Editing Polyethylene (section)

==Properties==
The properties of polyethylene depend strongly on type.  The molecular weight, crosslinking, and presence of comonomers all strongly affect its properties.  It is for this structure-property relation that intense effort has been invested into diverse kinds of PE.<ref name=Ullmann/><ref name="Kaiser">{{cite book|last1= Kaiser|first1= Wolfgang|title= Kunststoffchemie für Ingenieure von der Synthese bis zur Anwendung|date=2011|publisher= Hanser|location=München|isbn= 978-3-446-43047-1|edition=3.}}</ref> LDPE is softer and more transparent than HDPE. For medium- and high-density polyethylene the melting point is typically in the range {{convert|120|to|130|C|F}}. The melting point for average commercial low-density polyethylene is typically {{convert|105|to|115|C|F}}. These temperatures vary strongly with the type of polyethylene, but the theoretical upper limit of melting of polyethylene is reported to be {{convert|144|to|146|C|F}}. Combustion typically occurs above {{convert|349|C|F}}.

Most [[Low-density polyethylene|LDPE]], [[Medium-density polyethylene|MDPE]], and [[High-density polyethylene|HDPE]] grades have excellent chemical resistance, meaning that they are not attacked by strong acids or strong bases and are resistant to gentle oxidants and reducing agents. Crystalline samples do not dissolve at room temperature. Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in [[aromatic hydrocarbon]]s such as [[toluene]] or [[xylene]], or in chlorinated solvents such as [[trichloroethane]] or [[trichlorobenzene]].<ref name="Ullmann">{{Cite encyclopedia |title=Polyolefins |encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |date=2000 |doi=10.1002/14356007.a21_487 |isbn=3-527-30673-0 |last2=Heggs |first2=T. Geoffrey |last3=Koch |first3=Hartmut |last4=Mawer |first4=Ralph L. |last5=Immel |first5=Wolfgang |last1=Whiteley |first1=Kenneth S.}}</ref>

Polyethylene absorbs almost no [[water]].  The permeability for water vapor and polar gases of is lower than for most plastics.  On the other hand, non-polar gases such as [[Oxygen]], [[carbon dioxide]], and [[flavorings]] can pass it easily.

Polyethylene burns slowly with a blue flame having a yellow tip and gives off an odour of paraffin (similar to [[candle]] flame). The material continues burning on removal of the flame source and produces a drip.<ref>{{cite web |url=http://www.boedeker.com/burntest.htm |title=How to Identify Plastic Materials Using The Burn Test |work=Boedeker Plastics |access-date=8 May 2012}}</ref>

Polyethylene cannot be imprinted or bonded with adhesives without pretreatment. High-strength joints are readily achieved with [[plastic welding]].

===Electrical===
Polyethylene is a good [[insulator (electricity)|electrical insulator]]. It offers good [[electrical treeing]] resistance; however, it becomes easily [[triboelectric effect|electrostatically charged]] (which can be reduced by additions of [[graphite]], [[carbon black]] or [[antistatic agent]]s).
When pure, the [[dielectric constant]] is in the range 2.2 to 2.4 depending on the density<ref>{{cite web |title=Electrical Properties of Plastic Materials |url=https://www.professionalplastics.com/professionalplastics/ElectricalPropertiesofPlastics.pdf |website=professionalplastics.com |publisher=Professional Plastics |access-date=11 October 2022 |archive-url=https://web.archive.org/web/20220920173045/https://www.professionalplastics.com/professionalplastics/ElectricalPropertiesofPlastics.pdf |archive-date=20 September 2022 |language=en-US |url-status=live}}</ref> and the loss tangent is very low, making it a good dielectric for building [[capacitor]]s. For the same reason it is commonly used as the insulation material for high-frequency coaxial and twisted pair cables.

===Optical ===
Depending on thermal history and film thickness, PE can vary between almost clear ([[transparency and translucency|transparent]]), milky-opaque ([[translucent]]) and [[Opacity (optics)|opaque]]. LDPE has the greatest, LLDPE slightly less, and HDPE the least transparency. Transparency is reduced by [[crystallite]]s if they are larger than the wavelength of visible light.<ref>Chung, C. I. (2010) ''Extrusion of Polymers: Theory and Practice''. 2nd ed.. Hanser: Munich.</ref>