Texture of injection moulded poly(ethylene-2,6-naphthalene dicar☐ylate) parts
1997; Elsevier BV; Volume: 38; Issue: 12 Linguagem: Inglês
10.1016/s0032-3861(96)00848-8
ISSN1873-2291
Autores Tópico(s)Polymer Foaming and Composites
ResumoEvolution of structural gradients developed in injection moulded polyethylene naphthalate was studied using a variety of structural techniques including a newly developed micro-beam X-ray diffraction pole figure technique. PEN, being a slowly crystallizing high temperature polymer, forms a three layer structure: amorphous skin + shear crystallized intermediate layer + amorphous core in the interior at low mould temperatures. The thickness of the crystallized sublayers formed under the action of flow decrease with the increase of mould temperature as a result of reduction of stress history experienced by the flowing polymer chains. Their thickness increases in the narrow passages of the cavity as a result of increased fraction of the extensional component of the flow field which locally causes increases in crystallization rates. The crystalline structure of these layers were found to contain both α and β phases. The hot stage-WAXS experiments indicate that the β phase possess a melting temperature approximately 30°C higher than the α form. In the shear crystallized regions, the polymer chains are oriented along the flow direction and the naphthalene planes that are flexibly linked together along the polymer chain tend to be oriented parallel to the broad surfaces of the part. The preferential alignment of the naphthalene planes results in highly layered macrostructure in the shear crystallized zones with weak interlayer forces. As a result, these regions readily delaminate into plate-like structures observed in the SEM fracture surfaces.
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