Abstract

Using dynamic mechanical analysis (DMA), we investigate differences in
the mechanical properties of a single-filament wall of polyether ether ketone
(PEEK) constructed using fused filament fabrication (FFF) under a range of
different printing conditions. Since PEEK is a semi-crystalline polymer, we
employ a non-isothermal quiescent crystallization model, informed by infrared
(IR)-imaging measurements, to understand our findings. We propose that,
under typical FFF cooling conditions, the weld region between filaments remains
amorphous. In contrast, the core of the filament has increased time above
the glass transition temperature allowing for a signifocant crystal fraction to
develop. We correlate the predicted crystal fraction to a storage modulus using
the Halpin and Kardos model. With only a single model fitting parameter we can
make reasonable predictions for the perpendicular and parallel storage moduli
measured via DMA over a range of printing conditions. This work provides a
foundation for optimising crystallization for the mechanical performance of the
FFF printed PEEK.