Resol-type phenol resin adhesives

Resol-Type Phenol Resin Adhesives from Kraft Lignin... 

From liquified solutions of untreated wood, almost the same products have been prepared as those from chemically modified wood [7,8,23,26]. For example, resol-type phenol resin adhesives prepared from five parts of wood chips and two parts of phenol, liquified at 250°C without catalyst, did not require severe adhesion conditions and were comparable to the corresponding commercial adhesives in their gluability. Acceptable waterproof adhesion was attained from the adhesives after gluing wood veneers at 120-130°C with a hot-pressing time of 0.5 min to 1 mm-thick plywood [27]. 

Resol-type phenol resin adhesives were also prepared from wood-phenol solutions liquified at ISO C with phenolsulfonic acid catalyst and their gluabili-ties were examined [12]. The results revealed that when these adhesives were used, it was easily possible to realize completely satisfactory waterproof... 

Cure Rate of the Phenolated SEL Resins. 13C NMR spectra of the phenolated SEL formaldehyde-treated resins revealed the formation of methylol groups. A similar cure reaction to resole type phenolic resins is expected to occur with the phenolated lignin-based resins. Since cure rate normally determines production capacity of a board mill, it is important that new types of adhesives have at least the same cure rate as the conventional phenolic adhesives. Cure analysis of resins has usually been examined by... 

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. 

Choi and Chung [16] were the first to prepare phenolic resin/layered sihcate nanocomposites with intercalated or exfoliated nanostructures by melt interaction using linear novolac and examined their mechanical properties and thermal stability. Lee and Giannelis [10] reported a melt interaction method for phenolic resin/clay nanocomposites, too. Although PF resin is a widely used polymer, there are not many research reports on PF resin/montmorillonite nanocomposites, and most of the research investigations have concentrated on linear novolac resins. Up to now, only limited research studies on resole-type phenolic resin/layered silicate nanocomposites have been published [17-19] and there is still no report on the influence of nano-montmorillonite on phenolic resin as wood adhesive. Normally H-montmorillonite (HMMT) has been used as an acid catalyst for the preparation of novolac/layered silicate nanocomposites. Resole resins can be prepared by condensation reaction catalyzed by alkaline NaMMT, just as what HMMT has done for novolac resins. 

Various attempts have been made to prepare adhesives from lignin. The preparation of resol resin adhesives has been studied especially extensively. The introduction of phenols into the a or /2-position of the sidechain of the phenylpropane unit (phenolation of lignin) has been considered a key reaction for the formulation of these types of adhesives with adequate glu-ability. 

Carbohydrate-phenolic-based resins have shown promise for partial replacement of phenol and formaldehyde in exterior plywood adhesives (7,2). Such resins are produced in a two-stage reaction sequence. First, the carbohydrate is reacted with phenol, and sometimes urea, under acid catalysis at elevated temperatures (up to 150 °C), to produce an acid-stage resin. The acid-stage resin is then made basic, formaldehyde added, and the reaction continued at lower temperatures to produce a resol-type resin. Adhesives formulated from these resins have curing speeds consistent with present-day plywood production needs in the western United States, veneers are typically dried to 0 to 7% moisture content and the adhesive cured by hot pressing the panels at approximately 140 to 150 °C and 1.2 MPa. 

Phenolic adhesives are structural adhesives with specific applications, e.g. where wide gap bonding is required and where large structures need to be bonded. Phenolic resins are the product of a special reaction ratio of a phenol and formaldehyde in the presence of an organic catalyst. There are two main types of phenolic resins phenol or methylol terminated. The phenol terminated are called novalacs, while the methylol terminated are called resoles (one step resins). Modem phenolic resins are prepared in the presence of metal carboxylates and these resins contain a large number of benzylic ether linkages and have open para positions which have good temperature stability and are usually of low viscosity. 

Mildly condensed liquid resols, which are the more important of the two types of phenolic resins in the formulation of wood adhesives, have an average of fewer than two phenolic nuclei in the molecule. The solid resols average three to four phenolic nuclei but with a wider distribution of molecular size. Small amounts of simple phenol, phenolic alcohols, formaldehyde, and water are also present in resols. Heating or acidification of these resins causes cross-linking through uncondensed phenolic alcohol groups, and possibly also through reaction of formaldehyde liberated by the breakdown of the ether links. 

Adhesives of the aminoplastic (see Step polymerization) and phenol formaldehyde (see Phenolic adhesives single-stage resoles and Phenolic adhesives two-stage novolacs) types are most widely used. Although basically similar, an adhesive for plywood manufacture will require a different formulation to one for particle board, or medium-density fibre board (MDF) since methods of application and processing differ. Thus, in plywood, large sheets of veneer must be uniformly coated with adhesive, usually by a roller or curtain coater in particle board, chips or wafers must be coated with very fine adhesive droplets, while small bundles of wet fibres must be sprayed with adhesive in the manufacture of MDF. Hence, formulation and production of resins has become a mixture of art and science, with resin manufacturers able to produce resins tailored for use in a particular board-manufacturing plant, or with a particular species of timber. 

Phenol-formaldehyde This adhesive is most widely used in the manufacture of plywood. The resin is usually a resol type, prepared by the reaction of phenol with excess formaldehyde in the presence of an alkali catalyst. Curing occurs at elevated temperatures in the presence of an alkali. Phenolic adhesives need higher spreads, are slower curing... 

Although resol types are also used in the manufacture of wood chipboard, other forms of particle board, such as waferboard and oriented strand board (OSB) are usually made using novolac types. These resins are produced by reacting excess phenol with formaldehyde in the presence of an acid catalyst. The resin is converted to a fine powder, which is usually sprayed on to the large wafers along with molten wax, which helps the dry resin powder adhere to the wafers until it is cured under elevated temperatures of up to 200 °C. With this method, very small quantities of adhesive - as low as 2.5 g solid resin per 100 g dry wafers - can be used, while still achieving satisfactory bonding. 

Most phenolic adhesives are based on resoles, novolacs (or resorcinol-modified novolacs), and phenolic alloys. The last mentioned class includes the important blends of phenolic resins with epoxies, vinyl, polyamide, and nitrile rubber. Phenolic-based adhesives perform well on various types of surfaces the more common substrates are shown in Table III. 

Neoprene-phenolic contact adhesives, known for their high green strength and peel values, contain a resole-type resin prepared from 4-t-butylphenol. The alkyl group increases compatibility and reduces cross-linking. This resin reacts or complexes with the metal oxide, eg, MgO, contained in the formulation, and increases the cohesive strength of the adhesive. In fact, the reactivity with MgO is frequently measured to determine the effectiveness of heat-reactive phenolics in the formulation. 

Different phenolic resins are used for different types of wood for example, plywood adhesives contain alkaline-catalyzed liquid 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 stability, they are frequently made at or near the mill producing the plywood product. The... 

Phenolic Resins [9003-35-4], Curable phenol-formaldehyde resins of the resol type are of considerable importance as hot-setting reactive adhesives for bonding wood and metals. Suitable types are used also in combination with poly(vinyl acetals) and epoxy resins for special, in some cases filmlike, reactive adhesives for bonding metals. 

The most common types of adhesives used today in coated products are hide glues, varnishes, urea-formaldehyde, radiation-curable, and resole phenolic resins. Depending on the severity of the applications, the make and size bond formulations are modified to suit the job at hand. Combinations of the above systems are used to achieve special properties which may give certain products economic and performance advantages. 

There are two basic types of resin, one is called a two step novolac and the other is called a resole resin. The two step novolac is made using an acid catalyst with a stoichiometric excess of phenol to prevent the polymer from reaching a gel point where it crosslinks three-dimensionally. The novolac resins are cured by adding a methylene donor such as hexamethylene tetramine and then reheating the resin in its adhesive application. 

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... 

Phenolic resin is one of the common synthetic resins that have been used in a wide range of applications such as paints, adhesives, and composites. Phenolic resin is one of the thermoset class of polymers which has two types, namely resole type and novolac type, the formation of which depends on the synthetic method and catalyst used. Many attempts have been made to enhance the toughness and thermal properties of phenolic resin. By the fundamental concept of hybrid materials preparation, the sol-gel method can be utilized to incorporate inorganic components into the phenolic resin and improve its properties. These systems have been studied by Haraguchi et al. and Lin et al. ... 

Phenolic materials go back to the patents of Baekeland and are based upon the reaction of phenol and formaldehyde to yield a lower molecular weight resinous material that can be formulated with other resins and sometimes other curatives to yield a paste adhesive or a film adhesive. When phenol and formaldehyde are reacted in the presence of an acidic catalyst with an excess of phenol versus formaldehyde, they yield what are known as novolac resins. These materials are soluble in organic solvents and do not react further with themselves thus, they need to have a curative added. That curative is most often hexamethylene tetraamine. Another type of phenolic resin can be generated with an excess of formaldehyde and under basic conditions. These materials, known as resole phenolics, will react with themselves to yield a ftilly cured phenolic and thus must be stored frozen in order to limit this reaction. Thus, resole phenolics do not need an external CTOsslinker. Resole phenolics are widely used in the binding of paper products and the bonding of wood. Adhesives based upon these materials were brittle and could only be used to bond wood, where it is still widely used. A more widely usable adhesive was developed during World War II which modified the very brittle phenolic adhesive with poly(vinyl formal) resins. These materials were... 

In the manufacture of pure resorcinol resins, the reaction can be violently exothermic unless controlled by the addition of alcohols. Because the alcohols perform other useful functions in the glue mix, they are left in the liquid adhesive. PRF adhesives are generally prepared firstly by reaction of phenol with formaldehyde to form a PF resol polymer, that has been proved to be in the greatest percentage, and often completely, linear [95], In the reaction step that follows the resorcinol chemical is added in excess to the PF-resol to react it with the PF-resin -CH2OH groups to form PRF polymers in which the resorcinol groups can be resorcinol chemical or any type of resorcinol-formaldehyde polymer. 

Phenol-formaldehyde type polymers had been the only exterior-durable adhesives for wood bonding, until the recent limited use of isocyanates. Both systems are petrochemical-based. Several researchers substituted carbohydrates for part of phenolic adhesives (1-4) > producing solid, fusible novolak resins. Recently, reaction of carbohydrate acid-degradation products with phenol and formaldehyde has produced liquid resols (5). Gibbons and Wondolowski (6,7) replaced a considerable amount of phenol with carbohydrate and urea to pro-... 

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