The weak bonding between olefin molecules allows local thermal excitations to disrupt the crystalline order of a given chain piece-by-piece, giving it much poorer heat resistance than other high-strength fibers. Its melting point is around 144 to 152 °C (291 to 306 °F), and, according to DSM, it is not advisable to use UHMWPE fibers at temperatures exceeding 80 to 100 °C (176 to 212 °F) for long periods of time. It becomes brittle at temperatures below −150 °C (−240 °F).
Yeah, the molecular structure of UHMW is created as it is chemically formed. Reforming it through extrusion probably breaks those really long chains. It is listed as non-toxic.
Hoechst: Annealing (Stress Relief) of Hostalen GUR
When UHMWPE is annealed, the material is heated to 135 °C to 138 °C in an oven or a liquid bath of silicone oil or glycerine. The material is then cooled down at a rate of 5 °C/h to 65 °C or less. Finally, the material is wrapped in an insulating blanket for 24 hours to bring to room temperature.
The long polymer chains in UHMWPE are produced in modern synthesis processes by exposing ethylene gas to Metallocenes. Older techniques, like the Ziegler-Natta mechanism which dates back to the 1950s, use other organometallic catalysts.Here is a link to a nice, old book on the subject.Quote
Yeah, the molecular structure of UHMW is created as it is chemically formed. Reforming it through extrusion probably breaks those really long chains.
What's that mean? That one molecule of UHMWPE doesn't actually stick to other molecules of the same very well; but that doesn't matter because it's so dang long. Think about a woven-reed basket; the reeds don't stick to each other but they are long enough to hold each other in place quite well. Now image that the reeds are like a million times longer than that--that's kinda how UHMWPE holds together.Quote
It is made up of extremely long chains of polyethylene, which all align in the same direction. It derives its strength largely from the length of each individual molecule (chain). Van der Waals bonds between the molecules are relatively weak for each atom of overlap between the molecules, but because the molecules are very long, large overlaps can exist, adding up to the ability to carry larger shear forces from molecule to molecule. Each chain is bonded to the others with so many van der Waals bonds that the whole of the inter-molecule strength is high. In this way, large tensile loads are not limited as much by the comparative weakness of each van der Waals bond.