PHENOL-FORMALDEHYDE RESOL RESIN

Phenol-formaldehyde resole resins, preparations of, 429 Phenolic-based networks, 376 Phenolic compounds, 62 Phenolic cyanate resins, 418... 

A Statistical study of phenol-formaldehyde resol resin synthesis reaction... 

J. Monni, R Niemela, L. Alvila and T.T. Rakkanen, Online monitoring of synthesis and curing of phenol-formaldehyde resol resins by Raman spectroscopy. Polymer, 49, 3865-3874 (2008). 

Figure 1. Representation of a branched phenol-formaldehyde resole resin...

KI1 Kim, M.G., Nieh, W.L., Sellers, T., Wilson, W.W., and Mays, J.W., Polymer solution properties of a phenol-formaldehyde resol resin by gel permeation ehromatography, intrinsic viscosity, static hght scattering, and vapor pressure osmometric methods,/wJ. Eng. Chem. Res., 31, 973,1992. 

Journal of Applied Polymer Science 69, No. 11, 12th Sept. 1998, p.2175-85 IR SPECTROSCOPY AS A QUANTITATIVE AND PREDICTIVE ANALYSIS METHOD OF PHENOL-FORMALDEHYDE RESOL RESINS Holopainen T Alvila L Rainio J Pakkanen T T Joensuu,University Dynoresin Oy... 

An industrial phenol formaldehyde resole resin/catalyst system specifically developed for filament winding but also suitable for pultrusion, RTM and hand-lay in the manufacture of products offering superior flame resistance with low smoke generation as required in many sectors of the aerospace, construction and mass transportation markets. 

More details on the reaction rates and structures produced in a phenol-formaldehyde resole resin has been obtained in a carbon-13 NMR and gel permeation chromatography (gpc) study [34]. In this study an alkaline resole resin typrint of the wood products binder industry was prepared as described in preparation 2-8 below and samples withdrawn at various stages for analyses by NMR and GPC. Details of the analysis are described in the referenced paper, and the reader is referred to this... 

Most processors of fiber-reinforced composites choose a phenol formaldehyde (phenoHc) resin because these resins are inherently fire retardant, are highly heat resistant, and are very low in cost. When exposed to flames they give off very Htde smoke and that smoke is of low immediate toxicity. PhenoHc resins (qv) are often not chosen, however, because the resole types have limited shelf stabiHty, both resole and novolac types release volatiles during their condensation cure, formaldehyde [50-00-0] emissions are possible during both handling and cure, and the polymers formed are brittle compared with other thermosetting resins. 

Phenol-formaldehyde (PF) resins were synthesized to manufacture non-flammable insulating foam. When alkali catalyst, for example, barium hydroxide (Ba(OH)2), was present, lesol resins are produced[l]. In the analj s of molecular species of resol, capillary GC-MS had been used to separate hemiformal-type compoimds(acetylated hydroxybenzylhaniformals)... 

Phenolic resins for plywood are typically caustic-catalyzed phenol-formaldehyde resoles. Typical resins are water solutions containing 40-44 percent resin solids composed of 23 - 25 percent phenol, 5-7 percent sodium hydroxide and 10 - 12 percent formaldehyde. The ratio of formaldehyde to phenol in a resin has a decided effect on performance characteristics as does the synthesis procedure used in manufacturing the resin. 

Fast pyrolysis of biomass provides a method for the production of phenolics that has the potential to replace at least 50% or more of the phenol in phenol-formaldehyde thermosetting resins. The gel tests indicate that the P/N fractions from pine sawdust pyrolysis with paraformaldehyde have shorter gel times than commercial plywood resins such as Cascophen 313, even without prepolymer formation. A novolak formulation has been prepared using 1 1 by volume of phenol and P/N fraction and about half of the amount of formaldehyde that would be used than if phenol alone were employed. Very promising resols have also been made with a similar substitution of the P/N fraction for phenol. Wood testing and resin formulation development are ongoing activities. The projected economics suggest that additional research and development of this process are fully warranted. 

Including 4-bromophenol in the phenol-formaldehyde resol system impacts the cross-link density of the cured product. In a systematic study of this copolymer, a comparison was made among the polymers obtained using phenol only, a 9 1 mole ratio of phenol to 4-bromophenol and a 1 1 mole ratio of phenol to 4-bromophenol. Comparisons included measurement of interlaminar shear strength and cone calorimetry tests of composites prepared using these phenolic resins and S2-glass fiber plain weave. 

Whereas celluloid was the first plastic material obtained by chemical modification of cellulose, the phenol-formaldehyde (PF) resin was the first commercially successful synthetic plastic. This phenolic plastic was discovered by L.Fi. Baekeland in Belgium in 1907, and Bakelite was produced industrially in 1910. Baekeland used the term resole to describe PF resins made with an alkaline catalyst, and those made with an acidic catalyst were called novolac. The ability of formaldehyde to transform some products in resinous materials was observed by Butlerov (1859) and Bayer (1872) [3]. 

The melamine- and urea-formaldehyde resins are also called amino resins (118). The phenol-formaldehyde resoles are often called phenolic resins, which is rather easily confused with phenolic-terminated cross-linkers such as novolacs and bisphenol A terminated resins. 

Resorcinol-Formaldehyde Resins (Moult, 1977 Dick, 1987) - Resorcinol adhesives are eondensation products of resorcinol with formaldehyde or various phenol-formaldehyde resoles. Most of the adhesives manufaetured are of the second type due to their lower cost. Resorcinol is much more reactive with formaldehyde dian phenol since it has two meta hydroxyl groups. The two groups reinforce eaeh other in their activation of the ortho and para positions of the benzene ring. To make stable resorcinol/formaldehyde resins which do not gel on aging, 0.5 to 0.7 moles of formaldehyde is added per mole of resorcinol. At the time of use, some additional formaldehyde is added and... 

Special resoles are obtained with amine catalysts, which affect chemical and physical properties because amine is incorporated into the resin. For example, the reaction of phenol, formaldehyde, and dimethylamine is essentially quantitative (28). 

The in situ process is simpler because it requires less material handling (35) however, this process has been used only for resole resins. When phenol is used, the reaction system is initially one-phase alkylated phenols and bisphenol A present special problems. As the reaction with formaldehyde progresses at 80—100°C, the resin becomes water-insoluble and phase separation takes place. Catalysts such as hexa produce an early phase separation, whereas NaOH-based resins retain water solubiUty to a higher molecular weight. If the reaction medium contains a protective coUoid at phase separation, a resin-in-water dispersion forms. Alternatively, the protective coUoid can be added later in the reaction sequence, in which case the reaction mass may temporarily be a water-in-resin dispersion. The protective coUoid serves to assist particle formation and stabUizes the final particles against coalescence. Some examples of protective coUoids are poly(vinyl alcohol), gum arabic, and hydroxyethjlceUulose. 

Resoles. The advancement and cure of resole resins foUow reaction steps similar to those used for resin preparation the pH is 9 or higher and reaction temperature should not exceed 180°C. Methylol groups condense with other methylols to give dibenzyl ethers and react at the ortho and para positions on the phenol to give diphenyknethylenes. In addition, dibenzyl ethers eliminate formaldehyde to give diphenyknethanes. 

Different phenoHc resins are used for different types of wood for example, plywood adhesives contain alkaline-catalyzed Hquid resole resins. Extension with a filler reduces cost, minimizes absorption, and increases bond strength. These resins have an alkaline content of 5—7% and are low in free phenol and formaldehyde. Because many resins have a high water content and limited storage stabiHty, they are frequently made at or near the mill producing the plywood product. The plywood veneers are dried, coated with resin, stacked for pressing, and cured at 140—150°C. 

Reactions with Aldehydes and Ketones. An important use for alkylphenols is ia phenol—formaldehyde resias. These resias are classified as resoles or aovolaks (see Phenolic resins). Resoles are produced whea oae or more moles of formaldehyde react with oae mole of pheaol uader basic catalysis. These resias are thermosets. Novolaks are thermoplastic resias formed whea an excess of phenol reacts with formaldehyde under acidic conditions. The acid protonates formaldehyde to generate the alkylating electrophile (17). 

The importance of the nature of the catalyst on the hardening reaction must also be stressed. Strong acids will sufficiently catalyse a resol to cure thin films at room temperature, but as the pH rises there will be a reduction in activity which passes through a minimum at about pH 7. Under alkaline conditions the rate of reaction is related to the type of catalyst and to its concentration. The effect of pH value on the gelling time of a casting resin (phenol-formaldehyde ratio 1 2.25) is shown in Figure 23.15. 

---