New developments in flame retardancy of epoxy resins

Properties and Performance of Epoxy Resin/Boron Acid Composites

This research study focused on the effect of adding boric acid to epoxy resin in order to obtain a composite material with improved properties and performance. To this end, a fine powder of boric acid (H3BO3) was introduced into epoxy resin in different amounts, i.e., 0.5 g, 1.0 g, and 1.5 g. As the matrix of the epoxy composites, styrene-modified epoxy resin based on bisphenol A (BPA) (Epidian 53) was used. It was cross-linked with two types of curing agents, i.e., an amine (ET) and a polyamide (PAC). The mechanical properties of the obtained epoxy composites (in terms of compressive strength, compressive modulus, and compressive strain) were determined at room temperature in order to assess the effect of the addition of boron acid and of the type of curing agent employed to cure the epoxy on these characteristics. Calorimetric measurements were made to highlight any changes in the glass transition temperature (Tg) as a result of the addition of boric acid to epoxy resin. Finally, flammability tests were performed on both Epidian 53/PAC and Epidian 53/ET epoxy composites to analyze their fire behavior and consequently establish the effectiveness of the selected additive as a flame retardant.

Flame Retardancy and Mechanical Properties of Melt-Spun PA66 Fibers Prepared by End-Group Blocking Technology

Preparing flame-retardant polyamide 66 (PA66) fibers through melt spinning remains one of the biggest challenges nowadays. In this work, dipentaerythritol (Di-PE), an eco-friendly flame retardant, was blended into PA66 to prepare PA66/Di-PE composites and fibers. It was confirmed that Di-PE could significantly improve the flame-retardant properties of PA66 by blocking the terminal carboxyl groups, which was conducive to the formation of a continuous and compact char layer and the reduced production of combustible gas. The combustion results of the composites showed that the limiting oxygen index (LOI) increased from 23.5% to 29.4%, and underwriter laboratories 94 (UL-94) passed the V-0 grade. The peak of heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) decreased by 47.3%, 47.8%, and 44.8%, respectively, for the PA66/6 wt% Di-PE composite compared to those recorded for pure PA66. More importantly, the PA66/Di-PE composites possessed excellent spinnability. The prepared fibers still had good mechanical properties (tensile strength: 5.7 ± 0.2 cN/dtex), while maintaining good flame-retardant properties (LOI: 28.6%). This study provides an outstanding industrial production strategy for fabricating flame-retardant PA66 plastics and fibers.

Modified oligoether-diamine synthesis for the preparation of crystallizable polymers based on epoxyurethane oligomers

A modified synthetic method for amino-terminated oligo tetramethylene oxides is presented. Diamines were synthesized via a three-step route from oligo tetramethylene oxide diol with an average molecular weight of 2000. The final step – oligoether-diphthalimide hydrazinolysis – has been improved. The yield of the target product has been shown to be more than 1.5 times higher when the molar ratio of the reacting components was changed. The oligoether-diamine and the reaction intermediates have been identified by 1H and 13C NMR spectroscopy. It has been demonstrated that the synthesized amine can be used as a curing agent for epoxy urethane oligomers. It is shown that the glass transition temperature of the cured elastomers is lower than −70 °C. These elastomers can be recommended for the use in the conditions of the Arctic and the Far North or Far South of the globe.

The Effect of Polyepoxyphenylsilsesquioxane and Diethyl Bis(2-hydroxyethyl)aminomethylphosphonate on the Thermal Stability of Epoxy Resin

Polyepoxyphenylsilsesquioxane (PEPSQ) and diethyl bis(2-hydroxyethyl) aminomethylphosphonate (DBAMP) can improve the flame retardancy of epoxy resin (EP). In this paper, the results of the limiting oxygen index (LOI) and UL94 tests exhibited that PEPSQ and DBAMP had good synergistic flame retardancy. The non-isothermal degradation kinetics of EP containing PEPSQ and DBAMP was investigated by the Kissinger and Flynn-Wall-Ozawa methods. The results of the Kissinger method displayed that the addition of two flame retardants, PEPSQ and DBAMP, can slightly enhance the activation energy of EP, indicating that the additives delayed the thermal degradation of EP. The Flynn-Wall-Ozawa method further confirmed that the activation energy of EP during the whole thermal degradation process can be significantly increased by addition of the two flame retardants PEPSQ and DBAMP. When the degree of conversion exceeded 80%, the increase was more significant. This illustrated that the flame retardants finally achieved the purpose of improving the flame retardancy of EP by stabilizing the char layer.

Synergistic Effects of DOPO-Based Derivative and Organo-Montmorillonite on Flame Retardancy, Thermal Stability and Mechanical Properties of Polypropylene

Polypropylene (PP), as a general thermoplastic polymer, is broadly used in different fields. However, the high flammability, melt dripping and poor mechanical properties of PP are a constraint to the expansion of its applications. In this paper, PP composites containing a combination of a phenethyl-bridged DOPO derivative (PN-DOPO) and organic montmorillonite (OMMT) were prepared via melt blending. The synergistic effects of PN-DOPO and OMMT on the flame retardancy, thermal stability and mechanical properties of PP composites were investigated systematically. The results showed that 20 wt% addition of PN-DOPO with OMMT improved the flame retardancy of PP composites. In particular, the introduction of 17 wt% PN-DOPO and 3 wt% OMMT increased the LOI values of the PP matrix from 17.2% to 23.6%, and the sample reached the V-0 level and reduced the heat release rate and total heat release. TGA indicated that OMMT could improve the thermal stability of the PP/PN-DOPO blends and promote the char residues of PP systems. Rheological behaviour showed a higher storage modulus, loss modulus and complex viscosity of PP/PN-DOPO/OMMT composites, suggesting a more effective network structure. In addition, the tensile strength, flexural properties and impact strength of the PP/PN-DOPO/OMMT composites actually increased for a good dispersion effect. Combined with the char layer analysis, the introduction of OMMT promoted more continuous and compact structural layers containing an aluminium-silicon barrier and phosphorus-containing carbonaceous char in the condensed phase. OMMT can improve the flame retardancy, thermal stability and mechanical properties of PP, and, thus, PN-DOPO/OMMT blends can serve as an efficient synergistic system for flame-retarded PP composites.

Synthesis and Study of Physical and Mechanical Properties of Urethane-Containing Elastomers Based on Epoxyurethane Oligomers with Controlled Crystallinity

The influence of the molecular weight of oligoamine, oligoether, and the type of diisocyanate on the physical and mechanical properties of elastomers with urethane hydroxyl hard segments was studied. For this purpose, oligoetherdiamines with molecular weights ~1008 and ~1400 g mol⁻¹ were synthesized by a three-stage method. Epoxyurethane oligomers were synthesized according to a two-step route with an oligodiisocyanate as an intermediate product. A series of 12 elastomers with controlled crystallinity were synthesized from these elastomers and amines. The deformation and strength properties of the elastomers were studied.

High performance flame-retardant organic-inorganic hybrid epoxy composites with POSS and DOPO-based co-curing agent

Polyhedral oligomeric silsesquioxane (POSS) and a highly effective 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based flame retardant co-curing agent (D-bp) were chemically introduced into the 4,4′-diaminodiphenyl methane (DDM)/diglycidyl ether of bisphenol A (DGEBA) epoxy system to create organic–inorganic hybrid epoxy composites with simultaneously improved flame retardancy and mechanical properties. The results revealed that POSS/D-bp/DGEBA hybrid composites exhibited excellent comprehensive performance, in which the V-0 criterion of the UL-94 test was passed and the peak of heat release rate (P-HRR) was significantly decreased from 939 to 371 kW m⁻² when the phosphorus content was only 0.25 wt%. The glass transition temperature (T_g) increased by 16.2 °C and obvious improvement in the mechanical properties was also evidenced.

This paper introduces flame-retardant organic–inorganic hybrid epoxy composites possessing excellent comprehensive performance, which results from the phosphorus–silicon synergistic flame retardant effect of the glycidyl POSS and DOPO derivative.

Preparation, Structure and Properties of Urethane-Containing Elastomers Based on Epoxy Terminal Oligomers

The effect of polyester oligoethylene adipate molecular weight, diisocyanate structure, and chain extender on the properties of epoxyurethane-based oligomer elastomers was studied in this research. Oligoethylene adipates were obtained via polycondensation of adipic acid and ethylene glycol. Epoxyurethane oligomers were synthesized according to a two-step route with an oligodiisocyanate as an intermediate product. The elastomers with hard urethane hydroxyl blocks were synthesized from oligodiisocyanates. The deformation and strength properties of the elastomers were studied.

Synthesis and characterization of a chalcone-derived epoxy containing pyrazoline ring with excellent flame resistance

Traditional epoxy resins are made by the reaction of petroleum-based bisphenol A and epichlorohydrin. The disadvantages of these petroleum-based epoxy including certain biological toxicity and flammability. To solve these problems, we first synthesized a diphenol compound 3,5-(4-hydroxyphenyl)-2-pyrazoline (TPP), which was prepared by condensation reaction of bio-based chalcone with hydrazine hydrate to replace standard petroleum-based bisphenol A. Then it was condensed with epichlorohydrin under alkaline condition to form a fully aromatic pyrazoline ring epoxy (TPP-EP). For further research, we use 4,4′-diaminodiphenylmethane (DDM) as the curing agent. When compared with bisphenol A epoxy resin (DGEBA/DDM), TPP-EP/DDM possessed a higher glass transition temperature (233°C vs. 176°C), and even showed that the residual carbon (in N2) and the storage modulus (at 30°C) increased by 201% and 74%, respectively. What’s more, TPP-EP/DDM system also had good inherent flame retardancy. The limiting oxygen index of TPP-EP/DDM was 33.1, reaching the V-0 level tested by UL-94. From the cone test, the THR, p-HRR, p-SPR and TSP values of TPP-EP/DDM systems also showed different degrees of reduction. Since TPP-EP contained tertiary amine active groups that could be used as a kind of catalytic curing agents for epoxy resins, thus the compound had certain self-curing properties. This work was of great significance for the synthesis of pyrazoline bio-based environmentally friendly flame-retardant epoxy resin.

Experimental Study of Mechanical Properties of Epoxy Compounds Modified with Calcium Carbonate and Carbon after Hygrothermal Exposure

The objective of this paper is to analyze the effects of hygrothermal exposure on the mechanical properties of epoxy compounds modified with calcium carbonate or carbon fillers. In addition, comparative tests were carried out with the same parameters as hygrothermal exposure, but the epoxy compounds were additionally exposed to thermal shocks. The analysis used cylindrical specimens produced from two different epoxy compounds. The specimens were fabricated from compounds of epoxy resins, based on Bisphenol A (one mixture modified, one unmodified) and a polyamide curing agent. Some of the epoxy compounds were modified with calcium carbonate (CaCO₃). The remainder were modified with activated carbon (C). Each modifying agent, or filler, was added at a rate of 1 g, 2 g, or 3 g per 100 g of epoxy resin. The effect of the hygrothermal exposure (82 °C temperature and 95% RH humidity) was examined. The effects of thermal shocks, achieved by cycling between 82 °C and -40 °C, on selected mechanical properties of the filler-modified epoxy compounds were investigated. Strength tests were carried out on the cured epoxy compound specimens to determine the shear strength, compression modulus, and compressive strain. The analysis of the results led to the conclusion that the type of tested epoxy compounds and the quantity and type of filler determine the effects of climate chamber aging and thermal shock chamber processing on the compressive strength for the tested epoxy compounds. The different filler quantities, 1-3 g of calcium carbonate (CaCO₃) or activated carbon (C), determined the strength parameters, with results varying from the reference compounds and the compounds exposure in the climate chamber and thermal shock chamber. The epoxy compounds which contained unmodified epoxy resin achieved a higher strength performance than the epoxy compounds made with modified epoxy resin. In most instances, the epoxy compounds modified with CaCO₃ had a higher compressive strength than the epoxy compounds modified with C (activated carbon).

Synthesis and characterization of SPDSCD and its flame retardant application on epoxy resins

In this study, a flame retardant agent, 2,4,8,10-tetraoxo-3,9-diphosphospiro[5.5]undecane spirophosphate-4,4-diaminopair benzene disulfone-1,3,5-himetriazine (SPDSCD), is synthesized through a direct polycondensation reaction. SPDSCD is a chemically expanded phosphorus-containing flame retardant in epoxy resins (EP). The molecular structure of SPDSCD and thermal stability are characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and thermogravimetric analysis, and EP/SPDSCD composites were investigated in detail. These properties are associated with the phosphorus-containing spiro structure on the main molecular chain which can promote condensation polymerization into carbon during pyrolysis, the new nitrogen-containing carbon source, and the triazine structure. SPDSCD shows good thermal stability and low flammability, the weight loss from 500 to 800 °C was only 6.1 wt%, and the residual mass at 800 °C was 48.9 wt%. With the addition of SPDSCD, the flame retardant quality of the composites was gradually enhanced, the carbon residue becomes denser, which isolates heat transfer and inhibits the volatilization of flue gas. The addition of 20 wt% SPDSCD in the EP sample was associated with a limited oxygen index (LOI) value of 26% and a vertical burning V-0 rating. Cone calorimeter test shows that the peak heat release rate is reduced by 75%; the heat release rate curve enters the heat release platform area with a value lower than the first peak, TSP is reduced by 24%, the ac-CO₂Y value reduced by 25.6%, indicating that SPDSCD/EP produced less CO₂, which obviously prevented the combustion of volatile gas. SPDSCD exerted a charring and barrier effect in the condensation phase. Using basic characterization and flame retardancy testing, this work determined that SPDSCD has good flame retardancy when added to EP.

In this study, a flame retardant agent, 2,4,8,10-tetraoxo-3,9-diphosphospiro[5.5]undecane spirophosphate-4,4-diaminopair benzene disulfone-1,3,5-himetriazine (SPDSCD), is synthesized through a direct polycondensation reaction.

Preparation of a Novel Phosphorus-Nitrogen Containing Novolac Curing Agent for Epoxy Resin and flame-retardancy of its cured epoxy resin

In this study, DICY (dicyandiamide)-containing novolac (NN) was first prepared, and then DOPO (9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) was introduced to react with the unsaturated bonds from DICY to obtain a novel phosphorus-nitrogen-containing novolac resin (PNN), which was used as a curing agent for epoxy resins. The curing condition was confirmed by a non-isothermal curing kinetics study. The thermal stability and flame retardancy of the cured epoxy resin system were studied by thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL-94 test and cone calorimeter. The morphology of the burned chard residues was observed by Scanning electron microscopy (SEM). The results show that epoxy resin cured by the prepared PNN curing system presents excellent flame retardancy. The cured resin system, which contains only 1.31wt% phosphorus and 2.48wt% nitrogen, can achieve UL 94 V-0 rating.

Cardanol and Eugenol Based Flame Retardant Epoxy Monomers for Thermostable Networks

Epoxy materials have attracted attention for many applications that require fireproof performance; however, the utilization of hazardous reagents brings about potential damage to human health. Eugenol and cardanol are renewable, harmless resources (according to ECHA) that allow the achievement of synthesis of novel phosphorylated epoxy monomers to be used as reactive flame retardants. These epoxy building blocks are characterized by ¹H NMR and ³¹P NMR (nuclear magnetic resonance) and reacted with a benzylic diamine to give bio-based flame-retardant thermosets. Compared to DGEBA (Bisphenol A Diglycidyl Ether)-based material, these biobased thermosets differ by their cross-linking ratio, the nature of the phosphorylated function and the presence of an aliphatic chain. Eugenol has led to thermosets with higher glass transition temperatures due to a higher aromatic density. The flame-retardant properties were tested by thermogravimetric analyses (TGA), a pyrolysis combustion flow calorimeter (PCFC) and a cone calorimeter. These analyses demonstrated the efficiency of phosphorus by reducing significantly the peak heat release rate (pHRR), the total heat release (THR) and the effective heat of combustion (EHC). Moreover, the cone calorimeter test exhibited an intumescent phenomenon with the residues of phosphorylated eugenol thermosets. Lastly, the higher flame inhibition potential was highlighted for the phosphonate thermoset.

Synthesis and application of aminophenyl-s-triazine derivatives as potential flame retardants in the modification of epoxy resins

Novel DOPO-substituted aminophenyl-s-triazine (TAT-DOPO) compounds with controllable P/N element ratio were synthesized and applied as flame retardants for epoxy resins.

Novel Multifunctional Organic-Inorganic Hybrid Curing Agent with High Flame-Retardant Efficiency for Epoxy Resin

A novel multifunctional organic-inorganic hybrid was designed and prepared based on ammonium polyphosphate (APP) by cation exchange with diethylenetriamine (DETA), abbreviated as DETA-APP. Then DETA-APP was used as flame-retardant curing agent for epoxy resin (EP). Curing behavior, including the curing kinetic parameters, was investigated by differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). The flame retardance and burning behavior of DETA-APP cured EP were also evaluated. The limiting oxygen index (LOI) value of DETA-APP/EP was enhanced to 30.5% with only 15 wt % of DETA-APP incorporated; and the UL-94 V-0 rating could be easily passed through with only 10 wt % of the hybrid. Compared with DETA/EP, the peak-heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and peak-smoke production release (SPR) of DETA-APP/EP (15 wt % addition), obtained from cone calorimetry, were dropped by 68.3, 79.3, 79.0, and 30.0%, respectively, suggesting excellent flame-retardant and smoke suppression efficiency. The flame-retardant mechanism of DETA-APP/EP has been investigated comprehensively. The results of all the aforementioned studies distinctly confirmed that DETA-APP was an effective flame-retardant curing agent for EP.

Odd–even effect on the thermal properties of Schiff base functionalized dicyanate esters and thermo-mechanical properties of their blends with epoxy resins

An odd–even effect was observed in the case of dicyanate esters described in this work.