分散剂在氯乙烯悬浮聚合中的应用进展

对悬浮聚合法生产的PVC树脂所用分散剂做了介绍 ,并与国外同类产品做了比较 ,有助于了解国产分散剂的现状与发展     

Drop coalescence processes in suspension polymerization of vinyl chloride

A tracer dye technique was used to investigate the effect of turbulence intensity, stirring time, and the type and concentration of the suspending agent, partially hydrolyzed poly(vinyl acetate) (PVA), on the coalescence rate of vinyl chloride monomer (VCM) droplets in an agitated liquid–liquid dispersion. It was found that the extent of coalescence rises slowly with mixing time, is roughly proportional to the agitation speed, and decreases sharply when the concentration of stabilizer is increased. Coalescence rate depended on the degree of hydrolysis of the stabilizer. The method of addition of initiator during VC suspension polymerization was also studied and its effects on the polymerization conversion and final PVC particles' properties were determined. It was found that the polymerization reaction occurs more uniformly in all the VCM droplets when the initiator was predissolved in the VCM prior to reaction compared with the case when the initiator was predispersed in the continuous water phase. Also, for the same reaction time, the conversion was higher in the former case. During polymerization, the concentration of PVA in the aqueous phase decreased substantially and the porosity of the polymer particles was reduced. © 1996 John Wiley & Sons, Inc.     

Agitation scale-up model for the suspension polymerization of vinyl chloride

Photodegradation and loss of UV stabilizer resulting from natural and accelerated exposure in stabilized linear low density polyethylene (LLDPE) are investigated by spectroscopic techniques. It is found that the processes governing the loss of UV stabilizer are quite different under the two modes of UV exposure. This result clearly demonstrates that predictions concerning polymer lifetime based on the disappearance of additives must be avoided. For a large number of stabilized samples, acceleration factors according to different criteria have been estimated. Examination of the natural photodegradation process of stabilized LLDPE through mechanical property changes establishes that stabilized LLDPE undergoes catastrophic breakdown of the elongation at break the instant the carbonyl IR band begins to develop.     

Estimation of intrinsic rate coefficients in vinyl chloride suspension polymerization

The pre-exponential factor and the activation energy of the intrinsic rate coefficients for propagation, chain transfer to monomer, chain initiation by a Cl radical and termination in the suspension polymerization of vinyl chloride are estimated by regression of experimental data for the monomer conversion, ranging from 3 to 85%, and for the moments of the molecular mass distribution as a function of batch time over the temperature range of 308-338 K and for initiator (tert-butyl peroxyneodecanoate) concentrations from 0.026 to 3.0 wt%, based on the monomer. Termination by combination is the dominant termination mechanism. Cl radicals, formed in the chain transfer to monomer, contribute to the termination by recombination with macroradicals and, hence, attenuate the gel effect. Physically meaningful and statistically significant estimates for the pre-exponential factors and activation energies, 24.9 kJ mol⁻¹ for propagation and 54.3 kJ mol⁻¹ for chain transfer, allow to describe the experimental data over the full range of investigated conditions.     

铁离子对氯乙烯悬浮聚合反应的影响规律

在确保氯乙烯聚合试验过程可重复,试验数据可信的前提下,研究了铁离子含量对聚合时间、PVC树脂的白度与热稳定性的影响规律,发现铁离子会延长聚合时间,降低PVC树脂的白度与热稳定性,进一步获得了聚合时间、PVC树脂白度及热稳定时间随铁离子含量的变化关系。     

新型引发剂在氯乙烯悬浮聚合中的应用试验

通过试验,对过氧化新戊酸叔己酯与偶氮二异庚腈两种引发剂在氯乙烯悬浮聚合中的应用进行了比较.结果表明:过氧化新戊酸叔己酯的反应活性和相对分子质量比偶氮二异庚腈略低,水溶性略大;在相同条件下,过氧化新戊酸叔己酯的残留率高;在用量(物质的量)相同的条件下,二者使用效果相当.     

缩短氯乙烯悬浮聚合时间的动力学研究

研究了有机过氧化物引发剂引发氯乙烯悬浮聚合的过程和影响因素,给出了不同温度、不同引发体系的聚合动力学试验数据和聚合时间-转化率、聚合时间-转化速率曲线．讨论了不同引发体系对PVC树脂质量的影响。试验结果表明：采用适宜的复合有机过氧化物引发剂可缩短聚合时间1h,提高聚合釜的生产能力。     

氯乙烯悬浮聚合计算机在线实时检测及智能化

以实现氯乙烯悬浮聚合过程智能化为目的,在计算机集散控制的基础上,组建在线实时检测流程,建立检测和计算模型,开发数据采集处理、模型计算、结果显示界面等软件,建成计算机在线实时聚合转化率、聚合速率、传热系数检测系统。经对约200釜聚合过程的在线实时检测,最大误差在2％以内。该系统的开发应用对于优化引发剂体系和操作条件,缩短聚合时间、提高聚合釜生产强度有着重要的作用。     

Experimental investigation of vinyl chloride drop behavior during suspension polymerization

The effects of some polymerization conditions on poly(vinyl chloride) (PVC) particles produced by the suspension polymerization process were studied on a laboratory scale. The different stages of vinyl chloride suspension polymerization were investigated experimentally by using an on-line sample withdrawal technique during reaction. It was found that the method of addition of initiator has a great effect on the PVC particle uniformity as well as the size distribution. Furthermore, when the initiator was predispersed in the continuous phase, some latex particles were formed. The effect of the type of stabilizer was also studied with two different types of PVA [partially hydrolyzed poly(vinyl acetate)]. It was found that by changing the stabilizer, the particle size, the porosity, and the morphology could change. When H80 (PVA with a degree of hydrolysis of 80% and a molecular weight of 259,000) stabilizer was used, the rigidity of the PVC particles was weak. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 127–134, 1997     

On gradual dosage of the initiator in the suspension polymerization of vinyl chloride

Initiator dosage in the solid phase during the suspension polymerization of vinyl chloride has been investigated with the use of a special apparatus developed for this purpose. Results arc reported on a series of polymerizations in which the initiator was divided in various ratios between the starting and additional quantities, added either in one dose or repeatedly to the reaction mixture at various reaction times. Discussed is the kinetic course of polymerization and the effect of dosage on the rate of reaction heat release. It is found for the system used that a suitable dosage regime allows the total amount of the initiator to be reduced by as much as 15 percent, while the yield and the reaction time corresponding to the standard polymerization procedure remain unchanged.     

消泡剂在悬浮法聚氯乙烯生产中的应用

介绍了消泡剂消泡的机理和类型，分析了悬浮法聚氯乙烯生产中如何选择适宜的消泡剂，以及使用消泡剂后对悬浮法聚氯乙烯树脂质量的影响。     

氯乙烯悬浮法聚合分散体系综述

简单介绍了国内外氯乙烯悬浮聚合分散体系应用情况及常用的聚乙烯醇及纤维素类分散剂的品种和规格。具体分析了影响聚乙烯醇及羟丙基甲基纤维素分散剂分散能力及保胶能力的因素。指出了PVC生产中应用分散剂时的一般规律,并探讨了不同搅拌强度、转化率和充N2压力下分散剂的不同应用对聚合体系的作用情况。     

A calorimetric investigation of suspension and emulsion polymerization of vinyl chloride

An isothermal calorimeter for studying radical polymerization in heterogeneous systems is presented. The calorimeter was used for investigation of suspension and emulsion polymerization of vinyl chloride at 50°C. The results from the suspension polymerization experiments showed that the termination rate constant in the PVC phase was diffusion controlled and very sensitive to the vinyl chloride activity. During suspension polymerization the pressure started to drop at a much lower conversion than in emulsion polymerization. Mass balance calculations showed that this was due to entrapment of a large amount of liquid vinyl chloride in the fine capillary system of the suspension particles. The results from emulsion polymerization experiments in which the particle number spanned the range from 0.094.10¹⁸ to 1.7.10¹⁸ dm^?3, were analyzed according to the kinetic model developed by Ugelstad et al. Using the concentration-dependent termination rate constant obtained from the suspension experiments and assuming proportionality between the radical adsorption and desorption rate constants, this model gave a very good fit of the experimental rate over the entire interval II and most of interval III. The results strongly indicated that termination in the aqueous phase was of measurable importance during interval II and became the dominating termination in interval III.     

无机添加剂对氯乙烯悬浮聚合的影响

研究了添加未改性和表面改性的无机热稳定剂和CaCO3对氯乙烯悬浮聚合过程的影响,发现采用硅烷和铝酸酯改性无机热稳定剂和采用硬脂酸改性CaCO3,可以达到良好的表面有机改性效果．改性剂最佳质量分数为1．0％左右;热稳定剂对聚合起延缓作用,使一定压降(AP)时的聚合时间增加5～120min、转化率下降3．6％～17．5％;但经表面改性后,对聚合的延缓作用减弱;CaCO3使聚合△P提前10～20min,使一定△P时的聚合转化率下降2．4％～17．5％,但对实际聚合速率的影响不大。     

氯乙烯悬浮聚合防黏釜技术的改进

阐述了黏釜的机理,防黏釜技术的进程,并根据影响防黏釜效果的因素,提出了改进措施。     

氯乙烯悬浮(本体)聚合用过氧化物引发剂

介绍了氯乙烯(VC)悬浮(本体)聚合常用过氧化引发剂的合成方法，着重阐述引发剂与聚合动力学的关系以及聚合动力学的检测方法。研究了单一和复合引发剂条件下的VC聚合动力学，为优化引发剂体系、缩短聚合时间、提高聚合釜的生产能力提供理论基础。     

国产助分散剂油溶性聚乙烯醇HNB02

比较了国产助分散剂油溶性聚乙烯醇ＨＮＢ０２与进口助分散剂ＬＬ－０２在３０ｍ＾３釜上生产聚氯乙烯时的使用效果,对比了使用这两种助分散剂时生产树脂的质量、成本与粘釜状况。     

Bulk polymerization of vinyl chloride

The bulk polymerization of vinyl chloride initiated by AIBN at temperature levels of 30°, 50°, and 70°C has been studied. Molecular weight averages and distribution (MWD) were measured by gel permeation chromatography. A model has been proposed which accurately predicts conversion to high levels and MWD. Molecular weight measurements show that transfer to monomer plays the important role in controlling molecular weight averages. Disproportionation is probably the dominant mode of termination.