Phenol-formaldehyde resins, resole

In patients hypersensitive to phenol-formaldehyde resin (resol), simultaneous patch-test reactions to formaldehyde, colophony, hydroabietyl alcohol, balsam of Peru, perfume mixture and p-ferf-butylphenol-formaldehyde resin have been reported. In patients hypersensitive to p-terf-butylphenol-formaldehyde resin (resol), simultaneous patch-test reactions to hydroabietyl alcohol, balsam of Peru and phenol-formaldehyde resin have been reported (Bruze 1986). 

Phenol-formaldehyde resin (Resol), 5% petrolatum Phenol-formaldehyde resin (Novalak), 5% petrolatum PFR-2 (recommended), 1% petrolatum Own resin (important), 1% and 5% petrolatum Cashew-nut-shell oil, 3% alcohol (Fisher 1986) Cashew-nut formaldehyde resin, 1% and 5% petrolatum... 

Phenol-formaldehyde resins are the oldest thermosetting polymers. They are produced by a condensation reaction between phenol and formaldehyde. Although many attempts were made to use the product and control the conditions for the acid-catalyzed reaction described by Bayer in 1872, there was no commercial production of the resin until the exhaustive work by Baekeland was published in 1909. In this paper, he describes the product as far superior to amber for pipe stem and similar articles, less flexible but more durable than celluloid, odorless, and fire-resistant. ° The reaction between phenol and formaldehyde is either base or acid catalyzed, and the polymers are termed resols (for the base catalyzed) and novalacs (for the acid catalyzed). 

Crosslinking in phenol-formaldehyde resins is carried out on essentially linear prepolymers which have been formed by having one of the components in sufficient excess to minimise crosslinking during the initial step. These prepolymers may be one of two kinds the so-called resoles or the so-called novolaks. 

The route to crosslinked phenol-formaldehyde resins via resoles corresponds to that used by Baekeland in his original commercial technique. They now tend to be used for adhesives, binders, and laminates. The resole... 

Phenol-formaldehyde resins using prepolymers such as novolaks and resols are widely used in industrial fields. These resins show excellent toughness and thermal-resistant properties, but the general concern over the toxicity of formaldehyde has resulted in limitations on their preparation and use. Therefore, an alternative process for the synthesis of phenolic polymers avoiding the use of formaldehyde is strongly desired. 

Acid Curing. Urea-formaldehyde resins and resol-phenol-formaldehyde resins can be acid-cured by wastes from the production of maleic anhydride [1902]. The waste from the production of maleic anhydride contains up to 50% maleic anhydride, in addition to phthalic anhydride, citraconic anhydride, benzoic acid, o-tolulic acid, and phthalide. The plugging solution is prepared by mixing a urea-formaldehyde resin with a phenol-formaldehyde resin, adding the waste from production of maleic anhydride, and mixing thoroughly. 

V. B. Zhukhovitskij, M. I. Kolomoets, and A. M. Zagrudnyj. Polymeric plugging solution contains urea-formaldehyde resin, expandable resol-phenol-formaldehyde resin containing surfactant and aluminium powder, and maleic anhydride production waste. Patent SU 1728473-A, 1992. 

Molecular Weight Characterization of Resole Phenol—Formaldehyde Resins... 

Dase-catalyzed phenol-formaldehyde resins polymerized with a mole ratio of formaldehyde to phenol greater than one pose an interesting molecular weight characterization problem. This system is a dynamic one with active methylol end groups. Branched and crosslinked structures are formed, and in general, the separation of the resin from the reaction mixture is difficult. Figure 1 illustrates the chemical nature of a resole resin. 

Processing of phenol-aldehyde oligomers into various articles is based on a polycondensation reaction which leads to solidification of the material at temperatures below 200°C and pressures exceeding 10 MPa. The process is accompanied by volatile product formation. However, phenol-formaldehyde resins of the resol type can be cast without additional pressure and heat. The raw molding reactants contain different organic and mineral fillers and other additives in addition to the basic resin. 

Resorcinol-phenol-formaldehyde resins are produced by combining phenol with formaldehyde, under mild alkaline conditions, before the resorcinol is introduced. Thus these resins may be considered to be a resorcinol-modified resole type and would be a mixture of oligomers something like that shown in Figure 1. 

Resols (phenol-formaldehyde resins) are commercially used for effective crosslinking of EPDM in the production of thermoplastic vulcanisates [8]. General studies on rubber crosslinking for different diene rubbers are presented here. 

Phenol-formaldehyde resins find numerous applications in such areas as wood composites, fiber bonding, laminates, foundry resins, abrasives, friction and molding materials, coatings and adhesives, and flame retardants (JL). From a specialty chemicals standpoint, they are also used as developer resins in carbonless papers (2.). Conventional methods of preparation involve condensation of a phenol with formaldehyde under either acidic (novolak) or basic (resole) conditions (2). Their typical molecular weight range is from 800-4000 daltons (D) and includes a wide variety of alkyl or aryl substituted phenols (A)- The... 

Figure 14.7 Representative structures of phenol-formaldehyde resins (a) novolac (formed under acidic conditions), and (b) resole (formed under basic conditions).

Certain phenolic-formaldehyde resins can be made to cure in the absence of metals and they are ortho-ortho resoles, etc., and these adhesives will not be discussed further. 

These resins (Resole or Novolac) are used as curing agents or hardeners for epoxy molding compounds for electronics applications such as computer components. 0-cresol-formaldehyde resins have heen also used to modify phenol-formaldehyde resins, and in laminates. 

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