A possible mechanism to explain the synergistic effects exhibited by mixtures of alkyltin mercaptoesters as stabilisers for PVC

The phenomenon of synergism observed with mixtures of mono- and dialkyltin stabilisers for PVC has been recognised and exploited for many years, but remains largely unexplained. Whilst a similar effect in mixed metal (Ba/Cd or Ca/Zn) carboxylate stabilisers has been explained, mechanistic studies of the organotin systems have not appeared. Infra-red spectroscopy has now been used to study the Cl/mercaptoester exchange equilibria of alkyltin mercaptoester (isooctylthioglycollate) chlorine compounds which are undoubtedly produced when the organotin mercaptoesters act as PVC stabilisers. The exchange process is shown to be facile, even at ambient temperatures, and a regenerative mechanism, based on these observations, is proposed to explain the synergistic effect.     

Effect of calcium and zinc carboxylates on the thermal stabilisation of PVC

Metal carboxylate stabilisers are believed to replace labile chlorines in PVC with more stable ester linkages resulting in an increase in the stability of the polymer. In the present work, effects of combinations of stearates, palmitates and laurates respectively of zinc and calcium, in various proportions, on the thermal stability of PVC were studied. Combinations of palmitates and stearates having more than 75 mol% of calcium salt were found to increase the stability of the polymer. The combinations of the three carboxylates showed the following order of stabilising: palmitate > stearate > laurate. This effect is explained in terms of a critical chain length of the n-alkyl group of the carboxylate anion which is most effective in the stabilising process. Highly crystalline, low molecular weight polyethylenes are used as plasticisers for PVC. They were found to have a stabilising effect explained in terms of a dilution effect by the non-polar polyethylenes on the polar interactions in PVC; compatibility of polyethylenes with PVC is the limiting factor in this stabilisation.     

A 119mSn Mössbauer study of the degradation of organotin stabilised PVC by gamma-irradiation

The technique of ^119mSn Mössbauer spectroscopy has been used to study the changes which occur in three organotin stabilisers within a PVC matrix when exposed to doses of γ-irradiation up to 20 Mrad. The stabilisers studied were dioctyltinbis(iso-octylthioglycollate) [Oct₂Sn(IOTG)₂], dibutyltinbis(iso-octylthioglycollate) [Bu₂Sn(IOTG)₂] and dibutyltinbis(iso-octylmaleate) [Bu₂Sn(IOM)₂] incorporated into the PVC at the appropriate commercial level by conventional hot milling techniques or solvent casting. Extended doses up to 20 Mrad showed that the final degradation product for all three stabilisers is SnCl₄ and that the rate of degradation depends not only upon the type of stabiliser but also upon the extent of thermo-mechanical damage suffered by the PVC during processing. Mössbauer spectra were recorded at intermediate doses in the range 0·1 to 10 Mrad and yielded complex spectra containing unresolved lines corresponding to mixtures of original stabilisers and degradation products. Intermediate degradation products are proposed and rapid conversion to SnCl₄ is observed to start at doses greater than 3 Mrad.     

A 119mSn Mossbauer study of the thermal degradation of PVC stabilised by various organotin(IV) and tin(II) compounds

^119mSn Mossbauer spectroscopy has been used to study the chemical changes undergone by a range of tin-containing stabilisers (dialkyltin dilaurates, dialkyltin bis(ethylcysteinates), stannous stearate and stannous cysteinate) during thermal degradation of PVC at 185°C. The dialkyltin-laurate and -cysteinate stabilisers are converted to the dialkyltin dichlorides. Stannous stearate and stannous cysteinate are rapidly converted into stannic oxide and stannic chloride, respectively.     

Development of poly(vinyl chloride)/montmorillonite nanocomposites using chelating agents

Different chelating agents such as poly(ethylene glycol), propylene glycol monooctadecanoate and palm oil were used for modification of the surface-treated montmorillonite (MMT). The work also included the development of a technique for mixing chelating agents with MMTs using different methods and different proportions of MMT/chelating agent/ethanol. Evaluation of the result of mixing was performed by thermogravimetric analysis, X-ray diffraction and high-resolution scanning electron microscopy (HR-SEM). The results showed that the chelating agents used were intercalated in MMT, increasing the interlayer spacing. The OMMT was used in the manufacture of composites with rigid PVC using a microcompounder. The master batch concept turned out to be promising in terms of dispersion and delamination of clay, as observed in HR-SEM photographs. However, despite good dispersion and exfoliation of MMT, poor compatibility between clay platelets and PVC matrix remains to be solved to enable full exploitation of its engineering potential. Despite this drawback, good thermal stability and mechanical properties have already been achieved.     

Polymers and paper as packaging materials of irradiated foodAn NMR study

Effects of γ-irradiation on synthetic polymers and paper used as packaging materials for irradiated food have been studied by NMR. Polystyrene, polybutadiene and some copolymers were studied before and after the γ-irradiation treatment and in the presence or absence of antioxidants and stabilisers. In the absence of additives, the effect of γ-irradiation on polystyrene is negligible even irradiating at high doses. In turn, the role of antioxidants and stabilisers is crucial in polybutadiene and butadiene-containing copolymers. Wood pulp paper was also studied by NMR. Preliminary measurements on γ-irradiated wood pulp sheets show a shortening in the T₂ relaxation time component due to the bound water, i.e. some of the bound water is lost.     

Heat Degradation of PVC Stabilized by Treatment with Alkylaluminum Compounds

Thermal degradation of PVC treated with alkylaluminum compounds has been studied. Four PVC samples of different molecular weights have been treated with Me₃Al, and Et₃A₁, and the dehydrochlorination rates of the polymers were determined at 190 and 220°C under a nitrogen atmosphere. The alkylaluminum-treated low molecular weight samples show marked increase in thermal stability, i. e., slower rate of dehydrochlorination right from the beginning of degradation, whereas with the higher molecular weight samples stabilization becomes pronounced only after a few percent of dehydrochlorination. The color of R₃Al-treated samples was much lighter (yellowish) than those of controls (dark brown) at 1% HCl loss. The average polyene sequence lengths formed during the early stages of dehydrochlorination are found to be much shorter with RsAl-treated PVC than with virgin samples. It appears as though polyene sequences which arose by zipping- initiation from allylic and/or tertiary chlorine sites are longer than those which form by random initiation along the chain. The autocatalytic (i. e., HC1-catalyzed) dehydrochlorination observed with virgin PVC disappears after treatment with R3A1. The HCl-catalyzed dehydrochlorination is minimized when thin films are used instead of powdery samples, which may be due to higher rates of HC1 diffusion through thin films. Autocatalysis of dehydrochlorination is affected by the concentrations of double bonds and HCl and the length of polyene sequences. Interaction between polyenes and HC1 by hydrogen transfer may lead to the re-initiation of unzipping, thus lengthening the polyene sequences.     

The main elementary events of degradation and stabilization of PVC

The fundamental aspects of PVC degradation and stabilization are discussed. The primary process of thermal degradation (initiation, zip-elimination of HCl and simultaneous formation of polyene sequences, and termination of unzipping) is reevaluated in the light of results obtained with PVCs containing increased concentrations of labile chlorines. The effect of these defects on thermooxidative stability of the resin is also discussed. It has been shown that results obtained in recent systematic stabilization studies cannot be explained by the widely accepted Frye-Horst mechanism, i.e., substitution of labile chlorines by stabilizers. A new mechanistic proposition, the reversible blocking mechanism, for the stabilization of PVC is presented, and the effect of stabilizing reactions on the main elementary events of thermal and thermooxidative degradation is described in a unified manner.     

FTIR investigation of the specific migration of additives from rigid poly(vinyl chloride)

Commercial sunflower oil was epoxidized and used as organic costabiliser for rigid poly (vinyl chloride) (PVC) containing zinc and calcium stearates as primary stabilisers and stearic acid as lubricant. For applications in the packaging of foodstuffs, migration testing must be realised. For that purpose, two food simulants were used (sunflower oil and 15% (v/v) aqueous ethanol). The test conditions were 12 days at 40 °C. Circular samples of rigid PVC were immersed in a well known volume of food simulant. A circular sample and 10 ml of food simulant were taken off every day to be analysed. The specific migrations of the additives were investigated by using Fourier transform infrared spectroscopy.The direct analysis of the food simulants was difficult because overlapping of the bands of the additives. However, the analysis of PVC films obtained by dissolution of the circular samples in tetrahydrofuran and evaporation of the solvent was more conclusive. The specific migrations of the metal carboxylates and epoxidized sunflower oil were evidenced.     

N-picolinamido-N′-benzoylthiocarbamide transition metal complexes

A new series of CoII, NiII and CuII complexes derived from N-picolinamido-N-benzoylthiocarbamide has been prepared in which the Schiff base ligand is tridentate and/or bidentate, containing a potential ONS donor. The complexes have been characterized by elemental analyses, 1H-n.m.r., magnetic susceptibility, i.r., u.v., e.p.r. and thermal analyses. Stereochemistries are proposed for the complexes on the basis of the spectral and magnetic studies. The i.r. data indicate that the carbonyl oxygen of the benzoyl moiety constituents chelating backbone in most complexes.     

A 119mSn Mössbauer study of the photochemical degradation of organotin stabilised PVC

Although organotin compounds are widely used as thermal and photochemical stabilisers for PVC, their mode of action and their fate on degradation of the polymer are not yet fully understood. ^119mSn Mössbauer spectroscopy has been used to study chemical changes undergone by two commonly used stabilisers, dibutyltinbis(iso-octylthioglycollate) and dibutyltinbis(iso-octylmaleate), during irradiation of stabilised PVC in artificial sunlight. After 1000 hours' exposure, the maleate stabiliser is chemically unchanged, whereas the thioglycollate is rapidly converted to the monochloroester, Bu₂SnCl(SCH₂CO₂C₈H₁₇). Prolonged exposure of the thioglycollate stabilised polymer leads to the formation of stannic oxychloride.     

The effects of structural defects on the stability of poly(vinyl chloride): A critical review

Some of the theories which have been proposed to explain the thermal and photo-instability of poly(vinyl chloride) are reviewed. It is concluded that the defects introduced into PVC during manufacture cannot explain the very rapid HCl loss that occurs during processing. Hydrogen chloride and hydroperoxides are formed very rapidly during processing due to mechano-oxidation and it is concluded that a rapid redox reaction between these species produces radicals which lead to the HCl unzipping reaction. Photo-oxidation is initiated primarily by hydroperoxides produced during processing. The role of PVC stabilisers is reviewed in the light of these mechanisms.     

Structure and Dehydrochlorination of Poly(vinyl Chloride)

The wide applicability of poly(vinyl chloride) (PVC), a tough thermoplastic resin, is due to a combination of moderate cost with the following characteristics [1]: (i) good general properties as a plastic material: (ii) great variation in properties, e.g., increase in heat distortion temperature, resistance to hot melt flow, improvement in mechanical, electrical properties, and processability of unplasticized PVC through external plasticization, block and graft copolymerization (internal plasticization), and chemical modification, e.g., chlorination, Friedel-Crafts, and cross-linking reactions: and (iii) processing versatility including injection molding, extrusion, blow molding, calendering, and lamination to produce many products of potential uses.     

Thermal conductivity of poly(vinyl chloride)/polycaprolactone blends

Thermal diffusivity, heat capacity, and density of polyvinyl chloride/polycaprolactone (PVC/PCL) blends were measured by the laser flash method, DSC, and pycnometry, respectively. The thermal conductivity of the PVC/PCL blends was determined from the results. The miscibility of the blend and crystallinity of PCL were determined by DSC. The effect of blend structure on thermal conductivity is discussed. The phase compositions of the PVC/PCL blends are of three types depending on PCL content: i.e., up to 33%, from 33 to 70%, and above 70% PCL by weight. Thermal conductivity, thermal diffusivity, and heat capacity of the PVC/PCL blends are strongly affected by the phase composition of the blend, which changes in a complicated way with PCL content. © 1994 John Wiley & Sons, Inc.     

Removal of metal ions from aqueous solution by chelating polymeric microspheres bearing phytic acid derivatives

The aim of this study was to investigate the possibility to synthesize new chelating polymeric microspheres owing immobilized biocompatible agent as chelating functional groups and to evaluate their performance in metal ions removal from aqueous solution.The microparticles were synthesized via precipitation polymerization of 4-O-(4-vinylbenzyl)-myo-inositol 1,3,5-orthoformate with ethylene glycol dimethacrylate (EGDMA) and subsequent exhaustive phosphorylation of myo-inositol groups using phosphoric acid.Spherical geometry with monodisperse nature of the polymeric microparticles was confirmed by scanning electron micrographs (SEM) and dimensional analysis. A large surface area of the microspheres provided a maximum interaction of metal ions and the chelating functional groups on the surface. Absorption capacity of the beads for the selected metal ions, i.e., Cu(II), Ni(II), Fe(III), was investigated in detail in aqueous solution at pH 5.0 utilizing UV/Vis spectroscopy. This study showed that the macromolecular systems are very effective in chelating these metal ions and the affinity order of the microbeads toward metal ions is: Fe(III) > Ni(II) > Cu(II).The chelating beads can be easily regenerated by 1.0 M HNO₃ with high effectiveness. These features make the synthesized beads a potential candidate for metal ions removal at high capacity.     

Specific features of the structure of germanium(IV) complexes with polybasic acids

The specific features revealed in the structure of germanium(IV) compounds with ligands in the form of anions of polybasic acids (monoamine, diamine, and triamine complexones, i.e., hydroxyethylidene-diphosphonic and carboxylic acids) have been considered. The influence of the individuality of specific acids on the structure type (mononuclear, binuclear, trinuclear, hexanuclear, polynuclear), the coordination mode of monodentate ligands and donor atoms of polydentate ligands (terminal, bridging, chelating, chelating-bridging), and variants of the coordination of polydentate ligands, i.e., anions of polybasic acids, with metal atoms (germanium, rare-earth elements, copper, barium), as well as on the dependence of the Ge-O bond length on the individual nature of ligands (OH, H₂O, O(oxo)) and donor atoms of polydentate ligands α- and β-O(carb), O(hydr), O(P)] and their function in the structure (terminal, bridging, chelating, chelating-bridging), has been analyzed using 28 homometallic and heterometallic complexes as an example.     

Effect of solvent type on formation of PVC‐solvent complex

The effect of solvent type on the structural features of PVC gels prepared from the solutions of dibutyl phthalate(DBP) and butyl benzoate(BB) were investigated. The influence of solvent type, i.e., diester solvent or monoester solvent, on the mechanical responses was characterized by dynamic viscoelastic measurements as a function of temperature, aging time, and PVC concentration. In the case of PVC/DBP aged gels, the transition phenomenon appeared close to 50°C, whereas no such transitions were observed for PVC/BB aged gels. This transition is considered to be associated with polymer‐solvent complex which can be accounted for electrostatic interaction between C=O bond of solvent and H‐C‐Cl part of PVC. While BB solvent molecules can not form polymer‐solvent complex due to no capacity to act as a bridge between PVC molecular chains. FT‐IR spectroscopy and DSC investigation on either PVC/DBP gels or PVC/BB gels was reported and discussed together with the mechanical behavior. Electron micrographs of the dried gel prepared from the critical point drying technique reveal that the gel morphology consists of well developed three dimensional fibrous network structure independent of solvent type.     

Chloride formation and polymer coloration during thermal degradation of PVC stabilised with a Zn-Ca recipe

The part played by metallic chlorides, and especially zinc chloride generated during the stabilisation process of PVC with the zinc-calcium recipe, is analysed through a brief review of the mechanism established previously, a few additional data being presented. Correlations between polymer discoloration and chloride formation, estimated through a coulometric method based upon Ag⁺ ion precipitation in the presence of chloride ions, are analysed for different short-term and long-term secondary stabilisers. They allow the exact part played by each component to be explained.     

Determination of adipate plasticizers in poly(vinyl chloride) by microwave-assisted extraction

A new method based on the application of microwave radiation to the extraction of adipate plasticizers from poly(vinyl chloride) PVC plastics is described. The experimental conditions for microwave-assisted extraction (i.e. extracting solvent, temperature, time and microwave power) were evaluated in terms of recovery. The optimisation was carried out with pastes of PVC plastified with di-2-ethylhexyl adipate, and extracts were measured by gas chromatography with flame ionization detection. Six different adipate plasticizers were studied, and microwave-assisted extraction was compared with supercritical fluid extraction for the extraction of adipates and phthalates from PVC matrices. It has been observed that the microwave-assisted extraction parameters evaluated are tightly interconnected. It has been shown that the efficiency of microwave-assisted extraction depends on the kind of solvent, the temperature achieved and the heating time. Moreover, the final temperature reached depends on the microwave power, the number of vessels and the irradiation time. On the other hand, microwave-assisted extraction provides higher recovery values than supercritical fluid extraction for both phthalate and adipate plasticizers.     

Temperature and time dependence of diffusion of PCL into PVC

The phenomenon of diffusion between two joined polymers [poly(vinyl chloride) and poly(ε-caprolactone)] has been investigated by light microscopy and electron microscopy of thin sections taken perpendicular to the interface. It has been established that the diffusion is unidirectional, i.e., PCL into PVC, and that the solubility is limited and increases with temperature. Chlorine x-ray analysis has shown that the concentration profile consists of a sharp change at the PCL boundary and a gradual change at the diffusion front. The diffusion region morphology has been found to be inhomogeneous and reveals density fluctuations within the PVC matrix. The diffusion behavior is therefore different from the classical Fickian diffusion previously noted and can be well described by a sorption mechanism.