Restoring Old Plastic Parts ?

[Pete B]

I have a Panasonic Toughbook and several of the plastic parts are prone
to cracking. I have a feeling that they didn't use a very good formulation
for the plastic. I've broken something like 3 or 4 display bezels, got another
good one and would like to have it last.
Some old Thinkpads might also have similar problems with the plastics aging.
This article says to dip the parts in boiling water but that it only works for
some plastics. It also says that a long soak overnight at cooler temps should
work and I'd probably do a compromise of about 140 deg F overnight but was
wondering if a chemist or plastics expert might know if this makes any sense:
http://www.v8buick.com/showthread.php?2 ... stic-parts

Cut and pasted here:
Tired of breaking the old, brittle plastic clips that hold on exterior and interior trim? Worried that the plastic thermostat housing will either leak or crack after being over tightened? Hoping for a way to rejuvenate the yellowed plastic gears, slides and rollers in that window regulator? Having trouble sliding the plastic handles onto the metal rods that came with that new foosball table? The answer to these and other plastics conundrums is an elixir available at the nearest kitchen sink.
My dad was a plastics engineer for 30+ years. One of the best tips he has given me thus far is to rejuvenate and limber up old and new thermoplastic polymers by soaking them for a minute or so in boiling water. The results with nylon can be especially dramatic. Yellowish nylon goes into the water brittle and comes out supple and milky white. New composite thermostat housings, foosball table handles, and other plastic pieces that must be mounted to metal become slightly more flexible and are an easier and better fit.
The boiling water does not melt the plastic. Soaking nylon in room temperature water for a long time has the same impact as a short bath in boiling water. The chemistry is too complex for just the son of a plastics engineer to explain. Basically the moisture releases tension between polymer molecules that was created when the plastic was first made (molded, extruded, etc.) or that built up over time as the plastic was exposed to sunlight, heat, chemicals or otherwise aged.
Over the years I have only seen good results from putting my plastic parts in boiling water. At worst the plastic seems unaffected, probably a thermoset plastic (rigid body parts, distributor caps, Bakelite, etc.). However, there are myriad plastic resin recipes and plastic products out there and I must include a disclaimer and encourage common sense and caution. Do not soak plastic pieces that include electronics, gaskets, lubricants, paint, adhesives, decals, etc. that are not supposed to be exposed to water. Do not bring a plastic part out of a freezing garage and immediately dunk it into a boiling pot of water. Thin, molded plastic pieces like interior trim or milk jugs might lose their shape if exposed to heat. Heat and moisture from boiling water might not be uniformly transferred through very thick plastic pieces. If you are at all concerned about the temperature of boiling water, then maybe instead try soaking the plastic piece in unheated water for a day or two. Don’t boil a greasy composite valve cover in your spouse’s favorite spaghetti kettle…
Tom Taylor,
RockAuto.com

Ken Lisk responds:
Some additional info on this topic:
- thermoset plastics will not benefit for treatment in water, the cross linking of the plastic occurs chemically generally and it cannot be melted, it will ignite instead generally at a high temperature (distributor cap)
- thermoplastic materials (injection molded or extruded, etc) come in two forms; hygroscopic or hydrophobic
- hygroscopic plastics will absorb water and will become more supple, they will also grow in size slightly, over time they will acclimate water content to the ambient environment, nylon is a good example of this type of plastic as it will absorb a large amount of water, different polymers of this class will absorb different amounts of water (trim pieces, the aforementioned rollers,etc), you need to be a little bit careful as when you push water into this type of plastic, especially with heat, it could warp a internal molded in stresses are relieved
- hydrophobic plastics are unaffected by water as they do not absorb it, boiling in water will make no difference

http://en.wikipedia.org/wiki/Thermosetting_polymer

http://en.wikipedia.org/wiki/Thermoplastic

http://en.wikipedia.org/wiki/Hygroscopy#Polymers

[brchan]

The CF-51 toughbooks have a design flaw where the LCD bezel cracks in the corners, since the lid flexes and the hinges are very tight. Also, the battery flaps can rip off easily.

I have never tried boiling plastics, but you can use a Magic Eraser to help restore the ruberized finish of scratched lids and to a lesser extent, the plastics.

If you are looking for composition of the plastics, I have compiled an incomplete list on mainstream Thinkpads (T, W, X) from the T40 to Tx30 years:

Palmrest, LCD bezel, Keyboard Bezel:
-PC + ABS-FR(40) on T60 and newer
-PC/ABS on T4* and probably on X4*

Base cover:
-Magnesium alloy AZ91D on 's' model T series, most X models
-Carbon Fiber Reinforced Plastic PA6-CF20 FR(52+61) on all T models
-ABS (ABS-FR(40) maybe?) on all R-series models except 14.1" R61 and R400
-GFRP (W/T510 to W/T530), haven't looked at specific composition yet

Lid:
-Magnesium alloy AZ91D on T60, T4*, all X series
-PC cover on Magnesium alloy AZ91D LCD frame on T61, T400, T/W500, R61, R400
-ABS (ABS-FR(40) maybe?) on all R-series models except 14.1" R61 and R400
-HEPC on T410, haven't looked at specific composition yet
-CFRP + GFRP hybrid on T420, T430, 's' models, T/W510 - T/W530, haven't looked at specific composition yet

[Pete B]

Interesting, thanks. Do you have any idea if the boiling water idea should
work and if it is safe?

CF-51s are so cheap that I would just buy another one rather than digging
into them and I have quite a few at this point. Finally decided to dig, and
found actually that the screws that hold the rails onto the panel were loose
on everyone that broke. I think that a better thread locker is needed and
would hold it all together for a more rigid assembly. The lid should have
had ridges for more strength.

Oil on the hinge is a good idea also.

It runs too hot in my opinion and the cooling system is rather odd, so I'll
probably give up on it.

[MikalE]

Age and heat are any plastics two worst enemies. Plastic continues to outgas its entire life and the more it outgasses the more brittle it becomes. This is usually completely undetectable except in decades-old plastics. Some formulations become more brittle than others.

UV also destroys many plastics, polyethylenes, and polypropylenes. Not that anyone here leaves their Thinkpad out in the sun, but you get the idea.