Thermokinetic modeling of an epoxy resin I. Chemoviscosity

It is shown that the Williams-Landel-Ferry equation can be taken to describe the temperature dependence of viscosity of an amine-cured epoxy resin. Furthermore, for this resin system, the two parameters of the W-L-F equation can be expressed simply as functions of hardener concentration. Since the hardener concentration decreases with advancement, and since the reaction rate equation for advancement is readily determined and known, the viscosity can be calculated over any temperature (cure) cycle.     

Rubber modified epoxy resin. I: Cure kinetics and chemorheology

The curing and vitrification effect during the reaction of ATBN modified epoxy resin was studied through the dynamic differential scanning calorimetry method and a new reaction kinetic equation containing generalized WLF equation was developed to describe the reaction rate at both glassy and rubbery state. An autocatalytic mechanism was found to describe adequately the cure kinetics of the rubber modified epoxy resin and the overall order of reaction was assumed to be 2. The kinetic parameters were determined from the DSC data through the Marquardt's multivariable nonlinear regression method and Runge–Kutta integration technique. The presence of rubber indicated minor effect on the cure kinetics of epoxy resin. The Arrhenius type viscosity function was employed to establish a relationship between viscosity data measured by RMS and chemical conversion calculated from the reaction kinetic equation.     

Time–temperature–transformation (TTT) and TTT–viscosity diagrams of a typical benzoxazine resin

Benzoxazine resins have attracted much attention because of their excellent properties. As a new kind of thermosetting resin, their gelation and vitrification behaviors during the curing process are worth studying for promoting their development, but few research works have been done on this subject. In this work, an ordinary diamine-type benzoxazine resin (PH-ddm) was chosen as a research object. Its curing kinetics were studied by differential scanning calorimetry (DSC) and a phenomenological model was used to get equal curing degree curves reflecting the relationship among curing degree, curing temperature and time. Moreover, a gelation curve and a vitrification curve of PH-ddm based on an Arrhenius equation and a DiBenedetto equation were obtained by parallel plate rheometer and modulated DSC (MDSC), respectively. Then, a well-known time–temperature–transformation (TTT) diagram was plotted. Besides, the rheological behavior of PH-ddm was analyzed through rotatory viscometer testing and modified double Arrhenius equation to obtain the equal viscosity curves. A TTT–viscosity diagram was obtained through combining the equal viscosity curves with the TTT diagram. This is the first time for using the TTT diagram to investigate the curing process of benzoxazine resins. Our results provide an effective method to optimizing molding conditions of the benzoxazine resins.     

Curing kinetics and chemorheology of epoxy/anhydride system

The curing kinetics and chemorheology of a low‐viscosity laminating system, based on a bisphenol A epoxy resin, an anhydride curing agent, and a heterocyclic amine accelerator, are investigated. The curing kinetics are studied in both dynamic and isothermal conditions by means of differential scanning calorimetry. The steady shear and dynamic viscosity are measured throughout the epoxy/anhydride cure. The curing kinetics of the thermoset system is described by a modified Kamal kinetic model, accounting for the diffusion‐control effect. A chemorheological model that describes the system viscosity as a function of temperature and conversion is proposed. This model is a combination of the Williams–Landel–Ferry equation and a conversion term originally used by Castro and Macosko. A good agreement between the predicted and experimental results is obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3012–3019, 2003     

Curing kinetics and viscosity change of a two‐part epoxy resin during mold filling in resin‐transfer molding process

The curing kinetics and the resulting viscosity change of a two‐part epoxy/amine resin during the mold‐filling process of resin‐transfer molding (RTM) of composites was investigated. The curing kinetics of the epoxy/amine resin was analyzed in both the dynamic and the isothermal modes with differential scanning calorimetry (DSC). The dynamic viscosity of the resin at the same temperature as in the mold‐filling process was measured. The curing kinetics of the resin was described by a modified Kamal kinetic model, accounting for the autocatalytic and the diffusion‐control effect. An empirical model correlated the resin viscosity with temperature and the degree of cure was obtained. Predictions of the rate of reaction and the resulting viscosity change by the modified Kamal model and by the empirical model agreed well with the experimental data, respectively, over the temperature range 50–80°C and up to the degree of cure α = 0.4, which are suitable for the mold‐filling stage in the RTM process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2139–2148, 2000     

Thermoanalytical investigation of composite lamination

Glass cloth reinforced epoxy resins are commonly used to make composites. The performance of these laminates depends strongly on optimizing cure kinetics and rheology for a given chemical composition and temperature/pressure profile. Aborted flow tests (weight percent resin squeezed out during a given temperature/pressure cycle) is frequently used to emulate lamination processes and/or to evaluate new formulations. The cure reaction was monitored using differential scanning calorimetry, rheology, and dielectrometry. These techniques show that the cure kinetics are controlled by the temperature profile. The viscosity and the macroscopic flow, however, are affected by the temperature profile, i.e. decrease in viscosity with rising temperature, as well as the cross-linking kinetics which lead to an increase in viscosity. Gravimetric and thickness measurement indicated a non-uniform resin distribution across the laminate, with a lower resin content found at the edges. Macroscopic flow is controlled by three dimensional heat transfer, which leads to a dynamic temperature distribution and, concomitantly, to a cure/rheology profile. This was demonstrated graphically by marking layers of reinforced resin and monitoring the movement of the markers.     

一种可用于拉挤成型的改性苯并恶嗪树脂体系

将PM型苯并恶嗪与环氧树脂F-51按照质量比7∶3共混,加入适量的2-乙基-4-甲基咪唑作为固化剂,首次制备了能够适用于拉挤成型的树脂基体。采用凝胶时间测试,示差扫描量热分析,动态热机械分析(DMA)和力学性能测试研究了该树脂体系的粘度特性、固化行为和使用性能。结果表明,该体系150℃下的凝胶时间5 min,60℃粘度471 mPa.s,树脂浇注体的弯曲强度156.7 MPa,弯曲模量4.9 GPa,玻璃化转变温度180℃。该树脂体系具有凝胶快、粘度低以及较好的力学性能和耐热性等特点,能够满足拉挤成型工艺的要求。     

有机硅改性丙烯酸阳极电泳漆的合成

以乙醇为溶剂,将正硅酸乙酯(TEOS)与乙烯基三乙氧基硅烷(VTEOS)经酸催化合成了一种表面带有乙烯基的活性二氧化硅粒子,然后将其与丙烯酸树脂聚合得到透明的有机硅改性阳极电泳漆。研究了有机硅的添加方式对反应过程,有机硅含量对改性丙烯酸树脂的玻璃化转变温度、黏度以及电泳漆性能的影响,采用傅里叶变换红外光谱、差示扫描量热和热重分析等对改性丙烯酸树脂进行了表征。结果表明,有机硅的最佳添加方式是与部分单体预混后逐滴滴加。随着有机硅含量的增大,改性丙烯酸树脂的黏度、玻璃化转变温度和耐热性提高。当有机硅添加量为0.8%~1.2%时,电泳漆膜的综合性能较好。     

A diallyl bisphenol A ether and diallyl phenyl ether modified bismaleimide resin system for resin transfer molding

A modified bismaleimide (BMI) resin system for resin transfer molding was prepared by using o,o′‐diallyl bisphenol A ether and 1,4‐diallyl phenyl ether as reactive diluents for BMI. The processing behavior was studied through time–temperature–viscosity curves, gel characteristics, and differential scanning calorimetry. The results indicate that the injection temperature can be 80°C, at which its apparent viscosity is only 0.30 Pa · s. Moreover, after it had been maintained at 80°C for 15 h, the apparent viscosity was still less than 1.00 Pa · s. The cured resin had remarkable heat resistance, hot/wet resistance, and mechanical properties. The heat stability and mechanical properties of the composite based on this resin system and woven glass cloth are also discussed. For short beam shear strength, in tests at 150 and 180°C, 90 and 65% of the original room temperature strength was retained. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1649–1653, 1999     

Chemorheology of poly(urethane/isocyanurate) formation

Poly(urethane/isocyanurate) is a major resin used in the structural reaction injection molding (SRIM) process. In this study, the kinetics and viscosity changes of a poly(urethane/isocyanurate) resin were investigated by the adiabatic temperature/viscosity rise method and differential scanning calorimetry. The effect of the catalyst concentration and the volume ratio of isocyanate to polyol was investigated. It is found that isocyanate trimerization depends on the diffusion effect resulted from the urethane formation. A kinetic model including the diffusion effect is developed, which is able to predict the experimental results. The reaction induced viscosity rise depends on the concentration and the molecular weight of the formed polymer. The measured adiabatic viscosity rise correlates well with the calculated molecular weight growth using the recursive method.     

A chemorheological model for the cure of unsaturated polyester resin

A chemorheological model is developed, using the free volume concept, for the prediction of viscosity during the cure of unsaturated polyester resin. We have incorporated into the development of the chemorheological model a mechanistic kinetic model of curing kinetics that predicts the degree of cure as a function of cure time. The mechanistic kinetic model uses an approach of free-radical polymerization that takes into account diffusion-controlled curing reactions, In order to test the usefulness of the chemorheological model developed, we have conducted cure experiments and measured viscosities of partially cured resin samples, using a general-purpose unsaturated polyester resin. Specifically, the following measurements were taken: (1) the quantity of ethylenic double bonds in the resin system before and after the cure reaction by infrared spectroscopy, (2) the glass transition temperature by differential scanning calorimetry (DSC) and (3) the viscosity as a function of shear rate, at several temperatures, using a cone-and-plate rheometer. It is concluded that the chemorheological model developed is very useful for predicting the variation of viscosity during the cure of unsaturated polyester resin.     

5429双马来酰亚胺树脂的固化动力学研究

通过差示扫描量热法(DSC)研究了5429双马树脂的固化过程。分别使用Kissinger模型和Flynn-Wall-Ozawa模型计算得到了5429双马树脂动力学参数。结果表明Kissinger模型与FWO模型计算得到的动力学参数较为接近,验证了两个动力学模型的有效性。由于5429双马树脂的固化反应为一级反应,因此代入相应的固化动力学参数可得到其固化动力学方程。此外,通过T-β外推法可计算得到5429双马树脂凝胶化温度、固化温度和后处理温度等特征温度。     

Bismaleimide resin modified with diallyl bisphenol A and diallyl p‐phenyl diamine for resin transfer molding

O,O′‐diallyl bisphenol A (DBA) and N,N′‐diallyl p‐phenyl diamine (DPD) were used for the reactive diluents of 4,4′‐bismaleimidodiphenol methane (BDM). The objective was to obtain a modified BDM resin system suitable for resin transfer molding (RTM) process to prepare the advanced composites. The processing behavior was determined by time–temperature–viscosity curves, gel characteristics, and differential scanning calorimetry (DSC). The injection temperature of the resin system in RTM could be 80°C, at which its apparent viscosity was only 0.31 Pa/s, and the apparent viscosity was still less than 1.00 Pa/s after the resin was held at 80°C for 16 h. The gel time test result indicated that at low temperatures, the reactivity of the resin system is low, whereas at high temperatures, the resin could cure very fast, which was beneficial to RTM. The postcure of the cured resin at a given temperature was necessary because the resin had a wide and flat cure exothermic peak, observed by DSC curve. The cured resin displayed both high heat and hot/wet resistance and high mechanical properties, especially tensile strength, tensile modulus, and flexural strength at room temperature, which reached 96.2 MPa, 4.8 GPa, and 121.4 MPa, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2245–2250, 2001     

丙烯酸酯单体改性环氧树脂胶粘剂的研究

采用差示扫描量热法（ DSC）研究了用丙烯酸酯单体（ acrylate monomer ）改性环氧树脂（ EP）与脂肪胺固化的反应机理、性能与应用。结果显示,选用具有合适分子结构的丙烯酸单体并且用量达到环氧胶黏剂中树脂比例的20％时,不仅能显著降低环氧树脂胶黏剂的粘度而且能提高固化物的搭接强度和玻璃化转变温度（ Tg）。     

SCRIMP用原位分相增韧中温环氧树脂体系制备及复合材料性能

针对复合材料真空辅助树脂浸渍模塑技术(SCRIMP)对树脂体系要求进行配方设计及性能测试。采用动态差示扫描量热(DSC)法,运用Kissinger动力学方程研究了基础树脂的固化反应动力学。通过添加QS-VA-3型原位分相型增韧剂,改善了基础树脂脆性,依据力学性能测试结果确定最佳添加量。对增韧环氧树脂体系进行等温/非等温黏度特性研究,确定了SCRIM P灌注成型过程的适用期,并使用该技术成型了增韧环氧树脂体系/单向玻璃纤维布复合材料试样,发现与玻璃纤维复合后具有强度高、界面性能好及低电压绝缘性能良好特点,但牺牲了高电压环境下绝缘性能。     

Novel Vinylester Resin Based on Hydroquinone as Coating Materials

Abstract

Novel Vinylester resin of p-dihydroxy benzene (VER-HQ) was prepared by the reaction between diglycidyl ether of hydroquinone and acrylic acid. The VER-HQ resin was characterized by its viscosity, acid value, number a verge molecular weight and IR spectrophotometry. Curing conditions for the resin were established by differential scanning calorimetry. Thermal stability of the resin was studied by thermogravimetric analysis.

The VER-HQ resin was coated on mild steel panels and the coated panels were tested for their flexibility, impact strength, scratch hardness and chemical resistancy.

Vinyl monomer such as styrene lowers the curing temperature of all resin systems when incorporated prior to curing and significantly improves the properties of coating.     

Study of the Curing Kinetics toward Development of Fast-Curing Epoxy Resins

Rapid resin transfer molding is suitable for high-volume production of composite products. In this work, the epoxy systems with long pot life, i.e., with low reactivity at room temperature and low viscosity for fast injection into the mold cavity and reinforcing fabric, were developed by varying different concentrations of diluent and catalyst. Once infusion is completed, such epoxy formulations were capable of reacting fast at cure temperatures. Different formulations were developed to achieve such goals. This paper reports on the investigation of cure rate, cure temperature, cure time, glass transition temperature, and in situ cure monitoring using differential scanning calorimetry.     

风机叶片用环氧树脂体系流变性能研究

本文对风机叶片用环氧树脂体系的流变性能进行了研究,在粘度实验的基础上,依据双阿累尼乌斯方程建立了与实验数据较为吻合的流变模型。结果表明,两种树脂体系的粘度随温度变化情况基本一致,在23～50℃范围内,其粘度都低于300mPa.s,且低粘度保持时间大于30min,符合风机叶片真空成型对树脂低粘度的要求。所建立的粘度模型可有效预测和模拟树脂体系在不同工艺条件下的粘度行为,揭示树脂体系的优化工艺参数和低粘度平台工艺窗口,为合理拟订工艺参数和保证产品质量提供必要的科学依据。     

新型酚醛树脂固化反应动力学及固化机理研究

采用DSC热分析对S酚醛树脂的固化过程进行了动力学研究,得出了该树脂的固化工艺温度及固化动力学参数,其凝胶化温度、固化温度和后处理温度分别为360.7K、421.6K和463.4K;反应级数n=0.912、表观活化能E=76.14kJ·mol^-1,反应频率因子A=4.704×10^8min^-1。采用红外光谱分析初步探讨了该树脂的固化机理,结果表明其固化反应主要是苄羟基与苯环邻位上活泼氢产生交联缩合反应,少量为苄羟基之间的缩合反应。     

二氧化硅粉体改性E—Si／CE固化动力学的研究

采用非等温差示扫描量热法（DSC）研究了纳米二氧化硅（SiO2）和微米SiO2的混合粉体改性环氧基硅烷（E—Si）／氰酸酯（CE）树脂体系固化动力学;用Kissinger、Crane和Ozawa法确定固化动力学参数。结果表明,Kissinger式求得的表观活化能为66．09kJ／mol;Ozawa法求得的表观活化能为7001kJ／mol;根据Crane理论计算该体系的固化反应级数为0.89。计算了不同升温速率所对应的不同温度的频率因子和反应速率常数;求得了改性体系的固化工艺参数：凝胶温度130．74℃、固化温度160．96℃和后处理温度199.16℃,确定了体系的最佳固化工艺。与E—Si／CE体系对比表明,SiO2的加入可以降低E—Si／CE体系的活化能,使其固化能在较低温度下进行。