The effect of grain shape on the properties of PVC resins and compounds

The properties of PVC resin grains have been shown to influence the bulk density and flow properties of PVC resins and powder compounds. Bulk densities of PVC resins and powder compounds are highly dependent on grain shape. Lower bulk density has been related to more irregular grain shape. Flow properties of PVC resins and powder compounds improve with increased grain size. Twin screw extrusion rates are directly proportional to the compound bulk density in the feed throat.     

Factors influencing PVC resin apparent bulk density

Bulk density is one of the easiest measured and most practical physical properties of PVC resins and compounds, especially those used in rigid applications. The paper addresses the importance of bulk density of rigid PVC resins, both regular and antistat, and their compounds. The negative influence of static electricity on bulk density measurement of PVC resins is studied and discussed. Effective static removal and accurate, consistent bulk density measurement is explored through various methods such as compacted bulk density and conditioned bulk density (either by addition of silica, methanol or carbon black, or by treatment with an ionizer).     

An integrated study of die powder fill, transfer and compaction process using digital image correlation method

A major advantage of the powder metallurgical (P/M) manufacturing process is its ability to shape powder directly into a final component with a primary goal of a high quality, homogeneity of density and mechanical properties and productivity. In this research, powder die filling, powder transfer and powder compaction process have been studied in succession using a novel experimental set-up that utilizes a high strength transparent wall section to observe and record the particle movement and powder compaction during the entire sequence leading up to the formation of a green part. The natural powder pattern itself, as observed from the transparent wall section, is utilized for obtaining full-field displacement and strain measurement. The test set-up and the strain measurement technique offer a means of quickly obtaining density distribution data in select cases. In addition to the above, several powder flow characteristics during die filling, powder transfer and powder compaction under a range of test conditions have been noted through a series of high-speed photographic recordings.The observations reveal increased porosity in the die wall region due to friction and formation of shear bridges during powder transfer stages during suction filling. Spatial density data from optical strain measurements in the top, middle and bottom regions of the die are consistent with similar bulk density measurements from mass and volume of the 3 regions.     

Effect of poly(vinyl chloride) resin type in the preparation process of slush powder

During the preparation of the poly(vinyl chloride) (PVC) slush powder, we found that PVC resins obtained by different polymerization methods affected many properties of slush powder and its products. Two types of commercial PVC resins were used for slush powder preparation: mass poly(vinyl chloride) (M‐PVC) and suspension poly(vinyl chloride) (S‐PVC). We used the Haake rheomix test to characterize the absorption of plasticizers into PVC resins, and the results showed that M‐PVC absorbed the plasticizers more quickly than S‐PVC. The fusion behavior of the two slush powders was studied by the thermal plate test and Haake rheomix test, and the results showed that the slush powder of M‐PVC was easier to fuse than that of S‐PVC. The different properties of the two resins and slush powder could be explained by the morphology, average size, and size distribution. Due to the “skin” of the particles' surfaces, the wider size distribution, and the large size of particles, S‐PVC absorbed the plasticizers more slowly and was more difficult to fuse. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3331–3335, 2002     

Effect of preliminary treatment on the process properties of plasma-chemical oxide powders

The process characteristics of ultradisperse powders of alumina and zirconia, prepared by plasma-chemical synthesis, are investigated. It is demonstrated that the powders in the initial state are characterized by extremely low values of bulk density, fluidity, and compactibility. The effect of preliminary treatment on the process properties of the powders has been studied. By means of preliminary hydrostatic compaction, followed by planetary mill grinding, it is possible to change the shape and size of the powder particles and raise substantially the bulk density and fluidity. Preliminary treatment of the powders also has a positive effect on their compactibility and sinterability; the density of pressings attains 60% and the density of sintered ceramics, 98 – 99% of the theoretical value.Translated from Ogneupory, No. 2, pp. 4 – 7, February, 1994.     

聚氯乙烯粉体表面结构对加工工艺的影响

研究了不同PVC粉体颗粒的结构特性，分析了粉体表面形态差别对树脂表观密度、增塑剂吸收率等基本性能及加工工艺（特别是对粉体的配混工艺）的影响，认为颗粒有拖尾现象的PVC粉具有较低的塑化温度及较好的塑化能力，在配混过程中出为温度应相应降低。     

本体法与悬浮法PVC树脂生产工艺的比较及在管件生产中的优势

比较了本体法PVC7型树脂与悬浮法PVC-SG7型的生产工艺,介绍了本体法PVC树脂的质量、塑化性能和加工性能等在管件生产中的优势。     

Bulk density of solid polymer resins as a function of temperature and pressure

In a plasticating extruder, solid polymers are heated and are subjected to high pressures before they are melted and delivered to a die. In both the solids conveying and melting sections, these temperature and pressure increases will compact the unmelted polymer bed as it moves down the screw channel. Performance of the extruder depends in part on how well the screw design matches the compaction behavior of the resin for a given set of process conditions. The design of these screw sections, however, is often done based on past experience and with little knowledge of the resin compaction behavior. A much improved design would include screw performance prediction using variable bulk density and computer simulations. Computer simulations, however, are often performed using constant solid bulk density because of the lack of reliable density data as a function of both pressure and temperature. An instrument was developed for studying the compaction behavior of pellet and powder resins. Bulk densities and storage friction coefficients are reported for several important thermoplastic resins as a function of temperature and pressure. The bulk density data were fitted to a semi-empirical model.     

Measuring the bulk flow properties of PVC resins

The flow characteristics of PVC resin are often judged by measuring the time required for a given amount of dry resin to flow through a standard funnel. However, considerable variation in test results have been found between laboratories though the test is conducted well within the procedural limits of ASTM 1895-69, “Apparent Density, Bulk Factor and Pourability of Plastic Materials.” An examination has been made of the effects of funnel hole size, funnel alignment, its type metal and wall surface smoothness, filling technique, static generated, and degree of vibration. It was found that six of these seven variables need critical control, while one (alignment) has no measurable effect. It is suggested that the data presented be used for the development of an improved ASTM test for measuring the flowability of PVC resins.     

Studies of molecular weight distribution,particle morphology,and rheological behavior of ultra-high molecular weight suspension PVC

In this paper, the particle characteristics and rheological behavior of ultra-high molecular weight PVC (UHMWPVC) produced in both Japan and mainland China were studied. The molecular weight and its distribution of UHMWPVC were measured by GPC. By means of a series of techniques such as SEM, the measurement of surface pore size, plasticizer absorption, and photographic analysis, the morphology and general characteristics of UHMWPVC particles were investigated. A model of particle structure was proposed. It was found that compared to general PVC, UHMWPVC resins are more porous, having better plasticizer absorption properties. Similarly, compared to UHMWPVC made in mainland China, UHMWPVC made in Japan possesses particle characteristics preferred in PVC processing. In the studies of rheological behavior, the programmed temperature Brabender torque rheometer was used to study and compare the melting process of UHMWPVC resins and their plasticized systems under the same shear stress. The capillary rheometer and Brabender extrusion-rheometer were applied to investigate the rheological and extrusion properties of the plasticized systems mentioned above. The results showed that in melting and extrusion process, the particle characteristics of UHMWPVC result in the easy breakage of particles and the formation of “molecular flow,” On the other hand, the high molecular weight is unfavorable to processing. Generally speaking, much more research work is needed to improve the flow properties of UHMWPVC.     

Investigation of the thermal, mechanical, and fracture properties of alumina-epoxy composites

A combination of dynamic shear rheology, thermomechanical analysis (TMA), scanning electron microscopy (SEM), Near-Edge X-ray Absorption Fine Structure (NEXAFS), and fracture toughness testing was utilized to characterize the thermal, mechanical, chemical, and fracture properties of alumina (α-Al₂O₃)-filled epoxy resins as a function of average filler size, size distribution, particle shape, loading, and epoxy crosslink density. In general the cured properties of the filled composites were robust. Small changes in particle size, shape, and size distribution had little impact on the final properties. Resin crosslink density and filler loading were the most critical variables, causing changes in all properties. However, most applications could likely tolerate small changes in these variables also. SEM and NEXAFS characterization of the fracture surfaces revealed that the fracture occurs at the filler interface and the interfacial epoxy composition is similar to the bulk resin, indicating a weak epoxy-alumina interaction. These results are critical for implementation of particulate-filled polymer composites in practical applications because relaxed material specifications and handling procedures can be incorporated in production environments to improve efficiency.     

国产HPMC分散剂在127m3釜上生产PVC树脂的应用总结

上海氯碱化工股份有限公司在127m^3聚合釜中成功试用了国产HPMC分散剂,以替代价格昂贵的进口HPMC分散剂。共进行了50釜的应用试验,试生产了B、D、F三种牌号PVC树脂。通过分析B、D、F三种牌号PVC树脂的常规质量(如,表观密度、VCM残留量、“鱼眼”数及挥发分)、塑化性能、增塑剂吸收量及粒径分布,发现除了F牌号PVC树脂的平均粒径及粒径分布略微变宽、三目集中率略有偏低外,B、D牌号树脂的性能及F牌号树脂的其它性能均无明显变化。同时还指出,F牌号PVC树脂的粒径大小与分布可通过调整分散剂的用量来解决。     

S-500型低聚合度PVC树脂的开发研究

研究了S-500型低聚合度PVC树脂的合成技术,确定了使用链转移剂合成S-500型PVC树脂的聚合配方和工艺条件。结果表明:S-500型PVC树脂相对分子质量分布集中,颗粒规整度好,粒度分布集中,熔体流动速率较高,加工塑化性能良好。     

渣油加氢脱硫催化剂载体堆积密度的精确控制

采用挤出成型法制备氧化铝载体,考察挤出成型工艺条件、切粒频率、焙烧温度和焙烧气氛对渣油加氢脱硫催化剂载体堆积密度及物化性能的影响。结果表明,酸粉比（A+0.5） mL·g^-1、水粉比（B+0.10） mL·g^-1和混捏时间（t+5） min制备的载体堆积密度合适,物化性能优良;切粒整形频率为40 Hz时,载体条长分布中,（3~8） mm条占87.14%;随着焙烧温度的升高,载体比表面积减少,孔径分布中小于6 nm孔减少,堆积密度减小;随着焙烧气量的减少,载体比表面积降低,孔体积增加,堆积密度减小,孔径分布中小于6 nm孔减少,（6~20） nm孔增加。精确控制载体焙烧温度和气量,可制备出比表面积合适、堆积密度稳定、孔径分布集中和满足固定床渣油加氢脱硫要求的工业氧化铝载体。     

分散剂和非离子型表面活性剂对悬浮聚氯乙烯树脂颗粒特性的影响

研究了聚乙烯醇(PVA)分散剂和非离子型表面活性剂对悬浮聚氯乙烯(PVC)树脂颗粒特性的影响。结果表明随着PVA醇解度的增加，PVC树脂的颗粒规整性和表现密度增加，孔隙率和吸油率降低；随着非离子型表面活性剂添加量的增加，PVC树脂的平均粒径和吸油率增大。从PVA和表面活性剂在水一油两相分配出发，讨论了PVA醇解度和添加非离子型表面活性剂对PVC树脂的颗粒特性影响机理。     

固相烧结——Ⅲ 实验：超细氧化锆素坯烧结过程中的 晶粒与气孔生长及致密化行为

研究了超细Y-TZP和YSZ粉料成型体在烧结中期的晶粒生长、气孔生长和致密化行为.根据作者前文     

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     

Particle features and morphology of poly(vinyl chloride) prepared by living radical polymerisation in aqueous media. Insight about particle formation mechanism

The aim of this work is to evaluate PVC resins prepared by Single Electron Transfer Degenerative Chain Transfer Living Radical Polymerisation (SET-DTLRP) in a 150 L reactor under industrial conditions. The product features were analysed considering the standard resin features of PVC prepared by the conventional free radical polymerisation (FRP) method. It was proved that the FRP and SET-DTLRP have different particle growing mechanism and led to grains with completely different features (particle size, particle size distribution and morphology). It is critical for the PVC producers the preparation of PVC with a predetermined grain shape, particle size distribution and porosity which have an indubitable in?uence on polymer processing. It is presented a detailed study on the particle formation of the PVC synthesised by SET-DTLRP providing ?rst insights into PVC features associated with a new polymerisation technique taking into account the normal requirements of the PVC industry. A possible mechanism of the SET-DTLRP particle formation is proposed.     

Low pressure rheology of granular powders using a drawing plate technique

An analysis of a drawing plate test for easily monitoring the low-pressure frictional characteristics of powders is presented. The test is performed by measuring the force required to withdraw a plate from a cylindrical bed of dry powder. The characteristics of the drawing force profile are analyzed using Janssen's classical differential element approach to relate the product μK of powders as a function of packing of powder medium, where μ is the coefficient of friction of the powders against the solid drawing plate, and K is Janssen's constant, an anisotropic pressure distribution factor of a powder bed. The packing arrangement, expressed as the external void fraction, due to tapping, significantly alters the μK value and the effective sustaining strength of a powder bed. Experimental results on spherical glass beads having mono- and bimodal size distributions, and on three different poly (vinyl chloride) (PVC) powders are discussed. A spherical, high bulk density PVC powder has the combination of low μK and high, bulk density desirable for rigid powder compounding applications.