Starch from cereal grains such as corn and wheat shows promise as a component of plastics. especially where the introduction of a biodegradable component is important. For many years up to the early 70s, petroleum was readily available at $2 to $4 per barrel and starch sold for about 5 cents per pound. Since that time. petroleum has increased 5- to 10-fold while starch maintained a steady price or increased little more than 2-fold. These price changes and increased availability now make starch economically attractive as a substitute for petroleum.
Most common starches contain 17-27% amylose. a linear polysaccharide consisting of 400-1.000 1A-linked a-D-glucose units, and 73-82% amylopectin. a branched molecule consisting of D-glucose units linked a-D( 1-4) with branches at the C-6 position once every 26 or more D-glucose units. Starch readily gelatinizes (or disperses) in hot water to form a paste that can be cast into film. However, such films are sensitive to water and become quite brittle upon drying due to retrogradation of the starch. To alter these properties. starch has been blended with water-soluble plasticizers and synthetic polymers.
Introduction - The market for plastic bags, bottles, and food service ware that are degradable, biodegradable or compostable is growing rapidly. The use of compostable plastics to replace traditional plastics can have many potential positive environmental impacts, for example reducing dependence on fossil energy, reducing GHG emissions, reducing persistent waste in the environment, and fostering the development of sustainable and biodegradable products. However, these products may present challenges for policy makers and end users in regard to their end-of-life management.
Frequently Asked Questions About Plastic Shopping BagsPlastic shopping bags are convenient, lightweight, inexpensive--and everywhere. Since their introduction in the late 1970s, they have become a useful part of daily life, holding groceries and other purchases and then being reused as trash liners, lunch bags and pet waste bags. The fact that they are so lightweight yet sturdy, however, makes them potentially hazardous in the environment and an eyesore when they blow into trees, fences, storm drains and water bodies. With these problems in mind, recycling has increased. In addition a growing number of communities around the world have imposed bans or taxes on disposable plastic bags, and many others are considering similar actions. While many of these efforts have successfully reduced the use of plastic bags, tradeoffs and sometimes unexpected consequences may exist. This page answers some common questions about the issue. * What Are the Environmental Impacts of Plastic Bags? * How Big Is the Problem? * Is it Better to Ask for Paper or Plastic at the Store? * What About "Compostable" or "Biodegradable" Plastic? * Can I Recycle Plastic Shopping Bags? * What Happens to the Bags I Recycle? What Are the Environmental Impacts of Plastic Bags? Plastic bags have a number of environmental impacts throughout their lifecycle. These include greenhouse gas emissions and pollution from the process of extracting and refining petroleum or natural gas, manufacturing the plastic bags, and transporting them to market. One of the biggest negative impacts of plastic bags comes from their disposal. Plastic bag litter has been a driving force behind bans and other restrictions on their use. Problems caused by plastic bags in the environment include: * Bags clog gutters and sewer grates, causing flooding. * Bags get caught in trees, fences and other objects, where they become an eyesore. * Bags kill animals--particularly birds and marine life--when the animals become entangled in the plastic or when they mistake pieces of plastic for food. Plastic can take hundreds of years to degrade, and can pose risks even when it has degraded into smaller pieces, since these are especially attractive to animals as food. They are also believed to adversely affect landfill operations by interfering with moisture distribution and leachate flow within landfilled waste. How Big Is the Problem? According to several sources, including reusablebags.com [exit DNR], U.S. shoppers use an estimated 100 billion plastic bags every year and recycle only a small percentage of them, though market demand for the recycled bags is growing. Many of the bags are reused by consumers as trash liners or pet waste bags, but a large number also end up in landfills or causing harm in the environment without first being reused. Much of the plastic eventually makes its way downstream to the oceans. The California Coastal Commission estimates that 60 to 80 percent of all marine debris is plastic, with plastic bags making up a portion of that total. In the Pacific Ocean, currents push debris into one area. Since plastic-based materials do not readily break down, one researcher has estimated there is a floating mass of plastic and polystyrene foam in the north Pacific Ocean that is roughly the size of Texas. (Read an article from Natural History Magazine [exit DNR] about this topic.) The plastic does eventually break down into small pieces and particles--but these also present a problem because they closely resemble plankton, a major food source for many marine animals. Is it Better to Ask for Paper or Plastic at the Store? Both paper and plastic have environmental drawbacks. It takes 40 percent more energy (and releases more greenhouse gases and air and water pollution) to manufacture paper bags than plastic, according to the U.S. Environmental Protection Agency. It also takes more energy to transport paper bags because they are heavier than plastic. On the other hand, paper bags are currently easier to recycle in most locations, although again, recycling paper requires more energy than recycling plastic. They also break down much more quickly in the environment (in one month vs. 1,000 years, according to the U.S. Environmental Protection Agency), eliminating many of the problems of plastic-bag litter. The bottom line: the best option is to use a reusable cloth bag or other reusable container, and reuse or recycle paper and plastic bags when you do have them. Many grocery stores are now offering durable, washable bags to their customers at very affordable prices. These bags have sturdy handles, are easy to pack and have about the same capacity as paper bags. Using these bags is better for the environment than paper or plastic. What About "Compostable" or "Biodegradable" Plastic? A growing number of plastic products are reaching the market that claim to be "compostable" or "biodegradable," including shopping bags, trash bags and pet-waste bags. In some cases they may be a preferred environmental alternative to petroleum-based plastics, but this issue is not a simple one. Most of these compostable or biodegradable plastics, sometimes called "bioplastics," are made from plant starches and designed to break down only in carefully controlled composting conditions, such as at a municipal or commercial composting facility. Many of these plant-based bags do contain some oil-based components. At this point, most are not suitable for home composting. They will also not necessarily solve the problem of plastic bag litter, because they break down slowly in the environment. Some "bioplastics" may not be biodegradable or compostable at all. In addition, it is important to note that some plastics labeled as "biodegradable" are actually petroleum- or natural gas-based like traditional plastics, but many of these break down into smaller particles that can still pose environmental harm. The technology of making biodegradable/compostable bags is changing rapidly, so manufacturers continue to introduce new products with claims about how quickly, under what conditions and with what environmental side effects the plastic degrades. If you are purchasing compostable or biodegradable bags, read the labels carefully and look for brands that meet ASTM standards, which ensure that they will compost properly under certain conditions. These standards are maintained by independent ASTM International (formerly the American Society for Testing and Materials). Compostable bags are a good alternative if your municipality has a yard materials or food scrap composting program, and may be required in some communities. Check with your local government if you have questions about using compostable bags for their yard or food waste collections. Can I Recycle Plastic Shopping Bags? Yes, but right now the options are limited in many places. Recycling opportunities are growing, however, and include: * Several supermarkets and other retailers accept plastic shopping bags for recycling. They include: Roundy's (Copp's, Pick 'n Save, Rainbow Foods and Metro Market stores), Kohl's department stores, Trig's Foods stores and Wal-Mart. Check with these stores to see what types of plastic bags they accept. * Many dry cleaners accept plastic dry cleaning bags (and wire hangers) for recycling and reuse. Check with dry cleaners in your area to see which accept these items. Although most plastic bags and other films are made of a recyclable material, polyethylene plastic, local curbside collection programs in Wisconsin are generally not yet equipped to accept them. Plastic bags and films clog recycling machinery and are difficult to separate from other materials. For now, the best option is to take clean, empty bags to a retailer that offers a recycling bin to its customers. Of course, many consumers also reuse plastic bags for trash liners, pet-waste bags and other household uses. Compostable bags should not be placed in recycling containers for traditional, petroleum-based bags, because they will interfere with the recycling process. What Happens to the Bags I Recycle? While only a small percentage of plastic bags and other film are currently recycled, the demand for relatively clean scrap film is growing, according to the June 2007 issue of Resource Recycling. Products that are made from recycled grocery bags and other plastic film include new bags, composite lumber and playground equipment. As with any type of recycling, it's good to know where materials go after you put them in the recycling bin. Ask your retailer or waste hauler what happens to the plastic bags they collect for recycling.
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