Study on Preparation Process and Properties of Polyethylene Terephthalate (PET) JI Li-na

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1 Applied Mechanics and Materials Online: ISSN: , Vol. 312, pp doi: / Trans Tech Publications, Switzerland Study on Preparation Process and Properties of Polyethylene Terephthalate (PET) JI Li-na China Kunlun Contracting & Engineering Corporation, Beijing , China Keywords: Polyester, Polyethylene terephthalate, PET, Market perspectives. Abstract. PET is a ubiquitous material in modern life which is used in diverse applications from drink bottles and film to shirts and fabrics. A brief introduction of PET is given in this report, concentrating on the following aspects: the preparation process, the properties and the application of this product. Market perspectives and some recommendations of PET industry are also discussed in this report based on the current market analysis. Introduction Polyester is a category of polymers which contain the ester functional group in their main chain. Polyester is one of the most important classes of polymers in use today. Hundreds of polyesters exist although only about a dozen are of commercial significance. Although there are many types of polyester, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate (PET). Other types of polyester mainly include Polybutylene terephthalate (PBT), PTT, polyarylate and so on. Polyethylene terephthalate, commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family. The applications of Polyethylene terephthalate (PET) can be divided into three major categories: fiber, bottles, and industrial use. It can be used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; film, plastic and engineering resins often in combination with glass fiber. The two widely used applications are PET fabrics and PET bottles. Preparation of Polyethylene Terephthalate (PET) Research Background The raw materials to make PET are monoethylene glycol (MEG) and purified terephthalic acid (PTA) or dimethyl terephthalate (DMT). High purity is required of all raw materials. In either case, the first step of the reaction is the formation of a prepolymer, bis-hydroxyethyl terephthalate (bis-het). Subsequent polymerization of this material (with the removal of monoethylene glycol) forms the polymeric polyethylene terephthalate. The extent of polymerization (apparent from the molecular weight of the polymer) is a function of the polymerization conditions and significantly affects the properties of the resin that is produced. Until the mid-1960s, DMT had been the preferred feedstock for PET manufacture, partly because the ester could generally be made in purer form than the acid. With the development of high-purity terephthalic acid processes, the free acid gained acceptance and is now the preferred feedstock. The use of high purity terephthalic acid (purified terephthalic acid - PTA) eliminates the need to recover or recycle methanol and has the added advantage that esterification to the prepolymer is considerably more rapid than the transesterification reaction, which is the first step when starting from DMT. Although PTA is the preferred feedstock for process economic reasons, the DMT process is still in commercial use, especially in polyester film applications due its adhesion addition quality; however, no process description or economics are presented in this report. Using PTA and MEG to produce PET has been the mostly used process in nowadays. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-04/03/16,20:25:33)

2 Applied Mechanics and Materials Vol Conventional Melt Technology The main process steps include: raw material preparation,etherification/ transesterification, pre-polycondensation and polycondensation. Etherification/Transesterification When DMT is used, the DMT melt and catalyst are pumped with MEG into the transesterification system, where the reaction takes place under atmospheric pressure by splitting off the methanol. The materials split off are rectified and recovered. When starting with purified terephthalic acid (PTA), PTA is mixed with the MEG and catalyst solution in a paste and fed into the esterification system. The first step in the polymerization sequence is an esterification rather than a transesterification, the esterification takes place under atmospheric pressure by splitting off the water: HOOC- -COOH+2HOCH 2 CH 2 OH HOCH 2 CH 2 OOC- -COOCH 2 CH 2 OH+2H 2 O Note that water, rather than methanol, is liberated in the process, which simplifies the recovery facilities. The major breakthrough in the technology of this reaction involved operating at pressures above atmospheric and temperatures greater than the normal boiling point of glycol, to achieve shorter reaction times. Pre-polycondensation and Polycondensation Whether PTA or DMT is the starting material, the second step in the polymerization sequence, polycondensation of bishydroxethyl terephthalate is the same: nhoch 2 CH 2 OOC- -COOCH 2 CH 2 OH H[OCH 2 CH 2 OOC- -COO] n CH 2 CH 2 OH+(n-1)HOCH 2 CH 2 OH The product from the esterification/transesterification step is then sent to the prepolycondensation unit where the reaction takes place under a vacuum. The pre-polycondensation product is fed to the final polycondensation reactor which operates under increased temperature and vacuum. The polyester melt is processed either into fibers/filaments or sent to the solid state polycondensation (SSP) unit to make bottle grade chips. Conventional SSP Technology The conventional SSP production process consists of two discrete plant sections. The melt phase reaction to lower intrinsic viscosity product that is suitable for textile applications, but not for bottle grade and other high molecular weight applications. That lower intrinsic viscosity material is then further polymerized to bottle-grade intrinsic viscosity in a solid-state polymerization section. [Note that intrinsic viscosity (as well as molecular weight) indicates the degree of polymerization, which in turn is the main factor in setting the properties of PET.] Researchers have been looking for ways to remove the SSP stage. For example, Lurgi Zimmer has developed a direct process for making the PET bottle preforms without the SSP step. It is based on an integrated process that produces a high viscosity melt from which the chips can be fed directly to the perform unit. Properties of Polyethylene Terephthalate (PET) Introduction Polyethylene terephthalate (PET) exists both as an amorphous (transparent) and a semi-crystalline (opaque and white) thermoplastic. Generally, it has good resistance to mineral oils, solvents and acids but not to bases. The semi-crystalline PET has good strength, ductility, stiffness and hardness while the amorphous PET has better ductility. PET also has good process ability and can be recycled for other applications.

3 408 Applied Research and Engineering Solutions in Industry Intrinsic Viscosity One of the most important characteristics of PET is referred to as intrinsic viscosity (IV). The intrinsic viscosity of the material, measured in deciliters per gram (dl/g) is dependent upon the length of its polymer chains. The longer the polymer chains, the more entanglements between chains and therefore the higher the viscosity.the average chain length of a particular batch of resin can be controlled during polycondensation. The intrinsic viscosity range of PET is showed in the table 1. Table 1. The Intrinsic Viscosity Range of PET. Grade Species IV( dl/g) Fiber grade Textile dl/g tire cord dl/g Film grade BOPET (biaxially oriented PET film) dl/g Sheet grade for thermoforming dl/g Bottle grade Water bottles (flat) dl/g Monofilament, engineering plastic Carbonated soft drink grade dl/g dl/g Typical Properties of PET High hardness, stiffness and strength in thermoplastic Low friction and high abrasion resistance High dimensional stability Service temperature range, from 40 C to 100 C In the semi-crystalline state it is white In the amorphous state it is transparent (glass clear) High tracking resistance Physiologically acceptable Resistant to water at room temperature, dilute acids, neutral and acidic salts, alcohol, ethers, oils, fats, aromatic and aliphatic hydrocarbons. Not resistant to alkalis, superheated steam, phenols, esters, oxidizing acids and chlorinated hydrocarbons Resistant to stress cracking Amorphous PET has slightly lower hardness, stiffness and heat resistance than crystalline PET, but has higher toughness. Applications of Polyethylene Terephthalate (PET) Overview The majority of the world's PET production is for synthetic fibers (in excess of 60%) with bottle production accounting for around 30% and production for industrial use accounting for around 10% of global demand. The polyester industry makes up about 18% of world polymer production. PET Fabrics Polyester fabrics can have a synthetic feel when compared to fabrics made from natural materials. However, polyester does have the advantage of better wrinkle resistance and is often spun together with natural fibers such as cotton and wool to produce a fabric with blended properties. Polyester is the largest synthetic fiber used in the world. Filament yarns are used in clothing, furnishings, tyre cord and technical textiles. Staple fibers are employed in knitted and woven textiles for clothing and furnishings such as bed sheets, bedspreads, curtains and draperies. Polyester fiberfill can be used to stuff pillows and cushion padding.

4 Applied Mechanics and Materials Vol PET Bottles PET has taken market share in the bottled water market due to its good clarity and not leaving any taste in the water. PET has good barrier properties against oxygen and carbon dioxide. Its chemical inertness and physical properties made it particularly suitable in food packaging applications especially in beverages and drinking water. Indeed, PET packaging combines adequate gas barrier properties for the retention of carbonation with a glass like transparency, light weight and good recyclability. It has also found applications in more niche markets such as sports drinks and fruit juices, and is used to make bottles for cooking and salad oils, sauces and dressings. PET packaging resin markets have seen very strong growth over the last 20 years. It first penetrated the carbonated soft drinks market because it is lightweight and strong. PET bottles are virtually unbreakable while a typical 1.5 liter bottle weighs about 40-45gm, about one-tenth the weight of glass. PET Films Polyethylene terephthalate or PET film is a thermoplastic polymer commonly referred to as polyester film. Like most thermoplastics, PET films can be biaxially oriented or bubble extruded. Polyester film is one of the most common substrates used in the converting industry because of its balance of properties in relation to other thermoplastic polymers. The mechanical properties of polyester film make it a choice substrate for a variety of processing technologies, such as vacuum metalizing, coating and laminating. Additionally, polyester film is available in many variations, engineered for specific applications, this combined with the processing tolerance of PET films makes it a good substrate for a variety of applications. Engineering Plastic PET also as engineering plastics used in electronic, electrical and other fields, such as instrument case, hot air masks. Market Perspectives of PET Industry World Market Market perspectives look good for Polyethylene Terephthalate in middle-term period. World PET capacity will increase slower than demand bringing the market to balance. With average annual growth of 3.5% global capacity will reach 24.4mln tons/year by The Global PET Market is expected to grow in the Forecast Period after Recovery from Economic Slowdown. The global demand for PET was growing fast over the last decade. The effect of the economic slowdown has adversely affected the consumption of various commodities in many countries globally. Hence, demand for PET has also slowed down over the past two years. The global PET market in 2009 was 15.3 million tons. As the economies recover from the slowdown, the consumption of commodities will rise again and the global demand for PET will grow at CAGR of 4.9% up to Not considering the fabrics production, the largest PET consuming markets are Carbonated Soft Drinks and Bottled Water. CSD is the largest market for PET globally. Because of its light weight, toughness and clarity, PET is the most preferred material for CSD bottles. Bottled water is the second biggest PET consuming market globally. However, the packaged food segment is also a very important and growing market for PET. The beer market is largely untapped but has strong potential for growth with regard to PET applications. Asian Market Asia is the Largest Consumer of PET Followed by Europe. The demand for PET is highest in Asia. China is driving the majority of the demand for PET in the world. The demand in advanced countries like Japan has largely stabilized. With the large population in countries such as India and China, there is a huge consumption potential in these countries. The Asian demand by volume for PET in 2009 was nearly 4.7 million tons. The unparalleled growth of carbonated soft drinks and bottled water industries and thus the packaging industry can be primarily attributed to the changing lifestyles of people in the developing countries. Taking into account that India and China are heavily populated, it does not come as a surprise that these economies are key regional drivers for the global polyethylene terephthalate demand.

5 410 Applied Research and Engineering Solutions in Industry Recommendations Development of New Varieties of Polyester Although PET is the most widely used polyester, another trend is a positive development and promotion of new varieties of polyester such as PBT and PTT. For example, Polybutylene terephthalate (PBT) is a semi-crystalline, thermoplastic polyester which is completely analogous to PET except that it has a longer, more flexible butylenes chain linkage which imparts a rapid crystallization rate, thus making PBT well suited to injection moulding processes. This polyester is used widely for electrical and electronic components due to its high temperature resistance and good electrical properties. Development of New Technology of PET The technology of PET preparation has been mature for many years, but emerging technology should been developed to reduce the cost in the production and to be more green to the environment. In the other hand, PET industry requires new investments in research and development of specialty products, as well as new end-use applications, to provide future growth opportunities. Adjustment of Product Structure As we known, the majority of the world's PET production is for synthetic fibers in nowadays, but the demand for non-fiber PET is increasing, such as PET bottles and engineering grade PET. The product structure in China PET market will change in the future. Recycling of PET The recycling of PET is an important environmental topic as well as a commercial opportunity due to the widespread use, abundance and availability in bottles, packaging and fibers. While mechanical recycling of PET is now well established, new chemical recycling techniques rely on depolymerization routes which cleave the polymer chains into new monomer building blocks. References [1] John Scheirs, Timothy E. Long, Modern polyesters: chemistry and technology of polyesters and copolyesters, John Wiley and Sons, 2003 [2] Tony Yu Long River, Xu Chi polyester fiber Manual (2nd edition), Textile Industry Press,

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