Study On The Deep-dyeable Sea-island Polyester Fibers

The dyeing rate and the apparent color depth (K/S value) of polyester fibers are low, so thecolor style and performance of its products are restricted. Study on the microstructure of polyestershows that PET has high degree of crystallinity and compact structure, so it is difficult for dyemoleculars to penetrate into the fibers, which makes it hard to be deep-dyed. Besides, PETmolecular chain is lack of functional groups. The degree of crystallinity of sea-island polyesterfibers is higher than conventional polyester fibers and its microstructure is more compacted due toits ultrafine features. The dye moleculars can only enter into the fiber under high temperature andhigh pressure. For these reasons, the issue of sea-island polyester fiber deep-dyeable modificationwas put forward.As a common method of the polymer modification, blending modification is more suitablefor industrial production due to its simple operation, low cost, as well as easily preparation of arange of products by changing the blends ratio.This research used blending modification toimprove the dyeability of sea-island polyester fibers. The sea-island polyester fibers wereproduced by melt spinning through adding Easy Cationic Dyeable Polyester(ECDP), CationicDyeable Polyester(CDP) to the island of polyethylene terephthalate (PET) at a certain amount.Firstly, the pre-oriented yarn (POY) of sea-island polyester was produced with differentisland components. The fiber forming process was explored mainly by adjusting proportion of thesea-island components, spinning temperature and winding speed. The cross section of sea-islandfiber was observed by polarizing microscope. Results showed that the boundary between the seaand the island was clear. Besides, the sea-island POY was used for characterization for denier,strength and orientation. The denier of POY was126dtex. The elongation at break of sea-islandPOY was140%and its tensile strength at break was1.8cN/dtex. The tensile strength at break ofsea-island polyester POY decreased with the increasing of ECDP and CDP in the islandcomponents. Meanwhile, the draw texturing yarn (DTY) was produced. The DTY was also usedfor characterization for denier, strength, boiling water shrinkage and orientation. The denier ofDTY was115dtex. The elongation at break of DTY was22%and its tensile strength at break was3.0cN/dtex. The boiling water shrinkage of sea-island DTY was25%. The sound velocity value ofsea-island POY was1.6km/s and its sonic velocity orientation factor was0.3. The sound velocityvalue and its sonic velocity orientation factor decreased with the increasing of ECDP and CDP inthe island components. The sound velocity value of sea-island DTY was2.1km/s and its sonic velocity orientation factor was0.6.Secondly, the splitting of sea-island DTY was studied. The effect of alkaline cleaning wascharacterized by weight loss rate. Results showed that the optimal conditions of alkaline cleaningfor ECDP/COPET fibers were as follows:1wt%NaOH solution,100℃,30min and bath ratio1:20,and for CDP/COPET fibers were:2wt%NaOH solution,100℃,30min and bath ratio1:20. Thesurface morphology of fabric was observed by SEM after alkaline cleaning. The sea-island DTYformed superfine fiber and its diameter was2μm without adhesions occuring between single fibers.Besides, the surface of superfine fiber was smooth. After dyeing, the K/S value and the colordifference of standard color gray card for fabric had increased with the increasing of ECDP andCDP in the components of island, showing that adding ECDP and CDP into the components ofislands can obviously improve the dyeability of fiber. The dyeing depth of ECDP/COPET fibricwas higher than the CDP/COPET when the content of the ECDP was the same as CDP in inlands.As the content of the ECDP or CDP was50%in islands, the standard gray card series of cation-sea-island fibric was3.0meeting its deep-dyeable effect.Finally, the dyeing mechanism of sea-island polyester fibers was studied.The glass transitiontemperature and degree of crystallinity of sea-island DTY were analyzed by differential scanningcalorimeter instrument. Results showed that the fiber dyeability was improved due to thedecreasing of the glass transition temperature and crystallinity.