Investigation of the microwave curing of the PR500 epoxy resin system

Microwave heating has been used to cure a resin system, PR500 (3M). The same resin has been cured using a conventional oven. The cured resins have been compared using a number of techniques including modulated differential scanning calorimetry (MDSC), dynamic thermal analysis, infrared spectroscopy (IR) and solid-state NMR spectroscopy. The reaction path appears to be slightly different depending upon the nature of the heating. The epoxy-amine reaction occurs to a greater extent than the epoxy-hydroxyl reaction in the microwave cured resin compared to the thermally cured resin. The dielectric properties for the thermally and microwave cured materials were measured for degrees of cure greater than 75% and over this range are similar for materials cured by the two techniques and thus not sensitive to this change. Broadening of the glass transition for microwave-cured epoxy resins was observed. Since the IR and solid-state NMR results show small differences as does the DMA behaviour of materials cured using the two routes the broadening is attributed to a difference in network structure.     

Evolution of viscoelastic behaviour of a curing LY5052 epoxy resin in the rubbery state

In this work, we investigate the relationship between the rubbery modulus and the degree of cure for partially to fully cured LY5052 epoxy resin. In particular, this paper experimentally tests an existing model formulated for shear modulus by redefining for in the tensile storage modulus. Experiments to characterize viscoelastic behaviour were performed in a dynamic mechanical and thermal analysis (DMTA) instrument in the frequency domain. Master curves are then created from DMTA using general time–temperature–cure superposition. The master curves are then normalized using the model so that the master curve does not depend on the properties in the rubbery region. This results in a unique master curve that describes the viscoelastic behaviour of the LY5052 epoxy resin for the given conditions. Once the relationship between the rubbery modulus and the degree of cure has been established, the amount of experimental characterization can be reduced. This could lead to the development of simplified experimental methodologies and simplified models to characterize the viscoelasticity of low molecular weight resins like the LY5052 epoxy resin system.     

一种耐高温加成固化型酚醛树脂作为复合材料基体的评价

制备了烯丙基化程度可达 173%的烯丙基酚醛树脂(AN173),并与双马来酰亚胺(BMI)以 1 ∶1 的质量比进行共聚,制备了双马改性的烯丙基酚醛树脂(BMAN173) 。研究了该树脂工艺性,确定了其固化制度,考察了该树脂石英布复合材料层合板的耐热性和力学性能。实验结果表明,BMAN173 树脂具有良好的工艺性,适合于RTM、模压成型等多种成型工艺。BMAN173树脂固化物表现出良好的耐热性,其储能模量起始下降温度约为390℃, 起始热分解温度超过430℃。与传统酚醛树脂相比,该树脂的复合材料的高温力学性能优异,350℃弯曲强度和层间剪切强度保留率分别约为57%和62%;复合材料具有优异的热性能,其储能模量起始下降温度约为410℃,玻璃化转变温度超过了450℃。BMAN173树脂是耐高温复合材料的理想候选基体树脂。     

Excellent flexural properties of aminimide-cured epoxy resin as a matrix for mica-dispersed polymer composites

The flexural behaviour of mica-dispersed epoxy resin composites has been examined. The flexural strength and flexural modulus have been determined as a function of the volume fraction of mica flakes (V _f) for both aminimide-cured epoxy resin matrix and a conventional epoxy resin reference matrix. On the basis of microscopic observation of fractured surfaces, the effect of improving the particle-matrix interface has been analysed using the modulus reduction factor (MRF) in a modified form. It is found that there is a steady increase in the flexural modulus with the volume fraction of mica flake for the aminimide-cured epoxy resin matrix. In contrast, the increase in flexural modulus levels off at a high content of filler for the reference samples. It is noteworthy that the intact mica flakes without surface treatment exhibit a substantial reinforcing effect on the flexural strength in the case of aminimide-cured epoxy resin composites. A further surprise is the difference among the curing agents used. The reference epoxy resins behave just like conventional matrix resins, exhibiting 30 to 40% reduction in the flexural strength when a small fraction of mica is added. These superior properties of the matrix resin for the composites are ascribed to the characteristics of aminimide-cured epoxy resins such as hardness, toughness, and excellent adhesivity.     

Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating

Microwave processing holds great potential for improving current composite manufacturing techniques, substantially reducing cure cycle times, energy requirements and operational costs. In this paper, microwave heating was incorporated into the resin transfer moulding technique. Through the use of microwave heating, a 50% cure cycle time reduction was achieved. The mechanical and physical properties of the produced carbon fibre/epoxy composites were compared to those manufactured by conventional resin transfer moulding. Mechanical testing showed similar values of flexural moduli and flexural strength for the two types of composites after normalisation of the corresponding data to a common fibre volume fraction. A 9% increase of the interlaminar shear strength (ILSS) was observed for the microwave cured composites. This enhancement in ILSS is attributed to a lowering of resin viscosity in the initial stage of the curing process, which was also confirmed via scanning electron microscopy by means of improved fibre wetting and less fibre pull-out. Furthermore, both types of composites yielded minimal void content (<2%). Dynamic mechanical thermal analysis revealed comparable glass transition temperatures for composites produced by both methods. A 15 °C shift in the position of the β-transition peak was observed between thermally and microwave cured composites, suggesting an alteration in the cross-linking path followed.     

The evaluation of some flexural properties of a denture base resin reinforced with various aesthetic fibers

This study was performed to determine whether some flexural properties of a denture base resin material could be improved through reinforcement with five types of aesthetic fibers at 3% concentration by weight and in 2, 4, and 6 mm length. Five specimens of similar dimensions were prepared for each of the test groups; base resin and the same resin with glass, rayon, polyester, nylon 6 and nylon 6,6 fibers in three different lengths. Flexural properties were evaluated by using a 3-point bending test. A visual examination was also made to determine mode of fracture of the specimens. The incorporation of different fibers in varying lengths had no significant effect on flexural strength of the resin. The specimens reinforced with nylon 6,6 fibers of 6 mm length showed the highest flexural strength. Young’s modulus and maximum load suggests that such reinforcement makes resin resistant to fracture.     

Fibre reinforcement in heat-cured,microwave-cured and visible light-cured base resins

The mechanical properties at transverse deflection, bending and impact tests were examined in three fibre reinforced resins including reinforcing materials such as inorganic glass fibre and cloth, organic Kevlar fibre and combined fibres. Both heat-cured and microwave-cured reinforced materials had almost the similar pattern to the changes in the mechanical properties, as compared with those in visible light-cured reinforced resin. Their reinforcing materials increased modulus and impact energy by about two times as compared with the bases. The visible light-cured resin was, however, not effective as a base resin when reinforced with fibres tested here, indicating that the transverse deflection and modulus values in light-cured reinforced resin were similar to that in the plain base resin.     

Mechanical and morphological properties of fly ash/epoxy composites using conventional thermal and microwave curing methods

Conventional thermal and microwave curing methods were utilized to cure fly ash/epoxy composites, and the mechanical and morphological properties of the composites were evaluated. The conventional thermal curing was performed at 70 °C for 80 min while microwave curing was carried out at 240 W for 18 min in order to achieve the optimum cure of the composites, determined using Differential Scanning Calorimeter. The results suggested that the tensile and flexural moduli of the composites increased with increasing fly ash content while the effect became opposite for tensile, flexural and impact strengths, and tensile strain at break. Improved mechanical properties of the composite could be obtained by addition of N-2(aminoethyl)-3-aminopropyltrimethoxysilane coupling agent, the contents of 0.5 wt% being recommended for the optimum mechanical properties. Beyond these recommended contents, the mechanical properties greatly reduced, except for the flexural modulus. The comparative results indicated that the composites by the microwave cure consumed shorter cure time and had higher ultimate strengths (especially impact strength), and strain at break than those by the conventional thermal cure. The composites with higher tensile and flexural moduli could be obtained by the conventional thermal cure.     

Cure behaviour of visible light activated dental composites

In this paper, the non-isothermal cure behaviour of a dental composite, activated by visible light, is described using a heat transfer model that, coupled with a reaction kinetic expression, is able to predict the temperature and the degree of reaction in the composite. The temperature and the degree of reaction profiles inside the composite are calculated, as a function of the cure time, taking into account the system geometry, the thermal diffusivity of the composite, and the resin reaction rate. Material properties, boundary and initial conditions and the kinetic behaviour are the input data of the heat transfer model. Once the degree of reaction is known, the glass transition temperature profiles across the thickness of the composite are calculated. Experimentally measured glass transition temperatures are used for the evaluation of an extinction coefficient capable of accounting for the effects of the light absorption through the thickness on the polymerization kinetics. Finally, the effects of the non-isothermal cure conditions on the application of these materials in dental restorations are discussed.     

Morphology and properties of TGDDM/DDS epoxy systems toughened by amino-bearing phenyl silicone resins

A series of amino-bearing phenyl silicone resins (APSR) were synthesized for toughening the tetraglycidyl 4,4′-diaminodiphenyl-methane (TGDDM) epoxy resin cured with 4,4′-diamino diphenyl sulfone. The microstructure of the TGDDM/APSR resins was highly dependent on the amino content of APSR and the loading level of the modifier. Based on the SEM and TEM studies, microstructure evolution of the TGDDM/APSR resins in the curing process was imaged. The toughness of the TGDDM resin was effectively improved without sacrificing the tensile strength, the flexural strength, and the modulus. The thermal stability and water resistance were improved as well. However, the modifier brought in a noticeable lowering in the glass transition temperature.     

聚醚酰亚胺对氰酸酯树脂/环氧树脂共混物的增韧作用

采用聚醚酰亚胺以提高双酚Ａ二氰酸酯／酚醛环氧树脂共混物的断裂韧性．实验结果表明，聚醚酰亚胺是氰酸酯／酚醛环氧树脂共混物的有效增韧剂，加入１５％的聚醚酰亚胺可使断裂韧性（ＫＩＣ）提高到１４５ＭＰａ·ｍ０．５，弯曲强度也有所提高．用扫描电子显微镜和动态粘弹谱研究了改性共混物的微观结构，具有双连续结构的共混物的耐溶剂性能大大下降，共混物的韧性和耐溶剂性主要与相行为有关， 固化工艺对含１０％聚醚酰亚胺的共混物的断裂韧性和形态没有明显的作用．     

Syntactic foams from copolymers based on epoxidized soybean oil

Syntactic foams are been increasingly used as core of sandwich panels due to their light weight and good mechanical properties. This investigation evaluates the compressive, flexural and thermo-mechanical properties of syntactic foams made by embedding randomly dispersed hollow glass microspheres in bio-based resins obtained by partial substitution of diglycidyl ether of bisphenol A (DGEBA) with epoxidized soybean oil (ESO). Volume fraction of glass microballoons was 0.55 in all foam formulation. Flexural and compressive strength values decreased simultaneously with increasing ESO content. Similar trend was observed for the flexural and compressive modulus and glass transition temperature. The work further showed that mechanism of failure mainly depended on the fracture of microballoons regardless the ESO content in the formulation. Results reported herein suggest that large fractions of DGEBA can be replaced by ESO with minor effect on mechanical and thermal properties.     

Interactive effects of resin composition and ambient temperature of light curing on the percentage conversion,molar heat of cure and hardness of dental composite resins

The interactive effects of ambient temperature of cure and resin composition on the extent of cure are evaluated by the measurement of percentage conversion of double bonds, heat of cure and microhardness of visible light cure dental resin systems. Three bonding agents, including two BisGMA-based resins (Command Bond, Pentron Bond) and one urethane-dimethacrylate-based resin (Coe Bond), were evaluated. The results indicate a significant effect of ambient temperature of cure and resin composition on percentage conversion, molar heat of cure and microhardness. In the temperature range of 25–60 °C, thermal activation appears to be a promising approach to improve conversion and crosslinking in dental resins. At lower ambient temperatures of cure (25 °C), urethane dimethacrylate resin undergoes higher levels of conversion than BisGMA-based resins. At higher temperatures, the percentage conversion increases with temperature in all resins. However, the molar heat of cure and hardness values show a significant increase with temperature only in BisGMA-based resins, but not in the urethane dimethacrylate resin. The difference in percentage conversion and heat of cure variation with temperature and the similarity of the latter variation with that of microhardness, probably indicates that the heat of cure is a better predictor of the extent of cure in these thermoset resins. It appears that enhanced crosslinking due to thermal activation may significantly influence the extent of cure at higher ambient temperatures.     

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.     

稀释剂对环氧树脂电子束辐射固化性能的影响

对分别加入4 种稀释剂的双酚A 环氧树脂和酚醛环氧树脂的电子束辐射固化性能进行了研究。分析了稀释剂种类及含量对环氧树脂体系辐射产物的固化度、固化均匀性、固化区域大小及其动态力学性能的影响规律。结果表明: 电子束固化环氧树脂体系中加入稀释剂后, 辐射产物的固化度、玻璃化转变温度及储能模量有所下降, 但固化均匀性得到提高; 加入稀释剂的环氧树脂电子束固化区域的厚度均小于未加稀释剂树脂, 而底面直径却大于未加稀释剂树脂; 随着树脂中实际稀释剂含量的增加, 电子束固化环氧树脂固化度逐渐降低, 固化层厚度减小, 固化区域的底面直径先增加后减小。      

Application of Interlaminar Tests to Marine Composites. Relation between Glass Fibre/Polymer Interfaces and Interlaminar Properties of Marine Composites

The need for improved performance and the development of new composite manufacturing methods require a better understanding of the role of interface phenomena in the mechanical behaviour of these materials. The influence of the cure cycle on the bulk and surface properties of the matrix resin, and of composites based on polyester and epoxy resins reinforced with glass fibres has been studied. While the mechanical properties of the epoxy vary with cure temperature the surface tension is not affected. The increase in interfacial shear strength and interlaminar shear strength with increased cure temperature cannot be simply explained by the wetting of the fibres by the matrix. The importance of thermal stresses, generated at the interface by resin shrinkage and differences in thermal expansion, for the mechanical behaviour of the composite are demonstrated.     

Improvement of properties for biobased composites from modified soybean oil and hemp fibers: Dual role of diisocyanate

An environmentally friendly composite was developed from hemp fibers (HFs) and a biobased thermosetting resin that was formulated from the copolymerization of acrylated epoxidized soybean oil (AESO) and N-vinyl-2-pyrrolidone. The properties of the composites were enhanced through the incorporation of isophorone diisocyanate (IPDI). The FTIR and ¹³C NMR spectra reveal that the incorporated IPDI could react with the hydroxyl groups of both HFs and AESO by forming urethane connections; hence, IPDI plays two roles in composites, i.e., as a crosslinker and a coupling agent. The results show that both effects greatly contribute to increasing the tensile and flexural properties, storage modulus, and glass transition temperature of the resulting composites. However, the modification does not significantly influence the impact strength and slightly decreases the thermal stability of the composites. Further, the addition of IPDI into AESO resins results in resins with improved processability due to the lower viscosity and curing temperature.     

加成型酚醛改性双马树脂及其复合材料性能

双马来酰亚胺(BMI)树脂因其优异的性能已在航空航天、电子和其他工业领域获得应用,为满足其在高速飞行器结构件中需求,用加成型酚醛树脂改性BMI体系以改善其热-力学性能。通过Williamson醚化反应合成了炔丙基醚化酚醛树脂(PN)和烯丙基醚化酚醛树脂(AN),采用熔融共混法分别与N,N’-(4,4’-亚甲基二苯基)双马来酰亚胺(BDM)和2,2’-二烯丙基双酚A(DABPA)树脂体系(BD)共混,制备了三元热固性树脂：PN改性BD(BDPN)和AN改性BD(BDAN)。研究了两种加成型酚醛树脂改性的BD树脂体系的加工工艺性和固化行为的变化,并对改性前后固化树脂及其复合材料的热、力学性能进行了研究。结果表明：共混树脂体系都在极性溶剂中有好的溶解性,加工窗口都有50℃以上。BDPN和BDAN固化反应只有一个放热峰,最高放热峰值温度比BD树脂低。用FTIR跟踪验证了BD、BDPN和BDAN树脂体系发生的Ene、DielsAlder、Claisen重排和炔基与马来酰亚胺环的聚合反应。PN热氧稳定性好,改性的BDPN固化树脂空气中质量损失5wt%的温度(T_d5)高于400...     

Effect of reinforcement and solvent content on moisture absorption in epoxy composite materials

The effect of fibrous reinforcement and solvent content on moisture uptake in composite laminate was investigated. Two materials using identical epoxy resin systems but different reinforcements—glass vs. carbon fibers—and of different solvent content—low vs. normal—were examined. Samples were characterized in terms of water absorption and desorption. Mechanical and thermal properties including flexural modulus, flexural strength, and glass transition temperature were measured. Results clearly show the contribution of the fiber reinforcement as well as solvent content on the water absorption rate and mechanical property changes.     

The efficiency of various toughening agents in novel phenolic type thermoset resin systems

Two novel phenolic type thermosetting resin systems are investigated regarding the effectiveness of different toughness modifiers. These modifiers derive from different groups such as elastomers, thermoplastics, and core–shell polymers. Measurements are accomplished by mechanical, thermal, and microscopical studies. Toughness improvement is determined by increasing K _Ic and G _Ic values while glass transition temperature, flexural strength, and modulus must not suffer greatly. Suggestions on the mechanisms of toughness modification in the novel resins are made based on images from scanning electron microscopy.