Preparation and Application of Water-Soluble Polyvinyl Alcohol Films

In this paper, the concept of soluble packaging materials, soluble conditions, composition, process and characteristics were studied, especially the application of soluble packaging materials in the field of food packaging, and the analysis of the solubility of polyvinyl alcohol as the main raw material was analyzed. Packaging Materials.
First, the concept of soluble packaging materials Many packaging materials are soluble, but the required conditions are different. For example, paper packaging material is a typical soluble packaging material, while a large number of plastic packaging materials are insoluble packaging materials. Some packaging materials dissolve at room temperature, while others dissolve at high temperatures, and some require harsh additional conditions to dissolve, while others dissolve under natural conditions, and some dissolve in a short time, while others It takes a long time to dissolve, and some packaging materials can only be dissolved by various chemical and biological factors, and some packages cannot be dissolved at all (such as plastic packaging materials).
The soluble packaging material we are studying here refers to the packaging material that naturally dissolves at room temperature. At present, degradable packaging materials, such as self-removal packaging materials and water-soluble packaging materials, that people have studied more or are currently studying are all soluble packaging materials. Soluble packaging materials are mainly new types of materials that are researched and developed for plastic packaging (especially plastic packaging films) that are difficult to degrade and pollute the environment.
It can be seen from the above that the soluble packaging materials are those packaging materials that are placed in nature and can be automatically decomposed at room temperature. There are many of these materials, and here we focus on analyzing water-soluble packaging materials.
Second, the development and characteristics of water-soluble film The soluble package research here mainly refers to water-soluble film. At present, water-soluble films used or under development are made with polyvinyl alcohol as the main component. At present, polyvinyl alcohol is used as the main raw material at home and abroad to develop water-soluble films. For example, the water-soluble packaging material developed by the Zhuzhou Institute of Technology and identified at the ministerial level in 2000—a new type of water-soluble film for packaging materials. Here we analyze the water-soluble film with polyvinyl alcohol as the main raw material.
1. The water-soluble water-soluble film uses polyvinyl alcohol to achieve its water-solubility by its extreme sensitivity to water. The molecular structure of polyvinyl alcohol contains a large number of water-soluble hydroxyl groups.
Polyvinyl alcohol is obtained by hydrolysis of polyvinyl acetate. It has excellent crystallinity and strong attraction between adjacent molecules. The decomposition temperature of polyvinyl alcohol is lower than its melting temperature. Pure polyvinyl alcohol is soluble in water and controls the hydrolyzability of polyvinyl acetate. Change its solubility. The water-solubility of polyvinyl alcohol has been studied in more detail, but due to its relatively difficult film-forming process, it is particularly difficult to make films that remain water-soluble.
The water solubility of polyvinyl alcohol is related to its degree of saponification (polyvinyl alcohol can be obtained by saponification of polyvinyl acetate and alkali). Full saponification can only be dissolved in hot water, it cannot be dissolved in cold water, and some saponifications are soluble. In cold water.
2. Composition and role In the main components of the water-soluble film, the proportion of polyvinyl alcohol is from 75% to 78%, and the others are auxiliary additives. The auxiliary additives added are non-toxic and compatible with polyvinyl alcohol. At the same time, only physical dissolution occurs with polyvinyl alcohol to improve its physical properties, mechanical properties, process properties, and water solubility, but does not substantially change its chemistry. Reaction process and chemical properties.
The role of adding a surfactant is to increase the activity and dispersive mixing of polyvinyl alcohol in water, reduce the surface tension, eliminate bubbles and improve the peeling performance between the film and the carrier.
The purpose of adding a plasticizer is to increase the softness and plasticity of the water-soluble film.
The function of the anti-sticking agent is mainly to prevent the film from generating hygroscopic adhesion at high temperature conditions, so as to affect the normal use of the film.
The role of the quick-drying agent is to increase the speed of film production, accelerate the evaporation of water, and increase production efficiency and yield.
The use of the release agent is to make the film smoothly detached from the conveyor belt or the support carrier (transport roller, doctor blade, etc.) during film formation, and to improve the uniformity of the film.
3, production process Water-soluble film production process is similar to the casting process. It includes processes such as gluing, filtering, casting, drying, peeling, and winding.
In the production of water-soluble film, the choice of raw materials must require no impurities, otherwise the resulting water-soluble film is not smooth, there are pores, the occurrence of defects such as trachoma, therefore, after the glue must be filtered to remove impurities or undissolved substances.
The glue must be produced at a high concentration, and the glue quality should be strictly controlled. The time, temperature and pressure in the reaction tank must be determined according to the experiment.
Casting must be uniform and the amount of coating must be determined by experimentation. Hot air during drying (usually using hot air drying or other drying methods) The temperature and hot air flow must also be strictly controlled. Otherwise, if the temperature is too high or the hot air flow is too high, the film will harden and wrinkle and affect the effect. The temperature is too low or If the flow rate of hot air is too low, it will be difficult to achieve the purpose of removing water, or reduce the efficiency of film formation.
Other aspects, such as tension, running speed, etc. must also be strictly controlled.
4. Performance index The main mechanical properties of the water-soluble film can basically be determined with reference to other plastic films, but the performance parameters of the water-soluble film as a package have its particularity, such as water-soluble parameters.
The main performance indicators of general water-soluble films include elongation, various strengths (stretching, heat sealing, tearing, etc.), balanced moisture at different relative humidity, heat sealing temperature, and water-soluble effects. These performance indicators are shown in Table 1 to Table 3, respectively.
Table 1 The main physical properties of water-soluble films and test methods Performance name Unit data Test method Elongation at break% 180 ~ 300 GB / T13022-91 Tensile strength M pa 30 ~ 47 GB / T13022-91 Heat seal strength N / 15 mm 5 to 12 QB/T2358-1998 tear strength KN/m 150 to 200 QB/T1130-1991
Table 2 Balanced Moisture and Heat Sealing Temperatures of Water-Soluble Films at Different Relative Humidity Item Name Parameter (Value) Relative Humidity 45 RH 65 RH 80 RH Balanced Moisture 4 to 6 7-11 13 to 16
Heat sealing temperature 170 to 200 150 180 140 to 170 Table 3 Water-soluble film water-soluble data Name Parameter (numerical value) Water temperature (°C) 25 30 40 Dissolution time (S) <300 45 to 50 25 to 30
Among the listed performance indexes, Table 1 was measured under the conditions of an ambient temperature of 23°C and a relative humidity of 65% RH. Table 3 shows the results measured at normal temperature and pressure.
Third, the application of soluble packaging materials and the expansion of water-soluble film packaging material is the biggest advantage of water solubility and barrier properties (also known as barrier properties).
There is a great deal of technical difficulty in making water-soluble films from polyvinyl alcohol. Only a few countries such as Japan, the United States, and France can now produce, and China has just made progress in this respect.
Water-soluble films have hardly been developed and applied in packaging foods. The main reason is its sensitivity to water and humidity. Therefore, it is mainly used in the fields of pesticides, dyes, water treatment agents, mineral additives, pet cleaners, concrete additives, detergents, and chemical fertilizers. Its usage is to package pesticides in packaging bags made of water-soluble film, put them into containers together with the packaging, and then add water to dissolve the pesticides in water. After stirring, they can spray pesticides or fertilize as usual. Do your homework. Polyvinyl alcohol can be dissolved up to 100% without clogging the nozzles of the agricultural machinery and without affecting the properties and efficacy of chemicals. In the packaging of detergents, for example, detergents bring great convenience, especially as hospitals or laundry service companies, as long as dirty clothes (or bedding) and detergents packed in water-soluble film are put together Washing in the washing machine makes the staff more convenient for cleaning services.
The application of water soluble films in food packaging is the result of a combination of modern packaging technology and modern life. Many modern food packaging uses small packaging, packaging (one meal consumption packaging) and one-time packaging, these packaging foods need to have matching large packaging (bags, boxes, etc.). The role of the large package has the functions of sealing against moisture and the like, while the small package inside it is to provide convenience for consumption and handling. Therefore, the application of the water-soluble film in food packaging is a small package (bag) in a large package, such as a pouch package for soybean milk, cereal, green tea, and coffee, and a pouch seasoning package (ingredients in instant noodles). The pouch package will be a new area of ​​application for water soluble films.
In addition, the application of water-soluble film on food packaging can be used as a coating layer (combined with paper) for food packaging. After being compounded with the paper, the inner package made of paper can be used to facilitate the sealing of the heat, and it can also make it not contaminate the environment after being used up (when it is put into the natural world, the rainwater will melt and melt).
Another application area of ​​the water-soluble film in the future will be the anti-counterfeiting and quality identification of food packaging. Different levels of saponified polyvinyl alcohol are used to prepare water-soluble films with different dissolution temperatures and dissolution times. They are used as non-aqueous liquids for packaging (eg, milky, oily, etc.). These substances are easily adulterated by adding water ), After the authentic manufacturers use water-soluble film packaging, once the counterfeiter adds water, the packaging will melt, thus achieving the purpose of anti-counterfeiting. In addition, on the fresh meat on the market, many speculators inject water to injure the consumers. We can use water soluble films to identify them. Once the fresh meat is filled with water, contact with a water-soluble film, the film will soften and dissolve.
The application of water-soluble films in the food packaging field has just begun, and more applications need to be further developed. (Zhuzhou Institute of Technology Yang Fuxin Hao Xihai Liu Yubin) (From "China Packaging News")

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