Tuesday, December 4, 2012

How to Mix a Weight/Volume Paraloid B-72 Solution



What is Paraloid B-72?

Paraloid B-72 (formerly called Acryloid B-72) is a stable clear acrylic resin used in conservation as a coating, consolidant, and adhesive. B-72 is an ethyl-methacrylate copolymer soluble in acetone, toluene, xylene, and ethanol. Since most historic wood coatings are insoluble in aromatic hydrocarbons, B-72 has proved to be a safe barrier coat and surface consolidant on the majority antique furniture surfaces. Also, since the resin is not soluble in aliphatic hydrocarbons, paste waxing over the surface is still a viable maintenance procedure. Paraloid B-72’s thermoplasticity, solubility parameters, and durability are the primary reasons that it has found extensive use in conservation treatments.

Supplied Forms

B-72 can be purchased either already mixed in solution or in clear, odorless pellet form ready to dissolve in a custom solvent blend and concentration.  I have found the latter method easy enough for my practice. Requiring no more than a few minutes and a few simple tools, one can easily mix their own B-72 solution. The following is how I go about the task.


The Tools

Digital scale with 0.1 g resolution.
Small glass jar with lid
Cheese cloth
Cotton/ hemp string
Small funnel
Permanent Marker
Measuring cup measuring ml
Tap water
Desired solvent(s)
Paraloid B-72 pellets

Mixing it Up

Because we will be making a weight/volume solution, the first task is to decide the final desired volume. For this run I have decided I want only 100 ml of final solution. Using your measuring cup, measure out 100 ml of tap water and transfer it to the clean glass jar.


Mark the volume with a permanent marker on the side of the jar. You may discard the water and towel dry the jar. You now have a mark on your jar displaying your final volume.


Setting the jar aside, take your digital scale and weigh out your pellets in grams. To figure the concentration percentage of the solution, you only need to know the grams per 100 ml. If you want a 20% solution, you will use 20 grams pellets for the final solution of 100 ml. Note that I did not say “per 100 ml of solvent”. Weight/volume solutions are figured by adding solids first and then “topping up” with solvent to your desired final volume.



Once you have your 20 g (for the 20% solution), take a small square of cheesecloth and tie the pellets into a bundle with the string. You do not want to use synthetic string for this as it may end up dissolving depending on your solvent blend. Make sure to leave at least 6” of string for a handle for the pouch. Drop the pellet bundle into your glass jar with the string hanging out.



Now, using your funnel, “top up” with solvent to the permanent marker line at 100 ml. Pull the string up and screw the lid on a best as you can to allow the bundle to suspend in the solvent. 


Check every hour or two. Dissolution time obviously varies greatly depending on amount of resin and the solvent choice. When the B-72 is completely dissolved, you can pull out the cheesecloth and discard. You now have your 20% Paraloid B-72 solution. Simple as that. No mess, no fuss.




The Solution Dilution Solution

Ah, but wait… What if I want to try different concentrations for my project? The solution for your solution dilution is found in Pearson’s Square. Pearson’s square is a formula used to change concentrations of solutions. It is as follows:

A Stock Solution (%)
B New Desired Solution (%)
C Diluent (%)
X Part of Stock needed for New
Y Part of Diluent needed for New

X = B – C
Y = A – B
X + Y = D

So, for example, say I took my 20% solution and wanted to make a 5% solution out of it. In order to determine how much more solvent to add (diluent), I plug my numbers in the formula…

A Stock Solution (%) = 20
B New Desired Solution (%) = 5
C Diluent (%) = 0 (There are no solids at all)
X Part of Stock needed for New
Y Part of Diluent needed for New

Parts of stock solution needed:  5–0=5
Parts of Diluent Needed:  20-5=15
So, 5 Parts stock solution to 15 parts diluent = My 5% desired solution.


I hope this helps anyone who has wanted to try B-72. This method can be used for any resin. I found it is much preferred to allowing the resin to clump in the bottom and have to periodically stir it up. This cheesecloth method really is very hands off. Any questions? Leave a comment and I’ll get back to you.

RESOURCES

Paraloid B-72 pellets.  Available from Talas 330 Morgan Ave Brooklyn, NY 11211  212-219-0770 http://talasonline.com/


8 comments:

  1. Hi,

    Don't you have obtained the same result : a 20% Paraloid B-72 solution, just by adding 80 ml (= 80 grams) of solvent to the 20 grams of paraloid pellets?

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  2. Hello,

    In a Weight/Volume solution the resin is weighed and the liquid is measured by volume. This is not interchangeable because some resins that weigh a lot may not have a lot of volume or conversely they may be very light but not actually weigh much of anything. So trying to change to 'volume to volume' doesn't translate the same for each solution. Hope that helps.

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  3. Thank you for your explanation.

    And according to you: when some commercial products are sold already mixed, as for exemple this one:
    http://www.geant-beaux-arts.fr/Peinture/Peintures-acryliques/Additifs-et-mediums-pour-peintures-acryliques/Paraloid-B72.html

    Do you think they used the same method than you?

    I ask you this because when i see a solution such as a paraloid B72 in which is written 10%: i don't know what these 10% are? i mean : are they 10% in mass? in volume? in mass or volume of the maximal solubility of the paraloid in the solvent?... or are they always as you seem to say : a weight/volume solution ?

    At least , do you use vapour mask in order to protect you from the solvent?

    Thank you

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  4. This comment has been removed by the author.

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  5. W/v solutions are standard in the conservation profession. I would be surprised if this product isn't w/v.

    Yes, with aromatic hydrocarbons I always use a half mask respirator. If you are using something less toxic you might be able to get by with one of these excellent carbon fiber masks: Carbosorb Masks
    They are very comfortable to wear for long periods of time.

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  6. Hi Joshua - love the blog, and very jealous of your setup (it'll happen for me one day!!).
    I'm predominantly a book conservator, but my family has had a model galleon hanging around since I can remember, and now that I've got a little more time I want to try my hand at some minor repairs, and have decided on Paraloid B72 as the most logical adhesive. Thanks so much for the tips on how to make it, and I'm sure the cheesecloth method will work for making Klucel and SCMC too - however, I'm very unsure about what percentage to make up the solution - I don't want it so runny that it's dripping down my arms, but I'm also not aiming for a wax-like substance! Any advice on what would be the best % for a bog standard adhesive for wood. Many many thanks! Liz

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    Replies
    1. Hi Liz,

      I don't have much experience with B-72 as an adhesive but I would probably start at 50% and dilute it by eye. This kind of mixing is not uncommon. I do this with shellac all the time: mix it thick and dilute by feel. You could look for Stephen Koob's recommendations. I know he's spent a bunch of time working with B-72 as an adhesive. He's got a few articles published on the topic.

      Thanks for your interest. I hope you get your practice launched and out into the world soon. Be well!

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  7. Gracias,me ayudo mucho!

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