Molecular orientation distributions during injection molding of liquid crystalline polymers: Ex situ investigation of partially filled moldings

Jun Fang, Wesley R. Burghardt*, Robert A. Bubeck

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The development of molecular orientation in thermotropic liquid crystalline polymers (TLCPs) during injection molding has been investigated using two-dimensional wide-angle X-ray scattering coordinated with numerical computations employing the Larson-Doi polydomain model. Orientation distributions were measured in "short shot" moldings to characterize structural evolution prior to completion of mold filling, in both thin and thick rectangular plaques. Distinct orientation patterns are observed near the filling front. In particular, strong extension at the melt front results in nearly transverse molecular alignment. Far away from the flow front shear competes with extension to produce complex spatial distributions of orientation. The relative influence of shear is stronger in the thin plaque, producing orientation along the filling direction. Exploiting an analogy between the Larson-Doi model and a fiber orientation model, we test the ability of process simulation tools to predict TLCP orientation distributions during molding. Substantial discrepancies between model predictions and experimental measurements are found near the flow front in partially filled short shots, attributed to the limits of the Hele-Shaw approximation used in the computations. Much of the flow front effect is however "washed out" by subsequent shear flow as mold filling progresses, leading to improved agreement between experiment and corresponding numerical predictions.

Original languageEnglish (US)
Pages (from-to)774-786
Number of pages13
JournalPolymer Engineering and Science
Volume52
Issue number4
DOIs
StatePublished - Apr 2012

ASJC Scopus subject areas

  • Chemistry(all)
  • Polymers and Plastics
  • Materials Chemistry

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