Non-Polymeric Components of Plastics

Non-polymeric components are present in plastics either unavoidably as a result of the process of manufacture, or as the result of deliberate additions to the plastic in order to improve some aspect of ease of manufacture or final polymer properties. 

non-polymeric components can be subdivided into three groups  

Aluminium 40 Remnants of Ziegler organoaluminium-titanium halide catalysts 

Dissolved propylene 1 cm /cm polymer Residual polymerisation solvent 

Calcium 40 Possibly calcium stearate stabiliser for protecting polymer during moulding 

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All polymers, in addition to the basic plastic, contain usually several, if not a multiplicity, of non-polymeric components in amounts from less than 1 ppm to several percent. These substances obviously have implications in the suitability or otherwise of the plastic for applications involving contact with foodstuffs. Thus, although the plastic itself, due to its very high MW, might not contaminate the foodstuff, it is apparent that certain of the additives, which are usually of relatively low MW and therefore of higher solubility, will be transferred from the plastic to the foodstuff during storage. This raises questions about the toxicity of the additives, the amounts that transfer, and the possible implications of this, from the toxicity point of view, as far as the food consumer is concerned. 

Polymers blended with non-polymeric additives form subclass Bl. It can be distinguished into subgroup Bll, the plasticized or "soft" PVC and subgroup B12, the filled polymers, with fillers such as carbon black, silica, zinc oxide, etc. A filler usually is cheaper than the polymeric main component it can constitute as much as 40% by weight of the material. Other additives, such as pigments, accelerators, hardeners, stabilisers, flame-retardants, lubricating agents, etc. are used in much lower concentrations (functional composites). 

Materials Compatibility Einally, any lubricant is required to be compatible with non-metallic components used in the engine, such as plastics, resins and elastomers. In particular, polymeric materials used in seals and plastics need to retain their integrity when in contact with the lubricant. ACEA and most OEMs have material compatibility tests to ensure that the lubricant will not cause undue degradation in key physical parameters of the polymer. These parameters include tensile strength, hardness, volume and crack formation. Any such loss of polymer integrity could be manifest as oil seal leaks or in more extreme cases as a blown gasket. Current engine test examples for American, European and selected OEM specifications are shown in Table 9.5. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

The effect of the presence of compatibilized incompatible components is apparent in PVC plastisols. Monomeric and polymeric esters are good plasticizers for PVC because they have suitable solubility parameters. A good plasticizer is one which, in sufficient quantity, would almost be a solvent for the polymer. However, a good plasticizer, i.e. solvent, in a plastisol results in a high viscosity composition. This may be unsuitable for slush molding or other applications when low viscosity is desirable. The latter is obtained by adding a secondary plasticizer such as a hydrocarbon oil. In reality, the latter is not a plasticizer but actually a non-solvent which converts the good solvent plasticizer to a poor solvent mixture with resultant decrease in plastisol vis-... 

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