Methylolation adhesives

Phenolic resin substantially increases open time and peel strength of the formulation (80). For example, higher methylol and methylene ether contents of the resin improves peel strength and elevated temperature resistance. Adhesive properties are also influenced by the molecular weight distribution of the phenoHc low molecular weight reduces adhesion (82). 

Amino Resins. Amino resins (qv) include both urea- and melamine—formaldehyde condensation products. They are thermosets prepared similarly by the reaction of the amino groups in urea [57-13-6] or melamine [108-78-1] with formaldehyde to form the corresponding methylol derivatives, which are soluble in water or ethanol. To form plywood, particle board, and other wood products for adhesive or bonding purposes, a Hquid resin is mixed with some acid catalyst and sprayed on the boards or granules, then cured and cross-linked under heat and pressure. 

The condensation reaction of resorcinol with formaldehyde, on an equal molar basis and under identical conditions, also proceeds at a rate which is approximately 10 to 15 times faster than that of the equivalent phenol-formaldehyde system [16-18,123]. The high reactivity of the resorcinol-formaldehyde system renders it impossible to have these adhesives in resol form. Therefore, only resorcinol-formaldehyde novolaks, i.e. resins not containing methylol groups can be produced. All the resorcinol nuclei are linked together through methylene... 

Cure Rate of the Phenolated SEL Resins. 13C NMR spectra of the phenolated SEL formaldehyde-treated resins revealed the formation of methylol groups. A similar cure reaction to resole type phenolic resins is expected to occur with the phenolated lignin-based resins. Since cure rate normally determines production capacity of a board mill, it is important that new types of adhesives have at least the same cure rate as the conventional phenolic adhesives. Cure analysis of resins has usually been examined by... 

Evaluation of Adhesive Bond Strength. Since the cured product of LP-A was brittle, probably due to the low level of formaldehyde charged, LP-B and LP-C were selected as adhesive resins. In order to increase their cure rate, the pH s of LP-B and LP-C resins were adjusted to around 11.2 and 12.0, respectively, prior to adhesive formulation. For the purpose of comparison, the bond strength of the methylolated SEL resin adhesive was examined as well. 

The results are summarized in Table II. The bond strength of the adhesives from the methylolated SEL expectedly exhibit poor adhesion as compared to the phenolated SEL adhesives, especially after repeated boil. 

The urea-formaldehyde polymer is formed by a multi-step reaction process between urea and formaldehyde. The initial phase is a methylolation of the urea under slightly alkaline conditions with a formaldehyde-urea (F/U) molar ratio of 2.0 1 to 2.4 1. Condensation of the methylolureas from the methylolat ion reaction is at atmospheric reflux with a pH of 4 to 6. This condensation polymerization continues to a pre-determined viscosity, at which time the pH is adjusted with a suitable base to 7-3 to 8.0. The adhesive is then concentrated to a total solids content of 50 to 60 percent by vacuum distillation. Additional urea is then normally added to produce a final F/U molar ratio of 1.6 1 to 1.8 1. 

In alkaline media, phenolic units may react with formaldehyde, forming methylol derivatives that condense with themselves or with another phenol (J, Fig. 1.4). This formaldehyde condensation reaction forms the basis for using technical lignins in the production of adhesives. 

Considerable research activity has been directed toward producing wood composite adhesives from lignin, and this has been accompanied by very little practical success in terms of commercial implementation. By themselves, and regardless of source, lignins offer no advantages in terms of chemical reactivity, product quality, or color when compared to conventional wood composite adhesives. At low replacement levels (10 to 30%), lignins can and will continue to be employed as extenders for UF and PF resins. When they are used as extenders, best results are obtained when chemically activated (e.g., by methylolation). 

Typically, polymers of these acrylic and methacryUc esters are produced as copolymers with other acrylic and vinyl monomers. For example, acrylonitrile is often added to impart additional water and solvent resistance. Other features that can be improved include abrasion resistance, adhesion, elasticity, flexibility and film hardness. Enhanced durability to laundering can be achieved by incorporating reactive, especially crosslinking, monomers such as A -methylol acrylamide, hydroxyethyl acrylate, acrylamide, acrylic and methacrylic acid. Optimisation of polymer properties with the large variety of available monomers leads to near endless combinations of copolymers that are limited only by the imagination of the chemist and by the reality of the cost-efficiency ratio. 

Phenolic adhesives are structural adhesives with specific applications, e.g. where wide gap bonding is required and where large structures need to be bonded. Phenolic resins are the product of a special reaction ratio of a phenol and formaldehyde in the presence of an organic catalyst. There are two main types of phenolic resins phenol or methylol terminated. The phenol terminated are called novalacs, while the methylol terminated are called resoles (one step resins). Modem phenolic resins are prepared in the presence of metal carboxylates and these resins contain a large number of benzylic ether linkages and have open para positions which have good temperature stability and are usually of low viscosity. 

Methods of filler pretreatment lignin treated by methylolation decreases the rate of cure of phenolic adhesives " carbon fiber was anodicaUy oxidized and subjected to various treatments with coupling agents to improve interfacial interaction with phenolic resins and oxidative stability of carbon fibers titanate coupling of oxidized fibers resulted in improved adhesion to matrix and enhanced thermal stability of fibers ... 

The methylol compounds formed are fairly stable under neutral or alkaline conditions, and many amino resins (adhesives, for example) are simply mixtures of these methylolated monomers and low molecular... 

The simple methylol compounds and the low molecular weight polymers obtained from urea and melamine are soluble in water. They are quite suitable for the manufacture of adhesives, molding compounds, and some kinds of textile treating resins. However, amino resins for coating applications require compatibility with the film-forming polymer resins with which they must react. Furthermore, even where compatible, the free methylol compounds are often too reactive and too unstable for use in a coating formulation that may have to be stored for some time before use. Reacting the... 

Vinyl esters Resorcinol N-methylol acrylamide Woodworking adhesives Mudge et al. V.S. Pat., 5,434,216, 1995 National Starch... 

MAJOR USES Production of polyacrylamide polymers used as a chemical intermediate in the production of N-methylol acrylamide and N-butoxyacrylamide absorbent in disposable diapers, medical products and agricultural products sugar beet juice clarification adhesives printing ink emulsion stabilizers thickening agents for agricultural sprays. 

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