Polyvinyl Alcohol (PVA)

What is Polyvinyl alcohol?

Polyvinyl alcohol, abbreviated as PVOH, PVA, or PVAl, is a synthetic polymer that is colorless, odorless, and water-soluble. It usually appears in the formation of white, flaky, fluffy, or powdery solids. Polyvinyl alcohol (PVA) has a history dating back to the early 20th century. It was first discovered and synthesized in 1924 by German chemists W.O. Hemnann and W. Hachnel. At that time, PVA's main application areas were adhesives and processing aids for cellulose fibers.
In the 1950s, PVA began to be produced on a large scale industrially and gradually expanded into many fields, such as textile, paper, printing, and construction. Subsequently, with the progress of science and technology, its application areas continue to expand, and it is now widely used in food, medicine, cosmetics, electronics, environmental protection, and many other fields.
Specifically, in China, the research and development of PVA began in 1951, and in the 1970s, PVA commodities began to appear on the market. As a result of the continuous improvement of synthetic technology and decreasing prices, the use of PVA is becoming increasingly widespread, and the development is proceeding at a rapid pace.

What are the properties and classifications of Polyvinyl alcohol?

Properties: Polyvinyl alcohol (PVA) is a versatile water-soluble polymer with properties between those of plastics and rubber. Polyvinyl Alcohol is a solid that can be in the form of a white powder, flakes, or flocs, with a glass transition temperature of 60-85°C. Polyvinyl alcohol is soluble in polar water due to its many polar alcohol groups that can form hydrogen bonds with water. It is also soluble in hot hydroxyl-containing solvents such as glycerol and phenol but insoluble in general organic solvents like methanol, benzene, acetone, and gasoline. Classification: The polymerization degree determines the molecular weight, which can be classified into four categories: ultra-high degree of polymerization (250,000-300,000), high degree of polymerization (170,000-220,000), medium degree of polymerization (120,000-150,000), and low degree of polymerization (25,000-35,000). Alcoholysis degree generally has complete alcoholysis (alcoholysis degree 98-100%), partial alcoholysis (alcoholysis degree 87-89%) and alcoholysis degree 78%. Generally, the thousand or hundred digits of the degree of polymerization are put in the front, and the degree of alcoholysis is put in the back of the product grade; for example, polyvinyl alcohol 17-99 means that the degree of polymerization is 1.7k, and the degree of alcoholysis is 99%.

What is Polyvinyl alcohol used for?

Polyvinyl alcohol (PVA) has a wide range of applications due to its unique properties as a water-soluble polymer. Here are some of the main uses of PVA:
Textile Industry: PVA is commonly used as a sizing agent in the textile industry. It acts as a binder between yarn and other fibers, improving their strength and abrasion resistance. It also helps in the smooth operation of weaving machines.
Adhesives and Binders: PVA is an excellent binder and adhesive component in various applications. It can be used to manufacture glues, adhesives, and coatings for paper, wood, and other materials. Its good adhesion properties make it suitable for laminating and bonding tasks. Paper and Coatings: PVA is used as a surface coating agent in the paper industry. It improves the surface properties of paper, such as gloss, printability, and water resistance. PVA coatings can also be applied to other materials to enhance their durability and appearance. Film and Membrane Formation: PVA can be processed into thin films or membranes with specific properties. These films are used in various applications, including packaging, separation membranes for water treatment or dialysis, and as substrates for electronic components.
Fiber Production: PVA fibers, known as vinyl, are produced from PVA solutions. These fibers have excellent tensile strength and resistance to chemicals, making them suitable for use in clothing, ropes, and other industrial applications.
Emulsion and Suspension Polymerization: PVA solutions can serve as protective colloids in emulsion and suspension polymerization reactions, stabilizing the dispersed particles and promoting the formation of uniform polymer particles.
Paints and Coatings: PVA is used as a binder in water-based paints and coatings. It helps to improve the adhesion, durability, and appearance of the coatings on various surfaces.
Biomedical Applications: PVA and its derivatives have also found applications in the biomedical field. They can be used to produce biodegradable implants, drug delivery systems, and tissue engineering scaffolds.
It's worth noting that the specific applications of PVA can vary depending on its molecular weight, degree of polymerization, and alcoholysis level. Manufacturers often tailor the properties of PVA to meet the requirements of specific end-use applications.

How is Polyvinyl alcohol produced?

The production of polyvinyl alcohol (PVA) involves a number of steps, mainly including raw material preparation, polymerization reaction, purification, and processing. The following is the basic process of polyvinyl alcohol production:
Raw material preparation: The main raw material for polyvinyl alcohol is ethylene. Ethylene is usually an organic compound extracted from petroleum or natural gas, either by fractional distillation of alkanes in the petroleum refining process or by cracking hydrocarbons in petroleum.
Polymerization of ethylene: Ethylene is converted to polyethylene through a polymerization reaction. This step is usually performed by catalyst-initiated free radical polymerization. In the polymerization reaction, the double bonds in the ethylene molecule are opened and connected to form long chains.
Polyethylene conversion: Polyethylene is further converted to polyvinyl alcohol. This conversion process can be acid-catalyzed, base-catalyzed, or enzyme-catalyzed. In this step, some of the hydrogen atoms in the polyethylene chain are replaced by hydroxyl groups (OH) to produce polyvinyl alcohol. Purification and processing: The synthesized polyvinyl alcohol is purified and processed to remove impurities and meet specific product requirements， including steps such as solvent extraction, crystallization, and drying.Polyvinyl alcohol is usually used in granular form. The dried polyvinyl alcohol is fed into a pelletizing machine, where it is made into pellets by extrusion and cutting.
In addition to the basic steps described above, the polyvinyl alcohol production process can be fine-tuned for different raw materials and catalyst choices. Domestic production processes for polyvinyl alcohol mainly include calcium carbide acetylene, petroleum ethylene, natural gas acetylene, and bio-ethylene, with calcium carbide acetylene accounting for the largest share of production processes.

How is Polyvinyl alcohol packed, stored and distributed? Packages:20 kg/bag,25 kg/bag,500 kg/bag,1000kg/bag. Storage:Polyvinyl alcohol should be packaged in sealed woven bags or cartons lined with plastic bags to prevent the ingress of moisture and other impurities. Transportation:Vehicles transporting polyvinyl alcohol should be protected from moisture, sun and rain to keep the interior dry and clean to prevent possible chemical reactions or quality changes of the polyvinyl alcohol in a humid environment.

What are the harmful effects of Polyvinyl alcohol?

Polyvinyl alcohol is generally a non-toxic material, but its dust can be irritating to the respiratory tract. Polyvinyl alcohol was included in the list of group 3 carcinogens in the preliminary collation of the list of carcinogens published by the World Health Organisation's International Agency for Research on Cancer in 2017. Therefore, prolonged exposure to high concentrations of polyvinyl alcohol may pose a potential health risk. Staff should be well protected in case of contact and should immediately flush with running water if it touches their eyes and skin. Operations should be carried out in a well-ventilated environment.