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     

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。     

RFI用改性双马树脂膜的黏度特性

采用热塑性树脂改性双马来酰亚胺树脂,获得了适用于RFI成型的改性双马来酰亚胺树脂膜。采用DSC方法和黏度测试研究了该树脂的固化特性和黏度特性,并根据黏度特性建立了Arrhenius模型。结果表明,改性双马来酰亚胺树脂膜的黏度特性能够满足RFI工艺的要求,建立的Arrhenius模型能够较好地预测黏度特性,可为RFI工艺参数的制定提供理论指导。     

VARTM用乙烯基树脂体系流变性能研究

通过测试凝胶时间与温度的关系,得到乙烯基树脂的表观活化能并进行了分析。在粘度实验的基础上,依据双阿累尼乌斯方程建立了与之相吻合的流变模型。结果表明:乙烯基树脂的凝胶时间随温度升高而缩短,其表观活化能仅有3.04 kJ/mol。乙烯基树脂低粘度状态持续时间>30 min,符合树脂传递模塑成型工艺(VAR-TM)对树脂低粘度的要求。最终建立的粘度模型,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。     

新工艺合成低黏度双酚A型液态环氧树脂

采用新工艺合成了双酚A型液态环氧树脂,并研究了醚化反应催化剂和闭环反应碱用量对醚化反应后体系双酚A单体残留量、合成的环氧树脂的环氧当量和有机氯含量的影响。结果表明:采用新催化剂有效提高了醚化反应双酚A的转化率,醚化反应结束后双酚A残留量14%。随着碱用量的提高,环氧当量和有机氯显著降低。新工艺的重复性好,与一步法合成的环氧树脂比较,产品具有黏度低(25℃下约为7.80～7.98Pa.s)、环氧当量低(182g/eq)、有机氯含量低(200μg/g)的特点。     

RFI成型工艺中渗透率的研究及树脂流变模型的建立

渗透率测量是树脂膜熔渗(RFI)工艺在复合材料设计和优化中最关键的条件。随着纤维体积分数的增加,渗透率非线性降低,可见纤维体积分数的变化对整个树脂体系浸渍纤维预制体有很大的影响。在黏度实验的基础上,对用于RFI工艺的环氧树脂体系的化学流变特性进行研究,并根据双阿累尼乌斯方程建立树脂体系的流变模型,为合理地制定RFI工艺参数、保证产品质量和实现工艺参数的全局优化提供科学依据。     

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     

Viscosity modeling of a medium reactive unsaturated polyester resin used for liquid composite molding process

The development of new composite product for an application through liquid composite molding (LCM) process simulation requires submodels describing the raw material characteristics. The viscosity during resin cure is the major submodel required for the effective simulation of mold-filling phase of LCM process. The viscosity of the resin system during mold filling changes as the cure reaction progresses. Applied process temperature also affects the viscosity of the resin system. Hence, a submodel describing the resin viscosity as a function of extent of cure and process temperature is required for the LCM process simulation. In this study, a correlation for viscosity during curing of medium reactive unsaturated polyester resin, which is mostly used for the LCM process, has been proposed as a function of temperature and degree of cure. The viscosity and the degree of cure of reacting resin system at different temperatures were measured by performing isothermal rheological and isothermal differential scanning calorimetry experiments, respectively. A nonlinear-regression analysis of viscosity and degree of cure data were performed to quantify the dependence of viscosity on temperature and extent of cure reaction. Comparisons of model solutions with our experimental data showed that the proposed empirical model is capable of capturing resin viscosity as a function of extent of cure and temperature qualitatively as well as quantitatively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A model-centric approach for the management of model evolution in chemical process modelling

This paper explores the development of an automatic model-centric version control approach for managing the evolution of chemical models and to support model reuse. Unlike traditional versioning which is text-based, the basis of versioning in the proposed approach is based on structural changes of the chemical models. An implemented prototype tool incorporating the proposed approach and the use of an example XML-based representation of chemical models was used to illustrate the associated concepts. Some results associated with a case study are presented. Given that chemical modelling tools like HYSYS has just delivered an XML infrastructure that aims to support collaborative engineering, this proposed technique is timely and relevant. The benefit of the approach is that it provides a way of automatic storage and retrieval of the chemical models as well as the management of the different versions of the model as it evolves, thus allowing chemical process engineers to concentrate on the modelling and simulation.     

Kinetic modeling of esterification of cardanol‐based epoxy resin in the presence of triphenylphosphine for producing vinyl ester resin: Mechanistic rate equation

In this study, cardanol‐based epoxidized novolac resins and methacrylic acid were used to produce cardanol‐based epoxidised novolac vinyl ester resins. The reactions were conducted under nonstoichiometric condition using triphenylphosphine as catalyst in the temperature range of 80–100°C with an interval of 5°C. The first‐order rate equation and mechanism based rate equation were examined. Parameters were evaluated by least square method. A comparison of mechnism based rate equation and experimental data showed an excellent agreement. Finally, Arrhenius equation and activation energy were presented. The specific rate constants, based on linear regression analysis, were found to obey Arrhenius equation. The values of activation energy, frequency factor, enthalpy, entropy, and free energy of the reaction revealed that the reaction was spontaneous and irreversible and produced a highly activated complex. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A new model for simulating particle transport in a low‐viscosity fluid for fluid‐driven fracturing

Fluid‐driven fracture (i.e., Hydraulic fracturing) is an important way to stimulate the well productivity in the development of unconventional reservoirs. A low‐viscosity fluid called slickwater is widely used in the unconventional fracturing. It is a big challenge to simulate the particle (or proppant) transport in the low‐viscosity fluid in a field‐scale fracture. A new model to simulate particle transport in the low‐viscosity fluid in a field‐scale fracture is developed. First, a new parameter is defined, called the rate of proppant bed wash‐out, by which we incorporated the mechanism of proppant bed wash‐out into Eulerian‐Eulerian proppant transport model. Second, we proposed a novel way to consider the effect of proppant settling on the proppant concentration in the upper layer (or suspending layer) to accurately simulate the proppant transport. Additionally, a dimension reduction strategy was used to make the model quickly solved. Our simulation results were compared with published experimental data and they were consistent. After validation, the effect of fluid viscosity, injection rate, fracture height, and proppant concentration on the proppant distribution in a fracture is investigated. This study provides a new model to simulate particle transport. Meanwhile, it gives critical insights into understanding particle transport in the field‐scale fracture. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3542–3552, 2018     

Stabilization of entrapped catalase using photo‐crosslinked resin gel for use in wastewater containing hydrogen peroxide

Catalase immobilized using photo‐crosslinkable resin was applied to treatment of wastewater containing a low concentration of hydrogen peroxide. The structure of photo‐crosslinked resin gel was stable even in the acceleration test of concentrated hydrogen peroxide for a long period. Accordingly, the most important subject of this process was maintaining long term catalase activity. The stabilization of immobilized catalase was investigated by modifying gel carriers with some prepolymers and functional monomers, and adding some stabilizing materials without modification of catalase itself. But these gel carriers did not improve the stability beyond 20%. Addition of Tween 80, polyoxyethylene (5) sorbitan monooleate (hydrophilic/lipophilic balance, HLB: 10.0), to catalase was most effective for maintenance of the activity when the enzyme was immobilized in hydrophilic photo‐crosslinked resin, resulting in 80% of its initial activity. It was assumed that this surfactant did not influence the permeation of hydrogen peroxide into gel, but acted as a stabilizer for catalase in the gel carrier. © 2000 Society of Chemical Industry     

Hexaphenoxycyclotriphosphazene as FR for CFR anionic PA6 via T‐RTM: a study of mechanical and thermal properties

The production of carbon fiber reinforced (CFR) anionic polyamide 6 (APA6) plates by thermoplastic resin transfer molding (T‐RTM) processing is highly sensitive to the presence of polymer additives such as flame retardants (FRs). However, APA6 is flammable, and therefore, it is mandatory to protect the polymer matrix, especially if the produced materials are intended for aerospace applications. Typically used FR for PA6 cannot be incorporated in the T‐RTM processes. With hexaphenoxycyclotriphosphazene, an incorporable and effective FR additive for CFR APA6 was discovered. Cone calorimetry measurements indicate a char formation‐based mechanism, and the flame retardancy was further confirmed with limiting oxygen index tests, classification by UL94 (V‐0), and FAR25 tests. The influence of this FR on the thermal (thermogravimetric analysis and differential scanning calorimetry) and mechanical behavior (flexural, compressive and ultimate tensile strength, and Charpy impact tests) on CFR APA6 produced via T‐RTM processing is evaluated and indicates no interaction with the APA6; it works as a passive filler. Copyright © 2016 John Wiley & Sons, Ltd.     

Validation of mass‐transfer model for VIPS process using in situ measurements performed by near‐infrared spectroscopy

Combined experimental and modeling approaches were performed in order to investigate the influence of formulation and process parameters on mass transfers during VIPS process, using the water/N‐methyl‐pyrrolidone (NMP)/poly(ether imide) (PEI) system. The experiments were conducted using a thick polymer solution at increasing polymer concentrations for various operating conditions. The global water intake rate in the bulk solution was determined by gravimetric measurements (global), and insitu measurements were conducted by near‐infrared spectroscopy at three points in the solution. In parallel, a fully predictive model was developed for predicting mass‐transfer phenomena involved during the VIPS process. The comparison between experimental data and numerical predictions exhibited a good agreement for moderate polymer concentration, but for higher polymer concentrations, the model overestimated the nonsolvent‐transfer rate. This result was explained by the aggregation process of the polymer chains due to water intake. The numerical predictions were improved by modifying the average hole‐free volume expression. © 2012 American Institute of Chemical Engineers AIChE J, 59: 671–686, 2013     

A pseudo first order rate model for the adsorption of an organic adsorbate in aqueous solution

Five low rank, coal‐based adsorbents, i.e. coal, grus, two chars, and an activated carbon were used to adsorb a low molecular weight organic compound from aqueous solution. The rates of adsorption were found to conform to pseudo first order kinetics with good correlation (r² greater than 0.996). This kinetic model was used to calculate pseudo first order rate constants (k₁^′ min ⁻¹) and relative rate constants (rate constant/unit mass of adsorbent, k₁^″ min⁻¹ g⁻¹) for the adsorption process. Rate properties have been explained in terms of both a diffusion and chemically controlled rate determining step. Rate constants for the five adsorbents vary as expected on the basis of their physical properties, that is slowest for grus (compressed coal) and fastest for the activated carbon. © 1999 Society of Chemical Industry     

A phenomenological model for the viscosity reductions in blends of HMMPE containing a small quantity of thermotropic liquid crystalline copolyester HBA/HQ/SA

In this paper, we present a phenomenological model for the viscosity changes in bulk high molecular mass polyethylene (HMMPE) due to the addition of a very small quantity of a main chain longitudinal thermotropic liquid crystalline polymer (TLCP) containing flexible spacers. The chain alignment in the elongated TLCP domains causes chain alignment and disengagement in the neighboring HMMPE melt. In converging capillary flows, this occurs at a certain critical centerline velocity. After the onset of such transition, melt of elongated chain conformations forms from the center core and expands towards the capillary wall with increasing flow rates. The model successfully predicts both the drastic viscosity reduction effects and the critical yield stress in the HMMPE+TLCP blends without any adjustable parameters. Our model is also applicable to other systems that undergo flow-induced phase transitions, e.g. in biphasic liquid crystalline polymer melts.     

Investigation on strategies for optimizing process definition in rubber processing: A study on mechanical and chemical properties of vulcanizates as basis for the development of a new calculation model for quality prediction

Rubber compounds may exhibit significant batch variations due to multiple different ingredients mixed in one compound. Hence, defining the manufacturing process for constant part quality can be challenging. Common strategies in considering batch variations in rubber processing include the determination of reaction kinetics, and the definition of process parameters according to normalized vulcanization isotherms. Thereby, maintenance of the degree of cure is targeted. With this path, information on the mechanical properties of vulcanizates is lost, despite its visibility from the kinetic data and part quality assurance is missed. This contribution points out the differences obtained for parts produced to the same degree of cure at various temperatures and intends to emphasize new strategies in process definitions. Therefore, compression molded parts were produced from styrene-butadien rubber, which was then characterized with mechanical and chemical methods. Each of the methods revealed a significant difference in part behavior, which were manufactured to the same degrees of cure but at different temperatures. It was concluded that a temperature-dependent reaction rate should be considered when quality maintenance is targeted in the production. Only then will it be possible to predict the properties adequately, with simultaneous effect of enhancing sustainability policies in rubber processing.     

内循环气升式环流反应器生物降解苯酚废水过程的计算传质学模拟研究

利用计算传质学方法对内循环气升式环流反应器（ILALR）内生物降解苯酚废水过程进行了研究。采用欧拉多相流模型结合RNG k-ε湍流模型对ILALR中气-液两相流动过程进行模拟,采用气泡群平衡模型（PBM）对反应器内气泡的尺寸分布进行预测。利用近年来提出的计算传质学\overline{c^{\mathrm{2}}}-ε_c模型对湍流扩散系数进行计算,从而摆脱了传统需要预估湍流Schmidt数的经验方法。模拟得到的液相苯酚和菌体浓度与实验测量值吻合良好,从而证明了所建立模型的有效性。研究结果表明ILALR内湍流传质过程中湍流扩散系数及湍流Schmidt数并非常数,因此基于传递相似性假设得到的湍流Schmidt数经验模型不适用于ILALR内湍流传质过程的模拟。模拟得到的ILALR中液相剪应力随表观气速的增大而增大,局部最大值出现在导流筒的上部。