Mechanism of organotin stabilization of poly(vinyl chloride). 6. Compatibility of organotin stabilizers with PVC

Compatibility of PVC with liquid alkyltin alkylthioglycolate stabilizers was studied by thermal methods, including isothermal calorimetry of mixing, DSC, DMA, and dielectric relaxation. The enthalpy of mixing of PVC with the series of alkyltin alkyl thioglycolates was measured over the entire concentration range at ambient conditions. It was found that all tested compounds are compatible with PVC in a broad concentration range and form homogeneous mixtures. The results are discussed in terms of the superposition of glassy state and molecular interaction contributions to the enthalpy of mixing of the glassy polymer with liquid additives. The influence of organotin stabilizers on the glassy structure of PVC films was studied by means of DSC and the dielectric relaxation spectrum. The enhancement of the glassy structure of PVC by alkyltin alkyl thioglycolates is interpreted as the result of strong multi‐site molecular complexes between organotin molecules and PVC chains, which act as additional clips in the entanglement network of polymer chains.     

有机锡稳定封在PVC加工中的应用

考察了有机锡稳定剂F-50的用量对试样热稳定性能的影响。结果表明：F-50用量达到0．8份时,稳定效果达到最佳;再增加其用量,稳定效果无明显提高。     

Mechanism of organotin stabilization of poly(vinyl chloride). 2: Significance for PVC stabilization of structure and equilibria of alkyltin thioglycolates/chlorides

The stabilization effect of alkyltin thioglycolates was determined by the measurement of discoloration of PVC formulations. The results were interpreted considering the structure of these compounds, their equilibration with alkyltin chlorides, and their postulated association with chlorine atoms at PVC primary particle surfaces.     

Gamma radiation stabilization of PVC

A new class of additives combining heat and radiation stabilization has been shown to prevent the discoloration and associated undesirable hydrogen chloride formation encountered when PVC is exposed to sterilizing doses of gamma radiation. Various mechanisms that lead to the decomposition are described and the free radical processes that cause changes in physical and mechanical properties are discussed. The performance of the new additives demonstrates that rigid PVC can be exposed to high (> 5MRad) radiation with little or no discoloration and loss of physical properties.     

Study of PVC stabilization using capillary rheometry

Capillary rheometry allows monitoring of PVC thermal and shear stress degradations separately. Based on testing of PVC compounds with a capillary rheometer, stabilizers can be efficiently optimized to reduce both degradation processes. Capillary rheometry is an important tool for further improving productivity of PVC processing at high shear rates.     

The effect of organotin chlorides on the thermal stability of PVC

Metal chlorides formed from metal stabilizers under processing conditions have an influence on the thermal stability of PVC. Zinc chloride, e. g., has a strong destabilizing effect, whereas lead chloride behaves almost indifferently. Alkyltin chlorides however, have a stabilizing effect in as much as they cause a significant retardation of the thermal dehydrochlorination rate of PVC. Using 1-chlorobutene-2 as model substance, a chloro allyl isomerization could be proved caused by organotin chlorides under certain conditions. These results support a complex chemical isomerization concept to explain the stabilizing effect of organotin chlorides on PVC.     

Mechanism of organotin stabilization of poly(vinyl chloride). 1: The structure and equilibria of alkyltin thioqlycolates and their compatibility with PVC

A series of alkyltin thioglycolates was synthesized and their structure and equilibria with alkyltin chlorides studied by infrared analysis. Dynamic mechanical analysis was used to determine their compatibility with PVC. The implications of these results on PVC stabilization were discussed     

Role of organotin mercaptide stabilizer in heat and light stability of PVC

Infrared analysis can be used to study the conversion of organotin mercaptide stabilizers in PVC from dialkyltin dimercaptide to dialkyltin monochloride monomercaptide to dialkyltin dichloride. This technique is used to study the effects of the stabilizer level and thermal heat history on the light stability of PVC.     

Flexible PVC stabilization: the phosphite approach

Addressing environmental concerns while maintaining levels of performance and profitability is becoming increasingly important to processors. Advanced phosphite ester technology for flexible PVC developed by Dr. Don Stevenson, Mark Harr, Bill Hood and Tom Jennings of Dover Chemical Corporation is now demonstrating improved performance, reduced processing costs and a reduction or elimination of toxic heavy metals and solvents. Plastics Additives & Compounding reports on recent developments at Dover Chemical.     

New organic costabilizers for the stabilization of PVC

Organic costabilizers constitute a very important class of compounds where the replacement of heavy metals in PVC stabilizers is concerned. These materials are typically added at no more than 5% of the stabilizer formulation. They do, however, make a disproportionate contribution to performance based on addition level. This situation has spurred the search for new materials. Recent advances in this field are reviewed with particular emphasis on a new class of polyketones (pyrrolidine-2,4-diones) recently patented by Akcros Chemicals. The regulatory status, performance characteristics, and mechanism of action of this type of material are described.     

Electrostatic and steric stabilization of PVC primary particles

Problems related to the formation and stability of primary particles in VCM suspension and bulk polymerization were theoretically analyzed, based on the DLVO (Deryaguin-Landau-Verway-Overbeek) and HVO (Hesselink-Vrij-Overbeek) theories of stability of colloidal systems. In the absence of secondary stabilizers, PVC primary particles were solely stabilized by negative electric charges, as a result of the presence of HCl formed by a chain transfer reaction of chloride redicals to PVC polymer chains. The dependence of the stability of primary particles on the ionic strength of the medium, temperature, and total particle charge was quantitatively investigated in terms of the stability ratio and the particle coalescence rate constant. The steric stabilization of primary particles, arising from the addition of surfactants or polymers to the monomer phase, was examined, using the HVO theory. It was shown that PMMA improved the stability of primary particles and, thus, could alter the particle agglomeration kinetics. The effects of molar mass and the amount of the absorbed PMMA, as well as the influence of solvent quality on the steric stabilization of primary particles, were also investigated. The experimental results, published on the electrostatic and steric stabilization of PVC primary particles, were in good agreement with the theoretical predictions obtained in this study. © 1993 John Wiley & Sons, Inc.     

Some aspects of PVC paste rheology

Using the Weissenberg rheogoniometer, a technique has been developed which facilitates the measurement of shear stress data and which substantially overcomes the problem of sample loss that normally occurs at high shear rates. Using this technique, the apparent viscosities of PVC pastes based upon four different PVC paste polymers plasticized with dialphyl phthalate have been determined at a number of shear rates up to 9000 sec^?1 and the viscosity aging characteristics of these paste polymers have been compared. The effect of several common plasticizers upon PVC paste viscosity and viscosity aging have been studied at shear rates of the order of 10 sec^?1 and 1000 sec^?1.     

Char formation in polyvinyl chloride. III. Mechanistic aspects of isothermal degradation of PVC containing some dehydrochlorination/charring agents

We pyrolyzed PVC with and without the char-promoters iron (III) pyromellitate, zinc pyromellitate, and MoO₃ (1 phr) under isothermal conditions (207°C, nitrogen) and analyzed the soluble and insoluble residues to characterize the reactions important to charring. Both pyromellitates, apparently acting as their metal chlorides, catalyze dehydrochlorination and crosslinking that could lead to rapid charring; however, the zinc additive also catalyzes undesirable fragmentation. MoO₃, possibly acting as an oxychloride, has only a small effect on PVC degradation under the conditions used; however, it does suppress fragmentation. The relative rates of crosslinking to fragmentation are important in determining char yields.     

PVC stabilization mechanisms in the light of practical results

Based on the mechanism of reaction, the function of PVC stabilizers and co-stabilizers is described. In particular, the differing light stabilization abilities of recognized heat stabilizers are demonstrated. Reasons for the differences observed are put forth with chemical explanations.     

Use of organotin compounds in the thermal stabilization of PVC: 6. A radiochemical study of the effect of variations in molecular weight on the reaction between PVC and di(butylthiolato)dibutyltin

Reactions between PVC samples of differing molecular weight and di(butyl[³⁵S] thiolato)dibutyltin have been examined. There is an inverse relationship between the amount of radioactivity taken up by the polymer and its molecular weight.