不饱和聚酯树脂的固化收缩机理与收缩应力分析

本文用自由体积理论分析了不饱和聚酯树脂的固化收缩机理,理论计算与实验测定结果基本一致。用光纤应力传感器测定不饱和聚酯树脂由于固化收缩而产生的内部应力,得出收缩应力与固化过程中降温阶段的收缩率成正比的结论。     

树脂固化时体积收缩内应力的本质及消除途径

树脂固化收缩应力的主要原因是单体之间的分子间距离缩短变为共价距离。工艺上可通过降低官能团浓度，加入高分子增韧剂和无机粉状填料，改进固化工艺等方法来减少体积收缩率，进而减少内应力。利用膨胀单体共聚有可能根本消除收缩应力。     

高绝缘,耐低温浇注胶的防开裂

从树脂、增韧剂、填料及固化剂的种类和用量等方面讨论了如何降低固化收缩应力及低温收缩应力,从而减少因固化收缩和冷冻收缩引起的开裂现象,以保持所合成浇注胶固化物在常温和低温下的高绝缘性能。     

低收缩添加剂对聚酯树脂固化的影响

本文采用SPI法测定加入不同含量低收缩添加剂（LPA）的不饱和聚酯树脂的固化放热曲线。研究了低收缩添加剂的用量，以及中低温固化体系对不饱和聚酯树脂的凝胶时间，固化时间，放热峰温度，固化放热量的影响。     

国外低轮廓UPR固化收缩控制研究发展动态

本文详细介绍了国外低轮廓UPR固化收缩控制研究发展动态，概述了国外在这一研究领域中涉及的主要研究内容、实验方法和影响因素，以及低轮廓UPR收缩控制机理研究中的一些结论。     

UV-固化胶黏剂收缩率的研究

UV-固化胶黏剂固化过程中发生的体积收缩,是影响胶黏剂粘接性能的重要因素．本文分析讨论了UV-固化胶黏剂收缩率的产生原因、影响因素、研究方法,收缩率和收缩应力的关系,以期针对不同的使用需求,找到降低或消除收缩率的有效方法。     

新型低收缩添加剂研究

本文研究了自制低收缩添加剂用量对不饱和聚酯树脂固化收缩率与力学性能的影响.结果表明,在不饱和聚酯树脂中加入20%的该类低收缩添加剂,树脂的固化收缩率为2.1%,弯曲强度保有率为88%,弯由模量没有明显变化;并利用SEM对加有低收缩添加剂的树脂固化试件的断面形貌进行了表证,分析了低收缩添加剂的作用机理.     

PF用低收缩添加剂的研究

通过调整物料配比合成了端羟基封端和端羧基封端的聚氨酯 (PU)预聚物 ,并分别与酚醛树脂 (PF)固化 ,制备了两种低收缩体系的复合物 ,利用红外光谱对其结构进行表征。通过测试固化物的体系收缩率表明 :随着聚氨酯预聚物加入量的增加 ,PF/PU共混物的体积收缩率明显变小 ,并能达到负值。端羧基PU的低收缩性能更为显著 ,当其加入量在 5 相似文献   

低收缩乙烯基酯树脂的研究

本文选用聚氨酯、聚醋酸乙烯酯、丁腈橡胶等聚合物作为低收缩添加剂,研究了它们在降低乙烯基酯树酯固化收缩率方面的作用。探讨了树脂固化收缩率与添加剂种类、含量、分子量及成型温度等因素之间的关系,用DDV、SEM等现代分析手段对改性体系的亚微观结构进行了表征。在实验的基础上,找到了效果较为满意的改性配方。     

树脂固化过程中相分离的研究

本文通过体视显微镜观察了含低收缩添加剂树脂固化体系的相分离过程,从而研究了它的结构形成过程.     

The mechanism for occurrence of internal stress during curing epoxide resins

The mechanism for the occurrence of internal stress in the curing cycle of four-functional epoxide resins was investigated in detail. The internal stress in this system was generated at the vitrification point in the course of curing, because the modulus of samples was rapidly increased at this point. After the vitrification point, the internal stress was increased with an increase of the shrinkage in the curing and cooling processes. Moreover, the magnitude of the internal stress in the four-functional resin systems depended on the chemical structure of aromatic diamines used as curing agents. This was explained by the difference of curing shrinkage after vitrification in each system.     

Study on curing shrinkage and mechanism of DHOM-modified epoxy-acrylate-based UV-curing 3D printing materials

UV-curing 3D printing technology is one of the technologies with the highest molding efficiency and accuracy in the field of 3D printing. At present, the main problems of UV-curing 3D printing materials include the high curing shrinkage and the low toughness. In this work, free radical/cation hybrid curing system was developed, the effects of expansion monomer (DHOM, 3,9-diethyl-3′,9′-dihydro-xymethyl-1,5,7,11-tetraoxaspiro[5,5]undecanone) on the curing shrinkage, toughness, and other properties of the epoxy acrylate-based UV-curing 3D printing materials were investigated. The results showed that when the added amount of DHOM was 15 wt%, the best comprehensive performance of UV-curing 3D printing materials was obtained. At this time, the curing shrinkage rate decreased from 6.13% to 3.47%. The main reason was that DHOM undergoes ring-opening polymerization under the action of cationic photoinitiator, resulted in volume expansion. The impact strength increased from 9.61 to 12.13 KJ/m², which was because that the ring-opening reaction of DHOM reduced the curing shrinkage of the resin system and released the internal stress between the resin molecules.     

Analytical estimate for curing‐induced stress and warpage in coating layers

A thermoset coating that is applied to an elastic substrate will develop residual stresses during curing because of polymerization shrinkage of the resin. This shrinkage only partly contributes to the residual stresses because, before gelation, the stresses relax completely. In this study, we developed explicit analytical expressions for the curing efficiency factor, the residual stresses, and the resulting warpage. We did this by assuming that after gelation, the material was in its rubbery state and that viscoelastic effects were absent. A difference between the free and constrained warpages during curing was made. The analytical warpage models were shown to give results comparable to those of the numerical calculations with a fully curing‐dependent viscoelastic material model. Furthermore, for the first time, accurate analytical expressions for the stress‐free temperature and stress‐free strain were obtained. With these expressions, the effect of curing shrinkage on the residual stresses could easily be incorporated into existing (numerical) stress analysis without the need for extensive curing‐dependent viscoelastic material models. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

Water absorption in internally cured mortar made with water-filled lightweight aggregate

The increased propensity for shrinkage cracking in low water-to-cement ratio (w/c) concrete has inspired the development of new technologies that can reduce the risk of early-age cracking. One of these is internal curing. Internal curing uses saturated lightweight aggregate to supply ‘curing water’ to low w/c paste as it hydrates. Significant research has been performed to determine the effects of internal curing on shrinkage and stress development; however, relatively little detailed information exists about the effects of internal curing on fluid transport properties such as water absorption or diffusivity. This study examines the absorption of water into mortar specimens made with saturated lightweight aggregates (SLWA). These results indicate that the inclusion of SLWA can reduce the water absorption of mortar specimens. This observation was reinforced with electrical conductivity measurements that exhibited similar reductions.     

乙烯基不饱和聚酯固化放热及固化热应力的研究

本文讨论了乙烯基不饱和聚酯树脂的固化放热情况及其影响因素。利用自由体积理论和分子弹性网络理论分析固化收缩和固化热应力产生的机理,由此得出热应力与树脂固化峰值温度、交联密度和体积收缩率有关的结论,并指出减小热应力的途径和方法。     

Assessment of residual stresses during cure and cooling of epoxy resins

A new stress monitoring technique, a stress-tracking device, is described here. It has been used to study some important properties of epoxy resin. Residual stresses, including a curing shrinkage stress and a cooling shrinkage stress, were measured automatically and continuously during curing and cooling. Simultaneously, information such as an apparent gelation time and glass transition temperature were obtained directly during the experiment. These epoxy resin properties were related to the extent of cure. Varying cure temperature produced changes of cure behavior, which resulted in different residual stresses.     

Graphite Nanosheet as Low Shrinkage Additive,Curing Accelerator,and Conducting Filler for Unsaturated Polyester Resin

The effect of graphite nanosheets on electrical properties, curing behavior, and polymerization shrinkage of unsaturated polyester resin has been investigated. A solution of polystyrene was used as low profile additive to reduce shrinkage. The results showed that graphite nanosheets have been well dispersed/distributed in the unsaturated polyester matrix where they have high aspect ratio and high surface area. Graphite nanosheet exhibited an accelerating effect on the curing of unsaturated polyester and reduced the polymerization shrinkage as low as 3.6%. Despite large reduction of flexural properties by low profile additive, graphite nanosheet considerably increased the flexural strength and modulus of unsaturated polyester/low profile additive by 47 and 103%, respectively. Therefore, graphite nanosheet can be used as a new low profile additive for unsaturated polyester resins where it is also able to improve mechanical properties and curing rate.     

Apparent volumetric shrinkage study of RTM6 resin during the curing process and its effect on the residual stresses in a composite

A comprehensive characterization of the volumetric shrinkage of a commercially important aerospace resin (RTM6) during the various stages of the curing process was studied. The apparent volumetric shrinkage, evaluated from density measurements at room temperature, was correlated with the progress of epoxide conversion. During the entire curing process, the apparent volume shrinkage was found to be less than 3% and occurred before vitrification. A slight re‐expansion of the resin, attributed to self‐antiplasticization effects, was observed during postcuring at 180°C. It was concluded that residual stresses were not generated due to chemical cross‐linking during curing but rather from thermal contraction occurring during the cooling stage after cure. A photo‐elastic method was used to characterize residual stresses during cooling in a deliberately engineered resin rich hole of a carbon fiber/RTM6 composite. The residual stress was found to reach approximately 28 MPa, which is in good agreement with the value calculated from the shrinkage and elastic moduli. It is proposed that this simple method can be provide insights useful to the design and materials selection processes by measuring and localizing residual stresses from resin during curing and or thermal cycling. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers