新型氯乙烯非均相聚合动力学和成粒机理

对以正丁烷（But)为反应介质的新型氯乙烯（VC）非均相聚合动力学和成粒机理进行了研究，根据VC-But二元体系气液平衡方程，由聚合过程气相压力或组成变化计算VC聚合转化率，VC非均相聚合的诱导期不明显，自动加速现象一般发生在聚合前、中期，后期聚合速率较小，新型VC非均相聚合PVC树脂的体粒径与悬浮PVC树脂相当，数均粒径较小，PVC颗粒由基本不熔结的初级粒子组成，颗粒内部初级粒子分布密度大，粒径大，孔隙率高；而在颗粒表层初级粒子分布密度高，粒径小，孔隙率低；树脂的增塑剂吸收率远大于悬浮PVC树脂，根据PVC树脂的颗粒特性和PVC与VC／But混合液的溶解度参数差异，推断聚合成粒机理为：PVC分子链在很低转化率时就从聚合介质中沉析出来并聚集形成微区，初级粒子和颗粒；后期成粒过程包括颗粒内部初级粒子的增长和向表层的离心聚集，颗粒对新形成的大分子链及其初级聚集体的捕捉等。     

引发剂对氯乙烯微悬浮聚合转化率和聚氯乙烯粒径分布的影响

分别采用水溶性过硫酸铵(APS)和油溶性偶氮二异庚腈(ABVN)引发剂进行氯乙烯(VC)微悬浮聚合,并与APS引发的VC乳液聚合以及ABVN引发的VC悬浮聚合情况进行比较,考察了引发剂类型对聚氯乙烯(PVC)乳胶粒子粒径分布和增塑糊流变特性的影响。结果表明:引发剂浓度相同时,VC微悬浮聚合转化率大于悬浮聚合,而小于VC乳液聚合;APS引发微悬浮聚合得到的PVC乳胶粒子存在数目较多的纳米级粒子,而ABVN引发微悬浮聚合得到的PVC基本不存在纳米级粒子;引发剂和分解产生的初级自由基在水相/油相/胶束中的分配和成核机理不同是导致上述差异的主要原因。ABVN引发微悬浮聚合得到的PVC树脂成糊后呈剪切增稠特性,而APS引发微悬浮聚合得到的PVC树脂成糊后呈剪切变稀特性,且糊黏度较大。     

氯乙烯悬浮聚合减轻粘釜技术概况

工业上生产聚氯乙烯(＊＊C),是由氯乙烯(VC)单体以悬浮聚合、乳液聚合、本体聚合和溶液聚合四种方法进行游离基型聚合而得。其中悬浮聚合工艺成,后处理简单,所得树脂质量较好,适合于多种用途:故得到最广泛的应用。所以,悬浮聚合生产的树脂在PVC生产中占主要地位,其产量约为PVC总产量的 85 ％。‘。     

关于改进明胶分散体系PVC颗粒形态及其塑化性能的研究

以明胶作悬浮聚合分散剂的PVC,是一种吸收增塑剂速度较慢,吸收量较少和塑化加工性能较差的紧密型颗粒形态的树脂。以烷基芳香烃磺酸盐类表面活性剂可改造明胶体系,使之生产疏松型颗粒形态的PVC树脂。本文对于改进树脂颗粒形态的机理进行了分析和研究,对于影响明胶体系PVC颗粒形态有关因素的相互影响关系进行了方程式的理论推导。从而认识了树脂吸收增塑剂的量与树脂颗粒平均粒径p和烷基苯磺酸钠浓度C_s的X次方的乘积成正比,与聚合温度T的f次方乘积成反比。因而可以能动地控制明胶体系PVC的颗粒形态及其塑化加工性能。     

悬浮法PVC树脂粒径的影响因素

讨论了悬浮法PVC树脂生产过程中影响树脂粒径的主要因素,有针对性地从聚合釜搅拌、反应配方、体系氧含量、pH值、聚合温度和转化率等方面提出了粒径的控制方案。     

本体法PVC树脂生产工艺及产品性能优势

介绍了本体法PVC树脂生产工艺、预聚合釜及后聚合釜的原理及结构、本体法聚合反应的特点、本体法PVC树脂的性能及影响本体法聚合反应的因素.对比了本体法PVC树脂和悬浮法PVC树脂的粒径分布、颗粒形态和表观密度等性能.     

基于30m~3聚合釜的纳米CaCO_3原位聚合PVC树脂颗粒特性预测与优化

通过微乳化分散技术使CaCO3实现良好分散,通过氯乙烯原位悬浮聚合制得了纳米CaCO3微乳化法原位聚合PVC树脂(简称纳米PVC树脂)。为解决纳米PVC树脂的颗粒形态控制难题,提出了基于组合神经网络的软测量方法,建立了纳米PVC树脂颗粒特性的软测量预测模型,应用效果表明该软测量模型能较准确地预测纳米PVC树脂的平均粒径。利用该软测量预测模型在30 m3聚合釜上实现了纳米PVC树脂颗粒特性优化,制得具有较理想颗粒特性的纳米PVC树脂。     

VDC-VC悬浮共聚树脂的颗粒特性研究

合成了偏氯乙烯(VDC)-氯乙烯(VC)悬浮共聚树脂，研究了聚合时间分散剂用量和搅拌器转速等对共聚树脂颗粒特性的影响。结果表明：树脂粒径随聚合时间延长而增大，并趋于定值；增加分散剂用量，粒径先减小后增大，当分散剂用量为0．12％时，平均粒径最小；平均粒径随搅拌器转速提高呈马鞍形变化，在130r／min时粒径最小，树脂颗粒形态规整。     

悬浮态乳液聚合制备疏松型聚甲基丙烯酸甲酯树脂

以水为分散相、甲基丙烯酸甲酯(MMA)为连续相进行悬浮态乳液聚合,合成疏松型聚甲基丙烯酸甲酯(PMMA)树脂。研究发现:在聚合体系中加入一定量的PMMA不良溶剂才能制备疏松型PMMA树脂,随不良溶剂环己烷用量和水油比的增大,PMMA树脂的疏松性和邻苯二甲酸二辛酯(DOP)吸收量增加;加入乳化剂使树脂的初级粒子平均粒径变小,而引发剂用量对树脂颗粒内部形态的影响较小。     

悬浮PVC树脂颗粒形成新理论——凝聚理论

提出了一种悬浮PVC树脂颗粒形成的新理论——凝聚理论:液态氯乙烯在搅拌作用下以约0.7μm的微滴分散在水中发生聚合反应,当聚合转化率达到25%左右时,这些微滴凝聚成粒径约为130μm的树脂颗粒。通过实验研究、文献资料及逻辑推理证明了其正确性。     

Influences of individual and composed poly(vinyl alcohol) suspending agents on particle morphology of suspension poly(vinyl chloride) resin

Effects of individual and composed poly(vinyl alcohol) (PVA) suspending agents on the particle morphology of poly(vinyl chloride) (PVC) resins were investigated and discussed in the view of PVA absorption at the oil/water interface and interfacial behavior. It was shown that the percentage and surface coverage of PVA at the oil/water interface decreased with the increase of the degree of hydrolysis (DH) of PVA in the DH range of 70–98 mol %, while the interfacial tension of VC/PVA aqueous solution increased linearly with the increase of DH of PVA. PVC resin with more regular particle shape, increased agglomeration and fusion of primary particles, lower porosity and higher bulk density, was prepared by using PVA with a higher DH as a suspending agent. This was caused by the occurrence of drop coalescence at the very early stage of VC polymerization, the increase of particle shrinkage, and the lower colloidal protection to primary particles. It was also shown that the interfacial tension of VC/water in the presence of composed PVA suspending agents varied linearly with the weight composition of the composed PVA suspending agents. The particle properties of PVC resin prepared by using the composed PVC suspending agents were usually situated in between the properties of PVC resins prepared by using the corresponding individual PVA suspending agent. The particle morphology and properties of PVC resin could be controlled by the suitable choice of the composed PVA suspending agents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3848–3855, 2003     

Influences of some polymerization conditions on particle properties of suspension poly(vinyl chloride) resin

Effects of polymerization temperature, conversions, and nonionic surfactant on the particle properties of suspension poly(vinyl chloride) (PVC) resins were investigated. It was shown that polymerization temperature has no significant influences on the mean particle size of PVC resin, and that the cold plasticiser absorption (CPA) of resin decreases linearly with the increase of polymerization temperature. Agglomeration of VCM droplets finishes before 20% conversion, and the mean particle size keeps almost constant at later stages of the polymerization process, but the CPA continues decreasing with the increase of conversion. Scanning Electron Microscopy (SEM) micrographs show that the degree of agglomeration of primary particles increases with polymerization temperature and conversion. Addition of nonionic surfactant to the VCM suspension system, as a secondary suspending agent, has a great influence on the particle properties of PVC resin. The particle size and CPA increase as the concentration of nonionic surfactant increases. The nonionic surfactant with a greater HLB value is more effective in raising the mean particle size, but is less effective in raising the CPA. It is considered that the added nonionic surfactant would be absorbed faster on the VCM/water interface than the poly(vinyl alcohol) (PVA), which was used as the primary suspending agent. Because the colloid protection ability of the nonionic surfactant is less than that of PVA, droplets become less resistant to coalescence, and the mean particle size of the final PVC resin increases consequently. The increase of porosity is caused by the combined effects of increased coalescence of VCM droplets and the nonionic surfactant's steric effect inside the droplets. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1544–1552, 2002     

Effects of poly(vinyl acetate) suspending agents on suspension polymerisation of vinyl chloride monomer

Abstract

When partially hydrolysed poly(vinyl acetate) (PVAc) is used as a suspending agent in the suspension polymerisation of vinyl chloride monomer, it has significant effects on the morphology of the resulting poly(vinyl chloride) (PVC) particles. At the initial step of polymerisation, PVC molecules are grafted onto the molecules of the suspending agent forming a PVC–PVAc membrane. The properties of this membrane depend on the type of suspending agent, the polymerisation temperature, the mixing efficiency, and other factors. The morphology of the growing PVC particles and the properties of the PVC resin obtained depend in turn on the characteristics of the membrane. A model has been developed relating to the connection between the polymerisation conditions and the characteristics of the suspending agent on one hand, and on the PVC properties on the other hand. The model is based on an analysis of the characteristics of the PVC–PVAc membrane and their effect on PVC properties.     

BA悬浮溶胀接枝聚合PVC的制备与性能研究

采用水相悬浮溶胀聚合的方法在PVC颗粒内部原位接枝丙烯酸丁酯(BA),考察了反应温度、分散剂用量对接枝反应和颗粒形态的影响,结果表明:接枝率随反应温度的升高而增大,分散剂用量为1.0份时,产物的颗粒形态规则,与PVC共混物的力学性能较好.PVC-g-BA/PVC共混体系动态力学性能分析(DMA)的结果表明:两相呈微观相态分离的结构特点;转矩流变性能测试结果表明:交联剂用量为3份时,PVC-g-BA/PVC共混体系的塑化性能较好.     

Influences of initiator addition methods in suspension polymerization of vinyl chloride on poly(vinyl chloride) particles properties

Vinyl chloride suspension polymerization was carried out in a pilot‐scale reactor to study the effects of different methods of initiator addition on poly(vinyl chloride) (PVC) resin properties. The experiments used different arrangements for adding the initiator to the reactor, whereas other reaction conditions were the same: (i) initiator was added to the continuous aqueous phase and then monomer was dispersed in it (conventional method); (ii) initiator was predissolved in monomer before dispersing in the continuous aqueous phase; and (iii) suspending agents along with initiator were added to the monomer before polymerization. The PVC resin prepared by method of (i) had a higher monomer conversion and a higher Sauter mean diameter of grains with a narrow particle size distribution comparable to that of PVC resins by other methods. Scanning electron microscopy showed more uniform particles and fused primary particles in the grains, which confirms lower porosity and lower cold plasticizer absorption (CPA) for PVC grains produced by procedure of (ii). The results showed that when the suspending agents were also predispersed in monomer along with initiator (iii), CPA increases dramatically due to internal porosity of the grains. Simultaneously, a marked decrease in Sauter mean diameter was apparent. Scanning electron microscopy micrographs show that primary particles in the interior of PVC grains prepared by the latter method are looser, and there is more free volume between primary particles resulting the high internal porosity and consequently higher CPA. Mercury porosimetry analysis also confirms these results. K value as a molecular weight characteristic for all methods was the same . J. VINYL ADDIT. TECHNOL., 24:116–123, 2018. © 2016 Society of Plastics Engineers     

悬浮态乳液聚合条件对聚氯乙烯树脂颗粒特性的影响

Suspended emulsion polymerization of vinyl chloride was carried out in a 5 L autoclave. The influence of agitation, polymerization conversion, dispersant and surfactant on the average particle size (PS) and particle size distribution (PSD), particle morphology and porosity of polyvinyl chloride (PVC) resin was investigated. It showed that the agitator had great influence on the smooth operation of polymerization, PS and PSD. The PS increased and PSD became narrow as polymerization conversion became high. The porosity decreased with the increase of conversion. A convenient choice of additives, both dispersants and non-ionic surfactants, allows one to adjust PS and PSD. The PS decreased with the addition of polyvinyl alcohol or hydroxypropyl methylcellulose dispersants,and increased with the addition of Span surfactants. The addition of dispersants or surfactants also affected the morphology and porosity of resin, and PVC resin with looser agglomeration and homogeneous distribution of primary particles was prepared.     

The influence of poly(vinyl alcohol) suspending agents on suspension poly(vinyl chloride) morphology

The requirements for PVC suspension resin have changed considerably in the last few years, so much so that few companies have products on their ranges that are more than 4 or 5 years old. The suspending agent has a crucial influence on the morphology of the resin, so the changes in resin characteristics have largely been achieved by changes in the suspending agent systems. After a brief review of the mechanism of PVC suspension polymerisation, the properties of polymers made using PVOH suspending agents are related to changes in the latter. The effect of variations in PVAc degree of hydrolysis and viscosity are related to changes in surface tension. Methods of achieving higher porosity by using low hydrolysis co-suspending agents are described. It is shown that higher bulk densities can be achieved by delayed addition of the PVOH. Levels of conjugated unsaturation and copolymer distributions are also shown to have important influences.     

Investigation of the effect of delayed reflux on PVC grain properties produced by suspension polymerization

The effects of the condenser operation on properties of polyvinyl chloride (PVC) particles produced by suspension polymerization process were investigated in a pilot scale reactor. It was observed that delaying reflux operation increased the cold plasticizer absorption of the final resin. Both bulk density and K‐value of the PVC powder decreased by increasing time delay in the reflux operation. It was also found that commencement of refluxing before 20% conversion resulted in bimodal particle size distribution (PSD), while monomodal PSD was obtained for longer delays in refluxing. SEM micrographs showed that surface of produced particles were rough and smooth when reflux started before and after 20% conversion, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

氧化还原引发体系对多层核壳结构ACR乳液聚合的影响

采用多步乳液聚合方法合成多层核壳结构的ACR树脂。用过硫酸钾/亚硫酸氢钠体系作为氧化/还原引发体系,研究了氧化剂和还原剂用量的不同及氧化还原引发体系的加入方式对ACR的转化率、乳胶粒的粒径和PVC/ACR共混物加工流变性能的影响。实验结果表明:氧化剂和还原剂用量增加后,乳液聚合各个阶段的转化率提高,乳胶粒的粒径变大,明显改善了共混物的加工性能。过量的还原剂起阻聚和缓聚作用,采用分阶段加入氧化还原引发剂有利于提高转化率。