| Poly(trimethylene terephthalate), PTT, is a recently developed polyester combined with the good flexibility and elasticity of polyamide (PA) and the chemical stability of poly (ethylene terephthalate) (PET). Besides these competitive properties compared to traditional polyester, with the process development and piloting of a bio-based form of 1,3-Propanediol (PDO), it opens more opportunities to create eco-friendly products to meet the green industry transition.Large diameter polymer monofilaments with diameters range from 0.08mm to 5mm are produced by melt-spinning method. The forming process of large diameter polymer monofilament outstands itself from conventional forming process to produce staple fibers and conjugated filaments by successfully using steps like single-hole high-capacity polymer melt extrusion, liquid cooling and multi-step drawing. The large diameter polymer monofilaments have excellent mechanical properties and have been widely used in engineering industry. Herein, large diameter PTT/PET skin-core composite monofilaments were produced by melt spinning method, using PTT as sheath and PET as core. The effect of bicomponent disposition, spinning process conditions, draw process and heat treatment on the structure and properties of the obtained composite monofilament were studied. This shall provide guidance to future produce of large diameter PTT/PET skin-core composite monofilaments with different properties.In this study, large diameter PTT/PET skin-core composite monofilaments were produced by one step melt spinning-drawing method with a certain component ratio. The rheological behavior of PTT resin and PET resin was investigated to discuss the spinnability of obtained large diameter PTT/PET skin-core composite monofilaments. Besides, the impact of the spinning temperature and cooling conditions on its spinnability and properties were also studied and discussed. The influence of cooling conditions to the structure change and property difference was emphasized in the discussion.As-spun fibers can only reach the requirement of textile processing after drawing. It is necessary to study the drawing temperature, drawing medium and draw ratio to optimize the process. In this research, water bath and air were chosen as the first and second draw medium with the drawing temperature of 85℃and 180℃separately. To obtain composite monofilaments with reinforced strength, different drawing ratios were investigated in an increasing manner. The result shows that the optimum total drawing ratio is 5, while the first drawing occupied 80%. Under this condition, composite monofilaments with breaking strength of 5.0 cN/dtex and breaking elongation 20.2% were obtained. The morphology study of the breaking cross section by scanning electron microscopy (SEM) demonstrates that during the composite monofilament rupture, the fracture of PTT component happened before the PET component. This shows that the overall mechanical property of the obtained composite monofilament is dominated by the PET component.Large diameter PTT/PET skin-core composite monofilaments produced from different component ratios of 40/60,50/50 and 60/40 under the optimum spinning and drawing conditions were studied. Detailed studies were discussed in the dissertation including the mechanical property, orientation, thermal property, elastic recovery property and thermal shrinkage property. The results show that with the increase of PTT component, the breaking strength and the orientation degree decrease, while the breaking elongation and the elastic recovery ratio increase. Under any specified elongation testing condition, the elastic recovery ratio of obtained composite monofilaments was between the ones of the PET and PTT filament. The SEM characterization of the cross sections of as-spun and drawn composite monofilaments shows that the PTT and PET have great compatibility in the composite; the interface of the two in the composite monofilaments is more obvious after the treatment of drawing and heating. |
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