摘要:

AbstractA number of poly(vinyl alcohols), used in the suspension polymerisation of vinyl chloride, have been fractionated and characterised. The most effective had the highest molecular weight and contained the most unsaturation. The more insoluble fractions gave the best balance of product properties. Reactor sampling experiments have been used to determine the mechanism of polymerisation. In most polymerisations, the final grain size is determined by factors that control the coalescence and break‐up of the monomer droplets during the first 15% conversion. It is suggested that the structure within the grains is controlled by the formation of a continuous network of PVC primaries which retards droplet contractio

ISSN:0258-0322    

DOI:10.1002/masy.19890290103

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe most important technological procedure in the production of PVC is the suspension polymerization of vinyl chloride, as processibility of the polymer may be influenced to a considerable extent by the choice of polymerization conditions. Structure heterogeneities in PVC powders manifest themselves in plasticized PVC by the occurrence of “fish eye” particles. This review concerns the formation and properties of these particles and discusses the causes of their difficult processibility. Also, the relation between polymerization process and PVC dehydrochlorination is discussed and a new mechanism of its initiation based on the reactivity of cisoid enone structures is proposed. These structures catalyze elimination of hydrogen chloride from regular units of PVC by an interchain enzyme‐like mechanism giving rise to chloroallyl struc

ISSN:0258-0322    

DOI:10.1002/masy.19890290104

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe achievements of the past years are associated, in the first place, with solution of the problems of the abnormally low stability and the new ways of effective stabilization of vinyl chloride (VC) (co)‐polymers. A generalized approach to the quantitative description of the degradation of VC polymers, taking into account the short‐ and long‐range effects of neighbouring groups, which are fundamental for the chemistry of the halogen‐containing polymers, has been elaborated. The principal effects of the polymer phase state and the solvent nature on the degradation rate of VC (co)polymers have been elucidated. This fact predetermines different approaches to the stabilization of the polymer products in creation of rigid and plasticized compositions, including those in so

ISSN:0258-0322    

DOI:10.1002/masy.19890290105

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe 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 man

ISSN:0258-0322    

DOI:10.1002/masy.19890290106

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractA short introduction to polymer‐polymer miscibility and to the prediction of the miscibility of polymers is given. The four main types of polymer‐modified poly(vinyl chloride) (plastification, impact modification, processing aids and heat deflection temperature modification) are explained by examples. The thermal stability of poly(vinyl chloride) in such blends is discussed; the effectivity of tin‐stabilizers may be higher in such blends than in pure poly(vinyl chlo

ISSN:0258-0322    

DOI:10.1002/masy.19890290107

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper reviews research since 1980 on the equilibria and kinetics of transport of small organic molecules in rigid and plasticized PVC. The forms of both the solubility isotherms and the sorption kinetics are shown to change as the PVC/penetrant system undergoes a glass‐rubber transition with an increase of either temperature or penetrant concentration. The isotherms are of “dual‐mode” form (concave to the activity axis) for the glassy state, and show an inflection to Flory‐Huggins form when the penetrant concentration exceeds Cg, the transition composition at the experimental temperature. The solubility at a given penetrant activity is governed primarily by the PVC/penetrant interaction parameter, χ. Sorption kinetics are Fickian for conditions producing small changes of concentration in either the glassy or rubbery state. For sorption into initially unplasticized PVC, kinetics are anomalous if the final penetrant concentration is between about Cg/2 and Cg, and Case II if Cgis exceeded. The magnitude of the Fickian diffusion coefficients depends largely on the geometric factors of molecular size and shape of the penetrant; this dependence is much steeper in the glassy than in the rubbery state. Recent results show that carbon dioxide displays both high diffusivity and substantial solubility in PVC under high pressure; this combination makes compressed CO2uniquely useful in accelerating the absorption of low‐molecular‐weight addi

ISSN:0258-0322    

DOI:10.1002/masy.19890290108

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe Theological properties of PVC compounds reflect the state of the flow units. The steady state structure which may be found in PVC melts is predicted to depend on the interaction of stresses in simple flow and temperatures for transition from rubberlike solid to liquid state and transition from a liquid state containing crystallite aggregates to a liquid state without crystallite aggregates, called the gel destruction temperature Tdand the dynamic melting temperature Tdynm, respectively. The model predictions for Tdand Tdynmare compared with experimental data.

ISSN:0258-0322    

DOI:10.1002/masy.19890290109

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractPVC that has been processed exhibits two endothermic peaks in DSC heating curves. These endotherms are separated by a temperature. Tc, which is characteristic of the maximum temperature reached in prior processing. The relative value of the lower temperature endotherm has been proposed as a measure of degree of gelation of unplasticized PVC. This measure is not exact, however, because it does not reflect the extent of breakdown of primary PVC particles. An alternative DSC measurement technique is proposed that reflects the degree of fusion more accurately. The nature of the various endotherms that are observed is a subject of speculation in this article.

ISSN:0258-0322    

DOI:10.1002/masy.19890290110

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper discusses the most important parameters in terms of fire hazard and shows how PVC fares in relation to other polymers. The fire properties specifically addressed are: ignitability, flammability, flame spread, rate and amount of heat release, mass loss rate, smoke release and toxicity. Hydrogen chloride decay is also commented on, because it affects the toxicity of PVC smoke. The individual parameter most relevant to fire hazard is heat release. The two most useful tools for measuring rate of heat release (viz. the OSU and Cone calorimeters) are described. Results obtained from them are discussed.Smoke can best be measured by combined parameters from rate of heat release calorimeters, rather than in the traditional static NBS smoke chamber.Toxic hazard is being addressed by recognition that most smokes are of similar toxicity, so that the mass loss rate will, generally, govern the toxicity of smoke.Not all fire tests are equally good representations of the probable consequences of a full‐scale fire. Fire hazard assessment is best carried out based on those test results most relevant to real fires; they can be obtained from small and full‐scale experiments and fire models.The fire performance of PVC is excellent; PVC products generally represent low fire hazard in a scena

ISSN:0258-0322    

DOI:10.1002/masy.19890290111

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractGas chromatographic determination of unreacted monomers in periodically taken samples of a heterogeneous reaction mixture was applied in an investigation of the kinetics of suspension homopolymerization of vinyl chloride and of its copolymerization with 1‐olefins. Examples are given of the application of the method in a kinetic description of the synthesis of various types of PVC (K values 58–70), in the testing of various initiators and in the optimization of recipes and reaction conditions of the copolymerization of vinyl chloride with propene. The results presented in the form of conversion curves and time dependences of the reaction rates are discus

ISSN:0258-0322    

DOI:10.1002/masy.19890290112

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY