Electron micrographs, cellulose

Fig. 5. Scanning electron micrographs of hoUow fiber dialysis membranes. Membranes in left panels are prepared from regenerated cellulose (Cuprophan) and those on the right from a copolymer of polyacrylonitrile. The ceUulosic materials are hydrogels and the synthetic thermoplastic forms a microreticulated open cell foam with a tight skin on the inner wall. Pictures at top are membrane cross sections those below are of the wall region. Dimensions as indicated.

The results of mechanical properties (presented later in this section) showed that up to 20 phr, the biofillers showed superior strength and elongation behavior than CB, cellulose being the best. After 30 phr the mechanical properties of biocomposites deteriorated because of the poor compatibility of hydrophilic biopolymers with hydrophobic natural rubber(results not shown). While increasing quantity of CB in composites leads to constant increase in the mechanical properties. Scanning electron micrographs revealed presence of polymer-filler adhesion in case of biocomposites at 20 phr. 

Fig 1. Electron micrograph of a platinum/carbon replica prepared by the fast-freeze, deep-etch, rotary-shadow replica technique printed in reverse contrast. Cell walls of onion parenchyma have an elaborate structure with many thin fibres bridging between thicker cellulosic microfibrils. Scale bar represents 200nm. 

Finally, Muhlethaler (76) took electron micrographs of various woody tissues, before and after the lignin layer had been removed by mild treatment. The structural arrangement of the cellulose had not been altered, indicating that the cellulose was physically encased by the lignin. 

Figure 5. Electron micrograph of the W preshadowed carbon replica of the surface of an unannealed Loeb-Sourirafan-type cellulose acetate membrane (XI40,-000)...

Figure 81 is an electron micrograph of section of cellulose fibre, enlarged 39,000 times. The micellar texture of the fibre is clearly visible. 

Fig. 81. Electron micrograph of cellulose fibres, from purified cotton and wood pulp respectively, magnification 39,000, according to RSnby [41a].

Figure 3. Electron micrograph of cellulose from beechwood, boiled with 95% TFA for 8 hr. Negative staining with uranyl acetate.

The electron micrographs of the enzyme-treated sprucewood holo-cellulose revealed the loci of the removed substances when compared with untreated samples. The relative intensity of degradation at the ultra-structural level corresponded to the results obtained by chemical analysis of the dissolved carbohydrates. 

Figure 2.29 Scanning electron micrographs at approximately the same magnification of four microporous membranes having approximately the same particle retention, (a) Nuclepore (polycarbonate) nucleation track membrane (b) Celgard (polyethylene) expanded film membrane (c) Millipore cellulose acetate/cellulose nitrate phase separation membrane made by water vapor imbibition (Courtesy of Millipore Corporation, Billerica, MA) (d) anisotropic polysulfone membrane made by the Loeb-Sourirajan phase separation process...

Fig- 1-17. Surface replica of an aspirated bordered pit in a tracheid of Douglas fir (Pseudot-suga menziesii), showing the pit aperture (PA), the torus (To), the margo (Ma), and the pit border (PB). Arrows indicate supporting cellulose strands. Transmission electron micrograph. Courtesy of Dr. W. A. Cote, Jr. 

FIGURE 5.2 Transmission electron micrograph of the loose tangle of cellulose microfibrils in a cotton fiber cell wall. (Credit to Wilton Goynes.)... 

The polymer is about 0.8 nm in its maximum width and 0.33 nm2 in cross-sectional area, and can contain about 10,000 glucose residues with their rings in the same plane. In the cell wall these polymers are organized into micro-fibrils that can be 5 nm by 9 nm in cross section. These microfibrils apparently consist of an inner core of about 50 parallel chains of cellulose arranged in a crystalline array surrounded by a similar number of cellulose and other polymers in a paracrystalline array. Microfibrils are the basic unit of the cell wall and are readily observed in electron micrographs. Although great variation exists, they tend to be interwoven in the primary cell wall and parallel to each other in the secondary cell wall (Fig. 1-13). 

FIGURE 20.4 Scanning electron micrographs (SEM) micrographs of the cross section of a cellulose acetate membrane of 0.45 pm pore size after being used for beer CMF experiments. A dense fouling layer is observed on the membrane surface. (From Moraru, C.I., Optimization and membrane processes with applications in the food industry Beer microfiltration. PhD thesis. University Dunarea de Jos Galati, Romania, 1999.)... 

Figure 2. The technical nature of wood tissue. (A) Scanning electron micrograph (SEM) of the surface of a softwood resulting from a cut directed perpendicular to the tree axis. This view is known tecnnicallu as the transverse or cross-sectional plane. (B) Schematic showing the location of the major constituents of wood chemistry. (C) Transmission electron micrograph (TEM) of the transverse section of a white spruce wood lignin skeleton that was prepared by removing cellulose and hemicelluloses with hydrofluoric add. Key L, lumen W, wall and ML, middle lamella. (Reproduced with permission from Ref. 38. Copyright 1974, Forest Products...

Figure 10. Scanning electron micrograph of a composite of cellulose powder-lignin powder mixture. The hig, fibrous cellulose particle (right) appears to be bonded to the big amorphous lignin particle (left). A split in the cellulose particle suggests that bonding between lignin and cellulose particles was stronger than the tensile strength of cdlulose perpendicular to the fiber axis (12A).

Gel-permeation chromatography" is used to compare the pore structure of jute, scoured jute and purified cotton cellulose. Both native and scoured jute have shown greater pore volumes than cotton. The effects of alkali and acid treatment on the mechanical properties of coir fibers are reported." Scanning electron micrographs of the fractured surfaces of the fibers have revealed extensive fibrillation. Tenacity and extension-at-break decrease with chemical treatment and ultraviolet radiation, whereas an increase in initial modulus and crystallinity is observed with alkali treatment. FTIR spectroscopy shows that the major structural changes that occur when coir fibers are heated isothermally in an air oven (at 100, 150 and 200 °C for 1 h) are attributable to oxidation, dehydration and depolymerization of the cellulose component. 

Fig. 2 Transmission electron micrograph of a dilute suspension of a sugar beet cellulose...

Fig. 12.—Electron Micrograph of Mandibular Tendon of Lobster Dispersed with a Waring Blendor. (Fibrillar texture is similar to that of cellulose, with fibrils down to 150 A. visible.)...

Figure 5 Hierarchical microstructure of a linen fibre (a) from cellulose chains to the fibre and (b) a scanning electron micrograph showing the ultimate cells bundled in fibres...

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