Alkali treatment is a novel method whereby “Tetoron” fabrics may be uniformly reduced in weight and so brought to a sheer thin state which gives them added value. The author reported the effect of temperature and caustic soda concentration on the rate of solution and the properties of treated fabrics in the previous paper.
In this paper the mechanism of solution is discussed through the variation of rate constant of solution with OH-concentration, the degree of orientation and crystalinity of fibers, and the offect of the presence of alcohol on the rate constant.
(1) Solution of “Tetoron” in hot alkaline solution consits in topochemical hydrolysis of its ester linkages. The attack of OH- is most probable on the fiber surface owing to the hydrophobic character and compact physical structure of the fiber. Meanwhile OH- neutralizes and dissolves away terephthalic acid, the product of hydrolysis, from the reaction system. As the result, hydrolysis or solution proceeds gradually from the surface to the center of the fiber without attaining equilibrium.
(2) At the same normality, the rate of solution decreases in the order of KOH, NaOH, LiOH.
(3) In alcoholic caustic potash solution, alkoxide ions promote ester interchange and dissolve Tetron more effectively, which is illustrated by the difference of nucleophilic ability between hydroxide and alkoxide ions. The presence of water reduces the number of alkoxide ions and the rate of solution.
(4) Drawing of fibers decreases the rate, while heat treatment increases it. Further experiments are required to explain this result.
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