Properties of PVC

Commercial PVC is generally produced by addition polymerization. It may be produced by a variety of techniques such as suspension, emulsion, micro suspension and bulk. PVC, as normally prepared, is a white granular material, ranging in particle size from 5-400 microns and with apparent bulk densities of 0.5-0.8 g/cc. Emulsion type PVC is usually smaller in particle size. This type of PVC is also called dispersion type. Dispersion type PVC is grounded to further decrease particle size and this type of PVC is called paste type. Paste PVC particles are irregular in shape and have relatively high surface area. Both dispersion and paste type PVC are suitable for plastisol applications. 

Addition polymerized PVC has largely head-to-tail arrangement of vinyl chloride units with a helical structure of C2gH42Cl 4 repeating units. 

PVC is not hygroscopic and therefore normally does not absorb moisture. Commercial PVC contains 0.2-2% volatiles. Water absorption at 25 C in 24 hours is about 0.05 - 0.10%. At high tenqteratures such as 100°C water absorption may be ] 

PVC is soluble in cyclohexanone, dimethyl formamide, nitrobenzene, tetra hydrofuran. PVC is resistant to sulfuric, nitric, hydrochloric acid, sodium hydroxide, sodium hypochloride. It is not recommended for aromatic and or chlorinated hydrocarbons such as mono ordichlorobenzene, ketones, and alcohols. PVC wishstands to boiling water up to 140 F, moderately resists to detergent water and is not recommended for greases or oils (4). 

The density of PVC differs by production process. Typical commercial rigid PVC densities range between 1.3 - 1.41 g/cc, which is relatively high in comparison with other thermoplastic materials. The density of PVC is influenced by the degree of crystallization. Therefore, temperature of polymerization, and the thermal history of the PVC ariects the density. The density increases with reduced polymerization temperature. Density difference of approximately 0.5 -1.1% may be observed between quickly quenched and slowly crystallized PVC samples. 

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The properties of PVC may also he expected to depend on the molecular weight distribu n. Most commercial polymers, however, appear to have similar values for MJM and in any case there is little published information on effects of altering the parameter. It is perhaps rather surprising that there appears to be little work reported on the effect of blends of polymers of differing molecular weight on mechanical and rheological properties. 

Many other liquids have been found to be effective plasticisers for PVC but are of limited commercial value, at least in Britain. The effect of plasticisers on the properties of PVC is illustrated in Figure 12.20 (a-e). 

Because of the wide range of possible formulations it is difficult to make generalisations about the properties of PVC compounds. This problem is illustrated in Table 12.4, which shows some differenees between three distinct types of eompound. 

The effects of added DOP on the properties of PVC/ TPU blending material are shown in Table 2. 

Table 2 The Effect of Added DOP on the Mechanical Properties of PVC/TPU Blends...

Table 10 Effect of Short-Time Aging on Mechano-Chemical Properties of PVC-NBR Blend...

Two types of the homopolymer are available, the flexible and the rigid. Both types have excellent chemical and abrasion resistance. The flexible types are produced with high porosity to permit plasticizer absorption. Articles made from the rigid type are hard and cannot be stretched more than 40% of their original length. An important property of PVC is that it is self-extinguishing due to presence of the chlorine atom. 

Table 8. Heats of interaction and physico-mechanical properties of PVC-based filled plasticized compositions [100]...

The details of the process by which the reaction is initiated and propagated in each case have been discussed many times but are still far from being completely understood. It is generally agreed that the presence of various structural features in the polymer, which occur to different extents depending on the polymerization conditions, are important particularly since recent improvements in analytical techniques have made it easier to identify them and quantify their low concentration levels with greater certainty. Although deterioration of any of the physical or mechanical properties of PVC is undesirable much of... 

The fire properties of PVC have been put into perspective recently [4, 5]. They show that PVC is a polymer with a high ignition temperature and low flammability. Furthermore, PVC products are associated with a low rate of heat release as well as little total heat released [4-9]. This will depend, clearly, on the type of product, since plasticised PVC products are obviously more flammable than rigid ones. 

Similarly, one frequent prerequisite is that the pigments used have little or no effect on the physical and mechanical properties of the plastic. One example here is the change in rheological properties of PVC plastisols or of PVC melts during processing. 

Another example is the influence of the electrical resistance of PVC cable insulation. This is caused not by the organic pigment itself but by ethoxylated surfactants, which are added as auxiliaries in the manufacture of these pigments, especially azo pigments. Contrary to a repeatedly expressed view, a possible electrolyte content, which laked azo pigments for example can have, has no effect on the dielectric properties of PVC [34]. Some pigment manufacturers offer special product ranges with verified dielectric properties for this purpose. 

Table 6.8 contains general physical properties of PVC. Because of the variety of additives, the values for the plasticized PVC are approximate. 

Polyvinyl chloride is processed into a number of forms by including additives. Additives are used to vary the properties of PVC so that it can be made soft and flexible or hard and rigid. Additives are also used to inhibit decomposition as a result of exposure to sunlight, ozone, and chemicals. Plasticizers are the primary additive included in PVC materials. Di(2-ethylhexyl) phthalate (DEHP) and a host of other phthalates are the most common plasticizers. Plasticizers impart flexibility, thermal stability, strength, and resilience to PVC compounds. PVCs without plasticizers are classified as UPVC the letters stand for unplasticized polyvinyl chloride. UPVC is rigid and used for conduit, containers, gutters, and floor tiles. Other common PVC additives are biocides, lubricants, and pigments. 

The Swedish Royal Academy of Sciences, the Royal Academy of Engineering Sciences, and other professional organizations scathingly criticized the committee s 1997 report Towards a Sustainable Chemicals Policy.7 Expert criticism meant little to the Minister of Environment at that time (now Minister of Foreign Affairs), Anna Lindh, who, in the case of the alleged dangerous properties of PVC, declared that she had more confidence in Greenpeace than in the Academy of Sciences. 

It is surprising therefore that after such a lapse of time, we should consider it interesting to discuss laboratory techniques for the study of the effect of temperature on the properties of PVC plastisols. 

Voronkova IA (1969) Investigation of paste-forming properties of PVC. Candidate s Thesis, Moscow, MIIKhT... 

The reaction was carried out using up to 10% by weight of polybutadiene based on PVC. However, to avoid changing the properties of PVC other than the thermal stability, the preferred extent of reaction was 3-6%. 

Diffusion-Controlled Free Radical Polymerization - Effect on Polymerization Rate and Molecular Properties of PVC , Abstracts - Third International Symposium on PVC, Case Western Reserve University, Cleveland, August 10-15 (1980). 

The utilization properties of PVC are intimately linked to the molecular-weight distribution (MWD) of macromolecules. The MWD may be measured by appropriate techniques, such as gel-permeation chromatography, but also predicted by computation. Comparing experimental and calculated MWD allows the validation of a kinetic model as well as the tuning of parameters. On this basis, the operation procedure necessary to get a target MWD may be simulated. 

Tensile strength properties of PVC-U, filled with precipitated and ground calcium carbonate, have been investigated (381, 404). 

The influence of zeolites and iron oxide on the antistatic properties of PVC based composites have been established (426). 

The mechanical properties of PVC-U can be improved substantially by stretching the polymer, usually in both directions, at temperatures above the glass transition temperature, 90 °C is normally used. 

Complex polyphosphites such as DP12 and DP675 were shown to outperform simple phosphite esters as replacements for heavy metal components of mixed metal stabilisers for PVC. It was found that the zinc level was critical for optimisation of the performance of the phosphite blends. Synergistic performances were observed with combinations of several phosphite esters, with the additional benefit of cost effectiveness. Other properties of PVC compounds, such as clarity, light stability and plate-out resistance, also improved markedly when heavy metal components of mixed metal stabilisers were replaced with polyphosphites. 4 refs. 

EFFECTS OF CALCIUM CARBONATE NANOPARTICLES AND BLENDEX 338 ON MECHANICAL PROPERTIES OF PVC... 

The results are reported of an in depth study of the structure, thermal properties, dynamic mechanical properties, flammability and smoke properties of melt blended PVC-sodium montmorillonite nanocomposites. Investigative properties employed included X-ray diffraction, TEM, TGA, DMA and cone calorimetry. The effects of clay loading, DOP concentration, annealing, blending time and molec.wt. on the formation of the composites are discussed and fire properties of PVC-organically modified clay and PVC-sodium clay nanocomposites are presented and discussed. 15 refs. USA... 

The concept that friction between filler particles and breakdown of filler network is heat generating is applied to an understanding of the fusion behaviour of PVC. It is shown that the treatment of a PVC melt as a filler-containing polymer provides information on the anomalous effects observed in the rheological properties of PVC and that differences in the fusion behaviour of PVC compounds containing different impact modifiers and lubricants can be explained with the aid of this approach. 17 refs. 

The use is discussed of Sinstad multifunctional compositions for use in low-plasticised PVC pipe formulations as heat stabilisers and plasticisers. The research reported consisted mainly of investigating the physical and mechanical properties of the plastic compound, its ease of manufacture, and processing with partial replacement of the plasticiser and stabiliser and complete replacement of the lubricants. Properties of PVC compositions for the production of pipe connectors and pipes with varying formulations are discussed. 7 refs. (Article translated from Plasticheskie Massy, No. 11,2000, P-43)... 

EFFECT OF PHYSICAL AGEING ON THE GAS TRANSPORT PROPERTIES OF PVC AND PVC MODIFIED WITH PYRIDINE GROUPS... 

Details are given of the effect of processing on mechanical properties of PVC window profiles by altering the temperature profile set on the extruder and by varying the shear heating phenomena using different lubrication balances. The effect of filler level and type of impact modifier on the impact properties of extruded profiles with various levels of free volume are presented. 7 refs. 

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