Polyvinyl chloride: Polyvinyl chloride (PVC, commonly called "vinyl") incorporates chlorine atoms. The C-Cl bonds in the backbone are hydrophobic and resist oxidation (and burning). PVC is stiff, strong, heat and weather resistant, properties that recommend its use in devices for plumbing, gutters, house siding, enclosures for computers and other electronics gear.
PVC can also be softened with chemical processing, and in this form it is now used for shrink-wrap, food packaging, and rain gear. All PVC polymers are degraded by heat and light. When this happens, hydrogen chloride is released into the atmosphere and oxidation of the compound occurs. Clothing Polypropylene is a major polymer used in nonwovens, with over 50% used for diapers or sanitary products where it is treated to absorb water (hydrophilic) rather than naturally repelling water (hydrophobic).Other interesting non-woven uses include filters for air, gas, and liquids in which the fibers can be formed into sheets or webs that can be pleated to form cartridges or layers that filter in various efficiencies in the 0.5 to 30 micrometre range. Such applications could be seen in the house as water filters or air-conditioning-type filters.
Grades of PVC:
1. Versatile material
2. Properties can be varied over a wide range by the use of additives such as fillers, stabilizers, plasticisers , Lubricants, etc.
3. Grades can be broadly classified as
4. UPVC (Unplasticized PVC)
5. SPVC (Plasticized / Soft PVC)
Characteristics:
1. Good Stiffness
2. Good Insulation
3. Good Resistance to Acids, Alkalis, Oils and inorganic chemicals
4. Low water Absorption
Strengths:
1. Good Weather resistance
2. Self extinguishing
3. Electrical and thermal insulations etc.
4. Corrosion resistance
5. Unlimited colourability
6. Design Versatility
7. Temperature sensitiveness
8. Poor creep resistance at elevated temperature
9. Resistance towards non polar solvents but readily attacked by cyclohexanone and THF.
10. The Properties of PVC can be modified from soft to rigid formulations by modifying the basic resin system with suitable additives.
APPLICATIONS OF PVC
1. Automobile seat covers, steering wheel covers, crash pads, mud flaps.
2. Leather cloth
3. Rigid Pipes, Tubing, garden hoses
4. Footwear
5. Calendered sheets, flooring
6. Electrical wires, cables & Insulation tapes
7. Bottles
8. Doors, Profiles & Partitions
9. Blood bags, Infusion sets etc.
Compounding Ingredients: PVC cannot be processed as such, and it has to be compounded to make it useful for a wide range of applications.
Various additives can be;
1. Stabilizer
2. Plasticizers
3. Extenders
4. Lubricants
5. Fillers
6. Pigments
7. Processing Aids
8. Impact modifiers
PVC Typical Formulations
depends upon end use
-Typical general purpose insulation compound
Suspension PVC. - 100.0
DIOP. - 40.0 (Plasticizer)
Trixylyl phosphate. - 20.0 (Flame retardant &
Plasticizers)
China clay. - 20.0 (filler)
Tribasic lead sulphate. - 7.0 (Primary heat stabilizer)
Stearic acid. - 0.5 (Lubricant)
Pigment. - 2.0
Properties
1. Good strength.
2. Excellent water and chemical resistance.
3. Unlimited compounding possibilities.
4. Self extinguishing characteristics.
5. Good weather resistance.
6. Good electrical properties
7. Good abrasion resistance.
Flexible Polyvinyl Chloride (PVC) : Drying before processing is highly recommended, moisture rate should be lower than 0.3%.
Injection moulding:
Melt temperature should lie between 170 and 210°C.
Mold temperatures of 20 to 60°C are more suitable.
Mold shrinkage lie between 1 and 2.5%.
Extrusion moulding:
Extrusion temperatures are 10-20°C below injection molding temperatures in order to avoid premature thermal degradation.
Strengths:
1. Low cost
2. Good resistance to UV
3. Flexible
4. High impact strength
5. Good resistance to acids, alkalis, oils and many corrosive inorganic chemicals
6. Good electrical insulation properties
7. Non-flammable
8. Easier to process than rigid PVC
9. Versatile performance profile
Limitations:
1. Properties can change with time, due to
plasticizer migration
2. Tends to degrade at high temperatures
3. Attacked by ketones; some grades swollen or attacked by chlorinated and aromatic hydrocarbons, esters, some aromatic ethers and amines, and nitro- compounds
4. Non suitable for food contact with some
plasticizers
5. Lower chemical resistance than rigid PVC
Rigid Polyvinyl Chloride (PVC): Thermal stabilization is required for processing rigid PVC, otherwise material may decompose during processing.
PVC is sensitive to the thermal history and the window of processing temperatures is quite small.
Drying before processing is highly recommended, moisture rate should be lower than 0.3%.
Injection moulding:
Melt temperature should lie between 170 and 210°C.
Mold temperatures of 20 to 60°C are more suitable.
Mold shrinkage lie between 0.2 and 0.5%.
Screw with an L/D ratio of 15 to 18 is recommended.
Extrusion moulding:
Extrusion temperatures are 10-20°C below injection molding temperatures in order to avoid premature thermal degradation.
Strengths:
1. Low cost
2. High stiffness
3. Intrinsic flame retardant
4. Suitable for transparent applications
5. Better chemical resistance than plasticized PVC
6. Good electrical insulation properties
7. Good vapour barrier properties
8. FDA compliant
9. Good dimensional stability at room
temperature
Limitations:
1. Difficult to melt process
2. Becomes brittle at 5°C (when not modified with impact modifiers and/or processing
aids)
3. Limited solvent stress cracking resistance
4. Low continous service temperature of 50°C
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