Structure And Properties Of Lyocell Fiber From High Hemicelluloses Pulp

Cellulose derives from trees, cottons, hemps and other plants. Since Anselme Payen successfully made cellulose from wood, wood had become another popular cellulose material_Cellulose can be used to make viscose fiber, which has been industrialized since the beginning of the 20th century. However, viscose fiber process pollutes environment and is harmful to health. Therefore, its development has bottlenecked.Lyocell fiber is a regenerated cellulose fiber manufactured by means of precipitating of cellulose from cellulose and N-methlymorpholine-N-oxide aqueous solution (NMMO/H₂O). In contrast to conventional viscose process, Lyocell technology is a relatively simple and environmentally friendly way to produce regenerated cellulose fibers. Therefore, Lyocell fiber has attracted great attention in the textile field of the world since it was developed in the middle of 1970s. However, production of Lyocell fiber has bottleneckedsince its production cost is higher.Today, in Lyocell fiber process, it is still following the conventional viscose process i.e. employing high alpha-cellulose pulp to produce Lyocell fiber. This kind of pulp contains more than 90% alpha-cellulose. The high content of alpha-cellulose is to guarantee a high yield of fiber in the conventional viscose process. In addition, production of high alpha-cellulose pulp needs higher cost.On the other hand, a cheap (low alpha-cellulose) pulp, in which its alpha-cellulose content is lower than 90% but hemicelluloses content is higher than 10%, is called high hemicelluloses pulp.In our work, it was found that Lyocell fiber could not only be made from high alpha-cellulose pulp, but also could be made from high hemicelluloses pulp. And the yield of Lyocell fibers from high hemicelluloses and high alpha-cellulose pulps was approximately same, since most low molecular weight (MW) cellulose and hemicelluloses could be converted to Lyocell fiber.In this thesis, structure and properties of Lyocell fibers from high-hemicelluloses and high-alpha-cellulose pulps were compared.Fibrillation resistance of high hemicelluloses Lyocell fiber is better than that of high alpha-cellulose Lyocell fiber, since the fibril aggregate of former has smaller size and more stable structure than that of latter. Dyeing property of high hemicelluloses Lyocell fiber is also better thanthat of high alpha-cellulose Lyocell fiber. The reason are on one side, crystallinity of former is slightly lower than that of kitter, on the other side, accessibility and low molecular weight composition of former is a little higher that of latter.Tensile strength of high hemicelluloses Lyocell fiber is a little lower than that of high alpha-cellulose Lyocell fiber when these fibers are spun at the same cellulose content and spinning speed, but mechanical properties of high hemicelluloses Lyocell fiber are improved and even comparable to those of high alpha-cellulose Lyocell fiber when a higher cellulose content spin dope is used since high hemicelluloses spinning solution can be processed at higher cellulose content. Besides, a higher yield of Lyocell fiber is obtained when a higher cellulose concentration spin dope is used.Orientation of high hemicelluloses Lyocell fiber is slightly higher than that of high alpha-cellulose Lyocell fiber. It is due to the cellulose molecules are more easy to be orientated in Lyocell fiber formation process when high hemicelluloses spin dope. Crystallinity of high hemicelluloses Lyocell fiber is a little lower than that of high alpha-cellulose Lyocell fiber, since hemicelluloses have been suggested to be intimately integrated into the structure of the cellulose.These works showed that a cheap (high hemicelluloses) pulp could also be used as raw materials for producing Lyocell fiber.