The Impact Of Reactive Dyes On The Fibrillation Properties Of Lyocell Fibers

Lyocell fabrics are dyed with different types of reactive dye and with different dyeing processes. Then discussed how dyeing processes and dyes influence on fibrillation. And we use some analytical instruments to examine the results right.Among dip dyeing process, pad-cure dyeing process, pad-stream dyeing process, cold pad-batch process and beam dyeing process, we found cold pad-batch process have special effect on reducing fibrillation. This is because during the cold process with long time treatment of alkali of high concentration, fiber is swollen. Then the chain segment can move and rebuild a more stable equilibrium, which made the fibrillation tendency reduced. This can be demonstrated by infrared spectroscopy.Different types of active dye show different effect on fibrillation because of the difference of dyeing processes. In the dip dyeing process, some MCT/VS bi-functional dyes have some effect on restraining fibrillation because dyes are easy to diffuse to fiber inside. Then these dyes' chances to form cross-linking increase. But if using cold pad-batch process, these dyes can't restrain fibrillation fairly in that they have large configuration. So they can't diffuse into fiber easily and then react with cellulose molecule outside of the fiber and form a small quantity of cross-linking, which prevent the fiber from swelling.In the experiment we found reactive dyes can be divided into three categories according to their influence on fibrillation: the first category we call it A dyes, they do not have good effect on restraining fibrillation when the dye concentration is low, however, they have evident effect when the concentration is high. This category includes MCT/VS bi-functional dyes and Rective Black KN-B and so on. When dye's concentration is low, dye can form few cross-linking; at the same time dye molecule's dimensional size is big which will reduce the crosswise force among fibril. So they can't restrain fibrillation well. When the dye concentration increase, cross-linking amount increase that make fiber good effect on reducing fibrillation. The second category we call it B dyes. These dyes have few effect on restraining fibrillation, at least don't accelerate fibrillation.. They mainly are some bi-functional KE type dyes and some mono-functional dyes. Some mono-functional dyes can form hydrogen bond and van der Waals force with fiber macromolecules because they have good planar character; so can form "cross-linking". And KE type bi-functional dyes that have two reactive groups can form cross-linking with fiber. So they have some effect on restraining fibrillation, at least don't promote fibrillation. The third category we call it C dyes. These dyes don't have effect on reducing fibril. They are mostly some mono-functional dye, which can't form cross-linking. In the meantime, Dyes' influence on fibrillation also depends on the spatial configuration of functional groups in dye molecule and the distance between functional groups, also depends on the flexibility.This paper also inspects different dyeing process' effect on stiffness of Lyocell. And found Lyocell by dip dyeing process or cold process is much more flexible, and by pad-cure process or beam process is much more stiff.In the experiment, we find a proper method to value fibrillation tendency, a special wet rubbing method by sand. This method need less time and can get even measurable fibril, and can effectually imitate washing process in reality. Then evaluate the fibrillation degree by color difference.