Then it just takes a little chopping, melting and re-extruding to produce a new, moldable film. To turn an old bag into a new one, for example, you have to start with very clean recycled content.
Some uses of recycled plastic require the starting product to be clean and free of contaminants, such as food or other types of plastics. The recycling plant sorts and bundles the plastic, and sells it directly to manufacturers. After drop-off, the bags are either sent to a domestic recycling plant or exported. Many grocery stores now feature bag-recycling bins-ask yours why if it doesn’t. (Source: Plastics Division of the American Chemistry Council’s “2007 National Post-Consumer Recycled Plastic Bag & Film Report”) What happens to recycled plastic film may change in coming years due to many plastic bag makers agreeing to make plastic bags with 40 percent recycled content by 2015. Plastic bags, sacks and wraps accounted for over 4 million tons of plastic waste in 2007, the third-highest category of plastics. A little cooling, and you have your plastic film, which can be shaped into a bag, complete with handles, logos and recycling information. At the other end, the melted plastic gets squished through a hole onto a die that shapes it into a thin film. You dump your pellets into one end and move them through the tube by turning the screw. Heat the pellets in an extruder, which is basically a long, horizontal tube around a big screw. The “D” means density and the “H” stands for high, the “L” is low.)
(If you’ve seen “HDPE” or “LDPE” on plastics, that’s what the PE means. A chain of ethylene monomers is called polyethylene (PE). Next, chemically treat the monomers so that they combine to make polymers. Ethylene, one type of monomer, serves as the basic building block of a plastic bag. Apply pressure to “crack” or break these hydrocarbons into single molecules called monomers. What does it take to make a plastic bag? First take some oil, coal, natural gas or even plant material, all of which are made up of carbon and hydrogen atoms. Where does it come from? Where does it go? How much energy and raw materials are actually required to make plastic shopping bags, and how much do we save by recycling them?Īsked by Jim Salvia, PhD candidate in electrical engineering, Menlo Park Q: It's obvious that reusing plastic bags is a good idea, but it's not obvious that recycling them is worthwhile because they have so little mass.