1Government pharmacy college, Gandhinagar, Gujarat, india. Postal code: 382027.
2B. K. Mody Government Pharmacy College, Polytechnic Campus,
Near Aji Dam, Rajkot, Gujarat, India, Postal code: 360003.
3B. K. Mody Government Pharmacy College, Polytechnic Campus,
Near Aji Dam, Rajkot, Gujarat, India, Postal code: 360003.
4B. K. Mody Government Pharmacy College, Polytechnic Campus,
Near Aji Dam, Rajkot, Gujarat, India, Postal code: 360003.
5B. K. Mody Government Pharmacy College, Polytechnic Campus,
Near Aji Dam, Rajkot, Gujarat, India, Postal code: 360003.
6B. K. Mody Government Pharmacy College, Polytechnic Campus,
Near Aji Dam, Rajkot, Gujarat, India, Postal code: 360003.
*Corresponding Author E-mail: abp2038@gmail.com, akshatgol95@gmail.com, amitvyas77@gmail.com, aipvk84@gmail.com, ashvinvd@gmail.com, urvi_jc@yahoo.com
ABSTRACT:
Due to the tremendous growth of plastics in the world, Plastics have transformed everyday life. The variety of polymers and their special qualities are used to create a range of goods that expand their uses in engineering, medical and other societal advantages. PET is one of the widely used polymer in medical containers and bottling. It is evident that plastics bring many societal benefits and offer future technological and medical advances. However, concerns about poor management, disposal in unauthorized dumping sites or burned uncontrollably in the fields. This article emphasizes the properties, manufacturing, recycling, uses, health and environmental considerations of PET.
KEYWORDS: PET, Polyethylene Terephthalate, Plastic, Recycling, Containers.
1. INTRODUCTION:
Organic molecules are polymerized to form plastics. Plastic materials can be melted and formed into a variety of shapes using a number of techniques, including spinning, moulding, extrusion, and casting. Plastics are materials that are low-cost, lightweight, robust, resilient to corrosion, and have excellent thermal and electrical insulating qualities. The variety of polymers and their special qualities are used to create a range of goods that expand their uses in engineering, medical, energy conservation, and other societal advantages. Modern plastics have a number of very desirable qualities, including excellent thermal properties, great resistance to acids, solvents, and alkalis, high strength-to-weight ratio, electrical insulation, flexibility, stress resistance, and durability.[1] From 0.5 million tonnes in 1950 to over 260 million tonnes now, there has been a surge in the use of plastics over the past 60 years. the plastics sector Over 300 million euros in revenue and 1.6 million people are employed in only Europe.[2,26] Usually, several additives are used with the polymer resins to enhance performance. Inorganic fillers like carbon and silica that reinforce the material, plasticizers that make it useable, thermal and UV stabilisers, flame retardants, and colouring agents are some of these additions. Such additives are used widely and in large amounts in a variety of products. Some additional substances may be harmful (for example lead and tributyl tin in polyvinyl chloride, PVC). [3,4,27] PET is a polymer with significant value in the modern plastics industry. Being a thermoplastic, or recyclable polymer, has made it the top choice for many applications and meets the global demand for a more environmentally friendly substitute for widely used plastics like polyethylene and others. Today, two PET grades fiber-grade and bottle-grade dominate the global market. Since PET was first discovered around the turn of the 20th century, a number of businesses have been interested in offering production solutions to meet the rising need for vast quantities of PET. 5
Plastics are broadly classified into six major types as shown in Table 1, namely, PET (polyethylene terephthalate), HDPE (high density polyethylene), PVC (polyvinyl chloride), LDPE (low density polyethylene), P/P (polypropylene), and P/S (polystyrene). 6,7,28
Table: 1 Types of plastic and their monomers, typical end uses.
|
Plastic Identification Code |
Name of the plastic (Polymer) |
Constituents of the plastic (Monomers) |
Typical End Uses (Food and Non-Food) |
|
|
Polyethylene terephthalate (PET, PETE) |
Terephthalic acid + isophthalic acid + Ethylene glycol (or MEG) |
Bottles, Containers, Jars, Films, Strappings, Fibre and Filaments, Non- wovens, Medical devices, etc |
|
|
High-density polyethylene (HDPE) |
Ethylene |
Hair-oil and other household containers, Packaging films, furniture, Pipes, Fuel tanks, etc. |
|
|
Polyvinyl chloride (PVC) |
Vinyl Chloride monomer (VCM) |
Wire and cables, Footwear, Floorings, Packaging films, Pipes and fittings, Medical devices, Tarpaulins, toys, etc. |
|
|
Low-density polyethylene (LDPE) |
Ethylene |
Milk pouches, Containers, packaging films, tubing, Furniture, etc. |
|
|
Polypropylene (PP) |
Propylene |
Chairs, Furniture, Containers, Packaging films, Automotive and Electronic components, Textiles, Medical devices, Aerospace Applications, etc. |
|
|
Polystyrene (PS) |
Styrene |
Protective packaging applications, Disposable cups and containers, Foams, Insulations, etc. |
|
|
Other plastics [often Polycarbonate (PC) or Acrylonitrile butadiene styrene (ABS)] |
PC: Bisphenol-A + Diphenyl carbonate or Phosgene ABS: acrylonitrile + butadiene + styrene |
PC: Electronic, Aircraft, Security and Automotive components, Construction industries, Data Storage applications ABS: Electronic and Automotive components, Pipes, Instruments body parts, etc. |
PET abbreviated as polyethylene Terephthalate is a long-chain polymer belonging to the generic family of polyesters. Terephthalic acid (TPA) and ethylene glycol (EG), which are both generated from oil feedstock, are the intermediates used to create PET. Other polyesters are based on other intermediates, but they are all created through the polymerization of an acid and an alcohol. In its most basic form, PET resembles amorphous glass. It becomes crystallin under the effect of direct modifying chemicals. Heat treatment and melting produce the crystallinity. Polyester fibre uses have advanced to the point where PET accounts for more than 50% of the world's synthetic fibre production. Polyester was first patented and used by DuPont during the hunt for novel fiber-forming polymers. Later, PET underwent modifications to be utilised in extruded and injection-molded items, most of which were reinforced with glass fibre. 9,10,29
Table: 2 General properties of PET.
|
Physical Properties |
Value |
Mechanical Properties |
Value |
|
Density ( g cm-3 ) |
1.3-1.4 |
Coefficient of friction |
0.2-0.4 |
|
Flammability |
Self Extinguishing |
Hardness – Rockwell |
94-101 |
|
Limiting oxygen index |
21 % |
Izod impact strength ( J.m-1 ) |
13-35 |
|
Refractive index |
1.58-1.64 |
Poisson’s ratio |
0.37-0.44 (oriented) |
|
Resistance to Ultra-violet |
Good |
Tensile modulus ( GPa ) |
2 - 4 |
|
Water absorption –equilibrium |
<0.7 % |
Tensile strength ( MPa ) |
80, for biax film 190- 260 |
|
Water absorption - over 24 hours |
0.1 % |
Chemical Properties |
State |
|
Viscosity atT=75⁰C |
600 mPa.sec |
Acids resistance |
Good for mostmineral acids
|
|
Thermal Properties |
Value |
Alcohols, Ketones, Halogens, Greases andOil, resistance |
Good |
|
Flash points |
above 200 ⁰C |
Alkalis resistance |
Poor especially at high temperature |
|
Lower workingtemp.(°C) |
-40 to -60 |
Aromatic hydrocarbonsresistance |
Fair |
|
Specific heat (J.K-1.kg-1) |
1200 – 1350 |
Properties of PET bottle grade |
|
|
Thermal conductivity (W.m-1.K-1 ) |
0.15-0.4 @ 23 |
Properties |
Value |
|
Heat-deflection temp.1.8MPa ⁰C |
80 |
Melting temperature |
254- 256oC |
|
Heat-deflection temperature- 0.45MPa (⁰C) |
115 |
Crystallinity |
≥ 45% |
|
Coefficient of thermal expansion (x10-6 K-1) |
20-80 |
Density |
1.38~1.40g/mm3 |
|
Upper working temperature (⁰C ) |
115-170 |
Glass Temperature |
82oC |
|
|
|
Intrinsic viscosity |
0.65 to 0.85 dL/g |
Manufacturing of PET can be divided into two main sections; the first is TPA manufacturing, while the other is the polymerization step of TPA into bottle grade PET.
TPA can be produced using a variety of raw sources and processes. To obtain the most cost-effective method of production, numerous technologies have been created. The section that follows provides technical descriptions of several processes. 11,12
P-xylene is subjected to oxidation to create TPA. The majority of TPA procedures use p-xylene as their feedstock, while acetic acid in water serves as their reaction solvent. The reaction produces two intermediates, p-toluic acid and 4-formylbenzoic acid, before TPA is generated. 11,12,30
In the process of making TPA from p-xylene by oxidative esterification, DMT plays a significant role as an intermediary. It is created in four stages. In an oxidation reactor, p-xylene is first converted to p-toluic acid by oxygen from the air. Then, in an esterification reactor, p-toluic acid is esterified with methanol to produce methyl p-toluic. Methyl p-toluate is separated and put back into the oxidation reactor, where it is oxidised to MMT and then esterified to produce DMT, which is then purified. Finally, the DMT undergoes a hydrolysis stage that entails two reactions: first, the DMT transforms into MMT, and then the MMT transforms into TPA to enter the polymerization stage.11
TPA was produced using it as the first industrial process. The liquid phase oxidation of p-xylene by nitric acid at 165 °C and 1000 kPa was industrialised by Du Pont. Precipitation and centrifugation are used to separate the TPA that is produced. 14
Lummus originally obtained a licence for the ammoxidation process to produce TPA from p-xylene, and this modification allowed the technique to be made commercially viable. In order to carry out this procedure, p-xylene is first combined with ammonia on a catalyst to create TPN, which is then used in a hydrolysis reaction to create TPA and ammonia. 13,15,31
Figure 1: (A) Direct oxidation of p-xylene
(B) Hydrolysis of DMT
(C) Nitric oxidation of p-xylene (Du Pont process)
(D) Ammoxidation of p-xylene (Lummus process)
Either DMT or TPA can be combined with EG to create PET. The purity of all raw materials must be extremely high. In either scenario, the production of BHET as a prepolymer is the initial stage of the process. PET is created by further polymerizing this substance. Although it is uncommon, BHET can also be produced through the interaction of TPA with ethylene oxide. The polycondensation of BHET with the liberation of EG for recycling is the second phase in the polymerization process. Temperatures between 280 °C are more favourable for polycondensation because the reaction temperature must be above the polymer's melting point (260–265 °C) and below the temperature at which decomposition occurs too quickly (3,000 °C).13,32
Figure 2: Polymerization of TPA to PET
Because PET plastic cannot degrade, recycling it will become increasingly important. There are several ways to recycle PET polymers, including mechanical recycling and chemical recycling 16,33,34
The mechanical recycling of plastics is carried out in a five step process
(1) Plastics collection
(2) Manual sorting
(3) Chipping
(4) Washing
(5) Pelleting 17
Figure 3. Mechanical recycling of PET plastic.
Through a variety of depolymerization techniques, PET polymer is broken down into monomers or oligomers during chemical recycling. Recycling chemicals is more expensive than recycling mechanical materials. In order to be economically viable, it typically needs to be done on a big scale. The ability to produce PET with the same quality as virgin PET is a significant benefit of chemical recycling.18 PET waste can be chemically recycled by depolymerizing it using hydrolysis, methanolysis, glycolysis, and aminolysis to produce different monomers. 10,19,35
With the right solvents, PET can be hydrolyzed in the presence of acid and base. Waste PET can be neutrally hydrolyzed using various amounts of water and catalysts while being exposed to xylene. 10,20,21
PET is converted to the oligomer bis-hydroxyl ethylene terephthalate during glycolysis (BHET). The procedure is often carried out with excess EG and in the presence of catalysts at temperatures between 180 and 250 °C (acidic or basic). The oligomer goes through a fine filtration stage after glycolysis before being repolymerized into PET. 8,10,22
PET + 2nNaOH →nNa2C8H4O4 + nC2H6O2
In the process of methanolysis, PET is depolymerized with methanol to produce DMT (dimethyl terephthalate) and EG in the presence of catalysts at temperatures ranging from 180 to 280 °C and pressures between 2-4 MPa. DMT is extracted from the reaction mixture by precipitation, centrifugation, and crystallisation once it has been cooled. Following that, spinning and finishing procedures turn the recycled polymer into fibre. In addition to vapour methanol, supercritical methanol can be utilised for PET depolymerization. 8,10,22
It is a further strategy for the chemical recycling of PET waste that has not received as much attention as other methods. In this process, aminolysis of PET waste results in the production of bis (2-hydroxy ethylene) terephthalate (BHET). In the presence of several simple compounds, such as glacial acetic acid, sodium acetate, and potassium sulphate, the excess of ethanolamine is used as a catalyst. This process yields a significant yield of BHET (91%). 10,23,24
PET is a clear, strong, and lightweight plastic that is widely used for packaging foods and beverages, especially convenience-sized soft drinks, juices and water.
PET straps are used in packaging, baling, and for various applications in industry. A small percentage of PET produced goes into making these straps. PET straps are a convenient alternative to metal wires and other such packaging aids.
PET sheets are widely used in packaging a range of products such as consumer products, pharmaceuticals, food and beverages, engineering items.
PET monofilament is mainly used for making mesh fabrics for screen-printing, filter for oil and sand filtration, bracing wires for agricultural applications (greenhouses etc.), woven/knitting belt, filter cloth, and other such industrial applications. 11,36
The skin will stick to molten polymer, which might result in serious burns. Eye irritation, pain, and blurred vision may result from coming into contact with PET particles. TPA doesn't cause skin sensitivity or irritation. Products of decomposition may irritate the skin, eyes, or respiratory system. NTP and OSHA do not list PET as a carcinogen at quantities of 0.1% or higher. It's crucial to use local ventilation to manage PET production emissions. The ability of PET to be recycled into new goods reduces PET waste, which is a significant environmental benefit. PET is recycled chemically or mechanically, depending on whether the original polymer qualities are being preserved. Chemical recycling involves reprocessing PET back into its original intermediate or primary chemicals.
25
The most common type of polyester produced worldwide is PET, which is routinely recycled at a rate of around 25%. Even though this is the greatest rate among all plastic categories, there are still issues with product quality and supply chain economics. Since many of PET's final uses are not compatible with closed-loop recycling, a sizable amount of used PET leaks into the environment. It is clear that PET plastic needs to be more circular and over the past few decades, much effort has been made to address this issue. The two main recycling processes for PET at the moment are mechanical and chemical, however the former could result in plastic of worse quality than the original, while the latter has new difficulties in the form of higher financial and environmental costs. However, PET has the benefit of being easily reprocessable and recyclable. Additionally, the energy needed to produce the waste polymers can be recovered, at least to a large level. Therefore, it is important to dispose of waste plastics responsibly by using the right technology. With the help of business, the government, and the general public, an integrated strategy to waste management can be used to address the issue of garbage disposal without endangering the environment or business.
1. Nkwachukwu OI, Chima CH, Ikenna AO. Focus on potential environmental issues on plastic world towards a sustainable plastic recycling in developing countries. International Journal of Industrial Chemistry. 2013;4(34):1-13.
2. Archna, Moses V, Sagar S, Shivraj V, Chetan S. A review on processing of waste PET (polyethylene terephthalate) plastics. International Journal of Polymer Science Engineering. 2015;1(2):1-13.
3. Hamad K, Kaseem M, Deri F. Recycling of waste from polymer materials: an overview of the recent works. Polymer Degradation and Stability. 2013;98:2801-2812.
4. Thompson RC, Moore CJ, VomSaal FS, Swan SH. Plastics, the environment and human health: current consensus and future trends. Philosophical Transactions of The Royal Society B. 2009;364:2153-2166.
5. Scheirs J., Long TE. Modern polyesters: chemistry and technology of polyesters and co-polyesters; John Wiley and Sons Limited, Great Britain, 2003, pp 31.
6. Dodbiba G, Fujita T. Progress in separating plastic materials for recycling. Physical Separation in Science and Engineering. 2004;13:165-182.
7. Olabisi O. Handbook of Thermoplastics; Marcel Dekker Inc, New York, 1997, pp 449.
8. Shen L, Worrell E, Patel MK. Open-loop recycling: A LCA case study of PET bottle-to-fibre recycling. Resources, Conservation and Recycling. 2010;55:34-52.
9. Sinha VK, Patel MR, Patel JV. Pet waste management by chemical recycling: a review. Journal of Environmental Polymer Degradation. 2010;18:18-25.
10. Vakili MH, Fard MH. Chemical recycling of polyethylene terephthalate wastes. World Applied Sciences Journal. 2010;8(7):839-846.
11. Bohnet M. Ullmann’s Encyclopedia of Industrial Chemistry; 7th Edn; Wiley VCH Publication, New
12. York, 2011, pp 157.
13. Othmer K. Encyclopedia of Chemical Technology; 4th Edn; John Wiley and Sons Limited, Great Britain, 2001, pp 94.
14. Lefebvre CG. Petrochemical Processes: Technical and Economic Characteristics; 2nd Edn; Editions Technip, Paris, 1989, pp 279.
15. Alain C., Gilles L. Petrochemical Processe; 2nd Edn; Editions Technip, Paris, 1989, pp 281.
16. Donnell JP, Butler RM, Simpson LB. Ammoxidation of Aromatic Hydrocarbons to Aromatic Nitriles Using Substantial Quantities of Water in The Reaction Mixture. U.S. Patent US3462476A, 1969.
17. Tokiwa Y, Calabia BP, Ugwu CU. Biodegradability of plastics. International Journal of Molecular Sciences. 2009;10:3722-3742.
18. Suyama T, Tokiwa Y, Oichanpagdee P. Phylogenetic affiliation of soil bacteria that degrade aliphatic polyesters available commercially as biodegradable plastics. Applied and Environmental Microbiology. 1998;64:5008–5011.
19. Pranamuda H, Tokiwa Y, Tanaka H. Polylactide degradation by an Amycolatopsis sp. Applied and Environmental Microbiology. 1997;63:1637-1640.
20. Koo BM, JayKim JH, Kim SB. Material and structural performance evaluations of Hwangtoh admixtures and recycled PET fiber added eco-friendly concrete for emission reduction. Materials. 2014;7:5959- 5981.
21. Application of Recycled Pet Plastic, September 2022, http://www.gtz.de/gate.
22. Ochi T, Okubo S, Fukui K. Development of recycled PET fiber and its application as concrete reinforcing fiber. Cement and Concrete Composites. 2007;29:448-455.
23. Foti D. Use of recycled waste PET bottles fibres for the reinforcement of concrete. Composite Structures. 2013;96:396-404.
24. Abd El-Hameed RS. Aminolysis of polyethylene terephthalate waste as corrosion inhibitor for carbon steel in HCl corrosive medium. Pelagia Research Library. 2011;2(3):483-499.
25. Ramadevi K. Experimental investigations on the properties of concrete with plastic PET (bottle) fibers as fine aggregate. Cement and Concrete Composites. 2012;2.
26. Health, Safety and Environmental Considerations of TPA, September 2022, http://www.dakamericas.com
27. Khoramnejadian S. Improve Properties of Recycled Poly Ethylene Terephetalat (PET) By Polycarbonate. Asian J. Research Chem. 4(10): Oct., 2011; Page 1539-1541.
28. Dey U, Mondal NK, Das K, Datta JK. Development of New Methodology for Melting of Plastic: A Chemical Approach. Asian J. Research Chem. 5(3): March 2012; Page 397-400.
29. Saini RD. New Age Biodegradable and Compostable Plastics. Asian J. Research Chem. 2018; 11(1):179-188.
30. Chanchlani J, Keswani IP. Cycle Time Reduction in Plastic Industry. Int. J. Tech. 5(1): Jan.-June 2015; Page 25-29.
31. Thangavel S, Sujin DRS, Kevin BC. A Novel Approach to treat Bio Wastes Using Biodigesters and Microorganisms Employed to Increase Plastic Degradation. Research J. Engineering and Tech. 4(4): Oct.-Dec., 2013 page 221-225.
32. Priyanka U, Nandan A. Biodegradable Plastic – A Potential Substitute for Synthetic Polymers. Research J. Engineering and Tech. 5(3): July-Sept. 2014 page 158-165.
33. Verma G. Elastic-Plastic Transition Problems. Research J. Engineering and Tech. 6(3): July- Sept., 2015 page 338-342.
34. Purushothama KV. Plastic a cancer in Nature: Trends, Problems and Policies in India. Research J. Humanities and Social Sciences 2015; 6(3): 209-212.
35. Sehgal B, Kunde GB. Grafting enhances the thermal stability of thermoplastic elastomers. Research J. Engineering and Tech. 1(2): Oct. - Dec.2010 page 65-69.
36. Arajpure VG, Gaikwad HA. Performance Analysis of Plastic Worm Gear in Centerless Grinding Machine; Int. J. Tech. 3(1): Jan.-June. 2013; Page 52-62.
37. Garg N, Joshi HC, Pandey IP. Characterization of Crude Oil in an Exploration of Petroleum Geochemistry: An Overview. Asian J. Research Chem. 2017; 10(4):431-435.
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Received on 25.11.2022 Accepted on 25.04.2023 © EnggResearch.net All Right Reserved Int. J. Tech. 2023; 13(1):50-56. DOI: 10.52711/2231-3915.2023.00006 |
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