Preparation And Characterization Of PA/PU Eccentric Sheath-core Composite Filaments

Eccentric sheath-core composite fiber have a wide application in the fields of stockings,bedding,plush toys,sports wear,etc.Because of asymmetric distribution on cross section by two components and differences of performance and structure,eccentric sheath-core composite fiber have curled up after drafting process and heat treatment.The components of eccentric sheath-core composite fiber are mostly PET and PA,and specifications are mainly porous and coarse denier according to the current studies.Effects of components selection,preparation process and performance evaluation of eccentric composite fiber were studied systematically,to prepare elastic,frivolous and close skin products used in high-grade tights,underwear,etc.In this paper,PA and PU were employed as raw materials to prepare eccentric sheath-core composite filaments by melt spinning.Molecular structures,thermal properties and rheological properties of PA and PU were studied systematically.And mechanical properties,morphology,thermal shrinkage and crimp properties were investigated deeply.The results could provide a certain reference for the product development,production and industrialization.Molecular structures,thermal properties and rheological properties of PA and PU used as raw materials were studied through a seriYes of characterization methods like FT-IR,H-NMR,DSC,TG,Melt Flow Index Meter,Capillary Rheometer,and Rotational Rheometer.The experimental results show that,PU is mainly constituted of polyester polyurethane with a small content of polyether polyurethane.PA6 is a kind of crystalline polymer,its thermal stability is better than that of PU,which is an amorphous polymer.The relative viscosity of PU sharply decreases after heat treatment,which is mostly ascribed to thermal degradation.Rheological properties testing results show that rheological properties of PU are better than PA6.PA6 and PU are typical non-Newtonian fluid.Rotational rheometer test show the degradation of complex viscosity for PU at temperature of 260 ℃ is much fiercely with the extension of time than that at temperature of 230 ℃.It is necessary to control resident time of melt and spinning temperature strictly.Several kinds of UDY or DY of PA/PU eccentric sheath-core composite filaments were prepared.The mechanical properties,morphology,orientation and crystallinity were studied through a series of characterization methods.Composite spinning packs were designed based on the rheological properties of PA and PU.Thus obtained composite filaments show uniform monofilament linear density.Spinning process parameters are important for the preparation of composite filaments.PA/PU(50/50)filaments can be continuously spinning at 265 ℃.With the increase of the denier,the spinnability of composite filaments is improved,while the tensile strength is decreased and elongation at break is increased.With increasing draft ratio or decreasing heat setting temperature,the tensile strength is increased and elongation at break is decreased with the increase of orientation and crystallinity.Effects of drafting process and heat treatment(heat treatment temperature and time)on thermal shrinkage and crimp properties of PA/PU eccentric composite filaments were investigated via shrinkage ratio,morphology of crimp,crimp ratio,crimp modulus,and crimp stability.The results showed that shrinkage ratio of PA/PU eccentric composite filaments increase with higher drafting ratio,higher heat treatment temperature,longer heat treatment time or lower heat-setting temperature,which is similar to the change of crimp properties.Crimp ratio,crimp modulus,and crimp stability of PA/PU eccentric composite filaments reach 21.3 %,7.9 %,89.5 % after heat treated at 140 ℃ for 10~20 min,respectively.This work could contribute to the similar filaments treatment in commercial application.