Since all of my science columns are online, I frequently get questions out of the blue about past column topics. This week, for example, I received an e-mail from a mother whose nine-year-old had decided to do a third-grade science project on glue. They’d found my column on the topic from a decade ago, and wanted to know what kind of glue is the strongest.
Like usual, I had to explain that, alas, writing a single short column on the topic did not make me an expert, and I couldn’t answer the question. But though I wasn’t able to help with the science project, it helped me: it prompted me to re-read my old column, which in turn primed me to pick up on an interesting news story from Oregon about an exciting glue-related discovery.
First, some background (drawn, handily enough, from my own old column). A glue, or adhesive, is any substance that can strongly bond two surfaces together. In general, glues are soft when applied, then harden, or cure. Curing may occur through the evaporation of water or other solvents, through a chemical reaction called polymerization (changing from a liquid to a solid), or through cooling.
There are thousands of glues on the market of more than 100 distinct chemical types. Among the strongest are epoxies. Made from synthetic resins, these will stick to just about anything, but because they have to be carefully mixed with a hardener, they’re a bit inconvenient, and so not most people’s first choice.
“Super glues,” more properly known as cyanocrylates, cure through a very fast chemical reaction. This quick bond makes them good for gluing hard-to-clamp objects–and gluing your fingers to your screwdriver, workbench or nose. Fortunately, acetone (nail-polish remover) will dissolve the bond.
“Hot glue,” more properly known as thermoplastic glue, comes in a stick that has to be melted in a glue gun before it can be applied. It’s really just a modern (and much stickier) variation on one of the first adhesives ever used: wax. Like wax, thermoplastic glue flows easily when hot, then sets very quickly as it cools.
Then there’s good old white glue, which we all used in school. Because it’s water-based, it works well on porous surfaces such as wood: the water carries the adhesive into the pores in the two surfaces being glued, and then evaporates, binding the two surfaces together. But it’s emphatically not waterproof for that very reason, so you wouldn’t use it to glue your boat together.
In fact, most glues don’t work well in wet environments–which is why the new discovery from Oregon is so important.
Kaichang Li, an assistant professor from Oregon State University’s College of Forestry, has developed a new group of adhesives based on the small threads called byssus that mussels use to attach themselves to rocks on the seashore, so strongly they can withstand the pounding of ocean waves.
Li deciphered the unusual structure of the byssus thread, but making a commercially valuable adhesive out of it was another matter. Then one day, while eating tofu, Li had an inspiration. Soybean protein is inexpensive and, obviously, renewable. What if you could modify it so it was more like the mussel protein?
His research team set out to do so–and succeeded. They have since developed other strong, water-resistant wood adhesives from other renewable natural materials, all using mussel byssus protein as a model. They’ve so far published 11 papers and have three pending patents.
The new byssus-based adhesives, made from natural resources like soy flour and lignin (and in the future, possibly even from tree bark or fungus-decayed wood useless for other purposes), could replace the urea-formaldehyde wood adhesives currently used to make wood composite products like plywood and particle board. One of them is already cost-competitive with the current adhesives, and presents none of potential health and environmental risks associated with formaldehyde fumes. (Another strike against formaldehyde is that it is ultimately derived from increasingly expensive petroleum.)
And the new adhesives have superior strength and water-resistance. Plywood made with them can be boiled for several hours without coming unglued–unlike current plywood. (Mmmm. Boiled plywood. Shades of Sunday dinner in my college cafeteria…)
The forest products industry in the U.S. and Canada spends more than $2 billion U.S. a year on wood adhesives, and the wood composites industry is one of the largest manufacturing sectors in the United States. The new glues have a tremendously positive impact in terms of reduced cost and enhanced environmental friendliness.
Who knows? They might even inspire a new generation of third-grade science projects.