ABSTRACT:The effect of hydration on the dielectric constant and loss factor tan ␦ of viscose hydrocellulose, hydroxypropyl cellulose, and dextran was studied in a wide range of temperatures and frequencies. The results obtained reveal that (1) whereas hydration shows little effect on the variation with temperature of both and tan ␦ of hydrocellulose, the presence of adsorbed water significantly modifies the dielectric behavior of the other two samples; (2) only one relaxation denoted as ␥-process is observed in the case of hydrocellulose sample irrespective of its moisture content; (3) two absorption peaks are recorded with moistened hydroxypropyl cellulose and dextran specimens, one below room temperature denoted as ␤-process and a dispersion loss at high temperature; and (4) after drying of these samples, the dispersion loss peak disappears, the ␤-peak diminishes, and the ␥-peak, which is hidden behind the sizable ␤-peak, is observed and that, although with increasing frequency, the former peak disappears, the intensity of the latter one increases. The analysis of these results in view of the chemical and the fine structure of the test samples as well as the calculated activation energy indicates that the ␥-and ␤-relaxations recorded are of different natures. The satisfactory interpretation given clarifies to a great extent the contradictions reported in the literature concerning the relaxation phenomena in polysaccharides.

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SynopsisMeasurements of the dielectric constant of cotton cellulose, mercerized cellulose, cellulose acetate, methyl cellulose, and carboxymethyl cellulose have been carried out in the temperature range of 0-70°C at different frequencies. The results showed that the values of the dielectric constant, with all cellulose derivatives at a given frequency, are greater than that of cotton cellulose and lower than that of mercerized cellulose. The variation of the dielectric constant with temperature showed a transition a t 3O-4O0C with all the samples studied. These results, together with those from infrared spectra and specific volume measurements, indicated that the dielectric behavior depends greatly on the nature of the side group, the degree of hydrogen bonding between the different chains, and the micropores present in the fiber.

SynopsisA comparison between the fine structure of viscose hydrocelluloses prepared by acid hydrolysis of viscose fibers in the absence and presence of ferric chloride is given. The results indicate that ferric chloride has little effect on the change in x-ray crystallinity indices accompanying acibhydrolysis of the fibers. On the other hand, specific volume results show that the inner fine structure of hydrocelluloses prepared by hydrolyzing the fibers with free acid differs from that for hydrocelluloses prepared with an HCl-FeCls reagent. EXPERIMENTAL Hydrolysis ProcedureViscose rayon was hydrolyzed with 0.2,0.5,1, and 2N HC1 a t 100°C for different periods by keeping the liquor-to-material ratio at 501. The extent of hydrolysis was followed in an estimation of the sugar produced by a colorimetric method.24

The crystallinity of acid modified fibers prepared from viscose rayon and cotton cellulose is determined by x-ray diffraction and iodine adsorption methods. The results are analysed and interpreted in the light of the definition of each method. In addition, the role of low fractions as well as the effect of vacuum drying on the measured crystallinity are discussed. The literature shows a lack of consistency between crystallinity determined for cellulosic fibers using different methods. The present work is an attempt to analyse the crystallinities of hydrocellulose residues determined by the x-ray diffraction and the iodine adsorption methods. Results and DiscussionThe crystallinity percentage of cotton cellulose, viscose rayon, and their hydrolysis residues determined from x-ray (Cr,) as well as from iodine adsorption (Cr12) are shown in Tab. 1. The calculated crystallinity change percentages dCr, and dCrI, are plotted as a function of the hydrolysed fibers in Fig. 1.These results show that: (i) both ACr, and dCrI, increase rapidly in the initial stages of hydrolysis and soon attain a constant value with both fibers studied, (ii) in case of viscose rayon, the change of ACr,, and ACr, in the earlier stages of hydrolysis, the constant value attained, and the stage at which this value is reached, depend on the hydrolytic conditions, (iii) almost no effect of acid concentration on the change of crystallinity is observed with cotton cellulose, and (iv) with all samples studied dCrI, is greater than-ACr,. Different attempts have been made to differentiate between crystalline and non-crystalline components of cellulosic fiben-"), as well as to determine their quantitative ratio. The results obtained indicate that there is no sharp defined borderline between the crystalline and the so-called amorphous portions of cellulosic fibers. A system like cellulose probably contains every gradation between the state of perfect three dimensional order which is termed crystalline and the other extreme of randomly oriented chains with no order. Accordingly, when the glycosidic linkages of cellulose molecules are subjected to acid hydrolysis, the rate of action of acid solution on cellulose is not the same in the different parts of the fibers and, as a result, a complex mixture of particles of various lateral order of arrangement is f~r m e d '~-~' ' . Thus, it is expected that the use of different methods to determine the crystallinity of the complex hydrocellulose residues would give different results.In order to analyse the results shown in Fig. 1 and shed more light on the fine structure of the hydrocelluloses examined, it must be considered that the x-ray method of assessing the fine structure depends upon the quantity and the size of the larger units of submicroscopic