Structure of the right-handed helical crystal ribbon and multilevel fibrils in a tube fiber from a coir fiber

A coir fiber is composed of many tube fibers with large hollows that align in parallel. SEM observation has shown that the tube fiber existing in a coir fiber is packed by a right-handed helix crystal ribbon, and its length/diameter ratio is lower than that of the crystal ribbon by 1–2 orders of magnitude. Based on the results of TEM, the diameter of protofibrils extracted from coir fibers is 6–10 nm, while that of the microfibrils is 20–40 nm, and the length/diameter ratios of protofibrils and microfibrils are 50–250 and 25–150, respectively. According to these observed results, the packing models of the right-handed helix crystal ribbon and its multilevel fibrils have been derived and further verified through the calculation and comparison of both the crystallinity in volume and whisker sizes obtained by means of X-ray diffraction analysis.     

FTIR spectroscopic and NMR studies of hard elastic polypropylene

The variation of amorphous orientation and crystalline regularity of hard elastic polypropylene (HEPP) films during cyclic deformation and stress relaxation processes were studied using a FTIR spectrometer. The result proves entropic elasticity and shows the orientational hysteresis in the amorphous region or within the microfibrils, and also shows that the amorphous orientation increases, but that the crystalline regularity decreases with the increase of extension rate.Three spin-spin relaxation timesT _2f,T _2m, andT _2s and associated mass fractionsF _f,F _m, andF _s of HEPP fibers were measured with a solid echo of NMR method at different elongations and after relaxation or recovery for a long time A new possible interpretation was proposed that, while the microfibrils are formed in HEPP, the medium decay component should be ascribed to inner molecules of the microfibrils, and the slow decay component to the surface molecules of the microfibrils. According to this interpretation, the results implied that subfibrillation is the main process when HEPP is stretched up to 15% strain, and that at above 15% strain thinning and lengthening of the microfibrils become the main process. Thickening of the microfibrils was found in the recovery and relaxation processes.     

Multiscale modeling of the elastic properties of natural fibers based on a generalized method of cells and laminate analogy approach

In this article, a new method based on a generalized method of cells and laminate analogy approach was used to predict the elastic properties of natural fibers. The elastic properties of cellulose crystals and amorphous cellulose were adopted to calculate the effective properties of microfibrils. A ten-layer antisymmetrical laminated structure was used to predict the effective properties of cell walls. The effects of the aspect ratio and volume fraction of cellulose crystal, the microfibril angle in the S2 layer and the lumen ratio of fiber on the axial Young’s moduli of natural fibers were analyzed in detail. The results show that the predicted properties of fibers are those of the cell fibers, and the final elastic properties of natural fibers can be obtained with the volume fractions of cell fibers as the corresponding conversion coefficients. The multiscale method is very effective in the predictions of the axial Young’s moduli of natural fibers.     

Structure and mechanical behavior of nylon 6 fibers filled with organic and mineral nanoparticles. II. In situ study of deformation mechanisms

This study reports on the in situ characterization of the deformation mechanisms at room temperature of polyamide 6 (PA6) fibers filled with hyperbranched molecules or montmorillonite (MMT) platelets. A small‐angle X‐ray scattering study shows that the stretching and sliding of the microfibrils takes place concomitantly in the first stage of elastic loading of as‐spun and partially drawn fibers. In the second stage of loading, which is basically plastic, sliding turns out to be the main process of deformation, accompanied by a significant reduction in the microfibril radius. Fibers drawn close to their maximum draw ratio only display the deformation process of microfibril stretching. This in situ study also reveals subtle features of the reversible processes of deformation that could not be detected from ex situ experiments reported previously. A thickening of the crystal blocks in the microfibrils takes place under stress and disappears upon unloading, indicating that some reversible strain‐induced molecular ordering occurs in the amorphous layers close to the crystal surface. The tentative mechanical modeling enabled a characterization of the components of the fibers: the stiffness of the microfibrils appears to be insensitive to the presence of the particles that are excluded in the interfibrillar regions. The presence of HB molecules clearly increases the stiffness of the interfibrillar regions owing to a physical crosslinking effect. Moreover, it seems that the stiffness improvement of the drawn MMT‐PA6 fiber lies in a greater capability of chain unfolding in the interfibrillar amorphous region. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2633–2648, 2004     

Effect of coagulation conditions on the microfibrillar network of a rigid polymer

An important element in the microstructure of high performance fibers and films fabricated from rigid polymers is an interconnected network of oriented microfibrils, the lateral size of which is about 10 nm. This study is an attempt to elucidate the mechanism by which the microfibrils are formed so that larger lateral dimensions can be achieved by suitable processing. Because this morphology emerges in the coagulation stage of the spinning process, we compared the microfibrillar network formed by drastically different coagulation conditions. Ribbons, spun from solution of poly(p‐phenylene benzobisthiazole) in polyphosphoric acid through a slit die, were coagulated either in the ordinary rapid process with water (timescale of seconds) or in a slow process with phosphoric acid (timescale of hours). The coagulated microfibrillar network was dried with supercritical CO₂ for X‐ray scattering measurements and impregnated with epoxy resin for sectioning and imaging by TEM. Slow coagulation yields better‐aligned microfibrils of enhanced chain packing, but the lateral size of the microfibrils formed in both cases is similar, about 10 nm. Heat treatment increases the width of water‐coagulated microfibrils but not the acid‐coagulated ones. The observations do not support spinodal decomposition as the mechanism of microfibril formation during coagulation, as was previously suggested. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1087–1094, 2002     

Elastic Fiber-Associated Proteins of Skin in Development and Photoaging

Abstract— We sought to use antibodies against structural (tropoelastin, fibrillin) and nonstructural (decay-accelerating factor [DAF], serum amyloid P [SAP]) components of elastic fibers to characterize fiber structure in neonatal skin, normal adult skin and adult skin with solar elastosis from advanced photoaging. We found by immunohisto-chemistry and by western blotting that DAF, unlike SAP, is present on cutaneous elastic fibers in neonates and young children, suggesting that DAF may play an early, integral role in protecting elastic fibers from destruction by complement. The most superficial portion of oxytalan fibers stained with antibodies against fibrillin and DAF, while anti-tropoelastin stained only the deeper portion of oxytalan fibers. This suggests that deep oxytalan fibers are composed of both elastin and microfibrils, while the most superficial component is composed solely of microfibrillar proteins. Solar elastosis showed increased fibrillin, DAF, tropoelastin and SAP. Thus, solar elastosis is composed of both microfibrillar and elastin proteins.     

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.     

CP/MAS 13C-NMR技术对桉木浆纤维素微观结构的研究

利用交叉极化结合魔角旋转技术13C 核磁共振法(CP/MAS ¹³C 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.     

Elucidation of the fibrous structure of <Emphasis Type="Italic">Musaceae</Emphasis> maturate rachis

In the last years several composites and high performance materials with woody and non-woody natural fibers have been developed. In this study, a morphological study of agricultural residues as rachis from Musaceae plants cultivated in Colombia has been carried out. Fibrous structures as fiber bundles, elementary or ultimate fibers and even cellulose microfibrils grouped together into microfibril bundles have been observed. Both biological retting and chemical procedures like alkali treatments combined with alkaline peroxide and acid addition have been used. Different microscopic techniques as optical (OM), confocal (CM), scanning electron (SEM), and atomic force (AFM) ones have been used for analysis of isolated samples. A hierarchical arrangement from conducting tissues and fiber bundles to cellulose microfibrils in Musaceae rachis has been noted. All of these structures can be isolated by biological and chemical processes at the corresponding arrangement level. This means that Musaceae rachises constitute a source of new interesting biodegradable raw materials with multiple possibilities in dimensions and morphologies for several industries. A strong presence of crystal structures exists on fiber surfaces, being their occurrence related to the maturate state of rachis samples. Additionally, a top-down scheme is proposed for understanding the structuration of rachis at each length scale.     

Fragment analysis of different size-reduced lignocellulosic pulps by hydrodynamic fractionation

Micro- and nanocelluloses are typically produced using intensive mechanical treatments such as grinding, milling or refining followed by high-pressure homogenization to liberate individual nano- and microcellulose fragments. Even though chemical and enzymatic pretreatments can be used to promote fiber disintegration, the required mechanical treatments are still highly energy consuming and very costly. Therefore, it is important to understand the kinetics and factors affecting the disintegration tendency of cellulose. In this study, the disintegration tendency of three different wood cellulose pulps with varying chemical composition processed in a PFI mill was examined by analyzing the fractional composition of the microparticles formed. The fractional compositions of the microfibrils and microparticles formed were measured with novel analyzers, which fractionated particles using a continuous water flow in a long tube. The hydrodynamic fractionators used in this study gave valuable information about different size of particles. Results showed that the amount of lignin and hemicelluloses clearly affected the kinetics and the mechanics of cellulose degradation. The P and S1 layers were peeled off from the Kraft fibers, causing the S2 layer to be cropped out. The thermomechanical pulp (TMP) fibers were first degraded by comminution and delamination from the middle lamella and the primary wall. As the refining process progressed, the fibers and fiber fragments began to unravel. Surprisingly, the semi-chemical pulp (SCP) fibers degraded more like Kraft fibers than TMP fibers despite their high lignin and extractive content.     

Tensile deformation of high strength and high modulus polyethylene fibers

The influence of tensile deformation on gel-spun and hor-drawn ultra-high molecular weight polyethylene fibers has been investigated. In high modulus polyethylene fibers no deformation energy is used to break chemical bonds during deformation, and flow is predominantly present next to elastic behavior. Flow is reversible after tensile deformation to small strains, but becomes irreversible when yielding occurs.Stress relaxation experiments were used to determine the elastic and flow contribution to tensile deformation. A simple quantitative relation could then be derived for the stress-strain curve that directly links yield stress to modulus. Experimental stress-strain curves could be reasonably described by this relation.Flow during tensile deformation is shown to be correlated with the introduction of the hexagonal phase in crystalline domains. A mechanism of flow is proposed in which, at first, tie molecules or intercrystalline bridges are pulled out of crystalline blocks (reversible), followed by the break-up of crystalline blocks through slip of microfibrils past each other (stress-induced melting, irreversible).     

Nanofibrillation of dried pulp in NaOH solutions using bead milling

The drying process in typical pulp production generates strong hydrogen bonding between cellulose microfibrils in refined cell walls and increases the difficulty in obtaining uniform cellulose nanofibers. To investigate the efficacy of alkaline treatment for cellulose nanofibrillation, this study applied a bead-milling method in NaOH solutions for the nanofibrillation of dried pulps. NaOH treatments loosened the hydrogen bonding between cellulose microfibrils in dried pulps and allowed preparation of cellulose nanofibers in 8 % NaOH with a width of approximately 12–20 nm and a cellulose I crystal form. Both the nanofiber suspensions prepared in 8 and 16 % (w/w) NaOH were formed into hydrogels by neutralization because of surface entanglement and/or interdigitation between the nanofibers. When the dried pulp was fibrillated in 16 % (w/w) NaOH, the sample after neutralization had a uniquely integrated continuous network. These results can be applied to the preparation of high-strength films and fibers with cellulose I crystal forms without prior dissolution of pulps.     

Hydrophobization and characterization of internally crosslink-reinforced cellulose fibers

Transforming hydrophilic cellulose fibers into hydrophobic, non-hygroscopic fibers could potentially lead to a variety of new products, such as flexible packaging, self-cleaning films and strength-enhancing agents in polymer composites. To achieve this, softwood cellulose pulp was chemically modified with successive chemical treatments. First the C2 and C3 hydroxyl groups of the glucose units were selectively oxidized by periodate oxidation to reactive dialdehyde units on the cellulose chain, followed by a Schiff base reaction with 1,12-diaminododecane to crosslink the microfibrils within the fiber wall. This was done, because introducing high levels of alkylation resulted in fiber disintegration, which could be prevented by crosslinking. After internal crosslinking a second Schiff base reaction was performed with butylamine. This procedure yielded highly hydrophobic and low-hygroscopic cellulosic materials. The modified cellulose fibers were investigated by a variety of techniques, including Fourier transform infrared spectroscopy, nuclear magnetic resonance, field-emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, moisture sorption and water contact angle measurements. The water uptake of the fibers after being modified reduced from 4 to around 1 %. Various reaction conditions were studied for optimum performance.     

Preparation and characterization of iodinated poly(vinyl alcohol) microfibril

Iodination of poly(vinyl alcohol) (PVA) microfibril, which was obtained from saponification of poly(vinyl pivalate), was conducted before and after zone drawing at various conditions. The resulting PVA microfibrils were characterized by differential scanning calorimeter and scanning electron microscopy. Surface morphologies of these PVA microfibrils showed some differences between PVA microfibril iodinated after and before drawing. Crude shapes of PVA microfibrils iodinated after drawing indicated that iodine decreased the structural regularity severely. On the other hand, PVA microfibrils iodinated before drawing showed relatively ordered surfaces. This was ascribed to the enhanced molecular ordering of PVA microfibrils due on zone drawing. Iodinated PVA microfibrils showed a decrease in crystal melting temperature of about 100°C compared to the untreated sample. PVA microfibrils drawn after iodination showed relatively higher crystal melting temperature than those of microfibrils iodinated after drawing. These results were considered as the proofs of the changes in crystalline lattice of the PVA microfibrils. Effects, of drawing temperature on sublimation of iodine were also evaluated.     

pH within pores in plant fiber cell walls assessed by Fluorescence Ratio Imaging

The pH within cell wall pores of filter paper fibers and hemp fibers was assessed by Fluorescence Ratio Imaging (FRIM). It was found that the Donnan effect affected the pH measured within the fibers. When the conductivity of the added liquid was low (0.7 mS), pH values were lower within the cell wall than in the bulk solution. This was not the case at high conductivity (22 mS). The occurrence of the Donnan effect allowed the pH values within pores in normal regions of the cell wall to be compared to the pH in regions with misaligned microfibrils (dislocations) when FRIM was carried out in a low conductivity solution. Surprisingly, no pH difference was observed between normal regions and dislocations, suggesting that pore sizes within the two different regions are approximately the same. In another experiment the Donnan effect was shown to have an effect on hydrolysis of hydrothermally pretreated wheat straw only when conducted in a low conductivity solution and only for xylanase, not cellulases. The hydrolysis experiments indicate that under typical conditions where conductivity is high, the Donnan effect does not lower the pH close to the substrate to an extent that affects enzymatic activity during hydrolysis of lignocellulose.     

Real-time observation of the swelling and hydrolysis of a single crystalline cellulose fiber catalyzed by cellulase 7B from Trichoderma reesei

The biodegradation of cellulose involves the enzymatic action of cellulases (endoglucanases), cellobiohydrolases (exoglucanases), and β-glucosidases that act synergistically. The rate and efficiency of enzymatic hydrolysis of crystalline cellulose in vitro decline markedly with time, limiting the large-scale, cost-effective production of cellulosic biofuels. Several factors have been suggested to contribute to this phenomenon, but there is considerable disagreement regarding the relative importance of each. These earlier investigations were hampered by the inability to observe the disruption of crystalline cellulose and its subsequent hydrolysis directly. Here, we show the application of high-resolution atomic force microscopy to observe the swelling of a single crystalline cellulose fiber and its-hydrolysis in real time directly as catalyzed by a single cellulase, the industrially important cellulase 7B from Trichoderma reesei. Volume changes, the root-mean-square roughness, and rates of hydrolysis of the surfaces of single fibers were determined directly from the images acquired over time. Hydrolysis dominated the early stage of the experiment, and swelling dominated the later stage. The high-resolution images revealed that the combined action of initial hydrolysis followed by swelling exposed individual microfibrils and bundles of microfibrils, resulting in the loosening of the fiber structure and the exposure of microfibrils at the fiber surface. Both the hydrolysis and swelling were catalyzed by the native cellulase; under the same conditions, its isolated carbohydrate-binding module did not cause changes to crystalline cellulose. We anticipate that the application of our AFM-based analysis on other cellulolytic enzymes, alone and in combination, will provide significant insight into the process of cellulose biodegradation and greatly facilitate its application for the efficient and economical production of cellulosic ethanol.     

Mixing aqueous ferric chloride and O-phenylenediamine solutions at room temperature: a fast, economical route to ultralong microfibrils of assemblied O-phenylenediamine dimers

The direct mix of aqueous ferric chloride and o-phenylenediamine (OPD) solutions at room temperature has been demonstrated for the first time to be an effective, economic, and fast method for preparing microfibrils on a large scale. The formation of such large microfibrils is attributed to the self-assembly of the OPD dimers generated by the oxidation of OPD monomers by ferric chloride. It is also interesting that the resulting microfibrils can be broken into shorter ones by a simple sonication process and the final length of the microfibrils obtained can be controlled by varying the sonication time. The influences of both the amount of ferric chloride and the oxidant type on the size and the morphology of the microstructures are also examined.     

Comparative physical and chemical analyses of cotton fibers from two near isogenic upland lines differing in fiber wall thickness

The thickness of cotton fiber cell walls is an important property that partially determines the economic value of cotton. To better understand the physical and chemical manifestations of the genetic variations that regulate the degree of fiber wall thickness, we used a comprehensive set of methods to compare fiber properties of the immature fiber (im) mutant, called immature because it produces thin-walled fibers, and its isogenic wild type Texas Marker-1 (TM-1) that is a standard upland cotton variety producing normal fibers with thick walls. Comprehensive structural analyses showed that im and TM-1 fibers shared a common developmental process of cell wall thickening, contrary to the previous report that the phase in the im fiber development might be retarded. No significant differences were found in cellulose content, crystallinity index, crystal size, matrix polymer composition, or in ribbon width between the isogenic fibers. In contrast, significant differences were detected in their linear density, cross-section micrographs of fibers from opened bolls, and in the lateral order between their cellulose microfibrils (CMFs). The cellulose mass in a given fiber length was lower and the CMFs were less organized in the im fibers compared with the TM-1 fibers. The presented results imply that the disruption of CMF organization or assembly in the cell walls may be associated with the immature phenotype of the im fibers.     

Crosslinking and structural changes of cellulose fibers

The supermolecular structure of various cellulose fibers modified with crosslinking reagents has been investigated by electron microscopy methods. The density, degree of crystallinity (DC), and length changes in alkaline solutions were measured for the modified celluloses. The samples treated with monofunctional analogs of the crosslinking reagents as well as the fiber preparations containing linear and network polymer were also investigated. Three main problems are suggested for the discussion: (1) the general regularities of the structural changes in cellulose in the process of crosslinking; (2) the specific features of the structural changes, as observed in different cellulose samples; (3) the relation between the degree of modification, the type of modifying reagent, and the structure of the crosslinked cellulose. The characteristic structural changes, i.e., the increase in the thickness of fragments, the specific cogged edges, the increase in the lateral dimensions of structural elements all seem to be most representative in native cellulose fibers and are perfectly well distinguished. Similar changes are found in viscose fibers but are less clearly defined. Crosslinking proceeds rather uniformly through the whole of the fiber cross section. It appeared to be most evident when the cross sections are treated with solvents, or when etched in gaseous discharge. Only in cases when the modification is performed in nonaqueous solutions does the reaction proceed mainly in the peripherial regions of the fiber. In fibers subjected to strong swelling, crosslinking results in a real increase in the lateral dimensions of the microfibrils, with the layer thicknesses remaining the same. As a rule, the modification does not imply significant changes in the fiber surface. The crystallite size decreases in the process of crosslinking. This appears to be peculiar to viscose fibers, especially to those subjected to crosslinking in the swollen state. The degree of crystallinity and density of the fibers decrease sharply, which seems to be especially evident in epichlorohydrin-modified samples. Cellulose structure remains unchanged when linear or network polymer forms in the fiber or when the samples are treated with monofunctional reagents. Changes in properties and structure of cellulose caused by crosslinking are most apparent if elongation of the fibers in alkaline solution before and after the modification is compared.     

Mesoporous structures in never-dried softwood cellulose fibers investigated by nitrogen adsorption

Nitrogen adsorption was used to characterize mesoporous structures in never-dried softwood cellulose fibers. Distinct inflections in desorption isotherms were observed over the relative vapor pressure (P/P₀) range of 0.5–0.42 for never-dried cellulose fibers and partially delignified softwood powders. The reduction in N₂ adsorption volume was attributed to cavitation of condensed N₂ present in mesopores formed via lignin removal from wood cell walls during delignification. The specific surface areas of significantly delignified softwood powders were ~150 m² g^?1, indicating that in wood cell walls 16 individual cellulose microfibrils, each 3–4 nm in width, form one cellulose fibril bundle surrounded with a thin layer of lignin and hemicelluloses. Analysis of N₂ adsorption isotherms indicates that mesopores in the softwood cellulose fibers and partially delignified softwood powders had peaks ranging from 4 to 20 nm in diameter.