木材のポリ酢酸ビニル吸着における分子量選択性

抄録

High polymers are not homogeneous in that they consist of fractions with various chain lengths. It is said that there is some relation between the molecular weight distribution of adhesive polymer and adhesion. To obtain the basic information about this, we studied on the preferential adsorption about molecular weight of PVAc from benzen solution on wood and cellophane.
The PVAc used in the experiment was prepared from mixture of two kinds of PVA which had different average polymerisation grade of 550 and 1750, acetylating the mixture by ordinary method into PVAc, and dialysing in methanol. The wood (40∼60 mesh red lauan powder) and cellophane foil (#300) were first swollen in water, and then replaced by means of solvent by ethanol and further by benzen, to obtain swollen adsorbents.
The results of the experiment are as follows, on which discussions are made.
(1) The intrinsic viscosity [η] of the supernatant PVAc solution from each sample increased initially and then decreased with duration of time in shaking, and even after the amount of PVAc adsorbed seemed to reach its equilibrium in its adsorption rate curve, the intrinsic viscosity of the remaining PVAc solution changed slowly with continued shaking. Therefore, it seems probable that the lower molecular weight fractions are adsorbed faster than the higher molecular weight fractions, but that the former are replaced by the latter upon longer periods of shaking. This initial selective adsorption of lower molecular weight fractions is thought to come from their easier diffusion in solution and deposition on solid surface, and the later replacement will be interpreted by the entropy effect.
(2) From the studies of extraction and fractionation⁷⁾, some different phenomena were found with respect to the preferential adsorption about molecular weight, between cellophane foil which has the geometrically simple surface and porous wood powder. In the case of cellophane, following the initial selective adsorption of lower molecular weight fractions, the adsorbed low molecular weight actions were replaced simply from their lowest parts by the high molecular weight fractions, while, in the case of porous wood powder, the initial selective adsorption of lower molecular weight fractions occurred, the migration of the adsorbed polymer into the macro pore or crack of adsorbent followed, and then the replacement of the adsorbed low molecular weight fractions by high molecular weight fractions proceeded. Furthermore, some of macro pore or crack in the adsorbent were inaccessible to larger molecule, and so the replacement merely occurred on a certain surface of wood where the higher molecular weight PVAc was also approachable.