Stability Of PVC Research Articles

Fenbutatin acute toxicity on Artemia nauplii: effects of sublethal concentrations on ATPase activity.

During the last decades, the use of organotin compounds has steadily increased. The numerous applications of these compounds are primarily in industry as stabilizers for PVC, in agriculture as miticides and fungicides and in the marine environment as antifoulants. The increasing annual usage of organotin compounds raises the possibility of environmental pollution. The toxicity and degradation of organotins in the environment depends strongly on the number and nature of substituents (Muller 1987). In water, triphenyltin compounds decompose slowly (Bock 1981). Persistence of at least 8 months was found when triphenyltin was used against water snails at concentration of 1.0 ppm ( Deschiens and Floch 1963). Organotin compounds in the aquatic environment accumulate in the microlayer of the water surface, are readily adsorbed in sediments and on suspended particulates (Chernega et al. 1971, Cooney and Wuertz 1989). The half-life of organotins was found to be up to 5 months in freshwater sediments (Maguire and Tkacz 1985) and up to 2 years in deep and anaerobic estuarine sediments (Waldock et al.1990). Among organotins trisubstituted compounds are generally the most toxic to fish, to microorganisms and to other aquatic inhabitants (Bock 1981, Cooney and Wuertz 1989). Whereas the adverse effects of tributyltin, the main representative of antifouling agents , on the homeostasis of the aquatic ecosystems has been studied, few data are available concerning the environmental impact of the trisubstituted organotins used in agriculture as miticides. The aim of this project is to determine the median lethal concentration of the organotins used as miticides, in nauplii of the marine crustacea Artemia and to study the effects of sublethal concentrations on the activity of ATPase enzymatic system. In this study we will present the results from the experimentation with fenbutatin on the survival and ATPase activity of Artemia nauplii.

Mechanistic aspects of organotin stabilization of PVC

AbstractPrompted by commercial significance and academic interest, extensive model compound and in‐situ studies of PVC degradation/stabilization appear in the literature. This paper presents the results of some in‐situ studies of the chemical reaction pathways undergone by organotin thioglycollate esters during PVC stabilization. Infrared spectroscopy indicates that in the case of diocyltin bis(isooctylthioglycollate), not only is the mercaptoester/chloride generated, but also the corresponding thioglycollate (Oct2 Sn TG). The extent to which this species is observed is dictated by the processing technique. An attempt is made to correlate the chemical reaction pathway of the organotin compounds with the changes (unsaturation) within the polymer. The possible relevance of these observations to the phenomenon of mono/di synergism is also discussed. While these studies extend our knowledge of the organotin stabilization of PVC, they also show that our understanding is far from complete.

Mixed Ca/Zn thermal stabilizers for weatherable rigid PVC

AbstractRigid PVC profiles for window frames are required to follow quality standards (usage properties and aging resistance). Our concern is to describe the role of additives and mainly thermal stabilizers on the required properties. Until recently, PVC stabilization was based on heavy metal soaps in the European PVC building industry. Though their resulting efficiency was not questioned, problems of toxicity were raised. Regarding the ecological pressure increase, numerous investigations on co‐stabilizers have been carried out in order to improve the performances of mixed Ca/Zn systems. Our results show the properties of rigid profiles stabilized with Ca/Zn systems. First, the extruded profiles properties such as optical (color) and mechanical properties (impact resistance…) are shown. The aging resistance of toxic heavy metal free vinyl formulations is also studied in comparison with typical Pb/Ba/Cd. The performances achieved indicate that an opportunity to move from toxic heavy metallic stabilizers to mixed Ca/Zn systems, resulting, perhaps, in wider development of Ca/Zn stabilizing systems for food packaging and medical plastics.

Mixed Ca/Zn thermal stabilizers for weatherable rigid PVC

Rigid PVC profiles for window frames are required to follow quality standards (usage properties and aging resistance). Our concern is to describe the role of additives and mainly thermal stabilizers on the required properties. Until recently, PVC stabilization was based on heavy metal soaps in the European PVC building industry. Though their resulting efficiency was not questioned, problems of toxicity were raised. Regarding the ecological pressure increase, numerous investigations on co-stabilizers have been carried out in order to improve the performances of mixed Ca/Zn systems. Our results show the properties of rigid profiles stabilized with Ca/Zn systems. First, the extruded profiles properties such as optical (color) and mechanical properties (impact resistance…) are shown. The aging resistance of toxic heavy metal free vinyl formulations is also studied in comparison with typical Pb/Ba/Cd. The performances achieved indicate that an opportunity to move from toxic heavy metallic stabilizers to mixed Ca/Zn systems, resulting, perhaps, in wider development of Ca/Zn stabilizing systems for food packaging and medical plastics.

Novel micaceous reinforcing fillers with fire and smoke retarding qualities

Laboratory tests were intended to show differences in processing and weatherability which occur when various powdered and liquid barium/cadmium stabilizers are used alone and in combination with epoxy plasticizer and phosphite. The results show that in the selection of stabilizers it is not necessarily the metal content of the stabilizer which is important, but rather that optimum weathering stability is achieved by the correct combination of complex barium, cadmium and zinc components. Liquid barium/cadmium/zinc compounds of the IRGASTAB BC 445 type, combined with epoxy plasticizer and phosphite, give optimum stabilization of plasticized PVC, ease of processing and excellent weatherability.

Mechanistic aspects of organotin stabilization of PVC

Metallic flake pigments can be successfully incorporated in PVC compounds designed for high-quality service in automotive application provided suitable attention is paid to the formulation, color printing, mold design, and processing parameters.

Post-irradiation stability of polyvinyl chloride at sterilizing doses

Post-irradiation stability of plasticized PVC irradiated by 60Co gamma ray at sterilizing doses has been studied. Effects of irradiation upon chemical structure, mechanical properties and rheological behaviour of samples contained different amounts of Di(2-ethylhexyl)phthalate as plasticizer have been investigated. Formation of conjugated double bonds, carbonyl and hydroxyl groups have been followed by UV and FTIR spectrometers up to 6 months after irradiation. FTIR spectra of irradiated samples showed no significant changes in carbonyl and hydroxyl groups even 6 months after irradiation. However, changes in UV-visible spectra was observed for the irradiated samples up to 6 months post-irradiation. This has been attributed to the formation of polyenes which leads to the discoloration of this polymer. Despite a certain degree of discoloration, it appears that the mechanical properties of PVC are not affected by irradiation at sterilizing doses. No change in the melt viscosity of the irradiated PVC samples with post-irradiation was observed, which is in consistent with the IR results.

Stabilizers for flexible PVC

Recent trends in powder technology are reviewed in terms of five key words: advanced (fineness) powders; controlled quality; purity; multi-function; and composite structure. Especially the functions of fineness, including that of ultra-fine powder, are paid special attention to, both from the viewpoints of its associated positive and negative characteristics. Composite powder materials for making use of its positiveness by eliminating its negative are also discussed.

Organic zinc stabilizers for PVC

The objective of evidence-based medicine is to employ the best scientific information available to apply to clinical practice. Understanding and interpreting the scientific evidence involves understanding the available levels of evidence, where systematic reviews and meta-analyses of clinical trials are at the top of the levels-of-evidence pyramid.The review process should be well developed and planned to reduce biases and eliminate irrelevant and low-quality studies. The steps for implementing a systematic review include (i) correctly formulating the clinical question to answer (PICO), (ii) developing a protocol (inclusion and exclusion criteria), (iii) performing a detailed and broad literature search and (iv) screening the abstracts of the studies identified in the search and subsequently of the selected complete texts (PRISMA).Once the studies have been selected, we need to (v) extract the necessary data into a form designed in the protocol to summarise the included studies, (vi) assess the biases of each study, identifying the quality of the available evidence, and (vii) develop tables and text that synthesise the evidence.A systematic review involves a critical and reproducible summary of the results of the available publications on a particular topic or clinical question. To improve scientific writing, the methodology is shown in a structured manner to implement a systematic review.La medicina basada en la evidencia tiene como objetivo apoyarse en la mejor información científica disponible para aplicarla a la práctica clínica. Entender e interpretar la evidencia científica implica conocer los niveles de evidencia disponibles, donde las revisiones sistemáticas y/o metaanálisis de ensayos clínicos son la cúspide de la pirámide del nivel de evidencia.El proceso de revisión debe estar bien desarrollado y planificado de antemano para reducir sesgos y eliminar estudios irrelevantes o de baja calidad. Los pasos a seguir para la realización de una revisión sistemática incluyen: (i) formular correctamente la pregunta clínica a responder (PICO), (ii) desarrollo de un protocolo (criterios de inclusión y exclusión), (iii) realizar una búsqueda bibliográfica detallada y amplia, (iv) cribar los resúmenes de los trabajos identificados en la búsqueda y posteriormente de los textos completos seleccionados (PRISMA).Una vez seleccionados los estudios se debe: (v) extraer en un formulario diseñado en el protocolo los datos necesarios para resumir los estudios incluidos, (vi) evaluar los sesgos de cada estudio pudiendo identificar la calidad de la evidencia disponible y, por último, (vii) desarrollar las tablas y el texto que sinteticen la evidencia.Una revisión sistemática implica un resumen crítico y reproducible de los resultados de las publicaciones disponibles sobre un mismo tema o pregunta clínica concreta. Con el fin de mejorar la escritura científica, se expone de una forma estructurada la metodología para la realización de una revisión sistemática.

Degradation and stabilization of PVC in blends

AbstractPoly(vinylchloride) (PVC) was mixed with various poly(methacrylate)s, poly(carbonate)s and polymers containing nitrile groups (poly(acrylonitrile), poly(styrene‐co‐acrylonitrile), nitrile rubber, hydrogenated nitrile rubber) and/or C  C double bonds (nitrile rubber, high‐impact poly(styrene)). The thermal stability was measured at 180°C in nitrogen, and the evolved HCl was detected by conductometry.It is shown that the nature of the ester group and the content of nitrile groups and C ‐ C double bonds are the dominating factors for the thermal stability of poly(vinylchloride) in these blends. An influence of the miscibility of PVC with the various blend components on the thermal stability can not be clearly detected.Differential scanning calorimetry (DSC) was used as a powerful method to study the stabilizer distribution of heterogeneous PVC/poly(styrene‐co‐acrylonitrile) and PVC/poly(methylacrylate) blends. It is shown that the stabilizer can be solubilized either in the PVC phase (PVC/poly(methylacrylate)) or in both phases of the blends PVC/poly(styrene‐co‐acrylonitrile)).

Experimental investigation of vinyl chloride polymerization at high conversion: polymer microstructure and thermal stability and their relationship to polymerization conditions

Suspension poly(vinyl chloride) (PVC) samples with various monomer conversions were synthesized using batch and semi-batch polymerization processes at different temperatures. The concentration of tertiary chlorines in the PVC was determined using 13C nuclear magnetic resonance, and the concentration of internal double bonds was analysed by ozonolysis. The dehydrochlorination rate of the PVC was measured at 190°C by the conductimetric method under nitrogen environment. It was found that the concentration of tertiary chlorines increases significantly with increase in monomer conversion after the critical conversion at which the reactor pressure starts to fall. At the same conversion level, it increases with polymerization temperature. The concentration of allylic chlorines is much lower than that of tertiary chlorines. A conversion dependence of allylic chlorines was not found for the present PVC samples. However, the concentration of allylic chlorines increases with polymerization temperature. Excellent correlation between the dehydrochlorination rate and the concentration of tertiary chlorines was found based on the present experimental data, but no significant relationship was found between dehydrochlorination rate and concentration of allylic chlorines. Therefore, tertiary chlorines in PVC chains are probably the defect structure that is most responsible for the reduced thermal stability of PVC. The mechanisms of formation of internal defect structures and the effects of polymerization conditions on the concentration of the defect structures are discussed in some detail based on diffusion-controlled free-radical polymerization theory, and the monomer concentration effects are further confirmed by the results using a semi-batch polymerization process. The concentration of tertiary chlorines can be minimized by semi-batch operation at or near the saturation pressure, providing PVC of higher thermal stability.

Chemical Modification of Poly(Vinyl Chloride): Improved Thermal Stability by Partial Reduction with Organoboron Reagents

Abstract The thermal degradation of poly(vinyl chloride) (PVC) by a zipperlike dehydrochlorination is believed to initiate at abnormal structures present in the resin backbone. The allylic chlorines are major contributors to instability of the polymer. A selective replacement of the allylic chlorines with hydrogen on the PVC chain is accomplished by the use of organoboron reagents. Treatment of PVC with lithium triethylborohydride resulted in the reduction of chloroethyl chain ends, as well as the allylic chlorines. A considerable improvement in the static and dynamic thermal stabilities of PVC, treated with organoboron reagents, is observed. It is also demonstrated that the removal of chain end chlorines further enhances the stabilization effect. The reaction of certain model compounds, representing the defect structures present in PVC, with organoboron reagents was studied. The evidence for an addition—elimination mechanism in the reactions with substrates, containing allylic chlorines, is presented.

Preparation and application of low molecular weight poly(vinyl chloride). II. Thermal stability of blended poly(vinyl chloride)

AbstractThe blending effect of poly(vinyl chloride) (PVC) with relatively higher molecular weight (HMW‐PVC) and relatively lower molecular weight (LMW‐PVC) has been investigated by measuring various thermal stability and fusion times. The thermal stability of the blended PVC is improved when the small amount of LMW‐PVC obtained using mercapto compounds as a chain‐transfer agent is blended into PVC with HMW‐PVC. At the LMW‐PVC content from about 5–30 wt %, the thermal stability of the blended PVC is much more improved. Furthermore, the blended PVC with LMW‐PVC, obtained using mercapto compounds, exhibits significant improvement in the discoloration time. The fusion time of the blended PVC is related to the weight‐average polymerization degree of LMW‐PVC and the LMW‐PVC content. © 1994 John Wiley & Sons, Inc.

Thermal dehydrochlorination and stabilization of polyvinylchloride in solution: Part IX. Dialkyltin maleates: Diels-Alder reaction

Spectroscopic studies show that maleic anhydride undergoes a Diels-Alder reaction with conjugated double bonds such as β-carotene and partially dehydrochlorinated PVC. This reaction is also observed in the stabilization of PVC with dialkyltin maleate stabilizers. It follows that the efficiency of the stabilization is related to the saturation of the double bonds in the polymer backbone, in addition to the well established substitution reaction.

Thermal dehydrochlorination and stabilization of polyvinyl chloride in solution. Part X: Dialkyltin thioglycolates

The basic mechanisms already estabilished from model compound studies to explain the high efficiency of organotin thioester stabilizers for PVC have been confirmed by the study of PVC stabilized in solution at 194°C: the main reaction is substitution of thioglycolate groups either directly or through the thioesters resulting from the reaction of stabilizers with HCl, which are added to the double bonds of the degraded PVC. A new observation is that this addition reaction does not take place in the absence of HCl; it is suggested that HCl is first added, followed by a substitution reaction. These mechanisms are valid whether the stabilization, is carried out in air or argon.

Thermal dehydrochlorination and stabilization of poly(vinylchloride) in solution. Part XII. Tin-calcium-zinc interactions

The synergistic effect between calcium glycolate and organotin chloride which has been observed in the crosslinking process of poly(vinylchloride) (PVC) is not at all effective for the thermal stabilization of PVC. The addition of zinc compounds to an organotin recipe shows a moderate positive effect only for the initial coloration.

Effect of the dissociation of barium and cadmium stearates on the heat stabilization of PVC

Barium stearate (BaSt 2), due to its greater dissociating ability, is a less effective heat stabilizer than Cd stearate (CdSt 2) and exhibits considerably shorter induction times than CdSt 2. Curves obtained by plotting induction time against the content of one of the components in the mixtures were asymmetrical, with a maximum in the CdSt 2 range 60–65%, instead of 50%, which would be expected with stearates which have the same dissociating strengths. Kinetic calculations based on the different dissociating abilities of these stearates resulted in induction time curves having the same shapes as those measured.

Polaron mechanism in the thermal stabilization of poly(vinyl chloride). Part I: Metal soaps and secondary stabilizers

In the thermal stabilization of PVC, it has been shown that, by controlling the cis configuration of conjugated double bonds initially present or developing in the polymer during the stabilization, the alkyl chains attached to stabilizers favor the substitution of the allylic chlorine atoms by an esterification reaction proposed by Frye et al. By interacting with the conjugated double bonds to form polarons which inhibit the esterification reaction, the metal chloride leads to the chain dehydrochlorination of the polymer by a process reported previously. As far as the synergism due to costabilization of the secondary stabilizers and the metal soaps is concerned, we show that the efficiency of a secondary stabilizer arises essentially from the blocking of the polaron DHC to favor allylic chlorine substitution.

A comparative study of thermal and mechanical stabilities of gamma irradiated PMMA, PP and PVC

In this comparative study it has been tried to find a correlation between the thermal and mechanical stabilities of some γ-irradiated polymers. Among various mechanical properties evaluated, the best correlation was found between the toughness (energy to break point) and the time required for 10% weight loss (isothermally). Among three polymers irradiated up to 100 kGy in the form of thin films, the best fit was observed to be for PMMA while PVC and PP has shown poorer correlation.

Studies in the thermal degradation of poly(vinyl chloride)

AbstractThermal degradation of poly(vinyl chloride) (PVC) was studied in nitrogen atmosphere in the presence of rubber seed oil and epoxidized rubber seed oil, barium and lead soaps of rubber seed oil, and epoxidized seed oil at various temperatures. The rate of dehydrochlorination at 1% degradation and the time required to attain 1% degradation were used to assess the effect of the thermal susceptibility of PVC to dehydrochlorination. It was found that epoxidized rubber seed oil, the metal soaps of rubber seed oil, and epoxidized rubber seed oil markedly enhance the thermal stability of PVC. The order of increasing stabilizing influence was metal soaps of epoxidized rubber seed oil > metal soaps of rubber seed oil > epoxidized rubber seed oil > rubber seed oil. © 1993 John Wiley & Sons, Inc.