Someone asked me a question about PVA vs. EVA, and I didn’t know enough to answer. I researched a bit and came up with some intelligent sounding words, but how correct am I? I’ll be grateful, grateful for corrections and additions.
PVA vs. EVA – what’s the difference? Which is better?
Both PVA and EVA are synthetic adhesives. Both are made of acetate compounds suspended in a carrier. Both “cure” by forming long chains of molecules. “Heat cure” or “thermoplastic” or “heat set” adhesives require heat to cure. “Cold” or “cold set” adhesives cure when the carrier evaporates allowing the molecules to come in contact and react. Some adhesives react when exposed to air. “Gorilla Glue” is a type of glue that cures when exposed to air and water. It’s important to know the differences so you can select the correct adhesive for your application.
People often speak of allowing PVA to dry, but that’s not correct. The material doesn’t so much dry as react to form a different material that is a solid instead of a liquid, although there are probably some carrier/solvent materials that do evaporate.
Many forms of PVA exist with different names. “Jade” is one of these. PVA is polyvinyl acetate, a type of plastic. Formulations include the various Jade-named products, common “white glue” products such as Elmer’s, and woodworking glues. If it’s white and liquid, it’s probably some form of PVA.
PVA adhesives are composed of molecules that link together (polymerize) to form a (usually) flexible long-chain resin (polyvinyl alcohol) and acetic acid. I don’t know why they are called “acid free”. Maybe because there is no acid in the uncured product? Maybe the acetic acid released during the curing stage evaporates? Most PVA used in bookbinding (Lineco, Jade 402) is a strong adhesive that sets up fairly quickly. PVA is not usually soluble in water once cured.
Bookbinding PVA should be considered irreversible. If you glue up a book spine with PVA, you will have the devil of a time getting that glue off in the future if the book ever needs rebinding. This may not be a problem when making an inexpensive journal, notepad, box, or slipcase because you’re not likely to want to peel the paper or cloth or leather off the board in the future. Also, PVA doesn’t have much water in it, so it doesn’t cause as much cockling of paper or of paper-backed bookcloth as paste does.
PVA is great for adhering bookcloth to boards. To prevent cockling (on paper-backed cloth) and seep-through (on plain cloth) I like to use a roller to apply the glue quickly. I bought a small, thin paint roller designed for painting behind toilets and a thin white foam roller. Squirt some glue in a shallow tray, make sure there’s not too much on the roller, and go to town. Fast! Easy! But impossible to clean the roller, I find. I keep them in the freezer or fridge, tightly wrapped in something that won’t stick to the glue. I find that heavy freezer bags work well, and by putting a straw in the corner of the seal I can pull most of the air out of the bag as well. I don’t do that much glueing, so I don’t bother with a roller unless I’m doing a few books.
PVA is also great for making boxes – it sets up quickly and makes a strong bond to join walls to bases and to cover the boxes. I found that it made a good strong flat laminated board, but then if I had to sand the edge of the resulting layered board the glue layer was a problem. Paste doesn’t create the problem, but it takes longer to dry, and if you have different thicknesses of board the paste will pull the board into a curve as it dries. Is nothing simple? Are bookbinders simply incapable of giving straight up, yes-no answers? It’s like a darn philosophy class in here.
I think it’s not a crime to use synthetic adhesives on cookbooks, which can be subjected to hard use (by forcing the spine open) or exposed to organic contamination or moisture. The PVA is very flexible and can tolerate lots of abuse, and the cured adhesive resin isn’t delectable to fungi and insects.
The quick-setting nature of PVA can be a disadvantage. If you add just a small amount of starch paste to PVA, it will give you a much longer “open time” before it sets up. This is usually enough time to reposition materials and fuss with corners a bit. Some bookbinders claim that the addition of paste makes the PVA reversible. It makes sense that paste might cause the PVA to form shorter “chains” as it cures, but I can’t give you any proof one way or another. Paste does spoil, and PVA/starch paste “mix” will spoil, so I don’t make up much of that at a time. Methyl cellulose gel is not as strong an adhesive as starch paste, but it doesn’t seem to spoil, so making mix with MC is a good idea. You can mix up a larger amount and keep it handy for quite some time before it becomes runny, and then throw it out because your time is worth more than used mix.
EVA is an oversimplification. EVA stands for ethylene-vinyl acetate, which is another polymerizing compound. It’s similar to PVA but is more often formed into a phenomenal array of sticky, flexible, hot melt, or foamed plastics. Most formulations are inert and non-toxic. There are many different uses for EVA compounds – cling wrap, athletic shoe soles or cleats, foam insoles, padding materials, hot melt glue sticks, drug delivery formulations – too many too list here.
Bookbinding EVA is specific product called Evacon-R. I don’t know of any other brand-name formulations. Evacon-R is reversible. Since Evacon-R is a special purpose formulation, I can’t find as much in the literature regarding longevity tests, strength, reversibility, etc. compared with PVA. The link below is to a forum post in the Conservation Online archives (a wonderful resource) with the earliest mention I found of Evacon:
A newer posting confirms the reversibility of Evacon-R:
I get Evacon-R from Conservation Resources, since I live in the US. It’s more readily available in the UK, I believe.
Other polymerizing adhesives: are legion. Gane Brothers sells something they call “53S” that adheres to almost anything, including pyroxylin-coated bookcloth such as “imitation leather” and vinyls. I sometimes make semi-limp cases for personal bibles with imitation leather – NOT “bonded leather” which shall be mentioned no more – and 53S is the only thing that will form good bonds on round or folded corners or adhere labels to the imitation leather. There are adhesives go on hot and cure when they cool, so they are very convenient for large commercial binderies. I find that these thick hot-melt glues, often found on spines of modern perfect-bound books, almost always become inflexible and brittle over time. Avoid them in your hand binding work.
Exception: modern conservation “heat set” repair tissue has a very small amount of heat-activated adhesive which is normally reversible in alcohol. It can be very useful for repairs on modern, hard paper where it forms a thin, nearly invisible bond. BUT … over a long period, there is a risk that the polymers or breakdown products could migrate into the paper, so I would never recommend using such products to repair valuable or older books. The repair is very conspicuous on older, softer paper. Paste and paper make for a much more attractive repair on softer paper, and are very easily removed with water when the time comes. They do not create any breakdown products or migrate into the paper.
Bottom line? PVA is works very well for some applications. It should never be used where there is any chance the adhesive might need to be removed in the future. Evacon-R seems to do everything that PVA does, and has the advantage of being reversible and of emitting fewer smelly/toxic compounds. Don’t use it where the work might be exposed to moisture.
While I’m thinking about adhesives …
Starch paste is a little trouble to use – you have to mix it up or cook it, it spoils quickly, takes longer to dry, and can introduce moisture into a book that might cause problems with water-soluble inks or dirt (tide stains could result). But paste has one great advantage – it can be easily removed with water. It forms a strong, flexible bond when dry. It’s cheap. Dry starch powder (rice, wheat, etc.) keeps almost forever on the shelf. I prefer to use paste whenever I can.
Paste will “pull” boards. If you use paste to bond a thin piece of board to a thick one, the thin one will pull the thick board toward it, bowing the board slightly. I don’t know the exact reason why – I suspect it’s a combination of the water in the paste migrating into the board and causing it to expand. The moisture will penetrate further into a thin board. When you paste the two boards, thin and thick, then put the together and let them dry, the thin board has a bit further to shrink back to original size, and the adhesive bond is strong enough to pull the thick board around as it shrinks, forming a curve with the bowl of the curve facing the thin board. You can use this to your advantage. I like to have the covers of a hardbound leather book curve ever so slightly so they “cup” the book. It’s not that extreme a curve, but you get the idea – it’s better to have the board wrap lovingly around the text block than to have the corners and fore-edge flaring outward. If you are covering a board with paper to get a smooth surface under an inlay, you want to be sure to put the same paper on the other side of the board so it doesn’t warp. An extra paper lining on the inside of a board helps counteract the pull of leather on the other side. If you will be filling in the center of a leather-covered board (the area between the turn ins) you might want to put a thin paper on the outside, before you put the leather on, so that this card doesn’t pull the board too much to the inside. That’s a lot of words to describe something simple, but a bit of experimenting will show you how your materials work.
Paste is tasty starch, and it will spoil once mixed up. I spray Lysol in the jar and under the lid before I fill it with cooked paste, keep the plastic lid on the jar, keep the jar in the fridge and just scoop out what I need into a separate container. When it turns runny or stinky, it’s safe to toss into the compost. I wash jars – pint canning jars with plastic Ball lids work great – well after use, and alternate clean jars so I can run the dirty ones through the dishwasher to sanitize them. Once paste-eating goobers establish themselves in the jar, they grow faster and faster, so you really want to keep them out.
I also keep a jar of thick methyl cellulose gel on the shelf. It keeps almost forever. It’s not as strong as paste, so I don’t use it for repairs much. It’s perfect for making “mix” (PVA with paste) as the resulting mix doesn’t spoil for a long time. Or ever.
One thing I’d like to experiment with are flexible “fish” and “hide” glues – made of isinglass, hooves, or hides (such as rabbit skin) that are dried into crystals. When these are reheated with a bit of water, they form a glue that sets up instantly as it cools. Some old books with hide glued spines are still very solid, and sometimes the dried glue has become brittle and flakes right off. Some bookbinders add sugar in the form of honey or glycerine to hide glue to make it flexible, and you can purchase “flexible hide glue”. Hide glue gets between signatures and forms a very good bond, even if it cracks off the back. I’ve spent a lot of time getting old brown glue off old book spines, and I respect it. It gets a bad rap – maybe because it’s stinky when you take it off, it’s trouble to use, and it’s old fashioned. It has some great advantages, though. Spines glued up with hide glue can immediately go on to the next process without taking time to dry. I’m thinking springbacks and ledger books, which used to be made in large quantities. Pastedowns stick instantly with no cockling. But it’s unforgiving if you make a mistake.
This Just In – Exciting Guest Advice! A master bookbinder has contributed some meritorious words about hide glue, which I will quote here:
I use hide glue often. The brittleness you refer to can be cut not by honey or sugar, but by glycerin. This will keep it flexible and you can experiment with how much you want to add. Glycerin will break down if the general pot of glue is overheated, as hide glue can take a higher temperature and still keep its properties. The hide glue I use and the glycerin produce a dark tan glue. If overheated, the color gets very dark brown and should be discarded.
… Hide glues and paste form gallons for the cost of a small quantity of PVA and, as you suggest, hide glues and paste are relatively easy to store with a very long shelf life.
In my opinion, PVA has limited uses such as in box making. Otherwise, you simply have to weigh your time in using paste to the cost of using PVA. A little experience will help you understand the pulls of paste (thin pulls thick) and you can balance your materials appropriately. Again, if you add a few drops of glycerin to a pint of paste, it will help keep it flexible and there will be less “pull.”
PVA is a recent invention. For hundreds of years binders used paste and hide glues and mastered the question of pull and warping. Not much reason to change as far as I can see.
Now I really want to play with hide glue. I was told that I could get a small pot, such as the type used by calligraphers, and melt down scraps of parchment in a small amount of water to make my own glue. On the other hand, commercial formulations are available, and it might behoove me to learn using a known material before branching out. Stay tuned!
Spoilage and shelf life:
Uncured PVA can spoil. There are various types of fungi, molds, yeasts, etc. that eat it. Some PVA has anti-fungal stuff (such as thymol) added to prevent this. There was an outcry(thymol turns out to be a carcinogen), and much of the bookbinding glue no longer contains preservatives. Paste spoils. MC eventually can spoil. Hide glues spoil.
I deal with this by never dipping anything into the “mother jar” of adhesive. I pour out of the gallon jar of PVA into a quart jar that I keep on the shelf, and I pour out of the quart jar into a squeeze bottle. Squeeze bottles are great – I can scribble a luxurious amount of glue wherever you want and then spread it out by dabbing/brushing or by rolling with a small roller. Sometimes I drop the PVA from the bottle onto the brush if I just need a little. This way, any contaminants that might be on a brush or tool don’t work their way back up the chain. I have kept PVA for years without noticing any degradation – I just shake up the bottle before decanting, as there is a slight bit of settling. I’ve not seen any mold or visible degradation in the larger containers. I look to see if there is visible mold, discoloration, clumps, lumps, odd odor, or any thinning of the material before I decant it. I don’t see any changes and the material seems to perform well. I advise doing the same thing with any such material – glue, paste, methyl cellulose, alcohol – anything I get in a bulk container I decant, and never pour the excess back into the original container. It’s a lesson learned in my early lab rat days that has served me well.
Most acrylic or latex products including glue and paint come with warnings that say “protect them from freezing”. There’s so much dispute online about the effects of freezing on paint and glue! Freezing causes the polymers to form shorter, unbreakable bonds which result in clumps. It may be that as the water crystalizes out of the suspension as ice, the polymers to begin to link up in the more concentrated solution. Freezing may cause some other chemical reaction to take place that harms the effectiveness of the product.
Many claim that if the product (PVA glue or latex paint) simply freezes, and doesn’t actually form bonds, it is still usable. Some manufacturers say their products can tolerate up to five freeze/thaw cycles and still be OK. The most common advice is to let the product thaw, then shake or mix very very well. If it returns to normal consistency, it’s fine. If the product remains lumpy, throw it out. Obviously, no one wants to say “it’s fine” and be liable for someone who has trouble with a frozen product. If it’s a low-risk application, it may be worth taking a chance. If it’s an important project, chances are, well, chancier.