氰酸酯树脂改性热固性丁苯树脂的固化及其动力学

利用傅里叶变换红外光谱法(FT-IR)和差示扫描量热法(DSC)研究了氰酸酯树脂改性热固性丁苯树脂的固化反应特性及其动力学.以温度-升温速率外推法计算得到固化反应起始温度(Ti0)、峰顶温度(Tp0)和终止温度(Tf0)分别为414.2、444.5、460.6 K,对改性树脂的固化过程进行优化.采用Freeman-Ca...     

动态扭振法在树脂固化研究中的最新应用

用计算机全自动控制的LHX-Ⅱ型树脂固化仪对热固性树脂基蒙脱土纳米复合材料、热塑性树脂PMMA基蒙脱土纳米复合材料以及聚合物互穿网络等体系进行了固化反应的研究。借用Avrami理论来处理树脂基纳米复合材料的固化行为,求取固化反应表现动力学参数。     

介绍一本新书《热固性树脂和树脂基复合材料的固化——动态扭振法及其应用》

中国科学技术大学出版社近日在“当代科学技术基础理论与前沿问题研究丛书、中国科学技术大学校友文库”中出版了一本由何平笙、金邦坤、李春娥撰写的《热固性树脂及树脂基复合材料的固化——动态扭振法及其应用》专著^[1],值得向读者推介。     

应用扭辫分析技术研究环氧树脂的固化行为

热固性树脂作为固体材料使用,具有优良的工程特性,如尺寸稳定性好、耐溶剂性好、强度和耐热性较高等。但是以往对材料性能有直接影响的树脂固化过程,却未能得到充分的研究。主要是由于热固性树脂的固化过程从低分     

用红外光谱法对热固性酚醛树脂固化过程的研究

用红外光谱法研究了四种热固性酚醛树脂在固化过程中的化学变化。结果表明热固性酚醛树脂的固化过程,首先是羟甲基发生缩合反应,缩合反应形成醚键是主要的。热固性酚醛树脂在进一步固化时(150—200°)出现了羰基,它的出现不是亚甲基氧化所致,而是部分醚键断裂形成了醛羰基。对热固性酚醛树脂的固化过程的机理进行了讨论。     

一种加成固化型热固性树脂PN-PAA固化过程和热稳定性研究

研究了炔丙基醚化酚醛树脂(PN)与聚芳基乙炔树脂(PAA)的反应性共混物(以下简称PN-PAA共混树脂)的相容性,并对共混树脂的固化过程和固化物的耐热性进行了表征.相态、DSC、SEM、TEM等测试结果均表明共混树脂及其固化物是完全相容的均相体系.凝胶时间、粘度、DSC等结果表明共混树脂固化工艺性优良,适合多种成型工艺(如RTM),显著改善了PAA树脂的固化工艺缺陷.DMA、TGA等分析表明共混树脂固化物具有很高的耐热性,可作为新型的防热复合材料和高温结构材料的基体.     

热固性树脂的热机曲线研究 Ⅱ.以邻苯二甲酸酐固化的环氧树脂热机曲綫的研究

一些研究工作者指出:固化得不够完全的热固性树脂的热机曲线,由于在测量过程中的进一步固化,使树脂的弹性模量增大而引起形变减少,从而使得在曲线上呈現出一个反常的特征峯。但是当进一步去分析这个現象时,可以发現,在測定的过程中,样品从低温上升到較高的温度,树脂的变形逐渐减少,最后达到与在高温下(200℃)长期热处理(10小时)样品同样的形变值(图1)。因此如果被試样品形变減少,确系     

热固性聚酰亚胺树脂研究进展

热固性聚酰亚胺树脂是目前耐温等级最高的基体树脂之一, 以其为基础的复合材料在航空航天等领域有着广泛的应用。 本文对热固性聚酰亚胺树脂的研究进行了系统的综述, 并对其未来的发展方向进行了展望。     

双马来酰亚胺树脂固化过程的红外光谱分析

利用傅里叶变换红外光谱法研究双马来酰亚胺树脂固化过程中的结构变化,认为双马来酰亚胺树脂固化反应分两进行,第一步是低温下的“ENE”反应,第二步是高温下的Diels-Alder反应,树脂第一步固化反应达到一定程度后,要进一步提高固化反应程度,必须提高温度才能使第二步固化反应发生。     

动态扭振法研究聚甲基丙烯酸甲酸／蒙脱土纳米复合材料的本体插层聚合

用动态扭振法研究塑性塑料聚甲基丙烯酸甲酸（PMMA）／蒙脱土（MMT）复合体系的本体插层聚合，并试用处理交联体系固化的Folry理论，非平衡态热力学涨落理论和Avrami方程研究PMMA／MMT复合体系的本体插层聚合，求取表观活化能Ea.实验发现，PMMA／MMT插层聚合转化率曲线中后期与热固性树脂的固化曲线极为类似，表明剥离后的蒙脱土片层在复合材料中起到交联点的作用。     

Cure kinetics of light-activated polymers

The purpose of this article is to develop a mathematical model that describes photocure and photopolymerization kinetics. This model is neither wholly phenomenological nor mechanistic, but contains elements of both. We draw an analogy between the classical Avrami approach for first-order phase transformations and the kinetic phenomena that occur during photocuring, and take into account cure inhibition due to a decrease in mobility of the constituents. The result is an explicit algebraic two-parameter expression for the extent of cure versus time. More importantly, the two parameters have physical significance, and to some extent can be predicted a priori. The model is compared to three sets of unrelated data, and excellent agreement is obtained, except for part of the data at the onset of the reactions. Physical insight obtained by comparing our theory with experiments supports the existence of preferred sites for initiating the reaction, and indicates that irradiation is the rate-limiting step in the overall cure process in the limit of small irradiation intensities. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2887–2894, 1998     

Hybrid epoxy-based thermosets based on polyhedral oligosilsesquioxane: Cure behavior and toughening mechanisms

Polyhedral oligosilsesquioxane (POSS)-reinforced thermosets based on octaglycidyl epoxy polyhedral oligosilsesquioxane cured with 4,4′-diaminodiphenyl sulfone (DDS) were prepared and studied for their cure, thermomechanical, and microstructural characteristics. Particular attention was paid to nanometer-scale deformation processes responsible for toughening, as revealed by transmission electron microscopy (TEM) in conjunction with the thermal properties. A cure analysis investigated with calorimetry and rheometry showed a significant dependence of the cure mechanism and kinetics on the DDS content, but all hybrid thermosets reacted completely below 300 °C into rigid solids. A dynamic mechanical analysis of this hybrid resin system showed that increasing the DDS concentration used during cure increased the dynamic storage modulus in the glassy (temperature < glass-transition temperature) and rubbery (temperature > glass-transition temperature) states, simply through an increase in the crosslink density. The phase structures revealed by TEM with selective POSS staining were drastically affected by the DDS concentration and manifested as altered nanomechanical deformation structures. It was qualitatively found that the main toughening mechanism in the studied POSS-reinforced thermosets was void formation at the nanometer scale, possibly templated by limited POSS aggregation. As the crosslinking density increased with the DDS concentration, microshear yielding between voids prevailed, providing a balance of stiffness, strength, and toughness. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3299–3313, 2003     

环氧树脂/PAMAM体系的固化动力学研究

用动态扭振法研究以聚酰胺-胺(PAMAM)为固化剂的环氧树脂／PAMAM体系的固化动力学行为。结果表明,该实验体系能够很好地用Flory理论和Avami方程进行拟合。     

Tailoring the Properties of Diels-Alder Reaction Crosslinked High-performance Thermosets by Different Bismaleimides

A series of Diels-Alder reaction cross-linked thermosets with recyclability and healability were prepared from furan-containing aromatic polyamide and bismaleimides with different chemical structures.The structures of synthesized bismaleimides were confirmed by 1 H nuclear magnetic resonance(1 H-NMR)spectroscopy;their reversible cross-linking with the furanic polyamide was further detected by 1 H-NMR technique and sol-gel transition behavior.The dynamic mechanical analysis and tensile test revealed the variable thermal and mechanical properties of thermosets cross-linked by different bismaleimides and with different molar ratios of maleimide group to furan group(Ima/fur).The tensile test also demonstrated that the better recyclability and solvent-assisted healability of thermosets cross-linked could be achieved by more flexible bismaleimides.This work is expected to provide valuable information for design of recyclable and healable high-performance thermosets with desired properties.     

Cure behavior of epoxy resin/MMT/DETA nanocomposite

The Flory's gelation theory, non-equilibrium thermodynamic fluctuation theory and Avrami equation have been used to predict the gel time t _g and the cure behavior of epoxy resin/organo-montmorillonite/diethylenetriamine intercalated nanocomposites at various temperatures and organo-montmorillonite loadings. The theoretical prediction is in good agreement with the experimental results obtained by dynamic torsional vibration method, and the results show that the addition of organo-montmorillonite reduces the gelation time t _gand increases the rate of curing reaction, the value of k, and half-time of cure after gelation point t_1/2 decreases with the increasing of cure temperature, and the value of n is ~2 at the lower temperatures (<60°C) and decreases to ~1.5 as the temperature increases, and the addition of organo-montmorillonite decreases the apparent activation energy of the cure reaction before gelation point, but has no apparent effect on the apparent activation energy of the cure reaction after gelation point. There is no special curing process required for the formation of epoxy resin/organo-montmorillonite/diethylenetriamine intercalated nanocomposite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cure behavior of epoxy resin/montmorillonite/imidazole nanocomposite by dynamic torsional vibration method

Flory’s gelation theory, the non-equilibrium thermodynamic fluctuation theory and the Avrami equation have been used to predict the cure behavior of epoxy resin/organo-montmorillonite (Org-MMT)/imidazole intercalated nanocomposites at various temperatures and Org-MMT loadings. The theoretical prediction is in good agreement with the experimental results obtained by a dynamic torsional vibration method. The results show that the addition of Org-MMT reduces the gelation time t_g and increases the rate of the curing reaction, the value of the kinetic constant k. The half-time t_1/2 of cure after the gel point decreases with increasing of cure temperature, and the value of n is around 3 at lower temperature (<90 °C) and decreases to ∼2 as the temperature increases. The addition of Org-MMT has no obvious effect on the apparent activation energy of the cure reaction. There is no special curing process required for the formation of an epoxy resin/Org-MMT/imidazole intercalated nanocomposite.     

Synthesis and Characterization of Fluorinated Acrylic Polymer and the Properties of Epoxy Thermosets Modified With It

A novel fluorinated acrylic polymer poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)-r-poly(glycidyl methacrylate) (PHFMA-r-PGMA) was synthesized and used to modify the general performances of epoxy resin. Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H-NMR) successfully verified the synthesis of PHFMA-r-PGMA. In order to study the effect of epoxy groups in PHFMA-r-PGMA on the properties of modified epoxy resin, corresponding fluoropolymer without epoxy group (PHFMA) was also prepared, and the properties of epoxy thermosets modified by two kinds of fluoropolymers were comparatively studied. The contact angle measurements indicated that the PHFMA-r-PGMA and PHFMA modified thermosets both showed considerable hydrophobicity and lipophobicity. For further comparison, it was also found that the thermosets modified by PHFMA-r-PGMA had a little worse hydrophobicity and lipophobicity but better surface stability than which modified by PHFMA because the epoxy groups in PHFMA-r-PGMA “locked” more fluoropolymers in the bulk matrix of the thermosets, but PHFMA was more freely able to migrate to the surface of the thermosets. SEM images of the fracture surface of PHFMA-r-PGMA and PHFMA modified epoxy thermosets displayed “irregular ripples” or “protuberant island” structures, which suggesting both of these two copolymers could significantly toughen epoxy resin. The results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the thermosets modified by PHFMA-r-PGMA had better thermal stability than which modified by PHFMA due to the higher crosslinking density between PHFMA-r-PGMA and epoxy resin because of the epoxy groups in PHFMA-r-PGMA. The mechanical properties were investigated by tensile testing and impact testing. Although the tensile strength of the PHFMA-r-PGMA and PHFMA modified epoxy thermosets both declined slightly with growing the content of fluoropolymers, the elongation at break and impact strength both increased first and then decreased in the meantime, which indicated that the two kinds of modified thermosets had better toughness than pure epoxy resin. It may be because the macro-phase separation between the long fluorine carbon chain segments and epoxy resin during curing could absorb the impact energy effectively.     

不饱和聚酯/有机蒙脱土复合材料的固化动力学

用动态扭振法研究不饱和聚酯／有机蒙脱土复合材料的固化动力学行为。结果表明该实验体系能够很好地应用Flory理论和Avami方程进行拟合。用非平衡态热力学涨落理论对纳米复合材料的固化作了理论顸估,顸估结果与实验固化曲线有很好的相符性。有机蒙脱土的加入降低了不饱和聚酯的固化反应速率,对固化反应表现活化能和复合材料的形成过程没有很大的影响。根据实验结果分析不饱和聚酯在有机蒙脱土存在下的固化分为定型和熟化两个阶段,在一定的固化温度和填充含量下。从动态扭振曲线上可以明显地观察到这种“二次固化”现象。     

Circular Upcycling of Bottlebrush Thermosets

The inability to re-process thermosets hinders their utility and sustainability. An ideal material should combine closed-loop recycling and upcycling capabilities. This trait is realized in polydimethylsiloxane bottlebrush networks using thermoreversible Diels–Alder cycloadditions to enable both reversible disassembly into a polymer melt and on-demand reconfiguration to an elastomer of either lower or higher stiffness. The crosslink density was tuned by loading the functionalized networks with a controlled fraction of dormant crosslinkers and crosslinker scavengers, such as furan-capped bis-maleimide and anthracene, respectively. The resulting modulus variations precisely followed the stoichiometry of activated furan and maleimide moieties, demonstrating the lack of side reactions during reprocessing. The presented circularity concept is independent from the backbone or side chain chemistry, making it potentially applicable to a wide range of brush-like polymers.     

Relaxations in thermosets. VI. Effects of crosslinking on sub-Tg relaxations during the curing and aging of epoxide-based thermosets

The dielectric permittivity and loss of diglycidyl ether of bisphenol-A-based thermosets cured with diaminodiphenyl methane and diaminodiphenyl sulfone have been measured over a temperature range 77–400 K after curing or aging for a predetermined duration. Of the two sub-T_g relaxations, the height of the γ relaxation peak monotonically decreases during both the cure and postcure periods, and the height of the β relaxation peak first increases to a maximum value and then decreases. This decrease is attributed to physical aging effects. The height of the α-relaxation peak decreases. The γ- and β-relaxation peaks become increasingly separated in temperature. A concept of accumulated equivalent curing time which is based upon known chemical kinetics has been introduced for use in both theoretical and practical aspects of the study of thermosets. It is shown that substantial curing of the sample occurs during its slow heating to the curing temperature. The use of this concept in the curing of thermosets is illustrated. A procedure for the analysis of the distribution of relaxation times from a set of results limited in both frequency and temperature range is described. The distribution parameter is 0.20 and 0.16 for the γ and β process, respectively, and remains constant with postcuring and physical aging. The distribution parameter for the α process decreases from 0.60 to 0.36 on curing.