After long-term storage, PVA solution hardly has chemical change, but it may rust or mildew due to water quality and material of storage container.
In addition, the viscosity of PVA solution may increase with time if long time stored at room temperature.
Additives Used In PVA Solution
In order to prevent the occurrence of the above situations, the following additives could be used:
1. Antirust agent
For the rust prevention of iron containers, add 0.02~0.05% sodium nitrate of aqueous solution.
2. Fungicide
The starch solution may have serious mildew after long time storage, but polyvinyl alcohol is very stable for general microorganisms and rarely mildew.
However, it may be moldy because of water and additives quality. 0.1~0.5% formalin or sodium propionate of aqueous solution can be added to prevent mold, and the effect is good.
3. Prevent complete alcoholysis of polyvinyl alcohol aqueous solution.
After stored for a certain long time at room temperature, the viscosity will rise with time, and finally gel will occur. Moreover, the higher the degree of polymerization, the higher the concentration and the lower the placement temperature, the more obvious this trend will be. However, partial alcoholysis of polyvinyl alcohol changes very little on such viscosity.
Sodium thiocyanate, calcium thiocyanate, ammonium thiocyanate and other thiocyanates have the best effect on viscosity stabilizer of completely alcoholized polyvinyl alcohol aqueous solution. Phenol and butanol also have great effects. Total amount of these additives added is about 5-10% of polyvinyl alcohol. Due to the different uses of polyvinyl alcohol, and the newly added viscosity stabilizer will also have a serious impact on the quality and performance of the product,be attention when processing.