Rheological studies of high-concentration cellulose sulfate-acetate solutions

With the method of homogeneous synthesis, various salt forms of cellulose sulfate-acetate containing Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺, and Co²⁺ as compensating cations have been obtained. The flow curves, the concentration and temperature dependences of the shear viscosity of aqueous solutions of cellulose sulfate-acetate have a form characteristic of liquid-crystal systems. For solutions of all salts except for potassium salt, spontaneous formation of the anisotropic phase in the form of individual spherulites, spherulite bands, structures of the fingerprint type, and other more complex formations has been registered. A new hydrodynamic criterion that permits predicting the realization of lyotropic mesomorphism in solutions of cellulose derivatives is proposed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 41–47, September–October, 2005.     

The effects of cellulose nanowhiskers on electrospun poly (lactic acid) nanofibres

The effects of cellulose nanowhiskers on the microstructure and thermal behaviour of electrospun poly (lactic acid) (PLA) nanofibres have been investigated in this study. The PLA/cellulose nanowhiskers composite nanofibres are successfully produced by electrospinning the mixtures of cellulose whiskers with PLA solution. The diameters of PLA and its composites are around 300 nm. The scanning electron micrographs show that the cellulose nanowhiskers do not protrude out of the outer surfaces of PLA nanofibres. The existence of cellulose nanowhiskers in the electrospun PLA matrix nanofibres, and the microstructural evolution are investigated by using X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) analysis shows the formation trend of PLA α crystal with the addition of cellulose nanowhiskers. The electrospun PLA and PLA/cellulose nanowhiskers composites reveal very low crystallinity due to the rapid solvent evaporation and relatively slow crystallisation kinetics character of PLA. The electrospun nanofibres show particularly different thermal behaviour from that of the solution cast films. The nanofibres of pure PLA and PLA/cellulose nanowhiskers experience two consecutively overlapping crystallisation processes. The cellulose nanowhiskers act as heterogeneous sites for nucleation of PLA by decreasing the cold crystallisation onset temperature. The incorporation of cellulose nanowhiskers into PLA nanofibres is expected to improve mechanical properties and bring new functionalities to the electrospun matrix nanofibres.     

Elongational rheology of fiber forming polymers

The elongational rheology of some fiber forming polymers, such as polypropylene (PP), polyethylene (PE), nylon 66, and lyocell (cellulose dissolved in N-Methylmorpholine/water) solutions, has been characterized using hyperbolic convergent dies in a capillary rheometer, at different Hencky strains, processing temperatures, and as a function of elongational strain rates up to 600 s^{− 1}. The influence of melt flow rate (MFR) and molecular parameters is studied and it is shown that the elongational viscosity curves can be shifted with respect to both temperature and Hencky strain.     

A new class of electrorheological material: synthesis and electrorheological performance of rare earth complexes of phosphate cellulose

A new class of electrorheological (ER) material, rare earth (RE = Ce, Gd, Er and Y) complexes of phosphate cellulose, has been synthesized using microcrystalline cellulose, phosphoric acid, urea and RE(NO₃)₃ solutions as starting materials. The ER properties of suspensions of microcrystalline cellulose, phosphate cellulose [cellulose-P-ONH₄] and the [cellulose(-P-O)₃RE] complex particle materials in silicon oil have been investigated under DC electric field. The formation of rare earth complexes helps to decrease the shear stress and viscosity at zero electric field, and to enhance the ER effect of the materials. The shear stress (τ_E) of the ER fluid (20% weight fraction) of a typical yttrium complex [cellulose(-P-O)₃Y], the yttrium content of which is 0.04 mol/100 g, is 2.3 kPa at 4.2 kV/mm and 300 s⁻¹ with a τ_r value (τ_r = τ_E/τ₀, where τ₀ is the shear stress at no electric field and 300 s⁻¹) of 34.3, which is 18 times higher than that of pure microcrystalline cellulose suspensions. The improvement of dielectric loss tangent of the material, due solely to the formation of rare earth complexes, resulted in an enhancement in the ER effect of the material. In addition, the cellulose(-P-O)₃RE materials possess better thermal stability, and their suspensions are more stable in the anti-sedimentation than that of the cellulose-P-ONH₄ material.     

Phase separation and liquid-crystal state of cellulose triacetate in nitromethane

The existence of the liquid-crystal state of cellulose acetate in nitromethane has been shown on the basis of the calculation data, rheological and x-ray structural analysis, and polarization- and electron-microexamination. The conditions for the formation of the lyotropic phase have been revealed and the states of its concentration-temperature boundary have been determined and marked on the diagram. It is shown that the ratio between acetate and hydroxyl groups in the polymer strongly influences the temperature and concentration ranges of realization of a highly oriented state. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 6, pp. 1178–1187, November–December, 2008.     

Review of the recent developments in cellulose nanocomposite processing

This review addresses the recent developments of the processing of cellulose nanocomposites, focusing on the most used techniques, including solution casting, melt-processing of thermoplastic cellulose nanocomposites and resin impregnation of cellulose nanopapers using thermoset resins. Important techniques, such as partially dissolved cellulose nanocomposites, nanocomposite foams reinforced with nanocellulose, as well as long continuous fibers or filaments, are also addressed. It is shown how the research on cellulose nanocomposites has rapidly increased during the last 10 years, and manufacturing techniques have been developed from simple casting to these more sophisticated methods. To produce cellulose nanocomposites for commercial use, the processing of these materials must be developed from laboratory to industrially viable methods.     

Preparation of nanoporous cellulose foams from cellulose-ionic liquid solutions

Nanoporous cellulose foams have been successfully prepared by a procedure in three steps: (i) dissolving in a room temperature ionic liquid (1-butyl-3-methylimidazolium chloride); (ii) coagulation in water; (iii) rapid freeze drying using liquid N₂. The results show that the foam had a 3D open fibrillar network structure with the specific surface area as high as 186.0 m²/g and a porosity of 99%. Moreover, the cellulose foam shows cellulose II crystalline structure. Cellulose concentration in hydrogel as well as drying methods influences upon the structure and pore size of cellulose foams.     

Low frequency dielectric spectroscopy characterization of microcrystalline cellulose, tablets and paper

Cellulose fibres and particles in the form of powder, tablets and paper sheets have been investigated by very low frequency dielectric spectroscopy using a novel form of dielectric cell, in which two planar electrodes have been mounted in fixed positions at right angles. The broad pattern of response obtained from the samples is independent of the structural form of the cellulose sample, a loss peak in the 0.1–100 Hz range, and at lower frequencies a dispersion process which is dominated by an imperfect charge transport. Moisture has a significant influence on the rate of charge transport. In dry samples the dipolar loss peak was not evident but as the moisture content increased it appeared. Using a humidity normalizing technique the dielectric response for microcrystalline cellulose has been characterized over the equivalent of 14 decades in frequency. It has also been shown that there is a linear response between the capacitance and the density of microcrystalline cellulose samples. The consolidation of powder into tablets is discussed with respect of the observations of changes in capacitance, loss peak frequency and imperfect charge transport efficiency. Furthermore it was found possible to investigate differences between the dipolar relaxation rate “in” and “out” of the plane of paper in the stack. The relaxation time for dipoles “out” of the paper plane is 7 to 8 times longer than for dipoles “in” the paper plane. This revised version was published online in November 2006 with corrections to the Cover Date.     

Nanocomposites of cellulose/iron oxide: influence of synthesis conditions on their morphological behavior and thermal stability

Nanocomposites of cellulose/iron oxide have been successfully prepared by hydrothermal method using cellulose solution and Fe(NO₃)₃·9H₂O at 180 °C. The cellulose solution was obtained by the dissolution of microcrystalline cellulose in NaOH/urea aqueous solution, which is a good system to dissolve cellulose and favors the synthesis of iron oxide without needing any template or other reagents. The phases, microstructure, and morphologies of nanocomposites were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectra (EDS). The effects of the heating time, heating temperature, cellulose concentration, and ferric nitrate concentration on the morphological behavior of products were investigated. The experimental results indicated that the cellulose concentration played an important role in both the phase and shape of iron oxide in nanocomposites. Moreover, the nanocomposites synthesized by using different cellulose concentrations displayed different thermal stabilities.     

Development and characterization of cellulose/clay nanocomposites

Cotton is the most important textile fiber for apparel use and is preferred to synthetic fibers for reasons such as comfort and feel. A major drawback of cellulosic fibers is flammability. The development of cellulose/clay nanocomposites for use as flame-retardant materials based on cotton is reported in this paper. Novel nanocomposite materials have been produced from cellulose with layered silicate clays used as the nanofiller material. Three different methods were attempted in producing these organic–inorganic hybrids. The nanocomposites show significant improvements in thermal properties when compared with cellulose control sources. The degradation temperature of the nanocomposites increased by 45 °C and the char yields for some compositions doubled those of the controls. The crystalline melt of the materials decreased by 15 °C. Tensile testing revealed an increase of approximately 80% in the ultimate stress of the cellulose/clay nanocomposites.     

Low density polyethylene composites containing cellulose pulp fibers

Unbleached and bleached Kraft cellulose pulp fibers modified with a long chain carboxylic acid, i.e. oleic acid in cold plasma conditions have been used as reinforcements in low density polyethylene (LDPE). The purpose of the modification is to enhance the interfacial adhesion between cellulose and matrix and to increase the dispersability. Composites containing up to 10 wt.% of untreated and modified cellulose pulp fibers with LDPE were prepared by melt mixing. The samples were characterized by processing behavior, mechanical and rheological properties, SEM, contact angle measurements, TGA and DSC. It was found that when the modified pulp fibers were incorporated into composites matrix, most of the properties have been improved.     

再生纤维素食品包装材料应用进展及法规研究

目的 归纳总结再生纤维素基材料在食品包装行业的研究进展及各国法规情况,以促进再生纤维素在食品包装领域的应用和发展,同时确保其符合相关法规和标准,保障食品安全。方法 对再生纤维素概况及制备方法进行简要介绍,对再生纤维素在食品包装领域的研究进行详细综述,对再生纤维素在食品包装领域的应用前景及存在的困难进行总结及展望。结果 溶解与再生在再生纤维素制备过程中发挥着至关重要的作用;再生纤维素已经在抗菌、防腐、抗紫外线及抗水蒸气阻隔食品包装领域取得了一定的研究进展;目前不同国家和地区已经制定了相关的法规但仍存在一定差异。结论 再生纤维素已经成为新型包装材料的有力候选者之一,但仍需要在制备方法、法规制定等方面进行改进,以推动再生纤维素行业的持续健康增长和创新。     

Reinforcing potential of micro- and nano-sized fibers in the starch-based biocomposites

Starch-based biocomposites reinforced with jute (micro-sized fiber) and bacterial cellulose (BC) (nano-sized fiber) were prepared by film casting. Reinforcement in the composites is essentially influenced by fiber nature, and amount of loading. The optimum amount of fiber loading for jute and bacterial cellulose in each composite system are 60 wt% and 50 wt% (of starch weight), respectively. Mechanical properties are largely improved due to the strong hydrogen interaction between the starch matrix and cellulose fiber together with good fiber dispersion and impregnation in these composites revealed by SEM. The composites reinforced with 40 wt% or higher bacterial cellulose contents have markedly superior mechanical properties than those reinforced with jute. Young’s modulus and tensile strength of the optimum 50 wt% bacterial cellulose reinforced composite averaged 2.6 GPa and 58 MPa, respectively. These values are 106-fold and 20-fold more than the pure starch/glycerol film. DMTA revealed that the presence of bacterial cellulose (with optimum loading) significantly enhanced the storage modulus and glass transition temperature of the composite, with a 35 °C increment. Thermal degradation of the bacterial cellulose component occurred at higher temperatures implying improved thermal stability. The composites reinforced with bacterial cellulose also had much better water resistance than those associated with jute. In addition, even at high fiber loading, the composites reinforced by bacterial cellulose clearly retain an exceptional level of optical transparency owing to the effect of the nano-sized fibers and also good interfacial bonding between the matrix and bacterial cellulose.     

流变法测定纤维素的分子量标度及分子量分布

探索了流变法测定纤维素分子量标度及分子量分布的方法。该法认为,由Rouse期终(terminal)松弛时间公式计算得到的分子量为纤维素分子量分布中的峰值分子量(Mp),从而实现了将频率的倒数(表示相对分子量)转换为分子量标度(表示真实分子量),获得纤维素分子量标度分布曲线。将得到的结果与凝胶渗透色谱法(GPC)测定纤维素分子量及其分布的结果进行对比,对比表明,流变法与GPC法测得的Mp值非常接近,测得的多分散指数(PDI)趋势一致。因此,用流变法研究纤维素的分子量及其分布是可行的。     

Relationship between wood elastic strain under bending and cellulose crystal strain

Wood is a natural composite material with a complex multi-scale structure. Its stiffness is mainly due to crystalline cellulose fibrils reinforcing the cell walls. In order to quantify the contribution of cellulose to wood elastic properties in both tension and compression, the change in cellulose (0 0 4) lattice spacing (cellulose crystal strain) was measured by X-ray diffraction during a bending test on poplar specimens. A detailed methodology is presented to accurately quantify this cellulose crystal strain. Results show that during elastic loading, cellulose crystal strain is roughly proportional to wood strain. The strain ratio (cellulose crystal strain/wood strain) was close to 0.75, and did not differ significantly in tension and compression. Interpretation of the strain ratio with respect to cellulose orientation shows that part of the wood strain occurs without inducing cellulose crystal strain. This contribution amounts to 10–15% of wood strain, and its possible origin at different levels of wood ultra-structure is discussed.     

Extraction and characterization of cellulose whiskers from commercial cotton fibers

During the past few years, there has been a growing interest in incorporating cellulose whiskers from different sources as nanoreinforcement in polymer matrixes. The purpose of this study is to evaluate the performance of the cellulose whiskers obtained from Brazilian commercial cotton. In this sense, cellulose whiskers were prepared by acid hydrolysis which was carried out with a sulfuric acid solution 6.5 M at 45 and 60 °C for 75 and 20 min, respectively, and dried using different methods—an oven, a freeze dryer, and an air circulation oven. Cellulose whiskers were investigated in respect of crystallinity, thermal stability, and morphologically by scanning transmission electron microscopy. Cellulose cotton whiskers, independently of extraction conditions, provided an average length and a diameter of 150 ± 50 nm and of 14 ± 5 nm, respectively, and showed a rod-like shape. Whiskers extracted at 45 °C for 75 min have shown similar crystallinity and better thermal stability in oxidizing atmosphere. The use of the freezing dry process resulted in whiskers with better thermal stability and similar crystallinity than those obtained when dried in the air circulation oven process.     

Kinematic Viscosity and Density of Binary and Ternary Mixtures Containing Hydrocolloids,Sodium Chloride,and Water

The kinematic viscosity and density of binary aqueous solutions containing xanthan gum and ternary aqueous solutions containing carboxymethyl cellulose and sodium chloride have been measured from 303 K to 318 K at different values of pH. The viscosity and density for binary and ternary systems showed increases with a higher concentration of hydrocolloids (xanthan gum or carboxymethyl cellulose) and reductions with increasing temperature. The presence of NaCl in the ternary systems produced an electro-viscous effect that influenced the viscosity and density of the system. The models used to predict the viscosity, density, and apparent specific volume demonstrated satisfactory results in comparisons with experimental data.     

Slow crack growth in cellulose fibre cements

Slow stable crack growth is a prominent feature of the fracture behaviour of cellulose fibre cements. It is shown that this characteristic can be described by crack growth resistance against crack extension curves based on linear elastic fracture mechanics. Double-cantilever-beam specimens with side grooves are used to obtain such crack resistance curves for a commercial cellulose cement containing approximately 8% mass fraction of bleached fibres. Both dry and wet samples are tested. Compliances measured during slow crack growth by the unloading/reloading technique at successive crack increments are less than those obtained for saw-cut notches with similar crack lengths. Residual displacements due to either mismatch fracture surfaces or a large inelastic process zone at the crack tip are also observed at zero load. A modified elastic potential energy release rate (G _R ^* ), and hence its equivalentK _R ^* [= (EG _R ^* )^1/2], must be used to include this residual displacement effect in order to yield the true crack growth resistance curves. This is found to be necessary for the wet samples due to their large residual displacements. The crack growth resistances of the wet samples are superior to those of the dry samples: this is explained in terms of the improved ductility and toughness of the wet cellulose fibres.     

Zeolite-filled regenerated cellulose membranes for pervaporative dehydration of glycerol

Regenerated cellulosic membranes were prepared by dissolving linter pulp in N-methylmorpholine-N-oxide (NMMO) solution with four different cellulose concentrations (3, 5, 8 and 10 wt. % cellulose) at three different coagulation temperatures (5, 25 and 50 °C). Zeolite 13 X with an average particle size of 310 nm and Zeolite 4A with an average particle size of 270 nm were added during dissolution. The resulting composite membranes were characterized by Fourier Transform Infrared (FTIR), Thermogravimetric Analyzer (TGA), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Pervaporation performances of the zeolite filled and unfilled regenerated cellulose membranes were tested for glycerol/water mixture.Chemically and thermally stable regenerated cellulose membranes could be prepared by using submicron sized zeolite loading maximum of 50%. The SEM pictures showed that the zeolite particles in polymer phase were uniformly distributed. It was concluded that the zeolite filled regenerated cellulose membranes have minimum degradation during membrane preparation obtained from NMMO and could be used as pervaporation membranes. At 30 °C and with the addition of 20 wt. % Zeolite 13 X to the cellulose membrane, the flux and selectivity was obtained 65 gm⁻²h⁻¹ and 1681 for 90 wt% glycerol aqueous solution, respectively.     

Titanium dioxide–cellulose hybrid nanocomposite and its glucose biosensor application

This paper investigates the fabrication of titanium dioxide (TiO₂)–cellulose hybrid nanocomposite and its possibility for a conductometric glucose biosensor. TiO₂ nanoparticles were blended with cellulose solution prepared by dissolving cotton pulp with lithium chloride/N,N-dimethylacetamide solvent to fabricate TiO₂–cellulose hybrid nanocomposite. The enzyme, glucose oxidase (GOx) was immobilized into this hybrid nanocomposite by physical adsorption method. The successful immobilization of glucose oxidase into TiO₂–cellulose hybrid nanocomposite via covalent bonding between TiO₂ and GOx was confirmed by X-ray photoelectron analysis. The linear response of the glucose biosensor is obtained in the range of 1–10 mM. This study demonstrates that TiO₂–cellulose hybrid nanocomposite can be a potential candidate for an inexpensive, flexible and disposable glucose biosensor.