global content of MNH. Thanks to the better shielding effect of the integrated and self-supporting ceramic char, the peak heat release rate (p-HRR) and the total heat release (THR) of PE/MNH/PCS composites with 50 wt.% PCS modified MNH were remarkably decreased by 36% and 25% in comparison with PE/MNH with 50 wt.% MNH, respectively. The ceramic reaction between PCS and MNH, the superior thermal stability due to crosslinked PCS and the good barrier function of cohesive ceramic layer play important roles in the effective flame retardant mechanism.

Pine Cone and Boron Compounds Effect as Reinforcement on Mechanical and Flammability Properties of Polyester Composites

Natural fibers are known to be environmentally friendly, and they can be used as an alternative to glass and carbon fibers because of their low cost. Pine cone fibers are a good choice for use in composite manufacturing because they mainly consist of cellulose, hemicelluloses, and lignin macromolecules which provide a hydrophilic character.The potential pine cone forest reserve of Turkey is 54,000 ha. Boron compounds such as borax, boric acid. and zinc borate are generally used for their flame-retardant effect. In this study, three kinds of boron compounds, boron oxide, borax pentahydrate and borax decahydrate, were used to provide better mechanical properties and better incombustibility. The synergistic effects of both waste pine cone and boron compounds were sampled for the manufacture of polyester composites by using a casting process. The composites produced with different fiber contents were characterized by some mechanical properties (bending strength, flexural modulus, izod impact); physical analyses (water absorption, swelling thickness, open porosity, bulk density); flame retardancy (LOI); and TGA, SEM-EDS, and FT-IR analyses. According to mechanical test results, boron oxide showed better bending strength and flexural modulus compared to the other boron compounds. The LOI of composites with a boron compound was higher than the composites with only pine cone reinforcement.