[sdiy] D-70 red goo of death - polyurethane?

[David G Dixon]

There is a thermoplastics expert in my department.  I'll try to ask him some
questions next week.

> -----Original Message-----
> From: Robin Whittle [mailto:rw at firstpr.com.au] 
> Sent: Sunday, January 27, 2013 4:03 AM
> To: David G Dixon; David G. Dixon; synth-diy
> Cc: cheater cheater; Dave Brown
> Subject: Re: [sdiy] D-70 red goo of death - polyurethane?
> 
> Hi David,
> 
> My only guess is that the red material may have been a 
> polyurethane compound, perhaps to glue the weights into the 
> keys.  Polyurethanes can turn to crap of their own accord, 
> relatively suddenly, after long periods of time.
> 
> Spandex (Lycra) is a polyurethane material which is very 
> stretchy - but in a particular garment it can all turn to 
> stiff, brittle, stuff within some time period such as a year 
> or so, when the garment is 10 or more years old.
> 
> Clear, firm, self-adhesive "rubber" (not really) feet are 
> made of polyurethane.  I had two in my van, on the remote 
> (wired) volume and power control box for the sound system.  I 
> affixed them in 1985.  Last year, both of them turned into a 
> horrible sticky mess.  They were close together but not in a 
> sealed environment, other than being inside the vehicle.  I 
> don't know of any solvent which will touch it.  They were 
> still firm enough to scrape off, but some residue remains for 
> which there is no obvious method of dissolving.  While these 
> clear self-adhesive feet are attractive, I think it is better 
> to use real rubber feet with screws in the middle if you care 
> about how the machine will be in its dotage.
> 
> Most resilient foam, as used in seat cushions and for lining 
> carry cases, road cases etc., is polyurethane foam.  I had 
> some in a road case for a bass guitar and one year (it was at 
> around 20 years old) it all turned into a horrible sticky 
> mess - fortunately the guitar was not inside.
> 
> I understand that this material can degrade and produce a 
> byproduct of the degradation which itself catalyses the 
> reaction.  I think this is a gas or a volatile liquid.  So if 
> there is a particular kind of polyurethane in a sealed 
> environment, it will all tend to go bad together.  I recall 
> reading that higher temperatures and humidities are likely to 
> facilitate this reaction.
> 
> The only reference I have in my Bookmarks is is:
> 
>   The degradation of polyester polyurethane: preliminary study of
>   1960s foam-laminated dresses
> 
>   Doon Lovett and Dina Eastop    University of Southampton 2004
> 
> 
> http://www.iiconservation.org/archive/www.iiconservation.org/p
> ublications/pdffetch0a03.pdf?pub_id=139
> 
> As far as I know, there's no degradation of "Estapol" and 
> similar hard polyurethane sealants for wooden floors and the like.
> 
>   - Robin
>