Pontiac Solstice Forum banner

1 - 3 of 3 Posts

·
Registered
Joined
·
7,159 Posts
Discussion Starter #1
[Crosspost] Saw this in this month's RockAuto newsletter. Thought it bears exposing to a wider audience (no personal experience of if it works or not)...

(Calling chickenwire - dude, you know you want to jump in here!) :devil:

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
 

·
Registered
Joined
·
5,430 Posts
Spot on for the most part. Many thermoplastics are hygroscopic - they will absorb moisture. In fact, most of what we mold must be dried prior to molding or else we will have quality problems. The worst of which occurs with polyesters because they can show no visible signs of issues but, if molded wet, become nearly as brittle as glass.

Nylons are very sensitive to moisture, so much in fact that their manufacturers actually publish physical properties "dry as molded" and at "50 humidity". We even have some parts we mold that we moisture treat in the fall and winter months when the humidity is low. Even had a transmission governor gear that had a breakage problem....every Monday...only in the winter. Assembly line would leave the box open over the weekend and at start up on Monday the gears would break. They opened the next box and the problem went away.

I would shy away from the boiling water and recommend just soaking in warm water for a couple of days. Remember me discussing residual stresses? 212 degree water shouldn't cause the parts to warp, but as the author above stresses, it could. Thermoset plastics will not be affected by moisture at all. (Thermosets will not melt under heat - they undergo a chemical transition during molding and will not melt again.) The higher temperature resins tend to pick up less moisture so you're not going to affect their properties much at all. (Thermostat housings, water pump housings, etc.)

Nylons are amazing in the difference in performance. If you're pulling apart a rod and latch assembly or door clips, soaking them in water will make a HUGE difference. Even just squirting with a spray bottle a couple of times for a few days before youj tear it appart will be beneficial. A good example is many years back we had a box full of cheap zip-ties at the plant and they'd snap like potato chips when you tried to use them. Threw a bunch into a bucket of water and the next day you could tie them into knots no problem.

The smaller parts will not likely have a recycle identifier on them - a lot of which are molded from nylon. Parts that are big enough to be identified will have 2 or 3 letters between two chevrons > < to tell you what they are.

>PA< = polyamide = nylon.
 

·
Registered
Joined
·
5,430 Posts
Additional note - the article mentions the slides in windor regulator assemblies. Many of those are of >POM< polyoxymethylene or "acetal". This material is very lubricious and works great in sliding applications. It's wear resistance under light loads is great but more importantly it's coefficient of friction is outstanding compared to nylon. However, it is not affected by moisture.

Another key point the author makes - you will do no harm by moisture treating as long as you're not boiling off labels, gaskets, etc.
 
1 - 3 of 3 Posts
Top