木材へのポリビニルアルコールの吸着について (第2報)

Abstract

水溶液からの不均一部分けん化PVAの木材および関連物質への吸着について実験した。吸着量の決定は吸着前後の濃度差により, 溶液濃度の定量はPVAのヨード反応による呈色 (稀薄水溶液において, 不均一部分ケン化PVAは赤色を呈する)を利用し, 波長480mμにおける呈色物の吸光度を測定する比色法によった。実験結果および考察を要約すると, (1) 溶質の真の吸着量を求めるには溶媒の収着量を知らなければならないが, このために遠心力法を適用した。溶媒収着量は無処理木粉, アル・ベン抽出木粉, 酢酸セルロース粉では同程度であるが, α-セルロースではこれらよりもかなり大きい。(2) 各吸着媒の吸着速度曲線を決定し, いずれの場合も24時間以内に平衡吸着に達することを知った。(3) 吸着媒量の多い場合 (木粉 : 0. 5g, 1. 0g) はそれの少い場合 (0. 05g) よりも, 単位吸着媒あたりの平衡吸着量が低い。(4) PVAの水溶液からの木材および関連物質への吸着において, PVAと水が競合吸着する。したがって, 水との親和性の強い表面をもつ吸着媒ほどPVAの吸着量が少ない。(5) 無処理木粉, アル・ベン抽出木粉, 酢酸セルロース粉はほぼLangmuir型の吸着等温線を示すが, α-セルロース粉の場合には極大値をもつ吸着等温線が得られる。これはα-セルロースと溶媒 (水) の親和性が非常に大きいことと, 溶液濃度の増加でPVAの会合性が顕著になることによるものと考えた。(6) 完全けん化PVAが殆ど木材に吸着されないのに対し, 不均一部分けん化PVAはかなり吸着される。後者をけん化して得た完全けん化PVAの固有粘度 〔η〕 よりも, 不均一部分けん化PVAのそれがはるかに大きい。このことは不均一部分けん化PVAが分子内水素結合のより少い状態で溶解し, 分子の広がりが大きく, 分子鎖の可撓性が高いことを示している。

The adsorpion of partially saponified polyvinyl acetate (PVAc), containing 10.5mol% acetyl groups, from dilute aqueous solution on wood and related substances has been investigated. The amount of polymer adsorbed was determined from the difference in the concentration of polymer solution before and after the sorption period. For the determination of the concentration of polymer solution, a spectrophotometric method, based on the red color produced by the reaction of partially soponified PVAc with iodine, was used. The results and discussions were as follows: 1) In order to calculate the true adsorption value of solute, the sorption of solvent should be taken into account. So, it was determined by a centrifugal method. The sorption value of solvent (water) was almost identical with that by non-treated wood powder, alcohol-benzol extracted wood powder and cellulose acetate powder, but the value was considerably large by α-cellulose powder. 2) The rate of adsorption for the adsorbent used was determined, and the equilibrium adsorption seemed to be reached within 24 hours in each case. 3) The adsorption of partially saponified PVAc was considerably dependent on the concentration of the adsorbent (powdered wood) in suspension composed of PVA-water-wood. With the more wooden adsorbent, the less was the amount of polymer adsorbed. 4) In the adsorption of partially saponified PVAc on wood and related substances, there exists the polymer-solvent competition for sites on the surface. Therefore, the more the surface of adsorbent has the affinity to solvent, the less the polymer adsorbs on the adsorbent. The sequence of adsorption amount of partially saponified PVAc from aqueous solution is as follows: non-treated wood.> al.-ben. extracted wood.> α-cellulose.> cellulose acetate. 5) In the adsorption by non-treated wood, al.-ben. extracted wood and cellulose acetate, the adsorption data appeared to fit the Langmuir isotherm, but in the case of α-cellulose, the adsorption isotherm having a maximum was found. The latter seems to be attributable to the great affinity between α-cellulose and solvent (water), and the formation of the hydrogen bonded junction between PVA molecules with the increase of the concentration of polymer solution. 6) While the amount of perfectly saponified PVAc adsorbed on wood was very small1), that of partially saponified PVAc (acetyl group: 10.5mol%) was considerably large. Intrinsic viscosity〔η〕of the partially saponified PVAc was fairly larger than that of PVA obtained by the perfect saponification of the former. This indicates that, in comparison with the perfectly saponified PVAc, the partially saponified PVAc has the small amount of intra-and inter-molecular hydrogen bonds in aqueous solution and has the large easiness of inter-molecular rotation arround the chain. So, in the case of the partially saponified PVAc, the chain molecule can easily rotate and deform to adsorbe the surface.