Moisture sorption properties of polyacrylonitrile (PAN) fiber has been investigated. Sorption isotherm at 25°C and heat of wetting for PAN fiber were compared with those for acrylic fibers with known chemical compositions. The moisture regain at 65% r. h. was 1.37% (w/w) and heat of wetting for the dried PAN fiber was 0.6 cal/g, which were comparable values to those for the acrylic fibers. Diffusion of moisture into PAN fiber was observed using a gravimetric method at 25°C. The sorption/desorption curve below 70% r. h. was nearly identical, which indicated that interaction between water molecules and nitrile group in polymer chain was not significant. The results obtained in this study suggest that the averaged interaction between water and nitrile group is very weak. On the other hand, the exothermic property for heat of wetting and IR spectrum pattern for OH stretching indicated the possibility of the strong interaction between the sorbed water molecules and a very few nitrile groups.
Structural change of regenerated cellulose fibers caused by water was investigated with the small angle X-ray, the specific volume and thermally stimulated depolarized current (TSDC) analyses. From the small angle X-ray measurement of Cupro fiber with various water regain, the sudden change of long period for lateral direction was detected at 40% of water regain at 25°C. And the Tg determined by dilatometry at the same water regain was 25°C. The peak intensity of TSDC γ1 relaxation decreased with increase in water regain when the water regain was under 4_??_5%. TSDC β1 relaxation decreased while TSDC β2 increased with increase in water regain when the water regain was above 4_??_5%. From these findings, it was concluded that the structural formation followed by the local molecular movement may be occurred in hydrophobic domain assigned by TSDC γ1 relaxation at the water regain under 4_??_5%, and then the local molecular rearrangement from TSDC β1 region to TSDC β2 region was also occurred at the water regain above 4_??_5%, and finally the micro-Brownian motion of cellulose main chain assigned by tan δα2 relaxation was released at 30_??_40% of water regain at room temperature which brings the sudden change in long periodicity and the macroscopical swelling of the regenerated cellulose fibers.
The thermal properties of N-isopropylacrylamide (NIPA) gels in water have been investigated with differential scanning calorimetry (DSC). The dissociation enthalpy of hydrophobic bonding per NIPA monomer, ΔHN and the number of water molecules associated with the dissociation, (n-n0), were evaluated as a function of the gel preparation temperature, Tprep, where n and n0 are the number of water molecules per NIPA mole before and after dissociation, respectively. It was found that ΔHN is independent of Tprep. On the other hand, both n and n0 increase with increasing Tprep, while the difference, i.e., (n-n0) is constant irrespective of Tprep. These experimental findings suggest that the enthalpy and the number of water molecules associated with the dissociation are independent of Tprep although the number of trapped water molecules increases with Tprep in both the swollen and shrunken states.
Spin-lattice relaxation time, T1 of water molecules (H2O/Cellulose=0.08, 1.1, 2.0 (g/g)) was estimated by 1H-NMR technique for the five regenerated cellulose membranes with different water contents, and related to a biocompatibility and a structure of the membrane. In all water contents investigated here, two T1 components (T1, l>T1, s) were observed. A degree of complement activation, Ac which was estimated as an index of biocompatibility showed good correlation with porosity, Pr of the dried sample, not with an aggregation structure of cellulose chains (e. g. crystallinity), suggesting that the Ac was mainly influenced by a surface area of the membrane. In addition, it was found that the sample having the larger Pr or the higher Ac tends to have the shorter T1, l value, especially in the swollen state. These results lead to a conclusion that T1, l value estimated for the swollen sample can be regarded as an index parameter for a biocompatibility, because this value reflects a surface area of the swollen cellulose membrane.
Investigations have been made into the relationship between structure and states of water in unfrozen poly (vinyl alcohol) (PVA) hydrogels prepared by repeated freezing and thawing of aqueous solution with various PVA concentrations. The states of water were investigated by using a pulsed nuclear magnetic resonance spectroscopy. Every unfrozen PVA hydrogel gave only one spin-lattice relaxation time (T1) value. T1 of all unfrozen hydrogels were smaller than that of free water and decreased with increasing PVA concentration. These mean that the molecular motion of water in the unfrozen PVA hydrogels are more restrained than those of the free water molecules, and the mobility decreases with increasing PVA concentration. The activation energy, which was estimated from Ahrrenius type plot, for the motion of water molecules of all unfrozen PVA hydrogels was smaller than that of free water and decreased with increasing PVA concentration. These mean that hydrogen bonding force between water molecules of all unfrozen PVA hydrogels are smaller than that of free water and decreases with increasing PVA concentration. It was clarified by comparing with the results of fine structure of the unfrozen PVA hydrogels which have been studied in a previous paper that with increasing number of PVA chain in the uncrystallized region of unfrozen PVA hydrogels, the restrain of mobility of water molecules increased and hydrogen bonding force weakened.