Scientists have turned waste cooking oil into a variety of recyclable plastics with superior strength, some durable enough to tow a car.
Turning non-edible waste into useful polymers is a sustainable way to create new materials, researchers said in a new study published Nov. 28 in the Journal of the American Chemical Society.
“Waste streams offer a potentially attractive alternative to biomass-derived feedstocks [to make plastics]” the researchers wrote in their study.
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One such waste stream is used cooking oil, of which approximately 3.7 billion gallons are generated each year. This waste oil has traditionally been used as lubricants, non-stick coatings and fuel, but much of it is still thrown away. In new research, scientists have discovered a way to convert waste oil into a useful plastic material that is highly adhesive and recyclable.
Oils are made up of long chains of fatty acids attached to molecules of glycerol (also known as glycerin). The researchers chemically split petroleum molecules and converted the products into simpler molecules through a series of reactions.
By combining the final alcohol and ester molecules in different ways, the researchers were able to synthesize a variety of polyester plastics. (An ester molecule has a carbon atom double-bonded to an oxygen atom and also double-bonded to a single oxygen atom with a carbon side chain.)
Testing of the plastics’ properties, such as melting point and crystallinity, revealed that these polymers are similar to low-density polyethylene (LDPE), a plastic commonly used in packaging and plastic bags.
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Polyester was also sticky because the oxygen atoms in the polymer form strong bonds with various materials. This is different from LDPE, which is a hydrocarbon containing only carbon and hydrogen atoms.
Two metal plates bonded together with a cooking oil adhesive proved to be strong enough to withstand hundreds of pounds of weight (left) and being towed by a car (right). (Image credit: Mahadas et al.)
The researchers tested the adhesive strength of the polymer by bonding two stainless steel sheets together. The plates remained firmly attached even when loaded with up to 270 pounds (123 kilograms). We also had no problem towing a four-door sedan up a slight uphill slope using this glued piece of steel. This makes these polymers as strong or stronger than the commercially available adhesives the team tested.
These properties make these adhesives “ideal for laminate and adhesive applications used in packaging, automotive parts, medical devices, and electronics,” the researchers wrote.
Polyester plastic can be easily recycled back to its original components and later remade into plastic. Even after several cycles of recycling, the properties of the plastic were largely unaffected. Some plastics may be able to be recycled with other common plastics, such as high-density polyethylene and polypropylene.
“This study highlights the potential of non-edible biomass waste as a renewable feedstock for environmentally friendly alternatives to petroleum-based plastics,” the researchers wrote.
