Melt Spinning, Functionalization and Durability of Polyetheretherketone-Based Fibres

Abstract

Polyetheretherketone (PEEK)-based polymer fibres have attracted much interest due to their many outstanding properties. Along with one of the highest use temperatures among thermoplastics, PEEK also has excellent mechanical properties and chemical resistance. Because of these properties, PEEK and PEEK fibres are often used in demanding conditions. In this dissertation, PEEK-based polymer fibres were pushed to the limit in four different situations: melt spinning of fine filaments, photoageing, maximum recommended use temperature, and contaminants. To fight contaminants, PEEK was modified via a sulfonation reaction into sulfonated polyetheretherketone (SPEEK) and then melt compounded with polypropylene (PP) to produce antimicrobial and self-cleaning properties. The goal of this dissertation was not only to measure changes in the properties but also to improve the properties.<br/><br/>The general spinnability of PEEK was good with viscosity control deemed crucial to improving that spinnability. In addition to a long and large die and a short spinning path, a low viscosity PEEK grade and a high processing temperature are recommended. Tests provided new information on the quantitative effects of processing parameters on the smallest spinnable fibre diameter. The smallest obtained fibres had an average diameter of 18 µm and a mechanical strength of approximately 280 MPa.<br/><br/>Photodegradation was one of the main weaknesses of PEEK fibres. Ageing PEEK for up to 1056 h in a UV chamber degraded the fibres rapidly from elastic to brittle. Thermal ageing, for up to 128 d at 250 °C, produced effects similar to those of photoageing, including embrittlement, but also some different effects. In both cases, ageing caused crosslinking, which was verified by rheological measurements. Changes in the carbonyl group absorption band, measured by Fourier transform infrared spectroscopy (FTIR), were significantly bigger in photodegradation than in thermal degradation. Differential scanning calorimetry (DSC) turned out to be a poor method to detect ageing in photodegradation, but in thermal degradation it revealed a decrease in the melting temperature and an increase in the glass transition temperature. In both cases, decreased thermal stability was verified by thermogravimetric analysis (TGA).<br/><br/>A SPEEK/PP blend was successfully produced in various compositions. Compounding produced an immiscible polymer blend, in which approximately 1-µm SPEEK particles were homogenously dispersed in the PP matrix. According to electron paramagnetic resonance (EPR) measurements, this blend formed stable radicals with their number correlating with the SPEEK concentration. The thermal properties of SPEEK were inferior to those of PEEK, a reason that made the melt spinning of SPEEK/PP blend challenging. At 200 °C, stable melt spinning process was achieved and good quality yarns were produced. The mechanical tenacity of SPEEK/PP 5:95 yarns was approximately 20% lower than that of otherwise similar PP yarns.