Plastic is derived from natural gas or oil. so it is a source of energy. If you burn plastic for cooking it gives more heat than normal wood or charcoal. But it does pollute the environment while burning plastic in the open.
As part of a project Dow chemicals burnt 578 pounds of plastic ( linear low-density polyethylene (LLDPE), a material used in plastic bags, plastic wrap and films, as well as other products like cable covers and tubes) to convert plastic to energy. It claims that it could recover 96 percent of the energy by burning down the waste plastic materials. We in India should also consider option of burning plastic to convert it to energy instead of sending used plastic bags to landfill. More details of this news click here http://www.greenbiz.com/news/2011/05/24/for-dow-burning-hard-recycle-plastic-better-landfilling
Waste-to-energy plants are a mainstay of garbage disposal in Europe, as well as an important source of heat or electricity. About 400 plants are scattered across the continent, and together they take care of about 30% of the plastics Europe diverts from landfill. The Netherlands, for instance, landfills only 3% of its trash, and burns 35% for energy.
Hope we in India do our best to reduce use of plastic or convert plastic back to energy.