微波技术在环氧树脂及其复合材料中的应用

论述了近年来微波固化技术在环氧树脂及其复合材料固化中的应用,重点比较了微波固化与传统热固化后环氧树脂及其复合材料的力学性能、热性能和粘结强度的变化,并对环氧树脂复合材料微波固化的研究进行了展望。     

环氧树脂/DMP30体系的微波固化及性能研究

针对目前环氧树脂/固化剂体系微波固化的研究现状,通过预凝胶处理和间歇固化相结合的方法,初步研究了环氧树脂/DMP30[2,4,6-三(二甲胺基甲基)酚]体系的微波固化条件,利用红外光谱研究了微波固化过程,并表征了产物的结构和力学性能。实验结果表明,与传统热固化相比,微波固化可以明显缩短固化时间、降低能耗;微波固化产物和热固化产物具有相同的产物结构;微波固化产物具有更高的弯曲模量和弯曲强度,热固化产物的冲击强度略高一些。     

环氧复合材料用微波固化技术及其展望

本文综述了近年来环氧复合材料微波固化的研究进展及应用现状,重点讨论了微波固化对环氧树脂及其复合材料固化体系的固化速率、固化物力学性能和热性能等的影响,并对环氧树脂复合材料微波固化的研究应用进行了展望。     

环氧树脂基复合材料的微波固化研究

微波固化具有速度快、固化均匀、效率高等优点,在聚合物特别是环氧树脂基复合材料的固化加工方面有很大潜力。本文介绍了微波加热原理以及环氧复合材料微波固化工程的基本理论,并对国内外环氧树脂基复合材料微波固化的最新研究进展及应用现状进行了综述。     

环氧树脂固化技术及其固化剂研究进展

综述了近年来国内外关于环氧树脂的热固化、微波固化及光固化技术的研究情况。在热固化技术领域 ,着重介绍了具有高耐热性、阻燃性、韧性等性能的几种功能性固化剂以及几种新型改性胺类固化剂 ;通过与热固化的对比 ,对环氧树脂的微波固化体系进行了初步的分析与探讨 ;在光固化技术领域则主要概述了环氧树脂的阳离子紫外光固化体系与自由基 -阴离子混杂光固化体系的进展情况     

一种可免低温存储的中温固化树脂固化动力学分析

环氧树脂体系(JH2160)为可免低温存储的一种低成本高性能环氧树脂体系。针对JH2160环氧树脂体系的常温储存进行6个月前后固化分析，可知储存半年后的树脂固化反应程度为13.3%,说明此环氧树脂体系常温贮存性好。利用非等温DSC方法对环氧树脂体系(JH2160)进行固化行为研究，使用T-β外推法确定环氧树脂体系(JH2160)的特征固化温度，用Kissinger法和Ozawa法计算体系的活化能分别为78.16kJ/mol和81.03kJ/mol,二者的平均结果得出体系的活化能为79.59kJ/mol;通过Crane法计算出环氧树脂体系(JH2160)反应级数为0.95,确定了JH2160环氧树脂体系的动力学模型。     

微波固化技术及其在聚合物中的应用

微波固化以加热速率快、固化物均一、热能利用率高和过程控制容易等优点,在聚合物及其复合材料加工方面逐渐得到广泛应用。综述了微波固化工艺以及固化物的理化性能等,着重介绍了微波固化技术在环氧树脂及其复合材料中的应用,指出了微波固化技术今后的研究方向。     

均苯四甲酸二酐固化环氧树脂的工艺及热性能

将均苯四甲酸二酐与环氧树脂溶于丙酮中,在一定的温度条件下反应,制备了均一的、有一定固化程度的环氧树脂溶液,该溶液可在常温固化。傅里叶变换红外光谱分析表明,所得产物与预期结构相同,最佳反应时间为6 h。采用差示扫描量热法研究其固化工艺,不同升温速率下,体系的固化温度不同,随升温速率增加,固化温度提升,通过动力学计算得到其固化工艺为100℃固化2 h,150℃固化2 h,后处理180℃固化2 h,按此工艺固化的环氧树脂的耐热性能优于常温固化,起始分解温度达到368℃。     

常温固化环氧树脂浇铸体的制备与力学性能

利用活性稀释剂在常温常压下合成了无气泡的环氧树脂浇铸体，测试了浇铸体的冲击、弯曲和压缩等力学性能，对环氧树脂的环氧值凝胶时间和固化配方进行了研究。结果表明：采用活性稀释剂配制的环氧—乙二胺固化体系有较好的常温固化性能，可用于常温固化粘合剂及物体表面防腐，通过纤维增强改性提高力学性能，可用于工程材料     

微波辐照技术在聚合物合成方面的研究及发展

综述了微波辐照技术在聚合物合成方面的研究状况,介绍了微波技术在本体聚合、乳液和溶液聚合及功能高分子合成方面的应用。在聚合物微波固化方面,重点介绍了环氧树脂及其复合材料的微波固化,简要地介绍了其它聚合物的微波固化。最后探讨了微波技术在未来的发展趋势。     

Microwave and conventional curing of thick‐section thermoset composite laminates: Experiment and simulation

In conventional processing, thermal gradients cause differential curing of thick laminates and undesirable outside‐in solidification. To reduce thermal gradients, thick laminates are processed at lower cure temperatures and heated with slow heating rates, resulting in excessive cure times. Microwaves can transmit energy volumetrically and instantaneously through direct interaction of materials with applied electromagnetic fields. The more efficient energy transfer of microwaves can alleviate the problems associated with differential curing, and the preferred inside‐out solidification can be obtained. In this work, both microwave curing and thermal curing of 24.5 mm (1 inch) thick‐section glass/epoxy laminates are investigated through the development of a numerical process simulation and conducting experiments in processing thick laminates in a conventional autoclave and a microwave furnace. Outside‐in curing of the autoclave‐processed laminate resulted in visible matrix cracks, while cracks were not visible in the microwave‐processed laminate. Both numerical and experimental results show that volumetric heating due to microwaves promotes an inside‐out cure and can dramatically reduce the overall processing time.     

Dielectric analysis of epoxy/amine resins using microwave cavity technique

Dielectric properties (permittivity and dielectric loss factor) of stoichiometric mixtures of DGEBA (diglycidylether of bisphenol A) epoxy (DER 332) and amine (diaminodiphenyl sulfone; DDS) as a function of temperature and extent of cure have been measured at a microwave frequency of 2.45 GHz. Permittivity and dielectric loss factor of this resin increase with increasing temperature and decrease with increasing extent of cure. Dielectric loss factor is more dependent on temperature in the early stages of cure but becomes less dependent on temperature as the cure proceeds. Dielectric loss data can be related to extent of cure in order to monitor the cure process. Online measurements of temperature- and cure-dependent dielectric loss factor show three material structure stages and significant changes in dielectric loss factor during the microwave cure process. Dielectric Joss factor is also found to be the same for both thermal and microwave cured samples.     

Kinetics modeling and time-temperature-transformation diagram of microwave and thermal cure of epoxy resins

Stoichimetric mixtures of a diglycidyl ether of bisphenol A (DGEBA)/ diaminodiphenyl sulfone (DDS) and a DGEBA/meta phenylene diamine (mPDA) were cured using both microwave and thermal energy. Fourier transform infrared (FTIR) was used for the measurement of the extent of cure and thermal mechanical analysis (TMA) was used for the determination of the glass transition temperature (T_g). The cure kinetics of the DGEBA/mPDA and DGEBA/DDS systems were described by an autocatalytic kinetic model up to vitrification in both the microwave and thermal cure. For the DGEBA/mPDA system, the reaction rate constants of the primary amine-epoxy reaction are equal to those of the secondary amine-epoxy reaction, and the etherification reaction is negligible for both microwave and thermal cure. For the DGEBA/DDS system, the reaction rate constants of the primary amine-epoxy reaction are greater than those of the secondary amine-epoxy reaction and the etherification reaction is only negligible at low cure temperatures for both microwave and thermal cure. Microwave radiation decreases the reaction rate constant ratio of the secondary amine-epoxy reaction to the primary amine-epxy reaction and the ratio of the etherification reaction to the primary amine-epoxy reaction. T_g data were fitted to the DiBenedetto model. A master curve and a time-temperature-transformation (TTT) diagram were constructed. The vitrification time is shorter in microwave cure than in thermal cure, especially at higher isothermal cure temperatures. For the DGEBA/mPDA system, the minimum vitrification time is two to five times shorter in the microwave cure than in the thermal cure. For the DGEBA/DDS system, the minimum vitrification time is 44 times shorter in the microwave cure than in the thermal cure.     

Spatial and temporal control of the degree of cure in polymer composite structures

This paper describes current efforts to apply spatially and temporally localized microwave processing techniques to ensure uniformity of material properties in polymer composite materials. In large polymer composite structures, high temperatures caused by exothermic resin cure can degrade the mechanical properties of the composite. In this work, resin cure temperature data was obtained during microwave processing from a series of thermocouples embedded at various lateral locations relative to the microwave source and uniformly through the thickness of the composite structure. Using this temperature information, the potential for localized microwave‐accelerated cure to reduce the occurrence of material degradation from resin over‐temperature was evaluated. In addition, a theoretical model is presented that helps elucidate the influence of the microwave parameters on the temperature profile.     

微波固化碳纤维/环氧树脂胶的研究

介绍了微波固化热固性树脂的原理和特点,利用微波炉设备和选择的一种较好微波吸收剂,探讨了微波固化工艺。研究表明,利用微波固化环氧胶时,不仅固化时间短,而且剪切强度优于加热固化。     

Comparison of the curing kinetics of a DGEBA/acid anhydride epoxy resin system using differential scanning calorimetry and a microwave‐heated calorimeter

The cure of an epoxy resin system, based upon a diglycidyl ether of bisphenol‐A (DGEBA) with HY917 (an acid anhydride hardener) and DY073 (an amine–phenol complex that acted as an accelerator), was investigated using a conventional differential scanning calorimeter and a microwave‐heated power‐compensated calorimeter. Dynamic cure of the epoxy resin using four different heating rates and isothermal cure using four different temperatures were carried out and the degree of cure and reaction rates were compared. The cure kinetics were analyzed using several kinetics models. The results showed different activation energies for conventional and microwave curing and suggested different reaction mechanisms were responsible for curing using the two heating methods. Resins cured using conventional heating showed higher glass transition temperatures than did those cured using microwave heating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2054–2063, 2007     

Dielectric studies of three epoxy resin systems during microwave cure

Dielectric properties of three curing epoxy resin systems at an industrial microwave frequency, 2.45 GHz, were measured over a temperature range lower than the cure temperature. Extent of cure, which is determined by DSC, is used to describe the progress of the polymerization. It has been found that, normally, the real and the imaginary part of the complex dielectric constant increased with temperature and decreased during microwave cure. The changes of the dielectric properties during the reaction are related to the decreasing number of the dipolar groups in the reactants and the increasing viscosity. The Davidson-Cole model can be used to describe the experimental data. The Zong model is applicable to polymeric materials at high microwave frequencies and can be used to calculate the parameters of the Davidson-Cole model. The epoxy resins exhibit one γ relaxation, which can be described by the Arrhenius rate law. The evolutions of the parameters in the models are discussed.     

The effect of microwave resin preheating on the quality of laminates produced by resin transfer molding

Cycle times in resin transfer molding (RTM) of an unsaturated polyester have been reduced significantly using an in-line microwave resin preheating system. Microwave preheating lowers the resin viscosity during injection and modifies the thermal age of the resin, potentially influencing the quality of RTM laminates. The tensile properties of RTM laminates have been measured with regard to improved fiber wet-out by the lower viscosity resin. Degree of cure measurements have been included to establish the effect of microwave preheating on resin conversion within the laminate. Local pressure that develops within the mold during the cure phase can lead to mold deflections. Variations in the laminate thickness associated with these deflections are presented, and the use of microwave resin preheating to reduce these variations is discussed.     

Comparison of microwave and thermal cure of an epoxy/amine matrix

An investigation was carried out into the effect ofa microwave cure on an epoxy prepolymer with a cycloaliphatic diamine mixture, as compared to a standard thermal cure. The microwave waveguide and process (propagation mode TE₀₁) were adjusted to obtain large homogeneous samples. The extent of reaction, x, was measured during the microwave processing by size exclusion chromatography and differential scanning calorimetry. A good estimate of x was found using a modified DiBenedetto equation correlating x and the glass transition temperature T_g. The homogeneity of the samples was checked during the last steps of cure, showing the efficiency of the microwave processing and waveguide. The influence of the nature of the mold (metallic or dielectric) on the reaction kinetic was also investigated. Samples cured by both thermal and microwave processing were characterized by dynamic and static mechanical properties and then compared with those of fully crosslinked networks, i.e., postcured at a high temperature.     

Comparison between microwave and thermal curing of a polyimide adhesive end-caped with phenylethynyl groups

Microwave energy was investigated to cure phenylethynyl-end-capped polyimide adhesive using an industrial microwave oven at a frequency of 2.45 GHz and the adhesive properties, thermal performance and curing mechanism for bonding stainless steel were evaluated. The results are compared with those of thermal cured samples. It was demonstrated that while the lap shear strength properties and thermal performance of microwave cured samples were almost as good as those cured via a thermal process, the microwave curing process resulted in a significant reduction in the process cycle time and power consumption. The Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis of the cured resin structures suggested that there was no obvious difference in the chemical reactions taking place during the microwave and the thermal cure processes.