Microfibril diameter in celery collenchyma cellulose: X-ray scattering and NMR evidence

Cellulose isolated from celery collenchyma is typical of the low-crystallinity celluloses that can be isolated from primary cell-walls of higher plants, except that it is oriented with high uniformity. The diameter of the microfibrils of celery collenchyma cellulose was estimated by three separate approaches: ¹³C NMR measurement of the ratio of surface to interior chains; estimation of the dimensions of the crystalline lattice from wide angle X-ray scattering (WAXS) measurements using the Scherrer equation; and the observation that microfibrils of this form of cellulose have the unusual property of packing into an irregular array from which small angle X-ray scattering (SAXS) shows features of both form and interference functions. The interference function contributing to the SAXS pattern implied a mean microfibril centre-to-centre distance of 3.6 nm, providing an upper limit for the diameter. However modelling of the scattering pattern from an irregular array of microfibrils showed that the observed scattering curve could be matched at a range of diameters down to 2.4 nm, with the intervening space more or less sparsely occupied by hemicellulose chains. The lateral extent of the crystalline lattice normal to the 200 plane was estimated as a minimum of 2.4 nm by WAXS through the Scherrer equation, and a diameter of 2.6 nm was implied by the surface: volume ratio determined by ¹³C NMR. The WAXS and NMR measurements both depended on the assumption that the surface chains were positioned within an extension of the crystalline lattice. The reliability of this assumption is uncertain. If the surface chains deviated from the lattice, both the WAXS and the NMR data would imply larger microfibril diameters within the range consistent with the SAXS pattern. The evidence presented is therefore all consistent with microfibril diameters from about 2.4 to 3.6 nm, larger than has previously been suggested for primary-wall cellulose. Some degree of aggregation may have occurred during the isolation of the cellulose, but the larger microfibril diameters within the range proposed are a consequence of the novel interpretation of the experimental data from WAXS and NMR and are consistent with previously published data if these are similarly interpreted.     

A physico-chemical characterisation of new raw materials for microcrystalline cellulose manufacturing

A detailed physico-chemical characterisation of potential new cellulose sources (rice husk, hemp stalk, and coniferous needles), and microcrystalline cellulose (MCC) manufactured from them, was made in this work. The length and the width of the cellulose crystallites were determined by wide-angle X-ray scattering (WAXS), crystallinities were studied by means of WAXS and solid state cross polarisation magic angle spinning ¹³C nuclear magnetic resonance (NMR) spectroscopy, and the packing and the cross-sectional shape of the microfibrils were determined by small-angle X-ray scattering. When MCC was prepared from rice husks and hemp stalks an acceptable yield was obtained. Crystallinities obtained with solid state NMR spectroscopy and WAXS were highest for MCC prepared from hemp stalks, and lowest for rice husk MCC. The crystallite sizes of MCC samples studied in this work varied more than in those MCC samples which were prepared from conventional plant sources, and crystallite size and cellulose crystallinity were related. When taking into account rather high values of specific surface, hemp stalks and rice husks appear as a promising raw materials for MCC production.     

Hydration effects on spacing of primary-wall cellulose microfibrils: a small angle X-ray scattering study

Celery collenchyma cell walls are typical of primary plant cell walls in their composition but contain unusually well-oriented cellulose microfibrils that are packed with more regularity than normal, permitting small-angle X-ray scattering (SAXS) experiments that would not otherwise be possible. Small-angle scattering data were obtained for the cell walls in essentially their native state and for isolated cellulose, in a fibrous form that retained the physical shape and microfibril orientation of the native cell walls. The scattering patterns showed a distinct peak attributed to the interference contribution to the convolution of form and interference functions. The position of the peak attributed to the interference function implied a mean centre-to-centre microfibril spacing of approximately 3.2 nm in dry isolated cellulose and 3.8 nm in dry cell walls. Hydration increased the mean microfibril spacing in the cell walls to 5.4 nm but had only a small effect on the mean microfibril spacing of isolated cellulose. In the scattering profile from intact, hydrated cell walls it was just possible to discern the position of the first Bessel minimum, from which a microfibril diameter in the range 3.1–3.6 nm may be estimated. This estimate is likely to include attached hemicellulose chains. Porod plots of scattering intensity indicated a relatively sharp interface between microfibrils and their immediate surroundings. The SAXS data imply that cellulose microfibrils 2.6–3.0 nm in diameter are not quite in lateral contact with one another in the isolated cellulose and are augmented by hemicelluloses and separated by readily hydrated matrix polysaccharides in the native plant cell wall.     

Phase transitions in poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate). SAXS,WAXS and DSC study

The main-chain thermotropic liquid-crystalline poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate) (P7MB) was investigated by time-resolved small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and differential scanning calorimerty (DSC). Nonisothermal crystallisation with different rates of cooling and heating was used. On cooling, two phase transitions are observed, isotropic melt - smectic (I-Sm) and Sm- three-dimensional crystalline structure (Sm-Cr), whereas on heating only one transition is observed, Cr-I transition. The transition enthalpies were calculated. Temperature dependences of d-spacings of all crystalline peaks and of the peak observed at high values of scattering vector in the SAXS region were derived. The temperature dependence of the degree of crystallinity was established, based on the integrated intensities of the crystalline peaks and amorphous halo in WAXS.     

Influence of the layered silicate type on the structure, morphology and properties of cellulose acetate nanocomposites

This paper deals with the effect of different montmorillonite source clays, including pristine and organophilic montmorillonites, on the structure, morphology and properties of cellulose acetate (CA)/clay nanocomposites. In this study, the nanocomposites were prepared by melt extrusion in the presence of the environmentally friendly triethyl citrate plasticizer. The structure and morphology of the materials were analysed by X-ray diffraction and scattering (SAXS), X-ray microtomography and energy filtered transmission electron microscopy (EFTEM). SAXS and EFTEM results indicated that the nanocomposite morphologies were made up of tactoids together with exfoliated clay platelets in different proportions depending on the clay type. It can be concluded that well distributed clay tactoids and platelets can be achieved in CA nanocomposites prepared by melt extrusion and consequently property improvements can be found by using pristine or organophilic clays. In this case, the addition of a plasticizer, able to intercalate in the clay gallery, seems to be sufficient to promote the clay delamination mechanism under shearing inside the cellulose acetate matrix.     

Structure and spacing of cellulose microfibrils in woody cell walls of dicots

The structure of cellulose microfibrils in situ in wood from the dicotyledonous (hardwood) species cherry and birch, and the vascular tissue from sunflower stems, was examined by wide-angle X-ray and neutron scattering (WAXS and WANS) and small-angle neutron scattering (SANS). Deuteration of accessible cellulose chains followed by WANS showed that these chains were packed at similar spacings to crystalline cellulose, consistent with their inclusion in the microfibril dimensions and with a location at the surface of the microfibrils. Using the Scherrer equation and correcting for considerable lateral disorder, the microfibril dimensions of cherry, birch and sunflower microfibrils perpendicular to the [200] crystal plane were estimated as 3.0, 3.4 and 3.3 nm respectively. The lateral dimensions in other directions were more difficult to correct for disorder but appeared to be 3 nm or less. However for cherry and sunflower, the microfibril spacing estimated by SANS was about 4 nm and was insensitive to the presence of moisture. If the microfibril width was 3 nm as estimated by WAXS, the SANS spacing suggests that a non-cellulosic polymer segment might in places separate the aggregated cellulose microfibrils.     

SIMULTANEOUS SAXS／WAXS／DSC STUDIES ON MICROSTRUCTURE OF CONVENTIONAL AND METALLOCENE-BASED ETHYLENE-BUTENE COPOLYMERS

The fractions of one metallocene-based (mPE) and one conventional (znPE) ethylene-butene copolymer eluted at 80-82℃ from temperature rising elution fractionation were selected for DSC and time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) characterization. The DSC and WAXS results show that two crystal structures exist in both mPE and znPE: structure A with higher melting temperature and structure B with lower melting temperature. It was found that original znPE (s-znPE) contains more highly ordered structure A than original mPE (s-mPE) in spite of the higher comonomer content of znPE. Another structure C is also identified because of higher crystallinity measured by WAXS than by DSC and is attributed to the interfacial region. The SAXS data were analyzed with correlation function and two maxima were observed in s-mPE and s-znPE, in agreement with the conclusion of two crystal populations drawn from DSC and WAXS results. These two crystal populatiorts have close long periods in s-mPE, but very different long periods in s-znPE. In contrast, freshly crystallized mPE and znPE (f-mPE and f-znPE) contain only a single crystal population with a broader distribution of long period     

Contrast-Matched Small-Angle X-ray Scattering from a Heavy-Atom-Labeled Protein in Structure Determination: Application to a Lead-Substituted Calmodulin-Peptide Complex

The information content in 1-D solution X-ray scattering profiles is generally restricted to low-resolution shape and size information that, on its own, cannot lead to unique 3-D structures of biological macromolecules comparable to all-atom models derived from X-ray crystallography or NMR spectroscopy. Here we show that contrast-matched X-ray scattering data collected on a protein incorporating specific heavy-atom labels in 65% aqueous sucrose buffer can dramatically enhance the power of conventional small- and wide-angle X-ray scattering (SAXS/WAXS) measurements. Under contrast-matching conditions the protein is effectively invisible and the main contribution to the X-ray scattering intensity arises from the heavy atoms, allowing direct extraction of pairwise distances between them. In combination with conventional aqueous SAXS/WAXS data, supplemented by NMR-derived residual dipolar couplings (RDCs) measured in a weakly aligning medium, we show that it is possible to position protein domains relative to one another within a precision of 1 ?. We demonstrate this approach with respect to the determination of domain positions in a complex between calmodulin, in which the four Ca(2+) ions have been substituted by Pb(2+), and a target peptide. The uniqueness of the resulting solution is established by an exhaustive search over all models compatible with the experimental data, and could not have been achieved using aqueous SAXS and RDC data alone. Moreover, we show that the correct structural solution can be recovered using only contrast-matched SAXS and aqueous SAXS/WAXS data.     

Study of platinum and palladium aggregates intercalation into cellulose by waxs,spectroscopic, and microscopic methods

The WAXS, SAXS, SEM, TEM, XPS were used to study methods of platinum and palladium aggregates intercalation into the cellulose matrix and changes of cellulose structure after this intercalation. As a result new microcrystalline cellulose - metal compounds containing aggregates of platinum, and palladium were synthesised for the first time using the redox interaction reaction.     

CP/MAS ~(13)C NMR技术对木浆纤维微观结构的研究

利用交叉极化结合魔角旋转技术~(13)C核磁共振法(CP/MAS ~(13)C NMR)对桉木浆纤维的微观结构进行研究,为进一步研究木质纤维素材料开发过程中反应障碍特征奠定基础.通过对NMR光谱C1区(δ 102～108)进行洛仑兹拟合,得到桉木浆纤维中纤维素Iα的相对含量为26.92%,纤维素Iβ的相对含量为52.04%,主要以纤维素Iβ晶体形式为主.通过计算纤维素C4结晶区(δ 86～92)和非结晶区(δ 80～86)的相对含量得到桉木浆的纤维素结晶度为47%.通过洛仑兹和高斯函数的混合模型对NMR光谱C4区(δ 80～92)进行拟合得到基原纤尺寸和微原纤横向尺寸分别为4.0与17.9 nm,并通过计算不同形态的结晶纤维素的相对含量得到纤维素结晶度为51%,证实了在微原纤内部次晶纤维素的存在.     

On the morphology of oriented nylon-12

The morphology of drawn and annealed sheets of nylon-12 was investigated by transmission electron microscopy of stained sections, and the results compared with equivalent small-angle X-ray scattering (SAXS) patterns. A three-component structure was observed, consisting of crystalline (C) and amorphous (A) regions in the microfibrils and an interfibrillar component whose density was deduced to be intermediate between that of the C and A regions. The crystallite width was given satisfactorily by a Guinier analysis of the SAXS profile.Dedicated to Prof. Dr. R. Bonart on the occasion of his 60th birthday.     

AFM observation of ultrathin microfibrils in fruit tissues

Polysaccharide microfibrils in fruit tissue of higher plants (strawberry, peach, and rambutan) were examined by atomic force microscopy (AFM). For preserving native cellulose microfibrils, a combination of 2% NaClO₂ and 4% NaOH extraction was applied to the materials. This corresponds to mild alkali extractin of holocellulose, and denoted here as weak alkali-resistant polysaccharide, WARP. The amount of neutral sugars corresponded to 53–95% of that of WARP. Glucose was the most abundant in the neutral sugars, being 74–87%. AFM examination of microfibrils dispersed on mica substrate allowed accurate determination of fibril widths as 1.0–2.0 nm. Their straight fibrillar shape and the results of X-ray diffraction and infrared spectroscopy indicate that these fibrils are cellulose. These results constitute direct evidence for existence of ultrafine cellulose microfibrils hitherto assumed from X-ray diffraction and NMR analyses.     

Characterization of pore structure in metal-organic framework by small-angle X-ray scattering

MOF-5-like crystals were studied by small-angle X-ray scattering (SAXS) to reveal, both quantitatively and qualitatively, their real structural details, including pore surface characteristics, pore shape, size distribution, specific surface area (SSA), spatial distribution, and pore-network structure. A combined SAXS and wide-angle X-ray scattering (WAXS) experiment was conducted to investigate the variation of the pore structure with the MOF-5 crystalline phase produced at different cooling rates. The SSA of the MOF-5 crystals synthesized herein spanned a broad range from approximately 3100 to 800 m2/g. The real pore structures were divided into two regimes. In regime I the material consisted mainly of micropores of radius approximately 8 A as well as mesopores of radius 120 approximately 80 A. The structure in regime II was a fractal network of aggregated mesopores with radius >or=32 A as the monomer, reducing SSA and hydrogen uptake capacity at room temperature. The two regimes can be manipulated by controlling the synthesis parameters. The concurrent evolution of pore structure and crystalline phase during heating for solvent removal was also revealed by the in-situ SAXS/WAXS measurement. The understanding of the impact of the real pore structure on the properties is important to establish a favorable synthetic approach for markedly improving the hydrogen storage capacity of MOF-5.     

Structure and water sorption of polyurethane nanocomposites based on organic and inorganic components

Organic-inorganic polymer composites, consisting of a polyurethane organic phase and a mineral inorganic phase were prepared by the joint polymerization of the urethane oligomer with the water solution sodium silicate. The structure and the morphology of the composites, at a fixed weight fraction of the inorganic component of 20%, and of the corresponding pure polyurethane matrices were investigated by wide-angle and small-angle X-ray scattering (WAXS and SAXS, respectively). The results show similar size (5-7 nm) of the scale of heterogeneity of the composites due to the microphase separation of the rigid and the flexible blocks of the amorphous polyurethane matrix and due to the inorganic crystalline inclusions, i.e. the materials prepared are nanocomposites. The WAXS measurements indicate that the individual properties of the block inorganic component are lost in the nanocomposites, probably due to physical and chemical interactions between the two components. Water sorption from the liquid phase was studied gravimetrically in a composite and in the corresponding polyurethane. The results show high sorption capacity of the composite, due to the hydrophilicity of the inorganic phase and the elasticity of the polyurethane matrix, and allow to estimate the layer thickness of water adsorbed on the inorganic nanoparticle surface to about 20 nm, in reasonable agreement with a model adopted from the literature. WAXS and SAXS measurements on the swelled composite and the swelled-and-dried composite indicate changes in the structure of the inorganic component induced by water, which are, however, to a large extent reversible. These materials may find applications as gel electrolytes and as hydrogels in drug delivery systems.     

Time-resolved structural studies in fiber processing

Time-resolved and off-line synchrotron wide-angle and small-angle x-ray scattering (WAXS and SAXS) was used to study the structure formation in poly-p-phenylenebenzobisoxazole (PBO) fibers during various stages of spinning, coagulation, and heating processes. WAXS data could be explained in terms of liquid-crystalline structures of varying degrees of order. A structure model is proposed that is in accordance with the observed SAXS four-point pattern.     

Oligomer-to-polymer transition in short ethylene glycol chains connected to mobile hydrophobic anchors.

We studied the structure of short ethylene glycol (EG) chains with N repeating units (EGN, N = 3, 6, 9, 12, and 15) connected to hydrophobic dihexadecyl chains by means of a combination of differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS/WAXS). These synthetic amphiphiles dispersed in water form planar lamellar stacks and hexagonal cylinders confining the EG chains to restricted geometries. Owing to the self-assembly of the anchoring points, the lateral density of EG chains in planar lamella can be quantitatively controlled. Furthermore, the chain-melting phase transition of the anchors enables us to "switch" the intermolecular distance reversibly. SAXS/WAXS results suggest that the shorter EG chains (N = 3, 6, and 9) assume a helical conformation in stacks of planar lamella. When the EG chains are further elongated (N = 12 and 15), the lamellar periodicities cannot be explained by a linear extrapolation of shorter oligomers, but can be interpreted well as polymer brushes following the scaling theorem. Such rich phase behaviors of EGN molecules can be used as a simple model of oligo/poly-saccharide chains on cell surfaces, which act not only as flexible repellers between neighboring cells but also as stable spacers for functional ligands.     

利用小角/广角X射线散射联用及一维相关函数分析研究聚(ε-己内酯)片晶的形态

用小角/广角X射线散射(SAXS/WAXS)联用的实验方法考察了等温结晶温度(Tc)和等温时间对聚(ε-己内酯)(PCL)片晶形态的影响.根据WAXS数据计算了PCL的重量结晶度,进而求得其体积结晶度Vc(WAXS).在不同Tc下结晶的PCL样品的Vc(WAXS)均略高于50%.对SAXS谱线做一维相关函数(1DCF)分析,得到了PCL的片晶长周期(LP)和无定形层厚度(La).通过比较WAXS及SAXS的数据分析结果,认为PCL晶体需用"三相模型"予以描述,其过渡层厚度(E)约为LP的15%～18%,对片晶形态具有重要影响.随着Tc升高,PCL晶体的Lc、La及E均逐渐增大,但Lc的变化率最大,这使得结晶度上升.在50℃等温结晶不同时间,发现Lc随延长时间显著增加,而La及E则不断减小.等温10天后,PCL晶体的SAXS谱线上可观察到5级散射,表明片晶相当完善.     

Upgrading of paper grade pulps to dissolving pulps by nitren extraction: yields,molecular and supramolecular structures of nitren extracted pulps

Different paper grade pulps were extracted with nitren in order to produce dissolving pulps and polymeric xylan. The yield and molecular structure of the extracted pulps were investigated by carbohydrate analysis and HPSEC combined with fluorescence labelling in order to additionally monitor the carbonyl and carboxyl group profiles of the pulps. The supramolecular structure of selected pulps were further studied by solid state ¹³C-CP/MAS-NMR and wide-angle X-ray scattering (WAXS). These supramolecular data of nitren extracted pulps were compared to samples extracted with NaOH and a conventional dissolving pulp in order to classify the properties of nitren extracted pulps. Nitren extraction results in selective xylan removal without noticeable degradation or oxidation of the cellulose fraction. The resulting dissolving pulps have high molar masses, a narrow molar mass distribution and the typical contents of carbonyl and carboxyl groups. The supramolecular structure of cellulose is less affected by nitren compared to strong NaOH, and the resultant dissolving pulps still have the cellulose I structure. All laboratories are members of the European polysaccharide network of excellence EPNOE.     

Kinetics of fiber heat treatment. III Poly(butylene terephthalate) fibers

Small- and wide-angle X-ray scattering (SAXS and WAXS), shrinkage, and density experiments were performed on poly(butylene terephthalate) fibers which had been isothermally crystallized at different temperatures, and at constant tension, for times ranging from 100 to 1050 ms. A consistent correlation among WAXS, SAXS, and the kinetic results is demonstrated. Shrinkage results show that the crystallization process prevails over the chain-re-coiling process. Density measurements show that the rate of crystallization increases with temperature. Pinhole X-ray photos show that the orientation of the chains within the crystals remains constant with time and temperature. WAXS diffractometer scans show the development of wide-angle Bragg peaks. SAXS shows the development of small-angle Bragg peaks, as the annealing time is increased. The two-lobe arced pattern is the characteristic pattern. The value for long spacing ranged from 100 to 120 Å, increasing with temperature.