Chitin–cellulose blends: phase properties in dimethylacetamide–LiCl

Chitin–cellulose blends dissolved in dimethylacetamide containing LiCl (7% w/w) have been studied in a wide concentration range, from very dilute solutions to medium concentrations and up to solid films (absence of diluent). The intrinsic viscosities at various chitin–cellulose ratios, as well as the phase diagram behavior, imply a good compatibility between the components. The result is confirmed by the infrared measurements on solid films. The lack of anisotropic phase formation in chitin–diluent binary solutions and the anomalous trend of v′_CH–CE line on the phase diagram are both interpreted on the basis of aggregation phenomena.     

Surface characterization of TEMPO‐oxidized bacterial cellulose

In this study, we focused on the surface character of bacterial cellulose (BC) before and after oxidation mediated by 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO).Solid‐state ¹³C NMR, XPS, SEM, contact angle and surface free energy analyses were performed to investigate the effects of various parameters (reaction time and oxidant and catalyst concentrations) on the surface composition, morphology and polarity of the BC. The results provided by the combined use of these techniques showed that hydrogen bonds were disrupted on the BC surface after carboxylation occurred; therefore, the surface of oxidized BC was rougher than that of the original BC, and the surface free energy, especially the polar components, increased after oxidation. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of empirical polarity parameters of the cellulose solvent N,N-dimethylacetamide/LiCl by means of the solvatochromic technique

Empirical solvatochromic polarity parameters (α-, β-, and $ \pi ^* $, AN and DN, as well as E_T(30)-values) for cellulose, N,N-dimethylacetamide (DMA)/LiCl and cellulose dissolved in DMA/LiCl are presented. The following solvent polarity indicators were applied: 2,6-diphenyl-4-(2,4,6-triphenyl-1- pyridinio)-1-phenolate ( 1 ), bis(4-N,N-dimethylamino)-benzophenone (MK, 2 ), iron(II)-di-cyano-bis(1,10)-phenanthroline, Fe(phen)₂(CN)₂, ( 3 ), and copper(II)-N,N,N′,N′-tetramethyl-ethylendiamine-acetylacetonate tetraphenylborate/chloride/bromide (Cu(tmen)(acac)⁺ X⁻ ( 4 )). The solvatochromic shifts (ν_max) of the indicators 1 , 2 , 3 , and 4 adsorbed to cellulose or dissolved in DMA/LiCl reflect the corresponding properties of the surrounding, the dipolarity/polarizability ($ \pi ^* $), the hydrogen bond donating ability or Lewis acidity (α), and the hydrogen bond accepting ability or Lewis basicity (β), respectively. Any indicator employed is well characterized (r > 0.97) by a linear solvation energy relationship (LSER) taking the Kamlet and Taft parameter into account: ν_max(indicator) = ν_max,0 + s$ \pi ^* $ + aα + bβ. Cellulose, DMA/LiCl, and the cellulose/DMA/LiCl solution approach a similar polarity with an E_T(30) parameter about 52 to 53 kcal mol⁻¹. The hypothetical interaction strength parameter (acid-base interactions, dipolar–dipolar interactions) between cellulose and DMA/LiCl are calculated by means of the individual Kamlet–Taft parameters α, β, and $ \pi ^* $ of cellulose and DMA/LiCl via a multiparameter equation. The specific chloride/cellulose interaction plays a dominant role in the cellulose solvent DMA/LiCl. Comparison of the polarity parameters of DMA/LiCl with the polarity parameters of other mixtures—such as N,N-dimethyl- formamide/LiCl, DMA/NaCl, or DMA/LiBr—are presented as well. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1945–1955, 1998     

Investigation of the structure of cellulose in LiCl/DMAc solution and its gelation behavior by small-angle X-ray scattering measurements

Cellulose gels were prepared from cellulose in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) solution. When the cellulose concentration in the solution is above the one at which cellulose molecules overlap, cellulose gels were formed. While the gel prepared by the addition of water was turbid, the one prepared by the ion exchange was colorless, transparent, and optically anisotropic. In order to explain this gelation behavior of cellulose, small-angle X-ray scattering (SAXS) measurements of the cellulose solutions and the gels were performed. The SAXS profiles of the cellulose solutions and the gels suggested that the large-scale fluctuation of the molecular chain density in the solution can be the origin of the molecular aggregates formed in the gel. Furthermore, the differences in the structure of the gels at the macroscopic and the molecular level were discussed in terms of the phase separation and the molecular association.     

Dilute solution properties of cellulose in LiOH/urea aqueous system

Cellulose was dissolved rapidly in 4.6 wt % LiOH/15 wt % urea aqueous solution and precooled to –10 °C to create a colorless transparent solution. ¹³C‐NMR spectrum proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The result from transmission electron microscope showed a good dispersion of the cellulose molecules in the dilute solution at molecular level. Weight‐average molecular weight (M_w), root mean square radius of gyration (〈s²〉_z^1/2), and intrinsic viscosity ([η]) of cellulose in LiOH/urea aqueous solution were examined with laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 4.6 wt % LiOH/15 wt % urea aqueous solution was established to be [η] = 3.72 × 10^?2 M in the M_w region from 2.7 × 10⁴ to 4.12 × 10⁵. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were given as 6.1 nm, 358 nm^?1, and 20.8, respectively. The experimental data of the molecular parameters of cellulose agreed with the Yamakawa–Fujii theory of the worm‐like chain, indicating that the LiOH/urea aqueous solution was a desirable solvent system of cellulose. The results revealed that the cellulose exists as semistiff‐chains in the LiOH/urea aqueous solution. The cellulose solution was stable during measurement and storage stage. This work provided a new colorless, easy‐to‐prepare, and nontoxic solvent system that can be used with facilities to investigate the chain conformation and molecular weight of cellulose. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3093–3101, 2006     

Interfacial structure and properties of polyurethane/poly(methylacrylate-co-styrene) coating to regenerated cellulose film

A semiinterpenetrating polymer network (IPN) containing 72 wt % polyurethane (PU) and 6 wt % poly(methylacrylate-co-styrene) [P(MA-St)] was coated onto surfaces of regenerated cellulose (RC) film, which was prepared by coagulating a cellulose cuoxam from bagasse pulp. The interfacial structures, bonding manner, and the strength of the coated film were studied by infrared (IR),¹³C nuclear magnetic resonance (NMR), differential thermal analysis (DTA), transmission electron microscopy (TEM), and electron probe microscopy analysis (EPMA). It was shown that the RC film coated with PU/P(MA-St) has strong interfacial interactions, where covalent and hydrogen bonds are formed across the interface between cellulose and the PU/P(MA-St) coating. The interfacial structure of the coated film is regarded as a shared PU network crosslinked simultaneously with P(MA-St) and cellulose film. The tensile strength, water resistivity, and optical transmission of the coated films were considerably higher than that of the uncoated films. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2495–2501, 1997     

Basic studies on gas solubility in natural rubber–cellulose composites

This work reports sorption processes of oxygen, carbon dioxide, methane, ethylene, and propylene in films of both vulcanized natural rubber and vulcanized rubber–regenerated cellulose composites. The curves representing the pressure dependence of the concentration of carbon dioxide in the composites clearly exhibit a slight concavity with respect to the abscissa axis as a result of adsorption processes taking place in Langmuir sites located in the glassy cellulose component. Adsorption processes are also detected in the sorption curves of ethylene at low pressures. The concavity with respect to the ordinate axis of the curve concentration of propylene versus pressure at high pressure is pretty well described by the Flory‐Huggins formalism. The solubilities of the other gases mainly obey Henry's behavior, adsorption processes in the glassy component being in most cases negligible. Values of the interaction χ parameter for gas–natural rubber and gas–natural rubber composites are obtained from the comparison of the experimental solubility coefficients with those predicted by the Flory‐Huggins theory. The theory suggests that Henry's constant is a linear function of the boiling temperature of the gases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2131–2140, 2005     

LiCl／DMAc溶剂体系中长链脂肪酸纤维素酯的制备及其药物释放性能

在ＬｉＣｌ／ＤＭＡｃ溶剂体系中由纤维素与长链脂肪酸氯反应制备长链脂肪酸纤维素酯，并研究了反应条件对酯化反应取代度的影响。结果表明在适当的反应条件下，酯化聚代度可达到２．８５（９５％）。还研究了纤维酯作为药物控制释放载体对ＬＮＧ、Ａｓｐｉｒｉｎ、ＢＡＳ的释放性能。     

Supramolecular structure and properties of high strength regenerated cellulose films

Water-swollen cellulose films prepared from LiOH/urea solution were uniaxially drawn to investigate the effect of orientation on their supramolecular structure and properties. Their structures and properties were investigated with X-ray diffraction, atomic force microscopy and tensile testing. The results revealed that the drawing process led to substantial reorientation of the cellulose molecular chains, resulting in a significant improvement of their mechanical properties and water-resistance. With an increase of the drawn ratios from 1 to 1.22, the tensile strength of the films at dry and wet states increased from 89 to 213 MPa and 2.9 to 33.9 MPa, respectively. Furthermore, the drawn cellulose films also exhibited good biocompatibility with the capability of supporting cell adhesion and proliferation.     

5.4 Properties and applications of cellulose triacetate film

The CTA film can be characterized by e.g. its relatively high moisture regain, significantly low birefringence, and moderate mechanical strength. Having been commercialized more than fifty years ago, it has been widely used as photographic film, protective film for polarizing plate, and optical compensation film for liquid crystal display (LCD). The photographic film application exploits the optical isotropy and unique physical properties of the CTA film. In the application of the CTA film to protective film for polarizing plate, its low in-plane birefringence is of particular importance. In the optical compensation to enhance the viewing angle of LCD, the CTA film, because of its moderate retardation in thickness direction (Rth), serves as an element of compensator as well as a base film. Considering the growth of the LCD market, the demand for CTA film is believed to be further expanding.     

Structural modification of bacterial cellulose

The microfibrillar nature of bacterial cellulose produced by Acetobacter was modified by various chemical reagents in a culture medium. The chemical reagents included antibiotics to inhibit cell division or certain protein synthesis, and reducing reagents that induce reductive cleavage of disulfide bonds in proteins. Among the reagents tested, nalidixic acid and chloramphenicol induced elongation of bacteria, resulting in the formation of wider cellulose ribbons or aggregates of ribbons. The Young's modulus of the sheets made from such cellulose increased, while dithiothreitol, which produced ribbons having only 45% of the width of the control, produced sheets with undiminished Young's modulus. Although further study is necessary to clarify the effect of such modifications, nalidixic acid and chloramphenicol produced a bacterial cellulose with superior mechanical properties.     

Polyelectrolyte/surfactant mixtures at the air–solution interface

This review presents some of the recent developments in our understanding of the behaviour of polyelectrolyte/surfactant mixtures at the air–solution interface. The existence of a strong surface polyelectrolyte/surfactant interaction results in a complex pattern of surface adsorption. Recent studies, using a range of surface sensitive techniques, which include ellipsometry, neutron and X-ray reflectivity, surface tension and interfacial rheology, have considerably enhanced the understanding of their surface behaviour, which can be rationalized in terms of the competition between the formation of surface active polymer/surfactant complexes and solution polymer/surfactant micelle complexes.     

Reactivities of cellulases from fungi towards ribbon-type bacterial cellulose and band-shaped bacterial cellulose

We have investigated the reactivities of various cellulases onribbon-type bacterial cellulose (BC I) and band-shaped bacterial cellulose (BCII) so as to clarify the properties of different cellulases. BC I waseffectively hydrolyzed by exo-type cellulases from different fungi from twicetofour times as much as BC II, but endo-type cellulases showed little differencein reactivity on those substrates. One of the endo-type cellulases, EG II fromTrichoderma reesei, degraded BC II more rapidly thanexo-type cellulases even in the production of reducing sugars. The degree ofpolymerization (DP) of BC II was rapidly decreased by endo-type cellulases atanearly stage, while exo-type cellulases did not cause the decrease of DP atthe initial stage, though the decrease of DP was observed after an incubation of24 h. All exo-type cellulases adsorbed on BC I and BC II,whileendo-type cellulases except for EG II adsorbed slightly on both substrates. Itwas interesting to observe EG II adsorbed on BC I but not on BC II. It issuggested that the adsorption of enzyme on cellulose is important for thedegradation of BC I, but not for BC II. It is proposed that the ratio of aspecific activity of each enzyme between BC I and BC II represents thedifference in the mode of action of cellulase. Furthermore, the K _RW value, which we can calculate from thedecrease of DP/reducing sugar produced, is effective for discriminating themode of action of cellulase, especially the evaluation of randomness in thehydrolysis of cellulose by endo- and exo-type cellulases.     

Characterization of magnetic membranes based on bacterial and man-made cellulose

Ferrites were synthetized in situ in two different neutral cellulose gels: a never-dried bacterial cellulose membrane and a never-dried cast film using N-methylmorpholine-N-oxide as solvent. X-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometry (VSM) and Mossbauer spectroscopy were used to characterize the resulting magnetic nanocomposites. TEM micrographs showed the presence of ferrites in two different shapes, acicular and equiaxial, respectively hydrated ferric oxides (FeOOH) and the spinel oxides: maghemite (gamma-Fe2O3) or magnetite (Fe3O4). Thin sections of bacterial cellulose showed these particles to be located along the cellulose microfibrils, which are assumed to provide a site for their nucleation. Room temperature magnetization curves showed all samples to be superparamagnetic     

Synthesis and solution properties of anionic linear–dendritic block amphiphiles

The design and synthesis of novel linear–dendritic diblock amphiphiles with linear poly(acrylic acid) (PAA) as the hydrophilic block and dendritic poly(benzyl ether) as the hydrophobic block are described. The synthetic process consisted of two steps: a poly(methyl acrylate) (PMA)–poly(benzyl ether) dendrimer series were synthesized with atom transfer radical polymerization, and through the hydrolysis of linear PMA block into PAA, amphiphilic block copolymers, the PAA–poly(benzyl ether) dendrimer series, were obtained. The copolymers were characterized by ¹H NMR, Fourier transform infrared, and size exclusion chromatography and exhibited well‐defined architectures and low polydispersities. When the generation number of the dendritic block (G_i) less or equal to 3 and the degree of polymerization of the linear chain (n) was greater than 10, the amphiphiles were water‐soluble. The solution intrinsic viscosity increased with both the length of linear chain and the generation number of the dendritic block. The results obtained demonstrate that dendritic blocks play an unusual role in aqueous solutions of amphiphiles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4282–4288, 2000     

Synthesis and characterization of hydroxypropyl cellulose from bacterial cellulose

Bacterial cellulose produced by Acetobacter xylinum has been reacted with propyleneoxide to synthesize hydroxypropyl cellulose(HPC) under different reaction conditions while diluted by toluene. The effects of mass ratio of bacterial cellulose to propyleneoxide, dilutability of toluene, reaction temperature(T) and time(t) were investigated by series of experiments. The degree of substitution(DS), hydroxypropyl content(A) and yield(η) were compared. The optimized product exhibited cold-water solubility and hot-water gelatinization in aqueous medium. Further study was carried out with FTIR, TGA, XRD, SEM and 13C-NMR for characterization. The water/air contact angle measurement reveals that it is a good hydrophobic material with good mechanical properties.     

Synthesis of silicone–acrylate copolymer latexes and their film properties

Emulsion copolymerization of silicones (octomethyl tetracyclosiloxane, D₄ and methacryloxypropyl trimethoxy silane, MATS) and acrylics was carried out using three different polymerization processes: semicontinuous monomer emulsion addition, batch and initiator solution addition. Results showed that only the semicontinuous process led to a stable latex with monodisperse particles. Various polymerizations were carried out through this process with varying silicone/acrylic ratios and MATS content. Films were obtained from different latexes: their properties are significantly influenced by silicone and MATS contents in copolymers.     

Facile preparation of regenerated cellulose film from cotton linter using organic electrolyte solution (OES)

Regenerated cellulose (RC) film is an important cellulose-based product with a wide range of applications in the packaging industry and drug delivery. In this study, RC film was prepared using an organic electrolyte solution (OES)/ionic liquid (IL) system consisting of 1-ethyl-3-methylimidazolium acetate (EmimAc) and dimethyl sulfoxide (DMSO) to dissolve cotton linter at room temperature. Results showed that OES with EmimAc molar fraction in the range from 0.2 to 0.4 could rapidly dissolve cotton linter at room temperature, in contrast to 80 °C for EmimAc solution (control). The cellulose degradation was therefore much less than for the control, resulting in significant improvement in the mechanical properties and thermal stability of the RC film. In addition, the presence of DMSO significantly decreased the viscosity of the cellulose/OES system, being advantageous for casting of the RC film.     

Hydrogels prepared from unsubstituted cellulose in NaOH/urea aqueous solution

Novel cellulose hydrogels were synthesized through a "one-step" method from cellulose, which was dissolved directly in NaOH/urea aqueous solution, by using epichlorohydrin as crosslinker. Structure and properties of the hydrogels were characterized by using SEM, NMR, and water absorption testing. The hydrogels are fully transparent and display macroporous inner structure. The equilibrium swelling ratios of the hydrogels in distilled water at 25 degrees C are in the range from 30 to 60 g H(2)O/g dry hydrogel. Moreover, the reswelling water uptake of the hydrogels could be achieved to more than 70% compared with their initial swelling states. This work provided a simple and fast method for preparing eco-friendly hydrogels from unsubstituted cellulose.     

Structure and properties of novel fibers spun from cellulose in NaOH/thiourea aqueous solution

Cellulose was dissolved rapidly in a NaOH/thiourea aqueous solution (9.5:4.5 in wt.-%) to prepare a transparent cellulose solution, which was employed, for the first time, to spin a new class of regenerated cellulose fibers by wet spinning. The structure and mechanical properties of the resulting cellulose fibers were characterized, and compared with those of commercially available viscose rayon, cuprammonium rayon and Lyocell fibers. The results from wide angle X-ray diffraction and CP/MAS 13C NMR indicated that the novel cellulose fibers have a structure typical for a family II cellulose and possessed relatively high degrees of crystallinity. Scanning electron microscopy (SEM) and optical microscopy images revealed that the cross-section of the fibers is circular, similar to natural silk. The new fibers have higher molecular weights and better mechanical properties than those of viscose rayon. This low-cost technology is simple, different from the polluting viscose process. The dissolution and regeneration of the cellulose in the NaOH/thiourea aqueous solutions were a physical process and a sol-gel transition rather than a chemical reaction, leading to the smoothness and luster of the fibers. This work provides a potential application in the field of functional fiber manufacturing.