The foams manufactured by condensing PVA with formaldehyde are being used in various ways. Because of their open-celled structure, plus their excellent chemical and abrasion resistance, their applications include gas or liquid filters and washing sponges.
The current production of PVA foams amounts to 250-300 tons per year.

PVA-117 commonly used in making PVA foams. In many cases, however, other suitable grades of "KURARAY POVAL" are combined to produce foam with a particular performance or finish touch. The degrees of polymerization and hydrolysis of PVA affect not only the hardness, affinity with water, and strength of the foams, but also, to some extent, the manufacturing process itself. The selection of the proper grades of "KURARAY POVAL", therefore, requires some care. The following is the outline for the manufacturing procedure for PVA foams,

1. An aqueous solution of "KURARAY POVAL" of high concentration (about 15 to 20%) is prepared, and potato starch is mixed in.
2. The mixed solution, combined with formalin and acid (as reaction catalyst), is vigorously agitated. Here the condensation reaction is initiated. At this initial stage of reaction, the reacting solution containing a great number of bubbles, is poured into the mold.
3. During the reaction time of 10 to 40 hours at room temperature or above, the degree of acetalization reaches 60 to 70 mole %, thus the water-insoluble foams are formed.
4. The foams are then thoroughly washed off to remove starch and acid. Here the foams of open-celled structure are manufactured.

The size and number of cells within the foams are significantly affected by the viscosity of the "KURARAY POVAL" solution mixed with other chemicals, reaction conditions, the degree of acetalization, all of which are responsible for the performance of the formed sponge in actual use. Severe management and control, therefore, are required in the manufacture of PVA foams.

• With increase to a degree of 75 mole % acetalization, the foams have low elasticity even within water.
• Thermosetting resins are used together to improve the heat and acid resistances of the foams.
• Foaming agents are combined to make a close celled structure, thereby allowing for varying elasticity when wet.
• Polyhydric alcohols or these amines are added as a wetting agent to prevent the foams from losing resilience when exposed to the air.

1. PVA foams have open-celled (branched open-celled) structure. This provides the sponge with high filtration efficiency as a filtering material for water, air and oils, allows for repeated use through washing.
2. Because of its excellent chemical resistance, the sponge can be used as a filter for various materials.
3. The affinity of the sponge with water offers good elasticity and a comfortable skin-like touch when wet with water.
4. Since resistance to aging and abrasion is strong, PVA sponge lasts longer than viscose sponge.
5. The sponge has a wide range of application since any desired size and number of cells in unit volume can be made.

The PVA sponge has not only the out standing characteristics mentioned above, but also built-in features to simplify equipment and operation in manufacture.

• Filter for gas or liquid
  Air compressor intake filters, intake filters for all types of engines, filters for room air purifiers, filters for all kinds of industrial oils and chemicals, filters for industrial water, filters for paints.
  
  
• Sundries and cosmetics
  Washing sponges for automobiles, bath, kitchen, printing, etc.; Cleaner or wiping pads for glasses, camera lenses, furniture; Water absorption sponges for photographic uses, artificial chamois (leather) for automobiles, and other water absorbing materials; Cosmetics such as facial sponges, puffs, towels, etc.
  
  
• Special uses
  Dehydrating rollers for industrial purposes, paint roller brushes, acoustic filters, etc.