When polyvinyl alcohol (PVA) powder is mixed into putty powder, many small, undissolved particles appear after the putty is applied to the wall. This phenomenon is mainly caused by insufficient dissolution of the PVA powder.
Factors contributing to poor dissolution of PVA powder include:
1. Unstable degree of hydrolysis of PVA powder. PVA can be classified into two types according to its degree of hydrolysis: partially hydrolyzed and fully hydrolyzed. Partially hydrolyzed PVA is often referred to as type 88, and fully hydrolyzed PVA is often referred to as type 99. Type 88 PVA dissolves at room temperature, while type 99 PVA dissolves only above 90℃. If a degree of hydrolysis higher than 88 is used during the production of PVA powder; or if the sieve pipes are not thoroughly cleaned during the grinding and pulverizing process, or if other powders with high degrees of hydrolysis are mixed in with the type 88 powder, quality problems will occur.
2. Raw material issues with PVA. PVA powder is made by grinding and pulverizing PVA particles. Different sources of PVA raw materials affect the quality of the PVA powder.
Polyvinyl alcohol (PVA) granules are cryogenically ground with liquid nitrogen to produce PVA powder.
Some factories grind PVA granules into powder, and after a period of time, still produce insoluble, translucent clumps in the aqueous solution (excluding low temperature and rapid clumping). If such raw materials are used to pulverize and process PVA powder, small particles will definitely appear after the putty is applied to the wall.
3. Fineness of PVA Powder. There are two main grinding processes for PVA powder production in China: the disc grinding method and the turbine grinding method. The disc grinding method (i.e., the room temperature method) has low output and a high proportion of coarse powder in a single grinding step; under a microscope, the powder appears snowflake-like. The turbine grinding method (i.e., the liquid nitrogen cryogenic method) has high output and a high proportion of fine powder in a single grinding step; under a microscope, the powder appears spherical. The fineness of the PVA powder affects its dissolution rate in water; the finer the powder, the faster the dissolution rate! While it's theoretically true that finer PVA powder is always better, this is not achievable in actual production. Polyvinyl alcohol (PVA) is a high-molecular-weight organic compound. Whether using a grinding disc or turbine milling method, static electricity is generated during mechanical grinding, making it difficult for statically charged PVA powder to pass through very fine sieves. Based on our practical production experience, achieving 100% passability of PVA powder through a 120-mesh sieve represents the optimal balance between efficiency and cost. However, some vendors claiming to be able to grind PVA powder to 200 mesh or finer is false advertising! ANHUI LIWEI CHEMICAL offers a solution: test the powder with a sieve – the truth will be immediately apparent!
4. Adulterated PVA powder. Some unscrupulous vendors sell PVA powder at prices almost identical to PVA granules. Imagine selling bread at the same price as the flour – would you dare eat such bread?
ANHUI LIWEI CHEMICAL reminds you to purchase genuine PVA powder from reputable suppliers to avoid unnecessary losses!
Website: www.china-pva.net
Whatsapp: 0086-15380400285
E-mail: sales2@china-pva.net
