Compatibility stability exudation

A compatibility stability idiosyncrasy of diisodecyl adipate (DIDA) could pose a troublesome problem. A PVC plastisol formulated with DIDA and fused in an oven for 10 min at 175 C will exude but if the fusion period is lengthened to 0.5 h, it will not. One explanation is the dielectric constant of DIDA is below A it should be incompatible and therefore exude. However, upon extensive heating in air this oxidation-susceptible plasticizer builds up peroxides, undergoes chain scission and weight loss, and changes in compatibility. As shown in Table I, if the oxidation phenomenon is negated in per se DIDA by the presence of an antioxidant, bisphenol A, the plasticizer remains unchanged in dielectric constant and predictably would be incompatible (20). 

The manufacture of epoxy stabilizers begins with soya and linseed oils or oleate and other unsaturated fatty acid esters. When epoxidation is incomplete, residual unsaturation remains, leading to poor compatibility-stability. This results in exudation on products in the marketplace. Makers of epoxldized fatty acid esters strive to prevent such failure by ensuring more complete epoxidation and supplying products with the lowest possible iodine number. Vinyl formulators further protect themselves by diminishing the proportion of epoxidized stabilizer to an amount ca. 3% while maintaining plasticizer concentration at ca. 35%. 

Compatibility Many stabilizers exude from the polymer during fabrication, storage or irradiation. One way of preventing this is to incorporate long alkyl chains into the stabilizer molecule which acts as a link. 

The normal liquid chlorinated paraffins used as plasticizers for PVC have viscosities ranging from 100 to 40,000 MPa.s at 20°C. Products with chlorine contents ranging from 30 to 70% are on the market. Compatibility with PVC increases with increasing chlorine content but the plasticizing effect is reduced. The low viscosity products (chlorine content 30%—40%) are used as secondary plasticizers for PVC. They have a stabilizing effect on viscosity in plastisols. Chlorinated paraffins can be used up to a maximum of 25% of the total plasticizer content of the PVC plastisol without the risk of exudation. As chlorine-containing substances, these plasticizers also have a flame-retarding effect. 

Three other requirements, namely stability to processing, absence of plate-out during processing, and modification of rheological and mechanical properties according to the product s performance, are dependent on the compatibility of the components of the system and on the possible interaction between colorants and other components of the formulations. Sufficient compatibility is also necessary in order to avoid exudation. 

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