Low density polyethylene or LDPE is manufactured by free radical polymerization, and has long chains of ethylene molecules with a relatively large amount of branching. These give the product extremely desirable and exceptional flow properties. The product is not as puncture-proof as some of the higher densities of polythene, but its properties enable it to have thousands of everyday uses. You can find the product in all sorts of plastic sheeting such as packaging, plastic bags and cling-foil, as well as thicker and more robust sheeting to be used as canal and pond liners, surface protection, vapor barriers and tarpaulins. LDPE can also be manufactured into more rigid containers such as plastic bottles.
Linear low density polyethylene or LLDPE is manufactured by the copolymerization of ethylene along with a number of short branches that consist of olefins such as 1-butene and 1-hexene. The resulting product is more pliable than LDPE but is more flexible and has greater strength. It is commonly used in applications where both flexibility and strength are equally important. Examples of its use include bubble wrap, saran wrap, agricultural film and composite films. It is also used for toys, lids, containers, plastic piping, toys and for covering cables.
High density polyethylene or HDPE is less flexible than lower densities of polyethylene, but is stronger and tougher. It is manufactured using chromium and silica catalysts and has fewer side branches, giving it stronger intermolecular bonds and tensile strength. HDPE is used in the manufacture of such items as garbage bins, water pipes and detergent bottles. It is commonly used on golf courses to line ponds, as root barriers and to line industrial slurry ponds. HDPE is used in millions of applications where it is blended with lower density polyethylenes in order to give them strength. Most plastic toys are made from HDPE.
Ultra high molecular weight polyethylene or UHMWPE is a polyethylene with an extremely high molecular weight. It is manufactured using catalysts and is used in any application where an extremely tough plastic is required. This plastic can be found in bullet-proof vests, bearings, butchers' blocks, gears and artificial joints such as knee and hip replacement parts, where it is used to replace articular cartilage. UHMWPE is extremely resistant to chemicals, and for this reason you can find it being used for chemical storage.