Molecular weight fibre crystallinity

Polyketone containing mainly a-form crystallinity at room temperature was reported by Lommerts et al. [7] for drawn fibre samples. Both Lommerts and Klop [7, 10] concluded that low molecular weight as-polymerised oligomers crystallise at least partly in the a modification whereas virgin high molecular weight PK copolymer (polymerised under the standard conditions described in the patents [1, 3]) crystallises almost completely in the S modification with a... 

The two-component system—crystal lamellae or blocks alternating with amorphous layers which are reinforced by tie molecules— results in a mechanism of mechanical properties which is drastically different from that of low molecular weight solids. In the latter case it is based on crystal defects and grain boundaries. In the former case it depends primarily on the properties and defects of the supercrystalline lattice of lamellae alternating with amorphous surface layers (in spherulitic, transcrystalline or cylindritic structure) or of microfibrils in fibrous structure, and on the presence, number, conformation and spatial distribution of tie molecules. It matters how taut they are, how well they are fixed in the crystal core of the lamellae or in the crystalline blocks of the microfibrils and how easily they can be pulled out of them. In oriented material the orientation of the amorphous component (/,) is a good indicator of the amount of taut tie molecules present and hence an excellent parameter for the description of mechanical properties. In fibrous structure it directly measures the fraction and strength of microfibrils present and therefore turns out to be almost proportional to elastic modulus and strength in the fibre direction. 

This class of fibre is melt-spun from a nematic liquid-crystalline phase, which leads to the production of highly-oriented filaments at quite low elongational shear rates. The fibres have high modulus and, if thermally post-treated over an extended period to raise the molecular weight, they also have very high tensile strength. However, so far they are limited as additives by their fusibility and poor adhesive properties. 

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