Abstract
This study investigates melt spinnability of ethylene vinyl alcohol (EVOH) copolymers with various ethylene contents, which exhibits excellent biocompatibility but cannot easily undergo single-component fiber spinning. The chemical, thermal and rheological properties of EVOH were examined herein. Three EVOH copolymers, EV-32, 38 and 44, with different ratios of ethylene to vinyl alcohol (EV ratio), were used to evaluate the influence of the ratio on melt spinnability. The EV ratios of EV-32, EV-38 and EV-44 examined by nuclear magnetic resonance were 0.64, 0.82 and 1.0, respectively. The experimental results reveal that the melting temperature (Tm) and crystallinity (Xc) of EVOH decreased in the order EV-32 (178.9℃, 46.6 wt%) > EV-38 (171.9℃, 41.8 wt%) > EV-44 (166.0℃, 40.0 wt%). The thermal stability, however, increases in the order EV-32 < EV-38 < EV-44. The viscosity decreases in the order EV-32 > EV-38 > EV-44. EV-44 has much higher flow activation energy than EV-32 and EV-38, indicating that it has a temperature sensitivity higher than EV-32 and EV-38. The pellets of EV-32, EV-38 and EV-44 were melt spun. Three as-spun fibers, EV-32, EV-38 and EV-44 have cross-sectional diameters of 151.3, 150.9 and 154.1 µm and tensile stresses (strain (%) at breaking point) of 123.1 (205.2%), 121.4 (202.0%) and 131.1 MPa (180.2%), respectively. Most importantly, EV-44 can easily be spun at a relatively low temperature, 245℃, while the other two, EV-38 and EV-32, can hardly be made on condition that the spinning temperatures are higher than 255℃ and 265℃, respectively. Notably, once the spinning temperature of EVOH polymers was higher than 258℃, the degradation of vinyl alcohol segments would cause fuming and broken filaments to eventually terminate the entire spinning process. Ultimately, a brand new fiber, EVOH, with an EV ratio of 1.0, was successfully melt spun and mechanically characterized in this study.
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