Chie Sawatari

A Fourier transform infra-red spectroscopic analysis of the character of hydrogen bonds in amorphous cellulose

Abstract Hydrogen-bonding formation in amorphous cellulose was characterized by the analysis of Fourier transform infra-red (FT i.r.) spectra. Films of regioselectively substituted methylcelluloses were used to model components of amorphous cellulose. An artificial infra-red (i.r.) spectrum for amorphous cellulose was quantitatively synthesized by a suitable mathematical combination of the i.r. spectra obtained for the methylcellulose model compounds. A comparison between the i.r. spectrum for an amorphous film blend composed of 2,3-di-O- and 6-O-methylcelluloses and the artificial spectrum showed an almost complete overlap in the OH frequency region, indicating that after mixing there is no interaction between the OH groups of each component in the film blend. In other words, the OH bands in the artificial spectrum were considered to be simply a sum of hydrogen-bond absorptions contributed by each individual spectrum. The artificial spectrum was then compared to an experimental spectrum for an amorphous cellulose sample. The difference between the two spectra (real-artificial) was then analysed and interpreted by using results from a previous i.r. study on hydrogen bonding in alcohols and our own assumptions about the probable hydrogen bonds formed in amorphous cellulose. These analyses revealed that while the hydroxyl groups at the C(2) and C(3) positions in a glucose repeating unit are isotropically involved in intermolecular hydrogen bonding in amorphous cellulose, the hydroxyl group at the C(6) position is favourably engaged in an interchain hydrogen bonding that results in the formation of a crystalline state. Thus we conclude that amorphous cellulose might be composed, at least to some extent, by randomly distributed domains formed by intermolecular hydrogen bonds.

A gelation mechanism depending on hydrogen bond formation in regioselectively substituted O-methylcelluloses

This paper discusses how the hydrophobic interactions as well as hydrogen bonds contribute to thermally reversible gelation of aqueous solutions for O-methylcellulose. The gelation behavior of a series of regioselectively substituted 2,3-di-O-methylcellulose (2,3MC-n: n ¼ 1 – 3) differed from that for randomly substituted O-methylcellulose (R-MC). This was indicated by differential scanning calorimetry, near infrared spectroscopy (NIR) and small angle X-ray scattering. The formation of hydrogen bonds in 2,3MC-n and R-MC solutions was also determined by the curve fitting results of OH bands in NIR spectra. This method proved the presence of the intermolecular hydrogen bonds between the cellulosic samples and water. As a result, the gelation of the 2,3MC-n and R-MC solutions may be caused by cooperation of the hydrophobic interaction among methyl substituents with the intermolecular hydrogen bonds among hydroxyl groups at the C(6) position, which are dependent on the distribution of methyl groups. q 2003 Elsevier Science Ltd. All rights reserved.

Ultradrawing of High Molecular Weight Polyethylene Films Produced by Gelation/Crystallization from Solution: Effect of the Number of Entanglements

This paper describes the morphological properties of gel films of ultrahigh molecular weight (6×106) polyethylene by small angle X-ray scattering (SAXS), wide angle X-ray diffraction (WAXD), and scanning electron microscopy. The gel films were prepared by crystallization from solution with critical concentration associated with the maximum drawability of the dry gel films. Through a series of experimental results, it turns out that the number of entanglements causes significant changes in the profile of SAXS intensity distribution and in the orientation of crystallites estimated by WAXD patterns. Furthermore, stress-strain curves were dependent upon an increase of the entanglements. Based on the above results, it may be concluded that a suitable level of entanglements between crystal lamellae plays an important role for transmitting drawing force as intermolecular crosslinks in an ultradrawing process.

Intermolecular hydrogen bonding in cellulose/poly(ethylene oxide) blends: thermodynamic examination using 2,3-di-O- and 6-O-methylcelluloses as cellulose model compounds

Abstract This paper discusses the miscibility of cellulose/poly(ethylene oxide) (PEO) blend systems from the view point of the relationship between hydrogen bond formation and regiochemistry of hydroxyl groups in cellulose. Thermodynamic examination of the systems using 2,3-di- O - and 6- O -methylcelluloses (23MC and 6MC) as cellulose model compounds was carried out by differential scanning calorimetry. The values of two parameters, interaction energy density characteristic, B , and interaction parameter, x 12 , assessed by the thermodynamic analyses indicated evidence of polymer-polymer interaction in 23MC/PEO blends and lack of interaction between 6MC and PEO in their blends. Optical microscopic observation of the blend systems revealed the same phenomena. Results of the two investigations support our proposal of a regiochemical effect of hydroxyl groups in cellulose analysed by Fourier transform i.r. spectroscopy; that is, primary hydroxyl groups at the C6 position of the glucose unit of cellulose interact predominantly with ether oxygen in PEO, while secondary hydroxyls at the C2 and C3 positions are not engaged in hydrogen bonding. However, in pure cellulose/PEO blend each negative magnitude of the values was much larger than the sum of the values of each parameter for the 23MC/PEO and 6MC/PEO blends, indicating the presence of secondary polymer-polymer interaction.

Morphological and mechanical properties of ultrahigh-molecular-weight polyethylene/low-molecular-weight polyethylene blend films produced by gelation/crystallization from solutions

Polyethylene-polyethylene blend films were prepared by gelation/crystallization from semidilute solutions by using ultrahigh-molecular-weight polyethylene (UHMWPE) (w = 6 × 106) and low-molecular-weight polyethylene (LMWPE) (Mw = 4 × 104). The UHMWPE/LMWPE compositions chosen were 919, 6733 and 5050. Elongation was carried out in a hot oven at 115–130°C. Drawability was dependent upon the compositions. The maximum achievable draw ratios of the 5050 and 6733 blends were 200-fold, while that of the 919 blend was 300-fold. The storage modulus decreases with increasing LMWPE content, when the measurements were carried out using specimens with the same draw ratio. Such mechanical properties were discussed in terms of morphological aspects by using wide-angle X-ray diffraction, birefringence, differential scanning calorimetry and optical microscopy.

Structure and mechanical properties of polyethylene-fullerene composites

The microhardness of films of fullerene-polyethylene composites prepared by gelation from semidilute solution, using ultrahigh molecular weight polyethylene (PE) (6×106), has been determined. The composite materials were characterized by optical microscopy and X-ray diffraction techniques. The microhardness of the films is shown to increase notably with the concentration of fullerene particles within the films. In addition, a substantial hardening of the composites is obtained after annealing the materials at high temperatures (Ta=130 °C) and long annealing times (ta=105s). The hardening of the composites with annealing temperature has been identified with the thickening of the PE crystalline lamellae. Comparison of X-ray scattering data and the microhardness values upon annealing leads to the conclusion of phase separation of C60 molecules from the polyethylene crystals within the material. The temperature dependence is discussed in terms of the independent contribution of the PE matrix of the C60 aggregates to the hardness value.

Durable Water-Repellent Cotton Fabrics Prepared by Low-Degree Substitution of Long Chain Alkyl Groups

Three kinds of water-repellent cotton fabrics, A, B, and C-, are produced by alkylation with only 0.07 alkyl units per glucose unit. Sample A is prepared by alkylation by means of acetylation without mercerization, B is by direct alkylation after merceriza tion, and C is by alkylation by means of allylation and bromination. The merits of the methods are compared by contact angle measurements and spray tests after repeated laundry cycles. Sufficient water-repellency is attained with an alkyl length of over C12. These samples retain a fabric hand, water-vapor permeability, and biodegradability similar to those of untreated cellulose fabric. The end-use properties of alkylated fabrics before and after laundering are also tested.

Mechanical properties of ultrahigh molecular weight polyethylene-polypropylene blend films produced by gelation/crystallization from solution

Films of a polyethylene-polypropylene blend were prepared by gelation/crystallization from semidilute solutions using ultrahigh molecular weight polyethylene (Mv = 6 × 106 and polypropylene (Mv = 4.4 × 106). The polyethylene/polypropylene (PE/PP) compositions chosen were 7525, 5050 and 2575. The elongation was carried out in a hot poly(ethylene glycol) oil bath at 140°C. The mechanical properties of the resultant gel films were dependent upon the PE/PP compositions at each draw ratio. This interesting phenomenon is discussed using the second-order orientation factors of the c axes of polyethylene and polypropylene within the blend films. It turns out that the orientation factors of the polyethylene and polypropylene phases within the blend films at each draw ratio are different from those of their individual homopolymers with the corresponding draw ratio and this tendency is pronounced for blend films with a draw ratio of 20. Therefore, it is insufficient to explain the dependence of PE/PP composition on the storage and loss moduli by a composite law based on a simple model system in which polyethylene layers lie adjacent to polypropylene layers with the interfaces parallel and perpendicular to the stretching direction and the morphological properties of the two phases within the blend films are equivalent to those of their individual homopolymers at each draw ratio.

One-dimensional mathematical treatment of small-angle X-ray scattering from a system of alternating lamellar phases

A theory for the small-angle X-ray scattering (SAXS) from alternating lamellar phases is formulated on the basis of the concept that the scattering is due to positive and negative density deviations from the average density of the system. In contrast to all previous theories, the equation for the scattered intensity satisfies Babinets reciprocity theorem for crystallinity (in the case of a semicrystalline polymer) or volume fraction (for a block copolymer), when there is no fluctuation in the thickness of the alternating lamellar phases. It is also shown that in order to obtain the correct SAXS intensity distribution for the case where the thickness of the lamellar phases shows no fluctuation, the IC term, as defined by Hosemann and Blundell, must be included in the summation.

Drawability of poly(vinyl alcohol) films prepared by gelation/crystallization from semidilute solutions

Abstract Poly(vinyl alcohol) (PVA) films prepared by gelation/crystallization from dimethyl sulphoxide/water solutions were drawn in an oven at 125°C under nitrogen. Two PVA samples with degrees of polymerization of 2000 and 4400 were used. The drawability was affected by the composition of the solvent mixture as well as by the quenching temperature. This interesting phenomenon is discussed in terms of the morphology of the gels and dried films, as studied by crystallinity, wide-angle X-ray diffraction, birefringence and small-angle light scattering under Hv polarization. Thus, it turned out that crystallinity plays an important role in assuring facile drawability, while the solution concentration and the degree of polymerization have little effect on the drawability. The maximum draw ratio could be achieved only for specimens with the lowest crystallinity. This indicates that the deformation mechanism of PVA gel films is quite different from those of polyethylene and polypropylene gel films.