Crosslinked Polyethylene (XLPE)(PEX)
“Cross-linked polyethylene, commonly abbreviated PEX or XLPE, is a form of polyethylene with cross-links. It is formed into tubing, and is used predominantly in hydronic radiant heating systems, domestic water piping and insulation for high tension (high voltage) electrical cables. It is also used for natural gas and offshore oil applications, chemical transportation, and transportation of sewage and slurries. Recently, it has become a viable alternative to polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) or copper tubing for use as residential water pipes. PEX tubing ranges in size from imperial sizes of 1/4-inch to 4-inch, but 1/2-inch, 3/4-inch, and 1-inch are by far the most widely used. In metric PEX is normally available in 16 mm, 20 mm, 25 mm, 32 mm, 40 mm, 50 mm and 63 mm sizes.” (Wikipedia, Crosslinked Polyethylene, 10/19/2011)
Recent Journal Articles
Correlation between molecular structure parameters and network properties of silane-grafted and moisture cross-linked polyethylenes
(286–300)Advances in Polymer Technology 30 #4 (2011)
Aziz et al of the Iran Polymer & Petrochemical Institute, Iran, studied the degree of silane grafting and cross-linking of several high-density polyethylenes (HDPE) was studied. The results are compared with those of a low-density polyethylene (LDPE) and a linear low-density polyethylene (LLDPE). The results show that molecular weight plays the main role in silane-grafting and cross-linking performance. For samples with approximately similar PDI, the grafting level increased with both increasing number average molecular weight and weight average molecular weight, whereas the gel content increased with increasing weight average molecular weight. However, a zigzag relation was observed for the variation of grafting and cross-linking performances with PDI. The presence of long-chain branching affects the size of molecules and reduces the grafting efficiency due to coil contraction and more intramolecular entanglements. The order of the degree of grafting for the different polyethylenes investigated was LLDPE > HDPE > LDPE, whereas the order for the gel content was LDPE > LLDPE > HDPE. The presence of unsaturated groups led to increase in the grafting level. (RDC 10/11/2011)