Recycling Polyethylene Terephthalate
Polyethylene terephthalate (PET) is a highly recyclable plastic resin and a form of polyester. It is a polymer created by the combination of two monomers: modified ethylene glycol and purified terephthalic acid. It was first synthesized in North America by Dupont chemists during the 1940s.
Labeled with the #1 code on or near the bottom of bottles and containers, PET is frequently used to package a range of products including beverages, peanut butter, bakery goods, produce, frozen foods, salad dressings, cosmetics, and household cleaners. Prized for its strength, thermo-stability, and transparency, PET is a popular choice for packaging. PET also is inexpensive, lightweight, resealable, shatter-resistant, and recyclable.
Recycled polyethylene terephthalate is known as RPET, and it is the most widely recycled plastic in the world. According to PETRA, the PET Resin Association, the U.S. recycling rate is about 31% in 2012, while it is 52% in the European Union. In 2016, the U.S. recycling rate had fallen below 29%. Almost 1.8 billion pounds of PET were recycled in 2015, used to make a variety of end products. The U.S. Environmental Protection Agency (EPA) estimates that 1% of municipal solid waste in the United States is attributed to PET containers.
RPET is employed for new products such as:
- Polyester carpet fiber
- Fabric for T-shirts
- Long underwear
- Athletic shoes
- Luggage, upholstery
- Sweaters and fiberfill for sleeping bags and winter coats
- Industrial strapping
- Sheet and film
- Automotive parts
- New PET containers
The use of recycled PET in place of virgin resin typically results in reduced energy consumption, lower cost, and reduced environmental impact.
PET Collection and Sorting
Post-consumer PET material is collected through curbside recycling programs, involving both single-stream and dual-stream approaches. Additionally, other PET recycling programs are designed to divert empty PET bottles at locations of high accumulation such as at large events.
Recyclable materials such as PET may be sorted from other recyclables at material recovery centers, and baled for shipment to a PET recycling facility. As with other scrap material, focus should be on proper bale handling and storage practices to minimize product contamination.
After arriving at a recycling facility, bales may be staged before they are placed on the conveyor belt and fed to the bale breaker. Bales are then split open, and bottles are singulated. This material may be pre-washed and labels removed, using steam and chemicals. During the pre-wash stage, any polyvinyl chloride (PVC) bottles sent through a hot water or hot air trommel will turn slightly brown, providing for easier identification and removal during the manual sorting stage.
The pre-wash and label removal process allows for easier identification of material using near infrared (NIR) sorting equipment to remove other materials. Other technologies employed include metal detectors and manual sorting belts. Manual sorting techniques include either positive sorting results, such as removing the PET from the material flow, or negative results, such as removing the non-PET items from the material flow.
PET Recycling Process
After the sorting process, the PET material is ground into particles known as “flakes.” Flake purity is central to preserving the value of the reclaimed plastic. Further separation techniques involve washing and air classification as well as water baths, where material either sinks or floats, which helps separate residual foreign materials. Washing can be undertaken at standard or elevated heat levels. The use of disinfectants and detergents aids in achieving a complete cleaning.
After the completion of grinding, washing and separation, the material is rinsed to eliminate any remaining contaminants or cleaning agents. The recycled PET is then dried before reintroduction as a manufacturing material or before further processing.
Melt filtering can further purify material through the removal of any non-melting contaminants that may have survived earlier steps. Extruded material passes through a series of screens to form pellets while non-melted particulate is blocked. Pelletized plastic provides a uniform-sized material that can be reintroduced into the manufacturing process.
PET Recycling Outlook
Companies are increasingly recognizing the urgency of recycling PET into food-grade products such as new beverage containers. Coca Cola intends to use 50% recycled PET in its containers by 2030. While food-grade processing has been established, efforts are being made to improve the efficiency of processing technologies.
The availability of post-consumer PET material is a challenge. Recovery rates in the United States have remained flat or declining in recent years. This situation has been exacerbated by less material generation through curbside recycling programs, which, in turn, is related to the decreasing popularity of carbonated beverages, as well as the trend toward the design of light bottles. One way to improve PET recovery would be through the use of container deposit systems. The National Association for PET Container Resources (NAPCOR) and the PET Resin Association (PETRA) can provide additional information on PET recycling.