Polyethylene terephthalate (sometimes written poly(ethylene terephthalate)), commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids (soft drinks) and foods, thermoforming for manufacturing, and in combination with glass fibre for engineering resins.
It may also be referred to by the brand names Terylene in the UK, Lavsan in Russia and the former Soviet Union, and Dacron in the US.
The majority of the world’s PET production is for synthetic fibres (in excess of 60%), with bottle production accounting for about 30% of global demand. In the context of textile applications, PET is referred to by its common name, polyester, whereas the acronym PET is generally used in relation to packaging. Polyester makes up about 18% of world polymer production and is the fourth-most-produced polymer after polyethylene (PE), polypropylene (PP) and polyvinyl chloride(PVC).
PET consists of polymerized units of the monomer ethylene terephthalate, with repeating (C10H8O4) units. PET is commonly recycled, and has the number “1” as its resin identification code (RIC).
In 2016, it was estimated that 56 million tons of PET are produced each year. While most thermoplastics can, in principle, be recycled, PET bottle recycling is more practical than many other plastic applications because of the high value of the resin and the almost exclusive use of PET for widely used water and carbonated soft drink bottling. PET has a resin identification code of 1. The prime uses for recycled PET are polyester fiber, strapping, and non-food containers.
PET does however have some sub-groups like PET-A, PET-C and PET-G. For more information on this pls click here.
- Water bottles tend to be lighter than carbonated bottles
- Weights are averages across all brands in Hong Kong
*a contaminant in the HK mechanical recycling pathway
High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called “alkathene” or “polythene” when used for HDPE pipes. With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes and plastic lumber. HDPE is commonly recycled, and has the number “2” as its resin identification code.
It is commonly used as containers for cleaning products, bulk food products – ketchups and the like, as well as for items like personal care products – shampoo’s and conditioners.
In 2007, the global HDPE market reached a volume of more than 30 million tons.
- Weights may vary considerably as there is no standard size bottle
Purity of PET & HDPE Bales
As part of the Transparency which NLP will provide, NLP will further give accurate make up on the PET & HDPE bales which it receives for processing.
PET-A, PET-C and PET-G
PET is normally a semi-crystalline structure. For the fabric to become transparent, it is melted and suddenly cooled. Under this process the chains do not have the time to arrange themselves and are “frozen” in disorder. This PET is called PET-A (for amorphous) and is the material from which most beverage bottles, trays and blisters are made of today. If you give the same plastic time to get organized while cooling, crystalline PET-C would result. Both substances are chemically absolutely the same.
Who makes what is decided solely in the processing time. It is clear that PET-A and PET-C can be recycled together.
The problem with PET-A is that crystallization is only stopped. If the plastic is warmed up again to a certain extent (approx. 140 ° C), crystallization will still start and make the material cloudy and unsightly from a packaging perspective. The undesired cloudiness would arise if cups had to be sealed with protective films or PET-A was deep-drawn to produce cups and blisters. Solvents can also start the crystallization process to That’s why PET-A cannot be printed well.
To remedy this, PET-G was developed. During its manufacture, glycol is incorporated into the molecular threads made of PET. This makes the chains more difficult to build and to lose their ability to crystallize. The material is always crystal clear and can be heated and printed. It is less suitable for the production of bottles. And it is more expensive.
PET-G is difficult to distinguish from other PET. In addition, PET-G is often used in conjunction with PET-A for cost reasons. Since PET-G does not chemically correspond to PET-A or PET-C, it is difficult to recycle both substances together. In fact, PET is not just PET.
There are two ways to address this recycling problem.
The first way is to chemically recycle PET, i.e. the plastic is broken down into its individual building blocks. The glycol can be removed from the PET-G. Large quantities of waste plastic are required to build up chemical recycling. High investments are required. This path fails if the high investments are jeopardized by the fact that the material to be recycled is suddenly no longer available in the required quantities.
The second approach is to dispense with PET-G as a packaging material. There are absolutely comparable packaging solutions made from modified PP that would be significantly more recycling-friendly.
HDPE can be sub-divided into two main grades based around the manufacturing process of the said end item, namely injection molding or by extrusion.
The two grades carry different MFI and viscosity properties.
Injection grade HDPE is normally used for hard plastics such as crates, buckets, etc. For Extrusion grade HDPE the end products are usually films, bottles or sheets.
In recycling world, the bottle grade of recycled HDPE is usually used to produce rHDPE for pipes and plastic packaging’s – and normally produces a higher commercial value end pellet when compared to the injection grade rHDPE.
Sometimes the HDPE used in the injection mold process can be blended with filler and or glass filler that will directly damage the value of the recycled HDPE flake.
As such, when recycling HDPE, it’s important to keep these two grades separated.
For additional information about PET and HDPE, you may wish to visit these links: