A plastic extrusion machine, for making plastic sheets or tubes. Plastic pellets are fed into a funnel. The screw draws them...Read More >>A plastic extrusion machine, for making plastic sheets or tubes. Plastic pellets are fed into a funnel. The screw draws them through a heater and turns them into a thick, sticky liquid. This liquid is squeezed through a hole, called a die, to form a sheet (as pictured) or a tube. It hardens when cooled. A plastic is a substance that can be moulded, or given any required shape, during manufacturing. Plastics are synthetic compounds (molecules consisting of more than one element, such as carbon and hydrogen): they have been chemically manufactured, rather than occurring naturally. Plastics behave similarly to some natural substances, such as rubber, but only synthetic plastics are considered to be true plastics.
Most plastics are made from naturally occurring fossil fuels, such as petroleum, coal and natural gas. The most commonly used plastic is polyethylene, found in bags, containers and bottles, which is made from the natural gas ethylene.
Other plastics, known as bioplastics, are produced from plant-based raw materials, such as starch, produced by green plants as an energy store, and cellulose, which forms the cell walls of plants. Bioplastics have the advantage of relying on renewable raw materials, rather than on scarce fossil fuels. Bioplastics include cellulose, used for photographic film, and polyhydroxyalkanoates, used for medical products such as sutures, implants and dressings. Many bioplastics are biodegradable, which means that they break down over time into their natural raw materials.
About 13 billion plastic bags are produced every year. It takes them 500 years to biodegrade if they are disposed of in landfills.
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