Cross linked polyethylene (PEX) and Medium density polyethylene (MDPE)

Cross linked polyethylene (PEX) is a medium to high density polyethylene containing cross link bonds introduced into the polymer structure, changing the thermoplast into an elastomer. The high temperature properties of the polymer are improved, its flow is reduced and its chemical resistance is enhanced. Cross linked polyethylene (PEX) is used in some potable water plumbing systems because tubes made of material can expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water tight, connection.

Medium density polyethylene (MDPE) is defined by a density range of 0.926-0.940 g/cm3. Medium density polyethylene can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. Medium density polyethylene has good shock and drop resistance properties. It also is less notch sensitive than High density polyethylene (HDPE), stress cracking resistance is better than High density polyethylene (HDPE). Medium density polyethylene (MDPE) is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw closures.