Plastic is a very light material, which can be softened by heating at a very low temperature and made into various shapes at will. Plastic products are bright in color, light in weight, not afraid of falling, and economical and durable. Their appearance not only brings convenience to people's lives, but also greatly promotes the development of industry.

The commonly used food plastic bags are mostly made of polyethylene film, which is non-toxic, so it can be used to contain food. Another kind of film is made of polyvinyl chloride, which is also non-toxic, but the additives added according to the use of the film are often harmful to human body and have certain toxicity. Plastic bags are made of petroleum, which not only consumes a lot of resources, but also cannot be decomposed. Buried underground will pollute land and rivers. In many countries, waste plastics are disposed by incineration (thermal energy regeneration) or reprocessing (product regeneration). These two methods make waste plastics recycled and achieve the goal of saving resources.