Synthesis and properties of novel fluorinated epoxy resins based on 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane

A novel fluorinated epoxy resin, 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane (BGTF), was synthesized through a four-step procedure, which was then cured with hexahydro-4-methylphthalic anhydride (HMPA) and 4,4′-diaminodiphenyl-methane (DDM). As comparison, a commercial available epoxy resin, bisphenol A diglycidyl ether (BADGE), cured with the same curing agents was also investigated. We found that the BGTF gave the exothermic starting temperature lower than BADGE no mater what kind of curing agents applied, implying the reactivity of the former is higher than the latter. The fully cured fluorinated BGTF epoxy resins have good thermal stability with glass transition temperature of 170-175 °C and thermal decomposition temperature at 5% weight loss of 370-382 °C in nitrogen. The fluorinated BGTF epoxy resins also showed the mechanical properties as good as the commercial BADGE epoxy resins. The cured BGTF epoxy resins exhibited improved dielectric properties as compared with the BADGE epoxy resins with the dielectric constants and the dissipation factors lower than 3.3 and dissipation 2.8 × 10⁻³, respectively, which is related to the low polarizability of the C-F bond and the large free volume of CF₃ groups in the polymer. The BGTF epoxy resins also gave low water absorption because of the existence of hydrophobic fluorine atom.     

Electrical and positron annihilation study on epoxy and epoxy acrylate composites

Epoxy acrylate resin was prepared by endcapping the acrylic acid to epoxy resin backbone in the presence of triphenyl phosphene as catalyst. The structure was elucidated by IR and NMR spectroscopy. Epoxy and epoxy acrylate composites were prepared by mixing different concentrations of mica, magnesium hydroxide and calcium silicate with each epoxy/hardener and epoxy acrylate/styrene mixtures, respectively. The permittivity ε′, dielectric loss ε′′ and loss tangent tan δ were measured for these composites in the frequency range (10²-10⁶ Hz) and at 30 °C. The data obtained were analyzed into two absorption regions related to Maxwell-Wagner effect and to some local molecular motions rather than the main chain motion. The higher values of ε′ and the lower values of tan δ given for the composites containing the epoxy acrylate resin indicate some improvement in the dielectric properties when compared with those containing the epoxy resin. The effect of filler type and filler content on the positron annihilation lifetime and its intensity as well as S-parameter for epoxy and epoxy acrylate composites were also studied. The high values of S-parameter noticed by with increasing filler content indicates some increase in free electrons which lead to an increase in electrical conductivity. The highest value of hardness was obtained in the case of calcium silicate followed by mica and magnesium hydroxide.     

Multi-layer nanopaper based composites

Native cellulose nanofibrils (CNF) were prepared from bleached birch pulp without any chemical or enzymatic pretreatment. These CNF were modified by adsorption of a small amount of water-soluble polysaccharides and used to prepare nanopapers, which were processed into composites by lamination with an epoxy resin and subsequently cured. The results were compared to the properties of composites prepared using bacterial cellulose nanopapers, since bacterial cellulose constitutes highly pure and crystalline cellulose. It was found that both types of nanopapers significantly improved both the thermal stability and mechanical properties of the epoxy resin. As anticipated, addition of only 2 wt% of water-soluble polysaccharides efficiently hindered crack-propagation within the nanopaper and significantly improved the tensile strength and work of fracture compared to composites containing a conventional nanopaper reinforcement. The mechanical properties of the composites thus reflected the improvement of the nanopaper properties by the polysaccharides. Moreover, it was possible to predict the properties of the final composite from the mechanical performance of the nanopapers.     

The chemical and dielectric properties of epoxy/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 composites for embedded capacitor application

The characteristics of epoxy/(Ba_0.8Sr_0.2)(Ti_0.9Zr_0.1)O₃ (BSTZ) composites are investigated for the further application in embedded capacitor device. The effects of BSTZ ceramic powder filler ratio on the chemical, physical and dielectric properties of epoxy/BSTZ composites are studied. Differential scanning calorimeter (DSC) thermal analysis is conducted to determine the optimum values of hardener agent, curing temperature, reaction heat, and glass transition temperature (T_g). The hardener reaction process starts at about 115 °C and completes at about 200 °C, for that it is appropriate to process of epoxy/BSTZ composites in the range of temperature. The highest glass transition temperature (T_g) of 155 °C is obtained at one equivalent weight ratio (hardener/epoxy). Only the BSTZ phase can be detected in the XRD patterns of epoxy/BSTZ composites. The more BSTZ ceramic powder is mixed with epoxy, the higher crystalline intensity of tetragonal BSTZ phase are revealed in the XRD patterns. The dielectric constant measured at 1 MHz increases from 5.8 to 23.6 as the content of BSTZ ceramic powder in the epoxy/BSTZ composites increases from 10 to 70 wt%. The loss tangents of the epoxy/BSTZ composites slightly increase with the increase of measurement frequency.     

Effects of novel polyhedral oligomeric silsesquioxane containing hydroxyl group and epoxy group on the dicyclopentadiene bisphenol dicyanate ester composites

Two types of novel Polyhedral Oligomeric Silsesquioxanes respectively containing hydroxyl group and epoxy group (P-POSS and E-POSS) were achieved and evaluated. The structure had been characterized by IR spectra and NMR spectra. Dicyclopentadiene bisphenol dicyanate ester (DCPDCE) composites were then prepared using P-POSS and E-POSS respectively. Their effect on the curing kinetics, dielectric, mechanical, flame-retardant and thermal properties and water absorption of the resulting composites were investigated. The results suggested that the addition of modified POSS could facilitate the curing reaction of DCPDCE. Besides, the DCPDCE composites containing modified POSS exhibited excellent flame-retardant property over pure DCPDCE resin. Adding only a little amount as small as 1.5 wt% P-POSS or 2.5 wt% E-POSS could change the UL-94V of DCPDCE resin from V-2 to V-0. The composite with P-POSS exhibited better flame-retardant and thermal properties than the composite with E-POSS. However, composite filled with E-POSS presented better dielectric property and lower water absorption.     

Novel toughened cyanate ester resin with good dielectric properties and thermal stability by copolymerizing with hyperbranched polysiloxane and epoxy resin

A novel toughened cyanate ester (CE) resin with good dielectric properties and thermal stability was developed by copolymerizing 2,2′‐bis(4‐cyanatophenyl)iso‐propylidene (BCE) with a combined modifier (HBPSiEP) made up of hyperbranched polysiloxane (HBPSi) and epoxy (EP) resin. HBPSi was synthesized through the hydrolysis of 3‐(trimethoxysilyl)propyl methacrylate. The effect of differing stoichiometries of HBPSiEP on the curing characteristics and performance of BCE resin is discussed. Results show that the incorporation of HBPSiEP can not only effectively promote the curing reaction of BCE, but can also significantly improve the toughness of the cured BCE resin. In addition, the toughening effect of HBPSiEP is greater than single EP resin. For example, the impact strength of modified BCE resin with 30 wt% of HBPSiEP is 23.3 KJ/m², which is more than 2.5 times of that of pure BCE resin, while the maximum impact strength of EP/BCE resin is about 2 times of pure BCE resin. It is worthy to note that HBPSiEP/BCE resins also exhibit improved thermal stability, dielectric properties, and flame retardancy, suggesting that the novel toughened CE resins have great potentiality to be used as a matrix for advanced functional composites or electronic packing resins. Copyright © 2009 John Wiley & Sons, Ltd.     

Pyrolysis and fire behaviour of epoxy resin composites based on a phosphorus-containing polyhedral oligomeric silsesquioxane (DOPO-POSS)

The pyrolysis and fire behaviour of epoxy resin (EP) composites based on a novel polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-POSS) and diglycidyl ether of bisphenol A (DGEBA) have been investigated. The pre-reaction between the hydroxyl groups of DOPO-POSS and the epoxy groups of DGEBA at 140 °C is confirmed by FTIR, which means that DOPO-POSS molecules of hydroxyl group could easily disperse into the epoxy resin at the molecular level. The EP composites with the DOPO-POSS were prepared through a curing agent, m-phenylenediamine (m-PDA). The morphologies of the EP composites observed by SEM indicate that DOPO-POSS disperses with nano-scale particles in the EP networks, which implies good compatibility between them. The thermal properties and pyrolysis of the EP composites were analyzed by DSC and TGA, TGA-FTIR, and TGA-MS. The analysis indicates that the DOPO-POSS change the decomposition pathways of the epoxy resin and increase its residue at high temperature; moreover, the release of phosphorous products in the gas phase and the existence of Si-O and P-O structures in the residue Is noted. The fire behaviour of the EP composites was evaluated by cone calorimeter (CONE). The CONE tests show that incorporation of DOPO-POSS into epoxy resin can significantly improve the flame retardancy of EP composites. SEM and XPS were used to explore micro-structures and chemical components of the char from CONE tests of the EP composites, they support the view that DOPO-POSS makes the char strong with the involvement of Si-O and P-O structures.     

Nonaqueous synthesis of nanosilica in epoxy resin matrix and thermal properties of their cured nanocomposites

Nonaqueous synthesis of nanosilica in diglycidyl ether of bisphenol‐A epoxy (DGEBA) resin has been successfully achieved in this study by reacting tetraethoxysilane (TEOS) directly with DGEBA epoxy matrix, at 80 °C for 4 h under the catalysis of boron trifluoride monoethylamine (BF₃MEA). BF₃MEA was proved to be an effective catalyst for the formation of nanosilica in DGEBA epoxy under thermal heating process. FTIR and ²⁹Si NMR spectra have been used to characterize the structures of nanosilica obtained from this direct thermal synthetic process. The morphology of the nanosilica synthesized in epoxy matrix has also been analyzed by TEM and SEM studies. The effects of both the concentration of BF₃MEA catalyst and amount of TEOS on the diameters of nanosilica in the DGEBA epoxy resin have been discussed in this study. From the DSC analysis, it was found that the nanosilica containing epoxy exhibited the same curing profile as pure epoxy resin, during the curing reaction with 4,4′‐diaminodiphenysulfone (DDS). The thermal‐cured epoxy–nanosilica composites from 40% of TEOS exhibited high glass transition temperature of 221 °C, which was almost 50 °C higher than that of pure DGEBA–DDS–BF₃MEA‐cured resin network. Almost 60 °C increase in thermal degradation temperature has been observed during the TGA of the DDS‐cured epoxy–nanosilica composites containing 40% of TEOS. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 757–768, 2006     

氨丙基封端聚氰丙基甲基硅氧烷改性环氧树脂——两相相溶性及表界面形态研究

本文针对聚二甲基硅氧烷改性环氧树脂相溶性太差,性能不够理想等问题,提出用氰丙基替代部分甲基以减小聚硅氧烷与环氧树脂的溶度参数差,改善两相的相溶性。采用氨丙基封端的聚氰丙基甲基硅氧烷低聚体(表1)单独或与二乙烯三胺(固化剂)一同与双酚A环氧树脂反应,合成了一系列不同聚硅氧烷分子量和重量百分比的样品(表2)。并用示差扫描量热计(DSC)、动态力学谱(DMA)、光电子能谱(XPS)、接触角仪、扫描电子显微镜(SEM)、电子拉力试验机对其进行研究。结果表明在聚硅氧烷软段中引入氰丙基可提高两相的相溶性并使增韧效果明显改善。     

Improvement in mechanical and structural integrity of natural stone by applying unsaturated polyester resin-nanosilica hybrid thin coating

In this study, an unsaturated polyester resin (UPR) thin coating containing styrene monomer has been used to consolidate Marrón emperador marble pieces. Different amounts (0.5-3 wt.%) of nanosilica was added to improve several properties, particularly the mechanical properties. The uncured UPR-nanosilica hybrids were characterized by rotational rheology, the gelation was monitored by means of a texture analyser and the viscoelastic and thermal properties were determined in the cured UPR-nanosilica films. Transmission electron microscopy (TEM) was used to establish the degree of dispersion of the nanosilica in the UPR-nanosilica composites. The mechanical performance of the UPR-nanosilica thin coated marble pieces was measured by means of 3-points bending and impact strength tests.Addition of nanosilica imparted pseudoplasticity and thixotropy to the UPR resin and an increase in viscosity was also produced. The rheology of the UPR-nanosilica solutions was fitted to the Casson’s model and an increase in yield stress was obtained. The gel time of the UPR resin was significantly decreased by adding small amounts of nanosilica due to the interactions between the filler and the styrene in the UPR resin. In the cured composites, improved thermal properties in UPR were reached by adding nanosilica due to the creation of a network between the filler and the polymer matrix. Bundle nanometric size nanosilica agglomerates were observed which affected the glass transition temperature and the viscoelasticity of the UPR-nanosilica composites. Finally, the improved properties in UPR obtained by adding nanosilica produced enhanced impact resistance to coated marble pieces, as both stiffness and toughness were improved by nanosilica addition.     

Thermal stability of silver sulfathiazole-epoxy resin network

The aim of this study is to evaluate the thermal stability and thermal degradation behavior of an epoxy network based on bisphenol A modified with silver sulfathiazole and crosslinked with ethylenediamine. The sample was studied by thermogravimetric analysis coupled with differential scanning calorimetry over a range of temperature between 30 and 600 °C in N₂ atmosphere and using heating rates of 5, 10, 15 and 20 °C min⁻¹. The kinetic parameters of thermal degradation process were calculated. Fourier transforms infrared spectroscopy and mass spectroscopy coupled to thermogravimetry was used to identify the volatile products resulting from the degradation of the network. The study showed that the sample is stable up to temperatures exceeding 290 °C. The major degradation volatile products identified were: ammonia, water, carbon dioxide and compounds with aromatic structure such as bisphenol A and its degradation products.     

Modified cyanate ester resins with lower dielectric loss,improved thermal stability,and flame retardancy

Novel modified cyanate ester (CE) resins with decreased dielectric loss, improved thermal stability, and flame retardancy were developed by copolymerizing CE with hyperbranched phenyl polysiloxane (HBPPSi). HBPPSi was synthesized through the hydrolysis of phenyltrimethoxysilane, and its structure was characterized by ¹H‐NMR, ²⁹Si‐NMR, and Fourier transform infrared spectra. The effect of the incorporation of HBPPSi into CE resin on the curing behavior, chemical structure of cured networks, and typical performance of HBPPSi/CE resins were systemically evaluated. It is found that the incorporation of HBPPSi into CE network obviously not only catalyzes the curing of CE, but also changes the chemical structure of resultant networks, and thus results in significantly decreased dielectric loss, improved thermal stability, and flame retardancy as well as water absorption resistance. For example, in the case of the modified CE resin with 10 wt% HBPPSi, its limited oxygen index is about 36.0, about 1.3 times of that of neat CE resin, its char yield at 800°C increases from 31.6 to 35.4 wt%; in addition, its dielectric loss is only about 61% of that of neat CE resin at 1 kHz. All these changes of properties are discussed from the view of the structure–property relationship. The significantly improved integrated properties of CE resin provide a great potential to be used as structural and functional materials for many cutting‐edges fields. Copyright © 2011 John Wiley & Sons, Ltd.     

Enhanced conductivity composites for aircraft applications: carbon nanotube inclusion both in epoxy matrix and in carbonized electrospun nanofibers

The potential of carbonized electrospun nanofiber mats to render epoxy resin composites for aircraft applications electrically and thermally more conductive was investigated. The effect of carbon nanotube inclusion both inside the carbon nanofiber and in the epoxy resin matrix material was studied, in order to reveal any synergistic effects of multilevel presence of nanosized reinforcements on the conductivity and mechanical properties. The carbon nanotube inclusion into the carbonized nanofibers increased the electrical conductivity of the samples by 20–50% and the thermal conductivity by approximately three times leading to a higher value than that of the conventional composites. The preparation of layered composites with a conductive upper layer containing nonwoven carbon nanofabric and a load bearing lower layer with conventional unidirectional carbon fiber reinforcement can offer a cost‐effective and weight‐saving solution for the replacement of metal meshes in structural aircraft composites. Copyright © 2014 John Wiley & Sons, Ltd.     

新环氧树脂纳米复合材料的合成和结构研究

以具有层状硅酸盐结构的累托石(REC)为主体,以烷基季铵盐为改性剂合成了有机累托石(OREC),以有机累托石和环氧树脂复合,制备出纳米复合材料。累托石含量在0.8wt.% 时,纳米复合材料具有最佳力学和热学性能,冲击强度增加到65.6 kJm-2,断裂伸长率从4.7 %增加到20.2 %,玻璃化转变温度提高到 197.9 ℃。用X-小角衍射法、透射电镜和红外吸收光谱研究了材料的微观结构,XRD 衍射图显示,未经处理REC 的层间距d001 = 2. 2 nm,经有机改性后,累托石片层间距扩大到2.8 nm,与环氧树脂复合后,其层间距扩大到4.2 nm 左右,FT-IR图显示,有机累托石中出现十六胺的特征吸收峰,TEM照片显示该复合材料是一种纳米复合材料。     

含硅磷杂化物环氧树脂固化物性能研究

首先用γ-环氧丙氧基三甲氧基硅烷(KH-560)和亚磷酸二乙酯(DEP)反应的中间产物进行水解缩合反应,合成了一种含磷低聚硅氧烷杂化物.并用FTIR,NMR,GPC对其结构及分子量进行了表征.然后将含磷低聚硅氧烷引入到双酚A环氧树脂(E-54)制备硅磷杂化物环氧树脂的固化物.对这种含硅磷杂化物环氧树脂固化物的性能研究发现其极限氧指数为23～29,DSC分析结果玻璃化转变温度(Tg)可以达到204℃,失重5%的温度(Td)5%比纯E-54提高近20℃.该固化物具有阻燃性能,同时具有较好的热性能。     

Metal compound-enhanced flame retardancy of intumescent epoxy resins containing ammonium polyphosphate

A series of intumescent flame-retardant epoxy resins (IFR-EPs) were prepared only by adding a 5 wt% total loading of ammonium polyphosphate (APP) and metal compounds. All the samples could achieve V-0 rating and did not generate dripping during UL-94 testing. The limiting oxygen index (LOI) values of the samples with 4.83 wt% APP and 0.17 wt% CoSA increase from 27.1 to 29.4, compared with epoxy resin containing 5 wt% APP. The samples also showed excellent water resistance of flame retardancy in 30 °C and 70 °C water for 168 h. The LOI results show that the composition of metal compounds (metal ions and ligands/anions) and the mass ratios of APP to metal compounds affect the flame retardancy of the samples. TG results indicate that the catalytic effect of CoSA on the decomposition of both APP and the epoxy resins containing APP is better than that of CuSAO. The fire behavior of epoxy resin and epoxy resins containing APP with/without CoSA were investigated by cone calorimeter. Cone calorimeter parameters of the samples such as HRR, THR, TSP and COP indicate that the addition of APP and CoSA improves the fire safety of epoxy resin significantly, and CoSA shows an obvious catalytic effect.     

Fabrication of high thermal stable cured novolac/Cloisite 30B nanocomposites by chemical modification of resin structure

Cloisite 30B as a modified kind of nanoclay was utilized for the formation of 3D network based on novolac resin with high thermal stable properties. Two types of phenolic resins including neat novolac (NR) and modified novolac resin were used to create a compatible matrix with nanoclay. For this purpose, NR modified with (3‐chloropropyl)triethoxysilane (CPTES) to form SiNR. For improvement of thermal behaviors, Cloisite 30B was dispersed in matrix via ultrasonic waves and cured with hexamethylenetetramine (HMTA) to form 3D network. X‐ray diffraction (XRD) analysis was used to measure the d‐spacing in intercalated systems and results indicated the optimum amount of clay for appropriate thermal properties. Investigation of the thermal properties of the samples by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the presence of Cloisite 30B in matrix resulted in much higher thermal stability and char yield with respect to modification of novolac resin originated from formation of 3D Si–O–Si network. Also, cured modified resin and its nanocomposites showed much higher thermal stability than cured NR and its nanocomposites. Such nanocomposite materials with high thermal stability have potential applications in advanced fields such electronic, industrial molds, coatings, adhesives, and aerospace composites.     

Flame retardancy and flame retarding mechanism of high performance hyperbranched polysiloxane modified bismaleimide/cyanate ester resin

A novel kind of modified bismaleimide/cyanate ester (BCE) resins by copolymerizing with hyperbranched polysiloxane including high content of phenyl (HBPSi) was first reported. The effect of HBPSi on the curing mechanism, and that on the dielectric properties and flame retardancy of cured networks were systemically investigated. Results show that compared with BCE resin, HBPSi/BCE resin has obviously different cross-linked structure, and thus leading to simultaneously improved dielectric properties and flame retardancy. The reactions between HBPSi and the decomposition structure of BCE resin change the thermo-oxidative degradation mechanism of the first step in the thermo-oxidative degradation; in addition, the presence of HBPSi in BCE resin also significantly reduces the mass loss rate (MLR) and increases char yield at 800 °C under an air atmosphere. Therefore, the positive effect of HBPSi on improving the flame retardancy is attributed to the condensed phase mechanism. On the other hand, HBPSi/BCE resins exhibit improved dielectric properties (including decreased dielectric constant and loss) with increasing the content of HBPSi. More importantly, this investigation demonstrates that designing new polysiloxane with suitable chemical structure is important to develop high performance resins with attractive flame retardancy and dielectric properties.     

Fire Retardancy of Aluminum Hydroxide Reinforced Flame Retardant Modified Epoxy Resin Composite

A novel phosphorous containing flame retardant epoxy resin is synthesized by modifying the epoxy resin initially with phosphoric acid and further with aluminum hydroxide (ATH) to enhance the fire retardancy of the modified epoxy resin. The several phosphorous modified epoxy resin to ATH mass ratios were used to study the effect of ATH addition on epoxy. Thermal and mechanical properties. The structure of the modified flame retardant epoxy resin was characterized using Fourier-transform infrared spectroscopy (FTIR) while thermal degradation behavior and flame retardant properties were examined using thermo-gravimetric analysis (TGA) and UL-94 testing. Furthermore, ultimate tensile strength and young modulus were analyzed to study the effect of ATH addition on mechanical properties. The findings indicated that fire retardancy of ATH reinforced modified ep oxy resin is higher than virgin and phosphorous modified epoxy resin and depicted eminent flame retardant properties with suitable mechanical properties.