Guess what? Plastic shopping bags are recyclable. But if you think you can toss them in with the bottles, cans or cartons in your recycling bin, we have some bad news.

Bags require special sorting and processing machines and not every recycling plant has those. In most areas of the country, people should not mix plastic bags in with other recyclables. But people do, and on a massive scale, which causes severe technical problems at general recycling facilities.

Bags can break the recycling equipment used to sort material by jamming up the gears of the conveyor belt, said Mark Carpenter, assistant vice president of communications for the Institute of Scrap Recycling Industries , a nonprofit trade association that provides training and education on recycling.

Americans use 14 billion bags every year. Though its unclear how many are mixed in with curbside recycling, its not unusual for general recycling operations to shut down several times a day due to the catastrophe the bags cause, said John Hambrose, communications manager at Waste Management Inc. , one of the largest sanitation companies in the U.S.

Recycling plant employees must remove tangled bags by hand and put them in a pile to be sent to a landfill.

Whats baffling is that plastic milk jugs and plastic bags are made out of the same material. It seems stupid, but its literally an issue of machines not being suited to handle plastic bags, said Margaret Sobkowicz-Kline , an assistant professor in the plastics engineering department at the University of Massachusetts Lowell.