Resins, phenol-formaldehyde

1 Pyrolysis Products of Cured Phenol-Formaldehyde Resin 

The thermal production of volatile compounds progresses in the temperature range 450-620°C in phenol-formaldehyde resin. From novolacs about 20%, while from cured 

This work was supported by the Hungarian National Research Fund (OTKA contract no. T047377). 

Johansen, L. S. Ettre and R. L. Miller, Quantitative analysis of hydrocarbons by structural group type in gasolines and distillates I. Gas chromatography, J. Chro-matogr., 256, 393-417 (1983). 

Hayes and S. D. Anderson, Hydrocarbon group type analyzer system for the rapid determination of saturates, olefins, and aromatics in hydrocarbon distillate products. Anal. Chem., 58, 2384-2388 (1986). 

The formation of various types of phenol - formaldehyde resins (the so-called Bakelite) may be demonstrated by the following experiments. 

In a 500 ml. conical flask place 50 ml. of glachtl acetic acid, 25 ml. of 40 per cent, formaldehyde solution (formalin) and 20 g. of phenol. Wrap a cloth or towel loosely around the neck and opening of the flask. Pass dry hydrogen chloride gas (Section 11,48,1) into the mixture. Within 5 minutes, a large mass of pink plastic is formed the reaction is sometimes very vigorous. The yield is 36 g. It is frequently necessary to break the flask in order to remove the product completely for this reason a beaker, or metal flask or beaker, is preferable. 

In a wide-mouthed test-tube ( boiling tube ) place 5 g. of phenol, 15 ml. of 40 per cent, formaldehyde solution and 3 ml. of concentrated ammonia solution (sp. gr. 0-88). Warm the mixtme with a small flame until it becomes opaque. Cool, discard the aqueous layer, but retain the viscous material in the tube. Heat the latter in a water bath at 60° for 30 minutes and then heat the pasty mass in an air oven at 75° for 4-6 hours. A hard sohd resin is produced. 

Place 25 g. of methyl methacrylate polymer (G.B. Diakon (powder). Perspex (sheet) U.S.A. Lucite, Plexiglass) in a 100 ml. Claisen flask, attach an efficient condenser e.g., of the double smface type) and distil with a small luminous flame move the flame to and fro around the sides of the flask. At about 300° the polymer softens and undergoes rapid depolymerisation to the monomer, methyl methacrylate, which distils over into the receiver. Continue the distillation until only a small black residue (3-4 g.) remains. Redistil the hquid it passes over at 100-110°, mainly at 100-102°. The yield of methyl methacrylate (monomer) is 20 g. If the monomer is to be kept for any period, add 0 -1 g. of hydro quinone to act as a stabiUser or inhibitor of polymerisation. 

Place 10 g. of hquid methyl methacrylate in a test-tube, add 10-20 mg. of benzoyl peroxide (Section IV, 196), stopper the test-tube loosely and heat in a boiling water bath. After 20-25 minutes, the hquid suddenly becomes very viscous and soon sets to a hard, colourless mass of the polymer. 

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Ion-exchange resins. The constituent phenolic hydroxyl groups in the insoluble phenol-formaldehyde resins react with cations of salts ... 

Phenol-Formaldehyde Resin. Phenol-formaldehyde resin is prepared as follows ... 

Table 5.7 Calculated Values of a and f for Phenol-formaldehyde Resins Formed from Different Proportions of Reactants and Based on Experimental Values of n and n .

The synthesis in 1912 of phenol—formaldehyde resins by Baekeland, which forms the basis of many modern day adhesives. 

The first cellular synthetic plastic was an unwanted cellular phenol—formaldehyde resin produced by early workers in this field. The elimination of cell formation in these resins, as given by Baekeland in his 1909 heat and pressure patent (2), is generally considered the birth of the plastics industry. The first commercial cellular polymer was sponge mbber, introduced between 1910 and 1920 (3). 

Amino and Phenolic Resins. The largest use of formaldehyde is in the manufacture of urea—formaldehyde, phenol—formaldehyde, and melamine—formaldehyde resins, accounting for over one-half (51%) of the total demand (115). These resins find use as adhesives for binding wood products that comprise particle board, fiber board, and plywood. Plywood is the largest market for phenol—formaldehyde resins particle board is the largest for urea—formaldehyde resins. Under certain conditions, urea—formaldehyde resins may release formaldehyde that has been alleged to create health or environmental problems (see Amino RESINS AND PLASTICS). 

Phenol—formaldehyde resins are used as mol ding compounds (see Phenolic resins). Their thermal and electrical properties allow use in electrical, automotive, and kitchen parts. Other uses for phenol—formaldehyde resins include phenoHc foam insulation, foundry mold binders, decorative and industrial laminates, and binders for insulating materials. 

Amino resins are thermosetting polymers made by combining an aldehyde with a compound containing an amino (—NH2) group. Urea—formaldehyde (U/F) accounts for over 80% of amino resins melamine—formaldehyde accounts for most of the rest. Other aldehydes and other amino compounds are used to a very minor extent. The first commercially important amino resin appeared about 1930, or some 20 years after the introduction of phenol—formaldehyde resins and plastics (see Phenolic resins). 

Platinum-group metals (qv) form complexes with chelating polymers with various 8-mercaptoquinoline [491-33-8] derivatives (83) (see Chelating agents). Hydroxy-substituted quinolines have been incorporated in phenol—formaldehyde resins (84). Stannic chloride catalyzes the condensation of bis(chloromethyl)benzene with quinoline (85). 

Quinone dioximes, alkylphenol disulfides, and phenol—formaldehyde reaction products are used to cross-link halobutyl mbbers. In some cases, nonhalogenated butyl mbber can be cross-linked by these materials if there is some other source of halogen in the formulation. Alkylphenol disulfides are used in halobutyl innerliners for tires. Methylol phenol—formaldehyde resins are used for heat resistance in tire curing bladders. Bisphenols, accelerated by phosphonium salts, are used to cross-link fluorocarbon mbbers. 

Phenol, in its various purity grades, is used for phenol—formaldehyde resins to bond constmction materials like plywood and composition board (40% of the phenol produced), for the bisphenol A employed in making epoxy resins (qv) and polycarbonate (qv) (30%), and for caprolactam (qv), the starting material for nylon-6 (20%). Minor amounts ate used for alkylphenols (qv) and pharmaceuticals (10). 

Phenolic resins are also widely known as phenol-formaldehyde resins, PF resins and phenoplasts. The trade name Bakelite has in the past been widely and erroneously used as a common noun and indeed is noted as such in many English dictionaries. 

It is likely that the quinone methide and related structures formed at these temperatures account for the dark colour of phenolic compression mouldings. It is to be noted that cast phenol-formaldehyde resins, which are hardened at much... 

Woodflour, a fine sawdust preferably obtained from softwoods such as pine, spruce and poplar, is the most commonly used filler. Somewhat fibrous in nature, it is not only an effective diluent for the resin to reduce exotheim and shrinkage, but it is also cheap and improves the impact strength of the mouldings. There is a good adhesion between phenol-formaldehyde resin and the woodflour and it is possible that some chemical bonding may occur. 

The term aminoplastics has been coined to cover a range of resinous polymers produced by interaction of amines or amides with aldehydes. Of the various polymers of this type that have been produced there are two of current commercial importance in the field of plastics, the urea-formaldehyde and the melamine-formaldehyde resins. There has in the past also been some commercial interest in aniline-formaldehyde resins and in systems containing thiourea but today these are of little or no importance. Melamine-phenol-formaldehyde resins have also been introduced for use in moulding powders, and benzoguanamine-based resins are used for surface coating applications. 

Moulding powders based on melamine-phenol-formaldehyde resins were introduced by Bakelite Ltd, in the early 1960s. Some of the principal physical properties of mouldings from these materials are given in Table 24.1. 

A hard carbon with high capacity can be made from epoxy novolac resin [12]. The epoxy resins used cost about US 2.50 per pound and give pyrolysis yields between 20 and 30%. However, it is well known that phenolic (or phenol-formaldehyde) resins can be pyrolyzed to give hard carbons with a yield of over 50% [42]. In addition, these resins cost about USSl.OO per pound. Phenolic resins therefore offer significant cost advantages over epoxy resins, so we... 

Carbon, hydrogen and possibly oxygen Resin and derivatives Natural drying oils Cellulose derivatives Alkyd resins Epoxy resins (uncured) Phenol-formaldehyde resins Polystyrene Acrylic resins Natural and synthetic rubbers Carbon monoxide Aldehydes (particularly formaldehyde, acrolein and unsaturated aldehydes) Carboxylic acids Phenols Unsaturated hydrocarbons Monomers, e.g. from polystyrene and acrylic resins... 

Phenol-formaldehyde resins. These arc used to cure butyl rubber forming thermally stable carbon-carbon cross-links. 

Tackifiers. Resins are generally added to adjust the desired tack. In general, resins must be used with plasticizers to obtain a good balance between tack and cohesive strength. Typical tackifiers are polyterpenes, although hydrocarbon resins and modified rosins and rosin esters can also be used. In some cases, terpene-phenolics or phenol-formaldehyde resins are added to increase adhesion. 

Nitrile rubber is compatible with phenol-formaldehyde resins, resorcinol-formaldehyde resins, vinyl chloride resins, alkyd resins, coumarone-indene resins, chlorinated rubber, epoxies and other resins, forming compositions which can be cured providing excellent adhesives of high strength, high oil resistance and high resilience. On the other hand, NBR adhesives are compatible with polar adherends such as fibres, textiles, paper and wood. Specific formulations of NBR adhesives can be found in [12]. 

Prior to 1890, formaldehyde was not commercially available [2]. Thus the first phenol-formaldehyde resins were made using formaldehyde equivalents such as methylene diacetate or methylal [2,20]. The first true phenol-formaldehyde resin was made by Kleeberg at the direction of Emil Fisher in 1891 [2,21]. Saliginen (o-hydroxymethyl phenol) was recognized as a condensation product of phenol and formaldehyde in 1894 and was the subject of United States patents in 1894 and 1896 [22,23]. 

In general, the reaction between a phenol and an aldehyde is classified as an electrophilic aromatic substitution, though some researchers have classed it as a nucleophilic substitution (Sn2) on aldehyde [84]. These mechanisms are probably indistinguishable on the basis of kinetics, though the charge-dispersed sp carbon structure of phenate does not fit our normal concept of a good nucleophile. In phenol-formaldehyde resins, the observed hydroxymethylation kinetics are second-order, first-order in phenol and first-order in formaldehyde. 

Since few commercial phenol-formaldehyde resins are made at molar ratios of 3 1 (F P), Fig. 8 was generated at a molar ratio of 2 1 to see how Freeman s predictions would look. The concentration of reagents is still quite low compared to most commercial resins, but a comparison of species is easier if we maintain the same initial concentration of phenol used by Freeman and Lewis. As expected. 

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