Showing papers in "Cellulose in 2003"

Inorganic Molten Salts as Solvents for Cellulose

Abstract: Inorganic molten salts can be used as efficient solvents for cellulose in a wide range of degrees of polymerization. Furthermore, molten salts can be applied as reaction medium for the derivatization of cellulose. For both dissolution and derivatization of cellulose, knowledge of the solution state as well as information about chemical interactions with the solvent system is essential. Using the melts of LiClO4·3H2O, NaSCN/KSCN/LiSCN·2H2O and LiCl/ZnCl2/H2O as cellulose solvents, factors which determine the dissolving ability will be discussed. Besides the specific structure of the molten salt hydrate, the cation and the water content of the melt are the most important factors for the dissolving capability of a molten salt hydrate system. FT-Raman spectroscopy, 7Li and 13C NMR spectroscopy were applied to describe solvent–cellulose interactions and the state of cellulose dissolved in the molten salts. Using Raman and solid state NMR spectroscopy it was proved that cellulose is amorphous in the frozen solvent system. The application of inorganic molten salts as a medium for cellulose functionalization is demonstrated for cellulose carboxymethylation and acetylation.

Characterization of the supermolecular structure of cellulose in wood pulp fibres

Abstract: The hierarchic organization of cellulose fibrils (microfibrils) was investigated in holocellulose, sulphite pulp and kraft pulp using TEM, XRD, ED and FTIR. There were remarkable differences in both the fibril structure and fibril aggregation between the samples. TEM observations revealed more intimately associated fibrils in the kraft pulp compared to the sulphite pulp and the holocellulose, results in agreement with previous CP/MAS 13C-NMR data [Hult E.-L. et al. (2002) Holzforschung 56: 231–234]. Furthermore, the cellulose crystallinity was higher in the kraft pulp sample. With respect to the cellulose Iα and Iβ allomorphs, these samples were controversial when different analytical techniques were applied. Due to the small fibril size and the low degree of order of cellulose in these samples, the concept of crystalline triclinic and monoclinic components as determined by diffraction analysis may not be adequate. Instead the fibril can be regarded to have different degrees of lateral order (including paracrystalline ordering) that can be reoriented to Iβ type conformation and packing upon pulping.

Smooth model cellulose I surfaces from nanocrystal suspensions

Abstract: Removal of lignin, hemicelluloses and other minor components during pulping results in a porous fibrillar structure. Interactions of cellulose fibre surfaces with wet-end additives and other materials depend both on the interfacial properties of the cellulose and on the morphology of the surface. It would be useful to be able to separate the interactions with the cellulose from those that depend on surface roughness and porosity by preparing flat cellulose surfaces. Current methods give surfaces of amorphous cellulose or of cellulose II, differing in density and crystallinity from the original cellulose I surface. We propose a new route to prepare smooth model surfaces of cellulose I, starting from colloidal dispersions of cellulose I nanocrystals. The nanometer-sized width of these rod-like colloidal particles allows a relatively flat surface to be prepared from the suspension by casting an aqueous suspension on an appropriate surface and allowing the water to evaporate. Oriented films can be prepared by spin-coating or shearing. The surface composition and morphology of the films were examined by X-ray photoelectron spectroscopy and atomic force microscopy.

Depolymerization of cellouronic acid during TEMPO-mediated oxidation

Abstract: The mechanism of partial depolymerization of cellouronic acid (β-1,4-linked polyglucuronic acid sodium salt) during 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose was studied by treating cellouronic acid with one reagent or a combination of TEMPO-NaBr-NaClO under various conditions. Although NaClO, NaBrO and an alkali at pH 11 brought about partial depolymerization of cellouronic acid, the use of these reagents themselves did not seem to be the primary reason for depolymerization. On the other hand, when all the reagents, i.e. TEMPO-NaBr-NaClO, were applied to cellouronic acid at pH 11, a remarkable decrease in weight-average degree of polymerization (DPw) from 430 to ca. 20 was observed within the initial 10 min. Probably hydroxyl radicals formed from NaBrO and TEMPO at pH 10–11 cause the depolymerization during the oxidation. Some radical scavengers were then used for the TEMPO-mediated oxidation of cellulose in order to suppress the depolymerization. Although the addition of crotonic acid under certain conditions gave cellouronic acid having higher DPw, none of the radical scavengers examined so far could completely prevent the depolymerization. When regenerated celluloses having higher DP were used as the starting materials, cellouronic acids having DPw of more than 1000 were obtained, although they still had large low-molecular-weight fractions.

Unconventional Cellulose Esters: Synthesis, Characterization and Structure–Property Relations

Abstract: This paper summarizes selected results obtained during a two-year research project in the framework of the focus program ‘Cellulose and cellulose derivatives’ (SPP 1011), sponsored by the German Science Foundation (DFG). New synthesis paths for the preparation of the most important cellulose ester, cellulose acetate, were investigated. In contrast to conventional methods, cellulose was converted in a homogeneous phase reaction with acetyl chloride in the presence of different bases, including polyvinyl pyridine and cross-linked polyvinyl pyridine. Moreover, results of the conversion in the new solvent dimethyl sulfoxide/tetrabutylammonium fluoride trihydrate are discussed. The structures obtained were analyzed both on the level of the anhydroglucose unit (AGU) and along the polymer chain. It was found that the addition of a base can significantly change the selectivity of the reaction and thereby the properties of the products (e.g., solubility). No signs of a non-statistical distribution of the acetyl groups along the polymer chains were observed. Furthermore, reactivity and selectivity of the acylation reactions, using in situ activation with p-toluenesulfonyl chloride (Tos-Cl), were studied for different long-chain carboxylic acids (capric-, caprylic-, decanoic-, lauric-, palmitic-, stearic acid). The thermogravimetric analysis of these derivatives showed that the decomposition temperature increased with an increasing number of carbon atoms, starting from 292 °C (cellulose caprate) to 318 °C (cellulose stearate). New cellulose derivatives were synthesized, for example, cellulose adamantoyl ester. For this purpose cellulose was converted homogeneously in N,N-dimethylacetamide/LiCl with free acids in the presence of activating reagents, for example, Tos-Cl or 1,1′-carbonyldiimidazol.

Cellulose crystallinity and ordering of hemicelluloses in pine and birch pulps as revealed by solid-state NMR spectroscopic methods

Abstract: Solid-state 13C NMR spectroscopy was used to determine the degree of cellulose crystallinity (CrI) in kraft, flow-through kraft and polysulphide–anthraquinone (PS–AQ) pulps of pine and birch containing various amounts of hemicelluloses. The applicability of acid hydrolysis and the purely spectroscopic proton spin-relaxation based spectral edition (PSRE) method to remove the interfering hemicellulose signals prior to the determination of CrI were also compared. For softwood pulps, the spectroscopic removal of hemicelluloses by PSRE was found to be more efficient than the removal of hemicelluloses by acid hydrolysis. In addition to that, the PSRE method also provides information on the associations between cellulose and hemicelluloses. On the basis of the incomplete removal of xylan from the cellulose subspectra by PSRE, the deposition of xylan on cellulose fibrils and therefore an ordered ultrastructure of xylan in birch pulps was suggested. The ordered structure of xylan in birch pulps was also supported by the observed change of xylan conformation after regeneration. Similarly, glucomannan in pine pulps may have an ordered structure. According to the 13C CPMAS measurements conducted after acid hydrolysis, the degree of cellulose crystallinity was found to be slightly lower in birch pulps than in the pine pulps. Any significant differences in cellulose crystallinity were not found between the pulps obtained by the various pulping methods. Only in pine PS–AQ pulp, the degree of cellulose crystallinity may be slightly lower than in the kraft pulps containing less hemicelluloses.

Solubility and Solution Structure of Cellulose Derivatives

Abstract: Strongly interacting solvents are needed to dissolve cellulose; therefore, in the past the interpretation of the uncommon solution behavior of cellulose and its derivatives was based mainly on energetic (enthalpic) considerations, for example, hydrogen bonding. These attempts have not been very successful. The present paper demonstrates that entropic effects influence the solution behavior much stronger than hitherto supposed. In the well-known Flory–Huggins theory the driving force for dissolution of flexible chains is the configurational entropy of mixing. This large entropy is strongly reduced by the chain stiffness of the cellulose backbone and by the strictly regular primary structure of this polysaccharide. It strongly reduces the driving force for dissolution. The entropy of mixing becomes largely increased again by the attachment of long side chains and causes solubility with surprising efficiency (hairy rod principle). This effect is demonstrated with several examples. Among others, the surprising insolubility of short, regular-selectively substituted cellulose chains is explained, although long chains of the same substitution pattern are soluble. The striking behavior of cellulose ethers in water is based on the hydrophobic effect, which causes an increased order of the polymer surrounding water molecules. The induced order results in a very pronounced decrease of entropy of mixing that overcompensates the positive configurational entropy of mixing. Common rules of basic thermodynamics now predict phase separation on heating, contrary to the Flory–Huggins theory, which can only predict phase separation on cooling.

Cellulose Hydrolysis - The Role of Monocomponent Cellulases in Crystalline Cellulose Degradation

Abstract: Changes in the molecular structure of cellulose during hydrolysis with four recombinant β-1,4-glycanases from the cellulolytic bacterium Cellulomonas fimi were assessed and compared in an attempt to elucidate the mechanism of crystalline cellulose degradation. It was apparent that the two endoglucanases, Cel6A and Cel5A, degraded sigmacell cellulose differently; Cel5A liberated more soluble sugars (cellobiose and cellotriose) and significantly altered the molecular weight distribution, while Cel6A had a limited effect on the polymer size and liberated primarily cellobiose and glucose. Additionally, both endoglucanases slightly increased the crystallinity of cellulose. In contrast, the cellobiohydrolases, Cel6B and Cel48A, had no effect on cellulose molecular weight and liberated only cellobiose and cellotriose. However, Cel48A was shown to be effective at reducing the crystallinity of the cellulosic substrate, while Cel6B increased the crystallinity index. Synergistic hydrolysis using combinations of the different enzymes showed that, although the cellulose was extensively hydrolysed, the molecular structure of the substrate was similar to the original material. This phenomenon suggests that the actions of individual monocomponent enzymes are offset by the concurrent modification by the complementing enzymes during synergistic hydrolysis.

The porous structure of pulp fibres with different yields and its influence on paper strength

Abstract: The porous structure of the interior of papermaking fibres is a well-known important property of the fibres Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking In this paper, pore sizes and the pore size distribution of unbleached softwood fibres have been studied A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used Pore size and pore size distribution were measured by studies of the relaxation behaviour of 2H in fibres saturated with 2H2O Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres For both pulps, there is a maximum in pore radius at a yield around 46% Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51% It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/lignin matrix within the fibre wall at this yield level The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall

Application of the solvent dimethyl sulfoxide/tetrabutyl-ammonium fluoride trihydrate as reaction medium for the homogeneous acylation of Sisal cellulose

Abstract: Two types of Sisal cellulose were studied as starting material for homogeneous acylation in the solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) The native Sisal cellulose investigated contains 14% hemicellulose (mainly composed of xylose) as confirmed by 13C-NMR spectroscopy in DMSO-d6/TBAF and HPLC analysis after complete polymer degradation Alkali treatment of Sisal cellulose decreases the amount of hemicellulose, the degree of polymerization and the crystallinity Both Sisal cellulose samples can be dissolved in DMSO/TBAF after treatment at elevated temperature GPC measurements showed high aggregation in the solution Different homogeneous acylation reactions using carboxylic acid anhydrides and vinyl esters were carried out, showing a pronounced tendency of the anhydride towards hydrolysis in the solvent This disadvantage can be diminished by decreasing the amount of the salt hydrate (TBAF trihydrate) or by a distillative removal of the majority of water A strong interaction of the polymer with the water in the solvent was observed

Film-Forming Aminocellulose Derivatives as Enzyme-Compatible Support Matrices for Biosensor Developments

Abstract: Based on 6(2)-O-tosyl celluloses and 6(2)-O-tosylcellulose derivatives, it has been possible to synthesize a novel soluble aminocellulose type, P-CH2-NH-(X)-NH2 (P=cellulose, (X)=alkylene, aryl, aralkylene or oligoamine) with diamine or oligoamine residues at C6 and solubilizing groups (S) such as acetate, benzoate, carbanilate, methoxy and/or tosylate groups at C2/C3 of the anhydroglucose unit (AGU). Depending on the nature and degree of substitution (DS) of (S), the aminocelluloses are soluble either in DMA and DMSO or in water. They all form transparent films from their solutions. In the case of water-soluble aminocelluloses, for example, an enzyme-specific pH value can be adjusted by protonation of the NH2 end groups at C6. The aminocelluloses apparently form aggregates (on a scale of nanostructures) according to a structure-inherent organization principle. The nanostructures could be imaged on the aminocellulose film surface by atomic force microscopy (AFM) in the form of characteristic topographic structures – as a result of the aggregation of the aminocellulose derivative chains and their interaction with the functionalized film support. In this way, structural and environment-induced factors influencing the nanostructure formation were found. The aminocellulose films can be covalently coupled with biomolecules by bifunctional reaction via NH2-reactive compounds. With the aid of analytically relevant enzymes, e.g. glucose oxidase (GOD), horseradish peroxidase (HRP) and others, it was found that the enzyme parameters can be modified by the interplay of the aminocellulose and coupling structures. A number of new bifunctional enzyme coupling reactions, e.g. via L-ascorbic acid or benzenedisulfonyl chlorides, forming amide or sulfonamide coupling structures led to efficient enzyme activities and long-term stabilities in the case of GOD and HRP coupling to PDA cellulosetosylate films.

Molecular properties of hemicelluloses located in the surface and inner layers of hardwood and softwood pulps

Abstract: The molecular properties of hemicelluloses located in the surface and inner layers of fibers present in hardwood and softwood pulps, together with the effects of different bleaching processes on these properties, have been investigated in this study. In order to separate the hemicelluloses located in these two layers, fibers were subjected to mechanical peeling and then separated by filtration into surface (filtrate) and inner layer materials. The materials thus obtained were characterized with respect to their polysaccharide compositions and uronic acid contents. The molar mass parameters of the hemicelluloses (extracted by alkali) were determined by employing size-exclusion chromatography in combination with off-line MALDI mass spectrometry. For all of the pulps examined, the relative content of xylan was found to be greater in the surface layer of the fiber than in the corresponding inner layer. The xylan polymers of the surface layer exhibited higher molar masses and lower frequencies of uronic acid side groups than did the xylans in the inner fiber layer. In connection with ozone treatment, hexenuronic acid residues in the surface layer xylan were removed to a greater extent than in the case of the inner layers, indicating a gradient for the reaction with ozone across the fiber wall. The xylan polymer remaining on the surface of the softwood pulps after completion of the chlorine dioxide bleaching process was predominantly uncharged.

New insight into the mechanism of cellulose and callose biosynthesis: proteases may regulate callose biosynthesis upon wounding

Abstract: Using a silver-enhanced, gold-secondary antibody immuno-location approach, we investigated the mechanisms for the switch from β-1,4- to β-1,3-glucan biosynthesis upon wounding. Antibodies against β-1,4- and β-1,3-glucan synthases were used to locate these synthases before and after wounding of Mung bean (Vigna radiata var Berken) hypocotyls. Within 5 min of wounding, β-1,4-glucan synthases which were densely localized on plasma membranes adjacent to the secondary walls at the wound site completely disappeared, and β-1,3-glucan synthases became labeled. The immuno-location of the β-1,3-glucan synthases in the secondary walls was in good accordance with the region where the β-1,4-glucan synthases were localized before wounding. Aniline blue was also utilized to visualize the deposition of callose upon wounding. Within 5 min of wounding, callose had accumulated in the corresponding region where the immuno-labeling of β-1,3-glucan synthase was detected after wounding. The β-1,3-glucan synthases were always detected from the sieve plate and plasmodesmata which are known to have constitutive synthesis of callose regardless of wounding. Secondary walls located distantly into the tissue away from the wound site were consistently labeled by the β-1,4-glucan synthase antibody even after wounding. Immuno-blot analysis clearly shows that the levels of β-1,4-glucan synthase subunit Ces A decreased dramatically within 30 min, whereas the β-1,3-glucan synthase subunit CFL1 levels increased significantly after wounding. The intensity of labeling reached a maximum at the wound site, and gradually decreased in correspondence with the distance from the wound site. When a protease inhibitor cocktail was applied upon wounding, neither the β-1,3-glucan synthase appeared nor callose was deposited during the first 5 min of wounding. On the other hand, β-1,4-glucan synthase was detected at the wound site, implying that activation of β-1,3-glucan synthase may rely on the degradation of the β-1,4-glucan synthase. Our study may provide new insight into β-glucan synthesis in higher plants.

Highly hydrophobic sisal chemithermomechanical pulp (CTMP) paper by fluorotrimethylsilane plasma treatment

Abstract: Fluorinated thin layers were created on chemithermomechanical pulp (CTMP) sisal paper surfaces with fluorotrimethylsilane (FTMS) radio frequency-plasma conditions. It was found that the FTMS-discharge environments caused implantation of fluorine and –Si(CH3) x groups into the surface layers of the paper substrates. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy and Electron Spectroscopy for Chemical Analysis, as well as Atomic Force Microscopy and Scanning Electron Microscopy analyses revealed a smooth surface for the FTMS plasma-treated paper, apparently covered completely with a cross-linked polymerized network. Although the plasma reaction takes place with the cellulose, hemicelluloses and lignin, it appears that the chemical linkage is mainly to the lignin component on the CTMP paper surface by means of mainly C–O–Si–F, with some C–Si–F structures. The CTMP fibers apparently have a high lignin surface concentration. The water absorption for the plasma-treated CTMP paper was reduced from greater than 300 to 17 g of water/m2 and the contact angle increased from less than 15° to greater than 120° the strength properties were only slightly reduced and the brightness was essentially unaffected with the FTMS plasma treatment.

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

Abstract: 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 18 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)

Sorption of spruce O-acetylated galactoglucomannans onto different pulp fibres

Abstract: Sorption of spruce acetylated galactoglucomannans (GGM) onto different pulps, among which unbleached and peroxide-bleached mechanical pulps, and unbleached and bleached kraft (BK) pulps, was studied as a means of understanding the retention of acetylated GGMs in mechanical pulping and papermaking. The fibre surface coverage of lignin and carbohydrates was estimated by X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA). GGM sorption was clearly favoured on kraft pulps. Hardly any differences in sorption were, however, observed between unbleached and BK pulps, even if the surface coverage of lignin was lower on the bleached pulp. Neither thermomechanical pulp (TMP) nor chemithermomechanical pulp (CTMP) manufactured from spruce sorbed any acetylated GGMs. Peroxide bleaching of the pulp did not increase sorption. Only CTMP produced from aspen sorbed some GGMs. The anionic charge of neither chemical nor mechanical pulps influenced GGM sorption.

Nitroxide-mediated oxidation of cellulose using TEMPO derivatives: HPSEC and NMR analyses of the oxidized products

Abstract: Regenerated cellulose (viscose rayon) was oxidized using NaBr, NaClO and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) or one of ten related nitroxyl radicals in water at pH 10–11. The C6 primary hydroxyl groups in rayon were oxidized to carboxyl groups in most cases, thus giving water-soluble products. However, the oxidation times required for complete dissolution of the products varied substantially, depending on the nitroxyl radical used. Weight average degrees of polymerization (DPw) of the oxidized products were determined by means of high performance size exclusion chromatography (HPSEC) using pullulan standards. All the products had bimodal HPSEC distribution patterns, probably reflected by the solid-state structure of viscose rayon. When 4-acetamido-TEMPO and 4-carboxy-TEMPO were used, cellouronic acids having almost homogeneous chemical structures with higher DPw than for TEMPO were obtained quantitatively within 30 min. The oxidations using 4-amino-TEMPO, 4-carboxy-PROXYL and 4-carbamoyl-PROXYL gave cellouronic acids having the highest DPw, although reaction times of more than 4 h were required, and some side reactions occurred on the products.

Empirical Polarity Parameters of Celluloses and Related Materials

Abstract: Kamlet–Taft's α (hydrogen-bond donating (HBD) ability), β (hydrogen-bond accepting (HBA) ability), and π* (dipolarity/polarizability) parameters of native cellulose batches, carboxymethyl celluloses (CMCs), cellulose tosylates (CTs), and other derivatives with different degree of substitution (DS), chitine, amylose, amylopectine, and cellobiose are presented. Fe(phen)2(CN)2 [cis-dicyano-bis-(1,10)-phenanthroline-iron(II), (1)], Michler's ketone [bis-4,4′-(N,N-dimethylamino)benzophenone, (2)], 4-aminobenzophenone (3), coumarine 153 (4), and Reichardt's dye (5) were used as solvatochromic surface polarity indicators. The UV/Vis reflectance spectra of the five surface polarity indicators 1, 2, 3, 4, and 5, adsorbed on the samples from the organic solvents, were measured and the absorption maxima were used to calculate the α, β, π*, and ET(30) values of the polysaccharides surface. α, β, and π* depending on degree of crystallinity of the cellulose samples have been determined. α depends on both amount and strength of accessible acidic surface groups on the cellulose surface. It is significantly larger for crystalline sections than for amorphous parts. The π* scale is suitable for the classification of different cellulose batches, because it seems to be independent of inhomogeneities of the cellulose surface. The α-values of CMCs and CTs significantly decrease with increasing DS inasmuch the number of cellulosic-OH groups (Cell-OH) decreases. A slight increase of π* with DS is observed for CTs.

Regioselectively Modified Cellulose and Chitosan Derivatives for Mono- and Multilayer Surface Coatings of Hemocompatible Biomaterials

Abstract: In this study different synthetic strategies were developed and applied to introduce solely or in combination heparin/heparansulfate-like functional groups such as N-sulfo, O-sulfo, N-acetyl, and N-carboxymethyl groups into chitosan and cellulose with highest possible regioselectivity and completeness and defined distribution along the polymer chain. Completely substituted 6-amino-6-deoxycellulose and related derivatives were prepared from tosylcellulose (DS 2.02; C6 1.0) by nucleophilic substitution with azido groups only in the 6-position at 50 °C with subsequent reduction to amino groups and completely removing tosyl groups in the 2,3-position. 2,6-Di-O-sulfocellulose was prepared using the reactivity difference between C-2, C-6 and C-3 of cellulose. The reactivity difference between amino groups and hydroxyl groups was used to prepare various N-substituted derivatives. Partially 2,6-di-O-sulfated cellulose was obtained from trimethylsilylcellulose by the insertion of sulfurtrioxide into the Si–O ether linkage. Partially 3-O-sulfocellulose was synthesized by protecting C-2 and C-6 with trifluoroacetyl groups. A copper–chitosan complex was used to synthesize 6-O-sulfochitosan with a DS of 1.0 at C-6 and various partially 6-O-desulfonated products are possible. Using the phthalimido group to increase the solubility of chitosan in DMF, the regioselectivity of 3-O-sulfo groups was improved by regioselective 6-O-desulfonation of nearly complete 3,6-O-disulfochitosan. The platelet adhesion properties of immobilized regioselectively modified water-soluble derivatives on membranes have been tested in vitro. Some regioselectively modified chitosan and cellulose derivatives are potential candidates for the surface coatings of biomaterials if the regioselective reactions are somewhat further optimized.

Crystal Structure Refinements of Cellulose Polymorphs using Solid State 13 C Chemical Shifts

Abstract: Force field methods in combination with chemical shift target functions are used to investigate the structures of cellulose I and II. Since diffraction investigations of biopolymers like cellulose II are only of poor resolution, different models for the structure are discussed in the literature. These models were used as the starting point for force field optimizations with 13C chemical shift target functions. In these optimizations additionally to the total energy a pseudo-energy is minimized that depends harmonically on the difference between calculated and observed chemical shifts. In the case of cellulose II all four criteria: (i) total energy, (ii) pseudo-energy, (iii) chemical shift rms (root mean square) difference, and (iv) deviation from the diffraction data favour the structure model of Kolpak and Blackwell with two antiparallel carbohydrate chains. The CH2–OH group of one chain is in tg and that of the other chain in gt conformation. The chemical shift optimized fractional coordinates for cellulose II, Iα and Iβ are presented together with the calculated and experimental 13C chemical shifts.

Topochemically Modified Cellulose

Abstract: Selective topochemical reactions were carried out on particles of micro-crystalline cellulose. For this purpose these crystallites were chemically activated via hydrazone linkages at the reducing ends. Macromolecules, carrying reactive end groups, were attached to the reactive cellulose crystallites by coupling reactions (‘grafting to’ method). Amino-terminated polyethylene glycols and polydimethylsiloxanes were coupled to crystallites carrying phenyl carboxylic functions at their front faces. The cellulose-block-polydimethylsiloxane copolymer exhibits a pronounced tendency to form specific super-structures in slurries and films made from it. After freeze drying, layer structures are observable with the naked eye. Alternatively a radical polymerization of acrylamide could be started from the substrate surface after attaching reactive initiators (‘grafting from’ method). Both methods lead to selectively grafted cellulose particles. This was confirmed by SEC measurements after degrafting the attached polymers. A higher graft density resulted from radical polymerization due to the distinctly higher molecular weights obtained in this way. However, these grafted products did not form any special super-structures.

Silylation of Cellulose with Hexamethyldisilazane in Ammonia – Activation, Catalysis, Mechanism, Properties

Abstract: Synthesis of trimethylsilylcellulose (TMSC) from cellulose and hexamethyldisilazane (HMDS) in liquid ammonia is reviewed, with emphasis on the scope of the reaction and mechanistic features Conditions for complete and for controlled stoichiometric partial silylation have been established Stoichiometric desilylation of TMSC is also possible in tetrahydrofuran containing ammonia as hydrogen bond donor The activating effect of ammonia, solubility of reactants, catalysis and kinetics of the heterogeneous reaction are discussed Silylation follows first order kinetics in the presence of saccharin as the catalyst, indicating that the accessibility of hydroxy groups is not the rate-determining factor TMSCs have a solubility window in THF with a DS from 16 to 26 This window is narrower for higher molecular weight TMSC

Regioselective sulfation of trimethylsilyl cellulose using different SO3-complexes

Abstract: Trimethylsilyl cellulose (DSSi = 2.9) dissolved in dry tetrahydrofurane was reacted with SO3-complexes of N,N-dimethylformamide, triethylamine, pyridine and ethyldiisopropylamine. Under the given reaction conditions, i.e. 25 °C, 24 h, 2.2 mol equivalent SO3-complex, the SO3 attacks the trimethylsilyl ether groups followed by the formation of sodium sulfate cellulose under sodium hydroxide work-up conditions. The regioselectivity of the sulfation is controlled by the complex partner of SO3. Cellulose sulfates with preferred O-6 sulfation were obtained using SO3-N,N-dimethylformamide. In case of SO3-triethylamine, cellulose-2-sulfates could be prepared with good regioselectivity. Small residual amounts of silicon in the cellulose sulfates (0.1–0.2% w/w) can be quantified using inductively coupled plasma-optical emission spectroscopy (ICP-OES), and can be decreased up to 80% by heating (70 °C, 24 h) the polymers in vacuum.

Electrostatically generated fibers of ethyl-cyanoethyl cellulose

Abstract: Electrospinning was used to fabricate ethyl-cyanoethyl cellulose [(E-CE)C] fibers from tetrahydrofuran (THF) solutions. It was found that the solution jet is split or atomized during the flight to the grounded collector. Microcavities were detected on the surface of the fibers and these were attributed to the volatilization of the solvent (THF). The thinnest fibers generated had a diameter of about 250 nm. The crystallinity of the fibers varied with the voltage of the electrostatic field and it reached a maximum when the voltage of the electrostatic field was 50 kV.

Specificity of an Aspergillus niger esterase deacetylating cellulose acetate

Abstract: A purified acetyl esterase (AE), isolated from a commercial enzyme preparation, released acetic acid from water-soluble and water-insoluble cellulose acetates (CAs), native and chemically acetylated xylan as well as acetylated starch. The AE specifically cleaved off the acetyl substituents from the C2- and C3-positions from CAs of DS <1.8 and left the acetyl substituents at the C6-positions intact without degrading the polysaccharide. The activity of endoglucanase was enhanced by the presence of acetyl esterase, while the acetyl esterase derived no advantage from the presence of the endoglucanase; it was able to function independently.

Synthesis, characterization and properties of methylaminocellulose

Abstract: Homogeneously prepared tosylcelluloses (TC) with degrees of substitution (DS) of DSTos 0.1–1.8 were used as intermediates for the synthesis of methylaminocelluloses (MAC) by nucleophilic substitution with methylamine. TC with DSTos up to 1.1 were shown to be valuable intermediates for selective synthesis of MAC with DSMA varying from 0.1 to approximately 1. No nucleophilic substitution was observed at higher DSTos. At the chosen reaction conditions (60 °C, 48 h) residual tosyl moieties remained unchanged and little hydrolysis took place. The samples obtained were characterized by means of elemental analysis, FTIR and 13C CP/MAS NMR spectroscopy. 13C CP/MAS NMR spectroscopy was found to be an efficient tool for quantification of DSMA. Furthermore, the swelling behaviour in water was investigated and preliminary tests concerning the bilirubin adsorption capacity of MAC were carried out.

New process for producing cellulose acetate from wood in concentrated acetic acid

Abstract: To explore further potential applications of acetic acid pulp, an investigation was conducted to develop a direct method for producing cellulose acetate from wood in combination with atmospheric acetic acid pulping. The process consists of delignification, totally chlorine-free bleaching, and esterification, with the concentrated acetic acid aqueous solution being used as only solvent throughout the process. The acetic acid pulp with kappa number of 30 and ISO brightness of 16 was bleached with 5% ozone on pulp to kappa number of 1.4 and brightness of 61. The resulting bleached pulp was further bleached with peracetic acid to kappa number of less than 1.0 and brightness of 68. The final bleached acetic acid pulp was acetylated with acetic anhydride in the concentrated acetic acid for 45 min to produce cellulose acetate with an apparent degree of substitution (DS) of 2.54. Although the product was lower grade compared with commercially available cellulose diacetate because it was prepared from the chemical pulp but not dissolving pulp, the product was almost soluble in acetone. Eventually, the DS of the acetone-soluble fraction was 2.62. The acetone solubility might be attributed to the original acetic acid pulp that had been partially acetylated during the pulping.

Use of HMDS/hexane double layers for obtaining low cost selective membrane

Abstract: Sheets of paper commonly used for filtration were coated with double layers of HMDS (hexamethyl disilazane) and n-hexane using a low pressure plasma reactor. The organic compounds formed a thin film with very good adhesion to the substrate; the process produced water-repellent surfaces, with apparent water-contact angles higher than 100° and water adsorption around 15 g/m 2 . The paper porosity was not altered, indicating that the depositions were conformal. Preliminary tests to investigate the possibility of using the modified paper as a selective membrane for separation of water and organic-polar and non-polar compounds of different chain length were conducted. The non-polar compounds tested were: n-hexane, cyclohexane, heptane, dodecane, benzene and poly(dimethylsiloxane). The polar organic liquids were ethanol, 2-propanol, carbon tetrachloride, acetophenone and phenol. Three types of behaviour were observed: (a) in the case of water/non-polar mixture, the non-polar compound passed through the modified paper whereas water did not; (b) in the case of acetophenone, phenol and carbon tetrachloride, neither the water nor the polar compound percolated through the modified paper; (c) in the case of water/2-propanol or ethanol solution, it was observed that a minimum concentration of alcohol was necessary in order for both the alcohol and water to percolate through the paper; in this case the alcohol percolates first, followed by water.

Regioselective Nitrilotriacetic Acid–Cellulose–Nickel-Complexes for Immobilisation of His6-Tag Proteins

Abstract: The molecular and supramolecular structural design of cellulose derivatives represents important synthetic and structure analytical aspects of cellulose chemistry. Such tailored cellulose product can be used as substrate for proteins and biocatalysts. New cellulose derivatives, modified with nitrilotriacetic acid (NTA) residues, were synthesised by a nucleophilic substitution reaction starting from cellulose tosylates. These derivatives are able to form clear and thin films on glass surfaces and show remarkable complexation properties concerning nickel(II). The immobilisation of His-tag proteins succeeded on the surface of the transparent cellulose films. The detection of the specific cellulose-protein-binding results from optical measurements of fluorescence effects transmitted by optically marked synthetic proteins designed de novo.

Determination of the Molar Mass and the Radius of Gyration, Together with their Distributions for Methylhydroxyethylcelluloses

Abstract: Three molar mass series were produced by different methods of degradation (namely ultrasonic (seven samples), oxidation (seven samples) and autoclaving (eight samples)) from a methylhydroxyethylcellulose (MHEC) sample with an average degree of substitution (DS) of 1.3, a molar degree of substitution (MS) of 0.46, a radius of gyration of 67 nm and a weight-average molar mass, Mw, of 318,000 g/mol. The degraded samples were characterized in terms of their molar mass and particle size together with their respective distributions with a hyphenated apparatus consisting of size exclusion chromatography and multi-angle laser light scattering and concentration detector (SEC/MALLS/DRI) at 25 °C in 0.1 M NaNO3 solution (with 200 ppm NaN3 as antibactericide). The refractive index increment was determined as dn/dc = 0.135 cm3/g. It was possible to reduce the weight-average molar mass down to approximately 10% of the initial molar mass using all the methods. In a comparison of the three degradation methods it was shown that only ultrasonic degradation retains the monomodal distribution, whereas the other two degradation methods yield a bimodal molar mass distribution. Consequently, only ultrasonic degradation represents a suitable method for producing homologous molar mass series. An RG–M relationship of RG = 0.0511 × M0.56 was established for the sample used in this case, and from this it was possible to calculate an [η]–M relationship of [η] = 0.3587 × M0.68.