Phenol formaldehyde contact adhesive

An emulsion polymer-isocyanate adhesive, a crosslinked polyvinyl acetate adhesive, a resorcinol-formaldehyde adhesive, a phenol-resorcinol-formalde-hyde adhesive, and an acid-catalyzed phenolic-formaldehyde adhesive developed bonds of high shear strength and wood failure at all levels of acetylation in the dry condition. A neoprene contact bond adhesive and a moisture-curing polyurethane hot-melt adhesive performed as well on acetylated wood as untreated wood in tests of dry strength. Only a cold-setting resorcinol-formal-... 

Bonding, contact angle, heat-treated wood, penetration, phenol-formaldehyde adhesive, shear strength... 

PVAc-based commercial wood adhesives are evaluated using standard tests for non-structural applications, as reported in EN 205 [8], and they are classified in agreement with the standard EN-204 [9]. This standard allows to classify wood adhesives in 4 categories from D1 to D4. D1 adhesives show a good resistance only in dry conditions D2 adhesives should withstand a rather low water presence, such as in occasional exposure in kitchens and bathrooms D3 adhesives are suitable to come in contact with cold water, such as for outside windows and doors, kitchen and bathrooms furniture D4 adhesives are suitable to be used in extreme conditions (resistance to hot water). Vinyl acetate homopolymer can be used to formulate D1 or D2 adhesives. Vinyl acetate based adhesives cross-Unked with hardeners and urea-formaldehyde (UF) adhesives belong to class D3. Only the phenol-formaldehyde (PE), resorcinol-formaldehyde (RF) and melamine-formaldehyde (MF) adhesives, some special 2-component polyurethanes (PUs), and cross-linking vinyl adhesives belong to class D4. 

Resins, especially those containing epoxy, colophony, and PTEP-FR, are used as adhesives and glues in sports equipment. Reports of contact allergy include facial dermatitis from epoxy resin glue inside a helmet (Malanin and Kalimo 1985), erythematous facial dermatitis from colophony in a bowlsgrip (Elair 1982), and a well-demarcated linear erythematous vesicular patch on the back of a leg from the PTEP-FR and/or phenol-formaldehyde resin in a knee-guard (Vincenzi et al. 1992). 

Resins based on para-substituted phenols can be either one-step or two-step, but they cannot cure to a thermoset state. In the manufacture of phenolic resins, smaller quantities of acetaldehyde and furfuraldehyde are used in addition to formaldehyde. Furthermore, resorcinol, bisphenol A, and p-alkylphenols are employed, in addition to phenol, when special properties are desired. Formaldehyde concentrations of 37-50 weight % in aqueous solutions are most commonly employed. The catalysts most frequently used are acids such as oxalic, hydrochloric, sulfuric, p-toluenesul-fonic, and phosphoric and bases such as sodium, calcium, and barium hydroxide. In the weakly acidic range metal carboxylates are employed. Thermoset phenolic resins are employed as structural adhesives for laminating and bonding applications. Para-alkyl-substituted resins are employed as tackifiers in contact adhesives, pressure-sensitive adhesives, and hot-melt adhesives. 

Phenol formaldehyde resins have the largest voliune use of any synthetic adhesive. The major market is for adhesives for exterior grade plywood. This is due to their low cost and good water resistance. Other applications are as contact adhesives for furniture and shoes, in foundry sand applications, and brake lining composites. 

Polycondensation adhesives based on phenol or phenol derivates with formaldehyde are mainly used in the production of wooden constructions (in woodworking one traditionally talks of glueing instead of bonding ), for example, in the manufacturing of laminated bonds (plywood, chipboard, fiber board, beams). Since in these applications, the adherends are able to absorb the water developing during the polycondensation reaction, the processing occurs in heated presses to enable the application of the necessary contact pressure at the required temperature (Section 7.2.4). For applications in nonindustrial fields these adhesive are practically unimportant. 

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