Durability of Materials
By Richard Vance
Perhaps I can contribute to this interesting discussion, since I work for a firm that deals with polymer plant construction, although I am not personally an expert. Let me say that I am firmly in the camp which advocates the exclusive use of traditional adhesives in the original manner, for reasons so eloquently stated by other respondents that they need not be repeated.
As for rubber cement; there are several modern elastomers, such as Neoprene, which are truly stable, and could theoretically form the base of a long lasting rubber cement. However, unlike natural rubber, they can not be dissolved in anything one would want around the house, and more important, they are not tacky.
Normal rubber cements contain a good deal of natural rubber, and everyone here knows what ultimately happens to that. Natural rubber is a co- polymer of rubber latex, a liquid, and the "Rubbery" amorph of sulfur. If this amorph is produced in pure sulfur by heating, it reverts to the natural powdery form in a few days; when bound up with rubber latex, this decomposition is retarded for an unpredictable period, usually 20 to 50 years.
Sometimes this time is far longer, for reasons not well understood, as observed by Mr. Tuttle, but ultimately one ends up with rubber in three distinct phases; the filler, the powdered sulfur, and the latex either as an amber goop or oxidized away, depending on the environment.
Mr. Armstrong's claim [ Durrell Armstrong, Player Piano Co.], a few years ago, that "Aeolius" natural rubber would last a long time, while certainly well intentioned, must be viewed skeptically because no one (that I know of) knows enough to predict the life of rubber absolutely.
Shoemaker's rubber cement is a solution of the best quality rubber in Hexane, which makes a superb, long lasting, and quick-drying contact cement, but it ultimately can't outlast any other rubber product.
In my opinion, the only justified use for rubber cement in our work is as a thinned solution for sealing pouches in certain selected cases. Good rubber will last as long as leather; this application was mentioned a few days ago by another respondent; and is sanctioned by Dr. William Baird White, which is good enough for me.
(By the way, I have always wondered why Dr. Baird White's fine book on player piano servicing, the only independently written work of this kind that I know of published during the "era", has not been reprinted by the hobby. Does anybody out there know anything about this?)
As for the deplorable variability of quality in cloth and tubing which everyone has experienced, this is a consequence of commercial factors, not technology. Neoprene is an oxide, and therefore truly stable, and could probably be made into tubing or cloth that would last "forever". An old timer I know from DuPont has samples over 60 years old which are as good as new.
However, Neoprene alone is too stiff (and expensive) to be used pure. It has to be "compounded", that is, mixed with fillers, plasticizers, and perhaps other polymers, to make it useful. Here is where the problem lies. Ethical compounding is an art and science known to only a few, and involves a complex study and extensive testing for each individual application.
Compounding is successfully done all the time, by either products makers or polymer suppliers such as DuPont or Monsanto. But it is expensive and has to be paid for in one of two ways. Either the small-lot user has to pay up-front for the study, or the purchaser has to guarantee a really big order so that the supplier can absorb the cost.
Due to the limited market for player rebuilding supplies, neither of these approaches can be realistically be expected to be used. Faced with a small order, the producer must use a "standard" compound which may not be right for us, or worse, revert to tricks such as using cheap oil-based plasticizer to make the stuff look OK in the short term.
(Plasticizer acts like an inter-molecular lubricant, used, for example, to make PVC soft enough for upholstery; it is what formerly fogged the windows of a new car, and it dried up altogether after 5 years, leaving the upholstered seats stiff and cracked. While General Motors can solve this sort of problem, we may not be in a position to do so.)
If anybody out there is a Polymer Chemist or executive, and can figure out how to contribute an ethically based set of compounding specifica- tions for the different elastomeric items we use, we all would be eternally grateful.
Richard Vance
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(Message sent Sun 2 Feb 1997, 23:39:10 GMT, from time zone GMT.) |
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