Influence of the physical process parameters on the structure formation of lyocell fibres

The paper studies the influence of the draw ratio, fibre diameter and line speed on the structure formation during spinning of lyocell fibres, spun from a solution of cellulose in N-methylmorpholine-N-oxide. The evolutions of the filament diameter and orientation were measured, the relationship of orientation to drawing was determined and the structure and properties of the resulting fibres were studied. It was found that the draw profile of the filament in the air gap is controlled by the volumetric flow rate of the polymer solution. The relationship between the birefringence and the dimensionless velocity indicates the existence of chain slippage for high draw ratios. The birefringence of the dry fibre depends only slightly on the pre-bath birefringence except for highly unoriented fibres. With a 100 mu m spinneret, a draw ratio barely above 5 allows sufficient orientation of the macromolecules to give a highly oriented fibre.