Resorcinol based resin

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. 

Diglycidyl ether of resorcinol-based epoxy resins provide the highest functionality in an aromatic diepoxide. It is one of the most fluid of epoxy resins, with a viscosity of 300 to 500 cP at 25°C. Because of its high functionality, it is a very reactive resin and cures more rapidly than DGEBA epoxies with most conventional curing agents. 

The phosphorylation of phenol-furfural condensate affords a cation-exchange resin with improved thermal and chemical reristance. The heat treatment of phosphonic add resins from furfural redns, phenol-resorcinol-formaldehyde resin, and polystyrene at 100-180 °C for 10-48 h shows that the furfural-based phosphonic acid resins possess higher thermal stability than those from the other two polymers. 

Ultra thin microporous carbon films are derived via the pyrolysis of phenolic precursors. The latter can be prepared from resorcinol-formaldehyde resins using a base catalyst. After several hours at 50°C of curing, the solution forms a stable polymeric film. Followed by a solvent exchange and ambient pressure drying, the film is pyrolysed in argon atmosphere at temperatures above 800°C. The result is an electrically conducting polymeric carbon film, the structure of which resembles the organic precursor, but shows microporosity in addition. Hereby, films with thicknesses of > 5 microns and sufficient mechanical stability can be made. 

Figure 9 depicts the somewhat similar behavior for a room-temperaturesetting, urea-formaldehyde or phenol-resorcinol-formaldehyde resin-based glue. However, no initial heat-related drop in viscosity occurs during clamping, and the final polymerization hardening proceeds at a slower rate because it occurs at room temperature. 

The principal feature that distinguishes thermosets and conventional elastomers from thermoplastics is the presence of a cross-linked network structure. As we have seen from the above discussion, in the case of elastomers the network structure may be formed by a limited number of covalent bonds (cross-linked rubbers) or may be due to physical links resulting in a domain structure (thermoplastic elastomers). For elastomers, the presence of these cross-links prevents gross mobility of molecules, but local molecular mobility is still possible. Thermosets, on the other hand, have a network structure formed exclusively by covalent bonds. Thermosets have a high density of cross-links and are consequently infusible, insoluble, thermally stable, and dimensionally stable under load. The major commercial thermosets include epoxies, polyesters, and polymers based on formaldehyde. Formaldehyde-based resins, which are the most widely used thermosets, consist essentially of two classes of thermosets. These are the condensation products of formaldehyde with phenol (or resorcinol) (phenoplasts or phenolic resins) or with urea or melamine (aminoplastics or amino resins). 

Resorcinol-based adhesives are used extensively to bond structural grade, exterior laminated beams for building construction (see Chap. 29 on Resorcinol Adhesives). The coldsetting adhesives which dominate this field are based on phenol-resorcinol-formaldehyde (PRF) resins. The adhesive itself is composed of the PRF resin and a hardener that includes formaldehyde, often in the form of paraformaldehyde mixed with inert fillers. The performance of the resin is resorcinol dependent. The cost of the resin is also resorcinol dependent as this is a very expensive chemical produced industrially in only three locations in the world. The research work on these resins from their inception has then been based on the optimization of their bonding performance coupled with the decrease in the relative percentages of resorcinol used. It has the been a long and successful work of empirical research and development which still continues. 

With respect to application methods, blood glues can be spread on wood surfaces by most conventional means. These include roller, knife, and extrusion but do not include curtain coating or spray, for which the glues must be thinned below practical film retention levels. The major advantage of alkaline-dispersed blood glues over all other wood glues except resorcinol-based synthetic resin adhesives is their sensitivity to heat, resulting in extremely... 

Chem. Descrip. Hydroxymethyl dioxoazabicyclooctane CAS 6542-37-6 EINECS/ELINCS 229-457-6 Uses Crosslinking agent for resorcinol phenol-formaldehyde or protein-based resin systems, paints/coatings, adhesives, and inks raw material for synthesis... 

Epoxy resins formed by condensations of epichlorohydrin with resorcinol-based phenolic resins are also formed commercially ... 

Hydroxymethyl dioxoazabicyclooctane CAS 6542-37-6 EINECS/ELINCS 229-457-6 Synonyms 7-Hydroxymethyl-1,5-dioxo-3-aza-bicyclooctane 1H,3H,5H-Oxazolo [3,4-c] oxazole-7a(7H)-methanol Oxazolo [3,4-c] oxazol-7a-yl-methanol Ciassification Heterocyclic organic compd. Empihcai CeHnNOs Properties M.w. 145.16 Toxicoiogy Irritant TSCA listed Uses Antimicrobial in cosmetics crosslinking agent for resorcinol phenol-formaldehyde or protein-based resin systems raw material for synthesis for paints, coatings, adhesives, and inks... 

The use of hydroxymethylated resorcinol (HMR) as an adhesion promoter to enhance solid wood bonding is a recent development that holds considerable promise in improving the durability of the bonds between solid wood and adhesives. HMR consists of a mix of methylolated resorcinol monomers and low molecular weight oligomers [1]. Its usefulness as an adhesion promoter has been shown for a number of different wood species and different adhesives formaldehyde-based resins, epoxies and polyurethanes [2-7]. 

TGA, dynamic thermal analysis (DTA) and infrared (IR) techniques have been used [11-13] to determine E and n of BPA and resorcinol based epoxies. Figure 3.3 shows the TGA derived curves for BPA and resorcinol-based epoxy resins. The replacement of the phenyl group between two glycidyl ether groups in resorcinol diglycidyl ether by a 2,2-diphenylpropyl group increased appreciably the maximum decomposition rate. 

The best adhesive formulation for phloroglucinolic tannins, such as pine tannin extracts is, instead, a comparatively new and is also capable of giving excellent results when using resorcinol tannins such as a wattle tannin extract [68-71]. The adhesive gluemix consists only of a mix of an unmodified tannin extract 50 per cent solution to which paraformaldehyde and polymeric nonemulsifiable 4,4 -diphenylmethane diisocyanate (commercial pMDI) are added [68-71]. The proportion of tannin extract solids to pMDI can be as high as 70/30 w/w, but can be much lower in pMDI content. This adhesive is based on the peculiar mechanism by which the pMDI in water, is hardly deactivated to polyureas because it reacts faster with the hydroxymethyl groups of a formaldehyde-based resin, be it a tannin or another resin [69,71]. 

The standard aqueous treatment for textile adhesion is based on resorcinol/formaldehyde resin/latex (RFL) dip systems. A typical formulation for such an adhesive dip is given in Table 9.1. 

Resorcinol reacts rapidly with formaldehyde in the absence of catalysts, but both acid and alkaline catalysts have been used [36]. Resorcinol-formaldehyde resins are used to produce low-temperature curing resins alone or in combination with phenol-formaldehyde resin. Some combinations permit curing at room temperature under neutral conditions. This property of low-temperature cure is important in the manufacture of laminates and adhesives. Base resins for adhesives are made by reacting one mole of resorcinol with less than one mole of formaldehyde, and the condensate is usually dissolved in a solvent such as aqueous alcohol. The resin base at pH 7.0 has a long shelf-life and is hardened by the addition of formaldehyde or paraformaldehyde [37]. 

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