Study of thermal stability and ablation behavior of carbon/epoxy‐novolac composites

The use of carbon/epoxy‐novolac composites as advanced ablative materials for insulation of exit cone of solid‐propellant rocket nozzles are studied. In this article, three types of carbon fabrics are used and their composites are prepared by use of impregnation and hand lay‐up methods. To study the thermal stability and ablation behavior, these composites are tested by thermal tests such as thermogravimetric analysis (TGA) and oxyacetylene standard flame tests; the latter test is one of the most important standard tests of ablative materials. The test apparatus is made according to American standard, ASTM‐E‐285‐80, and over 33 polymeric composites and 3 steel specimens were carried out according to its standards. It is found that the composites that are made up of C‐9750 fabric (high‐strength carbon fabric) in comparison with steel and the other types of carbon fabric specimens have the highest thermal stability and the best ablation behavior. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2455–2461, 2003     

Dielectric and thermal properties of polymer network based on bismaleimide resin and cyanate ester containing dicyclopentadiene or dipentene. III

A series of bismaleimide‐triazine (BT) resins were prepared from commercial bismaleimide (DDMBMI) and 2,6‐dimethylphenol‐dicyclopentadiene dicyanate ester (DCPDCY) or 2,6‐dimethylphenol‐dipentene dicyanate ester (DPCY). The thermal properties of cured BT resins containing DCPD or DP were studied using a dielectric analyzer (DEA), dynamic mechanical analyzer (DMA), and thermal gravimetric analyzer (TGA). These data were compared with that of DDMBMI cured with bisphenol A dicyanate ester (BADCY). The cured DDMBMI/DCPDCY or DDMBMI/DPCY exhibits a lower dielectric constant, dissipation factor, and moisture absorption than those of DDMBMI/BADCY. The effects of blend composition on the glass transition temperatures and thermal stability are discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1942–1951, 2007     

Crosslinking reaction of polyacrylate soap‐free hydrosol with zirconium chelate

The crosslinking reaction mechanism of polyacrylate copolymer (monomer mass ratio of methyl methacrylate/butyl acrylate/acrylic acid = 48.77:46.69:4.54) hydrosol with triethanolamine chelate of zirconium isopropyloxide was studied with IR spectroscopy, NMR spectroscopy, differential scanning calorimetry, and ultraviolet spectroscopy. The instrumental analyses on the copolymer mixture heated at different temperatures were investigated, and we proved that the crosslinking adduct had amino groups that were provided by the chelate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3605–3609, 2004     

Crosslinking benzotriazolylimides and polymeric materials on base of them

A new kind of crosslinking oligobenzotriazolylimides with terminal maleimide groups has been synthesized via an interaction of an excess of bismaleimides with 5,5′‐bisbenzotriazoles in melt. Conditions of obtaining these oligomers were optimized via the syntheses of model compounds. Oligomers, according to dynamic thermogravimetric analysis (DTGA), fuse at 135–160°C, crosslink at 175–250°C, and possess the high thermal stability in air up to 410°C. Using these oligomers as thermosetting binders or crosslinking agents, tough laminate plastics reinforced by a glass‐fiber cloth as well as crosslinked films on base of a linear polybenzimidazole (PBI) matrix were obtained. The plastics and the crosslinked films possess high mechanical characteristics. It has been proved that the crosslinked films on base of the PBI matrix are perspective precursors to design the phosphoric acid electrolyte membranes for the medium temperature fuel cells. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Epoxy curing process with small shrinkage based on binary nucleophilic reagent system consisting of amine and carboxylic acid

A curing process of bisphenol‐A diglycidyl ether using amine‐carboxylic acid salts was studied with focusing on its small‐volume shrinkage. The characteristic point of the curing process was the initial high‐density created by strong interactions between the ionic species such as electro‐statistic one and hydrogen‐bonding, which disappeared on the consumption of these species by their reactions with the epoxide to give the low‐density neutral polymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Analysis of the crosslinking process of epoxy–phenolic mixtures by thermal scanning rheometry

The curing reaction of different mixtures of an epoxy resin (diglycidyl ether of bisphenol A type) and a phenolic resin (resole type) cured with different amine concentrations (triethylene tetramine) was studied with thermal scanning rheometry under isothermal conditions from 30 to 95°C. The gel time, defined by several criteria, was used to determine the apparent activation energy of the process. Moreover, with an empirical model used to predict the change in the complex viscosity versus time until the gel time was reached, and under the assumption of first‐order kinetics, the apparent rate constant and the apparent activation energy for the curing process were calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 818–824, 2005     

Effect of side‐chain length of succinic anhydride on coefficient of thermal expansion behavior of epoxy resins

The effect of an alkenyl side‐chain of succinic anhydride (SA) on the thermal behavior and the coefficient of thermal expansion (CTE) of diglycidylether of bisphenol A (DGEBA) epoxy resins was studied. The number of carbons in the side‐chain of SA was varied from 6 to 14 and N,N‐Dimethylbenzylamine was used as an accelerator. As a result, the reactivity of SA with epoxide groups was decreased on increasing the length of the alkenyl side‐chain of SA. The thermal stabilities of cured DGEBA/SA samples were approximately constant with varying alkenyl side‐chain of SA. Also, the CTE of the systems was increased as the length of the alkenyl side‐chain of SA increased. This could be attributed to the increased motion of the chain segments in the epoxy network structure induced by the longer alkenyl side‐chain of SA. The effect of amount anhydride, thermoplastics, and fillers on the CTE of the epoxy resins was also discussed. Copyright © 2006 Society of Chemical Industry     

The effect of storage temperatures below 100°C on the viscosity of a novolak resin propylene glycol solution

The aging of a novolak resin solution used in iron‐making blast furnace taphole clays is reported. The novolak resin propylene glycol solution was aged at temperatures between 2 and 80°C for up to 56 days. The viscosity was measured to evaluate the change in the resin's behavior. A cure reaction was found to occur with the addition of hexamethylenetetramine (HMTA) at temperatures lower than had previously been reported. Methods for handling and storage of taphole clay to avoid excessive increases in viscosity due to aging are discussed. An approach for estimating the long term aging at temperatures of 30 to 50°C was considered using shorter term aging data obtained at 70 and 80°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 267–276, 2004     

Ultrasonic and mechanical measurements for the detection of crosslink density of SBR and NBR based on various curing systems

The stress–strain measurements of styrene‐butadiene rubber (SBR) samples based on various curing systems were used to access the crosslink density of various rubber mixes. Same materials were subjected to various uniaxial compression strains. The thicknesses before compression and after recovery were recorded. After recovery, pulse echo method was used to measure the ultrasonic velocity for the dilatational wave and that of shear wave at a frequency of 2 MHz and at room temperature. Both of the ultrasonic velocities were used to determine the elastic moduli of the samples. The relation between the elastic moduli and the corresponding recovery values were used to determine the crosslink density of samples. The crosslink density values obtained from the two techniques were compared. Butadiene‐acrylonitrile (NBR) rubber mix was used to show that the ultrasonic technique is applicable for other rubber compounds. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Comparison of microwave and thermal cure of epoxy–anhydride resins: Mechanical properties and dynamic characteristics

The objective of this work was to compare the mechanical properties of epoxy resins cured by thermal heating and microwave heating. Epoxy–anhydride (100:80) resins were cured in a domestic microwave oven and in a thermal oven. The hardening agents included methyl tetrahydrophthalic anhydride and methyl hexahydrophthalic anhydride. Three types of accelerators were employed. Thermal curing was performed at 150°C for 20 and 14 min for resins containing 1 and 4% accelerator, respectively. Microwave curing was carried out at a low power (207 or 276 W) for 10, 14, and 20 min. All cured resins were investigated with respect to their tensile properties, notched Izod impact resistance, and flexural properties (three‐point bending) according to ASTM standards. The tan δ and activation energy values were investigated with dynamic mechanical thermal analysis, and the extent of conversion was determined with differential scanning calorimetry. The differences in the mechanical properties of the thermally cured and microwave‐cured samples depended on the resin formulation and properties. Equivalent or better mechanical properties were obtained by microwave curing, in comparison with those obtained by thermal curing. Microwave curing also provided a shorter cure time and an equivalent degree of conversion. The glass‐transition temperatures (tan δ) of the thermally and microwave‐cured resins were comparable, and their activation energies were in the range of 327–521 kJ/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1442–1461, 2005     

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     

Comparison between microwave and thermal curing of glass fiber–epoxy composites: Effect of microwave‐heating cycle on mechanical properties

The objective of this study was to compare the mechanical properties between epoxy composites cured by thermal heating and microwave heating. Epoxy‐anhydride resins reinforced with glass fiber were cured in a domestic microwave oven and in a thermal oven. Hardening agents included methyl tetrahydrophthalic anhydride and methyl hexahydrophthalic anhydride. Microwave curing was carried out at various conditions, including 1‐, 2‐, and 3‐step heating cycle, whereby each cycle employed different power level and time. Mechanical properties were tested according to ASTM standards. It is found that the microwave‐cured composites produced mechanical properties as good as the thermally cured composites. The 2‐ and 3‐step heating cycle used in the microwave curing process produced better mechanical properties higher than those obtained from the microwaved 1‐step and thermally curing process. This is attributed to the slow increase in temperature during the beginning of the microwave curing process whereby the very low power level was applied in the first cycle of the multistep heating process. This affected the slower rate of viscosity increment, resulting in better wettability of the glass fiber with enhanced interfacial adhesion between the fibers and the resins. The viscosity of resins affected the homogeneity of the crosslinked structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1059–1070, 2006     

Synthesis and thermal stability of a novel cycloaliphatic epoxy resin system

A novel cycloaliphatic epoxy resin was synthesized from dicyclopentadiene, ethylene glycol, and nadic anhydride. The chemical structures of the resultant epoxy resin and its precursor were characterized with Fourier transform infrared spectroscopy, ¹H‐NMR, and mass spectrographic analyses. The thermal stability of the cured polymer was investigated with differential scanning calorimetry and thermogravimetric analysis. Compared with the thermal stability of the commercial cycloaliphatic epoxy resin 3,4‐epoxy cyclohexyl methyl‐3′,4′‐epoxy cyclohexyl carboxylate, a higher thermal stability for the cured polymer of the novel epoxy resin was observed. The results imply that the novel cycloaliphatic epoxy resin has good potential applications in electronic encapsulation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Heterocyclic‐based epoxy‐terminated structural adhesive. II. Curing,adhesive strength,and thermal stability

We studied the curing behavior of heterocyclic‐based epoxy‐terminated resins using diaminodiphenyl ether, diaminodiphenyl sulfone, benzophenone tetracarboxylicdianhydride, and the commercial hardener of Ciba‐Geigy's two‐pack Araldite as curing agents. The adhesive strength of the adhesives was measured by various ASTM methods such as lap‐shear, peel, and cohesive tests on metal–metal, wood–wood, and wood–metal interfaces. All of these results were compared with those of an epoxy resin prepared from bisphenol‐A and epichlorohydrin resin with an epoxy equivalent value of 0.519. The thermal stability of both the virgin resin and its cured form was also studied by thermogravimetric analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3520–3526, 2002     

Studies of the curing kinetics and thermal stability of epoxy resins using a mixture of amines and anhydrides

This article describes the curing and thermal behavior of diglycidyl ether of bisphenol A with phthalic anhydride (PA)/pyromellitic anhydride/diaminodiphenyl sulfone (DDS) or a mixture of anhydrides and amines in varying ratios as curing agents. The kinetics of the curing behavior was investigated with a multiple‐rate method. The activation energy of the curing reaction as determined in accordance with Ozawa's method was found dependent on the structure of the anhydride and on the ratio of amines to anhydrides. The activation energy was highest with sample DP3 (0.25 : 0.75) and DM3 (0.25 : 0.75). We evaluated the thermal stability of epoxy resin, cured isothermally, by recording thermogravimetric traces in a nitrogen atmosphere. The char yield was highest for resins cured with a mixture of DDS and PA (0.5 : 0.5) and a mixture of DDS and pyromellitic dianhydride (0.25 : 0.75). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3919–3925, 2006     

Cure behavior of epoxy resin containing castor oil and cashew nut shell liquid and its derivative

The cure behavior of epoxy resin with a conventional amide‐type hardener (HD) was investigated in the presence of castor oil (CO), cashew nut shell liquid (CNSL), and cashew nut shell liquid–formaldehyde resin (CFR) with dynamic differential scanning calorimetry (DSC). The activation energy of the curing reaction was also calculated on the basis of nonisothermal DSC thermograms at various heating rates. A one‐stage curing was noted in the case of epoxy resin filled with CO, whereas the epoxy resin with CNSL and CFR showed a two‐stage curing process. A competitive cure reaction was noted for the epoxy resin/CNSL(or CFR)/HD blends. In the absence of HD, CFR showed lower values of curing enthalpy than that of CNSL. The activation energy of epoxy resin curing increased with increasing CNSL and CFR loading. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

辐射交联高密度聚乙烯泡沫塑料交联度的研究

与化学交联方法相比辐射交联的高密度聚乙烯泡沫塑料有光滑、均一的表面,闭孔和树脂的内在性质赋予它良好的机械性能、耐冲击性、绝缘性。研究了加入AC发泡剂、EVA、多官能团单体(SR444)的辐射交联高密度聚乙烯泡沫塑料与交联度相关的性质。测试的参数包括辐射剂量、凝胶含量、泡孔尺寸。高密度聚乙烯树脂中在不同辐照剂量条件下加入5～10份发泡剂及多官能团单体,辐射剂量10～50kGy。在泡孔形成和生长阶段,交联度对于凝胶含量、泡孔结构都有重要影响。     

Flame retardancy and dielectric properties of dicyclopentadiene‐based benzoxazine cured with a phosphorus‐containing phenolic resin

A dicyclopentadiene‐based benzoxazine (DCPDBZ) was prepared and separately copolymerized with melamine–phenol formaldehyde novolac or phosphorus‐containing phenolic resin (phosphorus‐containing diphenol) at various molar ratios. Their curing behaviors were characterized by differential scanning calorimetry. The electrical properties of the cured resins were studied with a dielectric analyzer. The glass‐transition temperatures were measured by dynamic mechanical analysis. The thermal stability and flame retardancy were determined by thermogravimetric analysis and a UL‐94 vertical test. These data were compared with those of bisphenol A benzoxazine and 4,4′‐biphenol benzoxazine systems. The effects of the diphenol structure and cured composition on the dielectric properties, moisture resistance, glass‐transition temperature, thermal stability, and flame retardancy are discussed. The DCPDBZ copolymerized with phosphorus‐containing novolac exhibited better dielectric properties, moisture resistance, and flame retardancy than those of the melamine‐modified system. The flame retardancy of the cured benzoxazine/phosphorus‐containing phenolic resins increased with increasing phosphorus content. The results indicate that the bisphenol A and 4,4′‐biphenol systems with a phosphorus content of about 0.6% and the dicyclopentadiene system with a phosphorus content of about 0.8% could achieve a flame‐retardancy rating of UL‐94 V‐0. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dynamics of mechanical,acoustical, and electrical properties of epoxy‐amine compositions during cure

Dynamics of mechanical, acoustical, and electric properties is studied in the cure of three samples of polymeric compositions produced on the basis of epoxy oligomer with different content of the curing agent. The measurements were made in a parallel mode with an automated measuring complex. Variations in elastic modules, sound speed, attenuation coefficient, relaxation of the shear stress, electric resistance of the samples during the complete cure in the transition from a liquid into a glass state are considered. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010