New curing agents for epoxy resins: protoporphyrins

Two similar macrocycles protoporphyrin IX and zinc protoporphyrin IX (ZPP) have been used as cross‐linking agents for curing the epoxy resin of bisphenol A diglycidyl ether (BADGE, n = 0). The enthalpies and the activation energies of the esterification reaction of the 2 systems are very close to each other. However, the temperature of the minimum in the differential scanning calorimetry thermogram is 38°C lower for BADGE (n = 0)/ZPP, thus requiring a less energy expenditure for curing the system. By the contrary, the enthalpy and activation energies for the etherification reaction are lower and higher, respectively, for BADGE (n = 0)/ZPP suggesting that the zinc ion affects it, although the involved mechanism is unknown.     

Flame retardant epoxy resins based on diglycidyloxymethylphenylsilane

Silicon‐containing epoxy resins were prepared from diglycidyloxymethylphenyl silane (DGMPS) and diglycidylether of bisphenol A (DGEBA) by crosslinking with 4,4′‐diaminodiphenylmethane (DDM). Several DGMPS/DGEBA molar ratios were used to obtain materials with different silicon contents. Their thermal, dynamomechanical, and flame‐retardant properties were evaluated and related to the silicon content. The weight loss rate of the silicon‐containing resins is lower than that of the silicon free resin. Char yields under nitrogen and air atmospheres increase with the silicon content. The LOI (limited oxygen index) values increased from 24 for a standard commercial resin to 36 for silicon‐containing resins, demonstrating improved flame retardancy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5580–5587, 2006     

Thermal degradation and flame retardancy of epoxy resins containing intumescent flame retardant

Pentaerythritol diphosphonate melamine-urea-formaldehyde resin salt, a novel cheap macromolecular intumescent flame retardants (IFR), was synthesized, and its structure was a caged bicyclic macromolecule containing phosphorus characterized by IR. Epoxy resins (EP) were modified with IFR to get the flame retardant EP, whose flammability and burning behavior were characterized by UL 94 and limiting oxygen index (LOI). 25 mass% of IFR were doped into EP to get 27.2 of LOI and UL 94 V-0. The thermal properties of epoxy resins containing IFR were investigated with thermogravimetry (TG) and differential thermogravimetry (DTG). Activation energy for the decomposition of samples was obtained using Kissinger equation. The resultant data show that for EP containing IFR, compared with EP, IFR decreased mass loss, thermal stability and R _max, increased the char yield. The activation energy for the decomposition of EP is 230.4 kJ mol⁻¹ while it becomes 193.8 kJ mol⁻¹ for EP containing IFR, decreased by 36.6 kJ mol⁻¹, which shows that IFR can catalyze decomposition and carbonization of EP.     

Evaluation of furfurylamines as curing agents for epoxy resins

Epoxy resin adhesives are widely used because of their strength, versatility, and ability to bond a variety of substrates. Furfurylamines represent a potential, new class of epoxy curing agents. Furfuryl amine (FA), tetrahydrofurfuryl amine (THFA), and 5,5′-methylenebis-2-furanmethanamine (DFA) were studied as possible epoxy curing agents. The utility of FA and THFA are limited by their volatility at the temperatures needed to effect cure of diglycidyl-ether of bisphenol A (DGEBA) based epoxy resins. DFA is a very effective epoxy curing agent with the ability to cure DGEBA at rates similar to that of standard epoxy curing agents such as liethylenetriamine.     

Silicon-containing flame retardant epoxy resins: Synthesis, characterization and properties

Epoxy resins with different silicon contents were prepared from silicon-containing epoxides or silicon-containing prepolymers by curing with 4,4′-diaminodiphenylmethane. The reactivity of the silicon-based compounds toward amine curing agents was higher than that of the conventional epoxy resins. The T_g of the resulting thermosets was moderate and decreased when the silicon content increased. The onset decomposition temperatures decreased and the char yields increased when the silicon content increased. Epoxy resins had a high LOI value, according to the efficiency of silicon in improving flame retardance.     

Kinetics study of thermal decomposition of epoxy resins containing flame retardant components

Hyperbranched polyphosphate ester (HPPE) and phenolic melamine (PM) were blended in different ratios with a commercial epoxy resin to obtain a series of flame retardant resins. The thermal decomposition mechanism of their cured products in air was studied by thermogravimetric analysis and in situ Fourier-transform infrared spectroscopy. The degradation behaviours of epoxy resins containing various flame retardant components were found to be greatly changed. The incorporation of phosphorus and nitrogen compounds improved the thermal stability at elevated temperature. The kinetics of thermal decomposition was evaluated by Kissinger method, Flynn-Wall-Ozawa method and Horowitz-Metzger method. The results showed that the activation energy at lower degree of the degradation decreased by the incorporation of flame retardant components, while increased at higher degree of the degradation.     

Modified amine curing agents of epoxy resins and materials on their basis

A review of the most commonly used amine curing agents of epoxy diane resins is presented. A method for radically improving the processing and performance properties of materials based on cured epoxy diane resins using the proposed technique for modifying curing agents is described. Examples of using formulated epoxy compositions in the building and cable-making industries are given.     

Synthesis and properties of new polyfunctional curing agents for epoxy resins based on dimerized fatty acid

The synthesis and properties of a number of devised imino(amino)amide derivatives of dimerized fatty acid are described. It is shown that synthesized products exhibit the properties of plasticized curing agents for epoxy resins.     

Photopolymerization and thermal behaviors of acrylated benzenephosphonates/epoxy acrylate as flame retardant resins

Di(acryloyloxyethyl) benzenephosphonate (DABP) and acryloyloxyethyl phenyl benzenephosphonate (APBP) were synthesized starting from phenylphosphonic dichloride, and characterized by FT-IR and ¹H NMR. DABP and APBP were blended in the ratios of 10-50 wt.% with a commercial epoxy acrylate oligomer (EB600) to obtain a series of flame retardant UV-curable formulations. The viscosity of the formulations greatly reduced by the addition of the reactive monomers, whereas the photopolymerization rate according to the photo-DSC analysis increased. The thermal degradation behavior and flame retardancy of the UV-cured films were investigated by thermogravimetric analysis and the limiting oxygen index (LOI). The results revealed that the blended epoxy acrylates with DABP or APBP possess improved thermal stability at elevated temperature and have higher char yields, together with higher LOI values. The data from dynamic mechanical thermal analysis showed that DABP and APBP have good miscibility with EB600. The crosslink density increased along with the content of DABP or APBP in the blend, whereas the glass-transition temperatures of the blended resins decreased compared to pure cured EB600.     

Synthesis,characterization, thermal,and flame retardant properties of phosphate-based epoxy resins

A new phosphorus-containing oxirane bis-glycidyl phenylphosphate (BGPP), and a diamine, bis(4-aminophenyl)phenylphosphate (BAPP), were synthesized. Both of these two phosphorus-containing compounds lead to phosphate-containing epoxy resin via curing reaction. The kinetics of the curing reaction of BGPP with various curing agents, including BAPP, were studied. The introduction of electron-withdrawing group into the compounds increases the BGPP and decreases the BAPP reactivity in the curing reaction. The thermal and the weight loss behavior of the cured epoxy resins were studied by TGA. High char yields (32–52%) as well as high limiting oxygen index (LOI) values (34–49) of these phosphorylated resins were found, confirming the usefulness of these phosphorus-containing epoxy resins as flame retardants. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 565–574, 1997.     

Lanthanide–imidazole complexes as latent curing agents for epoxy resins

Imidazoles have for some time been recognized as curing agents for epoxy resins. Once the resin and the imidazole compound are mixed there is a relatively short time in which the mixture can be used, since the polymerization (curing) reaction occurs to some extent even at room temperature causing the reaction mixture to thicken. In order to circumvent this problem we have found that imidazoles can be complexed with organo-lanthanide compounds thereby tying up the imidazole and retarding its rate of reaction in the cure of epoxy materials at ambient temperatures. When it is desired to enhance the rate of cure the temperature of the mixture is simply raised. This paper concerns studies of the epoxy cure reaction with the M(THD)₃–IM series. M represents the lanthanide metals Eu, Ho, Pr, Dy, Yb, and Gd, and THD is 2,2,6,6-tetramethyl-3,5-heptanedione. Cure reactions were followed by differential scanning calorimetry and in some cases by infrared spectroscopy. We have demonstrated that these organo-lanthanide–imidazole complexes are effective thermally latent curing agents for epoxy resins. At a temperature of 150°C cure is quite rapid. In the course of these studies it has also been determined that there is an inverse correlation between the lanthanide ionic radius in the complex and the temperature at which the cure reaction occurs. Thus the Yb compound, where the imidazole is most strongly bound, cures at the highest temperature and Pr, where imidazole is bound most weakly, at the lowest. Consistent with these facts is the observation that the Yb compound also gives the longest latency period when mixed with epoxy resin.     

Frontal cationic curing of epoxy resins

We studied the frontal curing of trimethylolpropane triglycidyl ether (TMPTGE) using two BF₃‐amine initiators and two fillers, kaolin and fumed silica. In the case of kaolin, the range of concentrations allowing for frontal polymerization to propagate was dependent on its heat absorption effect whereas in the case of silica it was a consequence of the rheological features of this additive. However, for both systems the velocity and front temperature show the same trends; in all cases front velocities were on the order of 1 cm/min with front temperatures about 200 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2000–2005, 2010     

Boron-containing novolac resins as flame retardant materials

Boron-containing novolac resins were prepared from novolac resins and bis(benzo-1,3,2-dioxaborolanyl)oxide and bis(4,4,5,5-tetramethyl-1,3,2-dioxa-borolanyl)oxide. The reaction of the model compound 2,6-dimethylphenol with these organoborates was complete but when the novolac resin was reacted, the degree of modification was moderate, even when there was an excess of boron compounds. The thermal degradation was investigated by TGA and pyrolysis, collecting volatiles which were investigated by GC-MS analysis, and the various compounds detected at different degradation temperatures were shown. The thermal degradation under air showed that the presence of boron is significant in the residue at high temperature. LOI values were high. Correlations between the high char yields and LOI values mean that the flame retardancy of the novolac resins improves when they are modified with bis(benzo-1,3,2-dioxaborolanyl)oxide.     

Phosphorylated cellulose/Fe3+ complex: A novel flame retardant for epoxy resins

A novel flame retardant containing cellulose, phosphorus and ferrum complex (Cell‐P‐Fe) was successfully synthesized and then it was used as flame retardants in epoxy resins (EP). Due to the present of acid sources and carbon sources, the Cell‐P‐Fe exhibits improved thermal stability and flame retardant properties. The EP/Cell‐P‐Fe composites with 10 wt% of Cell‐P‐Fe show remarkably improved LOI and UL‐94 values compared with the flame retardants without ferrum. At the loading of 10.0 wt% flame retardants, the char yield for EP/Cell‐P‐Fe composites increased to 29.1 wt%, indicating the improved thermal stability at high temperature. Moreover, thermogravimetric analysis, morphology of char residues and FTIR results demonstrate that stable char layers are formed on the surface of the composites during the combustion, attributing to the catalytic carbonization effect of Fe and phosphorus and the present of cellulose as carbon source. The stable char layers, which can protect the underlying materials from heat and oxygen, play an important role in the flame retardancy enhancement.     

The effect of a novel phosphorus-nitrogen reactive flame retardant curing agent on the performance of epoxy resin

A phosphorus-nitrogen reactive flame retardant curing agent poly-(isophorondiamine spirocyclic pentaerythritol bisphosphonate) (PIPSPB) was synthesized. The chemical structure of the obtained compound was identified by FTIR, ¹HNMR, and mass spectroscopies. Different proportions of DDS and PIPSPB were compounded as the curing agents to prepare a series of flame retardant epoxy resins with different phosphorus contents. The curing behavior of E-44/PIPSPB?+?DDS system was studied by DSC. A series of tests were conducted to characterize E-44/PIPSPB?+?DDS thermosetting system’s performance. The result demonstrates that the residual carbon content of EP/PIPSPB?+?DDS system is obviously higher than that of EP/DDS system after 500?°C with the increase of phosphorus content in the system, and the heat release rate of the system during combustion is significantly reduced. The generated phosphorus-containing carbon layer is obviously foamed, which shows that the flame retardancy of the system is the result of the combined action of condensed phase and gas phase. When the phosphorus content is 1.77wt%, EP-3 successfully passed UL94 V-0 flammability rating, the LOI value was as high as 29%, the impact strength and tensile strength of it were 6.08KJ/m² and 49.10MPa respectively, the adhesive strength could reach 13.89?MPa, the system presents a good overall performance.     

Synergistic effects of mono-component intumescent flame retardant grafted with carbon black on flame retardancy and smoke suppression properties of epoxy resins

Journal of Thermal Analysis and Calorimetry - A mono-component intumescent flame retardant named pentaerythritol phosphate melamine salt (PPMS) was grafted on the surface of carbon black (CB) to...     

The curing of epoxy resins with aminophenoxycyclotriphosphazenes

Aminophenoxycyclotriphosphazenes have been used as curing agents for epoxy resins. The thermal curing was performed in stages at 120–125 and 175–180°C followed by postcuring at 225°C to give tough brown polymers. The thermal curing reaction was monitored using FTIR and differential scanning calorimetry. Thermogravimetric analysis of the cured resins has shown thermal stability up to 350–340°C. The char yield obtained in nitrogen at 800°C was about 55–42% and in air at 700°C was about 40–32%. Graphite cloth laminates were prepared. The mechanical properties evaluated were found superior to those of commonly used epoxy resin systems. These resins are useful for making fire- and heat-resistant composites, laminates, molded parts, and adhesives.     

Comparative studies on the curing kinetics and thermal stability of tetrafunctional epoxy resins using various amines as curing agents

The curing reactions of the epoxy resins tetraglycidyl diaminodiphenyl methane (TGDDM) and tetraglycidyl methylenebis (o-toluidine) (TGMBT) using diaminodiphenyl sulfone (DDS), diaminodiphenyl methane (DDM) and diethylenetriamine (DETA) as curing agents were studied kinetically by differential scanning calorimetry. The dynamic scans in the temperature range 20°–300°C were analyzed to estimate the activation energy and the order of reaction for the curing process using some empirical relations. The activation energy for the various epoxy systems is observed in the range 71.9–110.2 kJ·mol^–1. The cured epoxy resins were studied for kinetics of thermal degradation by thermogravimetry in a static air atmosphere at a heating rate of 10 deg·min^–1. The thermal degradation reactions were found to proceed in a single step having an activation energy in the range 27.6–51.4 kJ·mol^–1.

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Zusammenfassung Die Vernetzungsreaktionen der Epoxidharze Tetraglycidyl-diamino-diphenyl-methan (TGDDM) und Tetraglycidyl-methylen-bis(o-toluidin) (TGMBT) unter Verwendung von Diaminodiphenylsulfon (DDS), Diaminodiphenylmethan (DDM) und Diethylentriamin (DETA) als Vernetzungsmittel wurden kinetisch mittels DSC untersucht. Die dynamischen Scans im Temperaturbereich 20°–300°C wurden analysiert, um unter Anwendung einiger empirischer Gleichungen die Aktivierungsenergie und die Reaktionsordnung des Vernetzungsprozesses zu ermitteln. Die Aktivierungsenergie der einzelnen Epoxy-Systeme liegt im Bereich 71.9–110.2 kJ·mol^–1. An der ausgehärteten Harze wurde mittels TG in einer statischen Luftatmosphäre un deiner Aufheizgeschwindigkeit von 10 Grad/min die Kinetik des termischen Abbaues untersucht. Man fand, daß die thermiscehn Abbaureaktionen in einem Schritt ablaufen und ihre Aktivierungsenergie im Intervall 27.6–51.4 kJ·mol^–1 liegt.