The correct name for plasticity threshold in epoxies

This is commonly called the zitsoftyet point.

Those fumes will make you stupid.

Worked with epoxy paints for 8 straight years best thing I ever did was get away from it. Are you talking about the flash point where the epoxy begins the drying process. We called it flashing because the chemicals are racing out of the epoxy at such a high rate of speed. Acetone evaporates so fast it heats up epoxy and begins the drying process or curing.

I refuse to work with any resin systems that depend on MEKP as a hardener. They can blind you instantly, or kill you in the long term so I appreciate your comments.

As for "flash point" no, that's not it.

I'm working on cored composites mostly where fiberglass or carbon fiber are saturated with a two part epoxy and allowed to cure at room temps.

Afterwards, the careful application of additional heat elevates the temperature of the part past what it was when it cured and bumps the threshold of plasticity beyond it's normal point as a room temp cure.

The composites industry has a name for that threshold and I'm trying to find out what it is.

Thanks for the response

Five boys! Wow! I thought I had my hands full with one daughter!

L. J.

I believe I found a place where you can get the answer. Try this link.

http://www.chemicalprocessing.com/experts/index.html

Well I do have a little girl too but she came much later and this screen name was already fixed.

We use to have problems at the shipyard with welders inside doing repairs and the painters using epoxy outide. Espically around the zinc plates. If there was a 30 degree rise in temp inside the boat within 10 ft of the area where expoxy paint was applied the paint would almost slide of the hull making a mess of bulging lumps. Then cleaning it to recoat was horrible a mix of wet /dry epoxy to cut with scrapers and then grind.

I would like to add support to Laughing Jaguar's comment: "I refuse to work with any resin systems that depend on MEKP as a hardener. They can blind you instantly ... ."

Years ago, Fine Woodworking magazine ran a series of reports from woodworkers who used various two part resin wood glues, catalyzed by MEKP, and were subsequently injured. According to one woodworker who lost an eye, one drop of Methyl Ethyl Ketone Peroxide splashed into his eye, polymerized his eyeball into what he called a hard boiled egg. Many products state safety warnings, and recommend using eye protection. For MEKP, those warnings are very very real. One drop and you lose an eye.

I stopped using MEKP forthwith.

I believe that MEK is the activator used in auto body filler. Is this the same as the MEKP?

Bob C asked: "I believe that MEK is the activator used in auto body filler. Is this the same as the MEKP?"

Judging from the smell. . . . I suspect it is. The MEK is standard fare, available from most hardware stores. The P stands for peroxide. In it's purist form, peroxide is said to be highly volatile.

After WWII, when the US army started testing captured V-2 Viking rockets at the White Sands, NM proving grounds, one guy got playful and is said to have tossed a small handful of sawdust in a bucket of peroxide sitting on the back of a jeep.

I am told that when the smoke cleared, the back of the jeep was gone!

The inhalation of fumes from resin systems catalyzed with MEKP can be deadly!

Many years ago, in a moment of shear stupidity, I gave in to a clients insistence that I use the same material as the mold to replicate the fender liners I was making for a production run of Ford GT-40 replicas.

I worked in a closed shop for two days, inhaling those fumes.

Four days after I completed the job, my wife and I could still smell the fumes of MEKP on my breath as I exhaled!

20 years later I appear to be fine. However, no telling what the long term effects of my stupidity might still be.

"Live and learn. . . "

Maybe!

MEK is methyl ethyl ketone. MEKP is the same but as stated, the "P" stands for peroxide. The stories told here about "boiled egg eye" and "missing Jeep parts" are exaggerations, but the stuff IS dangerous. It will catalyze fiberglas resins, but not eyeballs. It will burn readily, having a very low flash point and carrying its own oxygen source, but not on contact with sawdust.

Probably the greatest danger is expired shelf life. If you have this stuff around too long and you see crystals forming inside the cap or in the neck of the container, DON'T touch it! Call the nearest police bomb squad or military explosive ordnance disposal team. Those crystals are explosive and shock sensitive. We had this happen once with a case of 6 1-liter bottles at an Air Force Base where I was doing some contract work, and the EOD Chief told me after the fact that the explosion (out on the disposal range) was "pretty good".

Why didn't you tell me that a few years ago? When clearing out the old paint cabinet there was a small clear plastic tube of activator for fiberglass resin that had turned to crystals. I just picked it up and tossed it in the dumpster.

Oh, sorry, my bad - lemme jump in the wayback machine and re-post that info a few years earlier...

Are you asking about the glass transition temperature? But that's not applicable to a cross linked thermoset resin.

Bobguz

Actually in the composites world, Tg, is the term that is used to evaluate various thermoset resins. There are a variety of methods for measuring Tg, and you will get some variability based upon test method, but in most performance specifications for materials, the the glass transition temperature is a property which is provided by most manufacturers so that the design engineer can properly select materials based upon operating temperatures.

BobGuz asked: "Are you asking about the glass transition temperature?" .

That's it!

Thanks Bob, and all who responded. This time I'll write it down!

L. J.

More commonly, in the composites industry, the temperature you are referring to is called the heat deflection temperature. This temperature is improved (made higher) by post curing. Glass transition is a little different, and different ASTM tests apply.

http://www.matweb.com/reference/deflection-temperature.aspx

http://www.matweb.com/reference/deflection-temperature.aspx

The heat deflection temperature was (is) an issue for composite homebuilt aircraft, because dark paint can get the skin temp high enough (on a hot sunny day) to cause the wing to be "deflectable".

I believe you are referring to the Tg (glass transition temperature). This usually represents the temperature at which the thermoset begins to lose structural integrity.

Glass transition temperature (Tg) is correct. It's a general term used in polymer chemistry. It's the temperature at which a polymer goes from a glassy, rigid structure to a more flexible structure. In an epoxy system, the Tg is typically dependent not only upon cure temperature but also monomer/oligimer structure and curing agent.

How about the SLUMP temperature as when the material cannot support itself anymore.

Cheers garth

The odor you smell when dealing with resin systems catalyzed by MEKP is not the MEKP. More likely, it's styrene monomer. That's the characteristic smell you'll notice in an automotive body shp, boat shop, etc. MEKP is only present in very small amounts and its odor threshold is relatively high. Styrene, on the other hand, has a very, very low odor threshold and can linger on your clothing for several hours after exposure.

Are you thinking of:

Tg (pronounced "tea sub gee") as the Glass Transition Temperature is frequently called out?