Editing Polytetrafluoroethylene (section)

== Processing ==
Processing PTFE can be difficult and expensive because its high melting temperature, {{convert|327|C}}, is above its decomposition temperature. Even when molten, PTFE does not flow due to its exceedingly high melt-viscosity.<ref>{{cite web|url=http://www.cowie.com/thermal.htm|title=Cowie Technology – PTFE: High Thermal Stability|website=Cowie.com|access-date=2017-08-16}}</ref><ref>{{cite web|url=http://www.inoflon.com/pdf/PG_Free%20flow%20granular%20PTFE.pdf|title=Free Flow Granular PTFE|date=2017-08-16|website=Inoflon Fluoropolymers}}</ref> The viscosity and melting point can be decreased by inclusion of small amount of [[comonomer]]s such as perfluoro (propylvinyl ether) and [[hexafluoropropylene]] (HFP). These cause the otherwise perfectly linear PTFE chain to become branched, reducing its crystallinity.<ref name="Ebnesajjad2016">{{cite book |doi=10.1016/C2009-0-61247-2 |pages=31–32 |title=Expanded PTFE Applications Handbook |date=2017 |isbn=978-1-4377-7855-7 |first1=Sina |last1=Ebnesajjad }}</ref>

Some PTFE parts are made by cold-moulding, a form of [[compression molding]].<ref name=":1">{{cite web|url=http://www.daikinchem.de/downloads/PTFE-M.pdf|title=Polyflon PTFE Molding Powder|date=2017-08-16|website=Daikin Chemical}}</ref> Here, fine powdered PTFE is forced into a mould under high pressure (10–100 MPa).<ref name=":1" /> After a settling period, lasting from minutes to days, the mould is heated at {{convert|360 to 380|C}},<ref name=":1" /> allowing the fine particles to fuse ([[sintering|sinter]]) into a single mass.<ref>{{cite web |title=Unraveling Polymers: PTFE |publisher=Poly Fouoro Ltd. |date=26 April 2011 |url=http://polyfluoroltd.blogspot.com/2011/04/ptfe-myths-busted.html |access-date=23 April 2017}}</ref>