Facile synthesis of a novel transparent hyperbranched phosphorous/nitrogen-containing flame retardant and its application in reducing the fire hazard of epoxy resin

Synthesis of a Novel Flame Retardant Containing Phosphorus, Nitrogen, and Silicon and Its Application in Epoxy Resin

A novel flame retardant (TDA) containing phosphorus, nitrogen, and silicon was synthesized successfully via a controllable ring-opening addition reaction between 1,3,5-triglycidyl isocyanurate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 3-aminopropyltriethoxysilane, and TDA was then blended with diglycidyl ether of bisphenol A to prepare flame-retardant epoxy resins (EPs). The chemical structure and components of TDA were confirmed by Fourier transform infrared (FTIR) spectra, ³¹P nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Thermogravimetric analysis results indicated that after the introduction of TDA, cured EP maintained good thermal stability with a minimum initial decomposition temperature of 337.6 °C, and the char yields of a EP/TDA-5 sample significantly increased by 76.2% compared with that of the neat EP thermoset. Additionally, with the addition of 25.0 wt % TDA (1.05 wt % phosphorus loading), the limited oxygen index value of cured EP increased from 22.5% of pure EP to 33.4%, and vertical burning V-0 rating was easily achieved. Meanwhile, after the incorporation of TDA, the total heat release and total smoke production of the EP/TDA-5 sample obviously reduced by 28.9 and 27.7% in the cone calorimeter test, respectively. Flame-retardant performances and flame-retardant mechanisms were further analyzed by scanning electron microscopy, FTIR, energy-dispersive spectrometry, and pyrolysis gas chromatography/mass spectrometry. The results reveal that the synergistic effect of phosphorus, nitrogen, and silicon plays an excellent flame-retardant role in both gaseous and condensed phases. In addition, the mechanical and dynamic mechanical properties of cured EP thermosets are well maintained rather than destroyed. All the results demonstrate that TDA endows epoxy resin with excellent flame retardancy and possesses great promise in the industrial field.

Towards Selection Charts for Epoxy Resin, Unsaturated Polyester Resin and Their Fibre-Fabric Composites with Flame Retardants

Epoxy and unsaturated polyester resins are the most used thermosetting polymers. They are commonly used in electronics, construction, marine, automotive and aircraft industries. Moreover, reinforcing both epoxy and unsaturated polyester resins with carbon or glass fibre in a fabric form has enabled them to be used in high-performance applications. However, their organic nature as any other polymeric materials made them highly flammable materials. Enhancing the flame retardancy performance of thermosetting polymers and their composites can be improved by the addition of flame-retardant materials, but this comes at the expense of their mechanical properties. In this regard, a comprehensive review on the recent research articles that studied the flame retardancy of epoxy resin, unsaturated polyester resin and their composites were covered. Flame retardancy performance of different flame retardant/polymer systems was evaluated in terms of Flame Retardancy index (FRI) that was calculated based on the data extracted from the cone calorimeter test. Furthermore, flame retardant selection charts that relate between the flame retardancy level with mechanical properties in the aspects of tensile and flexural strength were presented. This review paper is also dedicated to providing the reader with a brief overview on the combustion mechanism of polymeric materials, their flammability behaviour and the commonly used flammability testing techniques and the mechanism of action of flame retardants.

Fire-Safe Polymer Composites: Flame-Retardant Effect of Nanofillers

Currently, polymers are competing with metals and ceramics to realize various material characteristics, including mechanical and electrical properties. However, most polymers consist of organic matter, making them vulnerable to flames and high-temperature conditions. In addition, the combustion of polymers consisting of different types of organic matter results in various gaseous hazards. Therefore, to minimize the fire damage, there has been a significant demand for developing polymers that are fire resistant or flame retardant. From this viewpoint, it is crucial to design and synthesize thermally stable polymers that are less likely to decompose into combustible gaseous species under high-temperature conditions. Flame retardants can also be introduced to further reinforce the fire performance of polymers. In this review, the combustion process of organic matter, types of flame retardants, and common flammability testing methods are reviewed. Furthermore, the latest research trends in the use of versatile nanofillers to enhance the fire performance of polymeric materials are discussed with an emphasis on their underlying action, advantages, and disadvantages.

Novel phosphorus/nitrogen/boron-containing carboxylic acid as co-curing agent for fire safety of epoxy resin with enhanced mechanical properties

It is a great challenge to develop a high-efficiency reactive flame retardant, applied to anhydride-cured epoxy resin (EP) system, simultaneously possessing good compatibility with matrix and mechanical reinforcement. In this respect, we successfully synthesized a novel phosphorus/nitrogen/boron-containing carboxylic acid (TMDB) through the facile esterification and addition reaction among 1,3,5-tris(2-hydroxyethyl)isocyanurate (THEIC), maleic anhydride (MAH), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and boric acid (BA). TMDB was utilized as a co-curing agent for EP/methyltetrahydrophthalic anhydride (MeTHPA) system and finally cured EP behaved great transparency, suggesting excellent compatibility of TMDB with EP. Compared with pure EP, modified EP exhibited comparable thermal stability and heat resistance but higher flame retardance. With only 15.1 wt% TMDB loading, the LOI value of anhydride-cured EP increased to 29.6% from 20.1% of pure EP, and UL-94 V-0 rating was achieved. The peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) remarkably decreased by 58.5%, 41.7% and 47.2% compared with that of pure EP, respectively. Besides, different measurements revealed TMDB simultaneously functioned in the condensed and gaseous phase during combustion. Furthermore, after incorporation of TMDB, mechanical properties of cured EP were improved and the maximum increments of flexural and tensile strength can reach 11.8% and 61.4%, respectively.

Flame Retardance and Char Analysis of an Eco-Friendly Polyurethane Hyperbranched Hybrid Using the Sol–Gel Method

This study used the sol–gel method to synthesize a non-halogenated, hyperbranched flame retardant containing nitrogen, phosphorus, and silicon (HBNPSi), which was then added to a polyurethane (PU) matrix to form an organic–inorganic hybrid material. Using 29Si nuclear magnetic resonance, energy-dispersive X-ray spectroscopy of P- and Si-mapping, scanning electron microscopy, and X-ray photoelectron spectroscopy, this study determined the organic and inorganic dispersity, morphology, and flame retardance mechanism of the hybrid material. The condensation density of the hybrid material PU/HBNPSi was found to be 74.4%. High condensation density indicates a dense network structure of the material. The P- and Si-mapping showed that adding inorganic additives in quantities of either 20% or 40% results in homogeneous dispersion of the inorganic fillers in the polymer matrix without agglomeration, indicating that the organic and inorganic phases had excellent compatibility. In the burning test, adding HBNPSi to PU made the material pass the UL-94 test at the V2 level, unlike the pristine PU, which did not meet the standard. The results demonstrate that after non-halogenated flame retardant was added to PU, the material’s flammability and dripping were lower, thereby proving that flame retardants containing elements such as nitrogen, phosphorus, and silicon exert an excellent flame-retardant synergistic effect.

Improving the flame retardancy of poly(lactic acid) using an efficient ternary hybrid flame retardant by dual modification of graphene oxide with phenylphosphinic acid and nano MOFs

A novel ternary hybrid nanoflake (GPZ) based on graphene oxide (GO), phenylphosphinic acid (PPA) and nano metal-organic framework (nano ZIF-8) particles has been designed and synthesized via a simple two-step strategy. GPZ shows high thermal stability and good compatibility with PLA matrix. When GPZ nanoflakes are added into PLA, the tensile strength and toughness of the PLA-4 with 2.0 wt% of GPZ reach 44.1 MPa and 86.0 MPa compared with 30.0 MPa and 12.8 MPa of pure PLA owing to the good dispersion of GPZ in PLA matrix and their reinforcing effects. The incorporation of GPZ also dramatically enhances the flame retardancy of PLA and the PHRR of PLA-4 with 2.0 wt% of GPZ achieves about 316.2 W/g, which is decreased by 39.5% relative to 523.0 W/g of pure PLA, respectively. The LOI of PLA-4 is 27.0%, increasing about 31.7% compared to 20.5% of pure PLA. Meanwhile, the HRR and THR in the cone calorimeter test curves for the PLA nanocomposites have also been evidently reduced. The TG-IR is applied to characterize the pyrolysis gaseous products and volatile components are suppressed with addition of GPZ. The SEM, Raman and XPS results of char residues show that a protective graphitized char layer plays a major role in improving the flame retardancy, which mainly because of the catalytic and cross-linking effects of GO, nano ZIF-8 and PPA during combustion of PLA nanocomposites.

Curing of Epoxy Resin DER-331 by Hexakis(4-acetamidophenoxy)cyclotriphosphazene and Properties of the Prepared Composition

The method of optical wedge revealed that the optimum temperature for compatibility of hexakis(4-acetamidophenoxy)cyclotriphosphazene (ACP) and DER-331 epoxy resin is in the range of 220-260 °C. The interdiffusion time of components at these temperatures is about 30 min. The TGA and differential scanning calorimetry (DSC) methods revealed the curing temperature of 280 °С for this composition. IR spectroscopy confirmed that the reaction between the resin and ACP is completed within 10 min. According to the DSC data, a glass transition temperature of 130 °С was estimated for the cured resin. Combustion test UL-94 demonstrated that the obtained material can be assigned to the fireproof category of V-0. Burning droplets were not formed during the burning. The coke formed during the combustion of samples possessed a dense and porous structure. The shape of pores is closed, while their size is in the range of 0.2-200 µm.