Flexible PVC Compounds Research Articles

Preparation and testing of a solid secondary plasticizer for PVC produced by chemical degradation of post-consumer PET

Post-consumer poly(ethylene therephthalate) (PET) obtained from milled water bottles was chemically degraded by glycolysis, using suitable amounts of diethylene glycol (DEG) and Ca/Zn stearate as catalyst system. The process was carried out by employing a melt mixer as the chemical reactor, which is the facility generally used for plastic compounding. The degraded PET products were first characterized from structural and thermal point of view by Fourier transform infrared spectroscopy (FTIR), Proton nuclear magnetic resonance (1H NMR), Size exclusion chromatography (SEC) Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA), and thereafter used alone or together with di(2-ethylhexyl) phthalate (DEHP) in poly(vinyl chloride) PVC formulations. The plasticization was, in fact, accomplished by using a binary system consisting of DEHP as primary plasticizer and a degraded PET product as secondary plasticizer (SP). The obtained materials were characterized through the main methods used to assess flexible PVC compounds: hardness in Shore A scale, thermal properties and quantitative migration of the plasticizer. The solid secondary plasticizer obtained from post-consumer PET improves both the processing characteristics and the thermal stability of the final flexible PVC compounds while maintaining their hardness within the top values of the Shore A scale. In addition, a considerable reduction of the plasticizers migration (23%) was obtained by optimizing the formulation.

Characterization of Thermal Reversible Cross-Linking Agents for Flexible Poly(vinyl chloride)

In order to improve thermal stability of Poly (Vinyl Chloride), a kind of thermal reversible cross-linking agents, the end cyclopentadienyl ethanethiol salts, sodium cyclopentadienyl ethyl mercaptan (CPD-C2H4SNa) was synthesized in this paper. The DSC results proved that the prepared CPD-C2H4SNa has obvious thermal reversible characteristics and the thermal reversible temperature was at 177 °C. The effects of cross-linking agent amount, cross-linking reactive time and temperature on flexible PVC compounds were evaluated through gel content testing. It was showed that the cross-linking agent with 3 Phr is optimum for PVC compounds. Moreover, both the cross-linking reactive time and temperature has effects on gel content of PVC compounds. The gel content of CPD-C2H4SNa cross-linked PVC compounds reaches maximum at 76% for 20 min at 160 °C.The static thermal stability of flexible PVC was measured according to congo red method. The results showed that the thermal stability of PVC compounds was enhanced with increasing cross-linking agent amount.

Lubrication, single screw extrusion rates, and plasticizer structure in flexible PVC compounds

AbstractIt is well‐established that changes in plasticizer structure affect (among other things) the melting temperatures, melt viscosities, and lubrication of flexible PVC compounds. In turn, these properties affect the extrudability of the compounds. The current study looks at the effects of plasticizer structure on lubrication, melt viscosities, extrusion rates, stock temperatures, and shear rates of PVC compounds in a single screw extrusion process. J. VINYL ADDIT. TECHNOL., 13:22–25, 2007. © 2007 Society of Plastics Engineers.

Thermogravimetric analysis as applied to prediction of plasticizer desorption from flexible poly(vinyl chloride) compounds

A fundamentally new procedure was proposed for evaluating the parameters of plasticizer desorption from flexible-PVC compounds by quantitative description in terms of a developed kinetic model and of TGA data obtained under the conditions of a linear rise in temperature up to the onset of chemical transformation. The obtained estimates were shown to satisfactorily describe the desorption of a plasticizer from PVC cables in the course of their actual long-term (longer than ten years) service. The method proposed makes it possible to shorten the duration of testing from several months to 1–2 days.

Hydrocarbon secondary plasticizers as functional additives in flexible PVC compounds

Secondary plasticizers are additives which, by themselves, have limited compatibility with the polymer but may be used in combination with a primary plasticizer. Within the secondary plasticizers group hydrocarbon (HC) secondary plasticizers are sometimes seen as inexpensive, volatile additives that can reduce flexible PVC compound costs but that are largely lost during processing and have little plasticizing effect. However, analysis of processed flexible PVC samples shows that, depending on processing conditions and end use exposure conditions, HC secondary plasticizers can show some degree of permanence in the plastic and contribute to its flexibility. Moreover, HC secondary plasticizers can significantly improve the low temperature properties of compounds and the release of compounds from hot metal surfaces, lower plastisol viscosities, and improve plastisol viscosity stabilities. Hydrocarbon secondaries (at least the nonaromatic secondaries) have little effect on compound melt viscosities. Compatibility of some of these secondary plasticizers can be quite adequate and their effects on compound processing temperatures can be slight. J. VINYL. ADDIT. TECHNOL., 11:76–82, 2005. © 2005 Society of Plastics Engineers

Effect of extrusion melt temperature on properties of flexible PVC

AbstractThis paper provides an insight on the relationship between the physical properties of profiles extruded from flexible PVC compounds and the extrusion melt temperature. The properties include tear resistance, tensile properties, brittleness temperature, and compression set. The effect of heat history on surface characteristics of the extrudate, such as surface roughness and gloss, and their relationship with the processing morphology are also discussed.

Photoluminescent properties of flexible PVC compounds and their interpretation for performance analysis of automotive exterior parts

AbstractStudy of fluorescence emission from flexible PVC‐based formulations, colored by exposure to road asphalt or degraded thermally or by UV aging, shows that fluorescent species are formed during the interaction of PVC with road asphalt. For the conditions found in exterior automotive applications, no other known degradation causes development of fluorescence. Flexible PVC‐based formulations discolored by asphalt staining or degraded thermally at moderate temperatures bleach completely under conditions of natural or artificial weathering. A simple technique, using visually observed photoluminescence and photobleaching, can thus identify photoactive groups formed during the interaction of PVC with road asphalt. Application of this test method will allow selective improvement of failed asphalt resistance without treating the “overall” stability of a compound.

A practical guide to the identification of monomeric plasticizers in flexible PVC compounds

AbstractThe performance of a flexible PVC compound is often defined by its plasticizer content and composition. A simple, accurate and fast method of plasticizer identification can therefore be an effective quality control test and benchmark performance in new product development studies. Gas chromatography provides the most effective plasticizer identification method. Gas chromatography can be supplemented by infrared and liquid chromatography and physical observations to confirm identity.

Study on the oxidative induction test applied to medical polymers

This article continues our study published earlier on the application of the oxidative induction test to a wide variety of medical polymers. In a series of thermoplastic olefin elastomers (TPO), the extrapolated induction time on the Arrhenius plot was found to coincide with published results based on oven aging mechanical studies extending to much lower temperatures and times as long as nearly a year. This agreement indicates the potential of the OIT for long term durability prediction. For medical flexible PVC compounds, the traditional measure of extent of degradation by color formation was found to correlate to measured oxidative induction times. Furthermore, three distinct regimes were also detected, where in the first phase, little color changes can be detected. In a longer time, lower temperature study, effect of room temperature fluctuations was clearly detected, emphasizing the need for good environmental control for sensitive detections. These and other recent results will be presented to illustrate the utility of this versatile test.

Improving gamma radiation resistance: Medical grade, flexible clear PVC compounds

AbstractFlexible clear PVC compounds tend to yellow and darken during and after exposure to gamma radiation. This has been an obstacle to their use in the medical market. The purpose of this investigation was to improve the gamma stability of flexible PVC. The variables of interest were resin molecular weight, plasticizer loading, stabilizer type, and choice of antioxidant. By screening resins, plasticizers, stabilizers, lubricants, and antioxidants, a promising candidate formulation was identified and optimized by statistically designed experiment, with hardness added as an additional variable. The criterion for improvement was color change after gamma irradiation, compared with an identical unexposed specimen. Thus, a series of gamma stable formulations were created exhibiting improved post irradiation color stability.

Elastomeric alloys of PVC

AbstractThe performance standards for flexible PVC compounds continue to become more demanding as manufacturers pursue more value‐added applications traditionally dominated by rubbers and thermoplastic elastomers. Blending of PVC with other polymers has proven to be a viable approach in developing higher performance flexible PVC‐based materials. This paper will review some of the typical approaches to producing PVC‐based elastomers, and show how these standard flexible PVC blends compare to a newly developed family of PVC alloys. The advantages of these materials will be discussed, and some examples of commercial materials and their application will also be reviewed.

Effect of plasticizer functionality on the performance properties of flexible PVC compounds

AbstractThis paper is on the enhancement of physical properties achieved through utilization of linear plasticizers in flexible PVC compounds. This paper also emphasizes the use of statistical methods and designs of experiments. In a series of experimental designs, electrical, oven‐aging, and low temperature performance of commercially available phthalate plasticizers were evaluated. Test data will be given to show the effect of plasticizer functionality on the performance properties of flexible PVC compounds.

Antioxidants and UV stabilizers: A summary of their utilization in PVC

AbstractWith the ever increasing demand for better performing products has come the enhanced use of stabilizers and stabilizer systems in both the production and processing of poly(vinylchloride). Antioxidants and chain terminators are commonly used in teh resin manufacturing to improve the initial color and overall quality of the polymer isolated from production. Hindered phenolics and organophosphites have been found to boost the performance of thermal stabilizers for PVC processing. Additionally, as both rigid and flexible PVC compounds have found greater and more demanding weatherable applications both indoors and outdoors, the utilization of UV stabilizers has grown proportionally. For most outdoor applications the UV stabilizer system is essential for the maintenance of color and mechanical properties of the PVC product. This paper attempts to review and discuss stabilizer usage for specific PVC formulations and applications and answer questions as to how and why they are used.

Specialty low gloss PVC resin vs. traditional low gloss modifiers

AbstractSpecialty low gloss PVC homopolymer resin effectively reduces gloss levels in flexible PVC compounds at replacement levels of 5 to 30 phr while having little effect on processing parameters. Compounds based on specialty low gloss homopolymers maintain their low gloss characteristics over a broad temperature range and during post heating. These compounds also out perform compounds based on other low gloss modifiers such as acrylics and silicas for physical properties.

The use of statistical process control in batch processed PVC compounding

AbstractThis paper describes the main Statistical Process Control (SPC) method that is being used by Canada Wire and Cable in the manufacture of their flexible PVC compounds. It outlines the benefits that are being realized by following a systematic approach towards using control charts. By employing SPC as a quality improvement tool, the operation has reduced its costs by an estimated $180,000 per year.

Rheology of flexible PVC compounds. Part I: The influence of resin crystallinity

AbstractThe changes occurring in torque during PVC processing in a torque rheometer have been interpreted in terms of the destruction of the supramolecular structure followed by a fusion of the grain fragments. In contrast to changes in torque, changes in elasticity occur in the absence of grain breakdown. It is proposed that the change in elasticity during processing is the result of changing crystallinity of the resin. In the early stages of processing, crystallites melt and elasticity decreases. As grains fuse together, new crystallites are formed in the previously unoccupied grain boundaries and the elasticity increases.

Rheology of flexible PVC compounds. Part II: Verification of the crystallinity concept

AbstractIt has been proposed that changes in elasticity associated with the processing of PVC are influenced by the crystallinity of the resin. In the early stages of processing, crystallites melt and elasticity decreases. As grains fuse together, new crystallites are formed in the previously unoccupied grain boundaries and the elasticity increases. A theoretical curve combining the percent of crystallinity with the developing boundary volume has been developed. This curve can be used to predict how elasticity changes with time. Experimental observations detailing the changes in elasticity with respect to processing verify these predictions.