The conversion produces significantly more energy than it requires and results in transportation fuels - diesel, for example - that can be blended with existing ultra-low-sulphur diesels and bio-diesels, researchers said.
Other products, such as natural gas, naphtha (a solvent), gasoline, waxes and lubricating oils such as engine oil and hydraulic oil also can be obtained from shopping bags.
There are other advantages to the approach, which involves heating the bags in an oxygen-free chamber, a process called pyrolysis, said lead researcher Brajendra Kumar Sharma, a senior research scientist at the Illinois Sustainable Technology Centre at University of Illinois.
"You can get only 50 to 55 per cent fuel from the distillation of petroleum crude oil. But since this plastic is made from petroleum in the first place, we can recover almost 80 per cent fuel from it through distillation," Sharma said.
Plastic bags make up a size-able portion of the plastic debris in giant ocean garbage patches that are killing wildlife and littering beaches.
Plastic bags "have been detected as far north and south as the poles," researchers said.
"Over a period of time, this material starts breaking into tiny pieces, and is ingested along with plankton by aquatic animals," Sharma said.
Fish, birds, ocean mammals and other creatures have been found with a lot of plastic particles in their guts.
Previous studies have used pyrolysis to convert plastic bags into crude oil.
Sharma's team took the research further, however, by fractionating the crude oil into different petroleum products and testing the diesel fractions.
"A mixture of two distillate fractions, providing an equivalent of US diesel, met all of the specifications" required of other diesel fuels in use today after addition of an antioxidant, Sharma said.
"This diesel mixture had an equivalent energy content, a higher cetane number (a measure of the combustion quality of diesel requiring compression ignition) and better lubricity than ultra-low-sulphur diesel," he said.
The researchers were able to blend up to 30 per cent of their plastic-derived diesel into regular diesel, "and found no compatibility problems with bio-diesel," Sharma said.
The study appears in the journal Fuel Processing Technology.