加工温度对聚氯乙烯凝胶化行为的影响

使用转矩流变仪模拟挤出机,探讨了加工温度对聚氯乙烯(PVC)凝胶化行为的影响。结果表明:凝胶化过程初期,低的加工温度有利于PVC颗粒破碎成初级粒子。随加工温度升高,存在某一最合适的最高加工温度,使凝胶化所生成的三维大网络的强度最高。     

凝胶化对硬质PVC管质量的影响

PVC树脂粉末在一定温度和剪切力作用下发生凝胶化是硬质PVC在挤出成型加工中的基本行为之一,凝胶程度和凝胶速度对硬质PVC管的质量控制,提高生产效率起着关键作用。实验结果表明,PVC的凝胶程度控制在60～70％之间,能够生产出综合性能最佳的高质量管子。PVC挤出成型期间发生的凝胶作用与其高温粘弹性密切相关。利用流变仪测定粘弹性,是迄今测定凝胶度的较理想方法。PVC的凝胶化不仅影响塑料制品的外观和物化性能,对加工能力也有很大影响。在PVC配合料中掺混高分子加工助剂ACR,能有效地促进PVC凝胶化,明显提高硬质PVC管的质量指标。     

高聚合度聚氯乙烯凝胶特性的研究

采用差示扫描量热（DSC）法和毛细管流变法对高聚合度聚氯乙烯（HPVC）的凝胶特性进行了研究。结果表明，PVC2500具有与通用PVC类似的凝胶化机理，符合Benjamin的粉碎理论；HPVC加工温度高于175℃时有较高的凝胶度，加工温度在175～185℃，PVC2500的凝胶度可以达到60％～85％。相同的加工温度和加工时间下，PVC2500未熔融的主结晶体及等温结晶体更多，造成PVC2500的凝胶度比PVC1000小。     

硬聚氯乙烯管材二氯甲烷浸渍试验方法研究

<正> 硬聚氯乙烯管材加工的特殊性与聚合物的形态结构有着密切关系。实际上,硬PVC在加工成型过程中都要经历凝胶化的过程,即颗粒的形态变化过程。通过对硬PVC管材凝胶化程度的间接测定可达到质量监控的目的。国外为预测硬PVC管材的长期使用性能,通常采用爆破试验,冲击试验和耐腐蚀性试验等~[1],然后根据这些试验结果推算它的寿命。但该法不适合生产     

聚氯乙烯加工中的凝胶化研究进展

聚氯乙烯凝胶化是国外70年代以来研究的热点之一。通过研究PVC材料的凝胶化行为,既表征了结构特性,又关联了制品性能,还提供了控制产品质量的内在方法。随着我国硬PVC的开发和生产,也为了使通用PVC高性能化,PVC凝胶化行为必将引起更广泛的研究和应用。本文系统讨论了凝胶化的一些基本问题及今后的研究动向。     

物料压缩比对PVC凝胶化行为的影响

利用转矩流变仪制备聚氯乙烯(PVC)共混物,研究了物料压缩比对PVC凝胶化行为的影响.结果表明:随着物料压缩比增加,PVC凝胶化速度加快,有利于破碎出更多微米级的初级粒子,在相同外部能量作用下,PVC凝胶化度先增加后降低.PVC共混物在扭矩最低点和最高点存在不同的结构和流动机理.     

丙烯酸加工助剂对聚氯乙烯拉伸流动的影响

采用毛细管粘度计测拉伸粘度的方法,研究丙烯酸加工助剂的类型、用量及测定温度对PVC拉伸流动的影响。实验证明,PVC熔体的拉伸流动对拉伸速率的依赖性近似于Troton行为;促进凝胶化型的丙烯酸加工助剂使PVC的拉伸粘度显著提高,且随助剂的用量的增加而增加,但随温度的升高而降低;润滑型丙烯酸加工助剂则使PVC的拉伸粘度有升有降。     

加工改性剂AS-935在PVC排水管件中的应用

介绍了加工改性剂AS-935在PVC排水管件中的应用效果,并与ACR 401进行了对比。结果表明:AS-935在用量较少的情况下,可有效促进PVC凝胶化,增加熔体流动性,提高熔体强度,增加制品表面光洁度及白度,并能降低配方成本。     

DOP凝胶特性及其对软质PVC力学性能的影响

以硬脂酸锂(Li-SA)为凝胶因子,将邻苯二甲酸二辛酯(DOP)凝胶化后制得DOP凝胶.利用该凝胶与聚氯乙烯(PVC)共混制得软质PVC材料,并与未凝胶化DOP制得的材料进行对比.通过测定Li-SA对DOP的凝胶化能力、凝胶-溶胶转变温度,并采用邵氏硬度计、电子万能试验机和场发射扫描电镜分析软质PVC的硬度、拉伸强度及...     

增塑剂对旋转模塑用PVC增塑糊性能的影响

通过增塑剂种类及用量对旋转模塑用聚氯乙烯(PVC)增塑糊粘度及其粘度稳定性、脱气性能、凝胶化性能的影响及温度对凝胶化性能的影响进行了研究。结果表明:选择自身粘度较小且溶剂化能力较弱的增塑剂及随增塑剂用量增加,PVC增塑糊粘度下降、粘度稳定性逐渐变好,有利于PVC增塑糊的排气性能提高,延长PVC增塑糊的凝胶化时间。通过调节加热温度及时间可在一定范围内有效控制凝胶化过程,以期获得制品所需性能。     

流变法与DSC法测量PVC凝胶度的原理与结果讨论

本文阐明了用零长毛细管流变仪和差示扫描量热计测定ＰＶＣ熔体凝胶度的原理，并用这两种方法测量了ＰＶＣ／ＣＰＥ／ＰＳ体系的凝胶度。讨论了凝胶度与加工温度及力学性能的关系，并对这两种测试结果进行了比较。     

Influence of crystallinity in the curing mechanism of PVC plastisols

The influence of the crystalline areas observed in poly(vinyl chloride) (PVC) the mechanical and thermal properties of PVC plastisols was studied. Several industrial‐degree PVC resins were used to obtain a broad range of molecular weights and processing conditions for PVC plastisols. The gelation process was fully studied at different temperatures and was related to the existence of crystalline areas at high temperatures, even near the glass transition. A simple explanation of the phenomena observed during the gelation of plasticized PVC is proposed, according to the variation in the mechanical and thermal properties at different temperatures. The final gelation was obtained at 140–150°C, which was a lower temperature than those at the beginning of the thermal degradation process. The thermodynamic aspects of the gelation of plasticized PVC were mainly controlled by the PVC resin properties, whereas the plasticizer only influenced the diffusion and stability of the material. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 538–544, 2004     

Plasticizer factors influencing take-up by PVC resins

The ease with which plasticizer is combined with poly(vinyl chloride) resin is a measure of processing characteristics critical in the dry blending of suspension PVC and the gelation of plastisols. By using commercial grade plasticizers, this study developed predictive equations for the following processing parameters of dialkyl phthalates in PVC:

• Relative dry-blend rates in suspension PVC as a function of plasticizer viscosity.
• Relative initial gelation temperatures in plastisols as a function of plasticizer molecular weight and solvating strength.
• Relative final gelation temperatures in plastisols as a function of plasticizer solvating strength.

This information allows one to predict the relative processing characteristics of any dialkyl phthalate plasticizer for PVC on the basis of its chemical and physical properties.     

Gelation of Plasticized Polyvinyl Chloride Compounds in a Co‐Kneader

The co‐kneader is a proper tool for processing polyvinyl chloride (PVC) compounds. Gelation of PVC is complex because of a narrow processing window. At low temperature, gelation is incomplete and leads to poor mechanical properties, while at high temperature, degradation may occur. The aim of this study is to gain a fundamental understanding of the gelation process of PVC in co‐kneaders. Careful examination of the gelation state of extruded PVC samples was carried out qualitatively by swelling the extruded samples in acetone and quantitatively by differential scanning calorimetry measurements. Gelation in various conditions of temperature and shear was firstly studied in a capillary device that ensures both pre‐shearing and extrusion through a circular die. This provided a reference basis for comparison with gelation state obtained in the co‐kneader. Samples were collected in the co‐kneader by means of opening the barrel. The gelation state was particularly examined in connection with the measured temperature at a fixed position along the screw at which a temperature sensor was positioned. The obtained results showed that the co‐kneader allows fast gelation with a mixing energy value lower than 200 kJ/kg when the temperature is higher than a critical value of 165°C for the studied formulation. J. VINYL ADDIT. TECHNOL., 2019. © 2019 Society of Plastics Engineers J. VINYL ADDIT. TECHNOL., 26:316–324, 2020. © 2019 Society of Plastics Engineers     

Untersuchungen zur struktur von emulsions-polyvinylchlorid

The structural characteristics of PVC prepared by bulk or suspension polymerization as well as their relationships to synthesis and processing conditions have repeatedly been investigated. Thus, grains aggregates, particles, domains and microdomains have to be discerned according to Geil. In our electron microscope studies emulsion PVC powder obtained by spray drying of aqueous PVC latices and used in preparing pastes were investigated. The grain structure was found to change in preparing pastes and subsequent gelation. With increasing temperature of gelation the grains disintegrate, particles arrange in dense packings and, finally, loose their individuality. Due to diffusion of the plastiziser the particles acquire distinctly discernible microdomain structures. Microdomains are found to be the dominating structural characteristic of PVC gelation products.     

Relationship between gelation and wall slip in unplasticised poly(vinyl chloride) compounds

Abstract

The degree of gelation reached upon processing influences heavily the properties of poly(vinyl chloride) (PVC) made parts. Gelation involves the conversion of the initial PVC particle structure into an increasingly homogeneous melt and therefore the rheological properties of PVC at low temperatures are very different from those at higher ones. Whereas the former involves both wall slip and particle flow, the latter yields a more conventional behaviour.

As a consequence, the nature and origins of the different mechanisms giving rise to wall slip in PVC compounds must be taken into account when trying to understand the relationship(s) between the processing conditions, the physics of the gelation mechanism, and the final product characteristics.

This work involves the study of the rheological properties of PVC compounds for different initial gelation levels and the identification of wall slip mechanisms using rotational rheometry.     

微悬浮法PVC增塑溶胶凝胶化和熔化特性的研究

用HAAKE转矩流变仪测定了微悬浮法聚氯乙烯(PVC)增塑溶胶的凝胶化和熔化特性,探讨了树脂品级、增塑剂类型和混合树脂对凝胶化和熔化速率的影响。实验还表明,单丝的拉伸强度和相对伸长率与它的加工温度、形态和熔化程度有密切的关系。     

The melting temperature (or not melting) of poly(vinyl chloride)

The best answer to what is the melting temperature of PVC is its previous processing temperature. That temperature is where secondary crystallites, created by gelation, melt and allow the primary particle flow units to flow again independently. In the case of powder compounds being processed for the first time, the question of melting is less relevant. The PVC, out of the polymerizer, contains crystallites that are not completely meltable. The issue is how easily the grains of PVC disperse to primary particle flow units. This property depends on polymerization conditions and the type of processing equipment. The temperature achieved affects the amount of fusion (gelation). J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Thermal and structural effects of poly(vinyl chloride)/(wood flour) compound gelation in the Brabender mixer

The processing of two unplasticized compounds of poly(vinyl chloride) (PVC) with and without wood flour (WF) was performed in a Brabender mixing chamber, at various chamber temperatures between 130 and 200°C and at a shear rate of 12.61 s^?1. The test was carried out up to the time corresponding to the equilibrium state of the torque, and the variations of torque and real melt temperature as functions of time were analyzed. It was found that the addition of WF led to fusion at lower chamber temperature and that during gelation, stronger self‐heating effects occurred in the WF‐filled PVC compound. Various characteristics of the real temperature gelation curves of PVC with and without the WF filler were observed and are discussed. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Processing of precipitated nongranular PVC in the brabender measuring mixer

The structure and properties of processed poly(vinyl chloride) (PVC) depend on temperature, shear rate, operations time, and morphology of the PVC grains. The aim of our research was the preparation of a nongranular PVC and the examination of its processing during kneading in a Brabender plastographometer in comparison with the processing of commercial PVC. It was stated that grains of virgin PVC‐S61, a commercial suspension resin, cause a self‐heating of the compound during kneading in such a way that point X of the plastograms occurs at a temperature 15°C lower than that of precipitated PVC (i.e., PVC without grains). As a result of self‐heating, time of compound processing needed to reach point depends largely on the grain morphology of the PVC. The less compact structure, the smaller bulk density, and the greater absorption of plasticizer, result in a longer processing time. Homogeneous, loosely packed particles of powder and the crystalline structure of precipitated PVC are different from PVC‐S61 morphology and cause a high degree of gelation and low melt flow rate values for compounds processed at 175°C and higher. J. VINYL ADDIT. TECHNOL., 18:147–152, 2012. © 2012 Society of Plastics Engineers