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On Apr 11, 1:35 pm, "N_Cook" wrote:

So wood pulp filler could lead to expansion but if a
mineral was used ,as a
filler, then dimensionally stable bakelite would result ?

Not pulp - well, OK... derived from pulp but not the same.
The wood
flour that is used is very nearly pure lignin - that part of
wood that
lends strength and is also hydrophobic - so that big oak
tree out
there does not dissolve in the rain.

So, to the extent that the wood flour used is contaminated
with other
wood components, it might expand when exposed to moisture.
But the
material is heated (twice) and formed under great pressure.
Most of
the water created by the initial chemical reaction is
dissipated in
first heating, the last done under great pressure and
greater heat
completes the thermosetting process - but most of the water
is already
long-gone. And any non-lignin components remaining were
mostly burnt
off in the first go as well.

The smelly plastic is Cellulose Acetate - which goes to
vinegar and a
few other smellies. And there are several other materials
that use
Cellulose Acetate in their formulations to a greater or
lesser extent
- which decay similarly with similar smells.

Peter Wieck
Melrose Park, PA

Celluloid is either cellulose acetate or cellulose
nitrate, both were used as photographic film base and
neither is stable. The acetate smells of vinegar when its
decomposing and nitrate often smells of camphor although
other substances were used as plasticizers. Both shrink,
distort, and disintegrate with age. Acetate does not support
flame while the nitrate is nearly impossible to extinguish
once ignited since it supplies its own oxygen. The latter is
the main reason cellulose nitrate was discontinued for film
base in 1951. Probably most plastic dial windows on old
radios are cellulose acetate.


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Richard Knoppow
Los Angeles
WB6KBL