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Formation, stability, and properties of in ‐ situ composites based on blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer
Author(s) -
Machiels A. G. C.,
Denys K. F. J.,
Van Dam J.,
De Boer A. Posthuma
Publication year - 1996
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.10643
Subject(s) - materials science , thermotropic crystal , composite material , polymer , ultimate tensile strength , polymer blend , morphology (biology) , elastomer , thermoplastic elastomer , thermoplastic , mixing (physics) , copolymer , liquid crystalline , physics , quantum mechanics , biology , genetics
This paper describes the preparation and properties of in‐situ composites based on polymers with no overlap in processing temperatures. The polymers used were Vectra A900, a thermotropic liquid crystalline copolyester (TLCP), and Arnitel em630, a thermoplastic elastomer. Blends were generated by feeding the two components from separate extruders into a Ross static mixer. Different morphologies were obtained by varying the number of mixing elements of the static mixer. Using 8 mixing elements led to a stratified morphology of Vectra layers in Arnitel, using 11 mixing elements resulted in the desired continuous fiber/matrix morphology whereas a pronounced skin‐core morphology was obtained with 14 mixing elements. It is argued that in‐situ composites can be generated by a distributive mixing process without the formation of an intermediate droplet/matrix morphology as occurs in common dispersive blending equipment. Tensile modulus and strength of all blends increased with extrudate draw ratio as a result of increased molecular orientation of the TLCP phase. The level of reinforcement, however, was lower than expected, probably due to the low temperature of drawing. Annealing and capillary instability experiments showed that above the melting point of the TLCP the fiber/matrix morphology rapidly breaks up into a droplet/matrix morphology. This process takes just a few seconds for fibers of thickness ∼ 1 μm. It is shown to be the probable cause of the skin‐core morphology obtained in case of 14 mixing elements.