Showing papers on "N-Methylmorpholine N-oxide published in 2002"

Cellulose solutions in N-methylmorpholine-N-oxide (NMMO) – degradation processes and stabilizers

Abstract: Efficient stabilization of cellulose solutions in NMMO(1) against side reactions and their harmful effects meansprevention of both homolytic and heterolytic side reactions, which is mainlyaccomplished by trapping radicals, formaldehyde, andN-(methylene)iminium ions (5). Whileradical trapping is commonly reflected by the antioxidativeefficiency, the effectivity against heterolyticdegradationin the Lyocell dope can be expressed by the newly introduced term‘formaldehyde trapping capacity’ (FTC). Propyl gallate (PG,4), the most widely applied Lyocell stabilizer nowadays, actsas a phenolic antioxidant, and is finally oxidized to a deeply colored, highlyconjugated chromophore (11) via ellagicacid (10). It was demonstrated that 4 is alsoa quencher of formaldehyde and N-(methylene)iminium ions,both in organic solutions of NMMO and in Lyocell dope. The processes of radicaltrapping and scavenging of HCHO/5 are competitive in the caseof propyl gallate. A novel oxa-chromanol derivative, PBD (14),was designed as stabilizer for Lyocell solutions. In analogy to propyl gallate,PBD acts as a scavenger of all three dangerous species, namely HCHO,5 and radicals. Upon oxidation by radical species, PBDreleasesacetaldehyde which acts as a very efficient HCHO trap. Thus, in contrast topropyl gallate, radical trapping and HCHO trapping are not competitive. Boththeantioxidative efficiency and the capacity to trap HCHO and 5are higher for PBD as compared to propyl gallate. In preliminary stabilizertesting, mixtures of PBD and PG proved to be especially effective.

Hemodialysis membrane prepared from cellulose/N‐methylmorpholine‐N‐oxide solution. I. Effect of membrane preparation conditions on its permeation characteristics

Abstract: Flat hemodialysis membranes were prepared from cellulose/N-methylmorpholine-N-oxide (NMMO) solutions (dope) with different cellulose concentrations (6–8 wt %) by using a phase-inversion method. The coagulant used was NMMO aqueous solution, of which the NMMO concentration and its temperature were varied in the range of 0 to 50 wt % and 5 to 60°C, respectively. The effects of these preparation conditions on the permeation characteristics, the ultrafiltration rate (UFR) of pure water, and sieving coefficient (SC) of dextran, were investigated. The decrease in cellulose concentration of the dope and the increases in both temperature and NMMO concentration of the coagulant gave a membrane with high UFR. Concerning the SC, the increase of the cellulose concentration and the decreases in both temperature and NMMO concentration gave a good result. Consequently, the membrane having the preferable UFR and SC as a hemodialysis membrane was obtained when the 8 wt % cellulose dope was coagulated in water at 5°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2302–2307, 2002

Modified cellulose fibers prepared by the N‐methylmorpholine‐N‐oxide (NMMO) process

Abstract: Cellulose fibers with modified properties have been prepared from cellulose solutions in N-methylmorpholine-N-oxide (NMMO). Poly(ethylene oxide) as a hydrophilic modifier and polyethylene as a hydrophobic modifier were added to the spinning solution. Based on microscope examination and measurements of such properties of fibers as porosity, moisture absorption, water retention, and tensile strength, structural changes as well as physical and mechanical properties of the resultant fibers depending on the amount of modifier added to the spinning solution were analyzed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 907–916, 2002

Atomic force microscopy of cellulose membranes prepared from the N‐methylmorpholine‐N‐oxide/water solvent system

Abstract: Cellulose membranes were obtained by solutions of cellulose being cast into a mixture of N-methylmorpholine-N-oxide (NMMO) and water under different processing conditions. Atomic force microscopy (AFM) was used to investigate the surface structures of the membranes. The AFM method provided information on both the size and shape of the pores on the surface, as well as the roughness of the skin, through a computerized analysis of AFM micrographs. The results obtained showed that the surface morphologies were intrinsically associated with the permeation properties. For the cellulose membranes, increasing the NMMO concentration and the temperature of the coagulation bath led to higher fluxes and lower bovine serum albumin rejection. These were always correlated with higher values of the roughness parameters and larger pore sizes of the membrane surfaces. When the cellulose concentration of the casting solution was 11 wt %, the membrane showed a nodular structure with interconnected cavity channels between the agglomerated nodules. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3389–3395, 2002

Preparation of novel alpha-cellulose membranes and studies on their performances

Abstract: Novel a-cellulose membranes were prepared by using amine oxides as solvent. The mechanical performance, liquid permeation rates and the chemical resistance of the membranes were investigated. The tensile strength of the a-cellulose membranes can be up to 133.3 Mpa and 30% similar to 60% stronger than the cellulose membranes prepared from other methods. The retentate ratio of bovine serum albumin of the a-cellulose membranes can be up to 98%, and the liquid flux of the membranes can keep constant in a rather large pH range from pH 1 to pH9. The effect of membrane preparation process on the performances of a-cellulose membrane was also revealed by comparatively studying the performances of other cellulose membranes which using different methods prepared.

Chitosan—Cellulose Films Fabricated from Mixtures of Polysaccharides in N-methylmorpholine N-oxide

Abstract: The possibility of fabricating composite chitosan—cellulose films from mixed solutions of polysaccharides in MMO was demonstrated. Unoriented films of inhomogeneous phase composition exhibit elevated swelling in aqueous media (500-600%) and could be of great interest as separating membranes or film dressings.

Spinning compositions containing water-containing N-methylmorpholine-N- oxide and useful in sausage casing manufacture have the regeneratable cellulose component pretreated to improve its solubility

Abstract: The cellulose component used in a spinning composition is pretreated to improve its solubility in aqueous N-methylmorpholine-N-oxide (NMMO), the claimed spinning composition including (a) water-containing NMMO; (b) the dissolved cellulose; (c) a filler which is soluble or insoluble in the composition but not completely dissolved; and (d) a component which changes the structure of the cellulose obtained on regeneration of the composition. An Independent claim is also included for production of the spinning composition by (1) suspending the pretreated cellulose and the component (D) in aqueous NMMO; (2) removing the water until the NMMO is converted to its monohydrate and the cellulose and component (D) are completely dissolved in the monohydrate; and, finally (3) distributing the filler uniformly in the solution.

Production of non-fibrillating cellulose fibers involves spinning cellulose N-methylmorpholine-N-oxide water solution so as to form a core-shell structure in a two-phase spinning nozzle

Abstract: Production of non-fibrillating viscose fibres by spinning from cellulose N-methylmorpholine-N-oxide (NMMNO) water solutions involves forming a core-shell structure in a two-phase spinning nozzle.

--- Preparation Process of Homogeneous Cellulose Solution by Using Surpercooled Liquid N-methylmorpholine-N-oxide Hydrates

Abstract: PURPOSE: Provided is a method of preparing a cellulose solution to improve the homogeneity of solution with minimizing the degradation of cellulose and N-methylmorpholine-N-oxide by using the overcooled liquid N-methylmorpholine-N-oxide hydrate solvent. CONSTITUTION: The method comprises the steps of overcooling a liquid N-methylmorpholine-N-oxide hydrate solvent rapidly below the melting point; and adding a cellulose pulp powder to the overcooled N-methylmorpholine-N-oxide hydrate solvent to swell it. The overcooling is carried out by spraying a cooling air into the spray stream of the liquid N-methylmorpholine-N-oxide hydrate solvent. Preferably the N-methylmorpholine-N-oxide hydrate solvent has a water content of 8-18 wt%, and is cooled below 65 deg.C at 20 deg.C/min. The cellulose pulp has a diameter less than 1000 micrometer.

Effect of Aprotic Solvents on Intermolecular Interaction of Cellulose Macromolecule with N-Methylmorpholine N-Oxide Monohydrate

Abstract: The influence of aprotic cosolvents dimethyl sulfoxide, dimethylformamide, and dimethylacetamide on interaction of N-methylmorpholine N-oxide with cellulose was studied.