Why BLO CA

[pegasus70]

I have been using the BLO CA finish for a while now. But I have to admit I use it because "it seems to be what most others do". Being the curious type, I was wondering why that particular combination is used? I suppose it is a chemistry question. Why not CA alone? Why not mineral oil and CA, or Lacquer and CA, or Polyurethane and CA. Anyone have an answer to the "why" for that particular finishing technique? What is the synergy between these two that makes the combination better than either alone and why that particular combination?

 

[ed4copies]

If you are up for a little "light reading", follow this link to about 100 threads addressing your question. (I doubt ANY will ANSWER the question, since we really KNOW very little about this)

http://www.penturners.org/forum/searchresults.php?cx=partner-pub-6184519705972353%3A6714782601&cof=FORID%3A9&q=why+BLO+with+CA&sa=Go

This particular thread has a lot of "expert" opinion, that might help:
http://www.penturners.org/forum/f28/why-does-blo-speed-up-ca-cure-time-49645/
(Entry #9 is the same as Don's quote below)

 

[D.Oliver]

I only use BLO on about 10% of the pens I do. Other than that I use staight CA. The reason I use BLO is to make the grain "pop" or to improve chatoyance. BLO is also a mild activator for CA. From my personal experience with BLO; less is more. If you get too liberal with it, you end up with cloudy spots.

 

[chrisk]

I use BLO for I became accustomed with after following a video uploaded by a member here. After that, every time I tried to apply CA without BLO it was a mess.
- Empirically I'd say that IMHO BLO acts as a lubricant.
- The activator function, as mentioned by Derek above, is my second guess.
- And finally, the pop-up effect is something more visible.

 

[its_virgil]

Here is an answer given to the question on another forum. Enjoy:

Linseed oil, a (semi-)drying oil, will polymerize under influence of
oxygen/radicals. The double bonds in the linseed oil fatty acids
'connect' to each other, and because there are three fatty acids in
each molecule, this creates a 3D network of polymer molecules, i.e. a
resinous 'plastic'.

BLO, a linseed oil with catalysts added, polymerizes a lot faster, but
yields basically the same resin. Since (B)LO is yellow to begin with,
the resin also is. Due to light influence over time, LO resin will
yellow some more. Can't think of anything that will turn it black,
other than fire, sulfuric acid, or maybe a wrong catalyst (or way too
much of it).

That being said, the CA/BLO resin is a completely different resin. In
BLO, the cross-links occur between individual fatty acid residues, so
the triglycerides (the BLO molecules) are attached to one another,
creating a true resin. In CA, the cyanoacrylate molecules attach to one
another, creating a polyacrylate linear polymer. In CA/BLO, the
cyanoacrylate monomers and oligomers (short chains of CA molecules in
the process of becoming a polyacrylate) basically act similarly to the
catalysts in BLO, in that they accelerate the activation of the fatty
acid double bonds. In contrast to the normal BLO reaction though, the
CA mono/oligomers actually attach to a fatty acid, then attach another
CA or BLO molecule on the other end of their chain. You basically get a
resin in which CA mono/oligomers form bridges between the LO molecules,
so you get a copolymer resin.

Interestingly, it should be possible to control the average CA chain
length in the bridges, thereby influencing the properties of the resin.
Whether that can be done by time control, temperature, additives, or
choice of CA (thin, thick; methyl, ethyl, octyl, etc), I have no idea.
Don't even know whether any research on CA copolymers exists. Haven't
found it yet...

Cheers

Henk

| Dr. Henk J.M. Verhaar | |
| Principal | e-mail: hverhaar@... |
| Ecotoxicology specialist | home: henk@... |
| ENVIRON Netherlands B.V. | |
| Zeisteroever 17 | phone: +31 30 698 6218 |
| NL-3704 GB Zeist | fax: +31 30 698 6239 |
| the Netherlands | |

 

[pegasus70]

Based on my experience, I agree with the "lubricant" idea as well as "popping the grain". But other substances can do that as well. Not sure that speeding the curing process for the CA is worth the effort. It isn't like the stuff takes days to cure after all. Certainly, one can add another coat very quickly, even without accelerator (which I never use).
I have seen videos where BLO is used with each coat. Others where it is used only on the first coat. Without knowing how this combination works, it is hard to say whether one technique has more merit than another,

OK, I admit I am overthinking this. What can I say, I like to understand what I am doing.

 

[pegasus70]

WOW Excellent reference Its Virgil! I actually understood a fair amount of it. (I would be lying if I said I understood every word).

Basically, the combination creates a polymer resin consisting of fatty acids from the oil linked to the CA molecules. Pretty cool. That, of course, leads to the next question. What is the advantage of the combined resin? is it harder? More durable? More flexible?

Any polymer chemists out there?

 

[its_virgil]

Another answer from Dr. Henk Verghaar, Phd. Henk is an eco-toxicologist and I assume his doctorate is in some field of chemistry. He was very active in the Yahoo! group a few years back. Anyway, enjoy.


BLO by itself cures through exposure to oxygen. Oxygen from the air will oxidize the double bonds in the fatty acid chains of the BLO triglycerides (and remember, all vegetable oils and animal fats consist of triglycerides). These oxidized triglycerides will then attack further double bonds, and attach to them, so that you get a (3D) network of triglyceride molecules. Basically what you get when BLO cures is a natural resin (plastic if
you like). BLO, in contrast to raw linseed oil, contains catalysts (called a siccatif, usually consisting of heavy metal salts) that considerably speed up the process. BLO cures in hours to days, whereas raw linseed oil needs weeks to months to cure. However, when combining BLO (or raw linseed oil) with CA, a reaction will take place between the CA and the double bonds of the fatty acids. In effect you get a co-polymer resin of CA and BLO molecules. Since CA is so reactive, this process is much more rapid than BLO curing. The BLO itself is, ideally, completely 'consumed' by the (excess) CA, so no actual normal BLO
curing will take place.

So, no, you don't need to wait -- that is the nice thing about CA-BLO. The advantage of CA-BLO over straight CA is that you get a more flexible, less brittle resin than with polymeric CA alone.

On a side note, I use CA as sanding sealer on certain things I make, notably on grainy (but very strong) hardwoods I use for making walking sticks, such as wenge and surinam brownheart (ouacapou). Gives a super smooth finish with all the grain filled in with the cured CA/sanding dust slurry -- this brings out the grain pattern nicely. If I treat these CA
slurry sanded sticks with BLO shortly after CA-sanding, apparently not all of the CA has completely polymerized, since it appears that I get a different type of finish than when putting on the BLO after a couple of days. Looks like the freshly cured CA still has potential for reacting with the BLO...
Dr. Henk Verhaar, Phd

WOW Excellent reference Its Virgil! I actually understood a fair amount of it. (I would be lying if I said I understood every word).

Basically, the combination creates a polymer resin consisting of fatty acids from the oil linked to the CA molecules. Pretty cool. That, of course, leads to the next question. What is the advantage of the combined resin? is it harder? More durable? More flexible?

Any polymer chemists out there?

 

[chrisk]

Thanks for the info Don. Really interesting and many parameters approached here.

 

[scottsheapens]

Virgil, you took me back 30+years to my high school and college chemistry. STOP - I realized I hated that subject....but your information from Dr. Henk was very informative. I actually followed a lot of it.

 

[sbwertz]

I use CA/BLO because it gives me the finish I like EVERY TIME. It is the most consistent finish I've tried. It is about the most foolproof CA finish I've ever tried. I've been using it for almost 4 years, and the only failures I've had were when I left my CA in the shop in 100 plus degree temperatures. As soon as I replaced the CA, the finishes came out perfect again.

 

[hilltopper46]

There are a number of us who use no BLO - just straight CA. I'm surprised no one else has jumped in here.

For me personally the use of BLO makes the finish too soft and slows the process. It's my go to finish, and while I don't even begin to hold a candle to some on here, I am currently in the process of completing my 800th numbered pen.

 

[Jim Burr]

There are a number of us who use no BLO - just straight CA. I'm surprised no one else has jumped in here.

For me personally the use of BLO makes the finish too soft and slows the process. It's my go to finish, and while I don't even begin to hold a candle to some on here, I am currently in the process of completing my 800th numbered pen.

I'm one of them Tony. The failure exists from people not trying. "Can some one tell me how to do this or how to do that...." Success exists from doing what Joe Blow does because he told you how to do it.
I am a few years from middle age and still prefer to learn on my own where possible. I did ask a few questions last year about kitless equipment and then again a few days ago about decals after trying several on my own. There are some basic "Do this and don't do that" that many people are unwilling to try on their own.
Having never used BLO on a pen (there was never a reason for it) and after several dozen attempts, I learned and moved on. I did use BLO on a canoe paddle in 1973 for a Boy Scout trip to Canada, so there is some history.
I guess society has reached a point where we ask to be taught rather than thinking about and learning on our own.

 

[pegasus70]

"The advantage of CA-BLO over straight CA is that you get a more flexible, less brittle resin than with polymeric CA alone"

There it is, the answer I was looking for. What this suggests to me is that each finish coat should be the combined CA BLO combination to make sure that each layer is the same "more flexible" polymer.

I appreciate the efforts by those who found the answers. Nicely done. Glad I joined the forum.

 

[its_virgil]

I use CA and boiled linseed oil and I use both on each layer.
Do a good turn daily!
Don

 

[steve worcester]

OK, (pardon my ignorance) do you do coats of BLO and then CA over it, of some mixture of the two for a finish?

 

[pegasus70]

Speaking only for myself, apply the BLO then immediately apply the CA. Allow to dry then repeat. I usually do this between 3 and 6 times. That's just me.

 

[mark james]

Well Yes... I do have access to a PhD. Polymer Chemist ("Wifey"). She's pondering an answer.

I'm up at 4:30 AM... so Wifey will get back to me. Something tomorrow!

 

[its_virgil]

I put both CA and boiled linseed oil on the same applicator and apply one followed by the other. Sometimes CA first and sometimes the oil first. You can see my application at http://www.RedRiverPens.com/articles (if you would like to.)

Do a good turn daily!
Don

OK, (pardon my ignorance) do you do coats of BLO and then CA over it, of some mixture of the two for a finish?

 

[mark james]

OK, got some info... just need to figure out what it says... I'll get back to you in about an hour after I get some coffee!:frown:

 

[mark james]

Well, I thought coffee might help...

Some background. I have college degrees in Music Therapy, Music Education and Recreation Therapy - got a b- in High School chemistry because I...tried. My wife has the PhD. in Inorganic Chemistry and has worked in Industry for the past 30 yrs... so questions will go "through" me .

From Wifey:


I am taking part of this from Wikipedia. Hope this helps.



Later today (I'm at work already), I'll try to get a more direct response to the original question.
"Linseed oil is a poly unsaturated fat. The unsaturation is where the reaction takes place between the different molecules linking and crosslinking them together. This linking and crosslinking reaction is what is called 'drying'.


Today, most products labelled as "boiled linseed oil" are a combination of raw linseed oil,petroleum-based solvent, and catalysts to accelerate drying. Linseed oil does not cover the surface as varnish does, but soaks into the (visible and microscopic) pores, leaving a shiny but not glossy surface that shows off the grain of the wood. A linseed oil finish is easily repaired, but it provides no significant barrier against scratching. Only wax finishes are less protective. Liquid water penetrates a linseed oil finish in mere minutes, and water vapour bypasses it almost completely. Because it fills the pores, linseed oil partially protects wood from denting by compression.


Cyanoacrylates may be different types. It may say on the label what type is in the glue. This may be why certain brands behave differently. Cyanoacrylates include methyl 2-cyanoacrylate, ethyl-2-cyanoacrylate (commonly sold under trade names such as "Super Glue" and "Krazy Glue"), n-butyl cyanoacrylate and 2-octyl cyanoacrylate. The latter are the surgical glues. standard "superglue" is 100% ethyl cyanoacrylate. Cyanoacrylate glue has a low shearing strength, which has led to its use as a temporary adhesive in cases where the piece needs to be sheared off later. Common examples include mounting a workpiece to a sacrificial glue block on a lathe.


CA's react with water, and other OH's to polymerize themselves. (skin moisture, wood moisture, cellulose OH's.) However they don't fill pores very well.


From what I saw linseed oil fills pores and penetrates the wood and allows moisture through so it may drag the CA deeper into the wood and allow the water that CA needs to react in. CA may also react with the unsaturated sites in the Boiled Linseed oil so a mixed polymer will be formed. The CA portion brings more water resistance and acts as additional crosslinking to the BLO."



Uh... OK Dear.

Later today I'll try to get a more direct "Woodturners" response to the original questions.

 

[KenV]

Mark - I have been doing the oil-CA finish for some years. I do not have Boiled Linseed Oil (BLO) around my place because of it's challenges with spontaneous combustion, and it's tendency to darken significantly over time when used with wood. (Many an antique has been degraded by application of BLO as a "restorative" finish)

I use "stand oil" -- a product made by partial polymerization of linseed under heat in the absence of oxygen. This product is available under several brand names as an oil finish. Tru-Oil Gun Stock Finish and Tried-and-True Oil are two products I can get locally or shipped through the mail (Alaska). The absence of petroleum products allows shipment by mail and airline baggage.

I get similar results as others report using the BLO. My observation is that the finish is a bit soft off the lathe, but hardens more as it sits a few days. My surmise is that the cross linking is not complete instantly, and continues a few days, especially with the thicker CA formulations. Never have a oil-CA finish do the brittle cracking.

The finish does have a yellow tint to it.

 

[mark james]

OK... Wifey's response to my "Huh..." (We have such stimulating conversations after 29 wonderful years of marriage) :biggrin:
---------------------------------------------------------------------------
"I think you asked the following. Why does mineral oil mixed with CA behave different than boiled linseed oil/CA. The second question is why urethane finish behaves differently also? Why are people getting cracking?

I think we've established that the linseed oil is unsaturated fat and that CA will react with it through those unsaturated sites building a 3D cross linked network copolymer. OK why doesn't mineral oil do that? Mineral oil is high boiling petroleum oil so it doesn't have the polyunsaturated fats that react to form a polymer. It won't form a polymer film. It is more like a solvent - diluting the CA, not adding to building more of a network.

Polyurethanes...now I can go on for a while about them. 90% of urethane coatings are Thermoplastic polyurethanes and are blocky linear co polymers with hard segments which give re-enforcing and soft segments which give flexibility so when the solvent evaporates the polymer will form a 3D network of these hard and soft portions that behaves like a covalently cross linked (the CA/BLO) network. The water born polyurethanes don't have the organic solvent and the polymer is delivered as suspended tiny beads in water that lay down and coagulate into a film. The water born polyurethane coatings are the ones that start out milky white and dry clear and have additives in the formulation that help the tiny beads form a good film. One part urethane coatings do not have many sites for CA to react with, so you will be diluting the CA. You do not form a good copolymer with the urethane. You'll be forming more of a mixture of 2 independent polymers. Don't mix water born urethanes with CA - Bad idea - the water will cause the CA to polymerize quickly - probably glob up before it can be spread.

Why are people getting cracking? This is tough because there are many unknown variables here. I'll give it a SWAG. 1st - what is the type and moisture content of the wood and temperature and moisture content of the air environment. CA reacts with moisture to polymerize. Hot humid days and moist wood will react faster than dry cold days or dry wood. What is the ability of the wood to absorb the BLO/CA mixture? Does it get down into the pores or sit up on the surface. I'm thinking that you need the reaction to get deep into the pores and react more with the cellulose OH's in order to avoid the cracking. I'm thinking that you need good 3D tough networks - i.e. good mixing and fairly equivalent reaction rates of the CA and the BLO with themselves and each other in order to avoid cracking. Patches of CA and patches of BLO where it is poorly mixed may be an issue? Poor mixing can be due to the temperature, moisture of the environment not the technique. On a hot humid day, the half life of the CA reaction will be shorter because there is more moisture driving that reaction.

It's a SWAG. Take notes keep data. "

(Mark's note: SWAG = Simply Wild A..S Guess).
(Mark's take: Bye honey... Thanks, I'm going to ruin some timber. :giggle: