High Performance Polyamide 6 Fibers Using Polycarbonate Based Thermoplastic Polyurethane Thin Film Coatings- a Novel Method

Polycarbonate based thermoplastic polyurethanes (CPU2) were prepared and coated onto polyamide 6 (PA 6) fibers. The CPU2 thin film coatings were prepared by dipping the PA 6 fibers into a viscous CPU2 adduct and cured at 100 °C for 12 h. Both the tensile strength and the elongation at break of the CPU2 thin film coated PA 6 fibers (CPU2-PA6) increased although both the magnitudes of CPU2 are much lower than for the original PA 6 fibers. FE-SEM observation revealed that there existed an interface interaction region of 10 μm at the interface of PA 6 fiber and the CPU2 thin film coating. Generally speaking, it is considered that the break of PA 6 fibers is due to the formation of the micro-cracks on the fiber surface when it is under a tensile load. The coating of CPU2 onto the PA 6 fibers reduced the formation of micro-cracks during the elongation process, resulted in the improvement of the mechanical properties. Also, the CPU2-PA6 fibers when exposed to weathering tests to check the weathering resistance, showed an increase in the tensile strength for 0–50 h of exposure. This was due to the UV light induced crystalline transformation, i.e., from the α crystalline phase to the γ crystalline phase. The CPU2-PA6 fibers almost retained the strength even after 200 h of exposure in a weatherometer. The crystalline transformations due to the UV irradiations have not been reported yet. Also, the CPU2 showed good adhesion property with the PA 6 films. The blending with various polymers or composites is generally employed for the performance enhancement of PA 6 fibers. On the contrary, the method employed in this study improved the performance of PA 6 fibers without changing its inherent morphological properties.