Polyvinyl Alcohol - Overview
Polyvinyl alcohol is a simple addition polymer. Its molecular formula is [–CH2CHOH-]n. It is water-soluble and slightly soluble in ethanol and insoluble in all other organic solvents, odorless, translucent, tasteless cream or white in appearance and it is available in a granular powder form. It is non-toxic; it has high tensile strength and flexibility, as well as high oxygen and aroma barrier properties.
This chemical is used as a moisture barrier film for food supplement tablets and for foods that contain inclusions that need to be protected from absorbing moistures from the air. Polyvinyl alcohol has excellent film-forming, emulsifying and adhesive properties. It is also resistant to oil, grease, and solvents, but increase its elongation and tear strength. A capturing point in this polymer is fully degradable and dissolves quickly.
Polyvinyl alcohol is an important the raw material, using this polymer many other polymers like Polyvinyl nitrate, Polyvinyl acetyls, Polyvinyl butyral and polyvinyl formal are produced. Polyvinyl alcohol is used as an emulsion polymerization aid, as a protective colloid, to make polyvinyl acetate dispersions mostly used is vinylon fiber production
Polyvinyl alcohol used in the production of Thickener, modifier, glues, Textile sizing agent, Paper coatings, release liner, as a water-soluble film useful for packaging. It also employs as Carbon dioxide barrier in polyethylene terephthalate (PET) bottles, PVA fibers nowadays used as a reinforcing agent in the concrete mixture. As a surfactant, it is also used for the formation of polymer encapsulated nanobeads, protective chemical-resistant gloves, fixative for specimen collection.
Manufacturing Process
The primary raw material used in the manufacture of polyvinyl alcohol is vinyl acetate monomer. It is manufactured by the polymerization of vinyl acetate followed by partial hydrolysis. The process of hydrolysis is based on the partial replacement of ester group in vinyl acetate with the hydroxyl group, and is completed in the presence of aqueous sodium hydroxide. Following gradual addition of the aqueous saponification agent. Polyvinyl alcohol is precipitated, washed and dried. The degree of hydrolysis is determined by the time point at which the saponification reaction is stopped.
The Uses of Polyvinyl Alcohol
The Application
Polyvinyl alcohol has various applications in the food industries as a binding and coating agent. It is a film coating agent especially in applications where moisture barrier/ protection properties are required. As a component of tablet coating formulations intended for products including food supplement tablets.
Polyvinyl alcohol protects the active ingredients from moisture, oxygen and other environmental components, while simultaneously masking their taste and odor. It allows for easy handling of finished product and facilitates ingestion and swallowing.
The viscosity of Polyvinyl alcohol allows for the application of the Polyvinyl alcohol coating agents to tablets, capsules and other forms to which film coatings are typically applied at relatively high solids contents.
Polyvinyl alcohol may be used in high moisture foods in order to retain the overall satisfactory taste, texture and quality of the foods. Confectionery products may also contain polyvinyl alcohol in order to preserve the integrity of the moisture sensitive constituents.
PVA is commonly used in medical devices due to its low protein adsorption characteristics, biocompatibility, high water solubility, and chemical resistance. Some of the most common medical uses of PVA are in soft contact lenses, eye drops, tissue adhesion barriers, and as artificial cartilage and meniscus.
PVA glue can be used as a bond in wood, paper, cloth and in porous material. It is the most commonly used wood glue. It is also termed as carpenter’s glue or yellow glue. Sometimes white glues are also used in proving bond between wooden surfaces. These glues are well used in surfaces where water resistance is required. Little glue can bind more pieces of wood. However, the carpenter needs to clamp the glue until it dries.
Some other uses of polyvinyl alcohol
Polyvinyl alcohol used in paper adhesive with boric acid in spiral tube winding and solid board production, Thickener, modifier, in polyvinyl acetate glues, Textile sizing agent, Paper coatings, release liner, as a water-soluble film useful for packaging. An example is the envelope containing laundry detergent in “liqui-tabs”. It is also used for Feminine hygiene and adult incontinence products as a biodegradable plastic baking sheet.
It also employs as Carbon dioxide barrier in polyethylene terephthalate (PET) bottles, As a film used in the water transfer printing process, As a mold release because materials such as epoxy do not stick to it. PVA fiber used as reinforcement in concrete. It is also used as a surfactant for the formation of polymer encapsulated nanobeads, protective chemical-resistant gloves, fixative for specimen collection, especially stool samples.
When doped with iodine, PVA can be used to polarize light and used in medical procedures, Carotid phantoms for use as synthetic vessels in Doppler flow testing and as agent in artificial Tears for treatment of dry eye.
PVA is widely used in freshwater sport fishing. Small bags made from PVA are filled with dry or oil based bait and attached to the hook, or the baited hook is placed inside the bag and cast into the water. When the bag lands on the lake or river bottom it breaks down, leaving the hook bait surrounded by ground bait, pellets etc. This method helps attract fish to the hook bait.
Anglers also use string made of PVA for the purpose of making temporary attachments. For example, holding a length of line in a coil, that might otherwise tangle while the cast is made.
Reactions and Fate in Food
The food products in which polyvinyl alcohol is intended to be used have neutral pH and are stored at either low temperature or at room temperature conditions that would not result in breakdown of PVA.
Similarly the food products in which polyvinyl alcohol is used have pH in neutral range and will not likely to have any impact on its stability. Water solutions of polyvinyl alcohol are also stable.
The structure of polyvinyl alcohol would not be conducive to hydrolysis reaction of the remaining ester groups or to esterification reactions undergone by secondary alcohols with relatively strong nucleophiles. Under intended conditions of use and storage there would be negligible interaction between polyvinyl alcohol and food constituents.
Hazards Identification
When swallowed, this chemical is very harmful and causes serious side effect, if not death. It also causes irritation if it comes into contact with the skin and eyes. If it spills on your clothes, wash them with plenty of running water. When working with it, or are in a room where it is stored, avoid as much as possible breathing its fumes or getting into contact with its dust.
PRODUCT IDENTIFICATION
Common Name | Polyvinyl Alcohol |
CAS No | 9002-89-5 |
Formula | [–CH2CHOH-]n |
H.S Code | 3905.30.00 |
Synonym | Ethenol, Homopolymer, PVA, PVOH |
PRODUCT SPECIFICATIONS
Property | Unit | Value |
---|---|---|
Purity | % | 93.5 |
Hydrolysis | mol % | 87.0 - 90.0 |
Viscosity | mpa.s | 4.5 - 6.0 |
Volatile Content | % | ≤ 5.0 |
Ash | wt % | ≤ 0.5 |
pH | - | 5 - 7 |