缠绕成型用BMI树脂化学流变性及流变模型研究

研制了用于缠绕成型的双马来酰亚胺树脂体系,研究该树脂体系的化学流变特性.经黏度实验证实,该体系黏度平台低,低黏度保持时间长,110℃下保持黏度低于1000 mPa·s的时间为864 min.在黏度实验和差示扫描量热(DSC)实验的基础上,建立了该树脂体系恒温情况下的双阿累尼乌斯黏度模型,该模型与实验数据吻合良好,可有效...     

RTM用环氧树脂体系的浸润性及化学流变特性研究

对树脂传递模塑（RTM）用环氧树脂体系对纤维的浸润性能进行了研究,同时在基本的黏度实验基础上,采用双阿仑尼乌斯方程研究了其化学流变特性。结果表明,纤维经丙酮处理后浸润性能提高,RTM环氧树脂浸润纤维变得容易;并通过双阿仑尼乌斯方程建立了RTM环氧树脂体系的化学流变模型,该模型揭示了RTM环氧树脂在35~75 ℃的温度范围内黏度低于800 mPa·s,且低黏度保持时间大于20 min,满足复合材料RTM成型的基本工艺要求。     

改性BMI/苯并噁嗪树脂的固化反应及其动力学研究

将改性双马来酰亚胺(BMI)树脂与苯并噁嗪(B-a)树脂进行共混共聚制备了改性BMI/B-a树脂,采用动态DSC技术研究了改性BMI/B-a树脂的固化反应过程。实验结果表明,在100～350℃范围内出现两个峰,其中100～153℃是树脂的熔融吸热峰(峰顶温度为134℃),156～303℃是树脂固化反应过程的放热峰(峰顶温度为232℃);改性BMI树脂与B-a树脂的固化反应级数为0.93,活化能为85.6 kJ/mol;改性BMI/B-a树脂的固化工艺为180℃×1 h+200℃×2 h+230℃×2 h,后处理工艺为280℃×2 h。     

苯并环丁烯封端的聚酰亚胺树脂的流变行为研究

用旋转流变仪研究了苯并环丁烯封端的聚酰亚胺树脂体系固化过程中的化学流变行为,用动态和静态两种方法分析了其固化过程,发现存在三个固化阶段,用Arrhenius方程确定了固化前的表观物理粘流活化能为195.9kJ/mol.并用Roller法确定固化反应过程中表现化学粘流活化能和表现固化反应活化能,分别为148.2kJ/mol和161.2kJ/mol.结果表明,在整个固化成型工艺温度范围内,苯并环丁烯封端的聚酰亚胺树脂的粘度特性符合Roller模型方程,通过该模型可较好地预测该树脂在固化过程中的粘度特性.     

VARTM用EP体系流变特性及固化工艺的研究

研究了真空辅助树脂传递模塑(VARTM)工艺用环氧树脂(EP)体系的流变特性,结合差示扫描量热(DSC)仪和旋转式粘度计对A1、A2、A3三种EP体系的测试结果,确定A2树脂体系适合于VARTM工艺,并根据双阿累尼乌斯方程,建立了A2树脂体系的流变模型。该模型可以预测树脂在不同温度下的粘度特性,为合理制定工艺参数提供了重要依据。用DSC仪对A2树脂体系的固化反应过程进行分析,利用外推法确定了固化工艺参数。     

双酚A型苯并嗪恶嗪树脂的流变特性研究

以双酚A、苯胺和甲醛为原料制备了双酚A型苯并口恶嗪(BOZ)单体,并对其进行了FT–IR、1H–NMR测试,重点研究了该单体聚合所得树脂的流变特性。在黏度实验的基础上,依据双阿累尼乌斯方程建立了与实验结果较吻合的等温化学流变模型。该模型可较准确地预测体系的低黏度工艺窗口,为该树脂的RTM工艺参数的优化提供科学依据。     

RTM用乙烯基酯树脂化学流变性研究

研究了RTM用改性乙烯基酯树脂体系的化学流变行为。采用DTA热分析技术和黏度测量手段,研究了该树脂体系固化反应特性以及固化过程中温度-黏度的关系,根据树脂的化学反应流变特性,建立了树脂体系恒温条件下的双阿伦尼乌斯黏度模型。研究表明,模型对树脂恒温条件下其黏度的模拟结果与实验结果具有良好的一致性。可揭示树脂体系在不同温度条件下的黏度变化规律,为合理制定RTM工艺参数、保证产品质量提供必要的科学依据。     

航空复合材料RTM工艺用环氧树脂的流变模型

航空高纤维体积含量复合材料树脂传递模塑成型(RTM)工艺要求树脂体系有较低的黏度,因此分别采用双阿累尼乌斯黏度模型和联合工程黏度模型对所配制环氧树脂体系的黏度变化进行预测。结果表明,联合工程黏度模型由于考虑了固化过程中温度变化的累积效应对树脂体系黏度的影响,所以相对于双阿累尼乌斯黏度模型,不管是反应初期还是后期更能准确预测所配制环氧树脂体系黏度的变化。通过联合工程黏度模型确定了该环氧树脂体系的最佳注射温度为35~45℃,该温度范围内树脂的初始黏度大于80mPa·s,且树脂从配制到黏度增加到200m Pa·s的时间大于29min,增加到500mPa·s的时间大于97min,满足航空高纤维体积含量复合材料RTM工艺的充模要求。     

VARTM用酚醛树脂的化学流变特性及模型分析

研究了一种新型的用于真空辅助树脂传递模塑成型工艺(VARTM)酚醛树脂的流变特性。根据实测等温粘度曲线,采用双阿累尼乌斯模型,建立了用于真空辅助树脂传递模塑成型工艺(VARTM)酚醛树脂的化学流变特性模型方程,分析表明模型拟合与实验结果之间具有较好的一致性,这为有效地预测RTM树脂的低粘度工艺窗口、合理制定复合材料成型工艺参数提供了必要的科学依据。     

双马来酰亚胺树脂反应性和黏度特性的研究

测试了双马来酰亚胺（BMI）树脂体系的反应性和黏度特性，研究了BMI树脂体系的流变性能。通过DSC分析得到体系的起始温度、峰值温度和终止温度分别为202℃、266℃和320℃；根据Arrhenius方程得到体系的反应活化能为E=58．1kJ／mol；经旋转黏度计测试得到该树脂体系的动态黏．温曲线和静态黏-时曲线，在140℃～180℃树脂体系具有一个较宽的低黏度工作平台和优良的工艺性能。其中，140℃下体系黏度小于300mPa·s可保持50min。     

Chemorheological characterization of thermoset cure

Thermosetting resin/glass cloth composites find extensive use in the packaging of electrical circuits into multi-layered circuit boards. To determine optimum processing conditions, it is necessary to understand the rheology of the resin as it cures. In this study, a squeezing flow geometry was used to determine the shear viscosity of a high performance epoxy resin during cure; Viscosity profiles were obtained during rising temperature cure. The results were compared with the complex viscosities obtained using the dynamic oscillatory parallel plate geometry. A numerical optimization algorithm was used to obtain the dual Arrhenius viscosity model parameters from the experimental viscosity data. The sensitivities of the model parameters and their effects on the predicted viscosity profiles were also determined.     

Chemorheological studies on polymer degradation

The degradation of dicumyl peroxide-cured natural rubber was studied by the stress relaxation method. Experiments were carried out in air, in nitrogen, and by irradiation of UV light in the temperature range of 30–200°C. We attempted to divide factors of the degradation into two parts: that caused by heat and that by light, and to study the respective degradation quantitatively. The degradation caused by UV light in nitrogen was almost independent of temperature. However, the degradation caused by UV light in air increased with temperature and the rate of degradation caused by the interaction between light and oxygen was greater at high temperature than at low temperature. It was found that scission along main chains occurs for dicumyl peroxide-cured natural rubber by photo-oxidation as well as thermal oxidation.     

Chemorheological analysis of unsaturated polyester-styrene copolymerization

An important feature of free radical crosslinking copolymerization of unsaturated polyester resin (UP) - styrene is the formation of a heterogeneous structure through intra-molecular reactions and phase separation. Such structure formation affects not only the cure behavior, but also the rheological changes. The chemorheology and the effect of shear on the structure formation, as well as the rheological changes, were investigated using rheometry, electron spin resonance spectroscopy, and dynamic light scattering goniometry. Based on experimental results, a conceptual model and a simple mathematical formulation are proposed to explain the shear effect on resin viscosity changes. Predictions obtained from the mathematical model are compared with experimental results.     

Chemorheological treatment of crosslinked EPDM. II

Stress relaxation mechanisms were investigated on three kinds of ethylene–propylene terpolymers (EPDM), differing only in the structure of the crosslinkage, in both nitrogen and air at 160°C. The crosslinking site in these polymers consists of a carbon–carbon bond, a polysulfide linkage, and a carbon–carbon bond and a polysulfide linkage, respectively. Stress relaxation in air for peroxide-cured EPDM was based on the oxidative scission of the main chain. Analysis of the stress relaxation data of sulfur-cured EPDM in nitrogen indicated the presence of stable mono- and disulfide linkages and that the main relaxation process resulted from an interchange reaction between polysulfide linkages. In air, in addition to the interchange reaction, oxidative cleavage of mono and disulfide linkages occurred. Further, the stress relaxation for peroxide–sulfurcured EPDM polymers containing various amount of sulfur was observed in air and nitrogen and was discussed in the connection with highly crosslinked polymers.     

Chemorheological studies on a dicyanate resin modified with polyethersulfone

The chemorheology of a dicyanate resin modified with a polyethersulfone (PES) was investigated. The rheological and dielectrical property changes during curing of the dicyanate resin system catalyzed by an organic metal salt were monitored by a rheometer and dielectric analyzer, respectively, and used to investigate the curing behavior and chemorheology of the resin system. The curing rate of the dicyanate resin system decreased as the PES content was increased. A function that can describe the viscosity change of the dicyanate resin system during curing was determined by a nonlinear regression method using the rheometer data. The gelation time of the dicyanate resin system decreased with increasing isothermal curing temperature and with decreasing PES content. The curing behavior of the dicyanate resin system monitored by the dielectric analyzer coincided fairly well with that measured by the rheometer Copyright © 2004 Society of Chemical Industry     

Chemorheological study of vulcanized rubbers under mechanical stress

At lower than the glass transition temperature, the cleavage of the molecular chains of extended vulcanized rubbers will occur. The crosslinking density of vulcanized rubbers, which were placed at room temperature for about 4 hr in nitrogen atmosphere, increased about 17% after extension of 200% at ?76°C. This may be due to the recombination of cleft chains, and this can be shown by the Maxwellian type of curves between crosslinking density and forced strain. Considering the decreasing proportion of crosslinking density by the radical acceptors included in the rubbers and the fact that crosslinking density increases because of recombination of cleft chains, this was attributed to the recombination of unstable chains produced by the added mechanical stimulus.     

APG工艺用环氧树脂体系的固化及流变模型

研究了自动压力凝胶工艺用环氧树脂混合体系在动态升温过程中的固化反应,采用Malek法确定了动力学模型并预测了相应的参数。该体系符合两参数自催化SB模型。用旋转流变仪测定了该体系在动态升温过程中黏度相对于温度的变化曲线,采用WLF和Macosko混合方程描述该体系的化学流变模型,用非线性拟合方法预测了模型中的参数。模型预测与实验数据比较吻合。     

Chemorheological changes in crosslinked epoxy resins subjected to large strains

Chemorheological changes in epoxy resins subjected to large strains while heated were observed earlier, but the subject was not treated quantitatively. This paper describes the investigation of an epoxy resin—Epon 826, of known chemical, structure, crosslinked with two different amines. By means of a simple calibrated apparatus, the epoxide samples were subjected to large strains in a non-oxidizing atmosphere and in air. They were heated to different temperatures for various times; the results were compared with data obtained from unstrained samples kept in otherwise the same conditions. The results show a linear-logarithmic relation between the torsion modulus, G₍₁₀₎ and the time of applied strain at a certain temperature and also a linear relation between G₍₁₀₎, and 1/T°K, both above T₍₁₀₎. The results obtained in swelling experiments support the data from 10 sec torsional modulus vs temperature measurements. An increase in the amount of solubles and in M_c is observed on extending the time of heating. A clear difference in properties between the strained and unstrained samples, kept in otherwise the sane conditions, is observed and the contribution of the applied strain to chemorheology has been shown. Both systems of crosslinked Epon 826 showed the same general behavior, although the specific data were different.