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A Guide to Compostable and Biodegradable Plastics

Posted on January 27, 2014 by Rachel Tardif There have been 0 comments

Plastic is everywhere, and while plastic products may make our lives more convenient, they also cause a great deal of environmental damage. Two hundred million tons of plastic are manufactured worldwide every year, and all of that plastic adds up to an extraordinary amount of waste. In the U.S. alone, 31 million tons of plastic are discarded per year – that’s 12.4% of all of the waste produced. Sadly, only 8% of plastic waste is recovered for recycling, which means that almost all that plastic ends up in landfills. Plastic is also a major ocean pollutant: 77% of ocean debris is plastic that threatens the health of animals and the integrity of marine ecosystems. And because plastic is not biodegradable, those plastics will remain in landfills and oceans for hundreds or even thousands of years.

The manufacturing of plastic is also closely tied to the petroleum industry. Most plastics are derived from petroleum, which means plastics contribute to the damage caused by oil extraction operations. The U.S. Energy Information Administration estimates that in 2006, 331 million barrels of petroleum – about 4.6% of U.S. petroleum consumption – was used to manufacture plastics. Because plastic come from fossil fuels, they are also a source of dangerous toxins. When burned, many plastics release toxic chemicals, including dioxins, benzene, and hydrochloric acid. There are also additives in plastic, including phthalates and bisphenol A (BPA), that are dangerous to human health and can leach from containers into food or water.

The dangers of traditional plastic have led to the development of a number of new types of less hazardous plastics.

Bioplastics

Bioplastics are plastics derived from renewable sources such as vegetable oils or starches instead of from petroleum. Although they currently make up only a small percentage of manufactured plastics, the use of bioplastic is growing quickly. Companies like Coca-Cola, Pepsi, and Wal-Mart all use bioplastics in their packaging, and many restaurants now use take-out containers made from bioplastics.

Biodegradable plastics

Many bioplastics are biodegradable, although they require composting in order to completely break down. They are also recyclable, although the technology is not widespread.  They cannot be recycled with more common plastics, so when possible bioplastics should be sorted out from other plastics before entering the recycling stream.

One of the most widely used bioplastics is polylactic acid (PLA), which is commonly used to replace Styrofoam and other plastics in takeout containers and single-use cutlery, plates, and cups. It is manufactured from corn starch or sugarcane and is similar to traditional plastics like polyethylene, although PLA cannot withstand high temperatures. It is important to remember that PLA is only biodegradable under compost conditions, where it is heated to 140° in the presence of the necessary microbes. When deprived of air and water in landfill conditions, PLA takes nearly as long as regular plastics to decompose. So if you use PLA products, be sure to dispose of them properly in your own compost bin or an industrial compost site.

Other biodegradable bioplastics include polyhydroxyalkanoates (PHAs), poly-3-hydroxybutyrate (PHB), and cellulose acetate, which has been used to make fabrics and film since the early 1900s.

Non-biodegradable bioplastics

In some cases, biological sources can be used to duplicate the chemical structure of petroleum-derived plastics. These plastics do not require the use of petroleum for production, but unlike the plastics listed above they are not biodegradable. Instead, once synthesized they are indistinguishable from petroleum-derived plastic and can be recycled alongside traditional plastics. The most common of these is bio-derived polyethylene, which can be manufactured from sugar cane, sugar beets, or wheat. When you see ads for recyclable “plant bottles” they’re usually made from this type of plastic.

Oxo-degradable Plastics

Petroleum-derived plastics can be made degradable by the addition of metal salts, which makes the chemical structure of the plastic vulnerable to oxygen and ultraviolet light. This process is known as oxo-degredation or oxo-biodegradation, although it does not result in complete decomposition. Instead, the oxygen and UV light break the plastic down into microscopic particles of plastic and metal that will remain in the environment until microorganisms are able to complete the decomposition. This process can take as little as a few weeks, although in the absence of the necessary microorganisms the plastic particles can exist indefinitely. As with the other plastics listed above, complete biodegradation will not occur without proper composting conditions. There is also some concern about the metal residue that oxo-degradation leaves behind.

The most common use for oxo-degradable plastic is in compostable plastic bags. There are a number of alternatives to these petroleum-derived plastic compostable bags, including ones made from cellulose or other bioplastics, that provide compostability without using metals or petroleum chemicals.

How to Compost Plastics

While a step forward, biodegradable plastics are still not as easily composted as food scraps and natural fibers like paper and cotton. Bioplastics like PLA require very high temperatures to fully decompose, so you might need to experiment with your backyard compost pile to see if it gets hot enough to handle plastics. If you’re finding that PLA isn’t completely breaking down, consider using a solar or insulated compost bin to help raise the temperature. If that doesn’t work, you may need to send your biodegradable plastics to an industrial compost facility that is designed to handle difficult waste.  Lastly, unless the label specifically states it can be recycled, try to keep bioplastics out of the green bin. It costs recycling centers time and money to sort out non-recyclable plastics, and materials like PLA and oxo-degradable bags can damage equipment and ruin other recyclable plastics.


This post was posted in Blog and Green Library, Reduce, Reuse, Recycle, Your Green Business and was tagged with COMPOSTABLE

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