Andreas Koschella

Effective preparation of cellulose derivatives in a new simple cellulose solvent

Full Paper: Ceflulore with a degree of polymerization up to 650 can be dissolved in dimethyl sulfoxide containing 10 to 20% (w/v: tetrabutylammonium floride trihydrate without any pretreatment within15 min at room temperature. The new solvent can be classified as a non-derivatizing one as concluded from 13 C NMR measurements. The solvent can be used as reaction medium for the homogeneous functionalization of the polymer. Cellulose esters are prepared very effective by transesterification reactions. The functional groups are deistributed in the order expected for a homogeneous conversion, i. e., a preferred reaction at the primary hydroxyl groups occurs. Moreover, carboxymethyl cellulose with a preferred functionalization at the primary hydroxyl groups and a nonstatic content of the different repeating units was accessible.

Solvents applied in the field of cellulose chemistry: a mini review

Important cellulose solvents are described based on the systematization of derivatizing and non-derivatizing solvents. Advances and limitations of the homogeneous phase chemistry of the biopolymer will be discussed based on new results considering adequately own research work in the field.

First Synthesis of 3-O-Functionalized Cellulose Ethers via 2,6-Di-O-Protected Silyl Cellulose

The present paper describes the synthesis of 2,6-di-O-thexyldimethylsilyl cellulose as a novel 2.6-di-O-protected cellulose derivative. This material was obtained by reacting cellulose in N,N-dimethylacetamide/ LiCl solution with thexyldimethylchlorosilane and imid azole for 24 h at 100°C. In a typical subsequent reaction the residual OH-group in position 3 could be completely etherified without loss of any protecting groups. Treatment with tetrabutylammonium fluoride leads to the novel compounds 3-O-allyl and 3-O-methyl cellulose. The structures of all polymers are revealed by means of one-( 1 H and 13 C) and two-dimensional (COSY and HMQC) NMR techniques.

Silylation of Cellulose and Starch – Selectivity, Structure Analysis, and Subsequent Reactions

The silylation of cellulose and starch under different starting conditions is reviewed. The control of the degree of substitution (DS) and regioselectivity in dependence of the reaction pathway are discussed in detail. The synthesis of trimethylsilyl cellulose (TMSC) in the system hexamethyldisilazane (HMDS)/ammonia leads to partially and completely silylated products controlled by the amount of the components. Hydrolytic desilylation of TMSC in tetrahydrofuran (THF)/ammonia gives the partially desilylated products. The desilylation proceeds statistically along the polymer chains. The reaction of cellulose dissolved in N,N-dimethylacetamide (DMA)/LiCl with bulky thexyldimethylchlorosilane (TDSCl) in the presence of imidazole leads to 2,6-di-O-TDS cellulose. The silylation of starch dissolved in dimethylsulfoxide (DMSO) with TDSCl/pyridine results in the formation of regioselectively 2-O and 6-O functionalized silyl ethers with DS values up to 1.8. 6-O Silyl ethers of cellulose and starch were synthesized with TDSCl highly activated in the reaction system N-methylpyrrolidone (NMP)/ammonia. Two- dimensional NMR techniques after subsequent modifications of the remaining OH groups have been established as important methods for the characterization of the substitution pattern of the described silyl ethers. In the case of starch, the distribution of the substituents could be detected not only in the anhydroglucose units (AGU) but also in the non-reducing end groups (NEG).

Comparison testing of methods for gel permeation chromatography of cellulose: coming closer to a standard protocol

A round robin on GPC of a wide range of different pulp samples was conducted among leading groups in cellulose analysis. The aim was to survey the status quo of the methods available to date. The pulp samples covered not only fully-bleached dissolving pulps but also bleached paper pulps and one unbleached sample. The methods applied were current state-of-the-art GPC with RI, MALLS, and viscosimetry detectors. Different dissolution protocols were compared as well. Following from the obtained results, more standardized protocols were proposed for approaches with different equipment (RI or MALLS/RI) and solvent systems (direct dissolution or derivatization). Major influencing factors, such as derivatization compared to direct solution, calibration versus light scattering and in-between lab variation, were discussed.

Novel regioselectively 6-functionalized cationic cellulose polyelectrolytes prepared via cellulose sulfonates

The synthesis of new 6-deoxy-6-trialkylammonium cellulose derivarives obtained by nucleophilic displacement reactions of p-toluenesulfonyl celluloses with various amines is described. Water soluble cellulosics could be prepared using a N,N-dimethylformamide/ water mixture as the reaction medium. Detailed studies conceming the influence of reaction time and temperature as well as the water content on the solubility of the products were carried out. Even the synthesis of large sample amounts was possible using optimized reaction conditions. The 6-deoxy-6-triallylammonium cellulose derivatives are water soluble even at low degrees of substitution, i.e., in the range of 0.2 and 0.5. The structure was confirmed by means of 1 H and 13 C NMR spectroscopies.

Syntheses and Comparison of 2,6-Di-O-methyl Celluloses from Natural and Synthetic Celluloses

2,6-Di-O-methylcellulose was prepared from natural and synthetic celluloses. Natural cellulose was converted to 2,6-di-O-thexyldimethylsilylcellulose, then to 3-mono-O-allyl-2,6-di-O-methylcellulose, and finally into 2,6-di-O-methylcellulose. Alternatively, 2,6 di-O-methylcellulose was synthesized from the synthetic cellulose derivative 3-mono-O-benzyl-2,6-di-O-pivaloylcellulose by depivaloylation and methylation to give 3-mono-O-benzyl-2,6-di-O-methylcellulose, which was debenzylated to yield the dimethyl ether. Both types of 2,6-di-O-methylcellulose are insoluble in water and common organic solvents. The structures of all cellulose derivatives were determined by NMR.

Hydrogen bond formation in regioselectively functionalized 3-mono-O-methyl cellulose

The hydrogen bond systems of cellulose and its derivatives are one of the most important factors regarding their physical- and chemical properties such as solubility, crystallinity, gel formation, and resistance to enzymatic degradation. In this paper, it was attempted to clarify the intra- and intermolecular hydrogen bond formation in regioselectively functionalized 3-mono-O-methyl cellulose (3MC). First, the 3MC was synthesized and the cast film thereof was characterized in comparison to 2,3-di-O-methyl cellulose, 6-mono-O-methyl cellulose, and 2,3,6-tri-O-methyl cellulose by means of wide angle X-ray diffraction (WAXD) and (13)C cross polarization/magic angle spinning NMR spectroscopy. Second, the hydrogen bonds in the 3MC film were analyzed by means of FTIR spectroscopy in combination with a curve fitting method. After deconvolution, the resulting two main bands (Fig. 3) indicated that instead of intramolecular hydrogen bonds between position OH-3 and O-5 another intramolecular hydrogen bond between OH-2 and OH-6 may exist. The large deconvoluted band at 3340cm(-1) referred to strong interchain hydrogen bonds involving the hydroxyl groups at C-6. The crystallinity of 54% calculated from the WAXD supports also the dependency of the usually observed crystallization in cellulose of the hydroxyl groups at C-6 to engage in interchain hydrogen bonding.

Evaluation of cellulose and carboxymethyl cellulose/poly(vinyl alcohol) membranes

Cellulose was isolated from rice straw and converted to carboxymethyl cellulose (CMC). Both polymers were crosslinked with poly(vinyl alcholo) (PVA). The physical properties of the resulting membranes were characterized by FT-IR, TGA, DSC and SEM. The cellulose and CMC were first prepared from bleached rice straw pulp. The infrared spectroscopy of the resulting polymer membranes indicated a decrease in the absorbance of the OH group at 3300-3400 cm(-1), which is due to bond formation with either the cellulose or CMC with the PVA. The thermal stability of PVA/cellulose and PVA/CMC membranes was lower than PVA membrane. The surface of the resulting polymer membranes showed smooth surface in case of the PVA/CMC membrane and rough surface in case of the PVA/cellulose membrane. Desalination test, using 0.2% NaCl, showed that pure PVA membranes had no effect while membranes containing either cellulose or CMC as filler were able to decrease the content of the NaCl from the solution by 25% and 15%, respectively. Transport properties, including water and chloroform vapor were studied. The moisture transport was reduced by the presence of both cellulose and CMC. Moreover, the membranes containing cellulose and CMC showed significantly reduced flux compared to the pure PVA. The water sorption, solubility and soaking period at different pH solutions were also studied and showed that the presence of both cellulose and CMC influences the properties.

Novel cellulose-based polyelectrolytes synthesized via the click reaction

Novel polyelectrolytes were prepared by conversion of 6-azido-6-deoxycellulose with acetylenedicarboxylic acid dimethyl ester and subsequent saponification. Up to 62% of the azide moieties were converted. The reaction was completed within 48 h using 2 moles of acetylenedicarboxylic acid dimethyl ester per mole of modified anhydroglucose unit. FTIR and NMR spectroscopy were applied to elucidate the molecular structure of the polymers. The polymer degradation was acceptable during this two-step reaction. The resulting biopolymer derivatives were water soluble and reduced the surface tension on water significantly. Moreover, they form ionotropic gels with multivalent metal ions.