Nutzung cellulosehaltiger Abprodukte bei der Biosynthese von Cellulasen

It was analysed the influence of different pretreatment methods of cellulosic materials to increase the productivity of the cellulase biosynthesis. The most effective pretreatment method for cotton cellulose is the thermomechanical destruction in a worm extruder (5–15 minutes) with hydrolysis catalysts. The enzymatic saccharification degree was increased about 4 fold. Utilizing a pretreated cellulose an increase of 70–120% in C₁-activity was found besides their level was stabilized in higher values. It was demonstrated that enzymatic hydrolysis parameters would be applied as model for biochemical utilization of cellulosic materials in the biosynthesis of cellulases.     

Esterification of cellulose-enriched agricultural by-products and characterization of mechanical properties of cellulosic films

Two agricultural by-products, wheat bran and maize bran have been examined for their suitability to be transformed into biomaterials by esterification by lauroyl chloride. Influence of biochemical characteristic of cellulose (cellulose content, viscosity-average degree of polymerization, crystallinity) was studied on eight samples enriched in cellulose after chemical removal of heteroxylans and lignin. After an acidic pre-treatment, esterification was carried out with lauroyl chloride and an optimized reaction time of 8 h was used.

Chemical compositions were similar for all cellulose esters obtained, but cellulose content of initial material had a marked influence on the amount of esterified product. A film was easily obtained by casting and the mechanical (tensile strength and elongation), thermomechanical and calorimetric properties were determined. The possible role of grafted fatty acid as internal plasticizer was finally discussed.     

The effect of the cellulose-binding domain from Clostridium cellulovorans on the supramolecular structure of cellulose fibers

The cellulose-binding domain (CBD) is the second important and the most wide-spread element of cellulase structure involved in cellulose transformation with a great structural diversity and a range of adsorption behavior toward different types of cellulosic materials. The effect of the CBD from Clostridium cellulovorans on the supramolecular structure of three different sources of cellulose (cotton cellulose, spruce dissolving pulp, and cellulose linters) was studied. Fourier-transform infrared spectroscopy (FTIR) was used to record amides I and II absorption bands of cotton cellulose treated with CBD. Structural changes as weakening and splitting of the hydrogen bonds within the cellulose chains after CBD adsorption were observed. The decrease of relative crystallinity index of the treated celluloses was confirmed by FTIR spectroscopy and X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the binding of the CBD on the cellulose surface and the changing of the cellulose morphology.     

Solubilization mechanism and characterization of the structural change of bacterial cellulose in regenerated states through ionic liquid treatment

A statistical approach was used to characterize the heterogeneous structures of bacterial cellulose samples pretreated with four kinds of ionic liquids (ILs). The structural heterogeneity of these samples was measured by Fourier transform infrared spectroscopy as well as solid-state NMR methods such as cross-polarization magic-angle spinning and dipolar-assisted rotational resonance. The obtained data matrices were then evaluated by principal components analysis. The measured 1-D data clearly revealed the modification of crystalline cellulose; in addition, the statistical approach revealed subtle structural changes that occurred upon pretreatment with different kinds of ILs. To investigate whether such regenerated structural changes occurred because of solubilization, we examined the intermolecular nuclear Overhauser effect between cellulose and an IL. Our results clarify how the nucleophilic imidazole is attacked and suggest that the cation of the IL is associated with the collapse of hydrogen bonds in cellulose.     

Characterization of the crystalline structure of cellulose using static and dynamic FT-IR spectroscopy

The cellulose structure is a factor of major importance for the strength properties of wood pulp fibers. The ability to characterize small differences in the crystalline structures of cellulose from fibers of different origins is thus highly important. In this work, dynamic FT-IR spectroscopy has been further explored as a method sensitive to cellulose structure variations. Using a model system of two different celluloses, the relation between spectral information and the relative cellulose Ialpha content was investigated. This relation was then used to determine the relative cellulose Ialpha content in different pulps. The estimated cellulose I allomorph compositions were found to be reasonable for both unbleached and bleached chemical pulps. In addition, it was found that the dynamic FT-IR spectroscopy technique had the potential to indicate possible correlation field splitting peaks of cellulose Ibeta.     

Dissolution of cellulose from AFEX-pretreated Zoysia japonica in AMIMCl with ultrasonic vibration

In this study, 1-allyl-3-methylimidazolium chloride (AMIMCl), an ionic liquid, was synthesized and characterized by a series of test methods. Pretreatment of Zoysia japonica by ammonia fiber expansion (AFEX) was shown to reduce significantly the mass of hemicellulose and lignin in biomass, thereby breaking the lignocellulosic structure. Z. japonica samples pretreated with AFEX showed reasonable solubility in AMIMCl upon ultrasonic treatment. The rate of cellulose regeneration from Z. japonica samples pretreated with AFEX increased with increase in applied power of ultrasonication within a certain power range from 0 to 110 W. The regeneration rate of cellulose from AFEX-pretreated Z. japonica reached a maximum of 97% when the ultrasonic power was 110 W. Fourier transform infrared spectroscopy and nuclear magnetic resonance analyses indicated that the regenerated cellulose was similar to microcrystalline cellulose.     

Quantitative analysis of cellulose nitrates by Fourier transform infrared spectroscopy

Quantitative express analysis of nitrogen content in cellulose nitrates by Fourier transform infrared spectroscopy has been developed. The slope of the dependence of the ratio of the band intensity (and area) to sample weight in a tablet, on the nitrogen content in a sample was used to find the reduced extinction coefficients for quantitative analysis of nitrogen content in cellulose nitrate samples by IR spectroscopy. The results were compared with the nitrogen content values in the same samples determined by the ferrosulfate method.     

Dependence of chemical and crystalline structure of alkali sulfite pulp on cooking temperature and time

This study investigates the change in chemical and crystalline structure of pulp samples during alkali sulfite process at different cooking temperatures and time, TAPPI and SCAN standard test methods and X-ray diffraction and FT-IR spectroscopy were used. It was shown that the crystalline structure of cellulose in hemp (Cannabis sativa L.) bast fibers was very strong and stable. Crystallinity of alkali sulfite pulp samples obtained from processing at 140 up to 180 °C increased, but then decreased at 200 °C. The crystallite size of cellulose in alkali sulfite pulp samples increased with cooking temperature. The crystalline allomorph of cellulose in alkali sulfite pulp samples obtained at 200 °C changed from monoclinic structure to triclinic structure. Crystalline structure of cellulose in alkali sulfite pulp samples was little affected by changing cooking time. It was concluded that cooking temperature during alkaline sulfite pulping process had more effect on carbohydrate components and crystalline structure of pulp samples than cooking time.     

Enzymatic acylation of hydroxypropyl cellulose in organic media and determination of ester formation by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy

Esters were prepared by acylation of hydroxypropyl cellulose with fatty acid catalyzed by immobilized lipase from Candida antarctica in tert-butanol. The nature of the substrates used, the initial water activity of the system, and the molecular weight of the hydroxypropyl cellulose were investigated. Moreover, Fourier transform-infrared (FT-IR) spectroscopy was used for determination of ester content on hydroxypropyl cellulose. Specifically, a linear relationship was established between the peak height assigned to the absorption of the esterified carboxyl groups of the cellulose and the ester content. At optimum reaction conditions, the ester content on the hydroxypropyl cellulose was about 11%.     

Polymorphism of cellulose I family: reinvestigation of cellulose IVI

Polymorphs of cellulose I, III(I), and IV(I) have been investigated by X-ray diffraction, FT-IR, and solid-state (13)C NMR spectroscopy. Highly crystalline cellulose III(I) samples were prepared by treating cellulose samples in supercritical ammonia at 140 degrees C for 1 h, and conventional cellulose III(I) samples were prepared by liquid ammonia treatment. The cellulose IV(I) sample of highest crystallinity was that prepared from Cladophora cellulose III(I) in supercritical ammonia, followed by the sample treated in glycerol at 260 degrees C for 0.5 h, whereas the lowest crystallinity was observed in ramie cellulose prepared by conventional liquid ammonia treatment followed by glycerol annealing. In general, the perfection of cellulose IV(I) depends on the crystallinity of the original material: either of the starting cellulose I or of the cellulose III(I) after ammonia treatment. The product thus obtained was analogous to cellulose I(beta), which is what it should be called rather than cellulose IV(I). If the existence of the polymorph cellulose IV(I) is not accepted, the observations on which it has been based may be explained by the fact that the structure termed cellulose IV(I) is cellulose I(beta) which contains lateral disorder.     

Engineering renewable cellulosic thermoplastics

Biopolymers are engineered physically, chemically, genetically or biochemically (i.e. via biotechnological fermentation process) with the purpose to meet specific industry requirements of a wide range of applications. Various technological strategies are reported to create biodegradable plastics with unique physicochemical properties and a predetermined service life. The combination of polymeric material in composites is considered to optimize their mechanical behavior and reliability. Extrusion, a thermomechanical process, is the most widely used technology for producing thermoplastic starch. However, the ease of cellulose accessibility for thermal processing is of increasing economic importance but is complicated by the presence of very strong intermolecular hydrogen bonds in cellulose. Chemical modification is still the common way to get cellulosic thermoplastic products from renewable resources. Therefore, STEP ITN research activities focus on understanding the fundamental chemistry governing polysaccharide transformation and shaping, to utilize this knowledge to introduce thermoplasticity and new functionalities in polymers such as unmodified cellulose.     

Degradation of wheat straw by Fibrobacter succinogenes S85: a liquid- and solid-state nuclear magnetic resonance study

Wheat straw degradation by Fibrobacter succinogenes was monitored by nuclear magnetic resonance (NMR) spectroscopy and chemolytic methods to investigate the activity of an entire fibrolytic system on an intact complex substrate. In situ solid-state NMR with 13C cross-polarization magic angle spinning was used to monitor the modification of the composition and structure of lignocellulosic fibers (of 13C-enriched wheat straw) during the growth of bacteria on this substrate. There was no preferential degradation either of amorphous regions of cellulose versus crystalline regions or of cellulose versus hemicelluloses in wheat straw. This suggests either a simultaneous degradation of the amorphous and crystalline parts of cellulose and of cellulose and hemicelluloses by the enzymes or degradation at the surface at a molecular scale that cannot be detected by NMR. Liquid-state two-dimensional NMR experiments and chemolytic methods were used to analyze in detail the various sugars released into the culture medium. An integration of NMR signals enabled the quantification of oligosaccharides produced from wheat straw at various times of culture and showed the sequential activities of some of the fibrolytic enzymes of F. succinogenes S85 on wheat straw. In particular, acetylxylan esterase appeared to be more active than arabinofuranosidase, which was more active than alpha-glucuronidase. Finally, cellodextrins did not accumulate to a great extent in the culture medium.     

CP-MAS NMR analysis of carbohydrate fractions of soybean hulls and endosperm

CP-MAS NMR spectroscopy was used to identify soybean cellulose and pectin extracts and to investigate the kinetics of cross polarization. The in vitro incubation of cellulose and pectin, extracted from soya hull and endosperm, respectively, with sheep rumen fluid was followed with this technique. The difference in enzymatic degradability between ChSS and DASS, two pectins with identical monosaccharide composition, was explained by the degree of esterification that is lower in DASS. Variable contact time CP-MAS NMR experiments of the cellulose fraction during the incubation revealed that cellulose was degraded in a layer-by-layer way.     

Morphological and optical characterization of polyelectrolyte multilayers incorporating nanocrystalline cellulose

Aqueous layer-by-layer (LbL) processing was used to create polyelectrolyte multilayer (PEM) nanocomposites containing cellulose nanocrystals and poly(allylamine hydrochloride). Solution-dipping and spin-coating assembly methods gave smooth, stable, thin films. Morphology was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and film growth was characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry, and optical reflectometry. Relatively few deposition cycles were needed to give full surface coverage, with film thicknesses ranging from 10 to 500 nm. Films prepared by spin-coating were substantially thicker than solution-dipped films and displayed radial orientation of the rod-shaped cellulose nanocrystals. The relationship between film color and thickness is discussed according to the principles of thin film interference and indicates that the iridescent properties of the films can be easily tailored in this system.     

Triplet quantum yields in light-scattering powder samples measured by laser-induced optoacoustic spectroscopy (LIOAS)

In recent years, different methods and techniques have been applied to study the primary photophysical processes occurring in dye-loaded light-scattering powdered samples. In spite of this, there are still no reliable methods for the determination of triplet quantum yields for this kind of systems. Laser-induced optoacoustic spectroscopy (LIOAS) has been extensively used for the determination of triplet quantum yields of dyes in solution. In a previous work, LIOAS was applied to the measurement of absolute emission quantum yields of highly fluorescent powdered samples. Excellent agreement was found with values obtained from reflectance data. In this work, we apply the same technique for the determination of triplet quantum yields of Rose Bengal and Erythrosine B adsorbed on microcrystalline cellulose. In contrast to water and other solvents, internal conversion cannot be neglected in the cellulose environment. The triplet quantum yield for both dyes is around 0.55 and does not change with dye concentration.     

Cell-wall structure and anisotropy in procuste, a cellulose synthase mutant of Arabidopsis thaliana

In dark-grown hypocotyls of the Arabidopsis procuste mutant, a mutation in the CesA6 gene encoding a cellulose synthase reduces cellulose synthesis and severely inhibits elongation growth. Previous studies had left it uncertain why growth was inhibited, because cellulose synthesis was affected before, not during, the main phase of elongation. We characterised the quantity, structure and orientation of the cellulose remaining in the walls of affected cells. Solid-state NMR spectroscopy and infrared microscopy showed that the residual cellulose did not differ in structure from that of the wild type, but the cellulose content of the prc-1 cell walls was reduced by 28%. The total mass of cell-wall polymers per hypocotyl was reduced in prc-1 by about 20%. Therefore, the fourfold inhibition of elongation growth in prc-1 does not result from aberrant cellulose structure, nor from uniform reduction in the dimensions of the cell-wall network due to reduced cellulose or cell-wall mass. Cellulose orientation was quantified by two quantitative methods. First, the orientation of newly synthesised microfibrils was measured in field-emission scanning electron micrographs of the cytoplasmic face of the inner epidermal cell wall. The ordered transverse orientation of microfibrils at the inner face of the cell wall was severely disrupted in prc-1 hypocotyls, particularly in the early growth phase. Second, cellulose orientation distributions across the whole cell-wall thickness, measured by polarised infrared microscopy, were much broader. Analysis of the microfibril orientations according to the theory of composite materials showed that during the initial growth phase, their anisotropy at the plasma membrane was sufficient to explain the anisotropy of subsequent growth.     

Chemical force microscopy of cellulosic fibers

Atomic force microscopy with chemically modified cantilever tips (chemical force microscopy) was used to study the pull-off forces (adhesion forces) on cellulose model surfaces and bleached softwood kraft pulp fibers in aqueous media. It was found that for the –COOH terminated tips, the adhesion forces are dependent on pH, whereas for the –CH₃ and –OH terminated tips adhesion is not strongly affected by pH. Comparison between the cellulose model surfaces and cellulosic fibers under our experimental conditions reveal that surface roughness does not affect adhesion strongly. X-ray photoelectron spectroscopy (XPS) and Fourier Transformed Infrared (FTIR) spectroscopy reveal that both substrate surfaces have homogeneous chemical composition. The results show that chemical force microscopy can be used for the chemical characterization of cellulose surfaces at a nano-level.     

Factors influencing the regeneration of cellulose I from phosphoric acid

The regeneration of cellulose I from phosphoric acid solution was studied, with emphasis both on the conditions required for the regeneration of cellulose I and characterization of the resulting cellulose by X-ray diffraction. Raman spectroscopy and SS¹³C n.m.r. As the conditions of regeneration were varied with respect to temperature and time a variety of polymorphs were produced. As previously reported, the cellulose I polymorph dominated at high temperature and long regeneration time. The question of the authenticity of the regenerated cellulose I was addressed, with several tests confirming that it was not an insoluble residue. Further analysis of the various regenerated celluloses revealed that they all had a small cellulose I component that could be isolated by acid hydrolysis. It is suggested that during regeneration, nuclei of different cellulose polymorphs are formed simultaneously, the proportion of each dependent upon the relative rates of nucleation. Under degradative regeneration conditions the polymorphs more susceptible to hydrolysis are attacked preferentially, leaving behind resistant cellulose I     

Improvement of biofouling resistance on bacterial cellulose membranes

Bacterial cellulose possesses excellent biocompatibility and mechanical strength that show great potentials for biomaterial applications. In this study, the surface modifications of bacterial cellulose (BC) membranes were facilitated using either simple coating or chemical grafting methods. The surface coating method is to simply immobilize BC membranes with poly(ethylene glycol) (PEG) solutions of concentration from 1 to 10%, followed by post-treatment with argon (Ar) plasma. The chemical method involved grafting mPEG (monofunctional methyl ether PEG) on BCs. The outcomes of surface modifications were characterized by surface chemical compositions (electron spectroscopy for chemical analysis (ESCA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetry analysis (TGA), and surface morphology (atomic force microscopy (AFM) and scanning electron microscopy (SEM)). The effects of resistance to biofouling were verified by quantifying the adsorption of proteins and mammalian cells. The results showed that the PEG coating on BCs improved the resistance to cell adhesion by more than 30%. On the other hand, the specific chemical grafting resulted in a particularly high resistance to biofouling that the density of adherent cells reduced by more than 70% when compared to that on pristine BC. We have demonstrated that the two proposed methods were effective for the preparation of bioinert BC membranes with great potentials for applications in biomaterials and tissue engineering.     

Effects of organosolv pretreatment and enzymatic hydrolysis on cellulose structure and crystallinity in Loblolly pine

Ethanol organosolv pretreatment was performed on Loblolly pine to enhance the efficiency of enzymatic hydrolysis of cellulose to glucose. Solid-state ¹³C NMR spectroscopy coupled with line shape analysis was used to determine the structure and crystallinity of cellulose isolated from pretreated and enzyme-hydrolyzed Loblolly pine. The results indicate reduced crystallinity of the cellulose following the organosolv pretreatment, which renders the substrate easily hydrolyzable by cellulase. The degree of crystallinity increases and the relative proportion of para-crystalline and amorphous cellulose decreases after enzymatic hydrolysis, indicating preferential hydrolysis of these regions by cellulase. The structural and compositional changes in this material resulting from the organosolv pretreatment and cellulase enzyme hydrolysis of the pretreated wood were studied with solid-state CP/MAS ¹³C NMR spectroscopy. NMR spectra of the solid material before and after the treatments show that hemicelluloses and lignin are degraded during the organosolv pretreatment.