Thursday, October 24, 2013

"Dear, Do These Jean Make My Butt Look Ultrahigh Molecular Weighty?"

In the never ending efforts to improve the fabrics of our lives (recall the earlier effort to make clothing photocatalytic, Plastemart reports (o.k., it looks like nothing more than a cut-and-paste job of a PR release) that Levi's jeans will soon be made incorporating ultrahigh molecular weight polyethylene (UHMWPE) fibers into the fabric. Arguably the strongest fibers in the world (at least on a per weight basis), these fibers should make for some pretty tough jeans.

I was first exposed to UHMWPE during grad school when I used it as part of my research. The production of the fibers with this resin is different than most fiber manufacturing processes, which simply extrude the molten plastic through a small circular hole and pull on it to orient and thin the fiber. Due to the very high molecular weight, such processing is well nigh impossible since the viscosity of the molten resin is too high and it would also undergo too much shear degradation. So an alternative method is employed: gel spinning. The resin is dispersed in a low viscosity liquid so it has 'gel-like' properties [*] which can easily be extruded and pulled thin. As the thinning is going on, the crystalliization expels the liquid leaving behind just the polymer. The liquid also helps lubricate the polymer chains so that orientation can be increased.

These fibers are going to show up in the Trooper styles of the 501 jeans. So nice time you get pulled over by a trooper for doing 50 in a 40, you can strike up a conversation about how strong his jeans look. Maybe he'll let you off.

[*] although it certainly doesn't meet the standards (either Flory's or IUPAC's) for being a gel.

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