Polyethylene terephthalate is composed of thermoplastic resin containing at least one epoxy group, carboxyl group or carboxylic anhydride. Polyethylene terephthalate known as PET is formed by the condensation of terephthalic acid and ethylene glycol. Polyethylene terephthalate belongs to the polyester family and is made up of glass fiber and phosphorus. Its composition possesses the ability to withstand temperature changes.
Polyethylene terephthalate exists as a polymer; as a semi-crystalline material which might be opaque or transparent depending on its particle size and crystal structure. Its monomer (bis-β-hydroxyterephthalate) can be fabricated by the esterification reaction between terephthalic acid and ethylene glycol water being a byproduct, or by practicing transesterification reaction between ethylene glycol and dimethyl terephthalate with methanol being the byproduct. Polymerization consists of a polycondensation reaction of the monomers with water being a byproduct.
PET is made up of polymerized units of ethylene terephthalate, C10H8O4, units being the repetitive unit. Its composition depicts the following properties: a Young modulus (E) of between 2800-3100MPa, Tensile Strength of about 55-74MPa, its Elasticity limit range between 50-150% and a notch test of about 3.55kJ/ m2 (ICS, 2010).
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PET also exists as a semi rigid component that is very thick and light in weight. This property makes PET a very effective material in preventing moisture and alcohol. Over the years PET, was considered being very strong and could handle pressure in any way possible.
Another property of PET is that it possesses an intrinsic viscosity which is very much dependent on the length of polymer units present. The more units of polymer chains the higher the viscosity
The Manufacturing Process of PET
The manufacturing process of PET commences when pellets formed are directly crystallized and then exposed to a solid-state polycondensation in a toppled drier or a vertical placed tube reactor. As the process continues in this step, the respective intrinsic viscosity of 0.80 – 0.085 d%u2113/g is restructured again and, at that very time, the acetaldehyde components are reduced to < 1 ppm(ICS, 2010). In order to cut on costs, many polyester intermediate producers like spinning mills, strapping mills, or cast film mills have opted on the direct adoption of PET-flakes, which is derived after treating used bottle, this is usually done with the intention of increasing the size of production of polyester intermediates. To adjust the fluidity without necessary using the procedure of drying flakes, it is more efficient and easily practical to check the fluidity by polycondensation in the molten state of the flakes.
The existence of Polyethylene terephthalate as a polymer and as a semi-crystalline material brings about the opaqueness and transparency during production. The immediate observance of crystals with the above properties depicts the right amount of energy being used for the whole process. The monomer (bis-β-hydroxyterephthalate) is the simplest unit used in the esterification process s to come up with polymers which are the main components of PET. The esterification process occurs when the terephthalic acid and ethylene glycol are subjected under intense heat to form the polymers. Water is always produced as the end result of the whole process. Another method that could be used to produce PET is by a process referred as transesterification reaction which basically involves the reaction that takes place between ethylene glycol and dimethyl terephthalate with methanol produced as a byproduct. Polymerization consists of a polycondensation reaction of the monomers with water being a byproduct.
The most recent latest Polyethylene terephthalate flake conversion processes involves the application of twin screw extruders, multi-screw extruders or multi-rotation systems and coincidental vacuum degassing which are used to take out moisture and avoid flake drying before the needed time. The above processes create an ample environment for the conversion of viscose PET flakes without considerable reduction of viscosity caused by hydrolysis.
Polymerized units of PET are made up of ethylene terephthalate; C10H8O4 is usually used as repetitive unit. The components of ethylene terephthalate include the features that have already been discussed above that is, a young Modulus, a greater tensile strength and an elasticity limit that measures way beyond the normal stretch.
The amount of Polyethylene terephthalate packaging materials have steadily been increasing over the years as its use and demand keep on rising. It is estimated that over 9 million tons of packaging materials are produced around the globe. Production of Polyethylene terephthalate is said to be cost effective as more than 5.85million tons of the raw material is derived from recycling. Efforts to come up with a major recycling plant in America have met several challenges making the nation unable to fully tap on the resource. Attempts in Japan to manage the recycling of Polyethylene terephthalate has become a mind boggling activity. This is because collection of Polyethylene terephthalate waste to a particular point was considered expensive and a possible risk of inconsistency. In the last ten years the price of baled Polyethylene terephthalate waste increased by ten times making the business less profitable.
The use of Polyethylene terephthalate package can either be used once and disposed or kept for some time depending on shelf life of the contents. If the contents are kept intact, that is, if the package does not get opened. The package itself is otherwise durable. Polyethylene terephthalate packages do not break easily or neither does it contaminate the content. Polyethylene terephthalate is air tight and therefore provides a favorable environment necessary for longer shelf life packaged products.
After a using Polyethylene terephthalate package, the package is more likely to thrown into a bin from where the recycling companies can collect it. When Polyethylene terephthalate is not recycled it can be burnt this is because it is not toxic, it is made from carbon, hydrogen and oxygen therefore when burnt carbon dioxide and water are the products .When intended for recycling materials recovery facilities (MRF) collect and recycle the material. The recycling process starts with collection of waste plastics and later Polyethylene terephthalate packages and other materials of the same kind such as bottles placed together.
During sorting, Polyethylene terephthalate of the same kind are placed together. This is in terms of color: colorless, blues and green, and the remainder colors together.
Products of Polyethylene terephthalate such as packages when not disposed well they tend to spread across towns or are even carried by wind to rural areas creating a bad scène. This often depicts untidiness of a place and most likely it covers the beauty of the natural environment.When Polyethylene terephthalate materials are not disposed well there are a couple of environmental threats that arise. This is especially in third world countries where recycling of Polyethylene terephthalate has not been well established. In developed countries there have been efforts to deal with the menace of Polyethylene terephthalate materials but the efforts has not been completely controlled.
When Polyethylene terephthalate material is left in the open it can act as water reservoir which forms a habitable breeding ground for disease causing organisms such as mosquitoes which cause life threatening diseases such as malaria and elephantiasis. Birds are also at risk especially scavenging birds as their feet tend to be entangled with Polyethylene terephthalate papers which after some time may amputate their toes rendering them unable to feed and thereby killing them in the process. In third world countries grazing animals are kept at risk as they may engulf Polyethylene terephthalate packaging’s which may end up killing them. When disposed on water bodies’ fish and other sea animals are also at risk. Large amount of the packaging material on water may prevent adequate diffusion of, the needed, oxygen with water exposing aquatic animals to risk.
When Polyethylene terephthalate materials are buried they take longer to decompose as they only decompose faster when heated by sun’s UV rays. Underneath the soil they tend to prevent water seepage to the ground below. This may cause flooding and therefore creating a disaster. When Polyethylene terephthalate is burnt in enough Oxygen it produces less toxic products of Carbon dioxide and Water. Excessive Caron dioxide produced is always a major cause of global warming. Carbon dioxide has high affinity to heat absorption and therefore it goes along way in creating a warmer environment. When Polyethylene terephthalate is burnt in incinerators at times there is insufficient Oxygen therefore Carbon monoxide is produced which is a highly toxic gas.
When Polyethylene terephthalate packages are carried by wind they may end up being sucked by airplanes’ engines creating a risk of accident. In the past there have been reports of accidents of this kind happening as a result of blockades from these materials.
During the manufacturing of Polyethylene terephthalate, there is evidently more amount of energy being laid to waste. The amount of energy used to link the different polymers together to produce Polyethylene terephthalate requires so much heat that it consumes every heating resource available.
The amount of amount of heat that wastefully emitted into the sky is referred as the Entropy Index. The Entropy Index is calculated by multiplying the dissipated energy during any process to a scaling factor. That is, EI= dissipated energy*scaling factor. The higher the resultant figure the more the energy released to waste.
This excessive amount of heat that is emitted into the sky leads to the warming of the planet and climatic changes are experienced everywhere. These causes damage to vegetation and other crops leading to a desperate situations in general. This overall effect is referred as global warming.