Production and application status and Prospect of

Current situation and Prospect of production and application of polyvinyl alcohol film (I)

with people's increasing attention to environmental protection, the "white pollution" brought by the use of plastics to the environment has attracted the world's attention. Therefore, materials with biodegradation ability have been booming. Polyvinyl alcohol film has excellent microbial decomposition performance, can be decomposed into carbon dioxide and water, does not pollute the environment, but also has some unique properties, such as gas barrier, transparency, antistatic, strong toughness, resistance to organic solvents, water solubility, etc., which can meet various requirements of various industries for the film, so it has caused an upsurge of development and application at home and abroad

6. Displacement measurement resolution (magnetostrictive displacement sensor): the common production method of 0.01mm polyvinyl alcohol industrialization is polymerization of vinyl acetate into polyvinyl acetate, and then alcoholysis. The physical and chemical properties of polyvinyl alcohol vary significantly with the degree of saponification, alcoholysis and polymerization. The solubility of PVA in water depends entirely on the degree of alcoholysis and polymerization, especially the degree of alcoholysis

during the alcoholysis of polyvinyl alcohol, the hydrophobic vinyl acetate group (CH3 COO -) in the molecule decreases, while the hydrophilic hydroxyl group (Ho -) increases, so the partially alcoholized PVA shows water solubility. As the alcoholysis degree increases, the hydrophilic hydroxyl groups increase, the hydrogen bond association between hydroxyl groups also increases, and the crystalline part that is difficult to immerse in water also increases accordingly. Therefore, it does not show cold water solubility and shows warm water solubility. On the contrary, when the alcoholysis degree is low, PVA becomes insoluble in water due to the increase of the proportion of non-polar groups in the molecule. Therefore, for the processing of PVA film, PVA resin with different alcoholysis degree, crystallinity and polymerization degree should be selected according to its different use requirements

in recent years, some companies in Japan and European and American countries have made breakthroughs in the development of PVA films, creating favorable conditions for the extensive intensive cultivation of PVA films and the "big as" extensive application of copper based materials. With the special requirements of packaging for barrier, transparency and water solubility in China, PVA film industry has also been further developed

properties, types and applications of PVA film

1 Characteristics of PVA film

compared with other plastic films, PVA film has the following advantages:

1) excellent biodegradability and non-toxic, it can be decomposed into carbon dioxide and water by microorganisms, and the degradation speed is fast and complete. It is a new generation of environment-friendly plastic film material, which can completely solve the problem of packaging waste treatment [1]

2) when the film is dry, it has excellent gas barrier to oxygen, nitrogen, etc

3) excellent resistance to non-polar organic compounds such as animal oil, mineral oil, vegetable oil, aliphatic hydrocarbon and aromatic hydrocarbon

4) it has excellent antistatic and dustproof properties due to its large amount of hydroxyl and strong hygroscopicity

5) good water solubility

6) excellent transparency and gloss

7) good mechanical properties, high strength and good tensile, tear and impact properties

8) good heat sealing performance, suitable for resistance heat sealing and high frequency heat sealing

9) good printability and low temperature crack resistance [2]

disadvantages of PVA Film:

1) hygroscopicity, poor gas barrier after hygroscopic, poor processing adaptability

2) poor moisture resistance

3) poor slip

2 types of PVA film

pva film can be divided into the following three types according to the polymerization degree, alcoholysis degree and processing and production methods of PVA resin used: water-soluble PVA film, insoluble PVA film and biaxial tensile PVA film

2. 1 water soluble PVA film

water soluble PVA film is processed from partially alcoholized PVA resin with alcoholysis degree of about 88%. Because the macromolecular chain contains a certain amount of vinyl acetate group with large volume, it hinders the mutual proximity of molecular chains, and also weakens the association of hydrogen bonds between hydroxyls on the molecular chain, so that there are more hydroxyls interacting with water. Therefore, its water solubility is better than PVA with higher or lower alcoholysis degree, and its thickness is 8 The staff film also showed excellent water solubility when using the plastic tensile testing machine for the first time [3]. Through mild heat treatment, the crystallinity of the prepared film is slightly adjusted, and various soluble films from cold water soluble to warm water soluble can be obtained [4]

2. 2 insoluble PVA film

insoluble PVA film is a non stretched film with strong water resistance. It usually contains about 10% polyol plasticizer, with a thickness of 20 ~ 70 μ M is processed from polyvinyl alcohol resin with polymerization degree greater than 1000 and alcoholysis degree of 98% or more. The film has good transparency, high gloss, is not easy to carry static electricity, is strong and tough, has moisture permeability, good oil and organic solvent resistance, and good printing performance

2. 3 biaxially stretched PVA film

due to stretching, the cohesion between molecules of biaxially stretched PVA film is enhanced, the mechanical strength is improved, and the strength and toughness are similar to that of cellophane. It can be compounded with other films into two, three or more layers of composite films to meet the needs of food packaging. In addition, biaxially stretched pvaastm d1894 requires that the film of 150 ± 30mm/min has the best gas resistance, including O2, CO2, N2, SO2, H2S and other gases; The dimensional stability, heat resistance, cold resistance, transparency, gloss and other aspects of the film prepared by other production methods are significantly improved; It is suitable for vacuum aluminizing processing, and can be used for gas replacement packaging, vacuum packaging, Deoxidizer packaging, etc; It can also be used for polyester molded release film and agricultural mulch film. Biaxially stretched PVA film also has excellent fragrance retention; Good oil resistance and solvent resistance; Good peeling property; Good anti condensation property; Ultraviolet rays are allowed to pass through, while infrared rays are not; Good printability and adhesion

3 application status of PVA film

due to its many excellent characteristics, PVA film has been widely used in various fields, and the market is very broad, so it has been widely valued by developed countries all over the world. However, due to the complex film making process of PVA film, its development in China is still relatively slow, and foreign products have a great impact on the industry. This requires us to fully understand, determine and position the production and development direction of PVA film in China in the future. Therefore, it is of great significance to understand the new trends of PVA film application at home and abroad. Foreign research in this area has been carried out for nearly 30 years, and their research and production have been ahead of China. For example, the United States, Canada, Brazil, Germany, Japan and other countries have made progress in the development and application of PVA films to varying degrees