Plastic is a synthetic polymer, capable of being molded into a variety of materials, including containers, textiles, and more. The first man-made plastic was revealed in 1862, when Alexander Parkes shared a new invention: a material that could be molded when heated, and that retained its shape once cooled. Other inventions soon followed, with resistance to heat and versatility drawing multiple industries into the plastics game.
But plastics really took off in World War I when petroleum (a main ingredient in most plastic materials) was made more available. During the war, plastics also replaced wood, glass, metal, and other harder-to-find materials — both at home in the U.S. and overseas. By the 1960s, plastics were a common household item, found in everything from Tupperware and packaging to household furniture.
Today, plastics have taken over. 40% of all plastic created is now used to create packaging, and the majority of that plastic is used for beverage bottles. Over 320 million tons of plastic are produced and — shockingly — only about 16% of it is recycled globally.
Of course, when properly recycled, many plastics can have a long (and useful) life.
The first step in the creation of plastics is called the polymerization phase. This is where oil (petroleum) and natural gases are collected. From there, crude oil and gas are converted into hydrocarbon monomers, such as ethlyene and proplyene. Depending on the plastic to be created, more processing may occur, which creates other monomers with different properties, such as styrene, polyproplyne, and more. Then, chemical bonding occurs, connecting chains of these monomers into polymers. Other elements, such as fluorine or chlorine, may be added to provide their specific benefits (fluorine and monomers creates teflon, for example), as well as additives for color, protection, and packaging properties.
Depending on the bonded chain created, the plastic will have different properties, such as higher heat resistance, durability, or flexibility. The plastics created, while varied in their function and capabilities, are either thermoplastics or thermosets. Thermoplastics are easily processed and recycled, while thermosets cannot be recycled. This is where the life cycle of plastics takes two separate courses.
Thermoplastics vs. Thermosets
If the plastic created is a thermoset, it cannot be recycled. This means that a thermoset product, such as epoxy resin, melamine counters, insulation, car parts, and carpet padding, cannot be melted down to create something new. Instead, they must be thrown away or re-purposed. While many consumers and manufacturers are getting creative with their re-purposing tactics, much of it will end up in a landfill (or in the ocean).
If plastic is thermoplastic, however, its life cycle may be somewhat longer.
The Life Cycle of a Thermoplastic
By breaking down their polymers using heat, thermoplastics can be melted down and reformed — in some cases indefinitely. In most cases, though, plastics can only be recycled 2 to 3 times before they break down. That’s why most recycled plastic is “down-cycled,” as is common with food-grade plastics that may be compromised. We see this in textiles made from recycled water bottles, for example, as well as a number of toys and household goods.
The biggest consideration in recycling thermoplastics, however, is the need for sorting. Different plastic types often can’t be mixed together for recycling; the different properties will separate, leaving a material that is soft and unusable. That’s why sorting plastics by type is so important.
Prior to being melted down, plastics must be sorted by category — something that is becoming easier but still causes some confusion on the part of the consumer. Plastic identification codes (01 – 07) are used worldwide to tell consumers and recycling facilities which plastics can be recycled. Once a plastics user has established that the material can be recycled, it’s put in a bin and collected by the local recycling facility. From there, it’s the job of the material recovery facility to sort by plastic types prior to melting down the product.
Once sorted, the materials are often transported to the actual recycling facility, where the plastics are washed and heated so residue, labels, and other contaminants are removed. Then, the plastics are ground into small pieces, washed and dried again, and then heated. Depending on the type of plastic and its intended use, it may be sterilized again (especially for food-grade plastics) and other plastics may be added for additional strength. Some plastics are melted into pellets, which are sold to manufacturers to use for their own needs. Others are formed into their intended material soon after melting. This end process depends on the recycling facility and its capabilities.
Pitfalls of Plastics Recycling
For material recovery facilities, plastic recycling is a great way to support the life cycle of plastic and prevent it from filling landfills and oceans. But it also presents its own challenges: plastic material is low density, making it harder to process without advanced equipment and personnel, and contamination slows down processing. However, with modern recycling equipment, MRFs can increase processing speed, accuracy, and profits, as well as your community’s desire to recycle more.
General Kinematics designs complete recycling systems for material recovery, including single stream and multi-stream units. Our recycling solutions can help increase efficiency and reduce costs, making it faster and easier for your facility to sort plastics for recycling. Contact us to discuss your plastics recycling needs.