Water solubility of PVA differs a little with different alcoholysises and viscosities. Based on the characteristics of our products, it’s suitable to adopt the dissolving procedures as follow:
1. Add a moderate amount of clean water into the dissolving kettle on condition of room temperature. The temperature shouldn’t over 30℃.As the hot water can form masses which will extend the dissolving time.
2. Add calculated PVA into the dissolving Kettle little by little (better in average and slow speed) and fully stir it. The stirring speed should be controlled at about 80- 100 revolutions per minute, and keep it soaked for 30-60 minutes after finishing stirring.
3.Rising the temperature slowly to 85℃(partly hydrolyzed) or 90℃ – 95℃（totally hydrolyzed）
4. Heat with steam to a proper temperature step by step, and at the same time, keep stirring till PVA is completely dissolved. Heating can be done directly on an open fire without steam, but the density of the mixed liquor can never be higher the 10%. Remember constant stirring can prevent it from being burnt. The right temperature for PVA of thorough alcoholysis is between 95c and 98c, and no boiling has to be dome. Heating to 60c may do to PVA 17-88.
5. Methods to distinguish whether PVA is completely dissolved:
a. Base on the operating experiences.
b. Put some dissolved PVA liquor in a beaker, and observe it in a bright place, if it’s clear and no transparent particles can be seen, and then PVA in the kettle is completely dissolved.
c. Measure the viscosity. The viscosity of the liquid won’t change under the same condition after about 30 minutes.
6. It is natural to blister when PVA is being dissolved. Heating and stirring at interval can be done if this phenomenon is serious, or lower down the dissolving temperature and stirring speed of revolutions to a proper degree. (If necessary, a moderate amount of deformers, such as caprylic alcohol and tributylphosphate can be added in.)
7. When the dissolution of flaky PVA is coming to the end, flow down from the kettle is to be employed, and the valve at the bottom must be opened and part of the bottoms have to be let out (This part can be put into the kettle again for dissolution). So that the valve at the bottom is unblocked.