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It is the registered trade mark of British Polythene Limited in numerous countries throughout the world. It is commonly between 4 and 10 mils (0.004 to 0.01 in./0.1 to 0.25 mm) thick and is available in clear, opaque, blue, and black. [1] [citation needed] Visqueen is used for many purposes.
Polyethylene – The most common plastic film is made of one of the varieties of polyethylene: low-density polyethylene, medium-density polyethylene, high-density polyethylene, or linear low-density polyethylene. Polypropylene – Polypropylene can be made a cast film, biaxially oriented film (BOPP), or as a uniaxially oriented film.
These photosensitive films are more costly than either the clear or black polyethylene sheeting. [3] Black plastic mulch controls evaporation from the soil and improves soil water retention. Plastic mulching proved to reduce irrigation requirements in pepper by 14-29% because of elimination of soil evaporation. [7]
In the case of polyethylene and other semi-crystalline polymers, as the film cools it crystallizes at what is known as the frost line. As the film continues to cool, it is drawn through several sets of nip rollers to flatten it into lay-flat tubing, which can then be spooled or slit into two or more rolls of sheeting.
Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it by accident in 1898 while investigating diazomethane. [12] [a] [13] [b] When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy substance that he had created, they recognized that it contained long −CH 2 − chains and termed it polymethylene.
HDPE is known for its high strength-to-density ratio. [4] The density of HDPE ranges from 930 to 970 kg/m 3. [5] Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength (38 MPa versus 21 MPa) than LDPE. [6]