Study of the microstructure formation mechanisms of poly(ether-ether-ketone) monofilaments via melt spinning

The microstructure formation mechanism of melt-spun Poly(ether-ether-ketone) monofilaments during poststretching was investigated using in-situ wide-angle X-ray diffraction in combination with polarizing microscopy, differential scanning calorimetry and universal testing machine. As PEEK monofilaments were stretched at 210°C, the crystallinity and microcrystal size first increased during the insulation state (Is-S), then decreased during the poststretching state (Ps-S), and further increased during the postcooling state (Pc-S), at last were observed to selective orientation. At 210°C, the anisotropically aligned molecular chains reach a meritocratic orientation in the stress direction under 4.0 times drawing conditions, resulting in the highest tensile strength and modulus. As the stretching ratio increases, the crystallinity and microcrystal size first increase during Pc-S and then decrease due to the effect of the stretched molecular chains on crystal growth and the degree of tearing in the crystalline region. The molecular chains of PEEK monofilaments stretched by uniaxial stress are aligned more flatly and uniformly along the fiber axis. We hope that this work will provide advice and guidance for the industrial production of high-performance fibers.