Date:	Mon, 31 Oct 1994 07:22:59 -1000
From:	vdhamer@prl.philips.nl
Message-Id: <9410311722.AA19265@isthp2.prl.philips.nl>
Organization: Division of Applied Sciences, Harvard University
Subject: Dyneema info

I spoke to a chemical engineer from DSM in the weekend. He is an old school pal,
and certainly not a marketing type. Some pieces of info I got from him on
Dyneema (for the trivia fans; probably not of much practical use):

* Dyneema floats, Keflar (=Twaron=aramide) doesn't.
* Dyneema is based on research work by a Dutch university (Groningen). The
  work (and ensuing patents) is about how to make the stuff: the basic idea
  that long strands of polyethyleen are strong was previously known. The
  problem is how to create very long chains with few defects and to allign
  them in the direction of the fibre.
* Spectra is from Allied Chemicals and was developed after the Dyneema patent.
  Somehow Allied managed to work around the patent. My friend couldn't tell
  whether this had any negative effects on the product (e.g. because they
  couldn't use a better/simpler/cheaper approach).
* Dyneema is primarily used in anti-ballistic applications. There has been
  a major contract for the stuff for fibre-reinforced army helmets.
* DSM talks about Dyneema pricing per unit of weight (yes, the stuff is
  expensive because it is VERY hard to make). The factory for Dyneema is located
  in Limburg, a so-called hilly part of Holland.
* Dyneema is (unlike other hi-tech fibres) not very relevant for reinforcement
  of vehicle tires because it "can't take the heat".
* Another property of Dyneema (which probably doesn't hurt for kiting) is that
  it "creeps": it sloooowly stretches under load. This is primarily due to
  mutual slippage of the long chains of polyethyleen.
* If you are still with me, here's the best part: my friend mentioned that
  Dyneema (and similar fibres) weren't very good at handling shearing strain.
  I asked (yes, I do have a PhD in something or other) how the hell you get
  lateral strain on a rope, and the answer was very enlightening: "that determines
  how well the fibre can handle knots". The tightening of a know causes lateral
  (shearing) strain on the fibles. This is similar (but not quite as drastic)
  as cutting the line with a pair of scissors. It is not untypical for a knotted
  rope to break at 100f its rated load.
* There is one thing I forget to ask: "where does a knotted line break and why".
  Sorry. If you really want to know, I can call him.

Disclaimer: the guy wasn't in the Dyneema part of the company, I could have
misunderstood him (I'm another type of engineer), most of the above also
applies to Spectra and is information in the public domain (as far as I can
tell).

Peter van den Hamer
vdhamer@prl.philips.nl


 = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =