Introduction of PVA
We all know that the main component of water soluble film is PVA, so let’s first understand what PVA is?
Polyvinyl alcohol is an organic compound, is an important chemical raw material, chemical formula for [C2H4O]n, appearance is white flake, flocculent or powdered solid, tasteless. From the perspective of production, according to the different raw materials, there are three ways to produce PVA:
(1) petroleum → ethylene → vinyl acetate → polyvinyl alcohol;
(2) Natural gas → acetylene → vinyl acetate → polyvinyl alcohol;
(3) calcium carbide → acetylene → vinyl acetate → polyvinyl alcohol.
Polyvinyl alcohol (PVA) can be used to manufacture polyvinyl acetal, fabric treatment agent, emulsifier, paper coating, adhesive, etc.,
but also the main raw material of PVA water soluble film.
What’s PVA film ?
PVA (polyvinyl alcohol) film, also known as PVA water-soluble film, refers to the PVA as the matrix of the film. Water soluble film is made of PVA film formation, water solubility and degradation, adding a variety of additives (such as surfactants, anti-stick agent, etc.).
It has good water solubility, degradability, gas selective permeability, mechanical properties, antistatic, oil and chemical resistance, excellent printing performance. And it has been favored at home and abroad, widely used in agriculture, medicine, food, daily necessities, electronics, textile, printing and other fields.
A plastic film which is water soluble and biodegradable
Since PVA, the material for the water-soluble film, is also derived from petroleum extract, could it also produce microplastics, as conventional plastics do?
After the PVA film is dissolved in water, the aqueous solution is colorless, tasteless, non-toxic and harmless. It can be decomposed in nature through hydrolysis and biodegradation, and the final decomposition products are H2O and CO2.
With the rapid development of economy and the improvement of living standards, environmental protection and health has become a common understanding of people. whether it is the packaging of daily necessities, fruits and vegetables, agricultural products, food and beverage packaging, or industrial packaging has put forward higher requirements. At the same time, in the field of packaging to pursue healthy performance, reduce costs and pay attention to environmental protection has become a development trend, in the premise of meeting the packaging function, packaging materials to lightweight, thin wall, functional, recyclable, natural degradation direction.
Polyvinyl alcohol (PVA) film has many excellent properties, such as high transparency, no static electricity, no dust, low cost, barrier and oil resistance, plus non-toxic, no pollution, completely biodegradable and excellent printability. PVA as raw material production of plastic film, abandoned after placed in the outdoor, after a few times of rain wash can be completely dissolved and run away with the rain, participate in the nature of the cycle, will not form “white pollution”, can effectively prevent the spread of toxic and harmful substances.
Thus, in addition to water soluble, PVA film is also biodegradable, is not like traditional plastic packaging, need hundreds of years or even thousands of years to degrade, and produce microplastics to enter the ecological cycle again.
Is water soluble film eco friendly ?
PVA (PVOH) water soluble film products belong to green packaging materials. The microbial experiment showed that PVA water soluble film was neither toxic nor hindered the growth and reproduction of microorganisms. And could be completely biodegradable. In terms of degradation mechanism, PVA (PVOH) water-soluble film material has the characteristics of water solubility and biodegradation. After being dissolved in water, PVA (PVOH) water-soluble film material forms colloids and penetrates into the soil, which increases the soil clumping, air permeability and water retention. PVA (PVOH) material in soil can be decomposed by bacteria strains isolated in soil. Eventually it degrades into CO2 and H2O.
Advantages of the water soluble film
Water soluble film products belong to green packaging materials, neither toxic, nor hinder the growth and reproduction of microorganisms, can be completely degraded.
PVA material has two degradation characteristics: water degradation and biodegradation.
Firstly, it dissolves in water to form adhesive liquid into the soil, which increases the soil agglomeration, air permeability and water retention. It is especially suitable for the transformation of sandy soil. The PVA material in the soil can be decomposed by strains of bacteria isolated in the soil and can eventually degrade to CO2 and H2O.
1. It is cold water soluble . The water soluble speed can be designed to choose. According to its dissolution speed, they can be divided into: instant, medium solution, slow solution three. The dissolution rate depends on the water temperature and film thickness. Usually , the higher the water temperature, the faster the dissolution, and vice versa.
2. According to the appearance can be divided into smooth surface and embossed
3. According to the color can be divided into colorless and colored (red, blue, yellow, green, etc.)
Water soluble film can avoid direct contact between users and toxic substances;
Transparency and gloss
The transparency and gloss of water – soluble film are better than other films.
The moisture permeability of water soluble film is similar to cellophane. It is a film with extremely high moisture permeability and does not produce fog drops when packing hot and wet items.
Water soluble film moisture content will change with the environmental humidity.
Usually, the water soluble film is encapsulated with PE film to keep its water content unchanged. When the PE film is removed, the water content will change with the environmental humidity . And the performance will change accordingly.
The water soluble film has strong permeability to water and ammonia, but has superior barrier to oxygen, nitrogen, hydrogen, helium, argon and carbon dioxide. The use of water soluble film can keep the composition of the packaged product and its own smell.
Many plastic films have a strong charge, and water – soluble films have little static electricity.
In the process of using water soluble film packaging products, it will not cause the reduction of plasticity or electrostatic dust.
Water soluble film strong polarity, good printing performance. It has been widely used in the special printing industry, such as water transfer film substrate.
Strength and weather resistance
It has strong toughness, tensile strength, tear strength . And its bidirectional tensile strength is superior, bending resistance is 10 times of other films. It also has good weather resistance, long service life.
Moisture and gas permeability
Water soluble film has strong permeability to water and ammonia, but good barrier to oxygen, nitrogen, hydrogen and carbon dioxide gas. These characteristics, so that it can be intact packaging product ingredients and original smell.
Resistance to oil and organic solvents
Water soluble film has excellent oil resistance (vegetable oil, animal oil, mineral oil), fat resistance, resistance to organic solvents and carbohydrates. But strong alkali, strong acid, chlorine free radicals and other substances that can react chemically with PVA (such as borax, boric acid, some dyes, etc.), such substances are not suitable for water soluble film packaging.
To sum up, although the main raw material of PVA water-soluble film is also from petroleum extract like traditional plastics, it is different from traditional plastics. Traditional plastics are difficult to degrade and take hundreds or even thousands of years. In addition, traditional plastics may produce microplastics to enter the ecosystem and harm the environment and human health. Water soluble film, due to its outstanding hydrolysis and biodegradation characteristics, can be quickly hydrolyzed or biodegraded into CO2 and H2O after entering the natural environment, without any harm to the environment, is becoming one of the most popular environmental packaging products.