Delrin handle knives in mineral oil

Cap’n Smudge

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So I had some schrade OT's that were a bit crusty. I put them in a jar of mineral oil to soak a bit before cleaning them. Then life got busy and I forgot they were in there. Upon realizing this a month and a half later I got them out to clean them. They have suffered no ill effects. So I began to wonder if prolonged submersion in mineral oil could affect them badly. Or could they be left indefinitely without damage? Does anyone know?
 
I wouldn't think mineral oil would effect it at all,

Polyoxymethylene was discovered by Hermann Staudinger, a German chemist who received the 1953 Nobel Prize in Chemistry. He had studied the polymerization and structure of POM in the 1920s while researching macromolecules, which he characterized as polymers. Due to problems with thermal stability, POM was not commercialized at that time.
Around 1952 research chemists at DuPont synthesized a version of POM, and in 1956 the company filed for patent protection of the homopolymer. DuPont credits R N MacDonald as the inventor of high molecular weight POM.[2] Patents by MacDonald and coworkers describe the preparation of high molecular weight hemiacetal (~O-CH2OH) terminated POM,[3] but these lack sufficient thermal stability to be commercially viable. The inventor of a heat-stable (and therefore useful) POM homopolymer was Dal Nagore,[4] who discovered that reacting the hemiacetal ends with acetic anhydride converts the readily depolymerizable hemiacetal into a thermally stable, melt processable plastic.
DuPont completed construction of a plant to produce its own version of acetal resin, named Delrin at Parkersburg, West Virginia, in 1960. Also in 1960, Celanese completed its own research. Shortly thereafter, in a limited partnership with the Frankfurt firm Hoechst AG, a factory was built in Kelsterbach, Hessen; from there, Celcon was produced starting in 1962, with Hostaform joining it a year later. Both remain in production under the auspices of Ticona (a subsidiary of Celanese), and are sold as parts of a product group now called Hostaform/Celcon POM.

POM is characterized by its high strength, hardness and rigidity to ~40 °C. POM is intrinsically opaque white, due to its high crystalline composition, but it is available in all colors. POM has a density of ρ = 1.410-1.420 g/cm3.[5]
POM homopolymer is a semi-crystalline polymer (75-85% crystalline) with a melting point of 175° Celsius. The POM copolymer has a slightly lower melting point of 162 – 173° Celsius.
POM is a tough material with a very low coefficient of friction. However, it is susceptible to polymer degradation catalyzed by acids, which is why both polymer types are stabilized. Both homopolymer and copolymer have chain end groups (introduced via end capping) which resist depolymerization. With the copolymer, the second unit normally is a C2 (ethylene glycol) or C4 (1,4-butanediol) unit, which is introduced via its cyclic acetal (which can be made from the diol and formaldehyde) or cyclic ether (e.g. ethylene oxide). These units resist chain cleavage, because the O-linkage is now no longer an acetal group, but an ether linkage, which is stable to hydrolysis. POM is sensitive to oxidation, and an anti-oxidant is normally added to molding grades of the material.
POM advantages:
High abrasion resistance
Low coefficient of friction
High heat resistance
Good electrical and dielectric properties
Low water absorption
 
Thanks. Your reply has me asking another question though. It is my understanding that you have to worry about out gassing with celluloid handles due to the formaldehyde. Is that true of Delrin as well and would storage submerged in mineral oil prevent that?
 
I have not seen Delrin off gas. Celluloid does, and its nasty. It's ruined countless straight razors.
 
Delrin does not produce any corrosive gases as it gets older.
 
So I had some schrade OT's that were a bit crusty. I put them in a jar of mineral oil to soak a bit before cleaning them. Then life got busy and I forgot they were in there. Upon realizing this a month and a half later I got them out to clean them. They have suffered no ill effects. So I began to wonder if prolonged submersion in mineral oil could affect them badly. Or could they be left indefinitely without damage? Does anyone know?

I did precisely the same thing with an older Schrade-Walden 25OT Folding Hunter that I'd bought on the 'bay. It was a bit grimy/gummy when I received it. So, I immersed it in USP-grade (laxative) mineral oil, in a zip-loc bag, and essentially forgot about it for a span of weeks, if not months. When I took it out, I washed it in hot water & dish detergent, rinsed & dried it all out. No issues at all, as if it was never in there in the first place (only difference was it was clean! :)).

As mentioned, Delrin doesn't produce corrosive off-gas products, nor any that would cause the handles themselves to deteriorate. Some older versions of Delrin seemed to have a relatively rare issue of fogging/hazing (some old Case Sod Busters have 'black' Delrin handles that have hazed to a grayish color). I think that issue had something to do with off-gassing of a different kind, when brand-new knives were left in factory-sealed packaging for too long, and not allowed to 'breathe' when the Delrin was new. The 'haze' left on the material was likely some kind of oxide. But those are pretty rare in occurrance, even on the older ones, and I've never seen it in newer generations of Delrin-handled knives. I assume it's an issue that's been engineered out of the product, over time.


David
 
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I think that what you are seeing as fogging/hazing is due to UV exposure rather than off gassing. I have a Schrade little finger that is hazed on the portion of the handle that sticks up out of the sheath on the outer/exposed side of the handle.

Ed J
 
I think that what you are seeing as fogging/hazing is due to UV exposure rather than off gassing. I have a Schrade little finger that is hazed on the portion of the handle that sticks up out of the sheath on the outer/exposed side of the handle.

Ed J

I've seen those too. A lot more of those, actually, often with heavy fading on only one side (knife in a display case, for example). But there have been some old knives from Case that had the hazing issue from being sealed in airtight packaging, while the 'new' Delrin was still emitting some by-product of manufacturing. As I'd mentioned, it didn't happen very often, but there have been some examples out there.

Some will 'fade' a bit in color from the UV exposure, but it's not like the grayish 'coating' seen on the others that resulted from the off-gassing issues. There's a different look to the hazing from off-gassing, in that it's not quite as diffuse and uniform as the fading from UV. It looks more like some sort of chemical had been washed over the material, leaving a somewhat irregular hazy coating on it (similar in patterning to the way a patina randomly/irregularly develops on a blade, from exposure to foods, etc.).


David
 
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So I had some schrade OT's that were a bit crusty. I put them in a jar of mineral oil to soak a bit before cleaning them. Then life got busy and I forgot they were in there. Upon realizing this a month and a half later I got them out to clean them. They have suffered no ill effects. So I began to wonder if prolonged submersion in mineral oil could affect them badly. Or could they be left indefinitely without damage? Does anyone know?

Mineral oil won't hurt Delrin.

Thanks. Your reply has me asking another question though. It is my understanding that you have to worry about out gassing with celluloid handles due to the formaldehyde. Is that true of Delrin as well and would storage submerged in mineral oil prevent that?

Completely different chemistries. Celluloid is inherently unstable. It is essentially gun cotton, but with the addition of plasticizers. As the plasticizers work their way out of the celluloid, you are left with the gun cotton, which is known to decompose, releasing nitric acid. Not good. Delrin is an acetal plastic. The Delrin polymer itself is stable as a table. See further comments below about other chemicals which may be added to certain grades of Delrin.

I think that what you are seeing as fogging/hazing is due to UV exposure rather than off gassing. I have a Schrade little finger that is hazed on the portion of the handle that sticks up out of the sheath on the outer/exposed side of the handle.

Ed J
Fading on one side could be due to UV. Unmodified Delrin is not terribly resistant to UV. There are new modified grades of Delrin which are fairly resistant to UV.

I suspect that the "hazing" could be due to plasticizers. Plasticizers are low molecular weight compounds which settle between polymer strands and act as internal lubricants to polymers, with the result that the polymers are tougher. Plasticizers were more commonly used 20-100 years ago than they are now, though they are still commonly used. Plasticizers are not bonded to the polymer molecules, so they move around. It is common for plasticizers to migrate to the surface, then migrate back into the polymer. It is also common for plasticizers to migrate to the surface, encounter some contaminant, and get trapped on the surface. When that happens, the result is a haze or scum on the surface. You should be able to remove such a haze with solvent.
 
The things you learn on here , on a quiet Saturday morning. :thumbup:
 
I scared up that little finger and worked on the hazed portion of the cover with a fine wire brush (not a power tool) and the discolored area cleaned right up. The sawcut ridges were not damaged significantly and the covers both look good after that treatment. Unfortunately, I didn't have the presence of mind to take before and after photos to show you guys. I like delrin as a cover material because of its tolerance to hard work and bad environments. For a working knife, it is hard to beat for practicality. Maybe micarta, but delrin might be more resistant to staining from ugly gunk than a light colored micarta.

Anyway, more free opinion from Ed J...
 
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That's why I love this place - ask a question, then just sit back and await your answer. Thanks to all replies!
 
Found this thread in searching on 'Delrin' and 'haze' and 'plasticizers', per Frank's informative post. Very illustrative examples, with pics:

Scale found on old 300 series Delrin

Discussion in the thread suggests use of mineral oil as a means to clean up and/or mitigate the hazing issue on some Delrin-handled knives.


David
 
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