Monday, March 31, 2008

Urea Formaldehyde Adhesive

Thermosetting Resin AdhesiveA thermosetting synthetic resin is one that on curing undergoes an irreversible chemical and physical change to become substantially infusible and insoluble. The term thermosetting is applied to the resin both before and after it is cured. It is not a good name because it implies only a relationship between temperature and curing

Some thermosetting adhesive are condensation polymer and some are addition polymers. The important examples are urea-, melamine, phenol- and ressorsinol-formaldehyde adhesive, epoxy, polyisocyanate and polyester adhesives. They will be considered in that order.

Amine Formaldehyde Adhesives
Although a number of amines condense with formaldehyde to produce resinous substances, reaction products from two only are of importance as adhesives, those from urea and those from melamine. The former, marketed many years earlier and used on a much larger scale, will be discussed first

Urea Formaldehyde Adhesive
A urea formaldehyde resin or glue (also commonly called a urea glue or a UF) is the condensation product of unsubtituted urea and formaldehyde. Thiourea is not included, resin from thiourea are of negligible importance as adhesive.

General purpose of urea formaldehyde applied such as on plywood, veneering and assembly gluing. The urea formaldehyde reaction in its relation to the preparation of an adhesive. The normal ration on reaction to form a glue use usually the molar ratio of 1U : 1.75 – 1.9 F, and rarely above 1 : 2 for the manufacture of wood particle board a somewhat lower is often used in order to keep the smell of formaldehyde to a minimum. A Rusian paper suggests the best molar ratio to be about 1:1.65, which is lower than that generally used except for making particle board, in the work referred to, a number of parameters were examined, unfortunately without relating them to the strength of glued joints.

In deciding the ratio of formaldehyde to urea, a compromise is sought between certain properties of the resin, a compromised that influence the method of manufacture of the resin solution. A high molecular ratio of formaldehyde to urea, for example exceeding two to one, result in a product having certain advantages as well as certain disadvantages. Among the advantages are increased stability in solution, and increased water-toleration or even infinite true solubility. Chief among the disadvantages is, firstly, a higher sensitivity to atmospheric moisture. In explaining this it should be understood that all uncured urea resins are to some extent hygroscopic; most powder resins have an equilibrium moisture content at between 60 % and 70 % RH, that is to say they neither absorb nor lose moisture at some relative humidity within these limits at a normal temperature.

My Experience on Using Urea Formaldehyde.
Urea formaldehyde on resin form still don't have strong stick of two wood, but this resin need a filler and hardener for gluing application. So for carpenter that is use this kind of resin usually will get a guide first from the vendor, even they don't learn on using this glue, they still have a good result after gluing their wood product.

1 comment:

  1. Dear sirs
    pls can i got the technical information to produce the urea formaldhyde resin powder?