The properties of Polyvinyl Alcohol
Polyvinyl Alcohol (PVA) is the hydrolysis of Polyvinyl Acetate, it has excellent performance membrane film, colorless transparent, oil resistance, solvent resistance, bacteria and fluorescent stability and many other properties. As the film production process, the following features must cause enough attention.
1. The PVA solvent is water, but its water solubility is greatly affected by the degree of polymerization of influence, especially controlled by the alcoholysis degree. Complete alcoholysis PVA dissolved in the minimal water, when the degree of alcoholysis is under 88 %, and when the temperature is under 20 ℃, it almost completely dissolved, but with the rise of the alcoholsis degree, the solubility of it is reduce greatly.
2. The viscosity of high degree of alcoholysis of Polyvinyl Alcohol water solution change by the different placing conditions, and the storage temperature directly affect the viscosity. Experiments show that when the temperature is between 20 to 50 ℃, the viscosity decrease a lot, and when the temperature is at 50 ℃, the decrease of viscosity is smaller, and when the temperature is more than 80 ℃, the viscosity is stable. The viscosity of PVA solution increases with the increase of the concentration of PVA. The surface of PVA solution crusts easily under stationary state, the crust phenomenon on the coating is extremely unfavorable.
3. PVA film has excellent oxygen barrier properties in dry conditions, oxygen permeation coefficient of it is the lowest in all kinds of resin film. The existence of a large number of hydroxyl (OH) groups on the molecular chain of PVA, in a wet environment, these hydroxyl groups and water molecules form hydrogen bonds, leading to PVA aggregation structure changes, the barrier property of PVA greatly decreased. And with the rise of relative humidity the amount of oxygen through also increase significantly.
4. PVA film in water has the phenomenon of swelling and shedding, if the composite coating film exposed in the moist environment, the high oxygen barrier property will be lost.
1. The PVA solvent is water, but its water solubility is greatly affected by the degree of polymerization of influence, especially controlled by the alcoholysis degree. Complete alcoholysis PVA dissolved in the minimal water, when the degree of alcoholysis is under 88 %, and when the temperature is under 20 ℃, it almost completely dissolved, but with the rise of the alcoholsis degree, the solubility of it is reduce greatly.
2. The viscosity of high degree of alcoholysis of Polyvinyl Alcohol water solution change by the different placing conditions, and the storage temperature directly affect the viscosity. Experiments show that when the temperature is between 20 to 50 ℃, the viscosity decrease a lot, and when the temperature is at 50 ℃, the decrease of viscosity is smaller, and when the temperature is more than 80 ℃, the viscosity is stable. The viscosity of PVA solution increases with the increase of the concentration of PVA. The surface of PVA solution crusts easily under stationary state, the crust phenomenon on the coating is extremely unfavorable.
3. PVA film has excellent oxygen barrier properties in dry conditions, oxygen permeation coefficient of it is the lowest in all kinds of resin film. The existence of a large number of hydroxyl (OH) groups on the molecular chain of PVA, in a wet environment, these hydroxyl groups and water molecules form hydrogen bonds, leading to PVA aggregation structure changes, the barrier property of PVA greatly decreased. And with the rise of relative humidity the amount of oxygen through also increase significantly.
4. PVA film in water has the phenomenon of swelling and shedding, if the composite coating film exposed in the moist environment, the high oxygen barrier property will be lost.
stevia - 12. Nov, 07:35
