Rigid cellular PVC—the next house siding material?

The technology for extruding rigid cellular PVC has grown substantially over the past decade. Formulation additives, tooling, and processing expertise have made possible a variety of applications—relatively complex profiles, foam-core pipe, thermoformable foam sheet, and house siding. In the U.S. market, vinyl house siding is typically a relatively thin extrusion that is folded into a final shape that resembles wood cladding in appearance. An alternative to conventional form vinyl siding could be a foam structure that is thicker and stiffer than the solid form, and with a density similar to that of wood. This paper presents several performance advantages of rigid cellular PVC cladding in comparison to the current solid product, in addition to mentioning certain limitations that exist in the foam product that is produced with the technology available today.     

Materials and testing for extrusion of RPVC construction products

Rigid PVC extruded construction products take many forms. Typical are house siding, window profiles, storm doors, pipe, fencing, and various accessory items generrally used for installation. In addition to these solid products, foam or cellular rigid PVC materials are entering the marketplace as substitutes for the traditional solid materials, or allowing PVC to capture other maintenance free applications; typical forms now in use include interior molding profiles and foam core pipe. This article focuses on the formulation ingredients constituting the articles mentioned above, how they are put together and influence the manufacturing process and final product, and how they can be tested to determine fit to the application requirements.     

The performance of ultrafine talc in rigid PVC

This paper demonstrates how ultrafine talc can be used in a rigid PVC formulation to design a compound with increased stiffness and high impact strength. The talc's shape and particle size, combined with the affects of increased levels of impact modifier, produce a PVC material with an outstanding impact stiffness balance. Although more expensive than conventional PVC formulations, it can compete with other resins, such as ABS, in high performance applications.     

A rigid poly(vinyl chloride) compound with improved combustion characteristics

By means of compounding, we have developed a rigid poly(vinyl chloride) (PVC) formulation with improved overall combustion properties. Newly developed analytical methods indicate a considerable reduction in the level of gases released during combustion, in addition to excellent flammability characteristics and low visible smoke emission levels. The analytical methods discussed are expected to aid in the selection of a feasible protocol for biological testing and in the interpretation of results obtained from such testing. The under-lying compounding technology is currently restricted to normal impact rigid PVC cube compounds but expected to be expanded into high impact PVC, flexible PVC, PVC powder compounds and cellular PVC.     

Extrudate swelling and viscoelasticity of rigid PVC compounds

In this paper, we investigate the effects of processing aids, impact modifiers, inorganic fillers, and resin molecular weight on the postextrusion swelling of rigid PVC compounds. Rotational rheometry measurements of the loss tangent in dynamic mode and of the recoverable shear in creep mode are made to evaluate PVC's elasticity. Long elastic relaxation times are found for rigid PVC. This apparent contradiction, i.e., relatively low swell but very high elastic relaxation time, is explained by taking into account the two-phase flow behavior of PVC.     

Plasticizer migration from plasticized into unplasticized poly(vinyl chloride)

There exist important industrial applications, such as hoses or plastic windows, dealing with closely combining plasticized and rigid poly(vinyl chloride). Nevertheless, migration of plasticizer causes severe variation of the mechanical performance of the end-products. This work comprises an effort to investigate and understand these phenomena, also as an extension of previous work of ours in migration to liquid environments. The common system plasticized PVC/dioctylphthalate/unplasticized PVC was studied under two-sided diffusion conditions, i.e., from a thin sheet of plasticized sheet. The whole assembly was placed between two glass plates and then was held in an oven at 64°C to simulate accelerated test conditions. Some pressure was also applied to ensure perfect contact between the plastic sheets. Three different levels of initial plasticizer concentration (48, 66, and 100 phr) have been considered for a period of about five months, until equilibrium was reached. During this period the migration process was monitored by weight changes. Plots of M_t/M_∞ vs. t^½, where M_∞ the amount migrated at equilibrium and M_t the amount lost at time t, resulted in evident linear relationship. Therefore, it was proved that the Fick's law approximation for short times can be used to describe the migration kinetics for this solid/solid system. On the other hand, macroscopic observations revealed that no plasticizer was accumulated at the interface, i.e. all plasticizer leaving the plasticized sheet entered the rigid ones. Finally, it seems that the controlling stage is the diffusion inside plasticized PVC while possible annealing of the plasticized polymer structure cannot be excluded.     

Calendering poly(vinyl chloride): Theory and experiments

An isothermal model for the calendering of power-law fluids which exhibit a slip boundary condition is presented. This model is based on lubrication approximation and Gaskell's theorxy. It Predicts sheet thickness, pressure distribution, velocity profiles, torque and power from rheological data for the melt and machine parameters. The predictions (sheet thickness, pressure distribution and torque) are compared with a set of experimental data for rigid poly(vinyl chloride)(PVC) provided to the authors by Solvay & Cie S.A.     

硬质PVC低发泡板材的加工技术

主要从板材的无屑加工、机械加工、连接、热成型、表面处理等几方面对硬质聚氯乙烯(PVC)低发泡板材在现阶段的加工技术进行了阐述,以期对硬质PVC低发泡板材的应用有所帮助。     

Conductive PVC composites: Part 1. Physical and electrical properties

Conductive-plastic enclosures, to compete successfully in the electronics industry, must be easily and rapidly moldable into a low-cost, lightweight, structurally sound, flame-retardant, and electrically-conductive rigid part. Such a material must combine the design flexibility and moldability of a plastic with the EMI shielding properties approaching those of a metal. PVC filled with aluminum flake makes an excellent conductive composite, provided it is correctly formulated and processed. A critical concentration of metallic filler must be used; it is a function of the plastic formulation; the uniformity of the filler's dispersion; the filler type, size, and morphology; and the method by which it was compounded into the resin.     

Stress cracking of rigid polyvinyl chloride by plasticizer migration

Environmental stress cracking (ESC) (failure caused by crack and craze formation at a stress less than the yield stress) reduces the service life of many plastic products. This paper is concerned with ESC of rigid PVC products which are in contact with a plasticized PVC material. The ESC affect (as measured by elongation to break) is reduced at faster strain rates and by higher plasticizer viscosity, which suggests a mechanism requiring flow of plasticizer into a growing craze. Well fused (gelled) PVC made at a higher melt temperature slowed but did not eliminate environmental stress cracking. Rubber impact modifier added to the rigid PVC had no effect on ESC. Environmental stress cracking can be avoided by using flexible PVC that has a non-migrating plasticizer or by designing the product so that rigid PVC is not stressed while in contact with plasticized PVC.     

History of the development of processing aids for rigid PVC

Bauman's polymerization of vinylchloride is generally regarded as the first documented preparation. British and German patents were granted in 1912 but the period from 1931 to 1933 based on work at BFGoodrich is considered as the beginnings of the flexible PVC industry, which grew rapidly during the 1940's and 1950's to become the dominant family of synthetic plastic resins. However, PVC degrades at about the same temperature required to process it. Therefore, without stabilizers and other additive modification, it could not have reached its present preeminence among rigid thermoplastics. The first processing aid patent appeared in 1953, and the first commercial processing aid appeared in 1957, which marked the beginning of the rigid PVC industry, the development of which is described in the paper.     

PVC: Packaging issues and regulations

As a result of reports that vinyl chloride monomer migrated at detectable levels into alcoholic beverages stored in poly(vinyl chloride) bottles, FDA proposed to ban the use of rigid PVC for distilled spirits in 1973. A review is presented of FDA's revised proposal for the regulation of PVC food packaging issued in 1986 and some recent developments that have further delayed FDA's issuance of a rule that would lead to the use of PVC in liquor bottles. Despite significant technological improvements in the manufacture of rigid PVC, which has led to drastic reduction of residual vinyl chloride monomer (RVCM) to safe levels, FDA action on PVC has remained stalled. It is concluded that final action by FDA may well depend not on scientific principles, but on the Agency's ability to effectively reconcile the correct scientific, health and legal solutions with the political pressure being exerted by environmentalist groups.     

Die Design and Extrusion Techniques for Rigid Cellular PVC

Abstract

Rigid cellular extrusion technology can be traced back approximately 20 years to the early 1950s. The commercial realization of this technology did not take place until the summer of 1970 when Goodyear began to market a rigid cellular PVC compound under the trade name Vycell. Since that time, several problem areas have demonstrated themselves to be common denominators for new entrants into cellular profile extrusion. The purpose of this presentation is to define these problem areas and to record the best solutions found to date.     

Prediction of vinyl chloride monomer migration from rigid PVC pipe

Data on the solubility and diffusion of vinyl chloride monomer (VCM) in PVC resin powders have been combined with published solutions of Fick's diffusion equation to yield predictions of the amount and rate of loss of residual VCM (RVCM) from rigid PVC pipe under storage and service conditions. The principal factors controlling VCM migration are the initial VCM content, thickness of the PVC section, temperature and the age of the PVC product. Analysis Solutions are presented for RVCM loss from freshly exturded pipe (uniform VCM concentration) into either the storage environment or the pipe contents. From these solutions, estimates are made for the real-world situation of closed-system service following variable storage periods. The validity of this approach for rigid PVC pipe in water-service is supported by reasonable agreement between its predictions and experimental laboratory data on the VCM content of water stored in PVC pipes. Both the predictive model and experimental data indicate that PVC pipe containing ≤ mg/kg (1 part per million) residual VCM will result in VCM concentrations in water of less than 0.002 mg/kg - under any expected service conditions.     

PVC packaging recycling

This study examines the recyclability of PVC bottles into other PVC products. Post consumer bottles can potentially be granulated and used, without further treatment, in the production of these products. Washing will allow the granulate to recover most of the properties of the original bottle compound, by removing paper labels and residual product contamination. Plastic contaminants, such as those from caps and other plastic bottles, show little effect on several physical properties at levels up to 3%. This granulate can thus be used as a significant portion of the raw material feed for a number of PVC products including DWV (drain/waste/vent) pipe, pipe fittings, rigid sheet, bottles, etc. Post consumer PVC bottle granulate thus constitutes a valuable resource; the recyclability of PVC packaging thus is a question of collection.     

Foaming of rigid PVC/wood‐flour composites through a continuous extrusion process

The effects of chemical foaming agent (CFA) types (endothermic versus exothermic) and concentrations as well as the influence of all‐acrylic processing aid on the density and cell morphology of extrusion‐foamed neat rigid PVC and rigid PVC/wood‐flour composites were studied. Regardless of the CFA type, the density reduction of foamed rigid PVC/wood‐flour composites was not influenced by the CFA content. The cell size, however, was affected by the CFA type, independent of CFA content. Exothermic foaming agent produced foamed samples with smaller average cell sizes compared to those of endothermic counterparts. The experimental results indicate that the addition of an all‐acrylic processing aid in the formulation of rigid PVC/wood‐flour composite foams provides not only the ability to achieve density comparable to that achieved in the neat rigid PVC foams, but also the potential of producing rigid PVC/wood‐flour composite foams without using any chemical foaming agents.     

Glutarimide acrylic copolymer: A new route to high heat PVC

PVC is the second largest polymer produced and used in the U.S. It is a self-extinguishing material with excellent chemical resistance and good dimensional stability. It's greatest asset, however, is it's versatility. By specifically formulating PVC with the numerous types of additives available, a balance of properties can be tailored for a wide range of applications. The most serious disadvantage of PVC is it's low heat resistance which limits the service temperature of finished articles to about 70°C. Now an additive is available that can be formulated with PVC to form miscible, transparent blends with increased service temperature. With proper formulating, the higher HDT can be achieved without sacrificing other properties. It is especially important in clear PVC applications where no increase in haze was noted with the addition of the acrylic imide copolymer. Indications are that substantial market opportunities exist for a high heat PVC. Major market segments include clear packaging with it's need for hot-fill containers, building products where the desire to use darker colors provides the driving force, and in custom injection molding applications where improved heat resistance would allow vinyl to compete more effectively with FR-styrenics.     

Effects of uniaxial drawing and heat-treatment on gas sorption and transport in PVC

Sorption and transport measurements for various gases in rigid poly(vinyl chloride) were made following uniaxial drawing and heat treatment. The permeabilities of He, Ar, N₂, and CH₄ were found to be essentially independent of pressure in PVC while CO₂ showed a complex pressure dependence which varied with prior exposure and degassing history. Sorption isotherms were analyzed by the dual mode sorption model, and the parameters obtained were correlated with the Lennard–Jones potential-well depth of the gas. The Henry's law coefficient for CO₂ was found to be significantly larger than expected which is believed to be the result of a specific interaction with PVC. Uniaxial drawing of PVC above its glass transition caused significant reductions in gas permeabilities, of which roughly one-third is attributable to the accompanying heat treatment rather than molecular orientation per se. The physical state of the polymer was characterized by density, birefringence, and calorimetry. Changes in gas sorption and permeation behavior are discussed in terms of these results.     

Impact modification of weatherable rigid PVC compounds

Rigid, weatherable PVC compounds used in the building products industry must have superior initial impact properties and maintain these when subjected to various environmental conditions. For instance the impact strength of a rigid PVC formulation changes when the temperature is lowered from ambient to sub-zero, when it is exposed outdoors, and when different types and quantities of impact modifiers are used. To measure the aforementioned changes, instrumented as well as more conventional impact testing techniques are used.     

Reinforcement of rigid PVC/wood‐flour composites with multi‐walled carbon nanotubes

Multi‐walled carbon nanotubes (CNT) were compounded with PVC by a melt blending process based on fusion behaviors of PVC. The effects of CNT content on the flexural and tensile properies of the PVC/CNT composites were evaluated in order to optimize the CNT content. The optimized CNT‐reinforced PVC was used as a matrix in the manufacture of wood‐plastic composites. Flexural, electrical, and thermal properties of the PVC/wood‐flour composites were evaluated as a function of matrix type (nonreinforced vs. CNT‐reinforced). The experimental results indicated that rigid PVC/wood‐flour composites with properties similar to those of solid wood can be made by using CNT‐reinforced PVC as a matrix. The CNT‐reinforced PVC did not influence the electrical and thermal conductivity of the PVC/wood‐flour composites. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.