Flexible PVC compounds

In a flexible PVC compound, ingredients in the recipe are chosen based on cost and/or thein contribution to physical and other properties and performance. Typical ingredients (16,17) are stabilizers, fillers, plasticizers, colorants, and lubricants. 

Fillers. These are used to reduce cost in flexible PVC compounds. It is also possible to improve specific properties such as insulation resistance, yellowing in sunlight, scuff resistance, and heat deformation with the use of fillers (qv). Typical filler types used in PVC are calcium carbonate, clays, siHca, titanium dioxide, and carbon black. 

The relationship between the physical properties of profiles extruded from flexible PVC compounds and the extrusion melt temperature was studied. The properties included tear resistance, tensile properties, brittleness temperature and compression set. The effect of thermal history on surface characteristics of the extrudate, such as surface roughness and gloss, and the relationship of the latter with the processing morphology were also examined. An increase... 

LOW-SMOKE, THERMALLY STABLE, LEAD-FREE FLEXIBLE PVC COMPOUNDS... 

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. 

The performance of a flexible PVC compound is often defined by its plasticiser content and composition and a simple, accurate and fast method of plasticiser identification could, therefore, be an effective quality control and benchmark performance test in new product development studies. Gas chromatography was shown to provide the most effective identification method and it was demonstrated that it could be complemented by IR spectroscopy, liquid chromatography and physical observations to confirm identity. 4 refs. 

BS 2782. Method 122A [199], measures the indentation of a weighted cylinder into a flexible PVC compound at a specified temperature and time. Test pieces 13 mm diameter by 1.27 mm thick are cut from sheet material and placed under a guided 3 mm diameter plunger having a load of 9.8 N applied to it. The initial thickness and final thickness after 24 hr at 70 C arc measured with a device reading to 0.002 mm. 

The phosphite esters function in this formulation as primary heat stabilizers by replacing labile chlorides on PVC via the Arbuzov rearrangement mechanism. When phosphites are used at optimized levels in combination with catalytic amounts of zinc and normal levels of epoxidized soybean oil, they provide excellent early color and adequate long-term stability to flexible PVC compounds. Their use also helps in lowering stabilization cost, elimination of toxic metals, elimination of plate out, poor printability, viscosity drift in plastisols, haze, bloom, water blush, and staining. 

A rigid glass fiber-reinforced PVC extrusion compound by Solvay replaced the metal in side-protection strips on the Opel Astra car. The compound was coextruded together with a flexible PVC compound. The compound provided a low coefficient of linear thermal expansion (2.5 X 10" K ) and good adhesion to the car body. Recycling was facilitated, because the two compounds were compatible and there was no metal insert. 

Applications Packaging is a major market for PVC. Flexible PVC compounds are used in food packaging applications because of their strength, sparkle and transparency, processability, and low raw-material cost.l ... 

Flexible PVC compounds incorporating the phthalate plasticizers have been used for a long time now in a wide range of tubing, hoses, films, wire, and cable jacketing applications in automotive, building, consumer, and health-care markets. However, the recent controversy over the migratability of phthalate ester... 

The recent proliferation of metallocene-based polyolefins and polyolefin elastomers have gained their popularity owing to their density, cost, and ease of processabUity. PVC/POE blends have therefore been investigated as flexible PVC compounds. However, these blends are thermodynamically immiscible and needed suitable compatibiUzers such as the chlorinated polyethylenes (Eastman and Dadmun 2002). Since they are not miscible, POEs do not lower the PVC modulus sufficiently unless some plasticizer or a compatible elastomer such as EPE is also added. Commercially, some PVC/POE alloys are offered by TeknorApex under Flexalloy trade name with a shore A hardness 40-60 and brittle points down to —50 °C. They are claimed to have excellent low-temperature toughness, flexibility, compression set-resistance, and oil resistance. Suitable applications include automotive hoses, seals, gaskets, wire jacketing, etc. 

Noraplas, Flexible PVC compounds. North America Plastics Inc. 

The established use of flexible PVC in the manufacture of medical devices is increasingly threatened by doubts about the toxicity of phthalate plasticisers normally used in the PVC compounds concerned. For many years BIP Vinyls Limited have been working to develop alternative flexible PVC compounds using plasticiser systems which are more acceptable than standard phthalates. 

This paper summarises this development work which has resulted in a comprehensive range of extraction resistant flexible PVC compounds and discusses application areas ranging from stomach feeding tubes and nutritional fluid bags to blood contact devices such as dialysis sets and blood bags. 

When plasticiser is extracted in this way the PVC becomes less flexible and can eventually assume a permanent set and possibly crack or fail under stress. Many types of plasticiser are available and some of these have good resistance to extraction from PVC compounds because of their chemical structure and molecular size. Use of this type of plasticiser enables an extraction resistant flexible PVC compound to be produced. 

Because of the interest shown by the medical device industry and demands for different compounds a wide range of extraction resistant flexible PVC compounds has now been formulated by BIPVL and this is illustrated in Table 5. While basically formulated for extrusion applications, some of these compounds have also been shown to be perfectly satisfactory for injection moulding of small components for medical devices, and also for film production by calendering and blown lay-flat film processes. 

Table 5. Extraction Resistant Flexible PVC Compounds for Medical Applications...

This paper has shown the many often conflicting requirements demanded of any new flexible PVC compound for use in medical applications. Even when the physical and technical properties are satisfied the new material has to meet toxicological requirements which are becoming increasingly demanding and complex. This inevitably means that development to the point where a new material can be offered to the medical device industry is a very time-consuming and costly operation. BIPVL therefore believes the newly developed extraction resistant flexible PVC merits serious attention for use in the manufacture of medical devices in the immediate future. 

A formulation for clear, flexible PVC compounds for medical products by Teknor Apex Plastics, Rhode Island, USA, allows processors to run at higher output, with less downtime because of the need to change the filter screen packs on the extruder. The key feature of the new system is that, unlike conventional FDA-approved stabilizers for medical applications, increasing the addition level does not reduce the resistance of the compound to sterilization by gamma rays. Resin degradation is also reduced (at 180°C, the time to onset of degradation is... 

In a flexible PVC compound the trimellitates are less volatile and have improved thermal stability over the phthalate and polymeric plasticizers. Their plasticizing effectiveness and compatibility are similar to phthalates. They offer better moisture and water resistance than the phthalates or polymeric plasticizers. Large volumes of trimellitate esters are used in 90°C and 105°C UL rated insulation compounds. Because of their extraction and migration resistance, thermal stability, and low volatility, the trimellitates are used in conjimction with 9IIP and DUP in automotive interior trim applications where windshield fogging is an issue. 

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