Kinetics of Precipitation of Cellulose from Cellulose−NMMO−Water Solutions

Abstract

The regeneration of a solid, crystallized cellulose solution in a N-methylmorpholine-N-oxide (NMMO)-water mixture was studied by measuring the diffusion coefficient of both the water uptake from the regenerating bath and the NMMO outflow to this bath. The diffusion coefficient of water going to the cellulose solution is about 10 times larger than the diffusion coefficient of NMMO leaving the solution. This difference expresses the strongly hygroscopic character of NMMO. None of these coefficients depends on cellulose molecular weight showing that no major rearrangement of cellulose chains occurs at the beginning of the regeneration. The diffusion coefficient of water is not influenced by the cellulose concentration, whereas the diffusion coefficient of NMMO decreases strongly when the cellulose concentration increases. Extrapolating the diffusion coefficient of NMMO versus cellulose concentration to zero shows that the maximal concentration of cellulose in NMMO-water is about 15%. Above this value, undissolved cellulose should be present. From the influence of the NMMO content in the water regenerating bath, it is possible to see that NMMO is removed from the solution if the bath has a NMMO content lower than 60%, to be compared with the 80% NMMO concentration in the solution.

Morphology of cellulose objects regenerated from cellulose–N-methylmorpholine N-oxide–water solutions

“…From Biganska and Navard (2005) Cellulose (2009) (Biganska et al 2002) that it is the solvent which is crystallizing. This is leading a variety of morphologies like large spherulites.…”

“…Cellulose-NMMO-water solutions were prepared in the R&D department of the Austrian company Lenzing AG using the method described previously (Biganska and Navard 2005). Several cellulose pulp samples and different cellulose concentrations were used in this study in order to describe the influence of these parameters on the morphology of regenerated solutions.…”

“…Rapid growth of finger-like voids in the fluid region under the skin occurs due to the moving interface created by the coagulant (less viscous) and the solution (more viscous). Measurements of the coefficients of diffusion of NMMO solvent from the solution into the bath and of the coagulant from the bath into the solution (Biganska and Navard 2005) show that the inflow of the coagulant is one order of magnitude higher than the outflow of the solvent. This result is in agreement with the fact that the formation of a fingerlike structure is favoured when the non-solvent enters the sample more rapidly than the solvent exits from it (Shen and Cabasso 1982).…”

“…The main objective of this work is the investigation of the morphologies of regenerated cellulose-NMMO-water solutions as a function of various parameters of both cellulose solutions and coagulation baths. These observations will be linked to the knowledge of the regeneration kinetic parameter obtained before (Biganska and Navard 2005).…”

Coagulation studies of cellulose/NaOH/thiourea/urea/H2O fiber spinning system

“…The explanation of the square root of time relationship which appears in the boundary movement is based on Fick's diffusion law [10,11] Ziabicki [8] had modelled the theory of diffusion with a moving boundary in wet-spinning by assuming a linear, one -dimensional system containing component 'b' into which diffuses the other component 'a' from outside and instantaneously reacts with 'b'. We shall consider first a diffusion coefficient in which a discontinuity occurs at each layer.…”