Organo-Mineral Composite Materials Based on Sodium Liquid Glass,Tolylene-2,4-diisocyanate,Epoxy Oligomer,and Polyisocyanate

Organo-mineral composite materials based on sodium liquid glass combined with tolylene-2,4-diisocyanate (TDI), polyisocyanate, and epoxy oligomer have been synthesized. When heated, the organic components of the composites form a polymer network through the trimerization reaction and TDI curing of the epoxy oligomer. The composite materials after heating to 130°C have a uniform structure. The resulting hybrid composite materials are not brittle and exhibit enhanced heat resistance as compared to common polyisocyanurate compositions. Hybrid composites can find wide application in various fields of engineering.     

Effect of functionalized multiwalled carbon nanotubes on the feasibility of fabrication of composite glass fiber reinforced plastic rebars

The effect of COOH-functionalized multiwalled carbon nanotubes on the temperature–velocity conditions of the fabrication of composite glass fiber reinforced plastic rebars (so-called needletrusion) used in building was studied. EPIKOTE 862 epoxy oligomer (Bisphenol F diglycidyl ether) in combination with EPICUREW curing agent (aromatic diamine) in 100 : 26.4 ratio was used as binder. The use of functionalized multiwalled carbon nanotubes as additives to the unmodified epoxy binder for fabrication of composite materials by needletrusion allows production of high-quality items with the required characteristics without loss in the production capacity. It is preferable to introduce nanotubes in an amount of no more than 0.2 wt %.     

Synthesis and mechanical behavior of functionally gradient polyisocyanurate materials based on hydroxy-terminated butadiene rubber

Functionally gradient polyisocyanurate-based structural materials in which the modulus of elasticity could be arbitrarily varied over a continuos range from 3 to 2000 MPa were prepared from hydroxy-terminated butadiene rubber and diphenylmethane diisocyanate. The materials are synthetically obtainable both via bulk polymerization (molding) and as composite materials with fillers of any type, including both highly porous compliant fillers that have no effect on the mechanical properties of the polymer matrix and reinforcing fillers, such as carbon and glass clothes. The trends in the main properties were studied; it was found that, over the entire range of elastic moduli relevant to the glass-to-rubber transition, the materials retain the elastic behavior inherent in polymer glasses, not the viscoelastic behavior characteristic of the transitional region between the glassy and rubbery states.     

Effect of Non-Woven Carbon Nanofiber Mat Presence on Cure Kinetics of Epoxy Nanocomposites

Summary : An investigation was carried out into the cure kinetics of carbon nanofiber (CNF) mat-epoxy nanocomposites, composed of bisphenol-A based epoxy resin and diethylene triamine as a curing agent. It was observed that the rate of cure reaction for CNF mat-epoxy nanocomposites was higher than that for neat epoxy resin at low curing temperatures and the presence of the CNF mat produced the maximum influence at a certain curing temperature and time. At high curing temperature and long curing times, the effect of CNF mat on the cure rate was insignificant. The CNF mat-epoxy composite exhibited somewhat lower value of activation energy than that of the neat epoxy system at the beginning of the curing stage. The weight fraction of CNF mat also affected the cure reaction of epoxy nanocomposites at the same curing temperature. As the amount of CNF mat increased, the cure rate was higher at the same cure time. However, at high CNF mat loading, the cure reaction was retarded since the amount of epoxy and hardener decreased dramatically at high CNF contents together with the hindering effect of the CNF mat on the diffusion of epoxy resin and the curing agent, leading to lower crosslinking efficiency. Although the curing efficiency of epoxy nanocomposites dropped at high CNF mat content, the glass transition temperature (T_g) was still high due to the ultra-high strength of the CNF mat. The cure kinetics of CNF mat-epoxy nanocomposites was in good agreement with Kamal's model.     

Automatic control systems for technological processes of curing products made of polymeric composites

The system of classification of the main types of automatic control systems for curing regimes of the products made of polymeric composite materials has been examined. The methods of formation of control signals have been determined. The means of controlling and taking into account exothermic effects arising in the curing process on the accuracy of controlling the temperature-time regimes of the technological processes have been studied. Hybrid composite materials based on epoxy binder with carbon and organic fibrous fillers used in rocket and space production have been considered as objects of study.     

Temperature effect during humid ageing on interfaces of glass and carbon fibers reinforced epoxy composites

Weight change behavior of fiber-reinforced polymer composites in humid and thermal environments appears to be a complex phenomena. The state of fiber/matrix interface is believed to influence the nature of diffusion modes. A significant weakening often appears at the interface during the hygrothermal ageing. It effects the moisture uptake kinetics and also the reduction of mechanical properties. The importance of temperature at the time of conditioning plays an important role in environmental degradation of such composite materials. An attempt has been made here to evaluate the deleterious effect of temperature on shear strength of carbon/epoxy and glass/epoxy composites during hygrothermal conditionings. Mechanical tests were conducted at room temperature to assess the effectiveness of the relaxation process in the nullification of environmentally-induced damage in the composites.     

Kinetic study of epoxy curing in the glass fiber/epoxy interface using dansyl fluorescence

The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.     

Features of formation and viscoelastic properties of epoxyurethanes based on aliphatic cyclocarbonate oligomers

By the methods of dynamic mechanical analysis (DMA) and IR spectroscopy, the kinetics of curing and viscoelastic properties of epoxy urethanes of network structure based on epoxy diane resin and bifunctional oligocyclocarbonates (OCCs) are studied. The dependence of glass transition temperature and gel fraction of the obtained polymer on the amount of injected cyclocarbonate is established. It is shown that modification of epoxy diane oligomer by aliphatic OCCs results in an increase in its mechanical properties, particularly cohesive strength.     

The nature of the structural gradient in epoxy curing at a glass fiber/epoxy matrix interface using FTIR imaging

The curing process of an epoxide system was studied at the interface formed between a silane-coated glass fiber and an epoxy matrix. The gradient in the structure of the epoxy resin as a result of the cure process at the fiber/matrix interfacial region was monitored by FTIR imaging. For comparison, the epoxy curing at the interface formed between the epoxy resin and (a) an uncoated glass fiber and (b) a polyorganosiloxane (obtained from the silane used for the glass-fiber coating) were also monitored. Chemically specific images of the OH and the H-N-H groups near the interface region were obtained. These images suggest that there is a chemical gradient in the structure of the matrix from the fiber surface to the polymer bulk due to different conversions. The basis of the different kinetics of the curing reactions is a result of amino group inactivation at the interface. This deactivation translates into an off-stoichiometry of the reaction mixture, which is a function of the distance from the surface of the glass fiber.     

Multi-walled carbon nanotubes functionalized with triethylenetetramine as fillers to enhance epoxy dimensional thermal stability

Multi-walled carbon nanotubes (MWCNT) have been used as fillers to improve thermal properties such as glass transition temperature (T _g) of epoxy materials. In this work, nanocomposites based on diglycidyl ether of bisphenol A resin and triethylenetetramine (TETA) were prepared by a three-roll mill process with TETA-functionalized (MWCNT–COTETA) and neat MWCNT. Thermogravimetric analysis of the nanofillers showed that in the case of MWCNT–COTETA, there is a 15 % mass loss that can be attributed to –COTETA and residual oxygen-containing functional groups. The influence of chemical modification on the behavior of the glass T _g was evaluated by dynamic scanning calorimetry. The MWCNT–COTETA allowed a ~20 °C reproducible increase of T _g in concentrations in the range of 0.5–1.0 mass%. Furthermore, images obtained by scanning electron microscopy were used to investigate the morphology of the polymer matrix and its interfaces. The quality of the dispersion and interaction of the nanotubes in the epoxy matrix was assessed from the images. Both the neat epoxy and the nanocomposite with MWCNT showed low thermal shrinkage upon curing.     

The crosslinking of epoxy resins at interfaces. II. At an aromatic polyamide surface

The first 200–400 nm of crosslinked epoxy resin adjacent to an aromatic polyamide (aramid) surface were characterized by internal reflection spectroscopy (IRS) using an aramid-coated IRS element. The crosslinking kinetics and final crosslinked state of an anhydride-cured epoxy resin were strongly affected by the aramid surface, which produced a localized increase in the rate of anhydride consumption and a decrease in the yield of ester products. An aromatic amine-cured epoxy resin was less affected by the aramid surface. Unidirectional aramid fiber:epoxy composites were examined by dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). The chemical changes detected spectroscopically were shown to correlate with mechanical and thermal transition data obtained by DMA and DSC. These results are rationalized on the basis of the effect of absorbed moisture in the aramid on the crosslinking chemistry.     

Physical principles of catalysis of the curing of epoxy polymers in the presence of carbon nanotubes

A structural interpretation of the catalytic action of carbon nanotubes on the curing of epoxy polymers is proposed. It is based on the fractal analysis ideas. It is shown that essentially the only factor determining the kinetics of the curing process is the microgel structure characterized by its fractal dimension. The most important conclusion from the obtained results is the fact that the reaction rate dependences on the structural parameters are described by the same correlation for the epoxy polymer curing reaction both in the presence and absence of carbon nanotubes. This means that the catalytic effect of carbon nanotubes consists in a change in the structure of microgels.     

基于松香酸酐的环氧树脂体系固化动力学及TTT图绘制

研制了基于松香酸酐固化剂的生物质环氧树脂体系,采用全动态DSC法研究了树脂体系的固化反应动力学,通过半经验的唯象模型拟合得到了固化反应参数,活化能Ea为59.68 kJ/g,指前因子A0为1.28×1015s-1,反应级数n为2.483,由此建立了体系固化温度/时间/固化度间的关系;采用恒温DSC及DMA方法测试玻璃化转变温度,应用DiBenedetto经验方程拟合得到了玻璃化转变温度与固化度间的关系.应用锥板旋转黏度计测试了树脂体系不同温度下的凝胶时间,通过线性回归分析得到了凝胶时间与温度之间的关系.由唯象模型和DiBenedetto方程分别计算得到凝胶时的固化度为0.386,玻璃化转变温度为26.22°C.由上述工作绘制了基于松香酸酐生物质树脂体系的TTT(time-temperature-transition diagram)固化图,可确定树脂体系在不同温度任意时间下的状态.     

Specificity of the application of disperse and fibrous fillers in heterophase polymer materials

The mechanism of the reinforcing effect of fillers in polymer composition is studied and the relation between the properties and structure of materials is established. It is shown that, upon the addition of even a small amount of filler, properties of polymers change markedly due to intermolecular interactions. Variations in the composition of filled polymers and conditions of their preparation make it possibly to regulate properties of polymers within noticeably wide ranges. Specific features of polymer compositions filled with polymer fibers, the effect of fiber length, and the degree of orientation on the strength of composition are considered. For crosslinked epoxy urethane polymers, the effect of glass and polycaproamide (capron) fibers on the mechanical properties of polymer clutches in glassy and rubbery states is studied. The possibility to realize the shape memory effect for shrinkable filled polymer clutches is demonstrated.     

Mechanical property evaluation of glass–jute fiber reinforced polymer composites

The natural fibers such as jute, coir, hemp, sisal etc. are randomly used as reinforcements for composite materials because of its various advantages such as low cost, low densities, low energy consumption over conventional fibers. In addition, they are renewable as well as biodegradable, and indeed wide varieties of fibers are locally available. In this study, glass–jute fiber reinforced polymer composite is fabricated, and the mechanical properties such as tensile, flexural and impact behavior are investigated. The materials selected for the studies were jute fiber and glass fiber as the reinforcement and epoxy resin as the matrix. The hand lay‐out technique was used to fabricate these composites. Fractured surface were comprehensively examined in scanning electron microscope (SEM) to determine the microscopic fracture mode. A numerical procedure based on the finite element method was then applied to evaluate the overall behavior of this composite using the experimentally applied load. Results showed that by incorporating the optimum amount of jute fibers, the overall strength of glass fiber reinforced composite can be increased and cost saving of more than 30% can be achieved. It can thus be inferred that jute fiber can be a very potential candidate in making of composites, especially for partial replacement of high‐cost glass fibers for low load bearing applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Study of the fire resistant behavior of unfilled and carbon nanofibers reinforced polybenzimidazole coating for structural applications

With increasing interest in epoxy‐based carbon fiber composites for structural applications, it is important to improve the fire resistant properties of these materials. The fire resistant performance of these materials can be improved either by using high performance epoxy resin for manufacturing carbon fiber composite or by protecting the previously used epoxy‐based composite with some fire resistant coating. In this context, work is carried out to evaluate the fire resistance performance of recently emerged high performance polybenzimidazole (PBI) when used as a coating material. Furthermore, the effect of carbon nanofibers (CNFs) on fire resistant properties of inherently flame retardant PBI coating was studied. Thermogravimetric analysis of carbon/epoxy composite, unfilled PBI and nano‐filled PBI shows that the carbon/epoxy composite maintained its thermal stability up to a temperature of 400°C and afterwards showed a large decrease in mass, while both unfilled PBI and nano‐filled PBI have shown thermal stability up to a temperature of 575°C corresponding to only 11% weight loss. Cone calorimeter test results show that unfilled PBI coating did not improve the fire retardant performance of carbon/epoxy composite. Conversely, nano‐filled PBI coating has shown a significant improvement in fire retardant performance of the carbon/epoxy composite in terms of increased ignition time, reduced average and peak heat release rate and reduced smoke and carbon monoxide emission. These results indicate that addition of carbon nanofibers to inherently flame retardant coating can significantly be helpful for improving the fire resistance performance of composite materials even with low coating thickness. Copyright © 2013 John Wiley & Sons, Ltd.     

Residual stresses at hardening of disperse-filled epoxy systems

The influence of MS-VP-A9 brand hollow glass microspheres and curing temperature on the kinetics of growth of residual stresses in disperse-filled polymer composites based on DER-330 and ED-20 epoxy oligomers was considered. It was shown that the introduction of hollow glass microspheres and change of generalized parameters of structure leads to a decrease of the level of residual stresses by approximately half during curing, differing in average molecular weight, molecular-weight distribution, and content of associates.     

碳纳米管改性环氧树脂的导热和阻燃性能

以双酚A二缩水甘油醚(DGEBA)环氧树脂(Epoxy Resin,EP)为基体、甲基六氢苯酐(MHHPA)为固化剂、以多壁碳纳米管(MWCNTs)为添加剂制备了环氧树脂/碳纳米管纳米复合材料。通过对微观结构、玻璃化转变温度(Tg)、热失重、热导率和锥形量热测试结果分析,研究了质量分数少于1.5%的MWCNTs对环氧树脂的导热和阻燃性能影响,结果表明,MWCNTs质量分数为1.5%时,复合材料发生团聚;纳米复合材料随着MWCNTs质量分数的增加Tg值先增加后降低;失重5%时,对应的温度先增加后降低,残炭量增加;样品的热导率呈现先升高后降低的趋势,当MWCNTs质量分数为1%时,复合材料的热导率最大;MWCNTs加入后环氧树脂的总释热量减少,释烟量增加,阻燃性得到一定程度的提高。     

Properties and structural features of nanodisperse powder fillers

Comparative characteristics of polymer materials based on epoxy binder reinforced by disperse and fiber fillers are given. The structural features of nanopowders of aluminum oxide and copper are considered with the aim to use them as nanofillers of polymer materials. The dependence of structures of nanopowders under investigation on the change of their specific surface is shown. The fractional composition of aluminum oxide is analyzed, and particle sizes of fine and coarse fractions are found.     

Calorimetric investigation of polymerization reactions. III. Curing reaction of epoxides with amines

The curing reactions of epoxy resin with aliphatic diamines and the reaction of phenyl glycidyl ether with butylamine as a model for the curing reactions were investigated with a differential scanning calorimeter (DSC) operated isothermally. The heat of reaction of phenyl glycidyl ether with butylamine is equal to 24.5 ± 0.6 kcal/mole. The rate of reaction was followed over the whole range of conversion for both model and curing reactions. The reactions are accelerated by the hydrogen-bond donor produced in the system. The rate constants based on the third-order kinetics were determined and discussed for the model reaction and for the chemically controlled region of curing reactions. The activation energies for these rate constants are 13-14 kcal/mole. At a later stage of conversion, the curing reactions become controlled by diffusion of functional groups. The final extent of conversion is short of completion for most isothermally cured and even for postcured samples because of crosslinking. It was quantitatively indicated that the final conversion of isothermal cure corresponds to the transition of the system from a viscous liquid to a glass on the basis of the theory of glass transition temperature of crosslinked polymer systems.