Effect of complex flow kinematics on the molecular orientation distribution in injection molding of liquid crystalline copolyesters

Wide-angle X-ray scattering (WAXS) is used to probe the molecular orientation in steady isothermal complex channel flows (in situ) and in injection molded plaques (ex situ) of a new, low-cost aromatic copolyester based on the mesogen 4,4′-dihydroxy-α-methylstilbene (DHαMS). Complex orientation state...

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Published in:Polymer (Guilford) 2004-07, Vol.45 (15), p.5341-5352
Main Authors: Rendon, Stanley, Burghardt, Wesley R., New, Anthony, Bubeck, Robert A., Thomas, Lowell S.
Format: Article
Language:English
Subjects:
Applied sciences
Channel flows
Exact sciences and technology
Injection molding
Injection moulding
Liquid crystalline polymer
Machinery and processing
Moulding
Plastics
Polymer industry, paints, wood
Technology of polymers
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cited_by cdi_FETCH-LOGICAL-c465t-166d6d4f46aba9c4ae2b9c815751f768e9263f17ecbf9a7c94f081aa4ef157583
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container_issue 15
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container_title Polymer (Guilford)
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creator Rendon, Stanley
Burghardt, Wesley R.
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Thomas, Lowell S.
description Wide-angle X-ray scattering (WAXS) is used to probe the molecular orientation in steady isothermal complex channel flows (in situ) and in injection molded plaques (ex situ) of a new, low-cost aromatic copolyester based on the mesogen 4,4′-dihydroxy-α-methylstilbene (DHαMS). Complex orientation states arise from the competition of inhomogeneous mixed shear and extension in isothermal flows. Slit-contraction flows lead to a significant but temporary increase in the average degree of molecular orientation, suggesting that this polymer is of the ‘shear-tumbling’ type. Conversely, bimodal orientation states are observed in slit-expansion flows, where transverse extension leads to a strong reduction in the average degree of molecular orientation along the flow direction. Similar bimodal orientation states are observed in injection molded plaques, suggesting that these kinematic concepts translate rather directly to the more complex transient non-isothermal case of injection molding. Variations in orientation state induced by changes in plaque thickness may be rationalized by systematic changes in the relative importance of shear and extension. These results suggest a complementary perspective on ‘skin-core’ morphologies in liquid crystalline polymer moldings, and provide a clear conceptual link between more fundamental studies in isothermal flows and structure development during processing.
doi_str_mv 10.1016/j.polymer.2004.04.073
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source ScienceDirect Freedom Collection 2022-2024
subjects Applied sciences
Channel flows
Exact sciences and technology
Injection molding
Injection moulding
Liquid crystalline polymer
Machinery and processing
Moulding
Plastics
Polymer industry, paints, wood
Technology of polymers
title Effect of complex flow kinematics on the molecular orientation distribution in injection molding of liquid crystalline copolyesters
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