Tatsuko Hatakeyama

Interaction between water and hydrophilic polymers

Abstract Various natural and synthetic polymers with hydrophilic groups, such as hydroxyl, carboxyl and carbonyl groups, have either a strong or weak interaction with water. Thermal properties of polymers and water are both markedly influenced through this interaction. The first-order phase transition of water fractions closely associated with the polymer matrix is usually impossible to observe. Such fractions are called non-freezing water. Less closely associated water fractions exhibit melting/crystallization, showing considerable supercooling and significantly smaller enthalpy than that of bulk water. These water fractions are referred to as freezing bound water. The sum of the freezing bound and non-freezing water fractions is the bound water content. Water, whose melting/crystallization temperature and enthalpy are not significantly different from those of normal (bulk) water, is designated as freezing water. Bound water in the water-insoluble hydrophilic polymers, such as cellulose, lignin and poly(hydroxystyrene) derivatives, breaks hydrogen bonding between the hydroxyl groups of the polymers. The bound water content depends on the chemical and high-order structure of each polymer. Aqueous solutions of water-soluble polyelectrolytes, such as hyaluronic acid, gellan gum, xanthan gum and poly(vinyl alcohol) form gels above a threshold concentration. In the above gels, water mostly exists as the freezing bound water, playing an important role in the junction zone formation. It has also been observed that various kinds of polysaccharide polyelectrolytes with mono- and divalent cations, and other polyelectrolytes, such as polystyrene sulfonate, form thermotropic/lyotropic liquid crystals in the water content, ranging from 0.5 to ca. 3.0 g of water/g of polymer.

Studies on Bound Water of Cellulose by Differential Scanning Calorimetry

The crystallization and melting of adsorbed water on cellulose samples such as cotton, kapok, linen, jute, various rayons, and wood cellulose have been studied using a differential scanning calorimeter (DSC). Two exothermic peaks of crystallization of adsorbed water on the cellulose samples are observed. One is a sharp peak (Peak I) observed at about 255 K in a DSC curve; the other is a broad peak (Peak II) observed at about 230-250 K. Judging from the amounts of water calculated from the results obtained by the DSC study, there seems to be some nonfreezing water which does not crystallize. Therefore, we have categorized water adsorbed on cellulose samples as one of three different kinds: free water (Peak I), freezing bound water (Peak II), and nonfreezing bound water. The bound water content is dependent on the degree of crystallinity of cellulose samples. The amounts of bound water estimated are from 1.0 to 2.2 moles per one glucose unit of cellulose. However, the amount of water bound to each glucose unit was 3.4 moles, if we took into consideration that water diffuses only into the amorphous region of each cellulose sample.

Lignin Structure, Properties, and Applications

Polymeric features of lignin and its potential as a bio-resource are reviewed, focusing on its characteristic structure and properties. Lignin is a random copolymer consisting of phenylpropane units having characteristic side chains. Lignin slightly crosslinks and takes an amorphous structure in the solid state. The molecular motion is observed as glass transition by thermal, viscoelastic and spectroscopic measurements. The hydroxyl group of lignin plays a crucial role in interaction with water. By chemical and thermal decomposition, a wide range of chemicals can be obtained from lignin that can be used as starting materials for synthetic polymers, such as polyesters, polyethers, and polystyrene derivatives. At the same time, a variety of polymers can be derived from lignin by simple chemical modification. The hydroxyl group acts as a reaction site for the above chemical reaction.

Cold crystallization of water in hydrated poly(2-methoxyethyl acrylate) (PMEA)

The structure of water associated with poly(2-methoxyethyl acrylate) (PMEA), which is known to exhibit excellent blood compatibility, has been investigated using differential scanning calorimetry (DSC). The total equilibrium water content (EWC) of PMEA was 9.0 wt%. Water in the PMEA could be classified into three types: non-freezing, freezing-bound and free water. Cold crystallization of water was clearly observed at about −42 °C on heating when the water content was more than 3.0 wt%. Cold crystallization is attributed to the phase transition from the amorphous ice to the crystal ice in PMEA. The relative proportions of freezing-bound water at the EWC is 48 % of all the water in hydrated PMEA. © 2000 Society of Chemical Industry

Differential scanning calorimetry investigation of phase transitions in water/chitosan systems

Transition temperatures of water/chitosan systems with water contents ranging from 8 to 300% (weight per cent of water per dry polymer weight) are measured by differential scanning calorimetry (d.s.c.). Upon heating, three kinds of phases, which vary with the water content, are observed for the system: cold crystallization, melting of freezable water, and a birefringent to isotropic phase which occurs for samples containing 44–190% water with a transition temperature that does not vary significantly with the water content. The glass transition temperature (Tg) of chitosan is observed at approximately 303 K for water contents ranging from 8 to 30%. From the d.s.c. data, a transition map for the water/chitosan system is compiled.

Studies on heat capacity of cellulose and lignin by differential scanning calorimetry

Abstract Heat capacities ( C p ) of wood cellulose, other natural celluloses having various crystallinities and of lignin are given for temperatures ranging from 330K to 450K using differential scanning calorimetry. The calculation of the C p of completely crystalline cellulose is based on a two-state model of cellulose which assumes linearity between the crystallinity and C p . The higher C p found in the amorphous region compared with the crystalline region, is apparantly due to differences in the frequency of molecular vibration in these two areas. The glass transition of lignin was observed as a sudden increase in C p at 400K. The precise T g of lignin was dependent on the samples origin, characterization, thermal history etc. When annealed at around T g enthalpy relaxation occurs, and this can be detected as an endothermic peak in the C p curve at the transition temperature. Moreover, the C p in the glassy state was found to decrease with both annealing time and temperature, suggesting that rearrangement of the local conformation of lignin molecules occurs in the glassy state temperature range.

Phase transitions of the water-xanthan system

Abstract The phase transitions of the water-xanthan system are studied using differential scanning calorimetry (d.s.c.). Upon heating, a glass transition, the cold crystallization of water, melting of water and transition from the mesophase to the isotropic liquid were observed for samples with water content ( W c ) ranging from 0.5 to 1.4. These transition temperatures vary depending on the water content. The glass transition was observed for water content ranging from 0.5 to 2.0. Enthalpy relaxation was observed to occur after annealing at a temperature lower than the glass transition temperature. From the heat of fusion of water, the amounts of non-freezing ( W nf ) and freezing water ( W f ) were calculated. There were 50 non-freezing water molecules per repeat unit (four pyranose units). The heat of transition from the mesophase to the isotropic liquid decreased with increasing W c . The heat capacity difference ( ΔC p ) between the glassy and liquid states was measured for the system, and it was found that this showed a good correlation with W c . The d.s.c. results indicate that both transitions, the liquid crystalline to the isotropic liquid state and the glass.transition, are caused by the molecular motion of xanthan sorbed on non-freezing water.

Non-freezing water content of mono- and divalent cation salts of polyelectrolyte-water systems studied by DSC

Abstract The number of bound water molecules restricted by mono-, di-, and trivalent cations in polyelectrolytes, such as polystyrene sulphonate, carboxymethylcellulose and alginic acid, was calculated using DSC. The number of bound water molecules decreases with increasing ionic radius in the series of mono- and divalent cations when polyelectrolytes form the liquid crystalline state. However, when polyelectrolytes form rigid junction zones in the presence of cations, the number of bound water molecules is maintained at a constant value regardless of ionic radius. The results indicate that the higher order structure of polyelectrolytes strongly influences the number of water molecules tightly bound by cations.

Vaporization of bound water associated with cellulose fibres

Abstract Vaporization of bound water associated with cellulose fibres of natural (cellulose I) and regenerated cellulose (cellulose II) was investigated by differential scanning calorimetry in both dynamic and static conditions. Factors which affect water vaporization, such as sample handling, water content, heating rate, gas flow rate and temperature of holding were examined. It was found that vaporization peak is split into two peaks, one is at around 60°C and the other is at around 120°C, when the samples were measured by slow heating rate ( −1 ) and low gas flow rate ( −1 ). The high temperature vaporization peak is related with the structural change of amorphous chains of cellulose by desorption of bound water.

Biodegradable Polyurethanes from Plant Components

Abstract Polyurethane (PU) sheets and foams having plant components in their network were prepared by using the following procedure. Polyethylene glycol (PEG) was mixed with one of the following; molasses, lignin, woodmeal, or coffee grounds. The mixture obtained was reacted with diphenylmethane diisocyanate (MDI) at room temperature, and precured PUs were prepared. The precured PUs were heat-pressed and PU sheets were obtained. In order to make PU foam, the above mixture was reacted with MDI after the addition of plasticizer, surfactant (silicone oil), catalyst (di-n-butyltin dilaurate), and droplets of water under vigorous stirring. The glass transition temperature, tensile and compression strengths, and Youngs modulus of the PU sheets and foams increased with an increasing amount of plant components. This suggests that saccharide and lignin residues act as hard segments in PUs. It was found that the PUs obtained were biodegradable in soil. The rate of biodegradation of the PUs derived from molasses an...