NMMO , cellulose solutions

Other patents (81,82) coveted the preparation of cellulose solutions using NMMO and speculated about their use as dialysis membranes, food casings (sausage skins), fibers, films, paper coatings, and nonwoven binders. NMMO emerged as the best of the amine oxides, and its commercial potential was demonstrated by American Enka (83,84). Others (85) have studied the cellulose-NMMO system in depth one paper indicates that further strength increases can be obtained by adding ammonium chloride or calcium chloride to the dope (86). 

The first section covers the chemistry of cellulose solutions in an amine N-oxide solvent (NMMO), the so-called Lyocell chemistry, as encountered in the industrial production of cellulosic Lyocell material. The system is characterized by high reaction temperatures, the presence of a strong oxidant and high complexity by multiple (homolytic and heterolytic) parallel reactions. Trapping was used to address the questions that reactive intermediates are present in Lyocell solutions and are responsible for the observed side-reactions and degradation processes of both solvent and solute. 

The second chapter deals with cellulose solutions in yet another solvent system for cellulose, namely DMAc/IiCl, which is not used on an industrial scale as is NMMO, but on the laboratory scale for analytical purposes. The presence of the somewhat exotic reaction medium poses special requirements on trapping methodology that was used to clarify the mechanisms of different degradation processes. This issue was of importance since maintenance of cellulose integrity is the key prerequisite for any analytical procedure which should report the polymer characteristics of the genuine cellulosic material. 

N-McLhylmorpholine-N-oxidc monohydrate, a tertiary, aliphatic amine N-oxide, is able to dissolve cellulose directly, i.e. without chemical derivatization, which is used on an industrial scale as the basis of the Lyocell process [ 1, 2], This technology only requires a comparatively low number of process steps compared for instance to traditional viscose production. Cellulose material - mainly fibers - are directly obtained from the cellulose solution in NMMO no chemical derivatization, such as alkalization and xanthation for rayon fibers, is required [3]. The main advantage of the Lyocell process lies in its environmental compatibility very few process chemicals are applied, and in the idealized case NMMO and water are completely recycled, which is also an important economic factor. Even in industrial production systems NMMO recovery is greater than 99%. Thus, compared with cotton and viscose the Lyocell process pertains a significantly lower specific environmental challenge [4]. Today, Lyocell fibers are produced on an industrial scale, and other cellulosic products, such as films, beads, membranes and filaments, are also currently being developed or are already produced commercially. 

Fig. 7. Gold GNPs by in situ protection with thiosemicarbazones carbohydrate derivatives and their UV-Vis spectra. (A) Synthesis of cellulose thiosemicarbazone (Cellulose-TSC). (B) Preparation and possible structure of a cellulose-conjugated gold nanoparticle. (C) UVAi is spectra and true-colour images of a GNP-free NMMO blank solution and GNPs/NMMO solutions a) Cellulose-free GNPs, b) Cel2oo-GNPs, and c) Celis-GNPs. Adapted from Ref 93. (See Color Plate 32.)...

Preparation of a homogeneous solution (dope) from cellulose pulp in NMMO water solution... 

NMMO process can be utilized to obtain highly concentrated cellulose solutions (25-35%). 

The degradation of cellulose in NMMO-water solution was one of the major obstacles in the early stages of Lyocell development process. Laszkiewicz studied the degradation of 5% cellulose solution in an NMMO-water solution at 80°C. He clearly showed that if there is no antioxidant present, the DP rapidly decreases [3]. As shown in Figure 10.23, DP decreased from 700 to around 140 after 120 min at 80°C. The use of antioxidants, particularly PG (see Figure 10.24) that is commonly used in the Lyocell process, prevents cellulose degradation. 

In particular the NMMO technology has inspired new developments, recognizing that the cellulose/NMMO/water solution can be considered in many aspects as a melt. As an example, cellulose has been shaped by a blown-film process similar to conventional thermoplastics [33,34]. A schematic of the blow-extrusion process is shown in Figure 3.8. 

Gu [9] applied the diluted assumption theory to the concentrated cellulose in N-methlymorpholine-N-oxide monohydrate (NMMOH2O) solution. He got relative differential MIVD curves of three kinds of cellulose pulps from the dynamic data of cellulose/NMMQH2O solution in 2000. But the results were not compared with the results reported by GPC. In 2004, the relative differential MIVD curves of four kinds of cellulose pulps were calculated on the basis of that method and the calculated results were compared with the non-calibrated GPC results by Zhang [10]. In their rheology experiments, the cellulose concentration in NMMO-H20 solution was fixed (9%, wt), and the polydispersity index (PDI) of cellulose was not calculated. 

In the present work, the effect of cellulose concentration in NMMO H2O solution on prediction of the MW and MWD of cellulose using the rheology-based method was... 

Preparation of cellulos NMMO-H20 solution. A mixture of cellulose pulp in 87%... 

NMMO -H20 (wt) was placed in a dissolving tank maintained at 100°C and stirred continually. The mixture gradually turned into a brown and clear homogeneous liquid. The solution with 12%, 11%, and 9% cellulose in NMMO-H20 solution (wt) was obtained, respectively. 

Effect of cellulose concentration In NMMO H2O solution on the rheology-based results... 

Fig.la, lb, and Ic show G and G master curves of the pulp 1 at various cellulose concentrations in NMMO H2O solutions according to the time-temperature superposition theory [13]. In terms of the Tuminello diluted assumption theory [6-8,14], these curves are converted to relative differential MIVD curves of the pulp 1 at different cellulose concentrations in NMMO H2O solutions shown in Fig.2a. Using the same ptrocedure, relative differential MIVD curves of the pulp 2 and 3 are obtained at various cellulose concentrations in NMMO H2O solutions and presented in Fig.2b and 2c, respectively. Meanwhile, the calculated log (1/cDp), cr and PDI values of the three pulps are given in Table 1.

Fig. 1. Master curves of the pulpl at different cellulose concentrations in NMMO H2O solutions (a) 9%, (b) 11%, and (c) 12%.

Results. Fig.2a, 2b, and 2c respectively represent relative MWD curves of the three pulps at various cellulose concentrations in NMMO H2O solutions. Choosing a concentration of 12%, these relative MWD curves are converted to the A41VD scale curves of the three pulp shown in Fig.3, using the above-mentioned method. Furthermore, in terms of the MWD scale curve, log Mp, a, and PDI of the three pulps are calculated and given in Table 2. From Fig.3 and Table 2, it can be found that the relation of p ak MW is pulp 3 > pulp 1 > pulp 2. For the MWD of the three pulps, pulp 1 appears the broadest, next is pulp 3, and then pulp 2. 

Fig. 3. MW scale curves of the three pulps by the rheology-based method with 12% cellulose concentration in NMMO -HtO solution.

The difficulty associated with extruding mesophase cellulose solutions to produce high-strength fibers remains a perplexing problem. Navard and Haudin [16] indicated that one of the problems of spitming liquid crystalline cellulose solutions in the NMMO/water system was the instability or solution fracture of the solutions during extmsion. This instability resulted in uneven fiber dimensions with correspondingly poor physical properties. In 1980, Chanzy et al. [17] also reported fiber formation from lyotropic cellulose solutions in NMMO/H2O. 

Rogers RD, Seddon KR (2003) Ionic liquids solvents of the future Science 302(5646) 792-793 Rosenau T, Hofinger A, Potthast A, Kosma P (2003) On the conformation of the cellulose solvent N-methylmorpholine-N-oxide (NMMO) in solution. Polymen 44(20) 6153-6158 Rosenau T, Potthast A, Sixta H, Kosma P (2001) The chemistry of side reactions and byproduct formation in the system NMMO/cellulose (Lyocell process). Prog Polym Sci 26(9) 1763-1837 Schaefer DW, Justice RS (2007) How nano are nanocomposites Mactomolecules 40(24) 8501— 8517... 

Figure 12.4 SEM images of electrospun cellulose fibers from 9 wt% DP210 cellulose/NMMO/water solution with a rotating collector (a) 1.2 rpm and (b) 6 rpm. Flowrate was kept at 0.03 mL/min. (Adapted from Reference [100]).

---