Effect of structure on properties of vinyl ester resins

The paper describes the synthesis of vinyl ester resins based on diglycidyl ether of bisphenol-A (epoxy equivalent = 450–465 g/eq) (VR resin) and tetrabromobisphenol-A (epoxy equivalent = 380–420 g/eq) (VR-1 resin). The viscosity of styrenated VR resin was higher than VR-1 resin. The effect of styrene andα-methyl styrene on curing of VR resins was studied. An increase in styrene from 30 to 50 wt% resulted in an increase in gel time and a decrease in exothermic peak. Addition ofα-methyl styrene delayed and depressed the exotherm. The mechanical properties of VR resin sheets and glass fabric reinforced laminates were better than VR-1 resins; whereas LOI of VR-1 was higher. A resin formulation containing 20–30 wt% of VR: VR-1 showed optimum mechanical properties and LOI.     

Emission modeling of styrene from vinyl ester resins with low hazardous air pollutant contents

Styrene is a commonly used co-monomer in vinyl ester (VE) resins, which acts as a reactive diluent and is required in most liquid molding fabrication methods to reduce viscosity and improve overall resin performance. Resins containing low hazardous air pollutant contents have been developed to reduce the styrene emissions during composite fabrication. VE monomers with a bimodal molecular weight distribution have been used to effectively decrease the amount of styrene in the system while maintaining low resin viscosities. Fatty acid vinyl ester (FAVE) resins partially replace styrene with non-volatile fatty acid monomers to reduce styrene emissions. The emissions from bimodal and FAVE resins were measured as a function of time and various parameters, including styrene content, VE molecular weight, and fatty acid monomer content and chain length. The initial emission rate from VE resins is only dependent on styrene content for constant evaporation geometry. Furthermore, the evaporation rate constant was the same regardless of VE molecular weight, styrene content, or the use of co-reactive diluent (MFA monomers). The diffusivity was not dependent on the styrene content in the resin, but decreased linearly as the VE molecular weight increased because of a corresponding increase in the resin viscosity. The diffusivity also increased as the content of MFA increased because of a decrease in the resin viscosity with high MFA content at high emission time. Furthermore, the emission profiles were accurately modeled using a modified version of 1D diffusion through a planar sheet that accounts for the depth change as a function of styrene evaporation. Overall, the model predicted emission profiles similar to the experimentally measured profiles as a function of time for various styrene contents, VE molecular weights, and fatty acid monomer contents.     

Composites based on bimodal vinyl ester resins with low hazardous air pollutant contents

Vinyl ester (VE) resins with a bimodal distribution of molecular weights were prepared via methacrylation of epoxy monomers. Bimodal VE resins and neat polymers had viscosities and mechanical properties similar to that of commercial resins. E-glass composites were prepared and also found to have similar mechanical and thermo-mechanical properties relative to composites fabricated using commercial resins. However, the fracture toughness of the bimodal resins was superior to that of the commercial resins partially as a result of increased molecular relaxations that were manifested in a broader glass transition. Overall, bimodal resins allow for the use of low styrene content (33 wt%), while maintaining excellent thermal, mechanical, and fracture properties for the neat resins and composites.     

酚醛氰酸酯树脂的固化动力学研究

通过非等温DSC对自制的酚醛氰酸酯树脂进行了固化动力学方面的研究，通过T～β外推法得到树脂凝胶化温度为211．00℃，固化温度为246．67℃，后固化温度为300．78℃。通过Kissinger方程求解树脂固化反应表观活化能为△E=74．14kJ／mol，碰撞因子为A=4．99×10^6。通过Crane方程求得固化反应级数为n=0．920。     

Rubber modified vinyl ester resins of different molecular weights

The morphology, as well as the related fracture and mechanical behavior of vinyl ester resins (DVER) of different molecular weights cured with styrene (S) and modified with two different liquid rubbers are presented and discussed. The liquid rubbers are: carboxyl terminated poly(butadiene-co-acrylonitrile) (CTBN), a common toughening agent for epoxy resins, and an almost unreactive rubber with the DVER and S comonomers, and a reactive rubber (vinyl terminated poly(butadiene-co-acrylonitrile), (VTBN). The initial miscibility of the modified systems and the reactivity of the rubber determine the final morphology of the material. This morphology will correspond to a continuous main phase (rich in the DVER-S copolymer) with simple rubber rich inclusions (as in the epoxy-rubber systems) or with inclusions with a complex internal structure, where phase separation occurs as in the low profile modified unsaturated polyester resins. The morphologies developed are strongly dependent on the resin molecular weight as well as on the elastomer added. In spite of the initially higher compatibility of the S-DVER-CTBN system with respect to the S-DVER-VTBN system, the reactivity of the vinyl-ended elastomer leads to a much finer distribution of the elastomeric phase. In particular, the low molecular weight resin cured with S and modified with 10% of CTBN leads to a cocontinuous structure with microvoids that generates a material of low density and poor mechanical and fracture properties. On the other hand, the use of VTBN as additive leads to a more compact morphology, with gradual reduction of the mechanical performance of the modified resins and improved fracture behavior.     

Thermal expansion of an E-glass/vinyl ester composite from 4 to 293 K

We have measured the thermal expansion of the three principal orthogonal directions of an E-glass/vinyl ester structural composite from liquid helium temperature, 4.2 K, to room temperature, 293 K. The linear thermal expansion at 4.2 K ranged from −0.23 to −0.71%, referenced to zero expansion at 293 K. We fitted the linear thermal expansion data from 4.2 to 293 K with a cubic polynomial for each of the three principal orthogonal directions.     

正交试验法优化乙烯基酯树脂增韧体系的研究

采用正交试验设计方法研究了固化体系的用量、乙烯基酯树脂的用量、增韧体系的内部配比,3个因素对乙烯基酯树脂力学性能的影响。通过测试树脂的凝胶时间和黏度特性,研究了树脂体系的反应性和流变性,制定树脂固化成型工艺。制作树脂浇注体,测试各个组分的冲击、弯曲性能。综合各种因素,优化选出了冲击韧性最好的一组配方,其冲击强度达到12.27kJ/m2,约为未改性树脂(冲击强度为3.11kJ/m2)的4倍。     

SW901环氧乙烯基复合材料的耐海水腐蚀性能研究

以玻璃纤维增强复合材料的腐蚀理论为基础,模拟海水环境,研究环氧乙烯基不饱和聚酯树脂（901树脂）浇铸体和GFRP的吸湿特性,对GFRP在不同介质盐度下拉伸性能、弯曲性能、抗冲击性能和巴士硬度的演变规律进行试验探索,通过扫描电镜观察分析了材料表观状况、微观结构的变化,并在湿热环境下研究基体与纤维之间膨胀系数不匹配和复合材...     

酚醛氰酸酯/环氧共固化树脂的结构和性能

研究了具有不同摩尔比的酚醛型氰酸酯（NCE）与双酚A型环氧（E-51）共固化树脂的化学结构与物理性能．结果表明,在共固化树脂的结构中,主要存在着三嗪、噁唑啉酮、异氰脲酸、醚键等化学结构．只有当氰酸酯的摩尔数大于环氧时,随着共固化体系中-OCN摩尔数的提高,化学结构中三嗪环含量增大,共固化树脂的力学性能、玻璃化转变温度（Tg）、烧蚀残留率、吸水率随之提高;当-OCN／epoxy的摩尔比大于1时,固化树脂的Tg比摩尔比小于1时提高30℃以上,力学性能的变化具有相同的规律．     

An investigation of the mechanical behaviour of vinyl ester resins cured by microwave irradiation

Compared to the commonly used curing process in natural conditions, microwave-assisted curing is significantly faster and, as such, appears to be a valid alternative for manufacturing composite structures in many industrial sectors. However the effects of microwave curing on the mechanical properties of the materials have not been extensively studied or considered in the literature.In this paper, the influence of natural and electromagnetic radiation curing on the mechanical properties of a vinyl ester resin for marine applications have been investigated and discussed. The results of a series of tensile and impact tests, reported in the present paper, have shown that microwave curing provide tensile strength, stiffness and impact strength values greater than those obtained by curing in natural conditions and, in addition, that long exposure to microwave radiation could be detrimental, leading to a quick degradation in the resin strength and absorbed energy.     

叔碳酸乙烯酯(VeoVaTM10)的研究进展与应用情况

叙述了叔碳酸乙烯酯(VeoVaTM10)以及共聚物涂层的优良特性,综合分析了各种叔碳酸乙烯酯合成技术的特点和进展,介绍了叔碳酸乙烯酯的应用情况,指明了行业方展中应注意的问题。     

乙烯基酯树脂浇铸体的高应变率压缩响应行为

利用电子万能试验机和分离式Hopkinson 压杆研究了乙烯基酯树脂浇铸体在准静态和高应变率下的压缩特性, 考察了试样压缩失稳和破坏的形貌。结果表明: 在准静态加载下(应变率为3.3 ×10 -4 / s～6.6 ×10-3 / s) ,材料呈韧性破坏, 失稳应力、失稳应变能密度均随应变率的提高而提高, 失稳应变随应变率的提高而降低; 在高应变率下(应变率为950/ s～5800/ s) , 材料呈脆性破坏, 失稳应力、失稳应变能密度均随应变率的提高呈增加趋势, 而失稳应变也随应变率的提高而提高, 这与准静态不同, 表明在高应变率下, 材料发生了“强迫高弹形变”。观察试样失稳和破坏后的形貌可以发现, 试样的破坏在失稳前正应力起主导作用, 失稳后切应力起主导作用, 使试样产生裂纹进而造成宏观破坏; 乙烯基酯树脂内部损伤的演化, 也依赖于应变和应变率。      

Failure analysis of styrene reactor tubes

The analysis of failure of the styrene reactor tubes made of stainless steel has been reported where the tubes contained catalyst as well as ethyl benzene in vapour form along with superheated steam at 570 °C. The tubes were exposed to flue gases causing heating of tubes to 790 °C in the upper part where cracking and failure were mostly noticed. The studies included microstructural examinations of cracked and uncracked tubes, fracture surface investigations and estimation of creep rupture strength, etc. The degradation in microstructure such as extensive grain coarsening, sigma phase formation, carbide formation along grain boundaries, etc., led to development of cracks/voids within the grains and along the grain boundaries and also excessive oxidation of tubes. Possible chemical attack by the feed on the inner surface of tubes further deteriorated the tube life. Suggestions for avoidance of failure have been listed.     

Mechanical and three-body abrasive wear behaviour of three-dimensional glass fabric reinforced vinyl ester composite

The mechanical and three-body abrasive wear behaviour of two- and three-dimensional E-glass woven fabric reinforced vinyl ester composites were studied in this article. The mechanical properties were evaluated using universal testing machine as per ASTM D-638. Three-body abrasive wear tests were conducted using rubber wheel abrasion tester (RWAT) under different abrading distances at two loads, wherein the wear volume loss were found to increase and that of specific wear rate decrease. The results indicate that the three-dimensional glass woven fabrics in vinyl ester (G_3D–V) have significant influence on wear under varied abrading distance/loads. Further, it was found that G_3D–V composite exhibited lower wear rate compared to two-dimensional glass woven fabric reinforced vinyl ester (G_2D–V) composite. The worn surface features, as examined through scanning electron microscope (SEM), show ruptured glass fiber in G_2D–V composite compared to G_3D–V composites.     

玻璃纤维/溴化环氧乙烯基酯加速老化与自然老化的相关性

选取我国典型气候条件下的万宁和拉萨这两个试验站,进行玻璃纤维/溴化环氧乙烯基酯3年的自然环境老化试验;同时在实验室环境下进行了玻璃纤维/溴化环氧乙烯基酯的湿热老化、热空气老化、光老化和高温浸水人工加速老化试验。测试老化后玻璃纤维/溴化环氧乙烯基酯的拉伸强度、弯曲强度和压缩强度等力学性能,研究了玻璃纤维/溴化环氧乙烯基酯在自然和实验室环境下的老化规律。用灰色理论中的灰色关联分析法计算了自然环境老化试验与人工加速老化试验的相关性。结果表明：以压缩强度为性能指标时,试验室加速光老化试验与自然环境老化试验的相关性最大,关联度达到了0.75左右。计算得到了加速光老化对拉萨和万宁自然老化的加速因子（AF）和加速转换因子（ASF）,两地的ASF最终分别稳定在5.28和7.25。     

锂离子电解液/环氧乙烯基酯树脂固态电解质的制备与性能

将具备优良化学稳定性及高电导率的双三氟甲烷磺酰亚胺锂（LiTFSI）溶于1-乙基-3-甲基咪唑双三氟甲磺酰亚胺盐（EMIM-TFSI）离子液体中制成LiTFSI-EMIM-TFSI电解液,加入环氧乙烯基酯树脂（VER）中对其进行改性。结果表明,添加了上述电解液后的锂离子电解液/环氧乙烯基酯树脂（LiTFSI-EMIM-TFSI/VER）体系可通过FTIR检测到离子液体的特征吸收峰。随着电解液含量的增加,LiTFSI-EMIM-TFSI/VER体系的孔隙率逐渐增大,沟壑与片层结构逐渐增多。这一变化有利于锂离子的传导,提高体系的电学性能,同时可在一定程度上改善树脂的塑性和韧性,提高LiTFSI-EMIM-TFSI/VER体系的力学性能。在本实验中,当电解液含量为40wt%时,LiTFSI-EMIM-TFSI/VER体系多功能性得以最好地实现。     

Applications of modeling in polymer-property prediction

Summary A number of molecular modeling techniques have been applied for the prediction of polymer properties and behavior. Five examples illustrate the range of methodologies used. A simple atomistic simulation of small polymer fragments is used to estimate drug compatibility with a polymer matrix. The analysis of molecular dynamics results from a more complex model of a swollen hydrogel system is used to study gas diffusion in contact lenses. Statistical mechanics are used to predict conformation dependent properties — an example is the prediction of liquid-crystal formation. The effect of the molecular weight distribution on phase separation in polyalkanes is predicted using thermodynamic models. In some cases, the properties of interest cannot be directly predicted using simulation methods or polymer theory. Correlation methods may be used to bridge the gap between molecular structure and macroscopic properties. The final example shows how connectivity-indices-based quantitative structure-property relationships were used to predict properties for candidate polyimids in an electronics application.     

Deformation response and constitutive modeling of vinyl ester polymer including strain rate and temperature effects

The deformation behavior of vinyl ester polymer under monotonic tensile loading is characterized and modeled. The Standard Linear Solid model, which is a physical model, was used and modified to represent the stress–strain behavior of this polymer over a wide range of strain rates and temperatures. This model was also used to predict the stress-relaxation and short-term creep behavior of this material. The comparisons between the predictions and experimental data from tensile and relaxation tests demonstrate that this model can represent the deformation behavior of the material reasonably well.     

Graft copolymerization of 2-vinyl pyridine and styrene onto isotactic polypropylene powder by the preirradiation method

Preirradiated isotactic polypropylene (IPP) powder has been modified by grafting 2-vinyl pyridine (2-VP) and styrene (Sty) in an aqueous medium. The graft copolymerization reaction was studied under different experimental conditions such as total dose, monomer concentration, amount of the solvent, time of reaction and temperature to determine the optimum conditions for affording maximum percentage of grafting (P_g). Maximum grafting percent of 2-VP (180%) and styrene (117%) was obtained under optimum conditions. The rate of grafting (R_g) of 2-VP and styrene has also been determined as a function of total dose, initial monomer concentration and the reaction temperature. From maximum P_g and different R_g values of 2-VP and Sty, 2-VP is more reactive towards grafting as compared to styrene under optimum conditions. Characterization of the graft copolymers is based on differential scanning calorimetric (DSC) analysis. Isolation of the grafted poly(2-VP) and poly(styrene) chains from the grafted samples provides an additional evidence of formation of the graft copolymer.     

氰酸酯树脂改性的研究现状

介绍了氰酸酯树脂改性的几种方法,阐述了热固性树脂、热塑性树脂、橡胶弹性体、晶须等改性氰酸酯的研究现状及优缺点,并展望了氰酸酯树脂的研究方向。