Shinichi Suto

Chemical crosslinking of hydroxypropyl cellulose and chitosan blends

Two liquid crystal forming polysaccharides, hydroxypropyl cellulose and chitosan, were blended in aqueous acetic acid solutions and were crosslinked with dialdehydes (glyoxal and glutaraldehyde) as crosslinker and hydrochloric acid as catalyzer. The crosslinkability, morphology, solubility, and tensile properties of the cross linked blend films are determined and the dependence of those properties on the blend composition and on crosslinker species are discussed. The crosslinked blend films cast from the aqueous acetic acid solutions were amorphous. The solubility, Youngs modulus, and tensile strength of the crosslinked blend films greatly depended on blend composition; those properties appeared to exhibit a maximum and a minimum around given blend compositions. The solubility for the crosslinked blend film cast from glyoxal system was greater than that from glutaraldehyde one.

Crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order : 2. Anisotropic swelling behaviour in water

Abstract Hydroxypropyl cellulose solid films crosslinked with two kinds of dialdehyde (glyoxal and glutaraldehyde), retaining cholesteric liquid crystalline order, were prepared by casting the liquid crystalline solution in methanol. Effects of crosslinking agent concentration and type, and heat treatment on the swelling behaviour of the crosslinked films in water were determined. The change in cholesteric pitch of crosslinked films during swelling was also determined by means of circular dichroism (c.d.) study. The swelling behaviour and the change in the peak wavelength of the c.d. spectrum were compared, and the anisotropic swelling behaviour of crosslinked films was discussed. The swelling ratio (B) in the film thickness direction was greater than that in width or length direction. B decreased with crosslinking agent concentration and heat treatment. B for the films crosslinked with glyoxal was greater than that for the films crosslinked with glutaraldehyde. The swelling behaviour and the shift in the peak wavelength of the c.d. spectrum as a function of soaking time were almost the same. The shift depended similarly on the concentration and type of the crosslinking agent as the swelling behaviour did. The similarity of the shift in the peak wavelength of the c.d. spectrum and the swelling behaviour clarified that the swelling in the film thickness direction is correlated to the change in the cholesteric pitch of the crosslinked films.

Evidence for retaining crosslinked liquid-crystalline order in hydroxypropyl cellulose solid films by polarized microscopy

Abstract Liquid-crystalline solutions of hydroxypropyl cellulose (HPC) in water or alcohols were mixed with p-formaldehyde (crosslinking agent) and hydrochloric acid (HCl, catalyst). HPC solid films were cast from those solutions, which were sheared, and fixing of the liquid-crystalline order was tried by chemical crosslinking. The texture of those solutions in the course of casting was observed by polarized microscopy and a solubility test of the resultant HPC cast films in water and alcohol was performed. Those liquid-crystalline solutions with or without p-formaldehyde and HCl formed a band texture after cessation of shear. This formation of the band texture is a characteristic of liquid-crystalline solutions. The band texture of aqueous solution decayed rapidly with time and finally changed to a globular texture, whereas the band texture of alcoholic solutions did not decay. The band or globular texture remained in the solid cast films. The HPC solid films cast from liquid-crystalline solutions with p-formaldehyde and HCl, which exhibited the band or globular texture, were insoluble in both water and alcohol. Our findings reveal that the liquid-crystalline order is perpetuated in the HPC solid cast films by crosslinking.

Capillary rheometry of lyotropic liquid crystals of hydroxypropyl cellulose

Abstract Rheological properties of hydroxypropyl cellulose solutions which exhibit liquid crystalline behaviour under certain conditions were determined by using a capillary rheometer. The Bagley end correction was taken into consideration by using three kinds of dies. Measurements included the shear and concentration dependence of the shear viscosity and three elastic parameters: the Bagley correction factor (v), the entrance pressure drop (ΔPent) and the die swell (B). The shear viscosity exhibits a general behaviour as a lyotropic liquid crystal. The shear dependence of v greatly depends on concentration, and v shows a maximum and minimum with respect to concentration. The pressure drop ΔPent increases with shear rate for all concentration ranges and the concentration dependence of ΔPent is the same as that of the shear viscosity. The die swell B increases with shear stress only for a single phase (isotropic or anisotropic) and decreases for the biphasic range; B also exhibits a maximum and minimum with respect to concentration. There seems to be a great similarity between the shear viscosity and the elastic parameters with respect to concentration; however, there is no similarity between them with respect to shear. The Bagley correction factor or entrance pressure drop is simply related to the die swell and the following relations are expressed experimentally: v∝B n Λ ent ∝B n′ where n and n′ are constants which are dependent on concentration and shear range. More rheological data are required to establish those relations between the elastic parameters.

Chemical cross-linking of cholesteric liquid-crystalline hydroxypropyl cellulose with dialdehydes

Cross-linking of the cholesteric liquid-crystalline order in a hydroxypropyl cellulose (HPC) aqueous solution was attempted and the swelling and mechanical (static and dynamic) properties of cast films were determined. HPC solid films cast from the liquid-crystalline aqueous solution with dialdehyde (glyoxal or glutaraldehyde) and hydrochloric acid were insoluble in water and retained the right-handed cholesteric liquid-crystalline order. The swelling and static tensile properties exhibited a general behaviour with respect to the concentration of the cross-linking agent and to the heat treatment. However, dynamic and loss moduli exhibited an opposite behaviour to the static tensile modulus. A cross-linking mechanism is proposed for HPC molecules and dialdehydes based on the swelling and mechanical properties of HPC films cast from two dialdehyde systems.

Permeability of oxygen and nitrogen gases in ethyl cellulose solid films retaining cholesteric liquid crystalline order

Ethyl cellulose (EC) films that retain lyotropic and thermotropic cholesteric liquid crystalline order, and an amorphous EC film were prepared. The liquid crystalline order was identified by optical measurements. The comparative permeability of oxygen and nitrogen gases for three kinds of EC film was determined, and the applicability of the EC films that retained cholesteric liquid crystalline order to oxygen enrichment are discussed. The permeability of oxygen or nitrogen gas for the liquid crystalline films was lower than that for the amorphous ones. The activation energy for the permeability coefficient of oxygen gas was ca. 3.5 kcal/mol. The ratio of permeability coefficient for oxygen gas to that for nitrogen gas was less than 4. Interestingly, the permselectivity of oxygen and nitrogen gases for the liquid crystalline films was greater than that for the amorphous ones.

Swelling behavior of crosslinked hydroxypropylcellulose films retaining cholesteric liquid crystalline order, II. Effects of temperature, solvent, and pH

Crosslinked hydroxypropylcellulose (HPC) films were cast from the cholesteric liquid crystalline HPC solution in methanol. The films retained the cholesteric liquid crystalline order. The dependences of swelling behavior of our films in water and propanol on temperature and on pH of the solvent were determined. The response of our films to the changes in water, temperature and in pH was discussed. In water, the equilibrium swelling ratio (B e ) decreased with temperature whereas Be increased with temperature in propanol. For a given composition of water and propanol, B e was independent of temperature. B e in the acidic solvents was higher than in the alkaline solvents. The response data to the stepwise change in temperature revealed that the deswelling behavior was more rapid than the swelling behavior in water, and the swelling-deswelling behavior was reversible. The response to the stepwise change in pH was almost the same as that of the change, in temperature, but the surface of the film was attacked by the acid and became fluffy with increasing soaking time.

Cellulosic solid films exhibiting cholesteric liquid crystalline order

Ethyl cellulose (EC) and hydroxypropyl cellulose (HPC) films were cast under different conditions and were observed optically. The creep behaviour of those films was determinedin vacuo as a function of applied stress or temperature and was analysed on the basis of the Eyring thermally activated process.EC and HPC films cast from liquid crystal-forming systems remained cholesteric liquid crystalline order (the cholesteric sense was different in each case), whereas EC film cast from non-liquid crystal system (benzene) had no liquid crystalline order and was amorphous. The Eyring activated process could be applied to the creep behaviour of our films and activated parameters could be evaluated. The activated volumeV was of the order of 1 nm3 and greatly depended on the casting conditions and testing temperature. The value ofV tended to decrease as the liquid crystalline order increased. The value ofV was smaller than the size of liquid crystalline domain.