Preparation of cellulose and cellulose derivative azo compounds

Wood pulp and cotton linter are the most common sources of cellulose forindustrial use. Methyl cellulose (MC) and cellulose sulfate (CS) were preparedusing bleached wood pulp and cotton linter. Coloured azo compounds were alsoprepared from coupling cellulose, wood pulp, MC and CS with aromatic diazoniumsalt. The presence of electron-releasing or withdrawing substituents affectedthe electrophilic substitution reaction. The produced azo compounds werecharacterized by FT-IR methodology, as well as mass spectrometry, in which thefunctional groups and the ion fragments of the products were analyzed.     

Unconventional cellulose products by fluorination of tosyl cellulose

The synthesis of novel deoxy-fluoro cellulose derivatives obtained by nucleophilic displacement reactions (SN) of p-toluenesulfonyl (tosyl) cellulose with tetrabutylammonium fluoride (TBAF) is described. Detailed studies concerning the influence of the reaction time and temperature as well as the water content of the TBAF on the composition of the products were carried out. The SN reaction occurs even at room temperature. The degree of substitution of deoxy-fluoro moieties (DSF) is in the range from 0.22 to 0.47. The polymers contain remaining tosyl groups. Preliminary 19F NMR measurements reveal the presence of the CH2F group. The degradation temperature of the deoxy-fluoro cellulose derivatives is increased compared to the starting tosyl cellulose, however, a distinct influence of the remaining tosyl groups appears.     

Self-reinforced cellulose nanocomposites

A self-reinforced cellulosic material was produced exclusively from regenerated cellulose microcrystals. The level of reinforcement was controlled by tailoring the crystallinity of cellulose by controlling the dissolution of microcrystalline cellulose (MCC) before its regeneration process. After the cellulose regeneration a self-reinforced material was obtained in which cellulose crystals reinforced amorphous cellulose. This structure was produced by dissolution of MCC in a non-derivatising cosolvent N,N-dimethylacetamide/LiCl followed by subsequent cellulose regeneration in distilled H₂O. The reduction of the overall crystallinity of self-reinforced regenerated cellulose was dependent on the dissolution time of the cellulose precursor. The crystallinity of regenerated cellulose was determined by wide angle X-ray diffraction. A reduction in crystal size from microcrystalline cellulose to regenerated cellulose was observed with increasing dissolution time in DMAc/LiCl cosolvent. The reduction in degree of crystallinity of regenerated cellulose led to a decrease in the tensile mechanical performance and thermal stability of the regenerated cellulose. The controlled dissolution of microcrystalline cellulose resulted in the modification of structural, physical, thermal properties and moisture uptake behaviour of regenerated cellulose.     

Adsorption of four non-ionic cellulose derivatives on cellulose model surfaces

The adsorption of four commercial non-ionic cellulose derivatives onto two different model surfaces of cellulose fibres has been studied with surface plasmon reflectance. The model surfaces of cellulose were ultrathin films of either nano fibrillated cellulose or regenerated cellulose on Au(s). Partial least squares models were used in the analysis of the data and it was found that the type of cellulose model surface seems to be most important for both the total adsorption and the initial adsorption rate of the studied cellulose derivatives. It is believed that this can be explained by morphological differences between the surfaces, and it was found that the properties of the cellulose derivatives that affect the adsorption of the two types of cellulose surface differ. For adsorption onto a NFC-based model surface, the type of cellulose derivative and the polydispersity index (PDI) of the cellulose derivative seem to be the two most important variables for the observed adsorption of these cellulose derivatives. For the regenerated cellulose surface the three most important variables are the M _n of the cellulose derivatives, the DS _NMR of the methyl celluloses, and PDI of the cellulose derivatives. Thus the adsorption of cellulose derivatives on the NFC-based cellulose model surface is strongly affected by the type of substituent, while the same cannot be said for a surface regenerated from N-methylmorpholine-N-oxide. Additionally, the DS _NMR of methyl celluloses affects their adsorption differently on the investigated cellulose model surfaces.     

Syntheses and characterizations of allyl cellulose and glycidyl cellulose

Allyl cellulose was synthesized by reacting cellulose with allyl bromide in homogeneous LiCl/DMAc solution containing NaOH powder. The degree of substitution (DS) per anhydroglucose (AHG) unit was determined by titrating the allyl cellulose with bromine in chloroform solution, and an allyl DS of 2.80 was found. Glycidyl cellulose was then prepared by reacting this allyl cellulose with peracetic acid in methylene chloride at ambient temperature for 6 days. The measured reaction rate constant was 1.33 × 10^?3 min^?1. The glycidyl cellulose thus obtained with a glycidyl DS of 2.58 was determined by titrating the product with perchloric acid in conjunction with tetrabutylammonium iodide. The 2.58 of glycidyl DS was also confirmed by ¹H-NMR integration. Both allyl cellulose and glycidyl cellulose were analyzed and characterized with FTIR, ¹H-NMR, ¹³C-NMR, TGA, and GPC. During epoxidation of allyl cellulose, possible side reaction leading to ester formation was evidenced from the continuous increase of v_{C? O} at 1735 cm^?1 in FTIR analyses. In addition, a bimodal distribution and a decreased molecular weight for glycidyl cellulose were found from GPC data, which might suggest a possible chain scission at the cellulosic ether linkage. © 1992 John Wiley & Sons, Inc.     

Highly charged nanocrystalline cellulose and dicarboxylated cellulose from periodate and chlorite oxidized cellulose fibers

Softwood cellulose pulp was oxidized by a two-step oxidation process with sodium periodate followed by sodium chlorite at pH 5.0. The oxidized product was first separated into two fractions by centrifugation, and the supernatant was further separated in two fractions by addition of ethanol and centrifugation. Different levels of oxidation were performed on cellulose, and the mass ratio and carboxyl content of each fraction were determined. The first precipitate, which amount decreases with increasing oxidation level, consists of short fiber fragments (microfibrils) with length of 0.6–1.8 μm and width around 120 nm, which for sufficiently high oxidation levels, could readily be made into cellulose nanofibrils by stirring. The second precipitate (after alcohol addition) has a very high crystalline index of 91 % and contains rod-like particles with length of 120–200 nm and diameter around 13 nm, reminiscent of nanocrystalline cellulose. The supernatant contains water-soluble dicarboxylated cellulose, as proven by liquid C-13 NMR.     

Characterization of the water-insoluble pyrolytic cellulose from cellulose pyrolysis oil

Water-insoluble pyrolytic cellulose with similar appearance to pyrolytic lignin was found in cellulose fast pyrolysis oil. The influence of pyrolysis temperature on pyrolytic cellulose was studied in a temperature range of 300–600 °C. The yield of the pyrolytic cellulose increased with temperature rising. The pyrolytic cellulose was characterized by various methods. The molecular weight distribution of pyrolytic cellulose was analyzed by gel permeation chromatography (GPC). Four molecular weight ranges were observed, and the M_w of the pyrolytic cellulose varied from 3.4 × 10³ to 1.93 × 10⁵ g/mol. According to the elemental analysis (EA), the pyrolytic cellulose possessed higher carbon content and lower oxygen content than cellulose. Thermogravimetric analysis (TGA) indicated that the pyrolytic cellulose underwent thermo-degradation at 127–800 °C and three mass loss peaks were observed. Detected by the pyrolysis gas chromatography–mass spectrometry (Py-GC/MS), the main pyrolysis products of the pyrolytic cellulose included saccharides, ketones, acids, furans and others. Fourier transforms infrared spectroscopy (FTIR) also demonstrated that the pyrolytic cellulose had peaks assigned to CO stretching and glycosidic bond, which agreed well with the Py-GC/MS results. The pyrolytic cellulose could be a mixture of saccharides, ketones, and their derivatives.     

Effect of cellulose crystallinity on bacterial cellulose assembly

Bacterial cellulose (BC) is a promising biomaterial as well as a model system useful for investigating cellulose biosynthesis. BC produced under static cultivation condition is a hydrous pellicle consisting of an interconnected network of fibrils assembled in numerous dense layers. The mechanisms responsible for this layered BC assembly remain unknown. This study used calcofluor as a fluorescent marker to examine BC layer formation at the air/liquid interface. Layers are found to move downward into the media after formation while new layers continue to form at the air/liquid interface. Calcoflour is also known to reduce the crystallinity of cellulose, changing the mechanical properties of the formed BC microfibrils. Consecutive addition and accumulation of calcofluor in the culture medium is found to disrupt the layered assembly of BC. BC crystalllinity decreased by 22 % in the presence of 12 % calcofluor (v/v) in the medium as compared to BC produced without calcofluor. This result suggests that cellulose crystallinity and the mechanical properties which crystallinity provides to cellulose are major factors influencing the layered BC structure formed during biosynthesis.     

Ionic-liquid-derived, water-soluble ionic cellulose

A new type of water-soluble ionic cellulose was obtained by means of the dissolution of cellulose in dimethylimidazolium methylphosphite at elevated temperatures over 120?°C. FTIR spectroscopy, (1)H and (13)C?NMR spectroscopy, and elemental analysis results revealed that the repeating unit of the water-soluble cellulose consists of a dialkylimidazolium cation and a phosphite anion bonded to cellulose. The degree of phosphorylation on the cellulose chain was between 0.4 and 1.3 depending on the reaction temperature and time. With an increasing degree of phosphorylation, water solubility was increased. Scanning electron microscopy and X-ray diffraction analyses revealed that the cellulose crystalline phase in the parent crystalline cellulose changed to an amorphous phase upon transformation into ionic cellulose. Thermogravimetric analysis showed the prepared phosphorylated cellulose was stable over 250?°C and a substantial amount of residue remained at 500?°C.     

Quantification of cellulose forms in complex cellulose materials: a chemometric model

In this paper, we present a chemometric model for quantifying the cellulose forms with different states of order found within cellulose I fibrils. The relative amounts of the different cellulose forms, that is crystalline cellulose I, para-crystalline cellulose and cellulose at accessible and inaccessible cellulose surfaces, were determined by non-linear least squares fitting of the C4-region in CP/MAS ¹³C-NMR (Cross-Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance) spectra. By correlating these results from the C4-region with the full spectral data we obtained a model which is able to provide an assessment of the relative amounts of the different cellulose forms directly from NMR-spectra of complex lignocellulosic samples. Furthermore, this model enabled new assignments to be made in the C1-region for signals from cellulose at accessible fibril surfaces.     

Challenge of synthetic cellulose

This article focuses on why and how the chemical synthesis of cellulose was accomplished. The synthesis of cellulose was an important, challenging problem for half a century in polymer chemistry. For the synthesis, a new method of enzymatic polymerization was developed. A monomer of β‐D ‐cellobiosyl fluoride (β‐CF) was designed and subjected to cellulase catalysis, which led to synthetic cellulose for the first time. Cellulase is a hydrolysis enzyme of cellulose; cellulase, inherently catalyzing the bond cleavage of cellulose in vivo, catalyzes the bond formation via the polycondensation of β‐CF in vitro. It is thought that the polymerization and hydrolysis involve a common intermediate (transition state). This view led us to a new concept, a transition‐state analogue substrate, for the design of the monomer. The preparation of cellulase proteins with biotechnology revealed the enzymatic catalytic functions in the hydrolysis and polymerization to cellulose. High‐order molecular structures were in situ formed and observed as fibrils (cellulose I) and spherulites (cellulose II). In situ small‐angle neutron scattering measurements suggested a fractal surface formation of a synthetic cellulose assembly. The principle of cellulose synthesis was extended to the synthesis of other natural polysaccharides, such as xylan and amylose, and unnatural polysaccharides. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 693–710, 2005     

Thermal behavior of cellulose acetate produced from homogeneous acetylation of bacterial cellulose

Cellulose acetate (CA) is one of the most important cellulose derivatives and its main applications are its use in membranes, films, fibers, plastics and filters. CAs are produced from cellulose sources such as: cotton, sugar cane bagasse, wood and others. One promissory source of cellulose is bacterial cellulose (BC). In this work, CA was produced from the homogeneous acetylation reaction of bacterial cellulose. Degree of substitution (DS) values can be controlled by the acetylation time. The characterization of CA samples showed the formation of a heterogeneous structure for CA samples submitted to a short acetylation time. A more homogeneous structure was produced for samples prepared with a long acetylation time. This fact changes the thermal behavior of the CA samples. Thermal characterization revealed that samples submitted to longer acetylation times display higher crystallinity and thermal stability than samples submitted to a short acetylation time. The observation of these characteristics is important for the production of cellulose acetate from this alternative source.     

Single crystals of cellulose IVII: Influence of the cellulose molecular weight

The influence of the degree of polymerization (DP) of cellulose was evaluated in the preparation of micron-sized cellulose IV_II lamellar crystals in order to ascertain whether a regular chain-folded morphology could develop during their growth. For this purpose, sharp fractions of cellulose acetate were collected by preparative gel permeation chromatography. Aliquots of these fractions were deacetylated and crystallized in dilute solutions containing water, methylamine, and DMSO, and held at 150°C under pressure. Well-developed cellulose IV_II lamellar crystals were obtained with fractions of DP 22–24 whereas higher-DP material gave polycrystalline aggregates. This behavior indicates that large lamellar crystals of cellulose IV_II can be obtained only with unfolded short cellulose chains. The occurrence of chain-folded crystals with high–DP cellulose samples cannot be demonstrated.     

Preparation of powder cellulose

Powder cellulose was obtained according to the scheme of hydrolysis-bleaching from the wood technical (unbleached) sulfate cellulose. In the first step, from the crude cellulose lignocellulose material was obtained, which in the second step was subjected to delignification by treating with hydrogen peroxide and chlorine dioxide.     

Continuous cellulose fiber-reinforced cellulose ester composites III. Commercial matrix and fiber options

Thermoplastic composites were prepared using two continuous regenerated cellulose fiber types, rayon and lyocell, and with several different commercially-available thermoplastic cellulose esters as matrix. Matrix options included cellulose acetate propionate (CAP), and several cellulose acetate butyrates (CAB) with different butyryl content, having different molecular weights and different methods of plasticization (adipates and very low molecular weight cellulose ester fractions). Choice of cellulose ester type was generally found to have little or no effect on mechanical properties. A significant effect, however, was revealed for fiber type. The lyocell-based composites thereby were reflective of the greater stiffness of a fiber produced from anisotropic solution state. Their modulus consistently exceeded 20GPa whereas the rayon fiber-based composites had moduli between 6 and 8GPa. The latter, however, possessed failure strains that were 3 to 4 times greater than their stiffer counterparts.     

Enzymatic hydrolysis of cellulose I is greatly accelerated via its conversion to the cellulose II hydrate form

Cellulose II hydrate was prepared from microcrystalline cellulose (cellulose I) via its mercerization with 5 N NaOH solution over 1 h at room temperature followed by washing with water. The structure of cellulose II hydrate changed to that of cellulose II after drying. Compared with cellulose II, cellulose II hydrate exhibited a slightly (8.5%) expanded structure only along the direction. The hydrophobic stacking sheets of the cellulose II were conserved in the cellulose II hydrate, and water molecules could be incorporated in the inflated two-chain unit cell of cellulose II hydrate. Enzymatic hydrolysis of cellulose I, cellulose II hydrate, and cellulose II was carried out at 37 °C using solutions comprising a mixture of cellulase and β-glucosidase. The hydrolysis of cellulose II hydrate proceeded much faster than the hydrolysis of the other two substrates, while the saccharification ratio of cellulose II was only slightly higher than that of cellulose I. The alkaline mercerization treatment was also applied to sugarcane bagasse. After its direct mercerization, the cellulose in bagasse was converted from cellulose I to cellulose II hydrate, and then to cellulose II after drying. Similar to in the case of microcrystalline cellulose, the rate of the enzymatic hydrolysis of the mercerized bagasse without drying (cellulose II hydrate) was much faster than the enzymatic hydrolysis of the other two substrates. Thus, the wet forms of cellulose and cellulosic biomass after mercerization, and after hydrolysis with cellulolytic enzymes, afforded superior products with extremely high degradability.     

Surfactant adsorption onto cellulose surfaces

The adsorption of the cationic surfactant, hexadecyl trimethyl ammonium bromide, C16TAB, onto model cellulose surfaces, prepared by Langmuir-Blodgett deposition as thin films, has been investigated by neutron reflectivity. Comparison between the adsorption of C16TAB onto hydrophilic silica, a hydrophobic cellulose surface, and a regenerated (hydrophilic) cellulose surface is made. Adsorption onto the hydrophilic silica and onto the hydrophilic cellulose surfaces is similar, and is in the form of surface aggregates. In contrast, the adsorption onto the hydrophobic cellulose surface is lower and in the form of a monolayer. The impact of the surfactant adsorption and the in situ surface regeneration on the structure of the cellulose thin films and the nature of solvent penetration into the cellulose films are also investigated. For the hydrophobic cellulose surface, intermixing between the cellulose and surfactant occurs, whereas there is little penetration of surfactant into the hydrophilic cellulose surface. Measurements show that solvent exchange between the partially hydrated cellulose film and the solution is slow on the time scale of the measurements.     

Xyloglucan in cellulose modification

Xyloglucans are the principal polysaccharides coating and crosslinking cellulose microfibrills in the majority of land plants. This review summarizes current knowledge of xyloglucan structures, solution properties, and the mechanism of interaction of xyloglucans with cellulose. This knowledge base forms the platform for new biomimetic methods of cellulose surface modification with applications within the fields of textile manufacture, papermaking, and materials science. Recent advances using the enzyme xyloglucan endo-transglycosylase (XET, EC 2.4.1.207) to introduce varied chemical functionality onto cellulose surfaces are highlighted.     

Temperature-responsive hydrogels from cellulose

The aim of this work is to prepare the temperature-responsive cellulosic hydrogels undergoing a large volume change in an aqueous solution on heating or cooling. To this end, we prepared 0-methyl cellulose (MC) and O-(Z-hydroxy-3-butoxypropyl) cellulose (HBPC) which precipitate out of solution on heating without forming gel. MC and HBPC derivatives prepared by homogeneous reactions were proved to be promising raw materials for the cellulosic hydrogels mentioned above. The results on the phase separation of the derivatives were discussed in terms of the distribution of substituents along the cellulose chain and in the anhydroglucose units.