Thermal-oxidative aging of DGEBA/EPN/LMPA epoxy system: Chemical structure and thermal-mechanical properties

The evolvement of chemical structure and thermal-mechanical properties of diglycidyl ether of bisphenol-A and novolac epoxy resin blends cured with low molecular polyamide (DGEBA/EPN/LMPA system) during thermal-oxidative aging were investigated by Attenuated Total Reflectance Fourier Transform Infrared spectrometry (ATR-FTIR) and Dynamic Mechanical Thermal Analysis (DMTA). The results revealed that the chemical reactions during thermal-oxidative aging contained oxidation and chain scission. Some possible chemical reaction processes were given. There was a new compound formed during aging processes and the change of its glass transition temperature (T_g) with aging time followed an exponential law. In addition, the changes of dynamic mechanical behavior of this epoxy system aged at four different temperatures (110 °C, 130 °C, 150 °C, 170 °C) were compared. An empirical formula was obtained through kinetic analysis and this formula can be used to predict the oxidative degree of the surface at different aging temperature.     

Characterization of Rubber Epoxy Blends by Thermal Analysis

Differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA) of the blends ofepoxy cresol novolac (ECN) resin toughened with liquid carboxy terminated butadiene-co-acrylonitrile (CTBN) rubber have been carried out. Exothermal heat of reaction (ΔH) due to crosslinking of the resin in presence of diaminodiphenyl methane(DDM, as amine hardener) showed a decreasing trend with increasing rubber concentration. Enhancements of thermal stability as well as lower percentage mass loss of the epoxy-rubber blends with increasing rubber concentration have been observed in TG. Dynamic mechanical properties reflected a monotonic decrease in the storage modulus (E′) with increasing rubber content in the blends. The loss modulus (E″) and the loss tangent(tanδ) values, however, showed an increasing trend with rise of the temperature up to a maximum (peak) followed by a gradual fall in both cases. Addition of 10 mass% of CTBN resulted maximum E″ and tanδ. This revised version was published online in July 2006 with corrections to the Cover Date.     

环氧呋喃树脂反应性增容改性聚乳酸/淀粉复合材料的研究

研究了环氧呋喃树脂反应增容改性聚乳酸/淀粉复合材料,对索氏提取法得到的淀粉进行1H-NMR、FTIR、XPS和静态接触角测试表征.结果表明在熔融共混过程中环氧呋喃树脂(FER)与淀粉及聚乳酸(PLA)发生化学反应,从而起到反应性增容的作用.另外,利用SEM、万能材料试验机和DSC分别对复合材料的界面相容性、机械性能以及热性能进行了表征,结果表明FER能够显著改善PLA和淀粉之间的界面相容性,在保持PLA高强度高模量的基础上,显著提高了PLA/starch复合材料的综合机械性能和结晶性能.     

环氧树脂/聚碳酸酯固化共混物的结构及性能

相结构;酯交换反应;力学性能;环氧树脂/聚碳酸酯固化共混物的结构及性能     

Morphology of Epoxy/Polyorganosiloxane Reactive Blends

The morphology of the diglycidyl ether of bisphenol‐A/poly(3‐aminopropylmethylsiloxane) (DGEBA/PAMS) reactive blends was studied by fluorescence techniques as a function of the initial composition. Some fluorescence results were compared with those from optical and electron microscopy investigations. Several morphological aspects were studied including the distribution of PAMS in the blend. The microsegregation of PAMS was discussed in terms of diffusion restriction of DGEBA through the PAMS dispersed phase.     

Toughness Behaviour of Vinylester/Epoxy Thermosets with Interpenetrating Network Structure

Vinylester/epoxy-based (VE/EP) thermosets of interpenetrating network (IPN) structure were produced by using a VE resin (bismethacryloxy derivative of a bisphenol-A type EP resin) and EP resins of aliphatic (Al-EP) and cycloaliphatic (Cal-EP) nature. Curing of the EP resins occurred either by an aliphatic (Al-Am) or a cycloaliphatic (Cal-Am) diamine compound. Dynamic mechanical thermal analysis (DMTA) and atomic force microscopy (AFM) suggested the presence of an interpenetrating network (IPN) in the resulting thermosets. AFM scans taken on the ion-etched surface of EP showed a featureless homogeneous structure. On the other hand, VE exhibited a two-phase microgel, whereas VE/EP a two-phase interpenetrating network (IPN) structure. Toughness was characterised by parameters of the linear elastic fracture mechanics, viz. fracture toughness (K_c) and fracture energy (G_c). Unexpected high K_c and G_c data were found for the systems containing cyclohexylene units in the EP network. This was attributed to beneficial effects of the conformational changes along the cyclohexylene linkages (chair/boat). The failure mode of the VE/EP thermoset combinations was studied by scanning electron microscopy (SEM) and discussed.     

Interlaminar Fracture Toughness of Carbon Fiber/Epoxy Composites using Short Kevlar Fiber and/or Nylon-6 Powder Reinforcement

Mode I (G_IC) and Mode II (G_IIC) interlaminar fracture toughness of carbon-fiber/epoxy composites have been investigated as a function of the amount of short Kevlar-29 fiber (SKF) and/or Nylon-6 powder (N6P) between continuous fiber layers. G_IIC increased with increasing crack length as a consequence of the presence of SKFs bridging in the wake of propagating crack. G_IIC of SKF alone could reach the maximum at an intermediate amount of SKF. G_IIC of SKF and N6P was lower than that of SKF alone because N6P prevented the orientation of SKF to out-of-plane. The extent of SKF's bridging phenomenon may be influenced by the amount and orientation of SKF. G_IC showed no significant effect with SKF and uniform irrespective of crack length. Scanning electron microscopy after G_IIC test showed that new surfaces were created by extensive fiber bridging, pull-out and fracture of SKF in random direction without any fixed pattern. © 1997 John Wiley & Sons, Ltd.     

热塑性淀粉/聚丁二酸丁二醇酯合金的制备和结构性能表征

制备了高填充的甘油塑化淀粉（GTPS）/聚丁二酸丁二醇酯（PBS）合金,并对其结构性能进行了表征。结果表明：GTPS/PBS在合金加工过程中其扭矩以及力学性能随PBS质量分数的增加及甘油质量分数的减小而增大;扫描电镜（SEM）显示甘油可提高合金的相容性;动态力学分析（DMA）表明合金在玻璃态时的储存模量高于纯PBS,黏流态时则相反;合金的热稳定性随PBS和甘油质量分数的增加而有所提高;PBS的加入将合金的吸水率由100%以上降低到10%以下;淀粉和甘油的存在则均可提高PBS的降解率。     

Interlaminar Fracture Toughness Characterization of Laminated Composites: A Review

Abstract

Interlaminar fracture toughness had been the subject of great interest for several years and is still interesting to the research community. In this article, a comprehensive analysis of fracture toughness in FRP laminates is presented. Primarily, toughness studies are undertaken on glass and carbon fiber reinforced composites under mode-I and mode-II loading conditions. The fracture behavior and its failure pattern depend on a number of parameters: fiber sizing/coating, matrix modification, insert film, fiber volume fraction, stacking sequence, specimen geometry, loading rate and temperature change. In fact, a state-of-the-art process enables increasing fracture resistance with “matrix toughening by carbon nanotubes (CNT) inclusion”. It enables production of materials having ultra-high strength and low weight. The present study has highlighted the available techniques of CNT incorporation: mechanical mixing, grafting and interleaving. Other aspects, such as the dispersion level, matrix viscosity, fiber surface roughness, loading weight %, bonding strength with epoxy, height and density of grown CNT, energy absorption mechanism during delamination, etc., have been examined as well. Although a clear correlation of all these parameters with fracture toughness is hard to establish, there is growing understanding of the surface-grown CNTs and interleaving processes as they ensure significant increase in fracture toughness.     

Effect of Fiber-Polymer Interactions on Fracture Toughness Behavior of Carbon Fiber-Reinforced Epoxy Matrix Composites

The effect of anodic oxidation on high-strength polyacrylonitrile-based carbon fibers has been studied in terms of fiber surface energetics and fracture toughness of the composites. According to contact angle measurements based on the wicking rate of a test liquid, anodic oxidation leads to an increase in surface free energy, mainly due to the increase of its specific (or polar) component. For the carbon-fiber-reinforced epoxy resin matrix system, a direct linear relationship is shown between the specific component and the critical stress intensity factor measured by the single edge notched beam fracture toughness test. From a surface-energetic point of view, the anodic treatment may be suitable for carbon fibers incorporated in a polar organic matrix, resulting in an increased specific component of the surface free energy. Good wetting plays an important role in improving the degree of adhesion at interfaces between fibers and matrices of the resulting composites. Copyright 2000 Academic Press.     

Mechanical and Morphological Properties of Bio-Phenolic/Epoxy Polymer Blends

Polymer blends is a well-established and suitable method to produced new polymeric materials as compared to synthesis of a new polymer. The combination of two different types of polymers will produce a new and unique material, which has the attribute of both polymers. The aim of this work is to analyze mechanical and morphological properties of bio-phenolic/epoxy polymer blends to find the best formulation for future study. Bio-phenolic/epoxy polymer blends were fabricated using the hand lay-up method at different loading of bio-phenolic (5 wt%, 10 wt%, 15 wt%, 20 wt%, and 25 wt%) in the epoxy matrix whereas neat bio-phenolic and epoxy samples were also fabricated for comparison. Results indicated that mechanical properties were improved for bio-phenolic/epoxy polymer blends compared to neat epoxy and phenolic. In addition, there is no sign of phase separation in polymer blends. The highest tensile, flexural, and impact strength was shown by P-20(biophenolic-20 wt% and Epoxy-80 wt%) whereas P-25 (biophenolic-25 wt% and Epoxy-75 wt%) has the highest tensile and flexural modulus. Based on the finding, it is concluded that P-20 shows better overall mechanical properties among the polymer blends. Based on this finding, the bio-phenolic/epoxy blend with 20 wt% will be used for further study on flax-reinforced bio-phenolic/epoxy polymer blends.     

环氧树脂共混物相结构的调控方法研究

研究了环氧树脂(E51)/聚砜(PSF)共混物相结构的控制方法.通过抑制相分离、控制预固化的反应程度控制环氧树脂的分子量,固化后可获得不同的共混物相结构.依据红外测定的固化反应程度设定固化程序,可有效控制共混物的相结构.加入促进剂三氟化硼-乙基胺(BTF-EA)可提高固化反应速度,使相分离结构在早期被抑制,以获得小微区的相结构.     

Preparation and Characterization of Cyclohexyl Moiety Toughened POSS-Reinforced Epoxy Nanocomposites

Polyhedral oligomeric silsesquioxane (POSS)-reinforced epoxy nanocomposites were prepared by reacting commercially available diglycidyl ether of bisphenol-A (DGEBA) and tetraglycidyl diamino diphenyl methane (TGDDM) epoxy resins with 1,1-bis(3-methyl-4-glycidyloxyphenyl)cyclohexane (Cy-Ep) separately and reinforced with POSS nanocluster. POSS (OAPS)-reinforced hybrid Cy-Ep-epoxy resin castings were characterized for their mechanical and morphological properties. The data obtained from mechanical studies indicated that the incorporation of nano OAPS into Cy-Ep modified hybrid systems results in improved stability. Among the epoxy systems studied, the TGDDM-based hybrid epoxy system exhibited higher values of tensile and flexural properties than that of the DGEBA hybrid epoxy system, whereas the impact strength of the DGEBA system was higher than that of the TGDDM system. The dispersion of POSS was confirmed by scanning electron microscopy and visual observation studies.     

Morphology Evolution during the Phase Separation of Polyetherimide/Epoxy Blends

The results of time‐resolved light scattering for the phase separation of epoxy/polyetherimide/anhydride blends show that the evolution of scattering vector q_m follows a Maxwell‐type relaxation equation. The relaxation time may be suggested as the time taken for the diffusion of the epoxy‐anhydride n‐mers from the PEI‐rich phase by their relaxation movement, and the apparent activation energy of the relaxation movement is obtained.

Values of q_m versus time at different temperatures.     

Acrylic Terpolymer-Based Blends with Improved Properties

Blending of acrylic terpolymer (AT) with vinyl acetate-vinyl chloride (VAc-VC) copolymer, polyvinyl alcohol (PVA) polymer, and polyvinyl acetate (PVAc) polymer, respectively, resulted in sealant compositions with improved properties and enhanced outdoor weathering resistance. The morphology of these blends was studied by SEM, energy-dispersive x-ray analysis (EDXA), and DSC. The blends are heterogeneous and consist of a continuous phase which is either pure or mixed AT and a particulate phase having the morphology of the added component. The particulate phase of AT and AT-(VAc-VC) copolymer blends contains mixed AT, whereas that of AT-PVA and AT-PVAc does not. The AT-based blends have generally improved mechanical properties (e.g., ultimate tensile strength, adhesive strength). The improvement in mechanical properties is particularly strong in mixtures of AT with (VAc-VC) copolymer, probably because the added component has greater specific interaction capabilities with AT than the polymers incorporated in the other blends. Whereas the unblended AT has very low outdoor durability, the AT-based blends display enhanced resistance to weathering, as evidenced by substantially higher ultimate tensile strength of weathered specimens than those of the controls (unweathered).     

Epoxy resins (DGEBA): The curing and physical aging process

Differential scanning calorimetry (DSC) and infrared spectroscopy (IR) were used to monitor the degree of cure of partially cured epoxy resin (Epon 828/MDA) samples. The extent of cure, as determined by residual heat of reaction, concurred with that determined by monitoring the infrared radiation absorbance of the epoxide group near 916 cm^?l. The fictive temperature T_{f, g} was found to increase with the degree of cure, increasing rapidly during cure until reaching a value near the cure temperature T_c of 130°C (approximately 80% cure) where the material vitrified. The greatly reduced reaction rate during the final 20% of cure was not only a consequence of vitrification but, as revealed by infrared spectroscopy, the result of the depletion in the number of reactive epoxide groups. The endothermic peak areas and peak temperatures evident during the DSC scans were used as a measure of the extent of “physical aging” which took place during the cure of this resin, and after, fully cured samples were aged 37°C below their ultimate glass temperature for various periods of time. The rate of physical aging slowed as the temperature increment (T_t,g ? T_c) increased. Although an endothermic peak was evident after only 1 h of cure (T_{f, g} = 138.3°C), such a peak did not appear until fully cured samples were aged for 16 h or more. Enthalpy data revealed that for partially cured material, the fictive temperature T_{f, a}, reflecting physical aging, increased with curing time. In contrast, the T_{f, a}, for fully cured samples decreased with sub-T_g aging time. The characteristic jump in the heat capacity ΔC_p which occurred at the T_{f, g} decreased as curing progressed. This decrease appears to be dependent upon the rotational and vibrational degrees of freedom of the glass. Finally, a graphical method of determining the fictive temperature T_{f, a}, of partially and fully cured epoxy material from measured endothermic peak areas was developed.     

Fracture Behavior of Covalently Re-Modified MWNT/Epoxy Nanocomposites

Summary: In this work, a surface re-modified multi-walled carbon nanotube (MWNT) was prepared by the chemical attachment of oligomeric unsaturated polyester on the MWNT surface. The re-modified MWNT was incorporated in two concentrations of 0.35 and 0.70 Wt.% into epoxy resin in order to investigate its effect on morphology and mechanical behavior of the MWNT/epoxy nanocomposite. The transmission electron microscopy showed that the re-modification of MWNT surface improves its dispersion state in the epoxy matrix. The tensile measurements for the nanocomposite having different amounts of surface re-modified/not-modified MWNT showed that the fracture mechanism changed from brittle to tough beyond a certain amount of surface re-modified MWNT. The scanning electron microscopy findings on the fracture surface morphology of the resulted nanocomposite substantiated the observed phenomena.     

丙烯酸化环状磷腈/环氧丙烯酸酯光固化体系热降解动力学研究

以TGA为手段, 进行了丙烯酸化环状磷腈/环氧丙烯酸酯光固化体系热降解动力学的研究, 同时与加入粉末状环状磷腈混合体系进行了对照. 采用Kissinger, Flynn-Wall-Ozawa和Friedman三种方法计算了固化膜降解反应活化能, 证明了磷腈结构的引入, 使得体系在高温阶段的活化能有所提高, 表明降解变得困难, 热稳定性得到提高. 而反应型丙烯酸化环状磷腈相对粉末状环状磷腈混合体系具有更高的降解活化能.