Curing of epoxy systems at sub‐glass transition temperature

Three epoxy‐amine thermoset systems were cured at a low ambient temperature. Evolution of the reaction kinetics and molecular structure during cure at the sub‐glass transition temperature was followed by DSC and chemorheology experiments. The effect of vitrification and the reaction exotherm on curing and final mechanical properties of the epoxy thermosets was determined. Thermomechanical properties of the low‐temperature cured systems depend on the reaction kinetics and volume of the reaction mixture. Curing of the fast‐reacting system in a large volume (12‐mm thick layer) resulted in the material with T_g exceeding the cure temperature by 70–80°C because of an exothermal temperature rise. However, the reaction in a too large volume (50‐mm layer) led to thermal degradation of the network. In contrast, thin layers (1.5 mm) were severely undercured. Well‐cured epoxy thermosets could be prepared at sub‐T_g temperatures by optimizing reaction conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3669–3676, 2006     

RTM用含硅芳炔树脂的流变特性与固化反应动力学

含硅芳炔树脂(PSA-R)具有优异的耐高温、优良的介电性能、高温力学性能,以及优异的工艺性能,适用于RTM成型工艺,广泛应用于航空航天、电子信息领域.本文采用动态差示扫描量热法(DSC)研究了含硅芳炔树脂的固化反应,试验表明含硅芳炔树脂的固化动力学符合n-级固化反应模型,固化反应级数约为2级,反应活化能为110kJ·mol~-1.用平板流变仪研究了PSA-R树脂的动态粘度及等温粘度变化,研究了凝胶时间与温度的关系,建立了凝胶模型,根据双Arrhenius方程,建立了含硅芳炔树脂的粘度模型,该模型预测粘度与实验结果相吻合.     

热固性树脂的化学流变性

本文讨论了热固性树脂固化时化学流变性问题,并通过两种途径模拟了热固性树脂的化学粘度.     

化学反应中聚合物流变动力学的研究进展

化学反应中聚合物流变动力学是联系化学反应动力学与聚合物流变学的交叉学科中的一类重要科学问题。文中从单体聚合、树脂固化、聚合物之间的反应以及聚合物接枝反应四方面综述了近年来聚合物流变动力学的研究进展,分析了尚存在的难点,并展望了其发展方向。     

中温固化阻燃结构胶膜流变特性与蜂窝粘接性能

研究了用于蜂窝夹层结构粘接的阻燃结构胶膜的化学流变特性与蜂窝粘接性能。通过流变仪研究了胶膜固化过程中化学黏度的变化,考察了固化反应(温度、时间)、阻燃剂、增韧剂对体系化学流变特性的影响。分析了流变特性和胶瘤形成在蜂窝夹层结构粘接过程中的作用,并测试了蜂窝夹层结构的剥离和平面拉伸性能。结果表明:阻燃剂的加入使得体系100℃前的黏度有所升高,固化活性略有降低,最低黏度温度从112℃推迟到120℃;加入增韧剂后的胶黏剂的黏度显著提高,制备的阻燃胶膜最低黏度在50Pa.s左右,固化过程中具有适宜的流动性和胶瘤形状,固化后具有较高的滚筒剥离强度和平面拉伸强度。     

聚硫醚酰亚胺热聚合反应的动力学模拟

用热重分析仪（TGA）和动态应力流变仪（DSR）分别测量了聚硫醚酰亚胺热聚合反应过程中转化率和粘度随时间的变化。考虑基团迁移和构象转换速率对热聚合反应过程的影响,通过将体系粘度～时间关系（化学流变模型）引入动力学模型,建立了用于描述聚硫醚酰亚胺热聚合反应的扩散限制动力学模型,模型预测和实验结果有很好的一致性。     

Chemorheology and Kinetics of High-Performance Polyurethane Binders Based on HMDI

Aliphatic diisocyanates, such as 1,6-hexamethylene diisocyanate (HMDI), are preferred curing agents for the formation of polyurethanes (PUs) in applications where resistance to abrasion or degradation by ultraviolet light takes precedence. Aside from the final properties, the curing agent plays a key role in the bulk manufacturing of such materials, and it mainly affects the polymerization kinetics and their rheology. The copolymerization of HMDI and a metallo-prepolymer derivative from hydroxyl-terminated polybutadiene (HTPB) is studied under isothermal conditions (50–80 °C). This study is carried out by means of an indirect method, using both rotational viscometry and dynamic rheometry. At the beginning of the process, the viscosity growth fit well to a first-order kinetic model. Afterward, the reactive system passes through gelation, from which only rheology is allowed for the investigation of the entire polymerization process. This transition is analyzed in depth together with predictions from percolation theory. The conversion degree is determined from rheological measurements, and then an autocatalytic kinetic model is applied to describe the overall process. Finally, an isoconversional method allows the evolution of activation energy to be studied. This analysis merits attention for the development of high-performance binders that are of great interest in aerospace propulsion technology.     

Numerical simulation for bubble growth during supercritical CO2 foaming epoxy resin process based on chemorheology

The bubble growth process of epoxy resin foams has been evaluated through a combination of numerical simulation and chemorheology. It was discovered that rheological properties play an essential role in forecasting bubble growth during supercritical CO₂ epoxy resin foaming. Time–cure superposition was conducted revealing that shear storage modulus increased from 10⁻³ to 10⁶ Pa during the curing reaction process. The complex viscosity increased up to 10⁵ Pa s and the characteristic relaxation time increased up to 53.1 s with the curing degree. The epoxy resin with high rigid modulus could effectively inhibit bubble growth. Furthermore, the simulation results indicated that the bubble growth process for epoxy resin foams was influenced by both the CO₂ content and CO₂ plasticization on rheology properties.     

Poly(methyl methacrylate)‐modified epoxy/amine system for reactive rotational moulding: crosslinking kinetics and rheological properties

BACKGROUND: The rotational moulding of thermosetting resins is hampered by their low viscosity and the abrupt increase in their viscosity as they polymerize. This study investigates the use of poly(methylmethacrylate) (PMMA) as a rheological processing aid in reactive blends of an aromatic diepoxy resin (diglycidyl ether of bisphenol‐A, DGEBA) and an aromatic diamine (diethyltoluenediamine, DETDA) by studying the miscibility, curing, rheology, dynamic properties and morphology of the uncured solutions and of the resulting highly crosslinked polymer blends. RESULTS: The PMMA was miscible in the uncured resins as expected from consideration of their solubility parameters, and the effect of PMMA concentration on the glass transition temperature, measured via differential scanning calorimetry (DSC), was fitted to several models. Addition of PMMA significantly increased the viscosity of the uncured blend which obeyed the log‐additivity rule. The curing behaviour was monitored using DSC, infrared spectroscopy and dynamic rheology and it was found that addition of PMMA caused a small reduction in rate due to a dilution effect. The dynamic and steady shear rheologies were used to determine the gel point and gel relaxation index. Dynamic mechanical thermal analysis provided evidence for phase separation of the components into PMMA‐rich domains and an epoxy‐rich matrix and this was confirmed with electron microscopy studies. CONCLUSION: These results indicate that addition of small amounts of PMMA to DGEBA/DETDA enlarges the processing window with regards to the rotational moulding of thermosets. In addition, the blending of small amounts (ca 10 wt%) of PMMA with the DGEBA/DETDA resin appears to cause only a modest sacrifice in thermal resistance. Copyright © 2009 Society of Chemical Industry     

不同添加剂对鸡肉盐溶蛋白质热诱导凝胶性质的影响

采用质构分析法、动态流变分析法、差示扫描微量热法研究大豆分离蛋白、花生蛋白、卡拉胶对鸡胸肉和鸡腿肉盐溶蛋白热诱导凝胶性质的影响。试验结果表明:不同添加剂可在不同程度上改善鸡胸肉和鸡腿肉盐溶蛋白热诱导凝胶特性,其中卡拉胶添加效果最好。由动态流变学分析可知,鸡胸肉和鸡腿肉盐溶蛋白形成凝胶存在不同作用机理。热稳定性分析表明,鸡肉混合蛋白热诱导凝胶形成主要与肌球蛋白有关,肌动蛋白作用效果不明显。不同添加剂可增强鸡胸肉和鸡腿肉盐溶蛋白的变性温度和变性热,其中大豆分离蛋白添加效果最显著。