Molding processes structure-property relations

Bowman [192] conducted a systematic study of the structure-property relations of injection molded polyacetals (polyoxymethylene or POM) and observed correlations between process conditions, structures and mechanical properties. Barrel temperature effects were studied as they are known to influence both microstructure and mechanical properties [193]. Increased barrel temperature was shown to reduce the outer skin layer while increasing the extent of the equiaxed, unoriented core, resulting in a decreased tensile yield strength parallel to the injection direction. 

Bowman [157] conducted a systematic study of the structure-property relations of injection molded polyacetals (polyoxymethylene or POM) and observed correlations between process conditions, structures and mechanical properties. 

This paper examines the structures that occur in rotomolded polyethylene and polypropylene produced under a wide range of processing conditions. The effects of pigments are investigated as well as the mechanical and thermal processes that plastic powders typically undergo during preparation for rotomolding. In all cases, the mechanical properties of the molded articles have been related to the microstructure. 

Structural foams are usually produced as fabricated articles in injection molding or extrusion processes they vary in properties (see Table 10.2). Again, the most important structural variables are polymer composition, density, and cell size and shape. Structural foams have relatively high densities (more than 320 kg/m3), and cell structures are primarily comprised of holes, in contrast to the pentagonal dodecahedral structure characteristic of low-density plastic foams. Because structural foams are generally not uniform in cell structure, they exhibit a considerable variation in properties with particle geometry (see Table 10.5) [24] these relations can provide valuable guidance. 

Whilst there has been extensive work done on the mechanical properties of rotomolded products and the heat transfer processes occurring during molding, " there has been relatively little work done on the unique microstructures that occur within rotomolded articles. This is surprising in view of the fact that the structures are very amenable to microstructural analysis. They display classic features in terms of spherulite geometries, and it is possible to relate mechanical properties to defects caused by the onset of thermal/oxidative degradation. 

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