Showing papers in "Cellulose in 1999"

A Review of the Relationship Between Thermally-Accelerated Ageing of Paper and Hornification

Abstract: A link is drawn between paper hornification and low temperature thermally-accelerated ageing of paper based on a review of existing research. Similarities between treatment temperature, humidity, resultant physical properties, and possible degradation mechanisms are enumerated. Hornification can be explained by irreversible intra-fibre hydrogen bonding, whereas accelerated ageing is normally attributed to chain scission and cross linking. However, in the light of the similar experimental protocols used to investigate each, the possibility of both mechanisms occurring in both experiments should be considered. The short timescales of hornification would seem to preclude chain scission and cross linking, but it seems possible that irreversible hydrogen bonding occurs during dry accelerated ageing.

Chemical conversion of various celluloses to glucose and its derivatives in supercritical water

Abstract: The supercritical water biomass conversion system was designed and developed in our laboratory. The reaction vessel with cellulose sample was treated with this system at supercritical state of water for a designated period (3–105 s) under the conditions of a tin bath temperature of 500°C and pressure of 35 MPa. The recovered products of hydrolysates were then analyzed by high performance liquid chromatography. The obtained results indicated that a high amount of glucose and levoglucosan can be achieved from both celluloses I and II for 5–10 s supercritical treatment, while that from starch for 3–5 s treatment. Although this difference could be due to a difference in the molecular structure between cellulose and starch, a difference between celluloses I and II was not significant. Instead, an accessibility of the water towards cellulose molecules seemed to be significant for their chemical conversion. With the longer treatment, amounts of these compounds observed were decreased due to decomposition. Therefore, it may be concluded that, compared with acid hydrolysis or enzymatic saccharification, cellulose may be hydrolyzed to glucose and its derivatives more or less to the same degree as in corn starch under supercritical state. This finding suggests that the supercritical treatment can overcome the difficulties in hydrolyzing cellulose to glucose, found in the acid hydrolysis or enzymatic saccharification techniques.

Spectroscopic Ellipsometry Characterisation and Estimation of the Hamaker Constant of Cellulose

Abstract: Calculations of Hamaker constants using Lifshitz theory require the availability of accurate dielectric data, especially in the visible-ultraviolet region. We present spectroscopic ellipsometry data on well-defined cellulose films of a limited thickness range (100–140 layers) deposited on an oxidised and hydrophobised silicon substrate. The spectral data, representing measurements from a perpendicular orientation to the fibre deposition direction, was used for estimates of the necessary spectral parameters, i.e. the oscillator strengths and characteristic frequencies in the UV-range. Our calculations show that cellulose has a relatively low Hamaker constant in air (58 zJ) and water (8.0 zJ). The implications for the surface energy estimates of cellulose and colloidal interactions between cellulose and various types of fillers and coating colours are indicated.

Two‐dimensional step‐scan FTIR: a tool to unravel the OH‐valency‐range of the spectrum of Cellulose I

Abstract: This article presents the results of the first application of dynamic mechanical analysis (DMA) coupled with 2D step‐scan Fourier transform infrared (FTIR) spectroscopy, to cellulose. It is demonstrated that the broad hydroxyl infrared absorption band between 3700 and 3000 cm−1 in the cellulose infrared spectra could be separated into distinct bands by this dynamic rheo‐optical investigation using FTIR‐spectroscopy as detecting system. The responses of the OH‐groups to an external perturbation were recorded as in‐phase and out‐of‐phase spectra. The cross correlation of these spectra gave the 2D synchronous and asynchronous plots, which showed clearly separated bands in the OH‐vibration range and the relation of the OH‐groups to each other. It is demonstrated that it is possible to establish relations between the OH‐bands and the cellulose structure.

The behaviour of cellulose in hydrated melts of the composition LiXċn H2O (X=I−, NO3−, CH3COO−, ClO4−)

Abstract: The dissolution behaviour of cellulose in low temperature molten salts was investigated Depending on the chosen anions in the melt, cellulose shows different reaction behaviour in different Li+‐containing melts Dissolution of the polymer was observed in molten LiClO4ċ3H2O and molten LiIċ2H2O In the hydrated melts of LiCH3COOċ2H2O and LiNO3ċ3H2O a fine distribution of cellulose was stated Cellulose can be regenerated by cooling the melt and removing the salt by dissolution in water

Microcrystalline cellulose powders: structure, surface features and water sorption capability

Abstract: Characterization of an Avicel PH 102 MCC powder through polymerization degree determination, X‐ray diffraction and N2 adsorptions at subcritical temperatures is described. Specific characterizations of MCC/H2O exchange in different environments were performed by means of thermogravimetric weight losses on time/temperature scale and analyses of water adsorption/absorption from saturated vapors at 310 K. The reversibility of MCC/H2O interactions and the influence of different ‘surface area probes’ on the specific surface area are discussed.

Properties and treatments of pulps from recycled paper. Part I. Physical and chemical properties of pulps

Abstract: The mechanical, physical, and chemical properties of recycled pulps were evaluated after a series of treatments designed to improve and/or modify the pulp characteristics. Tensile strength, bursting strength, and apparent density of the pulps decreased with recycling. However, the tear strength, in most cases, increased after the first recycle and then decreased after the second recycle. Carboxyl content and WRV of pulps also decreased with recycling. Chemical treatments did not increase the bonding ability of recycled pulps and, in most cases, decreased the physical properties of the pulps. Altering the physical state of the cellulose microstructure through additional swelling did not appear to be a significant factor for strength restoration. It may be that the hemicelluloses plan a greater role in recycling than originally thought.

Carboxymethylation of cellulose in unconventional media

Abstract: Carboxymethylation of cellulose in the new and highly efficient aqueous solvent Ni(tren)(OH)2, [tren=tris(2‐aminoethyl)amine] and in melts of LiClO4· 3H2O or N‐methyl‐morpholine‐N‐oxide (NMMNO), which is now widely applied for cellulose fibre production, was investigated. In case of Ni(tren)(OH)2, a totally homogeneous carboxymethylation of cellulose with sodium monochloroacetate, in the presence of an aqueous NaOH solution is possible for the first time. Structure analysis by means of HPLC and 1 H‐NMR after chain degradation showed results comparable with findings for CMC obtained by the heterogeneous slurry process, that is, a statistic distribution of substituents along the polymer chain and functionalisation of the hydroxyl groups in the order C‐6 ≥ C‐2 > C‐3. The etherification of cellulose in a melt of LiClO4· 3H2O, a new type of cellulose solvent, was shown to be possible and gave products of a statistic functionalisation pattern as well. In contrast, carboxymethylation starting from solutions of cellulose in NMMNO initiated with solid NaOH particles yields polymers with a nonstatistic distribution of functional groups along the chain, as observed for cellulose ethers prepared in reactive microstrctures starting from solutions of cellulose intermediates in dimethyl sulfoxide as well as of unmodified cellulose dissolved in N,N‐dimethyl acetamide/LiCl.

Reaction characteristics of cellulose in the LiCl/1,3‐dimethyl‐2‐imidazolidinone solvent system

Abstract: In order to elucidate the nature of the LiCl/1,3‐dimethy‐2‐imidazolidinone (DMI) solvent system as one of the homogeneous reaction media of cellulose, cellulose acetate (CA) and O‐methylcellulose (MC) were prepared using this solvent system, and the distribution of substituents within anhydroglucose units was examined by 13C‐NMR It was found that (i) homogeneous cellulose solutions can be easily prepared by heating 2, 5–12 and 100 parts of weight of cellulose, LiCl, and DMI, respectively, and (ii) the relative reactivity of hydroxyl groups is in the order C‐6 > C‐2 > C‐3 for both CA and MC A remarkable feature of this solvent system is that the reaction efficiency in etherification is very high compared with other homogeneous solvent systems

Surface properties of lignocellulosic fibers bearing carboxylic groups

Abstract: Fibers with various amounts of carboxylic acid functionalities as determined with FTIR and conductometric titration were prepared by chemical modification of high bleached kraft pulp (CP) and chemical thermomechanical pulp (CTMP) with succinic anhydride. The degree of the modification was dependent on reaction time and the type of fiber used. The modification levelled off after 15 h of reaction, and this effect was similar for both fiber substrates. The amount of carboxylic acid attached to CTMP, determined by weight gain, was however less than half of the amount of carboxylic moieties introduced to CP fibers at any reaction time. ESCA characterization of the succinylated fibers indicates that the carboxylic acid functionalities are predominantly introduced at the fiber surface. The wettability in water, measured as contact angle, of the succinylated CTMP fibers was significantly improved by the modification, whereas the wettability of CP fibers was slightly decreased. The differences in wettability are caused by the dispersive and polar characteristics of succinic acid attached to the fiber surface and its interaction with the fiber surface. The character of the ‘linkage’ group in the anhydride used for modification as well as the composition of the cellulose fiber surface are suggested to play a crucial role in the surface energy of the modified fibers and hence their wetting properties.

Thermoplasticization of cellulose acetates by grafting of cyclic esters

Abstract: A plasticization method for cellulose acetates (CAs) based on the selective grafting of e‐caprolactone (CL) and L-lactide (LACD) has been developed. The selective‐grafted products could be prepared by ring opening polymerization in the melt state at 140°C using stannous octoate as catalyst, where CAs with remaining hydroxyl groups worked as initiator. Plasticization of CAs by this selective grafting can solve the problem encountered in the previous reports (Yoshioka et al., 1996, 1998) that the bleeding of unreacted monomers and homo‐oligomers from the inside of molded articles to their surface was often found. By using adequate reaction conditions, the grafting reaction proceeded rapidly and could be completed within 10–30 min. LACD is grafted more rapidly than CL onto CAs, producing relatively rigid and brittle products in the earlier stages and elastomer‐like ones in the later stages. Transparent amorphous molded articles were obtainable depending on the reaction conditions. The analysis of the structure of the grafted side chains by means of high resolution NMR spectroscopy showed that, although the grafted side chains are composed of large amounts of e‐oxycaproyl or lactidyl block polymer portions depending on the reaction conditions, a large amount of randomly polymerized parts coexist in the grafted chains, which confer high thermoplasticity, elasticity and amorphous nature to the grafted products obtained.

Properties and treatments of pulps from recycled paper. Part II. Surface properties and crystallinity of fibers and fines

Abstract: Surface properties of bleached kraft pulps were evaluated before and after recycling, and after a series of chemical treatments designed to improve and/or modify the pulp characteristics The surface free energy characteristics of the pulps were determined using the Wilhelmy technique, and ESCA and ATR-FTIR methods were used to evaluate the chemical composition of the surfaces of the pulp fibers In general rather small changes were noted at the fiber surfaces with recycling and chemical treatment Recycling tended to increase the acid component and decrease the base component of the surface free energy of the pulps This could result from exposure of carboxyl groups from hemicelluloses and/or from oxidized layers from the bleaching process ESCA analyses also indicated increased carboxyl concentration at the surfaces of the recycled fibers Although treatment with aqueous bases and organic solvents tended to increase the hydroxyl content on the surface of recycled pulps, the chemical treatments were not beneficial to pulp quality AFM and SEM of fiber and fine surfaces of kraft pulps revealed that the fines fraction was altered to a much greater extent with recycling Although recycled fibers appeared to have improved wettability, these small changes in the surface characteristics do not appear to play the dominant role in the characteristics of recycled pulps Recycling did not change the crystallinity of whole pulps, but it increased the crystallinity of the fines fraction The increase in the crystallinity of the fines fraction and the reduction in the water retention value (WRV) and the bulk carboxyl content (xylan) of the recycled pulps, as noted in Part I of this paper, appear to play the predominant role in determining the characteristics of recycled pulps It appears that the loss of the hemicelluloses in the bulk of the fiber with recycling is much more important for internal fibrillation than the apparent small increase of hemicelluloses at the surface of recycled fibers

Swelling of mechanical pulp fines

Abstract: The objective of the study was to determine the swelling of different types of mechanical pulp fines. The physical and chemical characteristics of the fines were also examined. It was found that the degree of swelling correlates with the proportion of fibrillar material, that is fibrillar content of the fines. The fines with the lowest fibrillar content had a swelling comparable to mechanical pulp fibres (0.69 g/g), whereas the fines with a high fibrillar content had a swelling comparable to never‐dried kraft pulp fibres (1.41 g/g). Hemicellulose content and charge could not explain the differences in swelling of different types of the mechanical pulp fines. While the lignin content appears to be an important factor in the degree of swelling of mechanical pulp fines, the results suggest that structural differences between the particles are also important. The ‘bulk elastic modulus’ was determined by measuring the change in swelling for a known change in osmotic pressure. All the mechanical pulp fines had a high bulk elastic modulus compared to kraft fines. However, fibrillar fines had a lower bulk elastic modulus than flake‐like fines. Mechanical pulp fines, both fibrillar and flake‐like varieties, did not hornify appreciably. The swelling of both the fines and the fibre fractions increased slightly with the specific energy consumption in the refining.

Surface Composition and Surface Energetics of Various Eucalypt Pulps

Abstract: In this paper we report on our study of the surface chemical composition, surface energy and acid-base characteristics of plantation eucalypt pulps obtained using the kraft, neutral sulphite semichemical (NSSC) and cold soda processes. X-ray photoelectron spectroscopy (XPS) was used to quantify the surface coverages of extractives and lignin. Inverse gas chromatography (IGC) was used to analyse the dispersive component and the acid-base characteristics of the pulp samples. The pulp yield and the total lignin and extractives in the pulp increased in the sequences of kraft, NSSC and cold soda. The relative surface concentrations of extractives and lignin on the pulps (expressed in terms of the ratios of the pulp surface coverage to the total content of these materials in the pulp) did not increase in the same sequence. The relative surface concentrations of lignin and extractives on the kraft pulps were found to be distinctively higher than those of the NSSC and cold soda pulps. The dispersive components of the surface energy of all pulps were similar before extraction, but increased by different degrees after extraction, with that of the cold soda pulp showing the lowest degree of increase. The acid-base characteristics of the pulps were evaluated using the method of acceptor and donor constants described by Schultz and Lavielle and the method of work of adhesion described by Lundqvist and Odberg. A comparison of these methods has been made. The acidity of all pulps was found to increase after extraction. The degree of increase in pulp acidity is negatively correlated with the surface lignin concentration on the pulps. The low relative acidity of the cold soda pulp is probably associated with its high surface lignin coverage. An experimental model was established to test this hypothesis.

Effect of cellulase adsorption on the surface and interfacial properties of cellulose

Abstract: The surface properties of several purified cellulose (Sigmacell 101, Sigmacell 20, Avicel pH 101, and Whatman CF 11) were characterised, before and after cellulase adsorption. The following techniques were used: thin-layer wicking (except for the cellulose Whatman), thermogravimetry, and differential scanning calorimetry (for all of the above celluloses). The results obtained from the calorimetric assays were consistent with those obtained from thin-layer wicking – Sigmacell 101, a more amorphous cellulose, was the least hydrophobic of the analysed celluloses, and had the highest specific heat of dehydration. The other celluloses showed less affinity for water molecules, as assessed by the two independent techniques. The adsorption of protein did not affect the amount of water adsorbed by Sigmacell 101. However, this water was more strongly adsorbed, since it had a higher specific heat of dehydration. The more crystalline celluloses adsorbed a greater amount of water, which was also more strongly bound after the treatment with cellulases. This effect was more significant for Whatman CF-11. Also, the more crystalline celluloses became slightly hydrophilic, following protein adsorption, as assessed by thin-layer wicking. However, this technique is not reliable when used with cellulase treated celluloses.

Permeation and separation characteristics for benzene/cyclohexane mixtures through tosylcellulose membranes in pervaporation

Abstract: Tosylcelluloses (TosCells) with different degrees of tosylation were synthesized as membrane materials for the separation of benzene/cyclohexane (Bz/Chx) mixtures. TosCell membranes showed a high benzene‐permselectivity for the Bz/Chx mixtures in pervaporation (PV). An increase in the benzene concentration in the feed mixtures increased permeation rate but decreased the benzene‐permselectivity of the TosCell membranes. The increase in the permeation rate was attributed to the increase of the degree of swelling of the TosCell membranes by the feed mixtures and the decrease in the benzene‐permselectivity was mainly caused by the decrease of sorption selectivity. With low benzene concentrations in the Bz/Chx mixtures, the permeation rate of a TosCell membrane with a higher degree of tosylation was greater than that with a lower degree of tosylation, but was vice versa with a high benzene concentration. The benzene‐permselectivity of the former TosCell membrane was higher than that of the latter membrane. Differences of the permeation rate and benzene‐permselectivity with changes in the benzene concentration in the feed mixture and degree of tosylation of the TosCell membrane were significantly influenced by the degree of swelling of the TosCell membrane and the benzene concentration sorbed into the TosCell membrane. Mechanism of separation for the Bz/Chx mixtures through the TosCell membranes is discussed by the solution–diffusion model.

Characterisation of dissolving pulp using designed process variables, NIR and NMR spectroscopy, and multivariate data analysis

Abstract: Two processability variables, filter clogging and alkali resistance, were measured in a series of laboratory‐cooked viscose pulps. The pulps were also characterised by 13C‐CP/MAS solid state nuclear magnetic resonance (NMR) and near infrared (NIR) spectroscopy. Partial least squares (PLS) regression was used to investigate the information provided by the spectroscopic methods with respect to the processability measurements. The study showed that the alkali resistance, R18, of the pulp and the filter clogging value, Kw, of the laboratory‐prepared viscose can be modelled by NIR and multivariate data analysis (MVA). The alkali resistance, R18, of the pulp can also be calculated by NMR and partial least squares (PLS) regression. Analysis of the loading values in the PLS model showed that pulps with high alkali resistance have higher crystallinity than pulps with low alkali resistance. Analysis of variables of the cooking conditions showed that the chemical charge (Na2O) and pH should be kept low to give high alkali resistance, whereas high Na2O gives low filter clogging values.

Thermal stability of the cellulose synthase complex of Acetobacter xylinum

Abstract: The thermal stability of the cellulose synthase complex of Acetobacter xylinum has been analyzed in terms of enzyme activity loss as well as detection of its two major components (83 kDa and 93 kDa polypeptides) in polyacrylamide gels under different electrophoretic sample treatment conditions. The cellulose synthase complex intrinsically is a thermally unstable enzyme and quickly loses its in vitro activity beyond 35° C. The 83 kDa polypeptide has been found to be more labile than the 93 kDa polypeptide. When boiled in lithium dodecyl sulfate (LDS) buffer, the 83 kDa polypeptide is destroyed through peptide hydrolysis while the 93 kDa polypeptide remains uncleaved. The 83 kDa polypeptide is destroyed in LDS buffer at elevated temperatures beyond 55° C. When boiled in the absence of LDS buffer, the 83 kDa polypeptide is completely aggregated, while the 93 kDa polypeptide is only partially aggregated. In the absence of LDS buffer, the complete thermal aggregation of the 83 kDa polypeptide occurs at elevated temperatures beyond 85° C. The aggregation process has been quantitatively analyzed by a newly‐introduced quantitative index, Td (the temperature at which half the quantity of 83 kDa polypeptide disappears due to aggregation). The Td determined for the 83 kDa polypeptide in the product‐entrapped fraction is 48° C.

Water absorbancy of never‐dried cotton fibers

Abstract: Although never‐dried cotton (NDC) fiber has been known to exhibit extremely high water absorbency, the reason for this has not yet been elucidated. In this study, changes in water absorbency, bound water content as revealed by differential scanning calorimetry (DSC), cellulose content and fiber cross‐section observed by scanning electron microscopy (SEM) for NDC fibers at several stages of development (27–57 days post‐anthesis (DPA)) were investigated. It was found that the bound water content (27 g/l00 g) of NDC fibers at 50 DPA is much smaller than that (40–73 g/l00 g) for fibers at 27–43 DPA. Cellulose synthesis takes place within the cotton boll, a closed water‐containing system. Our results are rationalized by assuming that these water molecules are preventing the formation of intermolecular hydrogen bonds between the cellulose molecules as they are being formed. Other explanations for our experimental findings are: (i) the coexistence of precursors of cellulose and components, such as β‐(1,3)‐;glucans, that are very hydrophilic, and (ii) the presence in each NDC fiber of a prominent lumen that acts as a capillary system for water.

Solution properties and mesophase formation of 4‐phenyl‐benzoylcellulose

Abstract: Cellulose samples were derivatized in dimethylacetamide/LiCl (DMAc/LiCl) to give 4‐phenyl‐benzoylcelluloses (PBCs) The process is quantitative and leads to an highly substituted product, as verified by elemental analysis, IR and 13C‐NMR spectroscopy PBC samples were characterized by viscometric and light scattering measurements in DMAc The persistance length q is used to evaluate the theoretical critical volume fraction for mesophase formation (v′ th, which has been found higher than the experimental critical one (v′ exp)

Chiral Nematic Cellulose Acetate Films; Reflectivity and Effect of Deacetylation

Abstract: Cellulose acetate samples with a range of degrees of substitution (DS) were prepared by deacetylation of cellulose acetate (DS = 2.5). Chiral nematic solutions of the samples were prepared in formic acid. A handedness reversal from left to right was observed as the DS used to prepare the mesophase increased from 1.8 to 2.4. By selection of a suitably long-pitch mesophase, chiral nematic films cast from a CA (DS = 2.2)/formic acid solution showed a feint reflection of circularly polarized blue light. Deacetylation of this CA film gave a chiral nematic cellulose film with a more intense reflection band at the same wavelength. The improvement in intensity is attributed to the higher intrinsic birefringence of cellulose compared to cellulose acetate.

About the depolymerization of cellulose propionate to segments with low DP

Abstract: Low molecular weight cellulose propionate (CP) segments were synthesized by depolymerization with HBr under esterification conditions using either a commercial CP with residual hydroxyl groups (DSOH ca. 0.4) or a tripropionate (CTP). The depolymerization using CTP yielded segments having a minimum DP of as low as 7, whereas the depolymerization of the commercial CP resulted in segments having a minimum DP of 50. Differences were also seen in the rate of depolymerization and the Mark-Houwink exponent, which declined from 1 to 0.6 below DP 100 and 30 for commercial CP and CTP, respectively. The results are consistent with the hypothesis that branching is induced by transglycosidation when OH-containing cellulose derivatives are depolymerized with HBr in aprotic solution.