Re: Automobile tires and friction

[John Barrer <forcejb@YAHOO.COM>]

PMMA is a glassy polymer (so-called crystalline
polymers like some PE really just have regions of
order, but are not crystalline throughout). Glassy
polymers which are not cross-linked (as tire rubber
is) typically undergo several transitions as they are
heated; these transitions are characterized by large
declines in the elastic modulus. Since polymers have a
range of molecular weights, the final transition
occurs over a finite temperature range, not at a
single well-defined "melting point"(like water, eg).
John BArrere
--- Bernard Cleyet <anngeorg@PACBELL.NET> wrote:
> It destructs (as in destructive distillation in a
> vacuum) before it
> melts?
>
> What is the nature of the melting of poly methyl
> methacrylate?   Or are
> you implying it never solidifies (like glasses).
>
> bc who's curious and too lazy to research in my
> materials texts
>
>
> John Barrer wrote:
>
> > Tires do not melt when heated (moderately); rather
> > they soften. Vulcanized rubber is a cross-linked
> > structure that cannot "melt" unless some of the
> > cross-links (vulcanization sites) or other
> chemical
> > bonds are broken, so the prospect of a liquid
> rubber
> > layer seems pretty remote. John Barrere
> >
> > __________________________________________________
> > Do You Yahoo!?
> > Yahoo! Sports - Coverage of the 2002 Olympic Games
> > http://sports.yahoo.com


__________________________________________________
Do You Yahoo!?
Yahoo! Sports - Coverage of the 2002 Olympic Games
http://sports.yahoo.com