What are the properties and applications of PVA Film?

What are the properties and applications of PVA Film?
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Introduction of PVA film

PVA film-casting film

PVA film, also known as PVA water soluble film, is a polymer material whose basic component is polyvinyl alcohol. Due to its good water solubility, biodegradability, high transparency and wide range of uses, it is widely used in pharmaceutical packaging, agricultural packaging, and some building materials packaging. This film has several benefits for packaging applications, and it is mainly manifested in the following aspects
1. PVA film has high strength, good flexibility and good water solubility, making it an ideal choice for various applications.
2. Besides the good water solublility, the film is also biodegradable. They can be degraded into CO2 and H2O by microorganisms in water or soil. So it is non-toxic and harmless.
3. Polyvinyl alcohol itself has excellent qualities, such as solvent resistance, gas resistance, high transparency and anti-static. It is a type of green and environmentally friendly material. It has been recognized by national environmental protection departments in Europe, the United States, Japan and other countries. Third-party tests show that the biological oxygen demand (BOD) of polyvinyl alcohol is much smaller than that of starch.
4. Biological tests show that polyvinyl alcohol is non-toxic, will prevent the growth and reproduction of microorganisms, has no effect on solid waste treatment and environmental health. And polyvinyl alcohol can be almost completely decomposed. After entering the soil, it has the effect of improving the soil.

The scientific principles behind PVA water-soluble film

The scientific principles behind PVA water-soluble film mainly involve its physical and chemical properties, as well as its degradation process in the environment.

Water solubility

The dissolution process of PVA (polyvinyl alcohol) water-soluble film is not through chemical reactions, but by utilizing the physical principle of like-for-like. PVA contains a large number of -OH groups in its molecular structure, which makes it very hydrophilic. Therefore, when PVA encounters water, it can dissolve quickly. This process is mainly a physical change, not a chemical change.

Biodegradability

The biodegradability of PVA water-soluble film is due to its special molecular structure and composition. In the soil, PVA can be decomposed by specific bacteria, which decompose PVA into smaller molecules through redox reactions and enzymes, and finally degrade into carbon dioxide and water. This process includes the oxidation enzyme to catalytic PVA ,  followed by hydrolases that cut off the oxidized PVA main chain and further degrade it into smaller molecules.
Other excellent properties
In addition, PVA water-soluble film also has excellent mechanical properties, gas barrier properties, transparency, antistatic properties and resistance to organic solvents. These properties make PVA water-soluble film an ideal green and environmentally friendly packaging material. Which is widely used in medical, laundry gel beads, sanitary products and other fields.
In summary, the science behind PVA water-soluble film involves its physical and chemical properties, as well as the biodegradation process in the environment. These characteristics together constitute the environmental protection and functional basis of PVA water-soluble film.

Main production process of PVA film

 

At present, the process methods for manufacturing PVA water-soluble film at home and abroad mainly include casting method (wet method) and extrusion film blowing method (dry method). Both processes are “derived” from traditional plastic film production. Since PVA is a water-soluble substance, the film-making process conditions are different from thermoplastic plastics. So there are still many technical problems to apply the above two processes to the production of PVA film directly. And it also leads to some economic problems, such as difficult quality control, low efficiency, high energy consumption, large floor space, and high equipment investment. Therefore, it is very important to research and improve of these two types of process technologies and equipment to make them more suitable for PVA film production . And it is also the research and development focus of the industry at home and abroad.
Introduction of two processes

Casting method

The basic production process of solution casting method includes: water-dissolved PVA→cast coating→drying (heat treatment)→peeling→winding→finished product.
The process of casting method is relatively simple, but the product quality is not easy to control, the film output rate is low, the energy consumption is high, and the equipment investment is large.

Blown film method

The process of extrusion blown film is: PVA raw material, water, plasticizer, lubricant (pigment)→forced circulation mixing→extrusion granulation→melt extrusion blown film→modification treatment→winding→finished product.

Comparison between Casting film and Blown film

The extrusion blown film method has obvious improvements over the casting method in terms of product quality and production efficiency. But PVA must be modified and granulated in the early stage, which increases the process and the amount of auxiliary materials added. The resin and film must be heated repeatedly during the entire production process. And the water content in the film must be also maintained at 15% to 35%. The process is complex, the technology is difficult, and the energy consumption is high. Moreover, the film is formed, stretched, and shaped at the same time, the molecular chain is difficult to move, the orientation is poor. The strength of the resulting film is not high, and the inherent characteristics of PVA resin are not fully utilized.

Performance characteristics of cast film and blown film

Advantages and disadvantages of cast film

1. Advantages of cast film: uniform thickness, high transparency, good strength, and high flatness. It is suitable for making various packaging bags, kraft paper, binding covers, etc.
2. Disadvantages of cast film: the surface is slightly worse than that of blown film and is not smooth enough. Therefore, if a product with very smooth surface quality is required, it may be more suitable to be produced by blown film.

Advantages and disadvantages of blown film

1. Advantages of blown film

Fast production speed, good surface quality, good separation of mother-child film, suitable for making high transparency and high brightness products, and can be used to make cold drinks and frozen food packaging.
2. Disadvantages of blown film

Uneven thickness and poor flatness. Especially the edge of the blown film usually has a large thickness change, so it cannot be used for products with high gloss requirements.

How to make better use of PVA water-soluble film

The different applications of pva film

PVA water soluble film has excellent physical and chemical properties. And the film produced by different production processes has their own advantages and disadvantages. Then how to make good use of PVA water soluble film?
Firstly, from the perspective of water-soluble temperature, water soluble films are mainly divided into cold water soluble films and hot water soluble films.
Cold water-soluble films are mainly used for packaging products that need to be dissolved in cold water or room temperature water directly. It includes pesticide packaging, laundry detergent packaging, water treatment agent packaging, seed packaging, concrete packaging, etc.

Hot water-soluble films are mainly used for packaging products that don’t hope to be dissolved at room temperature but need to be packaged with water soluble products. It includes electronic product packaging, shopping bags, dog poop bags, laundry bags, etc.

Secondly, from a process point of view, water-soluble films are divided into cast film and blown film.
Cast film has uniform thickness, relatively high flatness and high transparency. Therefore, in some occasions where the performance requirements of water-soluble films are relatively high, cast film has relatively high advantages, such as cast film for release films of artificial marble or quartz stone.
While, the blowing films are usually used to make different bags.

In conclusion, it is important to understand the physical and chemical properties of water-soluble films, the advantages and disadvantages of different production processes. It will help us make better use of water-soluble films to achieve the purpose of improving production efficiency.
At the same time, it can also protect the environment well by using water soluble film.

Conclusion

PVA water soluble film is a type of revolutionary new technology that has completely changed the packaging industry or other industries. They are completely soluble in water and has many benefits for packaging applications. It includes being strong, flexible, and water-soluble. In addition, it is biodegradalbe,compostable, cost-effective, and versatile. For all these reasons, it is an ideal choice for a variety of packaging applications.

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