Fumitaka Horii

In situ crystallization of bacterial cellulose II. Influences of different polymeric additives on the formation of celluloses Iα and Iβ at the early stage of incubation

Effects of polymeric additives with different degrees of polymerization (DP) or substitution (DS) on the crystallization of celluloses Iα and Iβ have been examined at an early stage of the incubation of Acetobactor xylinum by using newly developed FT-IR spectroscopy. It was found that the mass fraction of cellulose Iα is greatly decreased with increasing concentrations of carboxymethyl cellulose sodium salt (CMC) or xyloglucan (XG) in the incubation medium. Such a decrease in the mass fraction of cellulose Iα, which corresponds to the enhanced crystallization of cellulose Iβ, is more prominent for CMC or XG with lower DPs, but the additives with too low DPs are not so effective probably due to higher solubility and the lower adhesion on the surface of microfibrils. Moreover, the mass fractions of celluloses Iα and Iβ are highly correlated with the crystallite size of microfibrils, indicating that Iα is crystallized in larger-size microfibrils while Iβ is produced in smaller-size microfibrils. On the basis of these experimental results, the mechanism of the crystallization of celluloses Iα and Iβ is discussed in the Acetobactor xylinum system.

Phase separation behavior in aqueous suspensions of bacterial cellulose nanocrystals prepared by sulfuric acid treatment.

Phase separation phenomena of aqueous suspensions of cellulose nanocrystals have been studied for bacterial cellulose (BC) prepared by sulfuric acid hydrolysis. Suspensions at concentrations above 0.42 wt % separated into the isotropic and chiral nematic phases with a clear phase boundary. The shape and size distribution of BC nanocrystals in both the phases were determined by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The surface charge density was determined by conductometric titration. The effects of added NaCl (0-5.0 mM) on the phase separation behavior of the aqueous suspensions were investigated for a fixed total cellulose concentration. The volume fraction of the chiral nematic phase had a minimum value at a NaCl concentration of ca. 1.0 mM. At NaCl concentrations ranging from 2.0 to 5.0 mM, the suspensions did not separate into two phases, but became entirely liquid crystalline. The size of the ordered domains in the anisotropic phase decreased with an increase in the NaCl concentration from 0 to 2.75 mM. At 2.75 mM, only tactoids were observed in the entire region. At 5.0 mM, chiral nematic domains were no longer observed. The chiral nematic pitch decreased with increasing concentration of added NaCl, reached a minimum value at approximately 0.75 mM, and then increased sharply with the NaCl concentration up to 2.0 mM.

Solid-state high-resolution 13C-NMR studies of regenerated cellulose samples with different crystallinities

SummaryCP/DD/MASS 13C-NMR spectra have been obtained for regenerated cellulose samples with different crystallinities as well as for cotton, β-D-glucose, β-D-cellobiose, and cellopentaose. The spectra of the regenerated cellulose samples exhibit broad multiplicities of the C-4 and C-6 resonance lines in a similar manner as those of native cellulose samples such as cotton and ramie, and, in addition, another broad tailing of the C-1 resonance. Since these multiplicities change linearly with crystallinity, it is concluded that they are ascribed to the contributions from the crystalline and noncrystalline components. Effects of hydrogen bonds and conformations of the β-1,4-glycosidic linkage on the chemical shifts are also discussed.

In Situ Crystallization of Bacterial Cellulose III. Influences of Different Polymeric Additives on the Formation of Microfibrils as Revealed by Transmission Electron Microscopy

Effects of polymer additives on the formation of microfibrils of bacterial cellulose have been examined by transmission electron microscopy. Among additives with different degrees of polymerization (DP) or substitution (DS), carboxymethyl cellulose sodium salt (CMC) with DP = 80 and DS = 0.57 is the most effective in producing separate, smaller-size microfibrils. By increasing the concentration of this CMC from 0.1 to 1.5%, the percentage of microfibrils measuring 3–7 nm wide is increased and levels off at around 1.0%. Other polymer additives such as xyloglucan are less effective than CMC in producing microfibrils with smaller sizes and the resulting microfibrils still tend to aggregate. The number of charged substituents and the molecular weight seem to be important factors in the production of highly separate smaller-size microfibrils. The reduction in average microfibril size is well correlated to the decrease in mass fraction of cellulose Iα in bacterial cellulose crystals. On the basis of these results, the mechanism of the crystallization of celluloses Iα and Iβ is discussed. The effect of colony types, smooth and rough, on the formation of microfibrils in the presence of CMC is also described.

Solid-state 13C-NMR study of conformations of oligosaccharides and cellulose: Conformation of CH2OH group about the exo-cyclic C-C bond

SummaryCP/DD/MAS 13C NMR spectra have been obtained for different monosaccharides, oligosaccharides, and cellulose. It has been found that a simple linear relationship exists between the chemical shift of the CH2OH carbon and the torsion angle χ about the exo-cyclic C-C bond. The chemical shifts fall into three groups of 60–62.6 ppm, 62.5–64.5 ppm, and 65.5–66.5 ppm, which are related to gauche-gauche, gauche-trans, and trans-gauche conformations, respectively. On the basis of these results the conformation of the CH2OH carbon of cellulose is also discussed.

Cross polarization/magic angle spinning 13C n.m.r. study of solid structure and hydrogen bonding of poly(vinyl alcohol) films with different tacticities

Abstract Cross polarization/magic angle spinning (CP/MAS) 13C n.m.r. measurements have been performed at room temperature for poly(vinyl alcohol) (PVA) films with different tacticities to obtain information about the structure and hydrogen bonding in the crystalline and non-crystalline regions. 13C spin-lattice relaxation analyses have revealed that three components exist for each sample, with different spin-lattice relaxation times T1C, which are assignable to the crystalline, less disordered non-crystalline and amorphous components. Using such differences in T1C, we separately recorded the spectra of the crystalline and non-crystalline components, and then analysed the triplets of the CH resonance lines appearing in both spectra in terms of three Gaussians which should be ascribed to CH carbons associated with two, one and no intramolecular hydrogen bond(s) in the mm, mr and rr sequences. As a result, it has been found that the relative intensities of the triplets are not in accord with the contents of the triad sequences, suggesting the formation of intramolecular and intermolecular hydrogen bonds in the meso sequences at almost equal probability. The effects of water on hydrogen bonding have also been examined for the almost atactic PVA sample.

Characterization of tension and normally lignified wood cellulose inPopulus maximowiczii

We have investigated unlignified tension wood and normally lignified wood celluloses inPopulus maximowiczii with particular reference to the composition of two crystalline phases Iα/Iβ (triclinic/ monoclinic). Four independent techniques, which enable us to detect the two phases, CP/MAS13C NMR, Fourier transform infrared microscopy, selected-area electron diffraction, and X-ray diffraction were applied. Because of the low crystallinity of wood celluloses, particularly in the case of celluloses in the lignified cell wall, no single method was decisive enough to be able to determine the composition of the two phases as one can with highly crystalline materials. The Iβ dominant structure (monoclinic crystal type) was, however, preferred for both tension and normal wood celluloses.

CP/MAS Carbon-13 NMR Study of Spin Relaxation Phenomena of Cellulose Containing Crystalline and Noncrystalline Components

Abstract Cross-polarization, 13C rotating frame spin-lattice relaxation and C laboratory frame spin-lattice relaxation processes have been studied for different cellulose samples by CP/MAS 13C NMR spectroscopy. It was found that the CP process can be described by a simple thermodynamic model and relative intensities of the respective resonance lines are consistent with the atomic ratios for the spectra obtained at a contact time of about 1 ms. The observed rotating frame spin-lattice relaxation times TC 10 were dominantly dependent on the time constant TD CH by which 13C nuclei were coupled to the 1H dipolar spin system. It was, therefore, impossible to obtain information about molecular

Preparation of hydrogels by radiation technique

Abstract Moderately concentrated, aqueous solutions of poly(vinyl alcohol) (PVA), poly(ethylene oxide), polyacrylamide, polyvinylpyrrolidone, and methyl cellulose were cast on a glass plate and irradiated with electron beams to yield crosslinked hydrogels. Irradiation was carried out also for water-swollen films of PVA. In all cases, no attempt was made to expel air from the polymer-water mixture to be irradiated, since the hydrogels were readily formed by placing a glass plate or a plastics film on the mixture. The measurement of tensile properties of the hydrogels revealed that the hydrogel from PVA, especially prepared by irradiation of water-swollen films, gave the highest tensile strength among the hydrogels. The swelling of once dried PVA hydrogels was recovered almost to the initial swelling state when boiled in water.

The phase structure of high-pressure-crystallized polyethylene

Abstract The phase structure of three linear polyethylene (PE) samples, crystallized from the melt at high pressure, has been studied by electron microscopy and high-resolution solid-state 13 C n.m.r. spectroscopy. In general, three phases are required to account for the n.m.r. data: the lamellar crystalline phase, the crystalline-amorphous interphase and the amorphous phase. All three are present in high-molecular-weight samples but there is no amorphous phase for samples with lower molecular weights and large lamellar thicknesses. The amorphous phase appears when the ratio of the number-averaged extended molecular chain length ( X n ) to the number-averaged crystalline stem length ( L n ) exceeds two. High-pressure-crystallized materials differ from those crystallized at atmospheric pressure in that the mass fraction of the amorphous phase does not exceed 0.05; the thickness of the crystalline-amorphous interphase reaches 8.0 nm for material with the highest molecular weight, a value which is considerably larger than those reported for samples crystallized at atmospheric pressure or which have been estimated theoretically. Extraordinarily long 13 C spin-lattice relaxation times have been found: a figure of T 1C = 7000 s, higher than any previously reported, for the highest-molecular-weight sample is still less than would be expected from the large lamellar thickness. In consequence, this relaxation is attributed to molecular motion in the vicinity of the crystal defects; this is in addition to 13 C spin diffusion to the non-crystalline region, occurring with a shorter T 1C . The discrepancy between the observed and calculated values of T 1C increases as the molecular weight falls in those samples for which the crystal stem lengths exceed the extended molecular lengths. For these, the unexpectedly shorter T 1C is attributed to defects such as methyl end-groups within the crystalline regions.