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Hope way PVA powder is usually processed in the form of aqueous solution. Since the solution is slightly acidic (pH 5~7), vessel should be made of materials, which will not contaminate the solution with corrosive material or rusts. Stainless steel vessel, enameled containers or polyester tanks are recommended.
The specific gravity of PVA is ranging from 1.26 to 1.31, which is heavier than that of water. Low agitation speed or unfavorable agitating condition sometimes causes coarse particles to precipitate and to block the outlet of the dissolving tank. Hence, a flush valve or tank valve is recommended to be installed in the bottom of the vessel to prevent the particles from blocking the discharge line.
PVA HWF-17 is usually used as a surface treatment agent for paper and paperboard. When higher coverage isrequired, HWF-05 or HWF-08 may be applied. A sizing solution of 2-5% is used, with a plasticizer for example glycerol, an insolubilizer for example glyoxal and defoamer added to the solution. A wax emulsion (10-50% of the weight of PVA ) may be added to prevent sticking to the dryer and staining on the calendar roll. Metallic stearates and rosins may also be applied.The applications of PVA for paper industry are listed as follows.
