Evaluation of PVC formulations meeting the various cell classifications in ASTM D-3034

Most PVC gravity sewer pipe is manufactured according to the specifications in ASTM Standard D-3034. This pipe must be extruded from a dryblend which meets one of the three cell classifications listed in the standard. Several PVC formulations which meet these cell classifications are evaluated in this paper. Physical properties such as tensile strength, stiffness, and izod and drop dart impact are measured using both laboratory prepared as well as production run samples. Dryblend flowability is studied using the Jenike and Johnson Flow-Factor-Tester. The results show dryblend flow properties will significantly vary as the calcium carbonate filler level in each formulation increases. The use of a coated vs. uncoated filler will improve flow properties especially at higher filler loadings. An analysis of dryblend cost vs. resin price shows resin prices will affect what cell classification is the optimum one to use. Also, maximum filler usage may not result in an optimum cost savings if additional additives such as processing aids or impact modifiers are needed.     

Processing Aids: The Effect of Polymethyl Methacrylate on the Fusion of Rigid Poly(vinyl chloride)

The fusion process of a PVC dryblend, both with and without a PMMA processing aid, was studied in a Brabender Plasticorder over a range of mixer temperatures. charge masses and rotor speeds. The progress of fusion was monitored by the examination of the morphology of the PVC samples taken during different stages of the fusion process. The technique of examining the acetone-swollen samples by optical microscopy before and after shearing,¹ provided an insight to the mechanism of action of the PMMA processing aid. The study established that the PMMA processing aid modified both the inter-grain coefficient of friction and the packed density which had a significant effect on the initiation of the fusion process. The fusion process of both PVC compounds, i.e. with and without PMMA processing aid, was shown to proceed via a comminution mechanism, where the PVC grains were randomly broken into sub-grains and primary particle agglomerates. Concurrent with this breakdown, the cohesion of PVC agglomerates was observed.     

Elimination or control of health and environmental problems associated with heavy metal stabilizers

The health, environmental, and economic problems associated with heavy metal stabilizers are readily controlled or eliminated by a new stabilizer manufacturing and product technology known as Poly-Checks®. The products are dustless, free-flowing, noncompactable powders carried on host resins. The impact of these unique physical properties on health, safety, and the environment will be discussed. Suggestions on the use of these products by compounders will be offered that, if put into operation in the user's plant, will open the door to substantial cost reductions in the manufacture of PVC dryblend compounds.     

Sintering of PVC

Although PVC is counted as one of the amorphous plastics it possesses a distinct powder grain structure. This structure is responsible for various effects; for example it is impossible to sinter thick pieces of rigid PVC dryblend possessing satisfactory mechanical properties. For this application, it is necessary to break down this powder structure into smaller parts, called primary particles, by mechanical shearing and covering these particles with processing auxiliaries enabling it to be sintered. PVC can then be melted by the influence of temperature and pressure in the same way as other thermoplastic materials. For this reason, tests were carried out to determine the best material configuration and the necessary data for the compounding and shearing process, and the sinter conditions. A continuously working roll mill was used to break down the structure. The rolls of this equipment are provided with grooves inclined at a certain angle. With this construction it is possible to achieve a high shearing rate at a low mass-temperature. Furthermore, all additives can be added during the rolling process, so that no additional mixing process is necessary. These gelable pellets, made by the roll mill, can thus be formed in a die into plates of different thicknesses. Samples were pressed by varying compounding and sintering conditions and these were tested for mechanical properties.     

U‐PVC gelation level assessment,part 2: Optimization of the differential scanning calorimetry technique

Differential scanning calorimetry (DSC) is one of the best techniques for assessing PVC gelation level. Thus, it is of great interest to understand and optimize the different aspects of the DSC method. In the present study, DSC experiments were carried out on PVC dryblend samples that were previously heat‐treated at different temperatures. Practical aspects such as sample preparation, heating rate, and ending temperature are described. Then, the obtained DSC patterns are compared and analyzed to clarify the origin of the measured events. The effects of PVC reprocessing on DSC patterns are presented, as well as the effects of heterogeneity issues (i) at the scale of a PVC window profile and (ii) at the scale of a PVC DSC sample. The method used for the determination of the gelation level is then analyzed. The choice of the integration limits that strongly affect the melting enthalpy values is discussed. Different ways of calculating the gelation level, including the conventional definition involving the ratio A/A + B as well as new approaches, are proposed. J. VINYL. ADDIT. TECHNOL. 12:108–114, 2006. © 2006 Society of Plastics Engineers.     

Influences of chlorinated polyethylene and oxidized polyethylene on the fusion of rigid poly(vinyl chloride) compounds

Fusion time, fusion temperature, and fusion torque of poly(vinyl chloride) (PVC) compounds with various components were studied in this article. Influences of chlorinated polyethylene (CPE), oxidized polyethylene (OPE), and calcium stearate on fusion characteristics of PVC compounds were illustrated. The synergistic reaction among CPE, OPE, and calcium stearate forms a powerful and effective processing aid that allows the PVC particles to fuse more quickly and uniformly. In PVC/CPE compounds, a higher concentration of CPE can function like a processing aid and help PVC particles to fuse together easily. Meanwhile, the interaction between a higher concentration of OPE and calcium stearate in PVC/OPE compounds can promote the PVC particles to fuse together easily in the beginning of the fusion process. However, the external lubricant property of OPE still exists and results in more intact PVC microparticles not fused. The fusion temperature of the PVC in a Haake mixing bowl increases as the fusion time increases. On the other hand, the fusion torque decreases as the fusion time increases. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 699–705, 1999     

Comparative effect of plasticizer interchange on flexible PVC processing as measured by a torque rheometer

Present testing methods of comparing dryblend and fusion characteristics of poly (vinyl chloride) address resin interchange, but not plasticizer interchange. The wide range of available plasticizers requires methodology to predict plasticizer performance from a processing viewpoint. Modification of the test parameters reported in this study makes it possible to predict how plasticizer interchange affects processing under dynamic conditions.     

Process and material considerations in the industrial application of lubricants in rigid PVC extrusion

The proper lubrication of rigid PVC compounds often plays an important role in the successful operation of a rigid PVC extrusion plant. Changes in a particular lubricant system can have a substantial effect on the fusion rates of a rigid PVC compound and on the thermodynamics of the fusion process. Recently published research on the morphology of PVC resin and rigid PVC finished products has provided new insights into the morphological changes rigid PVC undergoes during processing. Lubricants can have a substantial impact on the rates and extent of morphological changes of rigid PVC during processing. Successful industrial optimization of a lubricant system involves balancing the rheological characteristics of the compound against the shearing and heating characteristics of the extruder and die tooling. Changes in the extruder and die tooling or lubricant system will result in changes in the work and energy balance. The impact of increases in fusion promoting lubricants, as well as increases in fusion delaying lubricants, on the work and energy balance for a twin screw extruder is explained.     

The lubrication mechanism of calcium stearate/paraffin wax systems in PVC compounds

The lubrication mechanism in PVC was studied using calcium stearate and paraffin wax lubricants. Based on the results of the differential thermal analyses, percent haze, microscopy, metal release, Brabender fusion, and extrusion studies we have developed a new theory of PVC lubrication based on molecular structure. Lubricants containing polar groups, which preferentially wet the metal surface in the presence of PVC, such as calcium stearate, are excellent metal lubricants. Non-polar lubricants which do not wet the metal surface, such as paraffin wax, allow PVC to stick to the metal surface. However, these lubricants work in combination with the metal wetting lubricants to make the lubricant layer more fluid, providing a better lubricating system than either lubricant alone. Lubrication between PVC primary particle flow units is similar to that at the metal surface with the polar PVC surface acting in a similar manner as the metal surface. We find the common classification of lubricants as internal or external to be deficient in explaining performance.     

Studies of rigid poly(vinyl chloride) (PVC) compounds. IV. Fusion characteristics and morphology analyses

Poly(vinyl chloride) (PVC), PVC/chlorinated polyethylene (CPE), PVC/oxidized polyethylene (OPE), and PVC/CPE/OPE compounds were prepared in a Haake torque rheometer at various temperatures, rotor speeds, and totalized torques (TTQ). The fusion characteristics of these PVC compounds (fusion time, fusion torque, and fusion temperature) were studied. Longer fusion time results in higher fusion temperature. Higher fusion temperature results in lower fusion torque. The fusion time of PVC/OPE compounds is the longest among these PVC blends. However, the fusion time of PVC/CPE/OPE compounds is the shortest among these PVC blends. The fusion time of the PVC/CPE/OPE compound is significantly different from those of PVC, PVC/OPE, and PVC/CPE compounds at the medium starting temperature and the medium rotor speed. Scanning electron microscopy (SEM) analyses successfully revealed the surface morphological changes of the fusion of PVC, PVC/OPE, PVC/CPE, and PVC/CPE/OPE compounds. The lubrication mechanisms of these PVC compounds have also been postulated. © 1995 John Wiley & Sons, Inc.     

Assessment of degree of fusion of rigid PVC from inverse gas chromatographic measurements

Inverse gas chromatography of alkanes has been used to assess the degree of fusion of rigid polyvinyl chloride (PVC) extrudates. The relative degree of fusion is provided by ratios of the retention volumes of the alkane probe molecules in the bulk of the PVC. This method is nonintrusive and can be used to measure degree of fusion quantitatively if a completely fused reference material can be provided. The present analysis involves evaluations of the contributions to the overall retention volume of the alkane probes, resulting from adsorption and from bulk diffusion. The diffusivity of the alkanes was clearly dependent on the processing history of the PVC extrudate. A direct variation was observed between the size of the diffusing molecules and their residence time as adsorbates on the polymer surface. © 1995 John Wiley & Sons, Inc.     

Investigation of the effects of nonisothermal suspension polymerization of vinyl chloride on the fusion and degradation behavior of poly(vinyl chloride)

Thermal stability of poly(vinyl chloride) (PVC) samples polymerized under a temperature trajectory was studied from the point of view of morphological and microstructural characteristics. The results are compared with those of the PVC samples obtained by polymerization at constant temperature having the same K value. The Brabender^® plastograph data indicated that the final PVC synthesized with the temperature trajectory showed lower fusion time and higher thermal stability time. The nonisothermal condition also increased the degree of fusion of the final PVC resin, reflecting lower temperature/time required to process it. It was found that the thermal stability of nonisothermally produced PVC as characterized by dehydrochlorination rate decreased (improved) with the increasing monomer conversion until a minimum value was reached that corresponded to the conversion at the pressure drop. However, the dehydrochlorination rate remains almost constant with conversion for an isothermal grade PVC resin. Although the evolution of the number of internal double bonds as well as extent of discoloration of PVC with conversion shows a decreasing trend, the labile chlorine concentration exhibits a maximum at early conversion. The reason for the former can be explained by the temperature dependence of reactions forming defect structures, which are kinetically controlled and thus favored at higher temperatures. The latter, however, can be explained because of the increasing importance of transfer reactions to polymer with increasing polymer concentration. Finally, the results from differential thermogravimetry verify an improvement in thermal stability of the final PVC prepared by using a temperature trajectory during vinyl chloride monomer suspension polymerization. J. VINYL ADDIT. TECHNOL., 23:259–266, 2017. © 2015 Society of Plastics Engineers     

Viscosity effects in rigid PVC

The viscosity of PVC is better understood if the material is treated as a fluid which contains filler. Anomalous effects such as die swell increasing with increasing melt temperature and melting history causing changes to the viscosity can be explained if the PVC primary particles are viewed as filler which disappears during melting. The fusion torque peak is well‐described by this approach. The compaction minimum is a free‐flowing powder which changes to a filler‐containing viscous liquid. If another viscous liquid is added to a PVC compound, then the fusion peak will be at a lower torque, because the effective level of filler is reduced. This reduction helps to explain the fusion curve of PVC compounds that contain chlorinated polyethylene (CPE) impact modifier.     

扭矩流变测定法研究硬质PVC/木粉熔融性能

研究了扭矩流变仪中木粉含量、木材种类(软木和硬木)及粒度对硬质PVC/木粉复合材料熔融性能(熔融时间、熔融温度、熔融扭矩和熔融能)的影响。纯硬质PVC只有1个熔融峰,而PVC母体材料中加入木粉后会产生2个熔融峰。结果表明,增加木粉含量会使基本粒子间开始熔融时间、温度和能量明显增加,从而引起熔融扭矩的增加,与木粉种类无关;用木粉填充的硬质PVC应该在比纯树脂高的温度下加工;木材种类会影响复合材料的熔融性能,但软木和硬木之间确定不出一个明显的趋势;精细粒子的熔融速度比粗粒子快,需要的能量也较少。     

硬质PVC挤出发泡材料的塑化性能研究

采用Haake转矩流变仪测定了挤出发泡PVC混合料的恒温、升温熔融塑化性能，结果表明：随着PVC树脂聚合度增加，塑化时间和加工转矩增加；随着ACR加工助剂用量和分子质量的增加，塑化时间缩短，转矩增加；ACR抗冲改性剂具有类似ACR加工助剂的塑化改良行为；添加填充剂碳酸钙促进PVC熔融塑化；ADC发泡剂可延缓PVC混合料的塑化速率、提高熔体粘度，添加发泡剂NaHCO3将大大延缓混合料的塑化速率。     

Fusion characteristics of rigid PVC/wood‐flour composites by torque rheometry

This study was aimed at examining the effects of wood flour contents, wood species (softwood vs. hardwood), and particle size on the fusion characteristics (fusion time, fusion temperature, fusion torque, and fusion energy) of rigid PVC/wood‐flour composites in a torque rheometer. Neat rigid PVC exhibited one fusion peak, whereas the addition of wood flour into the PVC matrix led to two fusion peaks. Increased wood flour content caused a significant increase in the time, temperature, and energy at which fusion between the primary particles started, thereby leading to increased fusion torque, irrespective of the wood flour species. These results implied that rigid PVC filled with wood flour must be processed at higher temperatures than neat resin. Although fusion characteristics of the composites were influenced by the wood species, a clear trend between softwood and hardwood species could not be established. However, finer particles fused more quickly and needed less energy than coarse ones. J. VINYL ADDIT. TECHNOL., 13:7–13, 2007. © 2007 Society of Plastics Engineers.     

Understanding the functions of acrylic processing aids in rigid PVC injection molding

Poly(vinyl chloride) (PVC) compound use is growing in specialty injection molding applications such as appliances, business equipment, and electrical enclosures. A key factor in determining the appearance and physical properties of the molded parts is the processability of the PVC compounds, which can be improved through the use of acrylic processing aids. Processing aids promote PVC fusion, modify the melt rheology, and/or provide lubrication. Some processing aid products are designed to serve one of these functions while others provide a combination of functions. Each of these functions and its major benefits in rigid PVC injection molding are described. Some guidelines for selecting appropriate processing aid products for applications are provided.     

刚性微粒对硬聚氯乙烯性能的影响

概述了刚性微粒对硬聚氯乙烯加工性,热稳定性、光老化性以及力学性能的影响,并从结构－加工－性能关系角度分析说明刚性微粒的组成与形态。研究结果表明：聚氯乙烯的塑化状态是决定硬聚氯乙烯性能的关键因素,通过选择适当的刚性微粒,控制塑炼工艺条件可获得性能优异的硬聚氨乙烯材料。     

An evaluation of the cavity transfer mixer for the extrusion of rigid PVC on both single and twin screw extruders

PVC powder compound fed into single- and twin-screw extruders retrofitted with cavity transfer mixers improved PVC grain fusion. Consequent improvements in appearance and properties ought to reduce current tight comprises that must be made between materials costs, output rate, and quality.     

The influence of stabilizers on the fusion of rigid poly(vinyl chloride)

It is known that the fusion rate of rigid PVC in an extruder partly depends upon the lubricants that are used. In the present study it is shown that different stabilizers have a great influence upon the rate of fusion of rigid PVC. Results from extrusion experiments and the Brabender Plastograph strongly indicate that a correlation exists between rapid melting in the extruder and the melt viscosity-temperature relation of the polymer blend. The reason why certain stabilizers cause a more rapid fusion of the PVC is attributed to the chemical structure of the stabilizers.