Thermoplastic polyetherimide – a helpful aid for the drawing of fluoride fibres

A coating layer of thermoplastic polyetherimide (PEI) of less than 40 μm prevents fluoride preforms from moisture attack during the drawing process. If over-coated in-line with acrylate, the bending strength of the fibres, which was seen to depend strongly on the drawing speed, reached 1 GPa even under nitrogen atmosphere. A correlation between fibre strength and layer thickness was found. Furthermore, a strength comparison with fluoride fibres coated with a fluorinated copolymer was made.