Cross-linked polyethylene
It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, insulation for high tension (high voltage) electrical cables, and baby play mats.
[3] This is due to the introduction of crosslinks in the system, which can significantly improve the chemical, thermal, and mechanical properties of the polymer.
The behavior observed in PEX is also mimicked by the thermoplastic ultra-high molecular weight polyethylene (UHMWPE).
[6] The type of initial polymer structure and amount of crosslinking can have a large impact on the resulting mechanical properties of PEX.
[7] One study looked at the effect of crosslinking low-density polyethylene (LDPE) with different amounts of dicumyl peroxide (DCP).
[8] It was found that increasing the weight percent of the peroxide crosslinker resulted in a lower degree of crystallinity, as observed via differential scanning calorimetry (DSC).
In another study, the amount of silane crosslinker added to linear low-density polyethylene (LLDPE) was varied.
In the same study, the researchers looked at the effect of adding a filler known as montmorillonite (MMT) nanoclay and observed even higher Young's moduli and tensile strengths, indicating a strong interfacial interaction between the silane crosslinked LLDPE and the MMT.
Almost all cross-linkable polyethylene compounds (XLPE) for wire and cable applications are based on LDPE.
Numerous modifications in the basic polymer structure can be made to maximize productivity during the manufacturing process.
This results in higher line speeds in cases where limitations in either the curing or cooling processes within the continuous vulcanization (CV) tubes used to cross-link the insulation.
In each method, a hydrogen atom is removed from the polyethylene chain (top center), either by radiation (hν) or by peroxides (R-O-O-R), forming a radical.
The cross-linked bonds are formed through silanol condensation between two grafted vinyltrimethoxysilane (VTMS) units, connecting the polyethylene chains with C-C-Si-O-Si-C-C bridges.
It provides less uniform, lower-degree cross-linking than the Engel method, especially at tube diameters over one inch (2.5 cm).
However, it is the cleanest, most environmentally friendly method of the three, since it does not involve other chemicals and uses only high-energy electrons to split the carbon-hydrogen bonds and facilitate cross-linking.
One estimate from 2006 was that residential use of PEX for delivering drinking water to home faucets was increasing by 40% annually.
As users experienced problems with the internal build-up of rust, which reduced water volume, these were replaced by copper pipes in the late 1960s.
[20] Gradually, PEX became more accepted for more indoor plumbing uses, such as carrying pressurized water to fixtures throughout the house.
[39] This was due mostly to concerns about corrosion of the manifolds (rather than the tubing itself) and California allowed PEX to be used for hydronic radiant heating systems but not potable water.
In 2009, the Building Standards Commission approved PEX plastic pipe and tubing to the California Plumbing Code (CPC), allowing its use in hospitals, clinics, residences, and commercial construction throughout the state.
The aluminium layer also provides additional structural rigidity such that the tube will be suitable for higher safe operating temperatures and pressures.
[citation needed] This product in Canada has been discontinued due to water infiltrating between the Layers resulting in premature failures.
Compression fittings are tightened with normal spanners and are designed to allow sections of the system to be easily disassembled, they are also popular for small works, esp.
