Melamine-urea-formaldehyde

Both melamine—formaldehyde (MF) and resorcinol—formaldehyde (RF) foUowed the eadier developments of phenol—, and urea—formaldehyde. Melamine has a more complex stmcture than urea and is also more expensive. Melamine-base resins requite heat to cure, produce colorless gluelines, and are much more water-resistant than urea resins but stiU are not quite waterproof. Because of melamine s similarity to urea, it is often used in fairly small amounts with urea to produce melamine—urea—formaldehyde (MUF) resins. Thus, the improved characteristics of melamine can be combined with the economy of urea to provide an improved adhesive at a moderate increase in cost. The improvement is roughly proportional to the amount of melamine used the range of addition may be from 5 to 35%, with 5—10% most common. 

The primary adhesive used ia hardwood plywood is urea—formaldehyde (UF) mixed with wheat flour as an extender to improve spreadabiUty, reduce penetration, and provide dry-out resistance. A catalyst may also be added to UF resias to speed the cure or to cause the UF to cure. Scavengers also may be added to reduce formaldehyde emissions from finished panels. If more water-resistance is requited using a UF bond, small amounts of melamine maybe added, producing a melamine—urea—formaldehyde (MUF) adhesive. 

One type of thick hardwood plywood stiU available is imported from the northern Scandinavian countries and is generally known as Finnish birch. Characteristically, these plywoods are manufactured using multiple layers of veneer of the same thickness, about 1.5 mm (1 /16 in.), and bonded with a urea—formaldehyde or melamine—urea—formaldehyde adhesive. 

German patent DE 3442454 (1984), European patent EP0185205, B1 (1986). Process for the preparation of melamine-urea-formaldehyde condensates. Assigned to BASF AG. 

Breyer, R.A., Hollis, S.G. and Jural, J.J., United States patent USP 5,681,917. Low mole ratio melamine-urea-formaldehyde resin. Assigned to Georgia-Pacific Resins, Inc., 1997. 

Variation of Reaction Stages And Mole Composition Effect on Melamine-Urea-Formaldehyde (MUF) Resin Properties... 

In similar bending-creep tests, both control and acetylated pine particleboards made using melamine-urea-formaldehyde adhesive failed because T. palustris attacked the adhesive in the glueline ( ). Mycelium invaded the inner part of all boards, colonizing in both wood and glueline in control boards but only in the glueline in acetylated boards. 

The release of semivolatile compounds from a variety of nitrogen containing polymers, including ABS, PA 6 PU and melamine/urea formaldehyde resins can be found in the literature (52). The temperature of treatment runs from 70°C to 300°C, i.e., low temperature pyrolysis, if pyrolysis at all. 

In general, plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics. The materials that will respond satisfactorily in the range of 1010 and 1011 erg per gram are glass and asbestos-filled phenolics, certain epoxies, polyurethane, polystyrene, mineral-filled polyesters, silicone, and furane. The next group of plastics in order of radiation resistance includes polyethylene, melamine, urea formaldehyde, unfilled phenolic, and silicone resins. Those materials that have poor radiation resistance include methyl methacrylate, unfilled polyesters, cellulosics, polyamides, and fluorocarbons. 

We have to note that the two melamine-urea-formaldehyde boards do not satisfying this theory. This difficulty excepted, the curve family obtained fits without fault. However, we can say that for a loading rate of 0.5, near that used in the foregoing test, we should obtain a similar ranking, in spite of an inversion between two panels. However, a correlation factor between the two gas analysis methods does not exist, because the values are as follows ... 

The results and eflectiveness of Eqs. (7) were checked also for other, quite dilferent polymers, namely the polycondensates of resordnol-formaldehyde, of melamine urea formaldehyde (MUF), of PF, and of quebracho and pine polyflavonoid tannins hardened with formaldehyde. The comparison of the energies of interaction obtained by measures of TMA deflection and the use of this formula compared well with the results already obtained for their energy of adhesion with crystalline cellulose in previous work [16 10]. It appears, then, that the formula works also for entanglement rather than just cross-linked networks. 

Exactly the same type of approach can be used for the formulation of other polycondensation adhesives. For example, the formulation of melamine urea formaldehyde adhesive resins for wood panel products can also be successfully approached in the same way as has been shown above for the cold-setting PRF adhesives. 

Other rapid setting adhesive systems not containing resorcinol are those based on melamine-urea-formaldehyde resins and on one-component polyurethanes, described in Chap. 32 and Chap. 34, respectively [28,29]. 

Results obtained by a series of techniques for the curing of several resin systems [18,20-24] have indicated, however, that posttreatment and hotstacking (postcuring) conditions capable of improving the mechanical performance of aminoplastic resin-bonded particleboard without any degradation should instead exist. This is of some importance, firstly because the performance of UF- and melamine-urea-formaldehyde (MUF)-bonded particleboard could be improved with very little process change from the present industrial conditions to yield better board performance (or the same performance at lower adhesive content levels), and secondly because at parity of board performance such an approach may well lead to the use of even shorter industrial press cycles than today, even for aminoplastic resins. 

Melamine-formaldehyde (MF) and melamine-urea-formaldehyde (MUF) resins are among the most used adhesives for exterior and semiexterior wood panels and for the preparation and bonding of both low- and high-pressure paper laminates and overlays. Their much higher resistance to water attack is their main distinguishing characteristic from urea-formaldehyde (UF) resins. MF adhesives are expensive. For this reason, MUF resins which have been cheapened by addition of a greater or lesser amount of urea are most often used. Notwithstanding their widespread use and economical importance, the literature on melamine resins is only a small fraction of that dedicated to UF resins. Often MFs and MUFs are described in the literature as a subset of UF amino resins. This is not really the case, as they have peculiar characteristics and properties all of their own which in certain respects are very different from those of UF adhesives. 

Within the forest products industry, polymeric MDI competes against the formaldehyde based thermosets such as urea-formaldehyde, melamine-urea-formaldehyde. 

While pMDI wood binders are derived from formaldehyde, they are distinguished from other wood binders by a total laek of formaldehyde emission. This performance advantage has not displaced the less expensive UF and melamine-urea-formaldehyde... 

MPE metallized polyester film MUF melamine urea formaldehyde... 

TYPICAL COMONOMERS Melamines, urea, formaldehyde, ethylene urea, benzoguanamine, thiourea, acetoguanamine... 

Feetures Compat. with melamine-urea formaldehyde systems Properties Wh. fine crystalline powd. sol. 0.8 g/l in water bulk dens. 500-600 g/l pH 4 (10%)... 

Semek and Resnik [27] investigated the penetration behavior of four melamine-urea-formaldehyde (MUF) resins with different contents of melamine and different molar masses, also adding slightly different amounts of extender to the resin mix. The lower the viscosity of the resin mix, the deeper was the penetration into the wood surface. 

Melamine-urea-formaldehyde (MUF) resins are among the most commonly used resins for application as binders for wood panels [1]. However, the high cost of melamine has led over decades to a progressive decrease of melamine content in these resins while maintaining the high performance of the adhesive by improved resin formulation [2-7]. 

A. T. Mercer, NMR analysis of strength and emission of melamine and melamine-urea-formaldehyde resins for synthesis optimisation, PhD thesis. University of the Witwatersrand, Johannesburg, South Africa (1996). 

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