Comparison of molecular orientation and mechanical properties of lyocell fibre tow and staple fibres

Abstract

Samples of lyocell fibres were taken in the form of filaments from fibre tow of potentially infinite length and in their final condition of staple fibres. Mechanical testing showed comparable tensile strength, but a 50% lower modulus of elasticity for staple fibres and a higher elongation at break compared to filaments from fibre tow. Structural investigation by means of synchrotron wide angle X-ray scattering and birefringence measurement revealed a significantly lower degree of preferred orientation together with less fibre straightness for staple fibres than for filaments. It is concluded that plastic deformation during the processing of staple fibres from filaments induces permanent changes in the orientation of cellulose chains in the fibres, which in turn is responsible for the observed differences in mechanical performance.

Influence of process parameters on the structure formation of man‐made cellulosic fibers from ionic liquid solution

“…The birefringence, Δ n , of the fibers was obtained by dividing the retardation of the polarized light by the thickness of the fiber which was calculated from the linear density using a cellulose density value of 1.5 g/cm 3 . The total orientation factor f t was determined by dividing Δ n by the maximum birefringence of cellulose 0.062 …”

Renewable High‐Performance Fibers from the Chemical Recycling of Cotton Waste Utilizing an Ionic Liquid

“…Birefringence is defined as the retardation divided by the diameter,a nd av alue of 0.062 was assumed to be equivalent to 100 %orientation. [59,60] Solid-state NMR spectroscopy…”

Ionic Liquids for the Production of Man-Made Cellulosic Fibers: Opportunities and Challenges

“…The birefringence Δn of the specimen was obtained by dividing the retardation of the polarized light by the thickness of the fiber, which was calculated from the linear density (titer) using a cellulose density value of 1.5 g/cm 3 [127]. The total orientation factor f t was then derived by dividing Δn by the maximum birefringence of cellulose, 0.062 [128,129]. A factor f t ¼ 1 means perfect orientation parallel to the fiber axis, f t ¼ 0 for random orientation, and À1 for perfect transverse orientation.…”

“…3.2.2, the crystalline and total orientation of the fibers developed quickly with increasing draw. Because the tensile strength is connected to cellulose crystalline structure, this is directly reflected in the resulting tenacity values [128]. Even at small draw ratios the tenacity increased notably, reaching NMMO-based Lyocell values of 40 cN/tex at medium draw ratios of 4.8.…”