What is Polyvinyl Chloride (PVC)?
PVC is Polyvinyl Chloride. This is a plastic that has the following chemical formula: CH2=CHCl (see picture on the right).
Plastic covers a wide rage of synthetic or semi-synthetic polymerization products (i.e. long-chain carbon-based "organic" molecules) which name refers to the fact that in their semi-liquid state they are malleable, or have the property of plasticity.
PVC is a thermoplastic material.
Thermoplastic materials are those that can be melted again and again. These materials can be heated to a certain temperature and will harden again as they cool.
After the First World War, there were a boom in new forms of plastics due to the improvements in the chemical technology sector, including "polystyrene (PS)" and "polyvinyl chloride (PVC)", developed by the I.G. Farben company of Germany.
Nowadays, PVC is commonly used in the construction sector, for example in window frames and shutters, pipe cabling and coating, etc.. Vinyl is also used in gramophone records, and that is why we use the term vinyl records to refer to them. PVC can be used for tons of other applications from industrial ware and widely used in the healthcare sector, to car spare parts, toys factory, food packaging, raingear, etc. (This is described below).
PVC can be clear or colored, rigid or flexible, depending on the added compounds and final application that needs to be achieved; For example there exists different PVC grades such as coast or blow film, high impact, wire and cable grade, thermoforming, injection molding, rotational molding, etc.
How is it produced
The basic raw materials for PVC are derived from salt and oil.
Chlorine is manufactured by the electrolysis of sodium chloride, salt.
This is why the first PVC manufacturing plants were located close to natural sources of salt.
The electrolysis of salt water produces chlorine. The chlorine is then combined with ethylene that has been obtained from oil. The resulting element is ethylene dichloride, which is converted at very high temperatures to vinyl chloride monomer. These monomer molecules are polymerized forming polyvinyl chloride resin.
For example rigid PVC like the one which is used in windows frames is normally PVCU ("unplasticized"). On the other hand flexible PVC is achieved by adding plasticizers such as phthalates.
Furthermore, pure poly-chloroethene is unstable when exposed to visible light or UV. In order to modify this disadvantage and make it suitable for different applications antioxidants are added. Some other additives comprise:
|Additives ||Properties achieved |
|Anti-oxidants & other stabilizers ||Slow down the rate at which the polymer will be degraded by oxygen, heat, visible light or UV radiation |
| Compatibilizers ||Enable PVC to be mixed with other plastics and helps plastic recycling |
|Flame retardants ||Reduce flammability of plastic |
|Pigments ||To colour the plastic |
|To produce flexible and manageable plastic |
|Impact modifiers ||To absorb shock without damage |
|Fillers ||Inexpensive, inert materials that simply add bulk to the plastic |
Characteristics of Polyvinyl Chloride
These are some of the properties that makes PVC appropriate for several applications:
- Toughness, strength.
- Ease of blending, ease of processing
- Flame resistant and fire prevention properties
For example PVC is difficult to ignite and in the absence of a powerful external flame will not continue to burn. This is due to its chlorine compound. This makes it an ideal construction and cable material.
- It is compatible with other additives that can provide PVC clear or colored, rigid or flexible, etc..
- Excellent electrical insulation properties. This makes it ideal to be use in cables.
- Impact strength and resistant to bad weather conditions (i.e. it does not corrode and is very durable), appropriate to be used as a construction material
- Resistance to grease, oil and chemicals
- PVC is chemically stable and does not de-polymerize
- Density: 1.32-1.42 g/cc
Manufacture of PVC
The manufacturing plastics often creates large quantities of toxic chemical pollutants such as dioxin, hydrochloric acid, and vinyl chloride.
This poses a severe health risks to humans during the PVC life cycle. These toxins can produce sever illness like cancer, diabetes, neurological damage, reproductive and birth defects.
Dioxin is a persistent Organic Pollutants (POPs), this are chemical substances that persist in the environment, bio-accumulate through the food chain, and pose a risk of causing adverse effects to human health and the environment.
In addition, the chloro-ethene monomer is also a carcinogen released during PVC manufacture. This un-reacted monomer can also be present in the final PVC and released during its life cycle.
Plasticizers added to make PVC flexible, may leach out (ex. group phthalates) which are also toxic.
Plastic was almost too good, as it was durable and degraded very slowly. On the other hand this same properties is what makes plastic a dangerous material. Due to the quantity and different additives added to PVC (the PVC product may consist up to 60% of additives) and also due to its chlorine contain, the final disposal or recycling of PVC is a issue to be closely examine.
The options for disposal are recycling, landfill or incineration:
Thermoplastics can be remelted and reused, although the purity of the material tends to degrade with each reuse cycle. Furthermore, the separation of the different additives and compounds forming the plastic makes recycle a difficult option.
The biggest problem with plastics recycling is that it is difficult to automate the sorting of plastic waste, and so it is labor-intensive (ex. a mobile might have many different spare parts made out of different plastic materials).
Thus because the value of the material is low, recycling plastics is unprofitable.
Products such as automobiles are now being designed to make recycling of their large plastic parts easier.
The international standard for defining environmental claims on products or packaging can be found in ISO 14021: Environmental Labels and Declarations-Self-declared Environmental Claims.
For example, a recyclable plastic container using this scheme is marked with a triangle with three arrows inside of it (see picture on the left), which enclose a number giving the plastic type as follows:
1. PETE or PET (i.e. polyethylene terepthalate: termoplastic material used in plastic soft drink and rigid containers)
2. HDPE (i.e. high density polyethylene: the plastic commonly used to make milk and water jugs and two liter soda bottle bases)
3. PVC (i.e. polyvinyl chloride)
4. LDPE (i.e. low density polyethylene: the plastic used in cellophane wrap, diaper liners, and some squeeze bottles)
5. PP (i.e. a light, thermoplastic resin used in packaging, coating, pipes, and tubes)
6. PS (i.e. polystyrene)
The incineration of PVC causes the release of dioxins and other toxic chemicals.
Landfill of PVC has other environmental and social impacts. This is due to the not biodegradability of PVC which stays in place indefinitely; besides, attention should be taken to the fact that PVC may leach out toxic chemicals and contaminate the soil and water.
There are some "biodegradable" plastics that break down with exposure to sunlight but it still doesn't lead to complete breakdown of the plastic. In addition, some researchers have genetically engineered bacteria that synthesize a completely biodegradable plastic.
Due to PVC properties, as described above, around 50% of PVC (or vinyl) manufactured is used in construction replacing other materials such as wood or glass. Cheap, resistant, good weatherabiligy, ect.
PVC is strong, lightweight, durable and versatile. These characteristics make it ideal for window profiles. PVC's inherent flame retardant and excellent electrical insulation properties make it ideal for cabling applications.
It can be used for flooring, windows and door frames and shutters, water and waste pipes, electrical applications such as cable and wire insulation materials, architectural glazing systems, wallpaper, etc.
PVC has been widely used for surgery, pharmaceuticals, drug delivery and medical packaging. Some products include blood bags, medical containers, fluid bags, tubing, heart and lung bypass sets, masks, gloves, bottles and jars, drainage systems, ducting, etc.
The reasons to use it in the medical sector is its safety and chemical stability and bio-compatibility, chemical resistant and low cost. In addition, it is usable inside the body and easy to be sterilized.
Typical examples of PVC automotive components include: moldings, interior door panels and pockets, seat coverings, sun visors, seals, floor covering, wiring, exterior side molding and protective strips, anti-stone damage protection, etc. Brakes
PVC can be used for manufacturing toys, packaging, electric and electronic equipment, household goods, coating, plastic parts in motor vehicles, office supplies, insulation and adhesive tapes, furniture, etc.
For consumers in shoe soles, children's toys, handbags, luggage, seat coverings, etc.
Industrial sectors for conveyor belts, printing rollers.
Electric and electronic equipment such as circuit boards, cables, electrical boxes, computer housing.
|PHYSICAL PROPERTIES |
|Tensile strength ||2.60 N/mm² |
Notched Impact Strength
|2.0 - 45 Kj/m² |
Thermal Coefficient of expansion
|80 x 10-6 |
|Max Cont Use Temp ||60 oC |
|Density ||1.38 g/cm3 |
|RESISTANCE TO CHEMICALS |
|Dilute Acid ||Very good |
|Dilute Alkalis ||Very good |
|Oils and greases ||Good (variable) |
|Aliphatic Hydrocarbons ||Very good |
|Aromatic Hydrocarbons ||Poor |
|Halogenated Hydrocarbons ||Moderate (variable) |
|Alcohols ||Good (variable) |
More information about the elements of the periodic table
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