Plastic bags introduction and problem.
Plastic bags typically are made from one of three basic types: high-density polyethylene (HDPE), low-density polyethylene (LDPE), or linear low-density polyethylene (LLDPE). Those thick, glossy shopping bags from the mall are LLDPE, while grocery bags are HDPE, and garment bags from the dry cleaner are LDPE. The major difference between these three materials is the degree of branching of the polymer chain. HDPE and LLDPE are composed of linear, unbranched chains, while LDPE chains are branched.
Different from PP woven bags or PP bags,PE bags are not readily biodegradable, environmental costs of plastic bags are burdensome for communities and the planet, the cost of plastic bags for retailers is pretty low. Made from ethylene, a byproduct of petroleum or natural gas, plastic bags are so cheap and flimsy that cashiers use them freely, double bagging as a matter of course and often sticking just a few items in each bag. As a result, shoppers end up with piles of plastic bags spilling out of closets and threatening to take over cupboards, until we finally throw up our hands and either dump them in the trash or, if we’re lucky enough to live in an area where stores provide plastic bag collection bins, cart them back for recycling. Sure, some of us reuse plastic shopping bags to line our waste bins or to pick up dog poop, but the bags still end up in the landfill.
Plastic bags are easily picked up and carried by the wind. They can escape from trash bins, recycle bins, garbage trucks, and landfills, and end up littering the landscape. Blowing down the street, flapping from trees, clogging storm drains (costing municipalities millions of dollars in cleanup costs), and making their way out to sea,also can be dangerous to animals. And they persist in the environment, causing harm for a very long time.
Today,new plastic technology appeared, one solution to this problem is to make degradable bags, such as those from starch. Starch, obtained from corn or potatoes, can be converted into lactic acid, which can be polymerized to the biodegradable plastic known as polylactide. Another solution is to add an ultraviolet-light absorber to make the material degrade when exposed to sunlight. Unfortunately, these solutions can make the plastics more expensive, so they haven't caught on with consumers.
