Speeding Up Urea Formadehyde Resin Cure Times

      Either heat, or catalysts, or both can be used to accelerate UF cures. Here, pros provide details. December 14, 2005

Question
One type of UF resin needs 10 to 12 hours to cure. How can I shorten a UF resin's curing time?

Forum Responses
(Adhesives Forum)
From contributor A:
Adding heat speeds the chemical reaction required for UF glues to cure. This is why they are defined as thermosetting glues. Sometimes just turning up the heat in the shop can reduce cure time.



From contributor B:
I just throw an electric blanket (covered with other blankets for insulation) onto my glue-up, kick it up to 90+ degrees, and its cured in about 8 hours.


From Jeff Pitcher, forum technical advisor:
A quick rule of thumb is for every 10 degrees above 90 that you heat the UF glue line to, you can cut your cure time in half. Another way to speed up the UF cure is to use a different catalyst. There are liquid catalysts that will allow a UF resin to cure at room temperature in about 20 minutes.


From contributor B:
Can you tell us more about these catalysts? How do they work? Where they are available? What do you have to be careful of when using them?


From Jeff Pitcher, forum technical advisor:
There are a number of different powdered catalysts available from any company that sells UF resins. They vary according to speed, color, fill, use in auto mix equipment, etc. There is also a liquid catalyst available that is applied to the opposite surface from where the resin is applied. It can actually be applied early and allowed to dry. Because it is extremely acidic, proper precautions must be taken during its use but it is a great way to speed up UF cure. You can call Custom-Pak and ask about the separate application UF system.


From contributor D:
UF resins cure with a drop in system pH. Try mixing a small percentage of any simple acid-salt and then apply heat.


From contributor E:
Can the liquid catalyst be used with cold pressing, such as a vacuum press, or does it also need a raised temperature? Does curing neutralize the liquid catalyst? If not, does it cause a problem in finishing if applied to veneers? Does the change in pH create any long term issues in the bond?


From Jeff Pitcher, forum technical advisor :
The liquid catalyst will work at room temperature in a vacuum press. The key is to use it with a buffered catalyst as well. It doesn't take the place of the normal powdered catalyst. This will take care of the temporary pH change.


From contributor D:
I would avoid using a liquid catalyst in combination with a buffered catalyst. If the chemical is a true buffered catalyst, it should effectively drop the pH and initiate the curing mechanism, provided the UF resin and catalyst combination is appropriate for the pressing temperature. The principal advantage of using a buffer in the mix is to inhibit glue line dry-out, which leads to poor flow, spread, etc.

Regarding the low pH concern, a catalyst is not absolutely necessary to cure a UF resin. Since wood is relatively acidic, it will do the job of curing the UF polymer, but over a longer period of time. The bottom line is that the pH will be low anyway to cure the glue line.



From Jeff Pitcher, forum technical advisor:
Contributor D makes a good point. However, absent a catalyst you really risk dry out as the acid content of wood can vary considerably. The liquid catalyst system should only be used in room temperature curing. It wouldn't be needed in a hot press situation.



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