Secondary plasticizers definition

Plasticizers may also be further subdivided into primary and secondary types. Primary plasticizers are those used as the sole plasticizer or as the major component of the plasticizer system. Secondary plasticizers are typically blended with primary plasticizers to improve certain performance properties such as reduced flammability and improved processing, or simply to lower cost. Acmally, there are some overlaps in these definitions, since some secondary plasticizers, can function as primary plasticizers when used at relatively low levels. An example is di-2-ethylhexyl adipate (DOA). DOA is often used as the sole or primary plasticizer in PVC meat wrap, typically at 30 parts per 100 of resin (phr). But it also functions as a secondary plasticizer when added at the 10 percent level to a general purpose plasticizer, for example to improve the low-temperature flexibility or flex rating of a PVC shoe sole. Other examples would include the use of a primary plasticizer, such the higher-molecular-weight phthalate diisodecyl phthalate (DIDP) for use as a minor component in blends with polymeric plasticizers to help improve processability or to lower costs. 

PRESSURE FORMING. This variation uses elements of squeeze processes. A closed mold consisting of a core and a cavity half is constructed. A clamped, preheated sheet is moved into place between the mold halves that are then closed around it. A vacuum may be applied to the mold to improve definition. The resulting parts are removed from the mold and removed from the blanks by a secondary trimming operation. The amount of detail that can be achieved in the parts is limited (as with squeeze processes) because the plastic material is always below its true melting point and this limits how far it can be moved during processing. 

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