Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Plasticizer problem

Dr. Barry L. Ornitz wrote in message
...
"N Cook" wrote in message
...
I'm aware of the term "doll's disease" relating to the breakdown , to
vinegar, of the soft plastics used on antique dolls. But in my area of
electronics eg "rubber" grommets will "melt" hard plastic storage
drawers, a
mains cable wrapped around a hard plastic topped record deck, over a few
years such storage, will create "melted" ruts in the hard plastic.

Anyone
aware of a precise term for this plasticiser leeching process to

research
it
further, eg temp or humidity effect on the process, surface treatment to
avoid it etc.


What you refer to as "Doll's Disease" is an entirely different phenomena
that the leaching of plasticizer. Doll's Disease is actually a result of
cellulose acetate reacting with the moisture in air to produce degraded
cellulose and acetic acid (the vinegar smell). Originally it was seen in
celluloid movie film, collar stays, etc. Celluloid is cellulose nitrate
with a little plasticizer but the plasticizer has nothing to do with the
reaction. With cellulose nitrate, nitric acid is produced. Once the
reaction occurs, the acid catalyzes further degradation of the cellulosic
plastic. Museum storage in sealed glass cases actually promotes the
process. About all that can be done is to neutralize the acid by washing
in a dilute sodium carbonate or bicarbonate solution, drying carefully,

and
placing the item back in storage with flowing dry air.

The problem you are seeing is the leaching out of plasticizer from
polyvinyl chloride or polyvinyl acetate items. If you are old enough to
remember vinyl automobile seats, you probably also remember the greasy

film
formed on the inside of windows when the car was parked in the hot sun.
Over time, the vinyl would get brittle, shrink, and crack. The film was
plasticizer that evaporated from the vinyl. As it left the PVC, the
shrinkage. brittleness and cracking occurred.
One of the more common plasticizers was bis(2-ethylhexyl) phthalate, more
commonly known as dioctyl phthalate or DOP. It is still in wide use

today,
but many newer plasticizers are also available today such as
trioctyltrimellitate (TOTM), dioctyladipate (DOA), diisononyl phthalate
(DINP), di(2-ethyl hexyl) adipate (DEHA), acetyl triethyl citrate (ATEC),
and even tricresyl phosphate (TCP).

Plasticizers are incorporated with PVC in the manufacturing process.
Contrary to what Armor-All® and similar products might claim, you cannot
put plasticizer back into the vinyl with a surface applied product. Many
products may contain significant amounts of plasticizers. Very soft and
rubbery PVC compounds may contain as much as 40 to 50% plasticizer.
Preventing the leaching out or evaporation of plasticizers from vinyl
products is prevented more by the choice of plasticizer than anything

else,
although low temperatures slow the rate significantly. The Wiki page on
plasticizers lists a large number of plasticizers and tells where they are
most used.
http://en.wikipedia.org/wiki/Plastic...s_for_plastics

About the only way to prevent plasticizer damage to other plastics is to
keep vinyl products away from them. Most coaxial cables for radio
frequency use have a center conductor insulated with polyethylene, a wire
braid shield, and a plasticized PVC jacket. When the plasticizer leaches
from the jacket into the polyethylene, its electrical losses increase
greatly. One modern innovation uses either aluminum foil or metalized
polyester to wrap around the braid preventing the ingress of the
plasticizer. But it also provides better shielding allowing the braid
coverage to be lessened from 90 to 95% coverage to less than 75% coverage
leading to a much lower weight.

Powodzenia.

--
Dr. Barry L. Ornitz, Amateur Radio WA4VZQ

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Many thanks for the full reply.
I was totally unaware of the last point, so have added s.e.r as probably a
lot there are unaware also.
Recently reminded me of this effect because a "rubbery" presumably soft PVC
suspension inside a phono cartridge was leaching plasticizer and softening
the surrounding hard plastic etc. I don't know if it is also related but
often if one "rubber" drive band in a VCR or audio tape deck perishes, then
all the others are likely to fail in a sort of contagion -plasticizer gas
wafting around inside ?


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Default Plasticizer problem

"N Cook" wrote in message
...

Many thanks for the full reply.
I was totally unaware of the last point, so have added s.e.r as probably
a
lot there are unaware also.
Recently reminded me of this effect because a "rubbery" presumably soft
PVC
suspension inside a phono cartridge was leaching plasticizer and
softening
the surrounding hard plastic etc. I don't know if it is also related but
often if one "rubber" drive band in a VCR or audio tape deck perishes,
then
all the others are likely to fail in a sort of contagion -plasticizer gas
wafting around inside ?



You are quite welcome. Eastman Chemical Company, a former employer, made
both cellulosic plastics and a large number of plasticizers. I even worked
on a project to replace plasticized PVC in medical intravenous solution
bags with an elastomeric polyester because of the fears of plasticizers
leaching into the solutions (which they do!). While being more expensive
than PVC, our material was much stronger allowing thinner bags which offset
this higher raw material cost. But the perimeter radio frequency sealing
process required new equipment and the bag manufacturers were unwilling to
modify their manufacturing lines.

As far as VCR decks, I cannot think of any mechanism whereby the failure of
one drive belt via plasticizer migration would cause the others to fail
unless the plasticizer leaching from one belt actually dripped on another
belt. Remember that all belts were likely made at approximately the same
time, and had been in the VCR exposed to similar high temperatures for the
same time too.

--
73, Dr. Barry L. Ornitz WA4VZQ

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