Abstract

PET (Polyethylene terephthalate) play an important role in the engineering area and daily life.The history of PET and the development of PET was presented. Its excellent properties were analysed. And the manufacturing of PET is represented, and some novel manufacturing method is introduced. At last, life cycle analyse meant was constructed to analyse the recycling of PET and optimized methods are introduced. The novel application of PET is illustrated. 

Key words, History, Manufacturing, Sustainability, Nanochannel, 3D printing

History

The history of PET can be traced back to the 1940s. It was first produced in England when J. Rex Whinfield and James T. Dickson of the Calico Printers Association began the research on phthalic acid in 1940. Due to wartime restrictions, the patent of this new material was not immediately released. Together with others, researchers created the first polyester fiber in 1941, called Terylene. Later this year, the product was patented [1].

Realized the potential developing value of PET, DuPont purchased the US copyright in 1945 for further development. 

PET has developed rapidly in the 1950s, and due to the emergence of new technologies, many applications have taken shape. In 1950 researchers found a way to stretch extruded PET sheets to make it into films, which are now widely used as video, photography and X-ray films and packaging films. And then PET became the most widely produced synthetic fiber in the world. 

In the 1970s, PET entered a new field of application: making bottles. In the early 1970s, the technology was developed to allow PET to be blow molded into strong, lightweight and drop-resistant bottles.  This development lead to the rapid development of PET to produce strong bottles.  Then this bottle made of new materials was patented by Nathaniel Wyeth in 1973. The product was quickly accepted by the market. In 1977, the first PET bottle was recycled. Due to the its light weight, low price and strong durability, it gradually replaced polyvinylchloride (PVC) and glass bottles on the market.

In 2015, global PET resin production was 27.8 million tons, mainly used for manufacturing packaging materials and beverage bottles.  The reason for this development is its low production cost, chemical and physical stability, transparency, lightness and good recyclability [2]. 

Nowadays, PET is the most widely recycled plastic. however, even in the United States, only about 20 percent of PET material is recycled. In recent years, people have paid more and more attention to the safety of PET food packaging.  In fact, the migration of compounds from PET bottles to bottled water may pose a health risk to consumers. In the future development, the disposal of PET waste becomes more and more important.

                            Fig. 1 The picture  shows the development of PET.              

Sustainability of PET

Nowadays, PET is most recyclable material, the most economic recycled process including three steps Primary recycling, mechanical recycling and chemical recycling. The recycled PET is sheet, film and bottles which will be processed to powders for next step. And the accessed powders will go though chemical recycling to produce the raw material ready for re-manufacture[3]. The powders PET can be mixed with sawdust to produce the flat-pressed wood plastic composites. And the additive of PET significantly improves the mechanical strength of the wood plastic composites[4]. The PET material recycled from PET bottles can be applied as fine aggregate replacement in modified asphalt mixture, which contribute to the stiffness behaviour[5]. Also, the concrete mixed with recycled polyethene terephthalate (PET) reveals high mechanical property and durability performance[6].

There are three methods to recycle PET.

    Primary Recycling (Pre-Consumer Industrial Scrap)

Fist the recycled PET bottles were handle to scrap. The scraps were further processed by mixed with virgin material to assure product quality. The received product accord with high safety standard.[1]

    Mechanical Recycling (Secondary Recycling)

Mechanical recycling contains the selection and classification of the wastes, reduction of size ; melt filtration and reforming of the plastic material.[1] The main problem exist in this process is the deterioration of product properties.[4]

    Chemical Recycling (Tertiary Recycling) 

Large quality of Polyethylene terephthalate (PET) bottles are consumed every year, which poses severe economic and environmental problems. PET bottles can be recycled by several methods. PET bottles can be recycled by chemical degradation of PET. Depolymerization route can be classified: glycolysis, methanolysis and hudrolysis.

Novel application

• The biological field

PET can be used in the field of nanochannels. This research may have an important impact on the future development of medicine.

The novel nanochannel manufacturing technology and engineering properties of them have led to the emerging applications of nanochannels in DNA sequencing, ion separation, Coulter counters, and biomolecule detection and also helped to reveal the functional mechanism of biological ion channels. Compared with biofilm protein nanochannels in phospholipids, solid-state nanochannels are more powerful in measurement and application. In the research of nanochannels, ion transport is the basis of ion channels in biological cells. It is reported that nanochannels which sizes are equivalent to Debye's length show more efficient ion transport. 

In the recent work, polyethylene terephthalate (PET) tapered nanochannels were fabricated using potential ion trajectory etching technology, and then the ionic species and cationic species on the surface of the nanochannels were studied through a cyclic measurement system influence. The researchers discovered that the proposed mechanism for the transition of the transport state in PET nanochannels mimics the behavior of voltage-gated biological ion channels. These findings provide brand insights into the understanding of ion channel signaling and charged particle transport control in nanochannel applications.

 Fig. 2 The picture of  schematic diagram of ion channels and Current−voltage measurement[7].

The ion migration studies using PET nanochannels reported in this work not only provide an understanding of the surface charge control of inorganic ions and electric fields, but also enhance the functional mechanism of biological ion channels and the understanding of their applications in ion separation and molecules.

In the future, these acquired theoretical knowledge may further promote the application of PET in medical and other fields[7].

• The  environmental field

PET is one of the largest yield polymers, the treatment of PET waste is also an important research topic.

As a polyester with a high proportion of aromatic components, polyethylene terephthalate (PET) is chemically inert and therefore has antimicrobial degradation properties. In 2013 alone, about 56 million tons of PET were produced globally, which are widely used in plastic products worldwide, and its accumulation in the environment has become a global concern.

Although PET has a long history of development, the waste material after being used has not been handled well. Most of the used PET bottles are eventually landfilled, and the huge amount of PET that is difficult to degrade naturally continues to cause damage to the environment. At present, the pollution of plastics to the environment has become one of the most severe challenges facing mankind. Due to the lack or low activity of catabolic enzymes, it is difficult to decompose their plastic components, so many products have significant Indivisibility in the environment. At the same time, it is believed that the ability to enzymatically degrade PET is limited to several fungi, so biodegradation has not yet become a viable remedy or recycling strategy.

In recent report, the researchers isolated a new type of bacteria by screening the natural microbial community exposed to PET in the environment, which can use PET as its main energy source and carbon source. Experiments show that the strain can grow on PET. While growing on PET, the strain produces two enzymes and reaction intermediates that can hydrolyze PET. Once identified, microorganisms with the enzymatic mechanism required to degrade PET can be used as an environmental remediation strategy, as well as a degradation and/or fermentation platform for the biological recycling of PET waste products.

 Fig. 3  Time course of PET film degradation by no. 46. PET film degradation by microbial consortium at 30°C[8]. 

With the deteriorating environment and increasingly serious plastic pollution problems, this discovery may contribute to better recycling of PET materials, thereby reducing environmental pollution, and at the same time reducing the excessive development of resources, making PET a new environmentally friendly material[8].

• Application in new technology

PET can also be used as a 3D printing material, taking advantage of this new manufacturing method to better meet user needs. Polymer nanocomposite technology is widely used to manufacture 3D objects for various applications. The fused deposition modeling (FDM) method of melting polymers in 3D printing has been extensively studied in industry and research fields because it allows the use of various types of thermoplastic polymers. Among them, amorphous PETG has good impact resistance and shear strength, barrier properties, chemical resistance and transparency which made it used widely. Therefore, this material is suitable for 3D printing and deserves further research.

However, due to the limitations of the FDM 3D printing method, it will cause weak points between the layers, and the physical properties of the printed PETG are poor. To overcome this limitation, the researchers used polymer compounding technology.

In recent study, PETG and SEP were used to prepare composite materials and apply them to 3D printing. The resulting composite material shows higher strength than conventional injection-molded composite materials, and improves thermal performance, while introducing flame retardancy into the composite material.

Fig. 4  Material production, operation process and test characterization for 3D printing[9].

For the PETG-SEP composite filament passing through the nozzle of the 3D printer, its thinning behavior can be expected, and excellent material compatibility is confirmed. By identifying the behavior of SEP in the 3D printing environment, the researchers hope that this work will become the basis for applying nanomaterials to FDM 3D printing. Specifically, the application of oriented PETG-SEP in FDM 3D printing seems to overcome the physical limitations of existing 3D printing materials[9].