Resoles properties

Other Reactants. Other reactants are used in smaller amounts to provide phenoHc resins that have specific properties, especially coatings appHcations. Aniline had been incorporated into both resoles and novolaks but this practice has been generally discontinued because of the toxicity of aromatic amines. Other materials include rosin (abietic acid), dicyclopentadiene, unsaturated oils such as tung oil and linseed oil, and polyvalent cations for cross-linking. 

Alkaline Catalysts, Resoles. Resole-type phenoHc resins are produced with a molar ratio of formaldehyde to phenol of 1.2 1 to 3.0 1. For substituted phenols, the ratio is usually 1.2 1 to 1.8 1. Common alkaline catalysts are NaOH, Ca(OH)2, and Ba(OH)2. Whereas novolak resins and strong acid catalysis result in a limited number of stmctures and properties, resoles cover a much wider spectmm. Resoles may be soHds or Hquids, water-soluble or -insoluble, alkaline or neutral, slowly curing or highly reactive. In the first step, the phenolate anion is formed by delocali2ation of the negative charge to the ortho and para positions. 

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). 

Air and Oil Filters. Liquid resole resins are used to coat and penetrate the cellulose fibers of filters and separators in order to increase strength and stiffness and protect against attack by the environment. The type of phenoHc to be used depends on both the final property requirements and the papermaking process. 

The phenoHc resins used for particle board are NaOH-catalyzed resoles of low viscosity and high water miscibility, similar to the Hquid resole adhesives used in plywood manufacture. The higher resin and caustic content of the board frequently necessitates the addition of hydrophobic agents such as wax emulsions to increase the barrier properties of the board. The adhesive is appHed to the particles in thin streams using high agitation to maximize material usage. Boards are cured in presses for 5—10 min at 150—185°C. 

PhenoHc and furfuryl alcohol resins have a high char strength and penetrate into the fibrous core of the fiber stmcture. The phenoHc resins are low viscosity resoles some have been neutralized and have the salt removed. An autoclave is used to apply the vacuum and pressure required for good impregnation and sufficient heat for a resin cure, eg, at 180°C. The slow pyrolysis of the part foUows temperatures of 730—1000°C are recommended for the best properties. On occasion, temperatures up to 1260°C are used and constant weight is possible even up to 2760°C (93). 

In contrast to the caustic soda-catalysed resols the spirit-soluble resins have good electrical insulation properties. In order to obtain superior insulation characteristics a cresol-based resol is generally used. In a typical reaction the refluxing time is about 30 minutes followed by dehydration under vacuum for periods up to 4 hours. 

Resoles are usually those phenolics made under alkaline conditions with an excess of aldehyde. The name denotes a phenol alcohol, which is the dominant species in most resoles. The most common catalyst is sodium hydroxide, though lithium, potassium, magnesium, calcium, strontium, and barium hydroxides or oxides are also frequently used. Amine catalysis is also common. Occasionally, a Lewis acid salt, such as zinc acetate or tin chloride will be used to achieve some special property. Due to inclusion of excess aldehyde, resoles are capable of curing without addition of methylene donors. Although cure accelerators are available, it is common to cure resoles by application of heat alone. 

As with resoles, the central issue in design of novolacs is molecular weight. The effects of formaldehyde-to-phenol molar ratio and formaldehyde conversion on molecular weight of novolacs has been well studied and reported [192,193]. The effects of molecular weight on most of the important properties are also available [193]. These include Tg, melt viscosity, gel time, hot-plate flow, glass-plate flow. 

Standard-grade PSAs are usually made from styrene-butadiene rubber (SBR), natural rubber, or blends thereof in solution. In addition to rubbers, polyacrylates, polymethylacrylates, polyfvinyl ethers), polychloroprene, and polyisobutenes are often components of the system ([198], pp. 25-39). These are often modified with phenolic resins, or resins based on rosin esters, coumarones, or hydrocarbons. Phenolic resins improve temperature resistance, solvent resistance, and cohesive strength of PSA ([196], pp. 276-278). Antioxidants and tackifiers are also essential components. Sometimes the tackifier will be a lower molecular weight component of the high polymer system. The phenolic resins may be standard resoles, alkyl phenolics, or terpene-phenolic systems ([198], pp. 25-39 and 80-81). Pressure-sensitive dispersions are normally comprised of special acrylic ester copolymers with resin modifiers. The high polymer base used determines adhesive and cohesive properties of the PSA. 

The final structure of resins produced depends on the reaction condition. Formaldehyde to phenol (F/P) and hydroxyl to phenol (OH/P) molar ratios as well as ruction temperahne were the most important parameters in synthesis of resols. In this study, the effect of F/P and OH/P wt%, and reaction temperature on the chemical structure (mono-, di- and trisubstitution of methyrol group, methylene bridge, phenolic hemiformals, etc.) was studied utilizing a two-level full factorial experimental design. The result obtained may be applied to control the physical and chemical properties of pre-polymer. 

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. 

These thermoplastic resoles and novolacs are mixed with lubricants, pigments and additives, such as wood flour. The molding compound is converted to an infusible resin by heating it under pressure in a mold. A typical sequence of chemical reactions associated with the formation of this complex, three-dimensional polymer is shown in Figure 15.4. Typical properties of phenolic plastics are shown in Table 15.4. 

In order to prepare better adhesives, the effect of phenolation time, phenolation temperature, reaction time for resol resinification, and degree of lignin purity were examined on the adhesive properties. The results indicated that optimum conditions for phenolation involve 200°C for 60 min and 60 min resol resinification at 90°C and at pH 9. The conditions for resol resinification correspond well to those of the conventional manufacturing method (24). 

It was also found that the lignin-resol resin adhesives satisfied the JIS requirements for non-volatile content, pH value, viscosity, gel time, and dry and wet adhesion strength. Furthermore, the low temperature curability typically found in amino resin adhesives could also be achieved. Thus, it can be concluded that an effective utilization of lignin is possible with simultaneous improvement of the properties of resol resin adhesives. 

Numerous studies have probed how novolac microstructure influences resist lithographic properties. In one example, a series of resists were formulated from novolacs prepared with varying feed ratios ofpara-l/neta-ctesol. These researchers found that the dissolution rate decreased, and the resist contrast increased, as the para-/tneta-cresol feed ratio increased (33). Condensation can only occur at the ortho position ofpara-o.resol, but can occur at both the ortho- and ra-positions of meta-cresol. It is believed that increased steric factors and chain rigidity that accompany increasedpara-ctescA content modify the polymer solubility. 

Until recently, the materials made from epoxy binders and glass microspheres were believed to be the strongest syntactic foams. However, several papers 26,39) have shown that, when carbon microspheres replace those of glass, the material becomes stronger, more water resistant, and more capable to withstand hydrostatic pressure (for the same filler concentration) (Table 13). The smaller the carbon microspheres, the stronger are the resulting foams, 9 135). Carbon microspheres also improve the mechanical properties of phenolic and resol syntactic materials (Table 14) 38). 

These adhesives are generally based on blends of solid epoxy resins with resole-type phenolic resin. The epoxy resin component is often not the predominant component in the blend, depending on the end properties required. Phenolics are compatible with epoxy resins and will react through the phenolic hydroxyl group. The amount of phenolic resin used is generally much greater than that required to crosslink with the epoxy, so one can debate whether (1) the epoxy toughens the phenolic adhesive or (2) the phenolic increases the heat resistance of the epoxy. 

Experiment 2. Effect of Molar Ratio of Sodium Hydroxide to Phenol of Phenolic Resin on Strength Properties of Lignin-Phenolic Resin Adhesives. Sodium hydroxide has been the predominant chemical used as a catalyst in resol resin technology. Through variation in the amounts of the catalyst and the method of catalyst addition, a wide variety of resin systems can be formulated. This experiment examined the properties of phenolic resins formulated with various sodium hydroxide/phenol ratios and their effects on the bond properties of structural flakeboards made with lignin-phenolic resin adhesive systems. Variables for resin preparation were four molar ratios of sodium hydroxide/phenol (i.e., 0.2, 0.45,0.7, and 0.95). The formaldehyde/phenol ratio and solids content were fixed at 3/1 and 42%, respectively. 

Finally, various Mannich bases used as catalysts in the crosslinking of oligomers (see also Chap. V, A.2.), are worth mentioning. Their basic properties are applied in the curing of epoxy oligomers- as well as in the production of polyurethanes and, less frequently, in the crosslinking of resols. - Compounds of types 426 and 427 are employed mostly for the above purposes. 

This paper reports on radical polymerization of MMA in phenolic resol and confirmation of the structure by measurement of d3mamic mechanical properties, scanning electron microscopy, and tensile tests, then the damping ability of these vinyl compound/phenolic IPNs is evaluated. 

Dynamic mechanical properties of IPN 1, IPN 2, poly 23G and cured phenolic resol (CPR) were examined, in order to investigate IPN structure. 

From the results of the previous section, it is considered that IPN 1 has properties of both poly 23G and cured phenolic resol. 

Properties of vinyl compound/phenolic IPN were discussed and the following conclusions drawn. MMA radical polymerization proceeded rapidly in the presence of phenolic resol. Poly (ethylene glycol) dimethacrylate, 23G, and phenolic resol IPNs were synthesized by simultaneous radical polymerization and phenolic resol curing reaction. These IPNs had a structure of poly 23G chains and cured phenolic resol chains so well entangled with each other that the whole acted as a single phase. This type of IPN is considered to... 

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