Leveling-off Degree Of Polymerization Research Articles

Cellulose-Containing Fillers for Polymer Composites

The form and sizes of the particles of cellulose-containing disperse systems obtained by dry grinding or dispersing in water a source material (wood pulp and sawdust), destructed by the thermocatalytic method, have been investigated. Their physicochemical and rheological (for aqueous dispersions) properties as well as the physicomechanical properties of composites based on such systems have been studied. By dry grinding, a powder of microcrystalline cellulose (MCC) (in the case of wood pulp) and technical powder (in the case of sawdust) containing particles of sizes from 3 to 20 μm were obtained. By dispersing in an aqueous medium the wood pulp destructed to the levelling-off degree of polymerization (LODP), MCC dispersions containing separate microcrystallites and their aggregates were obtained. In the case of their sufficiently high concentration (≥ 8%), MCC gels having rheological properties typical of liquid-crystalline polymers were formed. It is shown that the cellulose-containing disperse systems obtained may be useful in composites made with polymer materials for improving their strength properties.

Mercerization and acid hydrolysis of bacterial cellulose

Structural changes in never- dried, disintegrated bacteria l cellulose by treatment with aqueous NaOH were examined by electron microscopy, X-ray diffractometry and acid hydrolysis behaviour and compared with those of cotton cellulose. The microfibril kept its fibrillar morphology after treatment with NaOH solutions of less than 9% (w/w), but changed into irregular aggregates when treated with NaOH above 12% (w/w), corresponding to the crystal conversion to cellulose II. The crystallinity of the resulting cellulose II was very low after a brief alkali treatment, but was increased significantly by elongated treatment (up to 10 days). In contrast, cotton cellulose was converted to cellulose II of fairly high crystallinity by alkali treatment of as little as 3 min duration, and the crystallinity did not change with longer treatments. The leveling-off degree of polymerization (LODP) of bacterial cellulose was decreased from 150 to 50 by 18% (w/w) NaOH treatment, while that of cotton linter decreased from 260 to 70. These characteristic differences between cotton linter cellulose and bacterial cellulose can be ascribed to a basic difference in microfibrillar organization in these materials: the microfibrils in cotton cellulose are in close contact with neighbouring microfibrils having opposite polarity, and in bacterial cellulose are isolated from each other and require chain folding to form the antiparallel cellulose II crystal

A Study on the Preparation, Structure, and Properties of Microcrystalline Cellulose

Abstract The preparation, structure, and properties of microcrystalline cellulose (MCC) from rice straw were investigated by IR, x-ray, viscometry, polarizing microscope, SEM, etc. The results are as follows: 1. The leveling-off degree of polymerization (LODP) obtained from rice straw is about 80–150. The dimensions of MCC granules are 20–30 μm length, 0.5–0.8 μm thick, and the crystallinity is about 80%. 2. The aqueous suspension of a certain concentration of MCC can form a gel under the effect of shear force. The viscosity of MCC gel increased with an increasing content of MCC in water. A sharper increase of viscosity occurred in the 3–6% range. 3. The addition of one or two valence salts into the MCC gel increased the viscosity. 4. The viscosity of MCC gel has its maximum value at pH 8. 5. The MCC gel as an emulsifying agent can form a stable emulsion in the oil/water system when the ratio of oil/water is below 6/4.

Acid hydrolysis behaviour of microbial cellulose II

A mutant strain of Acetobacter xylinum produces cellulose of anomalous band-like form (‘native band’), and this material has been found to be cellulose II, presumably having a folded-chain structure (according to recent work by Kuga et al.). In addition to the previous results of electron diffraction, X-ray analysis showed that this band material was composed of virtually pure cellulose II. We have studied the acid hydrolysis behaviour of this material to obtain additional evidence for the proposed structure. When hydrolysed with 1 N hydrochloric acid at 100°C, the degree of polymerization (DP) of the material decreased rapidly from 322 (DPw/DPn = 3.83) to 18.3 (DPw/DPn = 1.19). The latter value (levelling-off DP) corresponds to the observed width (10 nm) of strand-like constituents of the band material. The sample dissolved in and regenerated from 8.75% aqueous sodium hydroxide lost its original characteristic morphology and became irregular-shaped agglomerates. The leveling-off DP of this regenerated sample was 55.2 (DPw/DPn = 2.53), a typical value for common regenerated celluloses. These findings as a whole strongly suggest that the cellulose molecules in the native band are selectively cleaved at sharply folded parts by acid, producing fragments of the length of folding periodicity.

Properties of cotton fibers containing the cellulose IV crystal structure

AbstractComplete conversion of the crystal form in cotton fibers to cellulose IV (cell IV cotton) was obtained by heat treatment of ethylamine‐treated cotton cellulose in either saturated steam or formamide. Degradation of the fibers was not extensive during the conversion process; oxidative damage appeared to have been confined primarily to the accessible regions of the fibers. Examination by scanning electron microscopy indicated that the surface of the cell IV cotton was smoother than that of the same cotton with other crystal forms, namely, the starting cotton (cell I cotton), mercerized cotton (cell II cotton), and ethylamine‐treated cotton (cell III cotton). Fiber accessibility increased in the order cell I cotton < cell III cotton ≤ cell IV cotton < cell II cotton. Using leveling‐off degree of polymerization as the measure, it appeared that the lengths of the crystallites in cell I cotton were much higher than those in cell II, III, and IV cotton. The strength of cell IV cotton was comparable to that of cell I cotton even though its degree of polymerization was significantly lower. It is suggested that heat treatments in formamide have an annealing effect on cotton that results in increases of strength.

Studies on chemically modified cotton. V. Effect of zinc chloride solutions on swelling and other properties of cotton

This paper describes the effect of zinc chloride solutions of different molarity at different temperatures, viz., 10°, 25°, 36°, 55°, and 75°C, on various properties of cotton fiber such as degree of swelling, accessibility to water vapor and iodine absorption, infrared ratio, barium activity number (BAN), and leveling-off degree of polymerization (LODP). Zinc chloride solution caused inter- and intrafibrillar swelling in cotton fiber depending on conditions of treatment, viz., concentration of solution and temperature employed. Fibers treated in 10.07 moles/1. (M) solution of zinc chloride in slack state showed rapid increase in degree of swelling up to 2 hr, followed by a slow increase, reaching the maximum after 3 hr of treatment. Fibers swollen with fixed ends without allowing shrinkage showed gradual increase with maximum swelling after 6 hr of treatment. Cotton fibers treated in different molar solutions of zinc chloride at 55°C showed varying degrees of swelling (inter- and intrafibrillar) and a somewhat different trend compared to that observed at 10°C. Electron micrographs revealed mostly intercrystalline swelling in case of samples treated with 9.26M at 10°C, while the same concentration produced intracrystalline swelling at 55°C. Accessibility to water vapor, iodine absorption, and BAN of treated samples showed specific effect of temperature with regard to effectiveness of concentrations of zinc chloride solutions. Similar effects of temperature with regard to concentrations of reagent were observed on infrared ratio and LODP. Accessibility by iodine absorption and LODP correlate with BAN; also, the accessibility by iodine absorption correlates with the LODP.

Accessibility of Various Cellulose Preparations from Jute

Accessibility towards 2.4 N hydrochloric acid at 100° C. under nitrogen atmosphere has been determined for various cellulose preparations from jute. With the results of viscosity measurement in cuprammonium hydroxide solution of the hydrolyzed and unhydrolyzed material, leveling-off degree of polymerization has been determined and hence crystallite length calculated. The present study shows the effect of hemicellulose present in cellulose preparations on the accessibility and leveling-off degree of polymeri zation and hence on the crystallite length due to different treatments of jute cellulose.

CHANGES IN FIBRE STRUCTURE OF WOOD PULP DURING COLDPURIFICATION WITH CAUSTIC SODA SOLUTION AND SUBSEQUENT DRYING

Changes in fibre structure of cellulosic materials such as degree of crystallinity and lateral order and system of cavities during cold-extraction with caustic solutions of various concentrations and during subsequent drying under various conditions have been investigated experimentally.It has been found that if cellulosic materials are treated with caustic soda solutions of over certain concentrations, the amount of amorphous region increases at the expense of highly ordered region. These limiting concentrations at 20°C., are 10-12% for cotton linter, and 8-10% for wood pulp. The increased amorphous region, if dried under below 80% RH, becomes “horny” and losses capability of reaction that is completely recovered by wetting with water.Lateral order distribution was estimated from the solubility of the residue in caustic soda solutions of various concentrations after the leveling-off degree of polymerization has been attained by acid hydrolysis.Relative pore sizes of fibre texture were determined by measuring the dye-uptake from unswollen medium.

The Effect of Aqueous Hydrochloric Acid on the Cotton Cellulose III Lattice and Its Implications Concerning the Determinations of Crystallinity and Leveling-off Degree of Polymerization2

The Effect of Aqueous Hydrochloric Acid on the Cotton Cellulose III Lattice and Its Implications Concerning the Determinations of Crystallinity and Leveling-off Degree of Polymerization²