Post 559 —by Gautam Shah
Vinyl is a synthetic or man-made material. In chemistry, vinyl or ethynyl is the functional group. Vinyl groups can polymerize with the aid of a radical initiator or a catalyst, forming vinyl polymers. Vinyl polymers are of many types, all made from monomers in which one or more of the hydrogen atoms of ethylene are replaced by another atom or groups of atoms. One of the hydrogen atoms is replaced to produce Polypropylene, Polystyrene and Polyvinyl chloride. Two of the hydrogen atoms are replaced to produce Poly-isobutylene (a type of rubber) and Polymethyl methacrylate. And when both carbons are substituted, it produces a complex polymer, Polytetrafluoroethylene (DuPont –Teflon).
Vinyl (V) as a term, coined by the German chemist Hermann Kolbe in 1851, derives from Latin word vinum = wine, because of its relationship with ethyl alcohol. Vinyl Chloride (VC) (chloroethene) CH2=CHCl is a gaseous chemical intermediate, a monomer, not a final product. It is composed of two simple building blocks: ethylene, from petroleum and chlorine a common sea water product. Due to its hazardous nature, no end products use vinyl chloride in its monomer form. In popular usage, the vinyl relates to polyvinyl chloride, basis for one of the world’s most versatile plastic material. Polyvinyl chloride is made by polymerization of the monomer vinyl chloride (chloroethene) CH2=CHCl. Polyvinyl chloride (PVC) is very stable, storable, fine-grained white powder, and not as hazardous as its monomer. Compared with other plastic materials of vinyl formulations use substantial proportion of natural resources, with low energy requirements for processing and release low quantity of emissions.
Vinyl polymers or Polyvinyl resins are the most common and comparatively less expensive thermoplastic. The properties vary with chemical structure, crystallinity molecular weight, additives and modifying agents. Vinyl resins are non-oxidizing, permanently flexible tough and durable. These are resistant to moisture and humidity. Vinyl resins are resistant to mild alkali, acid, alcohol, grease, oils and aliphatic hydrocarbons. Vinyl resins degrade upon prolonged exposure to heat, and UV light. The degradation products include HCl which accelerates further degradation, leading to unsaturated polymer structure that can get oxidized. This results in brittleness, loss of flexibility, discolouration. Presence of chlorine offers excellent flame retardant properties making it a choice product for electrical conduit and wiring requiring high resistance to ignition and flame spread.
Polyvinyl can be made flexible, rigid, semi-liquid, clear or colourful. PVC are of two main varieties: Rigid PVC is used in construction industry and for industrial components. Uses also include, siding, flooring, pipes, extruded sections for doors and windows and hardware. Flexible PVC is softer and pliable due to addition of plasticizes, typically like phthalates. The uses include trims, sheets, sheathing for electrical wires and cables, handrail tops, toys, water buckets, water hose pipes, vinyl music records, imitation leather (Rexine), signage, inflatable products, and rubber replacement applications. PVC resins are used for coatings for metal finishes, collapsible tube finishes, plastic (or Latex) paints, marine and food coatings mastic compounds and strippable coatings. Emulsions based on vinyl acetate are popular compared to many other latex type of paints. Vinyl acetate emulsions are odourless, dry rapidly, durable on outdoor faces and surfaces can be washed easily.
Vinyl resins have TWO basic sets of product categories:
Polyvinyl acetate: It is a leathery colourless low temperature softening thermoplastic, with relative stability to light and oxygen. It is mainly used for water-based adhesives, binders (fabric printing) and emulsion paints.
Polyvinyl chloride: It is converted from monomer to a polymer PVC. The final product is in flakes or pellets form, which are used for product forming through solution, dispersion, injection moulding, and extrusion.
Other co-polymer variants include:
1. Carboxy modified Vinyl chloride and Vinyl acetate > Carboxyl modification makes it possible to formulate air drying metal coatings.
2. Epoxy modified Vinyl chloride and Vinyl acetate > Epoxy modification provides ability to cross-linked, with carboxy modified vinyl resins to achieve a thermosetting system. Such thermosetting systems have superior chemical resistance and toughness.
3. Hydroxy modified Vinyl chloride and Vinyl acetate > Hydroxy modification improves compatibility and adhesion, provides sites for cross linking.
Commercially several products of PVC are widely used.
Chlorinated polyvinyl chloride (cPVC) is a thermoplastic produced by chlorination of polyvinyl chloride (PVC) resin. Uses include hot and cold water pipes, and industrial liquid handling. cPVC is resistant to several acids, bases, salts, paraffinic hydrocarbons, halogens and alcohols, but not resistant to solvents, aromatics and some chlorinated hydrocarbons. It can carry higher temperature liquids than PVC. Due to its specific composition, dealing with cPVC requires specialized solvent cement. The cPVC capacity to bend, shape, and weld makes it suitable for many uses.
Various Thermoplastic Pipes used in ultra pure Water Systems polyvinylidene fluoride (PVDF), perfluoroalkoxy (PFA), ethylene chlorotrifluoroethylene (ECTFE) and polytetrafluoroethylene (PTFE)
Unplasticized polyvinyl chloride (uPVC) has strong resistance to chemical or electrochemical effects, sunlight, and chances of oxidation from water. As this is lead and plasticizer free, is used for potable water supply pipes.
(Molecular) Oriented Poly Vinyl Chloride oPVC is a comparatively a new technology material. This molecular-oriented bi-axial high performance product offers very high strength with extra impact resistance.