Medium Density Polyethylene (MDPE)

Medium Density Polyethylene (MDPE) is part of the polyethylene family of thermoplastics which include HDPE and LDPE. MDPE, is usually black or blue and may also be referred to as black alkathene. It has a relatively dense molecular structure, which is lower than HDPE and higher than LDPE.

When ethylene is polymerised it has straight polymer chains, with branches from a main chain. LDPE has the most branching and so is least dense, whilst HDPE has the least branching so is the more dense, whilst MDPE is in between. LDPE, HDPE, LLDPE, PP (polypropylene) are polyolefins, which are high molecular weight hydrocarbons. They are some of the few plastics that have a low specific gravity, weighing less than water. They are susceptible to oxidation and UV damage.

MDPE is, as with other polyethylenes, lightweight and flexible, so it is often used in the manufacture of gas pipes and fittings, sacks, carrier bags, and screw closures. On construction sites and factories it is often used as a shrink wrap, slightly heavier duty than LDPE shrink wrap.