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Some Important Conditions During the Preparation of Polyvinyl Alcohol PVA


Used as the fiber of PVA, the acetate content of the residual control of ≤0.2%, ( alcoholysis degree of 99.8% ). To meet this requirement, it is necessary to choose the right conditions, mainly:
The amount of methanol:
The amount of methanol concentration on the alcoholysis reaction PVAC influence. Practice has proved that, when other conditions remain unchanged, with increasing degree of hydrolysis of polymer concentration decreases, however, if the polymer concentration is too low, a large amount of solvent, solvent loss and recovery workload. Therefore, industrial production select a polymer concentration of 22%.
The amount of NaOH:
Currently the amount of NaOH in plant is 0.12 mol PVAC, i.e. : NaOH:PVAC = 0.12:1 (mol). Experimental results show, tha base amount is too high, the speed of the alcohol solution, the solution is not the degree of influence of alcohol, but increased system sodium acetate content, affect product quality.
The alcohol solution temperature:
The increasing of the reaction temperature will accelerate the alcoholysis reaction is carried out, shortening the reaction time. However, due to the temperature increase, accompanied by the alcoholysis reaction of the corresponding side reactions are accelerated, such an increase in consumption on the one hand to make the root base PVA remaining amount of acetic acid increased. Due to the increase of acetate in the system, affecting the quality of the prodcut, so the use of currently industrially alcoholysis temperature of 45 to 48℃. When we consider the various factors, we should keep in mind the characteristic of the alcohol solution, that is, PVAC is dissolved in methanol, and the PVA is not soluble in methanol, which the middle of a phase transition. Sooner or later, a variety of different conditions on the phase transition occurs, alcohol solution before and after the phase transition were more, less, difficult, easy to have a direct impact on the acetate content of PVA, which affect the size of alcoholysis degrees. In the laboratory, the key quality alcoholysis performed, in that when the system has just appeared jellies, must be strong stirring, jelly broken, alcoholysis in order to ensure more complete manner.

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