Flame retardant and mechanical properties of epoxy composites with ammonium polyphosphate and hyperbranched silicon-containing polymers

The epoxy resin was mixed with ammonium polyphosphate (APP) and hyperbranched silicon-containing polymers (HBP-B2). The cured composites were investigated by thermogravimetric analysis, Underwriters Laboratory standard for the flammability properties under vertical burning (UL-94V), and limited oxygen index (LOI) test methods. The LOI of 43.5 and could be obtained at the weight ratio of 70:25:5 for the epoxy resin:APP:HBP-B2, Sample A25B5, and the LOI was higher than that of the composite with 30 wt % APP only, Sample A30B0, of which the LOI was 34.5. It suggested that the HBP-B2 could cooperate with the epoxy/APP composite to form a more effective protection layer during combustion, which resulted in a higher second-stage thermal degradation temperature. During the UL-94V test, the flame was extinguished immediately once the burner was removed. Furthermore, the tensile and impact strength of the epoxy/APP composite could also be improved by using HBP-B2 compound as the toughening agent. The composite containing 20% of APP and 10% of HBP-B2, Sample A20B10, still had excellent flame retardant properties with a V-0 rating. Moreover, the tensile strength and impact strength of that composite got 19 and 25% increases compared with the Sample A30B0, which contained 30% of APP only. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48857.     

Flame retardant aircraft epoxy resins containing phosphorus

As part of a program to develop fire resistant exterior composite structures for future subsonic commercial and general aviation aircraft, flame retardant epoxy resins are under investigation. Epoxies and their curing agents (aromatic diamines) containing phosphorus were synthesized and used to prepare epoxy formulations. Phosphorus was incorporated within the backbone of the epoxy resin and not used as an additive. The resulting cured neat epoxy formulations were characterized by thermogravimetric analysis, propane torch test, elemental analysis, microscale combustion calorimetry, and fire calorimetry. Several formulations showed excellent flame retardation with phosphorous contents as low as 1.5% by weight. The fracture toughness and compressive strength of several cured formulations showed no detrimental effect due to phosphorus content. The chemistry and properties of these new epoxy formulations are discussed.     

Preparation of high‐performance flame‐retardant hybrid material by hyperbranched polyphosphate ester

A novel hyperbranched polyphosphate ester (HPPE) and a high‐performance hybrid flame‐retarding material HPPE/diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin are prepared. The effect of HPPE content and molecular weight on the mechanical performance, thermal performance, and flame‐retarding property of the hybrid material is studied. The results show that the overall performance of the hybrid material first increases and then decreases with the increase of HPPE content as well as the molecular weight and reaches maximum with 8–12 wt% of HPPE. When compared with the performance of pure DGEBA, the tensile strength, flexural strength, impact strength, fracture toughness, and limited oxygen index of the HPPE‐2/DGEBA hybrid material are enhanced by about 114%, 50%, 48%, 95%, and 20%, respectively. The toughening and reinforcing mechanism of the hybrid system is a novel in situ effect as revealed by the micrographs of the fracture surfaces using scanning electron microscopy. POLYM. COMPOS., 32:36–43, 2011. © 2010 Society of Plastics Engineers     

Epoxy resins possessing flame retardant elements from silicon incorporated epoxy compounds cured with phosphorus or nitrogen containing curing agents

New silicon-containing epoxy compounds were obtained by reacting a bisphenol-A type epoxy and an o-cresol-formaldehyde novolac type epoxy with diphenylsilandiol and triphenylsilanol, respectively. The reactions were performed with tin(II) chloride as a catalyst at 140-170 °C. With various feeding ratios of reactants, the epoxy compounds contained various silicon contents. The thermal stability and the flame retardant property of the cured epoxy resins were improved with this incorporation of silicon. Synergistic effects of phosphorus/silicon and nitrogen/silicon on enhancing limited oxygen index values were also observed for the epoxy resins from the silicon-containing epoxy compounds cured with phosphorus- and melamine-containing agents.     

Novel flame retardant thermosets from nitrogen‐containing and phosphorus‐containing epoxy resins cured with dicyandiamide

A novel phosphorus‐containing epoxy resin (EPN‐D) was prepared by addition reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) and epoxy phenol‐ formaldehyde novolac resin (EPN). The reaction was monitored by epoxide equivalent weight (EEW) titration, and its structure was confirmed by FTIR and NMR spectra. Halogen‐free epoxy resins containing EPN‐D resin and a nitrogen‐containing epoxy resin (XT resin) were cured with dicyandiamide (DICY) to give new halogen‐free epoxy thermosets. Thermal properties of these thermosets were studied by differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), thermal mechanical analyzer (TMA) and thermal‐gravimetric analysis (TGA). They exhibited very high glass transition temperatures (T_gs, 139–175°C from DSC, 138–155°C from TMA and 159–193°C from DMA), high thermal stability with T_{d,5 wt %} over 300°C when the weight ratio of XT/EPN‐D is ≥1. The flame‐retardancy of these thermosets was evaluated by limiting oxygen index (LOI) and UL‐94 vertical test. The thermosets containing isocyanurate and DOPO moieties showed high LOI (32.7–43.7) and could achieve UL‐94 V‐0/V‐1 grade. Isocyanurate and DOPO moieties had an obvious synergistic effect on the improvement of the flame retardancy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis,characterization, and properties of multifunctional naphthalene-containing epoxy resins cured with cyanate ester

Multifunctional naphthalene-containing epoxy resins derived from 2,7-dihydroxylnaphthalene were synthesized and the intermediates were characterized by Fourier transform infrared spectroscopy, elemental analysis, and mass spectrometry. The cured products from naphthalene-containing epoxy resin and the dicyanate ester of bisphenol A (DCBA) exhibited a better T_g and a lower coefficient of thermal expansion than those of the commercial epoxy system. The glass transition temperature, thermal stability, and moisture absorption were found to increase with the epoxy functionality when naphthalene-containing epoxy resins were cured with DCBA. Thermogravimetric analyses revealed that the DCBA-cured system had a better thermal stability than that of the 4,4′-diaminodiphenylsulfone (DDS)-cured system. The addition of a metallic catalyst into the epoxy resin/cyanate ester system not only facilitated the cyclotrimerization of the cyanate ester but also the polyetherification of the epoxy resin. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1611–1622, 1999     

脂环族环氧树脂／双酚A环氧树脂共混改性研究

采用脂环族环氧树脂（EPL-4221）与双酚A型环氧树脂E-51共混,用酸酐固化剂和促进剂使其固化,研究脂环族环氧树脂的用量对共混树脂性能的影响及其规律性,包括冲击强度、弯曲强度、拉伸强度、维卡软化点温度、漆膜的粘附力、铅笔硬度、耐磨性以及拉伸剪切强度。结果表明,随脂环族环氧树脂用量的增加,共混树脂的综合性能先增加后降低,脂环族环氧树脂的质量分数为15％-20％时,具有最大值。     

含磷本质阻燃环氧树脂的研究进展

综述了含磷本质阻燃环氧树脂(包括含磷协同本质阻燃体系)的发展、现状和未来趋势。与添加型阻燃剂阻燃环氧树脂相比,通过含磷环氧化合物和/或含磷固化剂把磷元素嵌入环氧树脂结构中制得的含磷本质阻燃环氧树脂,具有阻燃效率高、阻燃持久、物理力学性能不受影响、燃烧过程中毒性腐蚀性挥发物质的生成量低等优势。利用协同阻燃效应,可以进一步提高阻燃性能。但是,含磷本质阻燃环氧树脂和含磷协同本质阻燃体系存在制备工艺复杂、生产成本较高等不足。     

Chemiluminescence from amine cured epoxy resins modified with halogenated phenylglycidyl ethers

Chemiluminescence from thermooxidized epoxide alone and that modified with phenyl glycidyl ethers has been investigated in isothermal and nonisothermal regime. Isothermal curves are characterized by a monotonous fall of chemiluminescence intensity from some initial value to very low levels of light emission. Nonisothermal curves show a maximum intensity at temperatures above 473 K. The luminescence intensity is influenced by both T_g and thermal stability of epoxide. The higher T_g or higher thermal stability brings about the higher intensity of light emission and vice versa. © 1994 John Wiley & Sons, Inc.     

Are cured epoxy resins inhomogeneous?

The alternating mechanism of network formation in the curing of epoxy resins from bisphenol A diglycidyl ether (BADGE) and amine curing agents does not offer any special opportunity for the formation of inhomogeneities caused by partial segregation or inhomogeneous crosslinking. Etched fracture surfaces of resins cured with 4,4′-diaminodiphenylmethane, hexamethylenediamine and hexahydrophthalic anhydride at various initial ratios of BADGE, studied by electron microscopy, reveal globular structures 20–40 nm in size. However, similar structures are observed with etched surfaces of amorphous polystyrene and poly(methyl methacrylate). The small-angle X-ray scattering curves for cured epoxy resins do not differ in principle from those of common amorphous polymers; swelling in a solvent of a lower electron density does not lead to an increase in scattering within the particle size range 10–10² nm. It is pointed out that the physical structure of simple cured epoxy resins does not essentially differ from that of common amorphous polymers. With more complicated systems, a more pronounced inhomogeneity might be caused by thermodynamic incompatibility or by non-alternating mechanisms of the curing reaction.     

Kinetics of epoxy resins formation from bisphenol-A,bisphenol-S,and epichlorohydrin

The kinetics of formation of epoxy resins derived from bisphenol-A, bisphenol-S, and epichlorohydrin under stoichiometric conditions was considered. The kinetics of reaction was studied by taking into account the consumption of the added alkali and epoxide value of epoxide oligomers. The obtained results satisfactorily explained that the reactivity of bisphenol-A with epichlorohydrin is higher than that of bisphenol-S, the rate of dehydrochlorination of chlorohydrin ether in the presence of alkali and water is much higher than that of the rate of condensation of phenolic hydroxyl group with epichlorohydrin. The apparent reaction order of phenolic groups with epichlorohydrin and terminal epoxide group in the oligomer are all second order. The rate constants and activation energy were determined. The results are discussed. © 1993 John Wiley & Sons, Inc.     

环氧树脂改性超支化聚酯的合成及性能

以偏苯三酸酐、环氧氯丙烷及甲基丙烯酸缩水甘油酯为原料合成了超支化聚酯(HBP),再通过超支化聚合物的羧基与环氧树脂环氧基的反应得到环氧改性超支化聚合物;用GPC1、H-NMR、DSC、TGA表征了环氧改性超支化聚合物的结构和热性能;比较了不同环氧树脂用量改性前后树脂的光反应活性以及光固化涂层的耐擦洗性和硬度,测定了凝胶率-曝光时间曲线;以环氧改性超支化聚合物配制了光刻胶,在混合光源以及接触曝光的条件下,分辨率达到2~3μm,且图像十分清晰,断面整齐。环氧树脂用量为HBP羧基物质量的70%左右时,改性的超支化聚酯的光固化活性有明显提高,力学性能得到明显改进。     

Toughness and reinforcement of diglycidyl ether of bisphenol-A by hyperbranched poly(trimellitic anhydride-butanediol glycol) ester epoxy resin

Hyperbranched epoxy resin shows best comprehensive performance in epoxy resin system and is considered as a kind of toughness and reinforcement additive. This article reports on the use of novel hyperbranched poly(trimellitic anhydride-butanediol glycol) ester epoxy resin (HTBE) prepared by us as a functional additive to an epoxy amine resin system. The effect of molecular weight and content of the HTBE on the performance of the diglycidyl ether of bisphenol-A (DGEBA)/HTBE hybrid resin are discussed in detail, and their performance has maximum with the increase of content and molecular weight of HTBE. The impact strength and fracture toughness of the hybrid resin containing 9 wt% second generation of HTBE are 48.2 kJ/m² and 2.71 MPa m^1/2, and which almost are 2.77 and 1.5 times of DGEBA performance respectively. Furthermore, the tensile and flexural strength can also be enhanced about 17%. The fracture surface micrograph of hybrid resin shows no microphase separation of the HTBE/DGEBA blends that facilitates an enhanced interaction to achieve excellent toughness and strength enhancement of the cured systems by scanning electron microscope (SEM). A novel situ reinforcing and toughening mechanism and model are discovered and confirmed by SEM, molecular simulation, and dynamic mechanical thermal analysis technology. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Flame retardant epoxy resins based on diglycidyl ether of isobutyl bis(hydroxypropyl)phosphine oxide

Phosphorous‐containing epoxy resins were prepared from diglycidyl ether of isobutyl bis(hydroxypropyl)phosphine oxide (IHPOGly) and diglycidyl ether of bisphenol A (DGEBA) by crosslinking with 2,4‐diaminotoluene. Several IHPOGly/DGEBA molar ratios were used to obtain materials with different phosphorous content. Thermal, dynamomechanical, and flame retardant properties were evaluated and related with the phosphorous content. The weight loss rate of phosphorous‐containing resins is lower than that of the phosphorous‐free resin for the thermoxidative degradation. Char yields under nitrogen do not show significant differences among the phosphorous‐containing resins and the phosphorous‐free resin, while under air char yields increase with the phosphorous content. The presence of phosphorous increases the limiting oxygen index (LOI) values even when the phosphorous content is low, and no significant differences with the phosphorous content are observed. V‐0 materials were obtained when the resins were tested for ignition resistance with the UL‐94 test. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1367–1373, 2006     

Physical properties and shrinkage of epoxy resins cured with lactams

In order to reduce the shrinkage of epoxy resin during the curing process, lactam is incorporated into epoxy in a copolymerization reaction. In this study, various amounts of lactams and BF₃-MEA were added to epoxy, and the volume shrinkage of polymerization was investigated. It was found that shrinkage decreases with the increase of the lactam content and with the lactam ring size as well. Infrared spectroscopic analysis, scanning electronic microscopic analysis, and mechanical tests were used to investigate the structure and properties of the copolymers. The results show that the incorporation of caprolactam leads to an increase in tensile strength and elongation, but the Izod impact strength is not improved.     

Synthesis of hyperbranched polybenzoxazoles and their molecular composites with epoxy resins

Hyperbranched aromatic polymers have attracted great attention recently because they combined the processability of hyperbranched polymers and the high‐level performance of aromatic polymers. Here, a one‐pot strategy for the synthesis of hyperbranched Polybenzoxazoles (HBPBOs) by polycondensation of 2,2‐Bis (3‐amino‐4‐hydroxyphenyl) hexafluoropropane and 1,3,5‐benzenetricarboxylic acid in Polyphosphoric acid was reported. The HBPBOs exhibited good solubility in organic solvents because of the branched structure and the flexible hexafluoropropane groups in main chains. The structure and terminal functional groups could be tailored by adjusting the molar ratio of two monomers. FT‐IR, NMR and XRD measurements confirmed the structure of HBPBOs, while thermogravimetric analysis (TGA), UV‐vis, and photoluminescence spectra, combined with the comparison with linear PBOs demonstrated the intriguing optical properties and good thermal stabilities of HBPBOs. The good solubility of HBPBOs also permitted their usage as molecular reinforcement for polymer composites as demonstrated in this study of HBPBOs/epoxy composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41942.     

Reactive cyclic phosphonamide flame retardant for epoxy resins

To take the advantage of reactivity of five-membered cyclic phosphorus compounds, 1,2,3-tri-phenyl-1,3,2-diazaphospholidine-2-oxide (TPDPO) was explored as a reactive flame retardant for epoxy resins (EPs). Through model compounds, it has been established that TPDPO selectively reacts with the secondary hydroxyl group and is inert toward both aryl amino groups and epoxide groups. The result of Soxhlet extraction supports that TPDPO is permanently bonded to the cured EPs. At a loading of only 8 wt % (0.74 wt % phosphorus), TPDPO enables the cured epoxy to achieve a UL-94 V0 rating. The thermogravimetric analysis–Fourier transform infrared analyses of the gaseous products suggest that the excellent flame retardancy of EP–TPDPO is partly due to the enhanced dehydration process of the epoxy. Also an increased char yield and the formation of a coherent char layer contribute to the good fire performance of EP–TPDPO. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47411.     

The supermolecular structures found in cured epoxy resins

The work arose from the need to explain the beneficial effect of post-curing at an elevated temperature on the strengths of lap-shear joints made with amine-cured epoxy resins. Supermolecular structures were imaged by several electromicroscopy techniques, usually at 100,000 X. Three, if not four, stages of supermolecular structure were made visible. (i) A phase-contrast image of 1.3 to 2.1 nm diameter which are probably stacked residues of bisphenol A. The d-spacing seen in the diffracting mode of the microscope probably arises from within this structure. (ii) A nodular structure of ca. 5 nm. (iii) Aggregates of nodules of ca. 17 nm rising to 40 n m on post-cure. These dimensions were obtained from cumulative distributions of sizes based on photodensitometer records from the electron-micrograph negatives. Aggregate dimensions vary with curing agent and state of cure although minor variations occur with specimen preparation.     

Synthesis and characterization of free radical cured Bis-methacryloxy bisphenol-A epoxy networks

Synthesis and free-radical curing reaction of the bisglycidylmethacrylate of bisphenol-A (Bis-GMA) were investigated. Bis-GMA resin was synthesized by reacting Epon 825 with methacrylie acid, followed by characterization using IR and NMR spectroscopy. Various modifiers having reactive double bonds were co-cured with the methacryloxy resins using a free-radical initiator. The networks obtained were compared with a cycloaliphatic amine-cured epoxy network. Thermal characterization shows that methacryloxy-cured systems are more resistant to mechanical penetration and have higher glass-transition temperatures and better stability with regard to thermal decomposition as compared with the conventional diamine-cured epoxy networks. Dynamic mechanical experiments and stress-strain tests also indicate that Bis-GMA based networks have higher tensile moduli and lower elongation at break. Using different modifiers such as 2-ethylhexyl acrylate, the tensile and impact properties of the networks can be improved.     

室温固化含磷膨胀型阻燃环氧树脂清漆

室温条件下以酸式磷酸酯固化环氧树脂,制得了含磷膨胀型阻燃清漆。涂膜的理化和燃烧性能测试表明,酸式磷酸酯具有较好的固化和阻燃效果。当酸式磷酸辛酯(m(双酯)/m(单酯)/m(磷酸)=44.38/54.73/0.89))与E-51按质量比6.5/8.7混合时效果最佳,表干时间230 min,烧穿时间76.5 min,残炭膨胀高度5.92mm。而市售G-03胺类固化剂固化的E-51,表干时间240 min,烧穿时间2.3 min,无残炭膨胀。FTIR检测结果显示,室温下酸式磷酸酯可使E-51固化;热分析以及SEM照片显示,酸式磷酸酯提高了炭层密度和残炭量。