With the world’s largest bottle-to-bottle recycling plant opening in Riverside, California last month, we decided to follow the life of a PET bottle from the shelf in the supermarket to its life as a new plastic product.
Polyethylene terephthalate (PET) is one of the most common plastics on the market. It is the type of plastic with the number one inside the recycling symbol on the bottom of plastic containers. PET is the plastic often used to package soft drinks, water, juice, peanut butter, bakery goods, produce, frozen foods, salad dressings, oil, cosmetics and household cleaners. It is typically what your water or soda bottle is made of. It can be recycled into fiber for polyester carpet; fabric for T-shirts, long underwear, athletic shoes, luggage, upholstery and sweaters; fiberfill for sleeping bags and winter coats; industrial strapping, sheet and film; automotive parts, such as luggage racks, headliners, fuse boxes, bumpers, grilles and door panels; and new PET containers.
For this example, let’s follow a Coke bottle bought in a supermarket. After you are done with the bottle, you drop it into a residential recycling bin where it is picked up along with a variety of other recyclables such as aluminum cans, cardboard and paper, and take to a local single-stream material recovery facility (MRF). The contents of the recycling pickup truck are dumped into a pile at the MRF where the material is then transferred to a conveyor that carries the recyclables to a sorting station manned by workers known as pickers who are each assigned to pick a different type of material off the line, thus separating waste from recyclables and commingled recyclables into groups of plastic, aluminum, glass, paper, etc. Your Coke bottle is thrown into a pile with a variety of plastics, numbered 1 through 7, such as yogurt containers, milk gallons, bags, water bottles, Tupperware containers, shampoo bottles and spray bottles. These plastics must be separated according to category of resin content (1-7). Most plastic reclaimers use automated machines to do this using near infrared technology.
Your Coke bottle now sits in a mound of other plastic number 1 containers where it waits to be shipped to the processing plant to be recycled. Most often the plastic will be baled before shipping. Condensing the material this way saves space, thus reducing shipping and storing costs, financially benefiting both the sorting facility and the end-user manufacturers. Upon arrival at a plastic recycling plant, such as the new carbonLITE plant in Riverside, your Coke bottle is sent through some form of size-reduction machine, such as a shredder, granulator or hammermill that takes it down to a manageable and consistent size, preparing it to be melted down and molded into new plastic products.
A shredder works by using three methods to reduce material to a smaller size: shearing, tearing and fracturing. Shearing is the actual cutting of the material. The cutting edges work against one another to slice the plastic, so the sharper the blades are, the more efficient the machine operates. Tearing involves pulling the material with such force that it rips apart. This technique works best on soft plastics. Fracturing happens when brittle materials, such as hard plastics, are broken or shattered and usually occurs when cutters are not sharp or are loose. All three techniques work together to reduce the size of the material while the shredder is operating, however, shearing is the most efficient technique, making blade maintenance an important aspect of shredder upkeep.
The primary use of a granulator is for plastic recycling. As the material is fed into the granulator, it falls into the cutting chamber where rotating knives pass alongside stationary knives, shearing the plastic (think scissors). High impact plastics are granulated by knives cutting the plastic like an axe, shattering it. The output is chips of a random size and shape; the maximum chip size is dictated by a screen at the exit of the cutting chamber. The reclamation and reprocessing of plastic material saves money, time, capital landfill and space, and the granulator is the most efficient and cost effective plastic recycling device.There are two primary types of granulators: heavy-duty and light-duty. Heavy-duty granulators are used for reducing injection machine purgings and waste scrap. Light-duty granulators are used for reducing sprues, runners, films and upholstery materials. Granulators take care of the unwanted excess from the manufacturing process and rejected parts such as pieces with dimensional inaccuracies or cosmetic defects by converting them into a form suitable for further processing for reuse.
Hammermills are grinding machines used to shred or crush aggregate material into smaller pieces. Material is passed through a wide feed hopper, falling into the grinding chamber. The grinding chamber contains a rotating hammer rotor with swinging hammers that crush the material and drive it through a screen, thus using impact grinding to reduce the material into smaller scraps. Their durability, superior size reduction techniques and efficiency make hammermills an ideal solution for plastic reclamation.
After being sent through one of these machines and turned into small plastic shreds or flakes, the bottle is molded into new plastic products that can be further reused and recycled. At the Riverside plant, the Coke bottle would be processed using a method that allows 100% of the plastic bottle to be recycled and re-manufactured into new PET bottles and food containers, meaning that next week you could be drinking out of that same Coke bottle again.