Suitable dissolving pulps and their impacts on solution spinning of cellulose man-made fibers

Fiber demand and production of man-made cellulose fibers (MMCFs) such as Viscose rayon, Modal and Lyocell fibers have been increasing in recent years. Today they are mostly manufactured using wood dissolving pulps. However, the growing fiber demand cannot be satisfied by dissolving pulps from wooden sources only. So, alternative pulps, also based on non-wooden materials, are needed. In this study, novel pulps, namely hemp and oil flax from biogenic residues, untreated and enzymatically treated paper pulps and recycled cotton waste, were investigated and compared to wood dissolving pulps and used for application in Lyocell dissolution and solution spinning procedures using N-methylmorpholin-N-oxide. As a function of degree of polymerization (DP), molecular weight distribution (MWD) and polydispersity (PDI), three groups of pulps with distinct characteristics could be identified. Paper pulp offered the highest DP and PDI values and the broadest MWD. Properties similar to those of wood dissolving pulps could be achieved by an enzymatic treatment. Pulps from biogenic residues exhibited a different behavior. Hemp shives-based pulp held properties comparable to wood dissolving pulps. In contrast, fiber-based oil flax and hemp pulp possessed low PDI values and tight MWDs more comparable to pulp made from recycled cotton fibers. Pulp characteristics were also found to affect the rheological behavior of spinning solutions prepared from these pulps. In summary, suitable dissolving pulps have specific impacts on solution spinning of MMCF. A careful analytical characterization by means of molecular and rheological approaches is mandatory before using a pulp in fiber spinning activities.