ABSTRACT:For the cellulose crystals I and II, the spacings and intensities of some typical Xray reflections were measured over a range of temperature from room temperature to 200°C. The spacing vs. temperature curve for each reflection exhibited a distinct break at about 150''C for Cell I and at about lOO"C for Cell II. The thermal expansion coefficients estimated from this curve for the (I OT) reflection of Cell I were 5. I x 10-5 K -1 below I 50°C and 1.6 x 10-4 K -1 above I 50''C. The intensity vs. temperature curve for each reflection also exhibited a break at the same temperature as that for the break of the corresponding spacing vs. temperature curve. The reason for the appearance of these breaks is not yet clear.KEY WORDS X-Ray I Spacing I Intensity I Cellulose I I Cellulose II I Transition IIn our previous papers, 1 • 2 the fine structure of a cellulose crystal was investigated and a long spacing crystal structure was found. In the following study, attention is directed to thermal effects on the X-ray diffraction angle and intensity in two cellulose crystals. EXPERIMENTALThe lattices of the two crystal structures examined were of the types usually referred to as Cellulose I and Cellulose II. The samples used for Cell I were cotton and hemp yarns which showed clear equatorial reflections and a softwood hemlock-spruce which showed clear meridional reflections. The samples used for Cell II were a viscose rayon and merserized cotton and hemp yarns.X-Ray diffraction experiments on a given sample were performed at a number of temperatures from room temperature to 200°C, using a diffractometer equipped with a high temperature attachment. The entire diffraction profile was measured after the sample was maintained at the desired temperature for I h, and the profile at a specified Bragg angle as a function of temperature was determined by raising or lowering the temperature at a rate of 1.25 K min -1 . In the latter, the diffractometer was scanned repeatedly over the range of ± 2° about the specified Bragg angle at a rate of I o min -1 . The Xray source was the nickel-filtered Cu-Ka radiation from a generator driven with 40 kV and 20 rnA. A slit of I o was used for the divergence of radiation and a slit of 0.15 mm for the reception of diffracted rays.The sample yarns were uniformly wounded on a metal plate of25mm long, 15mm high, and 0.5mm wide, while the sample plates of hemlock-spruce were cut into pieces of 24 mm long, 15 mm high, and 1.4mm wide. RESULTS AND DISCUSSIONFigure lA illustrates the equatorial diffractograms of cotton (Cell I) and Figure I B the meridional diffractograms of hemlock-spruce (Cell 1), both at some selected temperatures. The following features can be seen from these diffractograms: the peak angle of the (101), (IOI), and (002) reflections decrease monotonically as the temperature is raised, while the peak angle of the (040) reflection first increases and then turns to decrease. For the (040) reflection the peak angle changed reversibly with a 675
ABSTRACT:To make clear the mechanism of the transition from Cell (cellulose) I to Cell II, the changes of the crystal structure and the chain conformation during the mercerization reaction process are studied under various conditions by means of wide angle X-ray diffractograms and CPIMAS 13 C NMR spectra. It was observed that Cell I and Cell II show the different 13 C NMR spectra resulting from the different chain conformations. In Na-cells treated with three conditions of fixing the fibers, CPIMAS 13 C NMR spectra show different patterns which result from two types of the chain conformations, that is Na-cell of Cell I type and that of Cell II type. By regeneration, the Na-cell of Cell II type conformation transforms to Cell II regardless of the temperature of washing water. On the other hand, the Na-cell of Cell I type conformation mostly transforms to Cell I by washing with water at higher temperature. From these results, it seems reasonable to conclude that the transition from Cell I to Cell II is caused by the change of the chain conformation, as proposed by Hayashi.KEY WORDS Cellulose I Transition I CPIMAS 13 C NMR I Mercerization I Chain Conformation I Chain Packing I It is recognized that cellulose I (Cell I) family can be transformed into cellulose II (Cell II), but that the reverse is impossible. Such an irreversible phenomenon has been explained by mainly two different proposals.1-5 One is the proposal by Hayashi et al., 1.2 which claims that the types of chain conformation in Cell I family and in Cell II family are different and the conformation of Cell II type is more stable than that of Cell I type. The other proposal by Sarko and Blackwell et al. 3 -5 is that Cell I and Cell II have parallel and antiparallel chain packings, respectively, and that antiparallel chain packing is the lowest energy form. However, it seems unclear which proposal is more plausible.Cell II does not exist naturally, but can be obtained from the native material by mercerization which involves swelling treatment with sodium hydroxide. Therefore, the study of the mercerization process is important to make clear the mechanism of the transttlon from Cell I to Cell II. In this paper, the changes of crystal structure and the chain conformation during the mercerization are investigated under various conditions by means of wide angle X-ray diffractograms and 13 C NMR solidstate spectra, and the transition mechanism is discussed. EXPERIMENTALThe starting material of Cell I was ramie, of which crystallinity measured by X-ray method was about 90%. The sodium cellulose I (NaCell I) was prepared from ramie by treatment with 15% aqueous NaOH solution 6 at 20oc for 1 hour, 1 day, and 1 week under the following three conditions of fixing fibers: the fibers were wound tightly around a glass plate to keep fixed length (A), the fibers were wound loosely around a glass plate to allow shrinkage by about 30% (B) and the fibers were allowed 855
ABSTRACT:DC electrical conductivity was measured from room temperature to about 230°C for Cellulose I and Cellulose II. The conductivity vs. temperature curve showed a break at about l 50°C for Cell I and at about 80°C for Cell II. The break points corresponded to those observed previously in the spacing vs. temperature curves. These phenomena may possibly be assoc-iated with the second order transition at which the restricted motion of chain segments in the crystals begins to acquire high mobility. The conductivity in the fiber axis direction was approximately ten times as large as that in the perpendicular direction.KEY WORDS Cellulose I / Cellulose II / Transition Point / DC Electrical Conductivity / In a previous paper,1 it was found for Cell I (Cellulose I) and Cell II (Cellulose II) that the temperature coefficients of the spacings and intensities of X-ray reflections change discontinuously at l 50°C for Cell I and at I 00°C for Cell II. This suggests that these crystals undergo second order transitions at these temperatures. The present work was undertaken to confirm this, by measuring the de electrical conductivity from room temperature to about 230°C for both Cell I and Cell II. Furthermore, the anisotropy of the de electrical conductivity was studied in the directions of intermolecular and intramolecular hydrogen (chain direction) bonds to observe the effects of hydrogen bonds on the electrical conductivity. EXPERIMENT ALThe samples of Cell I were prepared from softwood tsuga (Tsuga sieboldii CARR) and hardwood kaba (Betula tauschii Kornz), both of which showed clear X-ray meridional reflections. The crystallinities of the untreated samples were almost the same. The samples of Cell II were prepared by measerizing tsuga and kaba with 30% NaOH for 240 h followed by regeneration by washing with cold water. The degree of transformation from Cell I into Cell II was 0.9-1.0, when estimated by Ranby's equation. 2 All the samples were treated with 4N-HC1 at I00°C for 2-lOh to remove any lignin and hemicellulose in the wood.The sample was parallelpiped in form (l0mmx lOmmx 15mm). The arrangement of electrodes and the direction of electric current is illustrated in Figure 1. Stainless steel was used as the electrodes. Silver conducting paste (du Pont Electro-Chemicals Department No. 5504) was spread on both sides of the sample and heated at 200°C for 70 min in order to insure closer contact between the stainless steel and wood.DC electrical conductivity was measured with the de amplifier shown in Figure 2. The maximum applied voltage was 300 V and the standard resistance, I kQ. Prior to each measurement, the specimen was dried at l00°C for about 2h under a pressure of 10-3 torr. RESULTS AND DISCUSSIONThe temperature dependence of the de electrical conductivity a of Cell I (tsuga) hydrolyzed with 4 N-H Cl at I00°C for various hours is shown in Figure 3. Figure 3A is for the fiber direction and Figure 3B, for the direction perpendicular to it. Breaks are seen at temperatures of about l 50°C in both directions, an...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.