SYNOPSISThe porous structures of the highly swollen hydrogels of cellulose-acrylamide graft copolymers were studied by the solute exclusion technique. For these hydrogels, the cumulative volume of pores up to 560 8, in pore width was between 450 and 850 mL/g, and was between 20 and 30% of the total pore volume. With a n increasing in the amount of crosslinker added in the grafting procedure, the cumulative pore volume up to 560 8, decreased. Furthermore, larger pores shrunk preferentially. In the range of concentration from 0.003 to 0.3%, the viscosity of the hydrogels increased remarkably with an increase in concentration. The concentration dependence of the viscosity showed a transition a t about 0.03%, which corresponded to the reciprocal of the water retention values for each copolymer. At concentrations over 3%, fluidity of the hydrogels was lost and the water swollen copolymers became viscoelastic. This dynamic viscoelasticity remained essentially unchanged in the temperature range of 20 to 80°C. The dynamic viscoelasticity was dependent on the concentration, but the concentration dependence was smaller than that of the viscosity. The larger the amount of the crosslinker added, the larger the value of dynamic modulus became.
MASAHIRO YOSHINOBU, MlTSUHlRO MORITA, MITSUO HIGUCHI, and ISAO SAKATA D e p a r t m e n t of Forest Products, Faculty of Agriculture, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 81 2, J a p a n
SYNOPSISThe structures of the hydrogels of the partially hydrolyzed cellulose-graft-polyacrylamide copolymers as super water absorbents were examined by use of a cryogenic scanning electron microscope. The hydrogel of the wood pulp graft copolymer that had been not hydrolyzed ( P/PULP-AM) formed a spongelike structure with numerous circular micropores. The highly swollen hydrogel of the partially hydrolyzed wood pulp graft copolymer ( P / P U L P -AM-Hyd) , on the other hand, formed a honeycomblike structure with polygonal pores surrounded with membraneous walls. A hydrogel of a crosslinked polyacrylamide (PAM) formed a similar structure to that of P/PULP-AM, but the honeycomblike structure shown in P/PULP-AM-Hyd was not observed in the partially hydrolyzed PAM. The pore size of the honeycomblike structure of the hydrogel of P/PULP-AM-Hyd decreased with an increase in the amount of the crosslinker added at graft copolymerization. For the hydrogel of the P/PULP-AM-Hyd with less addition of the crosslinker, however, the honeycomblike structure had been broken. The hydrogel of the P/PULP-AM-Hyd without the addition of the crosslinker did not show a honeycomblike structure. In spite of no addition of the crosslinker, the cellulosic film and nonwoven fabric graft copolymers formed honeycomblike structures.
The Young's modulus (modulus of elasticity, MOE) in the longitudinal (L) and radial (R) directions and the shear modulus (SM) in the LR plane of Douglas fir were determined by the flexural vibration (FV) tests under the free-free condition based on Timoshenko's vibration equation. In the tests, the height/length (H/L) ratio was varied from 0.05 to 0.3. In addition, the test data were analyzed numerically and the effectiveness of Timoshenko's equation was examined. The MOE and SM were calculated based on the rigorous and approximated solutions of Timoshenko's equation. The inaccuracy of the approximated solution was enhanced when the H/L ratio of the specimen was too large. In contrast, the rigorous solution enabled the accurate calculation of these moduli in a wider range of length/depth ratios than the approximated solution.
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