Dec 17 2012
Polyester is a plastic that was invented in the UK back in the 1940s, and is considered as one of the greatest man-made inventions. It is a long-chain synthetic polymer consisting of a min 85% ester and terephthalic acid by weight. There are many types of polyesters available in the market today. The raw materials for producing polyester for use in fibers, films, and plastics are procured from petroleum.
Polyester resins can be saturated or unsaturated compounds. The unsaturated polyester resins are formed by the reaction of dibasic organic acids and polyhydric alcohols while the saturated polyester resins are formed by the polycondesation reaction between multifunctional organic acids and multihydroxy alcohols.
The key characteristics of unsaturated polyester resins are rigidity, resistance to chemicals, low creepage, high strength, low temperature impact resistance and good electrical properties. Saturated polyester resins are chiefly used as the main component in powder coating compositions. The most common polyesters are thermoplastics, which are based on polybutylene terephthalate (PBT) and polyethylene terephthalate (PET).
Today, many products are derived from polyester resin strengthened with glass fibers and extended with a number of inorganic filler materials such as talc, mica, calcium carbonate, or small glass spheres. This new composite material is referred to as fiberglass-reinforced plastic (FRP) or fiberglass.
Molecular formula - C7H2 Br3O3
Density - 1.37 g/cm3
Melting point – 250-300°C (482-572°F)
Chemical and Physical Properties of PES
The following are the chemical and physical properties of PES:
- Quick drying and easy to wash
- Lightweight, soft and durable
- Resistant to mold, mildew, and most chemicals
- Highly flammable
- Possesses elasticity but retains shape without shrinking or stretching
- Can be easily blended with other materials e.g. cotton and virgin wool
- Low moisture absorption
- Good flow properties
- High strength and rigidity
- Excellent color stability
- Stain and abrasion resistant
- Insoluble in most common solvents
Manufacturing process of PES
To make polyester, ethylene glycol and dimethyl terephthalate are mixed together. The chemical reaction results in bisterephthalate which is later heated to 132°C (270°F). The heating causes further reaction and forms polyethylene terephthalate. After synthesizing the polymer, the manufacturer can decide the final end product. To make polyester fiber, an extruder is used to produce very fine threads of PET.
To make a particular type of polyester called terylene, the raw materials used are tetraphthalic acid and ethylene glycol. Tetraphthalic acid being a dicarboxylic acid has two –COOH groups. It reacts with ethylene glycol that has two –OH groups so as to produce ethylene type ester. The polymerization reaction produces polyester and water.
Applications of Virgin Material PES
PES has a wide range of applications in a variety of fields such as textile, automotive, electronical/electronic, transportation, appliances, industrial and consumer.
The following are the key uses of PES:
- Textile industry – The easy to maintain and versatility quality of polyester has made it a popular synthetic fabric in outerwear due to its high tenacity and durability. The hydrophobic property makes it the ideal choice for clothes used in wet or damp environments. It is also used to make shirts, pants, suits, bed sheets, laundry bags, curtains, diapers, and carpets
- Synthetic artery replacements
- Sails, tents and ropes
- Automotive industry- seatbelts, transportation upholstery
- Conveyor belts,fan belts, films and filters
- Electronics – LCDs, wire, insulation tape, holograms etc.
Environmental Impact of PES
Polyester is a long polymer chain, hence it is non-biodegradable, especially in the ocean because of low temperatures. Recent research has shown that a single polyester garment can shed countless tiny fibers into the wash water, which then flows into the ocean. The pollution to the ocean is worsened by the fact that polyester tends to attract oily pollutants in seawater thereby becoming a vehicle for the transfer of hazardous chemicals into the food chain when the polyester fibers are ingested by fish and other sea creatures. Also many fish, turtles, marine mammals, and seabirds die as they get entangled or eat the plastic refuse.
Recycling Process
Natural polyesters and a few synthetic polyesters are biodegradable; however, most synthetic polyesters are not. Bioremediation is one method to reduce polyester waste that relies on biological processes to break down a variety of pollutants. A prime example is polyester polyurethane (PUR) that is widely used in industry and manufacturing and is vulnerable to biodegradation with the help of numerous endophytic fungi, which has been observed to have the ability to degrade synthetic polymer polyester polyurethane (PUR).
Polyester bottles can be recycled to form polyester. The recyling process is also simple. The disposed bottles can be collected from landfills, chopped up into small pieces, and fed to an extruder where they are heated to their melting point and made to flow into long thin strands. At this stage, the strands are cut into short pellets and stored for further use.
Applications of Recycled PES
Recycled polyester is exactly in the same form as virgin polyester material, and hence can be once again used to make polyester fiber or plastic products. For example, clothing manufacturers can use the polyester pellets to make fabric by heating the pellets and forcing them via small nozzles so as to produce fine fibers. These fibers are then woven to make the fabric.
This method keeps tons of polyester out of landfills, also recycling PET bottles by re-melting and extruding it as fiber saves a lot of raw materials and energy.
Biodegradable polyesters can be used in various fields. Some examples are listed below:
- Agriculture - temporary replanting pots, mulch films, vegetation nets and sheets, water retention sheets, and supply system for fertilizers and pesticides
- Fisheries - fishhooks, fishing lines and nets, and fishing gears
- Consumer products - golf tees, disposable plates, refuge bags, cups, bottles, bags, feminine hygiene products, containers, and cutlery
Sources and Further Reading