Low-density polyethylene is made by the co-polymerisation of Ethylene using olefins with longer chains. This polymer is different from LLDPE because it has long branches rather than short ones, processed at higher temperatures and pressures, and different molecular weight distribution and linear structure.
The process is operated under very high pressure (1000-3000 atm) at moderate temperatures (420-570 K). This is a radical polymerization process and an initiator, such as a small amount of oxygen, and/or an organic peroxide is used. There are about 20 branches per 1000 carbon atoms. The relative molecular mass, and the branching, influence the physical properties of LDPE. The branching affects the degree of crystallinity which in turn affects the density of the material. LDPE is generally amorphous and transparent with about 50% crystallinity. The branches prevent the molecules fitting closely together and so it has low density.
LDPE is used for making thin film liners, wrapping film, stretching film, etc. 80% of the world’s productions goes to food packaging due to its high puncture resistance, thus increasing the food’s shelf life. It is also used in extrusion coating applications where it protects the object like containers, paper, etc.
Juice and milk cartons are made of liquid packaging board, a laminate of paperboard and LDPE (as the waterproof inner and outer layer), and often with of a layer of aluminum foil (thus becoming aseptic packaging).