PVA, Urea, and Workspace Air Quality

      A discussion of substituting PVA for urea adhesive in a veneering operation. July 13, 2006

Question
We are trying to move away from urea resin glue for hot pressing. There are a few PVA glues for hot pressing. Some are pre-catalyzed and some are post catalyzed. There are also quite a few manufacturers out there. I would like to hear from people who have tried these glues and what their experience has been.

Forum Responses
(Veneer Forum)
From contributor A:
With all due respect, may I ask why? Urea has much lower cost, much higher heat resistance and higher moisture resistance. True urea is darker in color but it sands easier and cleaner.



From the original questioner:
It is mostly for health reasons. Our press is in a very confined space and the gases are truly a pain. I agree with you about the performance of the urea that we use (Borden's UF109).


From contributor B:
We use a Borden Urea and the fine folks at OSHA suggested that we needed to have testing done to see if the Formaldehyde emissions were acceptable. We got some 3M testing supplies as the law says that we had to know what the emissions were and be able to prove it. We have a large press and run it very hot. The day we tested we were running a lot of lumber core 5-ply with lots of glue. We sent the cartridges in to the 3M lab and they came back way under the acceptable limits. Certainly, if the glue makes you ill, you should change, but Im just passing this on for your information. You can get the testing tools from a number of online safety suppliers. You are required to know what your exposure is if you use any glue of this formulation.

We also use a lot of Wonderbond (Borden) in the hot press for bendable 2-ply and skins. It's a PVA and set up very fast in the press. It also is good for re-pressing as in step pressing etc. We like to UF glue whenever possible for the reasons mentioned above.



From the original questioner:
For the past 20 years I have been pressing with Borden's UF109. It is a great glue. The gases that come off when we open the press make our eyes water and are really overpowering. Various manufacturers (Borden's, Nacan, Durel) are offering a PVA that is pre-catalyzed and post catalyzed that has been tested to give a Type I and a Type II bond. If I can get a Type I bond with a pre-catalyzed PVA I will switch. I need to find out if anyone has any long term experience with PVA for veneer pressing.


From contributor B:
The PVA (Wonderbond) works great. We have used it for many years. Id rather use UF glue when we can. You sound like you know what you are doing, but are you sure the catalyst is mixed correctly? There are several catalysts that will work with that material. I have never had an eye burn problem and we use thousands of gallons a year. Do you have a multi-opening press? It sounds like a lot of gassing. What temperature do you run at? You should contact your supplier or Custom Pak.

What are your concerns with PVA? The biggest problem is that it adds more moisture to the panel and has to sit longer before machining. Also, do you hand roll your glue? We use a BB roller coater and use much less of a spread compared to hand rolling. What kind of press do you use? How many SF of panels do you press per run?



From contributor C:
You will not get a type I bond from any PVA that I know of. You may want to try some other ureas. We have customers that use PPR which can be used hot or cold (+70F).


From the original questioner:
Borden's XB-9325LF, Dural's G-2871, Nacan's Duro-Lok 68.6900 all claim to have a Type I bond. All are post catalyzed except the G-2871 made by Dural. They claim to have passed the tests for Type I bond at the labs in Montreal and Vancouver (Forintek).


From contributor D:
We're thinking of getting a hot press but one of the sticking points is my fears about exposing my workforce to Formaldehyde fumes. So this thread is quite interesting to me as I also want to use a PVA with the hot press. Here's my question: what's the difference between a Type I and Type II bond?


From contributor E:
Both of these tests are conducted using 6 by 6 birch laminates glued together to make three-ply plywood. The test for Type I is clearly more stringent than Type II, and involves boiling the glue bonds and testing the specimens while they are wet.

Type I testing involves cutting the 6" by 6" assemblies into 1" by 3" specimens, boiling them for 4 hours, then baking the specimens in a 145F oven for 20 hours. They are boiled for an additional 4 hours, then immediately cooled using running water. The specimens are sheared while wet, and the bonds must pass certain strength and wood failure requirements to pass the Type I specification.

Type II testing involves cutting the 6" by 6" assemblies into 2" by 5" specimens, soaking them for 4 hours, then baking the specimens in a 120F oven for 19 hours. This is repeated for a total of three cycles, and the bonds must not delaminate to pass the Type II specification.

To simplify, Type I is waterproof, i.e. Resorcinol for building boats, kayaks, canoes. Type II is water resistant - urea for plywood exposed to the elements but not particularly in direct contact with water - soaked or in water for extended periods of time.



From contributor E:
Hot pressing with urea should not be feared. There have been very few cases that I know of where a worker has a high sensitivity to urea.

Cite: HPVA study
LOW FORMALDEHYDE EMITTING HARDWOOD PLYWOOD
Hardwood plywood wood products are available today which emit 60-90% less formaldehyde than products manufactured in the early to mid 1980's. In the United States there is one federal standard which sets a limit on formaldehyde emissions from wood products. This standard was developed in 1985 by the U.S. Department of Housing and Urban Development (HUD) for plywood, particleboard, and industrial panels used in manufactured (mobile) homes, and the limits were established as follows:

Plywood Wall Panels 0.2 ppm @ 0.29 ft2/ft3 Loading Rate
Particleboard, Industrial Hardwood Plywood Panels 0.3 ppm @ 0.13 ft2/ft3 Loading Rate

The 0.2 ppm and 0.3 ppm levels are based on a large chamber test method which specifies the parameters of test such as product loading rate, temperature, relative humidity, and air change rate. One state standard (Minnesota) and industry standards have also been developed which contain requirements similar to those covered in the HUD standard. It should be noted that the loading rates used in testing are significantly higher than the loading rate found in most homes. Therefore, the formaldehyde concentration found in a home would be expected to be considerably less than the 0.2 or 0.3 ppm maximum limits established by the standards.

Now let's compare these emissions to other indoor formaldehyde pollutants:

Cite: Calif. EPA study
Formaldehyde Emissions from Selected Indoor Sources
Typical Conditions (g/m/hr)

Wet products
Wood floor finish 11,000
Fingernail hardener 300
Latex paint 9

Wood products
Cabinet door with acid-cured finish 460
Medium-density fiberboard cabinet door 360
Particle board 240
Particle board with vinyl laminate 16
Softwood plywood 4

Other
New permanent-press shirts 10
Washed permanent-press shirts 42
Fiberglass insulation 32

There is exposure to off gassing from a wide variety of sources, many with higher concentrations than those involving the use of urea glue lines. I would be interested in knowing if there is a greater exposure to urea as a result of ripping plywood on a table saw as opposed to hot pressing with Urea resin adhesives!



From contributor F:
Try using NationalCasein wp-2200 or National Starch Kor-lok. I`ve been using one or the other for the last 17 years and have had great success. Both glues are catalyzed with aluminum chloride and provide a Type I cross-linking bond


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor G:
Our operation that focuses on high end office furnishings originally employed UF resins. We gradually (for the sake of not wanting to deal with the issues associated with UF resins like off gassing and waste disposal) moved our operation to PVA adhesives in all areas. This includes edging, hot pressing, RF curing operations and edge gluing as well as assembly work.

Now, we are actually getting back into UF resins simply because they far out perform PVA's. We will still likely keep PVA's in use with our hot pressing operation (despite the issues of checking etc. that can occur). The fact of the matter is that no PVA will replace the bonding properties of UF resins, save that of PUR's which have their own issues. What prompted our shift was the fact that we were experiencing a tremendous amount of creep in laminated headers on curved surfaces. Some of these headers are made up of 10 4mm plys, so you can imagine how terrible the finish could look on a top surface when the plys began to creep slightly! Currently, we are using National Casein 705UR.



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