The mechanical properties of epoxy resins

Crack propagation in a series of epoxy resins described in Part 1 has been studied as a function of testing rate and temperature. It has been found that crack propagation is continuous at low temperatures but that as the temperature is raised the mode of propagation becomes unstable (stick/slip). Features on the fracture surfaces at the crack arrest lines have been shown to be of the same dimensions as those expected for a Dugdale plastic zone. It has been suggested that the slip process takes place by slow growth of a crack through the plastic zone followed by rapid propagation through virgin material. It has been shown that the stick/slip behaviour is due to blunting of the crack which is controlled by the yield behaviour of the resin. A unique fracture criterion has been shown to be applicable to epoxy resins which is that a critical stress of the order of three times the yield stress must be achieved at a critical distance ahead of the crack. Electron microscope replicas of the fracture surfaces have been obtained and an underlying nodular structure can be resolved. However, no direct correlation between the nodule size and fracture properties has been found.     

碳化钛/环氧树脂纳米复合材料的介电性能研究

采用溶液混合随后热压的方法制备了TiC/epoxy纳米复合材料.运用渗流阈值理论解释了TiC/epoxy复合材料的介电行为.研究了复合材料介电常数与填料体积百分比含量和测试频率的关系.结果表明:当TiC体积百分比含量为0.192时,复合材料的介电常数高达214(103Hz).复合材料介电常数在高测试频率范围(104～106Hz)不随频率的变化而改变.     

Properties of polymeric compositions based on epoxy and functional petroleum polymeric resins

We studied cross-linking, water resistance, and impedance characteristics of polymeric compositions based on epoxydiane and maleinized petroleum polymeric resins. It is shown that epoxy and petroleum polymeric components interact at temperatures of 150°C and higher to form cross-linked copolymers. The gel-fraction content of the composition increases with the acid number of the petroleum polymeric component. Small amounts of tertiary amine enhance the efficiency of its cross-linking. The water resistance and protective properties of epoxy-petroleum polymeric compositions improve as the acid number of petroleum polymeric resins increases and the content of the liquid fraction decreases. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 6, pp. 37–42, November–December, 1996.     

含氟对苯型酚醛环氧树脂的制备与性能研究

将三氟甲基引入到对苯型酚醛环氧树脂体系的分子结构中,制备了新型舍氟对苯型酚醛环氧树脂(FPE)和含氟对苯型酚醛树脂固化剂(FPN).系统研究了含氟基团对环氧树脂固化物的耐热性能、力学性能和阻燃性能的影响规律,并对由其制备的环氧塑封料的综合性能进行了评价.结果表明,以含氟对苯型酚醛环氧树脂体系FPE/FPN制备的塑封料不但具有突出的绝缘性能,同时表现出优异的本征阻燃性.     

一种含多面低聚倍半硅氧烷的环氧树脂改性剂及性能研究

采用自制的γ-氨丙基笼型齐聚倍半硅氧烷(POSS-NH_2)与一小分子反应,合成了一种新型环氧树脂改性剂(POSS-NH-R),并以此对环氧树脂E-51进行改性.考察了不同添加量对复合环氧树脂的各项性能的影响,发现当添加量为25%时,改性效果最佳.     

Effect of DOPO units and of polydimethylsiloxane segments on the properties of epoxy resins

New flame retardant epoxy resins containing phosphorus and/or silicon atoms were prepared by the introduction into the epoxy chemical structure of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and/or of polydimethylsiloxane segments. The structure and morphology of cured epoxy resins were evaluated by Fourier transform infrared spectroscopy and scanning electron microscopy analyses, respectively. The polymers exhibited good thermal stability, having initial decomposition temperature above 310 °C. Thermogravimetric analyses and limiting oxygen index values indicated that the incorporation of DOPO units/polydimethylsiloxane segments in the polymer structure significantly enhanced flame retardancy and thermal stability of char layer at high temperature. Broadband dielectric spectroscopy measurements over a wide range of frequency and temperature revealed two subglass transitions, γ and β. The experimental data were fitted to the Havriliak–Negami and Arrhenius models, and the obtained parameters were analyzed. An α relaxation process attributed to the glass transition was observed in the high temperature and high frequency ranges. The influence of DOPO units and polydimethylsiloxane segments on the properties of the polymers was examined.     

二氯二苯基硅烷改性双酚A型环氧树脂性能研究

以二氯二苯基硅烷对双酚A型环氧树脂进行改性,通过拉伸实验、冲击实验、DSC、SEM研究了二氯二苯基硅烷的含量对环氧树脂E-51固化物性能的影响.结果表明:用5.9份的二氯二苯基硅烷改性时,树脂固化物的拉伸强度达到了67.85MPa,断裂伸长率达7.59%,冲击强度达13.38kJ/m2,环氧树脂的玻璃化转变温度达146.56℃.分别比未改性提高了18.9MPa、3.6%、5.5kJ/m2、28℃.     

酚醛氰酸酯/环氧共固化树脂的结构和性能

研究了具有不同摩尔比的酚醛型氰酸酯（NCE）与双酚A型环氧（E-51）共固化树脂的化学结构与物理性能．结果表明,在共固化树脂的结构中,主要存在着三嗪、噁唑啉酮、异氰脲酸、醚键等化学结构．只有当氰酸酯的摩尔数大于环氧时,随着共固化体系中-OCN摩尔数的提高,化学结构中三嗪环含量增大,共固化树脂的力学性能、玻璃化转变温度（Tg）、烧蚀残留率、吸水率随之提高;当-OCN／epoxy的摩尔比大于1时,固化树脂的Tg比摩尔比小于1时提高30℃以上,力学性能的变化具有相同的规律．     

石墨烯纳米片/环氧树脂复合材料的制备与介电性能研究

以天然鳞片石墨为原料,通过Hummers法制备氧化石墨,微波热解剥离制备出少层数的石墨烯纳米片。以硅烷偶联剂KH-560为改性剂,超声共混制备石墨烯纳米片/环氧树脂复合材料。采用FT-IR和SEM分析样品的微观结构和形貌,测试其介电性能。结果表明,随着石墨烯纳米片添加量的增加,复合材料介电常数呈现先增大后减小的趋势,当石墨烯纳米片含量为0.3%(质量分数)时,介电常数达到最大;石墨烯纳米片对复合材料介电损耗的影响与之相反;偶联改性使复合材料的介电常数增大,介电损耗减小。     

The reinforcing effect of graphene nanosheets on the cryogenic mechanical properties of epoxy resins

The reinforcing effect of graphene in enhancing the cryogenic tensile and impact properties of epoxy composites is examined at a weight fraction of 0.05–0.50%. The micro-structure and cryogenic mechanical properties of the graphene/epoxy composites are investigated using scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering and mechanical testing techniques. The results show that the graphene dispersion in the epoxy matrix is good at low contents while its aggregation takes place and becomes severer as its content increases. And the cryogenic tensile and impact strength at liquid nitrogen temperature (77 K) of the composites are effectively improved by the graphene addition at proper contents. The cryogenic Young’s modulus increases almost linearly with increasing the graphene content. Moreover, the results for the mechanical properties at room temperature (298 K) of the graphene/epoxy composites are also presented for the purpose of comparison.     

Effects of colloidal nanosilica on the rheological properties of epoxy resins filled with organoclay

The rheological properties of epoxy resins filled with organoclay and colloidal nanosilica were investigated by employing a parallel plate rheometer in flow mode at 25 degrees C. Shear thickening and shear thinning behaviors were observed in the epoxy resins filled with a mixture of organoclay and colloidal nanosilica. Minima were observed in the relaxation time of the systems consisting of epoxy resins filled with organoclay and colloidal silica as the content of colloidal nanosilica was increased. It seems that the colloidal nanosilica increased the mobility of the filled epoxy resins and reduced the interactions between the silicate layers in the systems.     

Thermodynamic and mechanical properties of amine-cured epoxy resins using group interaction modelling

The prediction of thermal and mechanical properties of amine-cured epoxy resins by group interaction modelling is presented. The derivation of the group interaction based approach to the prediction of macroscopic engineering properties of both linear and crosslinked epoxy resins is described with specific application to MY721 resin. The glass transition temperature, bulk and tensile modulus and linear thermal expansion coefficient of tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) cured with 4,4′-diaminodiphenyl sulphone (DDS) are estimated using the model and compared with results from dynamic mechanical experiments. The glass transition of TGDDM/DDS is calculated to occur at approximately 248 °C and the reasons for a secondary peak in the spectrum cured to 180 °C are given. The bulk and tensile modulus of TGDDM/DDS are calculated to be 7.54 GPa and 5.34 GPa, respectively.     

The electric and dielectric properties of a coal tar epoxy coating

The dielectric properties of a coal tar epoxy coating on a steel surface in a dry dielectric layer, metal/organic coating/metal (MOCM) structures, as well as in electrochemical systems, metal/organic coating/electrolyte (MOCE), have been investigated by means of impedance spectroscopy. The influence of temperature and chemically-different contacting electrolytes on the electrical properties of the organic coating are discussed on the basis of the frequency-dependent impedance modulus ωZ(ω)ω and the phase angle Θ(ω) which are both accessible through measurements. The results are presented in the form of Bode plots. It was possible to model the measured values of the modulus by the linear relation lnωZ(ω)ω = K−n ln ω and in terms of Kramers-Kronig (KK) relations. It was shown that the poles and residues of the KK integrand [lnωZ(ω)ω/(ω²−ω²_c)] suffice to establish Θ(ω) uniquely. This means that if the modulus in the Bode plot can be represented by a linear relation with a slope -n, the phase angle is frequency-independent. The experimental results for Θ(ω) are in good agreement with this prediction for a dry (MOCM) and an electrochemical system (MOCE).     

Ultraviolet curable epoxy acrylic resins — network flexibilization in the presence of reactive diluents

Different reactive diluents suitable for inducing network flexibilization of a typical ultraviolet curable epoxy resin based on bisphenol-A-diglycidyl-ether-diacrylate (BGEDA) were investigated. Firstly the influence of some monoacrylic reactive diluents, e.g. 2-ethylhexyl-acrylate (EHA) and 4-hydrocybutil-acrylate (HBA) and of a bis-acrylic diluent, polyethylene-glycol-diacrylate (PEGDA) was examined. Subsequently a systematic study was carried out on the properties of coatings resulting from mixtures of BGEDA and a poly(diethylene-glycol-carbonate) diacrylate (PGCDA) as reactive diluent. The main mechanical, dynamic-mechanical and technological properties of both free films and films coated on steel sheets, were evaluated. Interesting network flexibilization properties were observed when PGCDA was used as reactive diluent of BGEDA. The formulations investigated allowed us to obtain a broad range of flexibility for the resulting ultraviolet cured resins and to correlate the coating flexibility with other fundamental properties such asT _g, elastic modulus, abrasion resistance, hardness, adhesion, impact resistance, accelerated ageing and resistance to chemicals.     

氰基苯并(口恶)嗪/环氧树脂共混体系的性能研究

采用三种带有氰基的苯并噁嗪(Ben)与环氧树脂(E51)共混,制备了Ben/E51共混体系.用红外光谱研究了Ben/E51共混体系的固化行为.利用TGA和DMA研究了Ben/E51固化物的耐热性能和动态力学性能,结果显示,共聚体系的分解温度与用酸酐或胺固化的环氧树脂相比提高了70～80℃,玻璃化转变温度提高了30～70℃.Ben/E51共混体系的力学性能和介电性能比苯并噁嗪树脂有明显提高.