There’s been a lot of discussions, both here in this blog, as well as in the industry in general about formaldehyde glues, particularly urea formaldehyde glue. I was talking with some friends of mine the other day about how the common representation in the industry is that the decision to use urea (as opposed to phenol or melamine or other options to bond with the formaldehyde) in wood resins is a purely cost based decision. Not being in the glue business, I asked if that was true—did throwing more urea formaldehyde into a product increase production and reduce cost? Was it really that simple?
I was told that it was not…that adding more urea formaldehyde resin to production could actually reduce productivity. Resin that was too thin/wet, could increase the moisture content of the wood and lead to everything from slower curing, failed bonding and “blown panels.” There is not a simple and clear relationship that “more urea formaldehyde equals more production volume equals cheaper cost.” Like everything else we talk about, it’s a lot more complicated than that sound bite.
So I asked, “why do companies around the world choose a urea formaldehyde (UF) resin?” Is it the “cheap choice?” And the response was “what do you mean by ‘cheap?’ UF offers a good value for a producer with a good performance for the customer.”
In the world today, “cheap” has come to be perceived as equivalent to “low quality” or even “poor quality.” A cheap product is one that will fall apart on you, a product that is unhealthy, a product where a corner somewhere has been cut, right? The choice to use UF does not imply any of those things. The selection of UF, like with many material choices, may be partially based on costs, but it’s the total cost package—how the product performs, not just the material cost. There are distinct differences in every glue formula, and a producer needs to pick the one that works for their facility and product.
During our discussion, I got a nice education in the history of glue production, about how we once used horses and other natural materials, and how these natural glues tended to either delaminate or mold/mildew in the face of moisture and how they weren’t ideal for mass production either. They were hard to make and slow to use. Synthetic glues, on the other hand, were great for mass production—they provided a consistency and a performance factor, both during production and post production that an old horse just couldn’t match. And synthetics are available in large commercial quantities, again, without depleting an entire stable per plywood production shift.
The first popular synthetic for wood was phenol formaldehyde (PF) which was used for exterior grade panels, followed shortly thereafter by urea formaldehyde (UF) for interior grade panels. I found out that urea was and is a cost saving choice over phenol, but that is not necessarily selected as a material cost savings – rather selection is typically based on required performance of the end panel product.
For a producer, UF resin cures faster, meaning more production per shift. And beyond that, it cures at low temperatures—the lower energy costs makes it a greener choice from that perspective. And since UF resins work in a variety of different curing conditions, you can use the same general glue in multiple types of presses. UF glues are water soluble, so they are generally easier to store/handle in the workplace. Finally, urea itself is widely available in commercial quantities.
For a user, UF glued composite wood products generally have better machinability, with fewer chipouts/tears than some of the other glue types. UF resins offer a high tensile strength but are still flexible and resistant to temperature related movement and provide a high surface hardness. UF is colorless so it is often used in products where a clear glue line would help. UF is less moisture resistant than PF, which makes it unsuitable for exterior applications, but when you add melamine to the formula to make melamine urea formaldehyde (MUF), you not only increase the product’s water resistant properties, you reduce post-production formaldehyde emissions.
(Remember that many MUF resins are rated “ULEF” which is Ultra Low Emitting Formaldehyde. So having urea in the content doesn’t automatically equal high emissions which is why I’ve previously said it is good that we’re moving away from content focused standards in green building.)
The bottom line? The use of “U” is not just a price choice, or at least not in the way it’s implied that it’s only a low-quality cheap material choice. When used properly, urea formaldehyde can be component of a high quality, completely safe and more efficient production method. It has value to both the producer in how it performs in the workplace and to the user in the final product’s function. Plus, with new resin technologies coming out daily to reduce the emissions from the final cured product, it can be a healthy choice too.
Finally, I want to highly recommend this essay I found on the history of glue. It is not too long, very readable and covers everything from the glues used in cave paintings to the glues on a gecko’s feet. It is absolutely amazing to consider all the materials—beyond horses—that we can use to make glues!
Reposted on May 23, 2017