How is Polyvinyl Alcohol Made and Why is it Important?
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PVA full form is polyvinyl alcohol. Polyvinyl alcohol is a man-made or synthetic polymer. PVA polymer molecule contains vinyl and alcohol groups. It is a very useful polymer due to its adhesive properties. PVA is water soluble, crystalline and flammable in nature. Presence of alcohol group in it makes it flammable.
Polyvinyl Meaning
Word poly means ‘many’ and vinyl is ‘ethenyl’ functional group. Formula of vinyl is -CH=CH2. When we remove one hydrogen atom from the ethylene or ethene molecule (H2C=CH2) we get vinyl group.
PVA Structure or Polyvinyl Alcohol Structure
PVA monomer unit is vinyl acetate. It means, it is formed by the polymerization of vinyl acetate. Vinyl acetate formula is H3C-CO2-CH=CH2. PVA is not prepared by direct polymerization of vinyl acetate. Instead, it is prepared by hydrolysis of polyvinyl acetate (PVAc) through an alcohol (generally methanol) in presence of an alkaline catalyst.
Properties of PVA
Physical Properties of PVA
PVA shows high tensile strength and flexibility.
It is soluble in water and has no odor.
PVA molecular weight or polyvinyl molecular weight ranges between 26,000-30,000.
Its melting point is 185°C.
It is insoluble in organic solvents but slightly soluble in ethanol.
Chemical Properties of PVA
Polyvinyl alcohol can react with butyraldehyde and formaldehyde.
It is atactic type material and resistant to oil and grease.
Polyvinyl Alcohol Uses
PVA polymer is used in many fields. It is used as main component in many drugs. Many of its applications are based on its adhesive property. PVA is a type of synthetic adhesive. PVA is used as PVA glue in many fields. Meaning of PVA glue is a glue or fixative made up of polyvinyl alcohol.
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PVA Glue Uses
PVA glue is soluble in water and used as emulsions also. It is mainly used for fixing porous material. It is used for gluing wood, paper and cloth.
What is PVA Adhesive? & How to Make PVA Glue?
PVA glue or PVA fixative is also known as PVA adhesive. PVA glue can be prepared by a simple method. To make PVA glue, simply take 200g of PVA and dissolve it in water to make 1000ml of solution. Now heat this solution and bring to boil. Continue simmering it for half an hour. After half an hour, remove the solution from heat and cool it down. PVA glue is ready.
PVA glue can be removed by PVA remover. Many PVA removers are available in market. PVA glue from fabric can be easily removed by using hot water as PVA remover, as PVA is water soluble.
Is PVA Glue Toxic?
PVA is widely used as glue. PVA glue is non-toxic. Although research is ongoing on the subject whether long term use of PVA glue harmful or not, researches have shown that oral administration of PVA is harmless. So, use of PVA as glue should also be harmless.
Use of PVA as Polyvinyl Fabric-
PVA is a very good absorbent. This property of PVA is very useful in textile industry. That’s why PVA is used in textile industry. PVA fabric can dry well.
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Use of PVA as Polyvinyl Alcohol Film
PVA films are used in packaging of different materials such as detergents, chemicals, disinfectants etc. in many industries. As PVA is water soluble, PVA packaging material is biodegradable.
How to Make Polyvinyl Alcohol Film?
Polyvinyl alcohol film is also known as polyvinyl sheet. Polyvinyl alcohol film can be made by PVA solution. PVA solution is prepared by dissolving PVA in water. PVA sheets are very useful in packaging. The main advantage of PVA film is that it is environment friendly, as it is biodegradable.
Polyvinyl Alcohol Hazards
Some drugs of PVA can cause some allergic reactions in eyes and skin. But mostly PVA is non-hazardous. It is biodegradable and environment friendly. It is debatable whether PVA’s long-term use in packaging or as a glue is harmful for humans, as research is still going on this.
FAQs on Polyvinyl Alcohol: Structure, Properties, and Uses
1. What is Polyvinyl Alcohol (PVA) and what is its basic chemical structure?
Polyvinyl Alcohol, commonly known as PVA, is a synthetic polymer that is notable for being water-soluble. Unlike most other vinyl polymers, it is not prepared by the direct polymerization of its corresponding monomer (vinyl alcohol), which is unstable. Instead, PVA is produced through the hydrolysis of polyvinyl acetate (PVAc). Its chemical structure consists of a repeating vinyl unit with a hydroxyl group attached, represented by the formula [-CH₂-CH(OH)-]n.
2. What are the key physical and chemical properties of Polyvinyl Alcohol?
Polyvinyl Alcohol exhibits a unique combination of properties that make it useful in various applications. Key properties include:
- Water Solubility: Its most distinct property, which depends on the degree of hydrolysis and molecular weight.
- Film-Forming Ability: It can form strong, clear, and flexible films with high tensile strength and abrasion resistance.
- Adhesive Qualities: PVA is an excellent adhesive and binder, particularly for porous, cellulosic materials like paper and wood.
- Chemical Resistance: It shows good resistance to oils, greases, and organic solvents.
- Biocompatibility: PVA is non-toxic and biocompatible, allowing its use in medical and pharmaceutical applications.
3. How is Polyvinyl Alcohol (PVA) commercially prepared?
Polyvinyl Alcohol is prepared commercially through a two-step process since its monomer, vinyl alcohol, is unstable and readily tautomerizes to acetaldehyde. The process involves:
1. Polymerization of Vinyl Acetate: First, vinyl acetate monomers are polymerized using free-radical polymerization to form polyvinyl acetate (PVAc).
2. Hydrolysis of PVAc: The resulting polyvinyl acetate is then hydrolysed, a process also known as alcoholysis. In this step, the acetate groups (-OCOCH₃) on the PVAc chain are replaced by hydroxyl groups (-OH) by reacting it with a base like sodium hydroxide in an alcohol medium like methanol. The extent of this reaction determines the final properties of the PVA.
4. Why is Polyvinyl Alcohol water-soluble when most other vinyl polymers are not?
The water solubility of Polyvinyl Alcohol is a direct result of its molecular structure. The polymer chain contains a large number of hydroxyl (-OH) groups. These polar groups are capable of forming strong hydrogen bonds with the polar molecules of water. This interaction allows the polymer chains to dissolve in water. In contrast, other common vinyl polymers like Polyvinyl Chloride (PVC) or Polystyrene have non-polar or less polar pendant groups (like -Cl or a benzene ring), which are hydrophobic and cannot form hydrogen bonds with water, making them insoluble.
5. How does the structure of Polyvinyl Alcohol (PVA) differ from that of Polyvinyl Chloride (PVC)?
The primary difference between PVA and PVC lies in the chemical group (pendant group) attached to the main carbon backbone.
- In Polyvinyl Alcohol (PVA), the repeating unit has a hydroxyl group (-OH) attached. This group is polar and hydrophilic, giving PVA its characteristic water solubility and flexibility.
- In Polyvinyl Chloride (PVC), the repeating unit has a chlorine atom (-Cl) attached. The large chlorine atom creates strong intermolecular forces, making PVC a rigid, durable, and water-insoluble material.
6. What are some important industrial and commercial uses of Polyvinyl Alcohol?
Due to its versatile properties, PVA is used across many industries. Some important applications include:
- Adhesives and Binders: Used in wood glue, paper adhesives, and as a binder in paper and textile production.
- Textile Sizing: Applied to yarn before weaving to increase its strength and resistance to abrasion.
- Water-Soluble Films: Famous for its use in single-dose detergent pods and laundry bags, which dissolve in water.
- Pharmaceuticals: Used as a binder in tablets, a lubricant in eye drops, and in other medical applications due to its non-toxic nature.
- Food Packaging: Serves as a barrier layer against oxygen and moisture to extend the shelf life of food products.
7. How does the degree of hydrolysis of polyvinyl acetate affect the properties of the resulting PVA?
The degree of hydrolysis refers to the percentage of acetate groups in PVAc that are converted to hydroxyl groups to form PVA. This is a critical factor that allows manufacturers to tailor the polymer's properties:
- Fully Hydrolysed PVA (>98% conversion): Has maximum hydroxyl content, leading to high crystallinity, maximum tensile strength, and solubility only in hot water.
- Partially Hydrolysed PVA (87-89% conversion): Retains some acetate groups. This disrupts the crystallinity, making the polymer more flexible and soluble in cold water. These grades are often preferred for adhesives and emulsifiers.
8. Is Polyvinyl Alcohol considered an environmentally friendly or biodegradable polymer?
Polyvinyl Alcohol is often considered more environmentally friendly than many traditional petroleum-based plastics because it is water-soluble and biodegradable under specific conditions. Its biodegradability requires the presence of certain microorganisms and enzymes that can break down the polymer backbone. While it dissolves in water, its complete degradation in natural environments like rivers or soil can be slow and depends heavily on factors like temperature and microbial population. However, in controlled environments like wastewater treatment plants, it can be effectively broken down, making it a better alternative to non-degradable plastics for certain disposable applications.
