| With a large number of hydroxyl and a high crystallinity, Ethylene/vinyl alcohol copolymer(EVOH) has been found to possess an excellent blocking performance hence used in packing materials field widely for a long time. Moreover, owing to the convenience of functionalization of hydroxyl, the application range of EVOH expands quickly in recent years. However, as a result of hydrogen bonding between the hydroxyl groups, EVOH melt shows a high viscosity whereas a low fluidity, difficult to form fiber. In this paper, the melting fluidity of EVOH has been improved by adding the chemical degradation masterbatch for the sake of melt spinning process. Furthermore, the sheath-core composite fibers were prepared from the modified EVOH and PA6, and the mechanical, moisture absorption and dyeing performance of composite fibers were investigated.Firstly, the chemical degradation masterbatch were prepared by melt mixing polypropylene with 1.5% or 2% of tertiary butyl peroxide respectively, and the latter was chosen as final modifier by analyzing the result of melting flow index tests for the blends of various proportion of masterbatch and EVOH. It has also been found that the blend of EVOH and 10% of modifier showed a fairly good spinnability from the spinning experiments for EVOH with 5%, 10% or 15% of chemical degradation masterbatch. Then the modified EVOH was prepared by coextruding pure EVOH and 10% of modifier. The results of DSC and TG tests showed that the addition of chemical degradation masterbatch impacted little on the melting point and crystallization temperature of EVOH, whereas slightly depressed its degradation temperature. It has also been found from the capillary rheological testing that the modified EVOH showed a kind of temperature sensitived pseudoplastic fluidity.In order to retain the excellent hygroscopic, dyeing and easy functionalization performance of EVOH and to enhance its mechanical properties, polycaprolactam(PA6) has been chosen as core portion as well as EVOH or modified EVOH as skin portion to make sheath core composite fibers, bcause its strong binding force with EVOH, great mechanical properties and similar flow performance parameters. During the spinning process, the sheath-core ratio was set as 3:7 and the spinning temperature was about 260?. It has been found that the pure EVO H/PA6 system was rather difficult to form fiber, however the modified EVOH/PA6 could be spun smoothly under a winding speed of 600 m/min. The modified EVOH/PA6 as-spun fibers could be drafted for 3~3.2 times with the convention technique but the pure system should be drawn in hot water under a low speed, getting a 4 times of extension. From the microscope observation of the fiber cross section, the sheath-core stripping could been found in pure EVOH/PA6 samples, which became even more serious after drafting. However, the modified EVOH/PA6 samples maintained a tight coupling throughout. The XRD curves of those fibers showed that the addition of chemical degradation masterbatch could inhibit the crystallization of EVOH, therefore, the relative portion of diffr action intensity of EVOH was found to fail in within the composite system. After drafting, the crystalline form of PA6 was changed from ? singlet into ? doublet and the peaks overlapped with that of EVOH, resulting in a wider diffraction curve. The results of tensile testing showed that the modified EVOH/PA6 composite fiber promised enough mechanical strength for post processing, though its elongation at break was still larger originated from insufficient drafting.The hygroscopicity investigation indicated that the hygroscopic rate of modified EVOH/PA6 composite fiber could run up to 3-4%, showing a fast absorbing & quick drying property that could not be found in unmodified ones. The composite fibers could be successfully infected with both reactive dyes and acid dyes, and the former showed high color fastness while the latter showed good through dyeing. |
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