Structure Of PVC Research Articles

Use of molecular modeling to predict ligand efficiency in thermal stabilizers

AbstractMolecular modeling software is employed to correlate the thermal stability of an organotin molecule in PVC and molecular structure. Synthesizing model organotin compounds, measuring dynamic properties in PVC, and calculating structural and electronic properties yield an empirical relationship between the stabilizing ability of the tin molecule and electron density of the heteroatom.

Influence of the physical characteristics of the polymer on the glass transition of various chemically modified PVCs

AbstractVinylchloride–vinylthiocresol and vinylchloride–vinylthionaphthol copolymers of various compositions were prepared by the substitution reaction of PVC with sodium thiocresol and sodium thionaphthol, respectively, in different solvents and at different temperatures. The variation of the glass transition temperature of these copolymers with chemical com‐position does not follow the Flory–Fox equation, but is found to depend on the solvent and the temperature at which the copolymer is obtained. The comonomer sequence distribution and stereosequence content of the above copolymers, and those of vinylchloride–vinyl‐thiobenzene copolymer, were determined by 1H‐ and 13C‐NMR spectroscopy. The depen‐dence of comonomer distribution and stereoregularity content with chemical composition for the three series of copolymers, prepared in different solvents and temperatures, are similar. The Tg deviations for the three series of copolymers were attributed to the con‐tribution of physical characteristics of the PVC structure, originating from polymer–solvent interactions. © 1995 John Wiley & Sons, Inc.

The effect of mechanochemical degradation on processability and porperties of PVC

The morphology and mechanical properties of PVC after vibro- or jet-milling as well as the rheological behavior of the mechanochemically degraded PVC were studied. The effect of vibro or jet-milling on the crystalline structure of PVC was examined through the crystalline absorption bands of FTIR spectra. The intensity of the crystalline absorption bands becomes weaker and indistinct with milling time. The PVC after milling results in improved melting efficiency, lower melt viscosity, shorter plasticizing time and higher tensile strength in comparing with those of the undegraded PVC due to the destruction of the crystalline structure and the decrease of molecular weight.

A Study on Morphological Structure of Low Molecular Weight PVC Prepared by Vibromilling Degradation

Abstract The effects of vibromilling on particle size, crystalline structure, optical density, and the plasticizer absorption of poly(vinyl chloride) (PVC) were studied through Fourier-transform infrared spectroscopy, scanning electron microscopy and physical property tests. The experimental results show that the intensity of the FTIR absorption band at 635 cm−1 of PVC becomes weaker and tends to disappear during vibromilling. The particle size of PVC is decreased, and the surface area and the amount of plasticizer absorption increase with increased vibromilling time. The low molecular weight PVC so prepared has lower crystallinity and glass transition temperature, and higher plasticizer absorption capacity; it should have good processability.

Homogenization in mechanical mixing involving polyvinyl chloride. II. Effect of different types of polymers on breakdown of PVC particulate structure and mixing mechanism

Abstract The process of mixing PVC with other polymers, including an examination of how these polymers contribute to the breakdown of the particulate structure of PVC, is described. The polymers were an immiscible nitrile rubber containing 22% acrylonitrile (NBR-22) and two miscible polymers, poly-e-caprolactone (PCL) and copolyester thermoplastic elastomer (trademark Hytrel). The mixing of PVC and NBR-30, as investigated in the previous paper (Part I), was also considered as a reference. The overall progress of mixing for the three systems (i.e., PVC/NBR-22, PVC/PCL, and PVC/Hytrel) was similar to that for PVC/NBR-30; the removal of skins was followed by breakdown of PVC particles. However, the rate of breakdown differed widely from system to system, depending on the inherent thermodynamic and viscoelastic nature of the individual polymers which served as the medium for stress transfer to the PVC particles. Molecular mixing, which provides a strong interfacial adhesion between PVC and the component polym...

Influence of conformational microstructure in the molecular motions of poly(vinyl chloride)

Conformational changes induced by physical modification (stretching) of poly(vinyl chloride) (PVC) have been investigated by means of wide angle X-ray diffraction (WAXS). The properties of the modified samples have also been studied by means of dielectric relaxation in the frequency domain in the α-relaxation region which is associated with the glass transition. Although the temperature of the loss peak is not drastically changed and the parameters describing the molecular mobility of the material are not appreciably altered within the experimental errors, the relaxation function in the frequency domain obtained in the modified samples is narrowed with respect to that obtained for the unmodified PVC. By an interpretation of the relaxation results in the frame of Ngai's coupling model, it is concluded that the modification of PVC by stretching leads to a decrease of the molecular interactions in the material. These results, as well as those obtained by WAXS, lead one to think that these changes are closely related to the fact that intrachain conformational structure of PVC has been changed during the stretching process.

Influence of processing on PVC structure property relationships

AbstractThe influence of the rheology of extruded PVC on the developed morphology and properties was explored. Extrusion conditions for PVC siding formulations with CPE impact modifiers have been investigated on a lab scale twin screw extruder using a factorial model in the experimental design. The independent variables were the barrel temperatures, the die temperature, the hopper feed rate, and the screw rpms. The dependent variables examined include the torque, melt temperature, output rate, fusion level, morphology, and impact resistance. The correlations of the dependent variables with the independent variables were evaluated with the statistical analysis package SASTM. The correlations among several of the dependent variables were also evaluated.

The effects of polyvinyl chloride hierarchical structure on processing and properties

AbstractThe hierarchical structures in PVC are such that the larger structures formed during polymerization are broken down to smaller structures during processing. These smaller structures have properties dependent on their microstructure. While PVC's microstructure is mostly amorphous, it contains crystallites that act as physical crosslinks connected together by tie molecules. The microstructure is extended to a larger three dimensional structure by melting during processing followed by recrystallization upon cooling. The strength of this larger three dimensional structure is interpreted from the roughness of extrudate from a zero land length die. This visual method is more sensitive for detecting large three dimensional network structure than measuring capillary entrance pressures, especially for very weak three dimensional structures. Both higher processing temperatures and higher molecular weight PVCs contribute strength to this three dimensional structure which plays a large role in determining lzod impact and stress rupture. Plasticized PVC has a structure similar to rigid PVC as judged by the roughness characteristics of its extrudate. In this case, the plasticizer is soluble in the amorphous phase leaving the crystallites intact.

Effect of metal stearate stabilizers on the thermal degradation of PVC in solution: The reversible blocking mechanism of stabilization

AbstractSystematic thermal degradation studies of PVC solutions have been carried out in the presence of different metal carboxylates (Pb‐, Cd‐, Ba‐, Ca‐ and Zn‐ stearates). ZnSt2 markedly accelerates degradation of the polymer. Significant induction periods (ti) for the appearance of free HCI are obtained in the presence of the other salts. CaSt2 acts mainly as an HCI‐scavenger and has no direct influence on the elimination process. Mainly short polyenes are formed during the induction period when PbSt2, CdSt2, and BaSt2 are used. After consumption of stabilizers rapid HCI loss occurs, and suddenly longer polyenes are formed, i.e., the amount of double bonds and the average length of polyenes sharply increases. At the same time, the rate of initiation (i.e., the rate of the polyene sequence formation) does not change at all around ti. None of the investigated stabilizers retard effectively the random initiation of HCI loss. In the presence of PbSt2, BaSt2, and CaSt2, and CaSt2, the initiation rate is nearly identical to that of the unstabilized PVC. The concentration of labile sites (h0) in PVC at the end of the induction period has been estimated by kinetic analysis. It has been found that in some cases h0 is higher than the concentration of labile structures in the virgin PVC. These results indicate that the main role of metal soap stabilizers is the blocking of the fast zip‐elimination of HCI from the PVC chain. It is likely that blocking occurs by attachment of a carboxylate group at the end of a propagating zip. This is a reversible process: the blocked structures become active again mainly after the consumption of stabilizers presumably by HCI‐catalyzed hydrolysis. In contrast to other stabilization mechanisms by Frye and Horst, Minsker and coworkers, and Michell the reversible blocking mechanism of PVC stabilization is able to explain the experimental findings presented in this study. It also explains such facts of practical importance as color stability of the resin during the induction period and fast blackening after the consumption of stabilizers.

Structure defects and thermal stability of poly(vinyl chloride)

AbstractThe presence of polyene and peroxide structures in PVC and their contribution to the rate of thermal decomposition were determined using a large number of commercial suspension PVC samples. Two types of PVC having conjugated ‐C=C‐bonds with different reactivity towards dienophiles were found. Polymer samples of the first type react with chlorine, organic phosphites and maleic anhydride under mild conditions whereas the second type PVC under the same conditions reacts only with chlorine. The obtained data show that polyene structures in these two types of PVC are of cis and trans configuration, respectively. It was also demonstrated that the contribution of diene and peroxy groups to the rate of PVC thermal decomposition is greater than the contribution of any other anomalous structures.

Phase and relaxational states of polyvinyl chloride

Dynamic calorimetry has yielded the thermograms of commercial PVC S-70 as a function of the prehistory of the samples. From the heat characteristics the authors isolate three stable states of PVC marked by constant parameters of melting and vitrification. Comparison of the PVC structure from the results of DSC and IR spectroscopy shows that the structural states of PVC isolated constitute three stable isomeric forms corresponding to the different conformational organization of PVC with complete identity of the configurational structure.

Study of the physical structure of PVC by infrared techniques: A short review

AbstractInfrared spectroscopy is an important analytical technique for investigating polymeric materials. The physical properties of poly(vinyl chloride) (PVC) depend on its chemical and physical structure. Fourier transform infrared spectroscopy (FTIR) and other infrared techniques are commonly used for studying crystallinity, configurational and conformational changes, and chain orientation in plasticized and non‐plasticized PVC. The C‐Cl stretching region is particularly sensitive to the macromolecular structure and important changes may be detected depending on fundamental parameters.

The ‘crystallinity’ of PVC

Examination of the solid state structure of PVC plasticized with deutero-di-n-octylphthalate using small-angle neutron scattering (SANS) combined with studies using SAXS (synchrotron X-ray source) and thermal mechanical analysis (TMA) gives new information about the ‘crystallinity’ of PVC. This is compared with the behaviour of a poly(ethylene terephthalate) copolymer with a similar level crystallinity. The latter serves as a model system which describes the thermal and mechanical behaviour of polymers with crystallinities in the region of 15%. A second model system is the polymer formed by addition of chlorine to poly(1,4-butadiene). This is head-to-head PVC and completely amorphous.

A SANS study of the structure of plasticized PVC

The structure and crystallinity of plasticized poly(vinyl chloride) (PVC) has been examined using small-angle neutron scattering (SANS) and a deuterated plasticizer. The scattering curve, which shows a prominent peak at a Bragg spacing of ∼ 11 nm, has been interpreted using a two-phase model where the phases are assumed to be plasticized amorphous material and unplasticized, probably crystalline, material. The volume fraction of the PVC that was unplasticized was obtained from the SANS invariant. The value found, 0.29, was relatively insensitive to the assumed amorphous density and consistent with the dependance of the scattering peak height on the fraction of the plasticizer that was deuterated.

Investigations of the formation, detection and reactivity of ketochlorallyl structures in PVC

Present knowledge of the influence of ketochlorallyl groups in PVC on the thermal stability of the polymer is discussed critically and compared with our results which are mainly based on non-isothermal investigations of dehydrochlorination in an inert atmosphere. It is shown that oxygen-containing defect structures could be formed during oxidative pretreatment of PVC. But it must also be concluded that the low thermal stability of PVC in general, as well as differences between different PVC samples, cannot be explained by ketochlorallyl groups, since such defect structures are usually not present in commercial PVC samples.

Contribution to the study of labile structures in PVC

A kinetic treatment that takes into account the occurrence of two degradation processes through labile and stable chlorine atoms has been developed. By means of simulation of dehydrochlorination curves, the degradation rate and the kinetic parameters may be calculated provided that the content of labile structures is known and that both processes obey the Arrhenius equation. Assuming that, as deduced in previous work, the labile structures are a definite type of isotactic triad, the content of which may be easily determined, the individual degradation rates at various temperatures were calculated for a PVC prepared at 90°C (sample A). The sum of the calculated rates for the stable and the labile processes agrees quite well with the experimental overall degradation rates. On the other hand, the degradation rates for another PVC of lower content of labile isotactic triads (sample B), were calculated from those of polymer A taking into account the differences in content of labile isotactic triads. The values obtained in this way were found to agree with the experimental overall rates obtained for sample B at the same temperatures of degradation. The results provide quantitative support of earlier conclusions about the salient role of certain isotactic triad conformations in the degradation of PVC.

The influence of the morphological structure of the matrix on the regularities of impact fracture of polyvinyl chloride materials

The influence of the morphological structure of PVC and of its compositions with elastomers on the work of fracturing has been studied over a wide range of loading rates with stretching. The relation of the specific surface of the initial polymer powder to the nature of rate dependence of the work of fracturing has been demonstrated. Some possibilities of enhancing the impact strength of PVC materials by increasing the degree of heterogeneity of their structure have been established.

Chemical methods for the characterization of anomalous structures in PVC

Journal of Vinyl TechnologyVolume 7, Issue 2 p. 53-59 Article Chemical methods for the characterization of anomalous structures in PVC T. Hjertberg, T. Hjertberg The Polymer Group, Chalmers University of Technology, Göteborg, SwedenSearch for more papers by this authorE. Sörvik, E. Sörvik The Polymer Group, Chalmers University of Technology, Göteborg, SwedenSearch for more papers by this author T. Hjertberg, T. Hjertberg The Polymer Group, Chalmers University of Technology, Göteborg, SwedenSearch for more papers by this authorE. Sörvik, E. Sörvik The Polymer Group, Chalmers University of Technology, Göteborg, SwedenSearch for more papers by this author First published: June 1985 https://doi.org/10.1002/vnl.730070204Citations: 7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume7, Issue2June 1985Pages 53-59 RelatedInformation

Particle structure of PVC based on cellulosic suspension system. III. Effect of monomer refluxing

AbstractThe effects of monomer refluxing on both resin properties and reactor fouling of suspension PVC have been studied in a laboratory‐scale 14‐L reactor. Process control equations were developed which related the particle properties to the reflux condenser operation by controlling the parameters of (1) the time at which refluxing is begun and (2) the rate profile of heat removal from the condenser. An operating envelope has been developed for laboratory scale operations which optimizes the cycle time of polymerization while minimizing the adverse effects on particle properties. These operating conditions may have application to production scale operations when the proper scaling factors are employed.

Quantitative determination of non-defect unstable structures in PVC through selective nucleophilic substitution with C6H5SNa

The nucleophilic substitution with C6H5SNa, at -30°C, is compared for five PVC samples with various contents of isotactic triads. The conversion curves consist of a very fast stage followed by a steady one. All the samples are found to behave in the same way except for the content of the structures involved in the fast period. This content is estimated by extrapolating the straight lines of the steady stages to zero time. The obtained values are found to be a linear function of the content of isotactic triads. The results, together with some earlier ones, allow for the content of the labile non-defect structures in PVC to be determined.