聚氨酯反应注射成型固化过程数值模拟

依据反应动力学和能量守恒方程的基本理论，对聚氨酯反应注射成型的固化过程进行了合理的假设和必要的简化，建立了体系反应程度和温度的数学模型。采用显示有限差分法并结合数学软件Matlab对固化过程进行了动态模拟.结果表明：固化初始的20s内交联反应剧烈。体系迅速升至最高温度，交联度达到80％所需时间与经验值一致．约为17s。同时为优化反应注射成型工艺因素，探讨了催化剂浓度、原料初始温度和模具温度等对体系的影响。结果表明：催化剂浓度增加，使体系固化周期缩短，制品内部交联度的变化减小，但延长了制品处于高温部分的时间；模具温度主要影响制品壁面附近的反应，而物料初始温度则能影响到体系的最高温度，尤其是在低模温情况下更加明显.     

环氧树脂/聚酰胺/DDM体系的固化行为及力学性能

通过非等温DSC法及拉伸性能测试研究了4,4'-二氨基二苯基甲烷(DDM)用量对环氧树脂/聚酰胺651体系的固化反应的影响,计算了固化反应的表观活化能和反应级数,确定了其胶粘剂体系的固化工艺参数。结果表明,胶粘剂中DDM的质量分数达到14%(以环氧树脂质量为基准)时,固化反应放热量达到最大值。固化体系的活化能为53.654 kJ/mol,反应级数为0.895。最佳起始固化温度为40℃,峰值温度为85℃,终止温度为120℃,体系的拉伸强度提高了约50%。     

端胺基聚氨酯/环氧树脂胶粘剂的固化反应特征及其反应动力学研究

采用差示扫描量热法(DSC)研究了含有柔性链和刚性结构单元的端胺基聚氨酯(ATPU)对环氧树脂E-44固化反应过程特点和反应过程动力学的影响。结果表明,固化剂(ATPU)的掺加量对环氧树脂E-44固化反应过程有显著的影响,随着ATPU的增加,固化放热量增加。当ATPU的掺加量为1.6时,固化反应放热量达到最大值。固化温度研究表明,ATPU/E-44固化体系的等温固化起始温度和最高温度分别为121℃和177℃。固化反应的动力学研究表明,ATPU/E-44胶粘剂固化反应的表观活化能为81.8kJ/mol;固化反应的级数为1.3。     

DSC法研究聚异氰酸酯/环氧树脂胶粘剂的固化反应动力学及固化工艺

采用差示扫描量热法(DSC)研究了聚异氰酸酯/环氧树脂的固化过程,研究了不同配比对固化反应的影响、固化度与固化温度的关系,计算了固化反应表观活化能和反应级数,确定了聚异氰酸酯/环氧树脂胶粘剂的固化工艺。结果表明:胶粘剂中固化剂的含量对环氧树脂的固化反应过程有显著的影响,随着聚异氰酸酯含量的增加,固化放热量增加。当聚异氰酸酯的含量达到1.2份时,固化反应放热量达到最大值;在不同升温速率下,体系固化温度有很大差异,随着升温速率的提高,固化温度升高。通过动力学计算得到体系最佳固化温度为108℃,固化时间为6—8h,固化体系的活化能为43.31kJ/mol,反应级数为1.17。     

改性氰酸酯树脂反应动力学研究

采用动态DSC法研究了酚改性氰酸酯树脂体系的固化反应动力行为。研究表明:有机钛催化剂的加入降低了改性氰酸酯的固化反应的活化能和反应温度,加快了固化反应的速率;建立了酚改性氰酸酯树脂体系的固化反应动力学模型,反应级数都为1;有机钛催化剂的加入并不改变体系的固化反应机理。     

玻璃纤维对环氧基体预浸料固化特征的影响研究

采用动态差示扫描量热法(DSC)研究了玻璃纤维/环氧树脂预浸料体系的固化过程,考察了玻璃纤维对环氧树脂固化动力学的影响;利用Kissinger法和Crane公式计算了体系的反应活化能、指前因子、反应级数等固化动力学参数。结果表明,玻璃纤维使环氧树脂体系的理论凝胶化温度、固化温度和后处理温度升高;同时,增大了固化反应活化能,而固化反应的反应级数基本不变。说明玻璃纤维使环氧树脂体系固化反应变难,但不改变其固化反应机理。     

有机脲固化环氧树脂行为研究

采用非等温差示扫描量热法研究了有机脲/环氧树脂体系的固化反应的动力学。用Kissinger动力学模型计算得到该体系固化反应的表观活化能为58.1 kJ/mol,指前因子为5.83×106 min-1。通过Crane模型得出固化反应级数n为0.884,表明有机脲/环氧树脂体系的固化反应属于复杂反应。根据特征温度-升温速率外推法,得到前固化温度为110℃,固化温度为130℃,后固化温度为150℃。在实际应用中,为确定有机脲/环氧树脂体系的固化工艺提供参考。     

环氧灌封料固化反应动力学及其性能研究

采用非等温示差扫描量热法(DSC)研究了环氧树脂(E-51)/甲基四氢苯酐/DMP-30/球形SiO2体系的固化反应动力学,采用Kissinger法和Crane公式对体系的DSC数据进行了处理,获得了固化反应动力学参数,确定了固化工艺。同时通过力学性能和热性能测试研究了球形SiO2添加量对复合材料性能的影响。结果表明,SiO2质量分数为10%的体系其起始固化温度为109.7℃,峰顶固化温度为134.8℃,终止固化温度为154.3℃;较好的固化工艺为100℃/2 h+140℃/2 h+160℃/2 h。该体系反应级数n=0.917,表观活化能Ea=78.52 kJ/mol。当SiO2添加量为30%时,其弯曲强度达到最大值97 MPa,同时热分解温度达到最大值332℃,试样热膨胀系数也明显降低。     

环氧树脂/有机蒙脱土体系非等温固化动力学研究

通过差示扫描量热法(DSC)研究了改性芳胺固化环氧树脂/有机蒙脱土(EP/OMMT)纳米复合材料的非等温固化动力学,采用Ozawa-F lynn-W all法、K issinger法和Crane公式计算了体系的反应活化能、反应级数、频率因子等固化反应参数,并估算了理论凝胶温度和理论固化温度。结果表明,有机蒙脱土的加入降低了环氧树脂体系固化反应活化能和频率因子,但对反应级数影响不大。这说明有机蒙脱土对体系的固化反应有一定的促进作用,但不改变固化反应机理。     

风机叶片用环氧树脂固化因素研究

采用DOE法将树脂型号、模具初始温度和固化温度三因素三水平进行试验设计,分析其对固化度和固化物拉伸强度的影响,并采用DSC法对优选固化条件进行了验证.结果表明,影响固化度和固化物拉伸强度的主次因素为树脂/固化剂型号>固化温度>模具温度.模具温度50℃和固化温度80℃时,其固化度较大,固化物拉伸强度较优;利用DSC测得的...     

Moldability studies for the reaction injection molding of polydicyclopentadiene

Moldability diagrams for the filling and curing stages of a dicyclopentadiene (DCPD) based reaction injection molding (RIM) system were established based on a simplified engineering approach. Initial monomer temperature and filling time are the critical parameters for the filling stage whereas in the curing stage, mold wall temperature and demold time proved to be the main processing variables. The physical and thermal properties of the molded samples were examined and the results indicate that such simplified moldability diagrams are sufficiently accurate to establish the processing conditions for the system under investigation.     

Effect of cure cycle on mechanical properties of thick section fiber-reinforced poly/thermoset moldings

One of the major factors of concern in compression molding of fiber-reinforced thermosets is the mold cycle time which directly affects the processing cost. An ideal system would be the one which cures in a relatively short time resulting in excellent mechanical and physical properties. However, in practice, a compromise has to be made between the mold cycle time and ultimate property requirements. The effects of cure cycle time, temperature, preheating and post-cooling on mechanical properties of continuous as well as chopped glass fiber reinforced polyester and vinyl ester systems involving 1/4 to 1 in thick sections have been studied. Mold cycle time is strongly influenced by the part thickness and mold temperature. Internal heat generation due to curing reaction causes high thermal gradients across the thickness. Preheating offers advantages of reducing both the mold cycle time and the thermal gradient. The flexural and interlaminar shear strengths are strongly dependent or, the mold cycle time. Maximum strengths are obtained when the mold is opened at the instant when there is no thermal gradient across the thickness.     

Engineering analysis of reaction injection molding process of epoxy resin

An engineering analysis of reaction injection molding (RIM) process of epoxy resin was carried out through numerical simulation and actual experiment. In order to simulate the RIM process, and reaction kinetics and the viscosity function of the epoxy system were obtained from thermal analysis and rheological measurement, and the balance equations of the chemical species, momentum, and energy within a mold cavity were set up in cylindrical coordinates. As the result of the simulation, the temperature and conversion profiles within a disc type mold were obtained and a moldability analysis was made to find the optimum molding conditions. The temperature change during the curing reaction, at a fixed point within the mold cavity, was measured through the actual RIM experiment on a small scale, and was compared with the simulated results.     

Curing of epoxy–urethane copolymers in a heated mold: Effect of the curing conditions on the phase‐separation process

The curing process of an epoxy–urethane copolymer in a heated mold was studied. The epoxy resin (DGEBA, Araldyt GY9527; Ciba Geigy), was coreacted with a urethane prepolymer (PU, Desmocap 12; Bayer) through an amine that acted as crosslinking agent (mixture of cycloaliphatic amines; Distraltec). The study focused on the effect of the curing condition and PU concentration on time–temperature profiles measured in the mold and the consequent final morphologies obtained. As the PU concentration increases, the maximum temperature reached in the mold decreases as a result of the dilution effect of the elastomer on reaction heat, whereas the T_g of the piece also decreases. Phase separation is a function of conversion and temperature reached in the curing part and was analyzed using experimental data and a mathematical model that predicts temperature and conversion throughout the thickness of the mold. Scanning electron microscopy and atomic force microscopy were used to determine the characteristics of the dispersed phase for the different formulations and conditions of curing. It was shown that the size of the dispersed phase increased with the initial PU concentration, whereas there were practically no differences in the separated phase as a function of position or temperature of curing (in the range of 70 to 100°C studied). The superposition of the phase diagrams with the conversion–temperature trajectories during cure provided an explanation of the morphologies generated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 889–900, 2001     

Resin transfer molding (RTM) process of a high performance epoxy resin. I: Kinetic studies of cure reaction

The cure kinetics of a high performance PR500 epoxy resin in the temperature range of 160–197°C for the resin transfer molding (RTM) process have been investigated. The thermal analysis of the curing kinetics of PR500 resin was carried out by differential scanning calorimetry (DSC), with the ultimate heat of reaction measured in the dynamic mode and the rate of cure reaction and the degree of cure being determined under isothermal conditions. A modified Kamal's kinetic model was adapted to describe the autocatalytic and diffusion‐controlled curing behavior of the resin. A reasonable agreement between the experimental data and the kinetic model has been obtained over the whole processing temperature range, including the mold filling and the final curing stages of the RTM process.     

Curing reaction of molybdenum–phenolic resins

The curing behavior and curing reaction kinetics of novel molybdenum–phenolic resins were studied with differential scanning calorimetry and thermogravimetry methods, the thermal degradation properties of the cured products were studied with thermogravimetry, and the mechanism of the curing reaction was investigated with Fourier transform infrared. When the mixing ratio of the molybdenum–phenolic resin (with 12% molybdenum) to the curing agent was 100/10 (w/w), the curing temperature and activation energy were at a minimum, the thermal degradation stability of the cured product was optimal, and the temperature corresponding to the maximum extent of curing was 200°C. The curing mechanism was similar to that of conventional phenolic systems. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1410–1415, 2003     

Reaction injection molding process of glass fiber reinforced polyurethane composites

Structural reaction injection molding (SRIM) was used to produce polyurethane composites containing random continuous glass fiber mats. A long rectangular mold was used to carry out the SRIM experiments. 4,4′‐diphenylmethane diisocyanate and poly(propylene oxide) triol were used to formulate a thermoset polyurethane system. Dibutyltin dilaurate was used as a catalyst. A second order Arrhenius equation described the PU polymerization kinetic data obtained from the adiabatic temperature rise measurement. A viscosity as a function of temperature and conversion was developed using rheometer data. The pressure rise at the gate was measured during filling. The flow behavior within the mold was described by Darcy's law and the Kozeny's equation. The temperature profile within the mold measured by thermocouples during filling and curing coincided fairly well with the simulation results. The thermal transient problem at the wall was solved using the overall heat transfer coefficient, and it was analyzed as a function of Biot number. The dimensional stability of the fiber reinforced PU parts was excellent compared to the pure PU parts.     

Reaction and thermal analysis for SMC (sheet molding compound) molding in complicated geometries

A finite element technique has been developed for coupled reaction and heat transfer analysis in which mass diffusion is negligible. The temperature unknowns are located at nodal points, while the reaction variables (species concentrations, reaction rates) are at the Gauss points in each element. With a mechanistic kinetic model, the SMC (sheet molding compound) cure in 2-D and 3-D geometries was analyzed. The results for plate-and-rib configurations show the progression of cure and heat transfer and the influence of geometry on the progression. The analysis for a flat sheet of SMC in a mold with localized heating using bubblers indicates the thermal interaction between the mold and the curing SMC. Temperature and reaction profiles are given for each case.     

Curing characteristics of particulate-filled thermosets

A model to describe the effect of participate fillers on the heat transfer and curing characteristics of a thermosetting polymer is presented. It is assumed that the reaction kinetics are not altered by the addition of the filler and that the thermal characteristics of the composite are adequately described by the “spherical inclusion model.” The model is used to examine the effect of fillers on several important molding characteristics: time-temperature profiles, peak temperatures, extent of reaction, and gel time. Results are presented for the curing of a typical polyester resin with varying filler content and filler type (glass, calcium carbonate, and aluminum). These results indicate that:

• mold cycle time can be reduced at higher filler content by increasing the mold temperature without inducing thermal degradation, and
• the progression of cure fronts through the thickness of the mold is significantly altered with increasing filler content; at low filler content the cure front progresses from the centerline toward the wall; at higher filler content, the cure front progresses from the wall toward the centerline.