Polyamide 6 fibre recycling by twin-screw melt extrusion of mixed thermoplastic polymers

Textile wastes consist of multi-component materials are hardly recycled due to challenge to sort and separate the waste into a single component. Textile products dominantly produced from a non-renewable source that can be recycled several times before the end of life. Mixed-waste can be recycled together without sorting by thermo-mechanical process to produce hybrid fibres. The aim of this study was to investigate the potential on upcycling polyamide 6 (PA6) polymer mixed with secondary polymers via one-step twin-screw melt extrusion. Three secondary polymers were chosen in this study; thermoplastic polyurethane (TPU) which has interaction with PA6, and two polymers which do not have interaction with PA6; polyethylene terephthalate (PET) and polypropylene (PP). Different blending composition was prepared between PA6 and secondary polymers before being extruded into hybrid fibres through melt extrusion. The secondary polymers were then removed from the hybrid fibres to investigate the properties of the leftover of PA6 component. The fibres were characterised using attenuate total reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and microscopy techniques, the mechanical and thermal properties were investigated via tensile strength and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results showed that the blending of PA6 with interacting polymer TPU creates novel fibres morphology with multi-connected porous fibres. The mean diameter of PA6:TPU hybrid fibres when the PA6 content at 50% and 80% are 136 and 126 µm, respectively. Thermal and chemical results demonstrated strong interaction happen between PA6 and TPU. Meanwhile, the co-extrusion of PA6 with non-interacting polymer PP and PET formed PA6 micro and nanofibres in the blend, respectively. In PA6:PP blend, the SEM images show the PA6 microfibres with mean diameters of 0.76 µm and 1.13 µm developed in the hybrid fibres with PA6 content 50% and 60%, respectively. The phase inversion between PA6 and PP happened at the composition of 65% of PA6 showing the development of PA6 microfibres in a unique fibre morphology. In PA6:PET blend, PA6 nanofibres with mean diameter of 532 nm to 1026 nm were obtained. The diameter of PA6 nanofibres increase when PA6 content increase in the blend. Later, single jersey knitted fabric was produced from PA6:PP 60:40 blend composition and was treated later to remove the PP component. The treatment process exposed the development of PA6 microfibres fabric which has excellent behaviour in wicking and improved in ball burst strength compared to the untreated fabric. The success of upcycling PA6 fibres with value added properties through single-step melt extrusion can be applied to other mixed polymer waste.