PVC compounds formulations

PVC compounds, formulated with all the necessary additives for the end-use, are supplied in gelled granule form, powder dry blend or liquid paste. Obviously the gelled form only requires to be heated and processed through the appropriate equipment, whereas the powder dry blend or liquid paste must include a gelation phase within the processing stage. 

Advanced statistical and experimental design techniques speed up the selection of the proper PVC compounding formulation (19, 20, 21). 

Cost bilizers. In most cases the alkyl tin stabilizets ate particularly efficient heat stabilizers for PVC without the addition of costabilizers. Many of the traditional coadditives, such as antioxidants, epoxy compounds, and phosphites, used with the mixed metal stabilizer systems, afford only minimal benefits when used with the alkyl tin mercaptides. Mercaptans are quite effective costabilizets for some of the alkyl tin mercaptides, particularly those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyl tin mercaptide ate currendy the most efficient stabilizers for PVC extmsion processes. The level of tin metal in the stabilizer composition can be reduced by up to 50% while maintaining equivalent performance. Figure 2 shows the two-roU mill performance of some methyl tin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. 

The basic metal salts and soaps tend to be less cosdy than the alkyl tin stabilizers for example, in the United States, the market price in 1993 for calcium stearate was about 1.30— 1.60, zinc stearate was 1.70— 2.00, and barium stearate was 2.40— 2.80/kg. Not all of the coadditives are necessary in every PVC compound. Typically, commercial mixed metal stabilizers contain most of the necessary coadditives and usually an epoxy compound and a phosphite are the only additional products that may be added by the processor. The requited costabilizers, however, significantly add to the stabilization costs. Typical phosphites, used in most flexible PVC formulations, are sold for 4.00— 7.50/kg. Typical antioxidants are bisphenol A, selling at 2.00/kg Nnonylphenol at 1.25/kg and BHT at 3.50/kg, respectively. Pricing for ESO is about 2.00— 2.50/kg. Polyols, such as pentaerythritol, used with the barium—cadmium systems, sells at 2.00, whereas the derivative dipentaerythritol costs over three times as much. The P-diketones and specialized dihydropyridines, which are powerful costabilizers for calcium—zinc and barium—zinc systems, are very cosdy. These additives are 10.00 and 20.00/kg, respectively, contributing significantly to the overall stabilizer costs. Hydrotalcites are sold for about 5.00— 7.00/kg. 

The PVC formulations shown in Table 2 represent typical compounds used by the wine and cable industry. PVC compounders have developed new PVC-based formulations with very good fire and smoke properties (can pass the UL 910 Steiner Tunnel test) that compete with the more expensive fluoropolymers. These can be used in fabricating telecommunication cables usable for plenum area appHcations. 

The dry blend can also be extmded and the extmdate chipped to produce pellets of PVC compound which can then be subsequendy reprocessed to produce the final product. This has the benefit of ease of storage of raw materials since all the formulation ingredients are contained bound in the gelled compound. Many producers of flexible PVC only purchase PVC compound, and many companies exist solely to produce PVC compound rather than a tme end product such as sheet, flooring, or pipe. 

In the formulation of PVC compounds it is not uncommon to replace some of the plasticiser with an extender, a material that is not in itself a plasticiser but which can be tolerated up to a given concentration by a polymer-true plasticiser system. These materials, such as chlorinated waxes and refinery oils, are generally of lower solubility parameter than the true plasticisers and they do not appear to interact with the polymer. However, where the solubility parameter of a mixture of plasticiser and extender is within unity of that of the polymer the mixture of three components will be compatible. It may be shown that... 

There are a number of applieations such as bottle and film where tough materials of high elarity are desired. The advent of MBS material has been a significant advance to meet the requirements. It has been found possible here to produce an additive with sufficiently different solubility parameters from the PVC for it to exist in the disperse phase but with a very similar refractive index to the PVC so that light scattering at the interface between the two phases is at a minimum. However, owing to differences in the formulation of PVC compounds, a particular MBS modifier may not have exactly the same refractive index as the PVC eompound. 

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. 

Based on these considerations, Croft prepared six formulations containing various combinations of NBR and NBR/PVC with CR and SBR and measured their oil, heat and ozone resistance, physical properties, and adhesion characteristics. Whereas the physicals are satisfactory for aU compounds, formulations based on NBR, NBR/PVC with CR performed better on heat and oil aging than the compounds containing SBR as shown in Tables 11.6 and 11.7. However, the adhesion is better with the latter compounds. It has been suggested that cuprous sulfide formed on the wire surface interacts with the double bond in SBR to provide the improvement in adhesion. 

Fig. 5. Rigid PVC Conduit Formulation. (Reproduced with permission from Ref. 2. Copyright Plastics Compounding 1985).

PVC compounds can be formulated, using plasticisers, into flexible materials, usually called PVC-P. Compounds without plasticiser for rigid applications are designated PVC-U. 

Another important consideration is powder flow time as it governs the speed and ease of polymer discharge from a silo or from a mixer. This is influenced by the PVC particle shape, size distribution and compound formulation ingredients. 

The results are reported of studies on PVC formulations, which show that lead-free, heat stable, flexible PVC compounds can be prepared through the proper selection of calcium/zinc stabilisers combined with selected costabilisers, fillers and other additives. The preparation of PVC insulation and sheathing compounds having oxygen index values greater than 30% using a combination of Firebrake ZB zinc borate and a phosphate ester plasticiser is also demonstrated. 6 refs. 

Polyvinyl chloride window profile formulations containing organic-based and calcium-zinc stabilisers were produced and the performance of the stabilised PVC compounds compared. Properties evaluated included rheological properties, heat stability, colour, gloss,... 

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)... 

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