Masakazu Matsumoto

Viscosity of Dilute Aqueous Solutions of Heat Treated Polyvinyl Alcohol

湿式紡糸で得たPVA繊維を210～180℃, 数分程度の条件で空気中, 乾熱処理し, その熱処理繊維を水に煮沸溶解して, 粘度を測定した。その結果, 粘度は煮沸溶解時間とともに顕著に低下するが, なお原PVAあるいは未熱処理繊維に比して粘度の上昇していることを認めた。熱処理を125℃ あるいは120℃で2時間, 飽和ボウ硝液中で行ない, また煮沸溶解を窒素気流中で行なっても, 同様な現象が認められるから, これらの現象に空気が必ずしも必要ではない。しかしモノマーの精製から注意してつくられたPVAの繊維では, このような現象は認められなかった。上述の熱処理による粘度上昇は単なるミセル分散によるものではなく, 化学変化による糸状分子の横結合あるいは分岐の生成に基くものであり, この化学変化は水素イオンによって接触され, またその分解も水素イオンによって促進されるものであることを認めた。このような化学結合としては, PVA中の微量カルボニル基によるケタール結合が考えられる。すなわち, 熱処理に伴う化学変化はPVA中の異種結合の多少と紡糸の際紡糸浴からPVA中に導入される水素イオンの多少によって左右される。PVA粉末は水素イオンを含まないで, 常に多少とも酢酸ソーダを含むものであるが, これを窒素中150℃, 0.5時間あるいは120℃, 2時間熱処理したものと65℃, 15時間減圧乾燥処理したものとは同一粘度を与えた。

Intrinsic viscosity of aminoacetalized polyvinyl alcohol sulfate in 1/10 N potassium sulfate solution

The intrinsic viscosity of the sulfate of aminoacetalized polyvinyl alcohol (Am-PVA) in N/10 K2SO4 solution has been studied to disclose the influence of the number of ionic substitutents on the intrinsic viscosity of the polymer. The number of ionic substitutents is easily changed by controlling the degree of aminoacetalization, which is determined by a selection of the conditions of aminoacetalization. β-Cyclohexylamino n-butyraldehyde dimethylacetal, CH3(C6H11NH)CH·CH2·CH(OCH3)2, and β-cyclohexylamino-n-propylaldehyde dimethylacetal, (C6H11NH)CH2·CH2·CH(OCH3)2, were used as aminoacetals. The aminoacetalization reaction was carried out in a system of aminoacetal, polyvinyl alcohol (PVA), sulfuric acid, and water. The reaction product was purified by dialysis, and the degree of aminoacetalization was estimated from the nitrogen content as given by the semimicro Kjeldahl method. The PVA was used unfractionated and its degree of polymerization, as determined by the viscosity method, was found to be between 900 and 2400. The solution viscosity was measured in an Ostwald viscometer designed to reduce the kinetic energy term for which a correction was made. It was first ascertained that the viscosity in N/10 K2SO4 solution was not influenced by the rate of shear in the range of our experiment. The intrinsic viscosity was found from linear extrapolation, a linear relation between ηsp and c, being well realized in the concentration range from 1.5 to 9 g./l. The intrinsic viscosity increased with the degree of aminoacetalization in an S-shaped fashion. Compared to the same degree of aminoacetalization, Sakurada-Houwinks equation [η] = KPa was found to hold well at each degree of aminoacetalization, and the index a was found to increase with the degree of aminoacetalization. The volume expansion α3 of the polymer in the solution was estimated from [η]M/[η]θM0 according to Florys theory, in which M is the molecular weight of the sulfate of Am-PVA, M0 the molecular weight of each original PVA, [η] the intrinsic viscosity of the sulfate of Am-PVA, and [η]θ is the mean intrinsic viscosity of each original PVA in Florys unperturbated state. The viscosity in a mixture of acetone (35.2%) and water (64.8%) was used for [η]θ, its value being calculated from [η]θ = 1.06 P1/2, having reference to Sakuradas report. Then (α5 − α2/M1/2) was calculated and plotted against the degree of aminoacetalization x. It was found that these points fall on one curve, independently of the degree of polymerization of the original PVA. When [(α5 − α3)/M1/2]x − [(α5 − α3)/M1/2]0 was plotted against x in a log-log scale (we are subtracting the value [((α5 − α3)/M1/2]0 for PVA) it was found that a linear relation between them holds well independently of the degree of polymerization of PVA. The empirical formula [(α5 − α3)/M1/2]x − [(α5 − α3)/M1/2]0 = Axn was thus obtained. In both Am-PVAs n is 1.45, but A differs slightly. When the ionic strength is constant, {[(α5 − α3)/M1/2]x − [(α5 − α3)/M1/2]0} should be proportional to x2/(M/r)3/2 by Florys theory of polyelectrolytes. The fact, therefore, that the former was found to be proportional to x1.45 in our result suggests that (M/r)3/2) is not constant but may be changed by the degree of aminoacetalization, first, because the volume effect of the cyclohexyl-aminoacetal group introduced cannot be disregarded, and second, because the molecular weight M increases with aminoacetalization. The overlapping of the two effects apparently yields the exponent 1.45.