Phenol-formaldehyde polymers. Scientific Review. Engineering Science What polymer materials are made on the basis of phenol

Phenolic polymers are the products of polycondensation of various phenols with aldehydes.

Phenol SbN50N is a crystalline substance with a melting point of 41 ° C and a boiling point of 182 ° C, mixes with alcohol and when heated with water, soluble in ether, glycerin, chloroform, etc. Phenol is obtained from coal tar - a product of dry distillation of coal - and synthetically ...

Of the aldehyde components in the preparation of phenolic polymers, formaldehyde and furfural are most often used, which form three-dimensional polymers with phenol. Formaldehyde CH20 is a gas readily soluble in water; water absorbs up to 50% formaldehyde. Aqueous solutions of formaldehyde are called formalin. When obtaining phenolic polymers, auxiliary substances are used, the most important of which are the catalysts NaOH, NH4OH, Ba (OH) 2) contact Petrov, HC1, etc. solvents - ethyl alcohol, acetone and stabilizers - ethylene glycol, glycerin, etc.

During the polycondensation of phenol with aldehydes, thermoplastic or thermosetting oligomeric products are formed. Thermoplastic phenolic polymers are called novolac polymers, and thermosetting polymers are called rezole polymers.

In the reaction of phenols with aldehydes, the formation of polymers of one type or another depends on the functionality of the phenolic component, the molar ratio of the starting materials, and the pH of the reaction medium.

When heated, the resoles cure, that is, they pass into a three-dimensional state, while the curing process goes through three stages: A, B and C.

The first stage is A-resol. The oligomer is in a liquid or solid soluble state, melts when heated and, when heated further, transforms into a solid insoluble and infusible state. In stage A, the polymer has a linear structure or slight branching of linear chains.

The second stage is B-resitol. The oligomer is hard and brittle, does not dissolve in the cold, but only swells in solvents, softens at temperature and turns into a three-dimensional infusible and insoluble state. In stage B, the polymer is in a branched state, and there are crosslinks between individual macromolecules.

The third stage is C-res. The polymer is a hard and brittle product, insoluble and infusible when heated. The polymer in this state has a three-dimensional structure with different densities of intermolecular cross-linking. The transition of an oligomer to a three-dimensional infusible and insoluble state (resit) is the result of intermolecular interaction of methyl groups and the formation of a polymer structure with a spatial structure.

The duration of the transition of the oligomer from stage A to C characterizes the rate of its curing, which can vary within wide limits from several minutes to several hours, which depends on the curing conditions and properties of the initial polymer. Technological processes for the production of novolac and rezole phenol-formaldehyde oligomers differ little from each other and practically include the same operations, with the exception of drying the finished products.

In the board industry, phenol-formaldehyde oligomers are used in the form of liquid resols for the production of plastics, plywood, fibreboard and chipboard. In the production of plywood, fibreboard and chipboard, mainly resins of the following grades are used: SFZh-3011; SFZh-3013; SFZh-3014; SFZh-3024.

To increase the shelf life and stability of the properties of hot-curing phenol-formaldehyde resins, stabilizers are used ethylene glycol (EG), diethylene glycol (DEG), polyacetal glycol with vinyloxy group and polyacetal glycol (PAT). Stabilizers are added during resin synthesis. The use of these stabilizers allows to increase the shelf life up to 4 months, with the stability of the main indicators.

The adhesive properties of these resins are influenced by their molecular weight, monomer content and the number of functional groups. For example, resins with a molecular weight of 300 ... 500 provide the greatest strength of adhesive joints. It should be noted that the formation of the properties of resole resins is possible at the stage of their preparation by changing the conditions of polycondensation.

Studies carried out at the Central Scientific Research Institute of Physics (TsNIIF) found that the lower the content of free phenol in the resin, the lower the temperature required for its curing, and the curing rate of resins with a low content of free phenol changes slightly depending on the temperature. Although with increasing temperature, the strength and water resistance of phenol-formaldehyde resins increase.

To reduce the duration of gelatinization of phenol-formaldehyde resins, when used in the production of board products, various curing accelerators are used, such as resorcinol, paraformaldehyde, guanidines, etc. Their use can reduce the curing time by 30 ... 60%.

At present, organic hardeners, isocyanates, have been found for phenol-formaldehyde resins in the manufacture of chipboards, which, in addition to reducing the curing of resins, reduce the degree of absorption of the binder by wood, which improves the processes of resinification of chips and pre-pressing of packages. In addition, various sulfonic acids are used to accelerate the curing process of phenol-formaldehyde resins. The use of sulfonic acids reduces the curing time of resins by 1.5-2 times.

In order to increase the speed and depth of curing of resins at temperatures of 105 ... 120 ° C, effective combined hardeners containing dichromates and urea have been developed and tested in industry.

In addition to the hot curing resins discussed above, cold curing adhesives based on SFZh-3016 resins have found application in the woodworking industry for gluing solid wood; SFZh-309 n VIAMF-9. As a rule, sulfonic acids are used as hardeners for cold-curing adhesives.

For the manufacture of cladding films based on kraft paper, phenol-formaldehyde impregnating resins SBS-1 are used; LBS-1; LBS-2 and LBS-9. Special-purpose plywood is faced with these films.

Chipboards and press masses based on phenol-formaldehyde oligomers are distinguished by increased water and heat resistance, as well as high resistance to weathering. For the production of chipboard, it is recommended to use oligomers with a low viscosity. Possessing high physical and mechanical properties, phenol-formaldehyde oligomers require longer pressing conditions and high temperatures.

The disadvantages of chipboards based on phenol-formaldehyde oligomers include the release of free phenol and formaldehyde, a specific smell and a dark color.

Foreword

Phenol-formaldehyde resin has been manufactured commercially since 1912 under the name Bakelite. Like many new products, Bakelite was initially viewed with skepticism and found it difficult to compete with established materials in the marketplace.

The situation quickly changed when its valuable properties were discovered - Bakelite turned out to be an excellent electrical insulating material, which at the same time has high strength. Today at home we hardly see wall plugs, plugs and electrical switches made of porcelain. They were replaced by products made of thermosetting plastics. Bakelite and related plastics have also taken pride of place in mechanical engineering, automotive and other industries.

Introduction

The synthesis of macromolecular compounds is the process of combining many molecules of individual chemical substances (monomers) by normal chemical bonds into a single polymer macromolecule.

The reaction of formation of a polymer that proceeds without the release of other chemical compounds is called a polymerization reaction. The transformation of monomers into polymers, accompanied by the release of by-products, is called polycondensation.

The high molecular weight organic compounds from which most plastics are made are also called resins.

The group of polycondensation resins includes polyester resins obtained by condensation of polybasic acids with polyhydric alcohols, phenol-formaldehyde and others.

On the basis of phenol-formaldehyde resins, plastics are made, called phenoplastics.

All plastics are divided into simple and complex in composition. Simple plastics consist mainly of a binder, sometimes with the addition of a small amount of auxiliary substances (dye, lubricant, etc.). In addition to the binder, most plastics also include other plastics. Such plastics are called complex and composite plastics.

Press materials are called compositions based on high polymer products (artificial resins, cellulose ethers, bitumen) of which different methods formations (direct pressing, casting) produce a variety of products.

Pressing materials containing resins that are cured during the pressing of products are called thermosetting.

As a result of the curing of the binder, the product acquires mechanical strength already in the mold at the pressing temperature and loses its ability to soften when reheated: the resin in the cured product is unable to melt and dissolve. This curing process is irreversible.

Thermosetting materials include phenolic, aminoplast-type press materials containing mainly polycondensation resins.

Pressing materials, called thermoplastics or thermoplastics, contain binders that do not cure during the pressing or molding process. In this case, the products acquire mechanical strength only after some cooling in the mold.

For the manufacture of phenolic plastics, phenol-formaldehyde resins are used as a binder, as well as resins obtained by partial replacement of phenol with other substances (aniline, etc.) and partial or complete replacement of formaldehyde with other aldehydes (furfural, etc.).

Depending on the ratio between phenol and formaldehyde of the catalyst used (acidic, alkaline) and the conditions of the resin formation reactions, two types of resins are obtained - novolac and resole.

Novolak resins retain the ability to melt and dissolve after repeated heating to the temperature adopted for pressing products from phenolic plastics.

Resol resins at elevated temperatures, and during long-term storage even at ordinary temperatures, pass into an infusible and insoluble state.

Rapid curing of novolac resins occurs only in the presence of special curing agents, mainly urotropine (hexamethylenetetramine). No curing agents are required to cure the resole resins.

In the process of curing resole resins, there are three stages. In stage A (resol), the resin retains the ability to melt and dissolve. In stage B (resitol), the resin practically does not melt, but is still capable of swelling in appropriate solvents. In stage C, the resin (resin) is infusible and does not even swell in solvents.

Formulations of press materials and process chemistry

Theoretical ideas about the mechanism of interaction of phenol with formaldehyde in the presence of catalysts, about the structure of phenol-formaldehyde resins in the processes of their curing are insufficiently developed.

The main components common to various press materials are: resin, fiber filler, hardener or resin curing accelerator, lubricant, colorant and various special additives.

The resin is the basis of the molding material, i.e. a binder that, at the appropriate temperature and pressure, impregnates and combines the particles of the remaining components to form a homogeneous mass.

The properties of the resin determine the basic properties of the press material. For example, on the basis of phenol-formaldehyde resin obtained in the presence of a sodium hydroxide catalyst, it is impossible to obtain a press material that, after pressing, would have high water resistance or high electrical insulating properties.

Therefore, in order to transfer certain specific properties to the press material, first of all, you need to choose the right resin (starting materials, catalyst, resin formation mode).

This makes the polymer hard, insoluble and infusible. This product of the final polycondensation stage is called resite.

In industrial processing, the resin is poured into molds at the stage of resole formation and cured in them. Curing often takes several days. This is necessary so that the water formed during the reaction evaporates slowly. Otherwise, the resin will be opaque and bubbly. To accelerate the curing, you can bring the polycondensation to the formation of a resite, then grind the resulting resin, place it in molds under a pressure of 200-250 atm and cure at 160-170 50 ° C.

If we carry out this reaction at a pH above 7, i.e. in an alkaline medium, then it will greatly slow down on the formation of a resole.

Novolak resins

In production, phenol-formaldehyde resins of both types are mainly used: novolac and resole.

In the manufacture of phenol-formaldehyde resins, synthetic phenol is used, as well as phenols obtained from coal tar (phenolic and phenol-cresol fractions, tricresol, xylenols). In addition to the listed phenols, their mixtures are used, as well as mixtures of phenol with aniline (phenol-aniline-formaldehyde resin). Formaldehyde is sometimes partially or completely replaced with furfural.

To obtain novolac resins, condensation is usually carried out in the presence of acid catalysts with an excess of phenol.

The technological process of obtaining solid novolac resin consists of the stages of condensation and drying, carried out, as a rule, in one apparatus.

In a mixture of phenol with formaldehyde, such an amount of an acid catalyst is introduced so that the pH of the reaction mixture is 1.6-2.3. The mixture is heated to boiling for 40-60 minutes with constant stirring at atmospheric pressure (less often in vacuum) with a reflux condenser turned on. ... 20 minutes after the start of boiling, an additional portion of catalyst (0.056 parts by weight of acid per 100 parts by weight of phenol) is introduced into the still. Boiling the mixture at 95-98 ° C is continued for another 1-1.5 hours. Upon reaching the specific gravity of the mixture close to 1.2 g / cm 53 0, the condensation of the resin is considered to be basically complete, turn on the direct refrigerator and begin drying, at a residual pressure of not more than 300 mm Hg, heating the apparatus with steam 5-8 at. Drying is continued until the dropping point of the resin reaches 95-105 ° C. After that, the resin is drained from the apparatus and cooled.

Lubricants (oleic acid) and colorants are often added to novolac resins.

Phenolic-formaldehyde novolac resin in solid state has a color from light to dark brown, specific gravity its about 1.2 g / cm 53 0. Such a resin is capable of repeatedly melting and re-solidifying, it dissolves well in alcohol and many solvents. The transition of the resin from the unmelted state at 150-200 5 0 0С to the infusible and insoluble state in the absence of the hardener occurs very slowly.

The melting point, viscosity and cure rate of novolac resins change very slowly over time. Therefore, such resins can be stored for several months at any temperature.

Resol resins

Unlike novolac resins, different grades of resole resins have dissimilar properties and have different purposes. Often, one brand of resole resin cannot be fully replaced by another.

To obtain resole resins, the same raw materials are used as for novolac resins (phenols, mixtures of phenol with aniline, formaldehyde). The catalyst is alkalis and bases, caustic soda, barium hydroxide, ammonia, magnesium oxide.

In the production of resole resins are used in solid and liquid state. Resol resin in a liquid state is a mixture of resin with water. Such mixtures containing up to 35% water are called emulsion resins. Partially dehydrated emulsion resins (with a moisture content not exceeding 20%) are called liquid resins.

The viscosity of emulsion resins ranges from 500-1800 centipoises, liquid resins - in the range of 500-1200 centipoises.

Hard resole resins differ little in appearance from solid novolac resins. The technological process for obtaining solid resole resins is in many ways similar to the production of novolac resins. Condensation and drying are carried out in one apparatus. Condensation, as a rule, occurs at the boiling point of the reaction mixture, within a certain time set for each brand of resin, drying is carried out at a residual pressure of no more than 200 mm Hg. The drying process is controlled by determining the rate of cure of the resin on the tile.

The finished resin is drained from the apparatus as quickly as possible and cooled in thin layer to avoid hardening.

The most important indicator of the quality of emulsion and liquid resole resins is viscosity, which sharply decreases with increasing temperature.

Storage of resole resins is allowed only for a short time (2-3 days after production), since during storage the viscosity of emulsion and liquid resins, as well as the dropping point and curing rate of solid resins, increase relatively quickly.

An important indicator is the fragility of hard resole resins. Resins with a dropping point and cure rate that are within specification sometimes lack brittleness. Then they are difficult to grind, and in the crushed state they quickly cake.

Resol resins are ground on the same equipment as novolac resins. Since the crushed resole resin, even with good brittleness, cakes quickly, it should not be stored in this state.

The most convenient containers for in-plant transportation of solid resole resins with a separate location of resin production are bags made of thick, dust-proof fabric (belting), and for emulsion resins - standard metal barrels.

Methods for the production of phenolic plastics and their processing into a product

The filler for press powders, such as phenolic plastics, is most often wood flour, much less often fine-fiber asbestos. Of mineral powdery fillers, fluorspar and pulverized quartz are used.

Pressing materials such as phenolic plastics are made by "dry" and "wet" methods. For "dry" methods, the resin is used in dry form, and for "wet" methods in the form of alcohol varnish (varnish method) or water emulsion (emulsion method).

Processing of phenolic plastics into a product is carried out different ways... The oldest and most common industrial method is direct pressing (also called hot or compression pressing) applicable to all types of described press materials.

The method of injection molding, also called transfer or syringe, is used only for processing press powders, when the product must include complex fittings.

The continuous extrusion method is used for the manufacture of various shaped products from press-powders (tubes, rods, corners).

Faolite properties

Faolite is an acid-resistant plastic mass obtained on the basis of phenol-formaldehyde resole resin and an acid-resistant filler of asbestos, graphite and quartz sand.

Thermosetting phenol-formaldehyde resin is capable of transforming into a solid, infusible and insoluble state under the influence of heating. In accordance with this, the faolite mass, in which the filler particles are bound together by a viscous soluble resin, solidifies during heat treatment, becomes infusible and insoluble.

Faolite is one of the most valuable construction materials. It has proven itself in operation in various corrosive environments in a wide temperature range. In terms of corrosion resistance, faolite is superior to lead.

A large amount of faolite is produced as a semi-finished product of uncured sheets from which consumer factories make various products and fittings.

Faolite has found wide application in many industries as a structural material. In some cases, it replaces non-ferrous metals, especially lead. The lightness of faolite (p = 1.5-1.7 g / cm 53 0), chemical resistance to acidic aggressive media makes it possible to make resistant equipment from it, weighing several times less than metal.

Faolite can be used at a higher temperature than many other acid-resistant plastics.

The main raw material for Faolite and the preparation of resole resin

For the production of faolite, a resole resin is used, which is a condensation product of phenol with formaldehyde in the presence of a catalyst - ammonia water. Resol resin in when heated is capable of passing into an infusible and insoluble state.

Pure phenol is a crystalline substance with a specific odor. The boiling point is 182 ° C and the density at 15 ° C is 1.066 g / cm3.

Phenol dissolves well in a 30-40% aqueous solution of formaldehyde (formalin), alcohol, ether, glycerin, benzene.

Cooking and drying of resole resin

Cooking and drying of the resole resin is carried out in a cooking and drying apparatus. The apparatus is equipped with a stirrer for 40-50 rpm. Sight glasses, fittings for measuring temperature and pressure are mounted on the lid of the apparatus. Working pressure up to 2 atmospheres.

During the cooking of the resin, a condensation reaction occurs - the interaction of phenol with formaldehyde in the presence of an ammonia catalyst. This forms a resin and a water layer. Drying mainly removes water and unreacted components. The drying process largely determines the quality of the finished resin.

Raw materials are loaded into the boiler in the following quantities: phenol (100%) - 100 parts by weight, formalin (37%) - 103.5 parts by weight, ammonia water (in terms of 100% ammonia) - 0.5 parts by weight.

The processing of dry faolite into a product can be carried out by the method of forming, pressing. Due to the fact that mechanical processing of the faolite is a laborious work, it is necessary to strive to ensure that the manufactured faolite part is given a certain shape in the uncured state.

From raw faolite are made: pipes, tsars, cylindrical vessels, stirrers.

Elbows, tees, baths are made from hardened faolite.

Pipes and products from textofaolite

The currently produced faolite in some cases cannot be used due to insufficient mechanical strength. Reinforcement or textolization of faolite with fabric makes it possible to obtain a material with significantly improved mechanical properties.

Faolite pipes are produced in a conventional manner. The uncured faolite product is tightly wrapped with strips of fabric, smeared with bakelite varnish. If the reapplication of the faolite is not required, then the textofaolite is cured in this form.

In this way, pipes and sidebars of various diameters are obtained from which devices or exhaust pipes are subsequently mounted.

Other

For varnishing wooden products self-curing varnishes are used, which are also made from phenol-formaldehyde resins.

Resol phenol-formaldehyde resins can also glue wood to wood or metal. The adhesion is very strong, and this method of adhesion is now finding more and more widespread use, especially in the aviation industry.

In industry, phenolic resin bonding is used in the manufacture of plywood and wood fiber plastics. In addition, such resins are successfully used for the manufacture of brushes and brushes, and in electrical engineering they perfectly adhere glass to metal in incandescent lamps, fluorescent lamps and radio tubes.

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1

In this paper, the general characteristics of phenol-formaldehyde resins are given; novolac and resole resins are considered separately. The reactions are presented and the mechanisms of formation and hardening of novolac and resole resins, as well as their main properties, are considered. Technologies for obtaining novolac resins and varnishes, resole resins and varnishes, emulsion resole resins, phenol alcohols and phenol-formaldehyde concentrates are considered. The recipes and technological parameters obtaining the resins under consideration by batch and continuous methods. Based on this information, a comparative assessment of novolac and rezole phenol-formaldehyde resins, as well as compositions based on them, was carried out, which makes it possible to assess the advantages and disadvantages of their use in various fields, including in the production of phenolic plastics and products from them.

phenol formaldehyde resins

novolac resins

resole resins

hardening

urotropin

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6. Kutyanin G.I. Plastic masses and household chemicals / G.I. Kutyatin - M .: Chemistry, 1982 .-- 186 p.

7. Mikhailin Yu.A. Heat-resistant polymers and polymer materials/ Yu.A. Mikhailin - SPb .: Professiya, 2006 .-- 624 p.

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TECHNOLOGY OF PREPARATION AND PROPERTIES OF PHENOL-FORMALDEHYDE RESINS AND COMPOSITIONS BASED ON THEM

Vitkalova I.A. 1 Torlova A.S. 1 Pikalov E.S. 1

1 Vladimir state university named of Alexander Grigorevich and Nikolay Grigorevich Stoletov

Abstract:

In this article presented general characteristics of phenol-formaldehyde resins, are considered separately novolac and resol resin. Represented reactions and the mechanisms of formation and curing of the novolak and resol resins and their basic properties. Examines the technology of novolac resins and varnishes, resol resins and varnishes, emulsion resol resins, phenol-alcohols and phenol-formaldehyde concentrates. Presented the formulation and technological parameters of obtaining the considered resins by batch and continuous methods. On the basis of this information a comparative assessment novolac and resol phenol-formaldehyde resins, and compositions on their basis, which allows to evaluate the advantages and disadvantages of their application in various fields, including in the production of phenolic plastics and products from them.

Keywords:

phenol-formaldehyde resin

hexamethylenetetramine

Currently, in construction and various industries, synthetic resins are widely used, obtained as a result of polycondensation or polymerization reactions. They are most widely used as binders for the production of composite materials, adhesives and in the paint and varnish industry. The main advantages of using synthetic resins are their high adhesion to most materials and water resistance, as well as mechanical strength, chemical and thermal stability.

At the same time, synthetic resins are practically not used in their pure form, but are used as the basis of compositions, which include various additives such as fillers, thinners, thickeners, hardeners, etc.

The introduction of additives makes it possible, within a wide range, to regulate the technological properties of the compositions and the performance properties of the products obtained from them. However, the properties of the composition are largely determined by the properties of the synthetic resin. The choice of resin also determines the choice of technology and parameters for molding products from the composition.

The most widely used synthetic resins today include carbamide, alkyd, epoxy, polyamide and phenolic resins (mainly phenol-formaldehyde).

general characteristics phenol-formaldehyde resins PFS [-C6H3 (OH) -CH2-] n are liquid or solid oligomeric products of the polycondensation reaction of phenol C6H5OH or its homologues (cresols CH3-C6H5-OH and xylenols (CH3) 2-C6H5-OH) with formaldehyde Н2 (methanale -C = O) in the presence of acidic catalysts (hydrochloric HCl, sulfuric H2SO4, oxalic H2C2O4 and other acids) and alkaline (ammonia NH3, ammonia hydrate NH4OH sodium hydroxide NaOH, barium hydroxide Ba (OH) 2) type.

Formaldehyde is usually used in the form of an aqueous solution stabilized with methanol called formalin CH2O. H2O. CH3OH. In some cases, phenol is replaced by substituted phenols or resorcinol (C6H4 (OH) 2), and formaldehyde is partially or completely replaced by furfural C5H4O2 or by the product of formaldehyde polymerization - paraform OH (CH2O) nH, where n = 8 - 100.

The role of reactive functional groups in these compounds is played by:

In phenol, there are three C - H bonds in two ortho and para positions (easier replacement is in progress in two ortho-positions);

In formaldehyde, there is a C = O double bond capable of attachment at the C and O atoms.

Depending on the nature in the ratio of the components, as well as on the catalyst used, phenol-formaldehyde resins are divided into two types: thermoplastic or novolac resins and thermosetting or resole resins.

The formation of phenolic resins is very complex. Below are the reactions of formation of phenol-formaldehyde resins, established on the basis of the works of Kebner and Wansheidt and are now generally accepted.

Characteristics of novolac resins

Novolak resins (NS) are predominantly linear oligomers, in the molecules of which phenolic nuclei are connected by methylene bridges -CH2-. To obtain novolak resins, it is necessary to carry out the polycondensation reaction of phenol and formaldehyde with an excess of phenol (the ratio of phenol to aldehyde in moles 6: 5 or 7: 6) and in the presence of acid catalysts.

In this case, at the first stage of the reaction, p- and o-monooxybenzyl alcohols will be formed:

In an acidic environment, phenolic alcohols quickly react (condense) with phenol and form dihydroxydiphenylmethanes, for example:

The resulting dihydroxydiphenylmethanes react with formaldehyde or phenol alcohols. Further chain growth occurs due to the sequential addition of formaldehyde and condensation.

The general equation for polycondensation in an acidic medium, leading to the formation of HC, has the form:

where n ≈ 10.

Under normal conditions of novolac condensation, the addition of formaldehyde to the phenolic core occurs mainly in the para-position, and the above formula does not reflect the true structure of the resin. Ortonolacs, i.e., phenol-formaldehyde oligomers with attachment only in the ortho-position, are obtained only with special polycondensation methods. They are of considerable interest due to their regular structure and the possibility of obtaining relatively high molecular weight compounds.

Molecules of novolak resin are not able to enter into a polycondensation reaction with each other and do not form spatial structures.

Curing of novolac resins

Novolak resins are thermoplastic polymers that soften and even melt when heated, and harden when cooled. Moreover, this process can be carried out many times.

Novolak resins can be converted into a non-melting and insoluble state by treating them with various hardeners: formaldehyde, paraform or, most often, hexamethylenetetramine (urotropine) C6H12N4:

Urotropin is added in an amount of 6-14% and the mixture is heated at a temperature of 150-200 ° C. A crushed mixture of novolac resin with hexamethylenetetramine (urotropine) is called pulverbakelite.

When heated, the decomposition of urotropine occurs with the formation of dimethyleneimine (I) and trimethyleneamine (II) bridges between the resin molecules:

These bridges then disintegrate with the release of ammonia and other nitrogen-containing compounds, and methylene bridges —CH2— and thermostable bonds —CH = N — CH2— are formed between the resin molecules.

When heated with urotropin, novolac resins undergo the same three curing stages as resole resins.

Properties of novolac resins

Depending on the production technology, novolac resins are hard, fragile glassy substances in the form of lumps, flakes or granules in color from light yellow to dark red (Fig. 1).

Rice. 1. Appearance novolac resins

Table 1

Properties of novolac resins in the presence of 10% hexamethylenetetramine (urotropine)

Notes: * Dropping point is the temperature at which the resin begins to take on a liquid form and falls in the form of drops or floats out of the measuring vessel under the influence of gravity. ** Gelation time - the time during which the resin polymerizes and turns into a solid, infusible and insoluble state. During this time, the resin remains liquid, suitable for processing and use.

Novolak resins are readily soluble in alcohols, ketones, esters, phenols and aqueous solutions of alkalis. In water, novolac resins swell and soften, and in the absence of moisture they are stable during storage.

The main properties of industrial novolac resins (SF grades) are presented in table. 1 .

Characterization of resole resins

Resole resins (RS), also called bakelites, are a mixture of linear and branched oligomers containing a large number of methylol groups —CH2OH, capable of further transformations. To obtain resole resins, it is necessary to carry out the polycondensation reaction of phenol and formaldehyde with an excess of formaldehyde (the ratio of aldehyde to phenol in moles 6: 5 or 7: 6) and in the presence of basic catalysts.

In this case, at the first stage of the polycondensation reaction, mono-, di- and trimethylol derivatives of phenol (phenol alcohols) will be obtained:

At temperatures above 70 ° C, phenolic alcohols interact with each other to form two- and three-core compounds:

The resulting dimers can react with monoalcohols or with each other to form oligomers with a higher degree of polycondensation, for example:

The general equation of polycondensation in this case can be represented as follows:

where m = 4 - 10, n = 2 - 5.

The resin obtained as a result of such a polycondensation reaction is called resole.

Resole resins in some cases may also contain dimethylene ether groups —CH2 — O — CH2—, due to which formaldehyde is released from them when heated.

Curing resins

Resole resins are thermosetting polymers that, when heated, undergo irreversible chemical destruction without melting. In this case, an irreversible change in properties occurs as a result of cross-linking of molecular chains by cross-links. The resin cures and goes from molten to solid. The curing temperature can be either high (80-160 ° C) for hot curing, and low for cold curing. Curing occurs due to the interaction of functional groups of the material itself or with the help of hardeners similar to those used for novolac resins.

Resol resins also cure during long-term storage, even at normal temperatures.

There are three stages of condensation or three types of resole resins:

Stage A (resol) - a mixture of low molecular weight compounds of the products of the polycondensation reaction;

Stage B (resitol) is a mixture of resole resin and high molecular weight infusible and insoluble compounds.

Stage C (resit) is a resin consisting mainly of three-dimensional high molecular weight compounds.

These transformations occur as a result of condensation of methylol groups with mobile hydrogen atoms in the ortho and para positions of the phenyl nucleus:

As well as the interaction of methylol groups with each other:

The structure of resits can be simplified as follows:

The curing of resole resins can also proceed in the cold in the presence of acids (hydrochloric, phosphoric, p-toluenesulfonic acid, etc.). Resites hardened in the presence of petroleum sulfonic acids RSO2OH (where R is a hydrocarbon radical) are called carbolites, and in the presence of lactic acid С3Н6О3, they are called neoleucorites.

When heated, the curing of resole resins is accelerated by the addition of oxides of alkaline earth metals: CaO, MgO, BaO.

Resol Resin Properties

In the initial state (stage A), the resole resins are separated into solid and liquid. Solid ("dry resins") are solid brittle substances from light yellow to reddish color, depending on the catalyst used and in appearance differ little from novolac resins (see Fig. 1). Resole resins contain a higher amount of free phenol than novolac resins, which leads to a decrease in their melting point. Resole resins, like novolac resins, dissolve in alcohols, ketones, esters, phenols, aqueous solutions of alkalis, and also swell in water.

The main properties of solid resols produced by the industry (IF grades) are presented in table. 2.

table 2

Properties of hard resole resins

Liquid resins are a colloidal solution of resin in water (Fig. 2), obtained in the presence of an ammonia or ammonia-barium catalyst, and are subdivided into liquid bakelite and water emulsion resins.

The main properties of liquid resols produced by the industry (grades BZh and OF) are presented in table. 3.

Rice. 2. Appearance of liquid resole resins

Table 3

Properties of liquid resole resins

When heated or stored for a long time, the resole goes into stage B (resitol), and then into stage C (resit). Resitol is insoluble in solvents, but only swells in them, does not melt, but softens when heated.

Resit is solid color from light yellow to cherry or brown. Resit does not melt or soften when heated, it is insoluble and does not swell in solvents.

The main properties of resites obtained during the curing of resole resins are presented in table. 4 .

Table 4

Resite properties

Index	The magnitude
Density	1250 - 1380 kg / m3
Degradability from temperature
Water absorption after 24 hours
Tensile strength: When stretched When compressed In static bending	(42 - 67) .106 Pa (8 - 15) .107 Pa (8 - 12) .107 Pa
Brinell hardness
Specific electrical resistance	1.1012 - 5.1014 Pa
Electrical strength	10 - 14 kV / mm
Dielectric constant at 50 Hz
Arc resistance	Very low
Resistant to weak acids	Very good
Resistant to alkalis	Collapses

Modifying additives for FFS

For a directed change in the properties of phenol-formaldehyde resins, the method of chemical modification is used. For this, components capable of interacting with phenol and formaldehyde are introduced into the reaction during their preparation.

First of all, these are the hardeners that were discussed earlier. Sulfates, phosphates and ammonium chlorides in an amount of 0.1-5% are used as accelerators for the curing of phenol-formaldehyde resins.

It is possible to use a mixture of resole and novolac resins. This results in less rigid materials with better adhesive properties.

With the introduction of aniline C6H5NH2, the dielectric properties and water resistance increase, with the introduction of carbamide CH4N2O - lightfastness, with the introduction of furyl alcohol C4H3OCH2OH - the chemical resistance. To improve the resistance to alkalis, the resins are modified with boron fluorides or filled with graphite or carbon, and up to 20% dichloropropanol is added.

To impart the ability to dissolve in non-polar solvents and combine with vegetable oils, phenol-formaldehyde resins are modified with rosin C19H29COOH, tert-butyl alcohol (CH3) 3COH; resins of this type are widely used as a base for phenolic varnishes.

Phenol-formaldehyde resins are combined with other oligomers and polymers, for example, with polyamides, to impart higher heat and water resistance, elasticity, and adhesive properties; with polyvinyl chloride - to improve water and chemical resistance; with nitrile rubbers - to increase impact strength and vibration resistance, with polyvinyl butyral - to improve adhesion (such resins are the basis of BF-type adhesives). To reduce fragility and internal stresses, reactive rubbers (thiokol, fluorlon) are used.

Phenol-formaldehyde resins are used to modify epoxy resins in order to impart higher thermal, acid and alkali resistance to the latter. It is also possible to modify phenol-formaldehyde resins with epoxy resins in combination with urotropin to improve adhesion properties, increase the strength and heat resistance of products.

Recently, phenol-formaldehyde resins have often been modified with melamine C3H6N6 to produce melamine-phenol-formaldehyde resins.

Technology for obtaining PFS and compositions based on them

The main stages technological process production of FFS and compositions based on them are the preparation of the reaction mixture, polycondensation and drying.

Rice. 3. Block diagram of the technological process for the production of FFS and compositions based on it: 1- mixing in a hermetically sealed vacuum reactor with simultaneous heating; 2 - polycondensation in a tubular cooler, collection of distillate and discharge into a common tank (stage A); 3 - dehydration and removal of low molecular weight (volatile) components (stage B); 4 - solidification in the refrigeration unit (stage C); 5 - obtaining solutions; 6 - cooling to a given viscosity and separation of over-resin water in the sump; 7 - vacuum drying and dilution with solvent

Preparation of the reaction mixture consists in melting phenol and obtaining aqueous solutions of the catalyst. The reaction mixture is prepared either in aluminum mixers or directly in the reactor. The composition of the reaction mixture and technological modes of production depend on the type of resin obtained (HC or RS), functionality and reactivity of phenolic raw materials, pH of the reaction medium of the catalyst used and the additives introduced.

Production of novolac resins and varnishes

In the production of novolac resins, hydrochloric acid is used as a catalyst, less often oxalic acid. The advantage of hydrochloric acid is its high catalytic activity and volatility. Oxalic acid is a less active catalyst than hydrochloric acid, however, the polycondensation process in its presence is easier to control, and the resins are lighter and more lightfast. The catalytic effect on the polycondensation process is also exerted by formic acid always present in formalin.

Usually, for the production of novolac resin, the following ratios of components are used (wt. H.): Phenol = 100; hydrochloric acid (in terms of HC1) = 0.3; formalin (in terms of formaldehyde) = 27.4. Formalin is an aqueous solution containing 37-40% formaldehyde and 6-15% methyl alcohol as a stabilizer.

With the periodic method of obtaining NS (Fig. 4), polycondensation and drying are carried out in one reactor. To carry out polycondensation, a mixture of phenol and formaldehyde is loaded into a reactor equipped with a heat exchange jacket and an anchor-type stirrer. At the same time, half of the required amount of hydrochloric acid is fed (the catalyst is added in portions to avoid an overly violent reaction). The reaction mixture is stirred for 10 minutes and a sample is taken to determine the pH. If the pH is in the range of 1.6-2.2 steam is fed into the reactor jacket and the reaction mixture is heated to 70-75 ° C. A further rise in temperature occurs due to the thermal effect of the reaction.

Rice. 4. Technological scheme for obtaining PFS in a periodic way: 1 - 3 - measuring tanks; 4 - reactor; 5 - anchor stirrer; 6 - heat exchange jacket; 7 - condenser refrigerator; 8 - condensate collector; 9 - conveyor; 10 - cooling drum; 11 - sump; 12 - valve for supplying condensate to the reactor; 13 - tap for removing water and volatile components from the reactor

When the temperature of the mixture reaches 90 ° C, stirring is stopped, and to prevent violent boiling, cooling water is fed into the jacket, the supply of which is stopped after uniform boiling has been established. At this point, the stirrer is turned on again, the second half of the total amount of hydrochloric acid is added, and after 10-15 minutes the steam supply to the reactor jacket is resumed. The vapors of water and formaldehyde formed during the boiling process enter the refrigerator-condenser, from which the resulting aqueous solution again enters the reactor.

If oxalic acid is used instead of hydrochloric acid, then it is loaded in an amount of 1% of the mass of phenol in the form of an aqueous 50% solution and in one step, since the process is not as intense as in the presence of hydrochloric acid.

The polycondensation is finished when the density of the resulting emulsion reaches 1170 - 1200 kg / m3, depending on the nature of the phenolic raw material. In addition to the density of the resulting resin, the ability to gel formation is determined by heating to 200 ° C. In total, the duration of the process is 1.5-2 hours.

At the end of the reaction, the mixture in the reactor stratifies: the resin collects at the bottom, and the water released during the reaction and introduced with formaldehyde forms the top layer. Thereafter, the resin drying step is started. Water and volatiles are distilled off by creating a vacuum in the apparatus and using a condenser to drain them into a condensate collector. The vacuum is gradually increased to avoid overflow of the resin into the refrigerator. By the end of drying, the temperature of the resin is gradually increased to 135-140 ° C. After drying is completed, exposure at an elevated temperature follows (heat treatment). The end of drying and heat treatment is determined by the resin dropping point, which should be in the range of 95-105 ° C.

A lubricant is introduced into the finished resin (for some types of press powders), mixed for 15-20 minutes and poured onto a cooling drum. The resin is crushed, enters the conveyor blown with air, where it is cooled down completely, after which it is packed in paper bags.

To obtain a varnish, the dried resin is dissolved in ethyl alcohol, which is poured directly into the reactor at the end of the drying process. Before dissolution, steam supply to the jacket is stopped and the refrigerator is switched to reverse. Often carry out joint condensation of formaldehyde with phenol and aniline. Resins obtained in this way are binders for press powders, from which articles with increased dielectric properties are obtained. A negative property of anilinophenol-formaldehyde resins is their ability to self-ignite during the manufacturing process and when draining.

Receiving NS in a continuous way (see Fig. 7) is carried out in column apparatus operating on the principle of "ideal" mixing and consisting of three or four sections, called tsargi. A mixture of phenol, formalin and part of hydrochloric acid is prepared in a separate mixer and fed to the upper drum, where it is mixed again. After that, the partially reacted mixture passes through the overflow pipe from the upper part of the drawer to the lower part of the next drawer, sequentially passing through all the sections of the apparatus. At the same time, an additional portion of hydrochloric acid is fed into each tsarga and the mixture is mixed. The process is carried out at a boiling point of the mixture equal to 98-100 ° C.

Rice. 5. Technological scheme for obtaining PFS in a continuous way: 1 - column reactor; 2.4 - refrigerators; 3 - mixer; 5 - drying apparatus (heat exchanger); 6 - resin collector; 7 - sump; 8 - Florentine vessel; 9 - gear vessel; 10 - cooling drum; 11 - conveyor

The water-resin emulsion from the lower tsarga enters the separator, which is a Florentine vessel, for separation. The water part from the upper part of the separator is fed into the sump, and then for further cleaning, and the resin part from the separator and sump is pumped by a gear pump into the tube space of the heat exchanger, into the shell space of which heating steam is supplied under a pressure of 2.5 MPa. The resin in the form of a thin film moves along the surface of the heat exchanger tubes, heating up to a temperature of 140-160 ° C. The resulting mixture of resin and volatile substances enters the resin receiver - standardizer. Here volatiles are removed from the resin and through the top of the apparatus are discharged for subsequent condensation and feeding into the mixer for the initial reaction mixture.

The hot resin from the resin tank is drained into a drum, which is internally and externally cooled with water. The result is a thin film of resin that is fed to a moving conveyor where the final cooling and evaporation of the water takes place. The finished resin can be bagged or mixed with additives to produce various compositions.

Resin and varnish production

In the production of resole resins, an aqueous solution of ammonia is mainly used as a catalyst. With a larger excess of formaldehyde, NaOH, KOH, or Ba (OH) 2 can act as catalysts.

Usually a resole resin is obtained with the following ratios of components (parts by weight): phenol = 100; ammonia (in the form of an aqueous solution) = 1 - 1.5; formaldehyde = 37.

The technological scheme for the production of resole resins is largely similar to the scheme for the production of novolac resins (see Figures 6 and 7), however, there are some differences. Since the heat effect of the reactions of obtaining resole resins is much less than in the synthesis of novolac resins, the catalyst is introduced into the reaction mixture in one step. The readiness of a resin is determined by determining its viscosity and refractive index.

Drying of the resin begins under vacuum (93 kPa) at a temperature of 80 ° C with a gradual increase in pressure and temperature (up to 90-100 ° C) towards the end of the process. Drying control is carried out by determining the gelation time of the resin at 150 ° C.

When obtaining resole resins, it is important not to exceed the temperature and strictly maintain the time, since if the temperature-time regime is not observed, the resin may begin to gel in the reactor. To avoid gelation of the dried resin, it is rapidly cooled immediately after it is drained from the reactor. To do this, it is poured into refrigerated cars, which are bogies with vertical hollow metal plates. The resin is drained so that there is cooling water in the cavities of adjacent plates.

Resole-based varnishes and anilinophenol-formaldehyde resins are prepared in the same manner as novolac resin compositions.

Production of emulsion resole resins

Emulsion resole resins are prepared from a mixture of phenol or cresol with formalin in the presence of a catalyst, which is most often used as Ba (OH) 2. The reaction mixture is heated in the reactor to 50-60 ° C, after which it is heated due to the heat effect of the reaction. The temperature of the mixture is maintained in the range of 70-80 ° C, and in case of overheating, cooling water is supplied to the reactor jacket. The synthesis ends when the viscosity of the resin at 20 ° C reaches values ​​of 0.16-0.2 Pa.s.

After that, the reaction mixture is cooled to 30-45 ° C, and then fed into a settler to separate the upper aqueous part, or the resin is dried under vacuum to a viscosity of 0.4 Pa.s, followed by dilution with a small amount of acetone. It should be borne in mind that further spontaneous polycondensation of the resulting emulsion resin is possible, for the exclusion of which it is stored in refrigerated containers.

In the production of emulsion resins, NaOH is used as a catalyst to obtain press materials with long-fiber filler. In this case, the preparation time of the resin is 100 minutes, followed by cooling at a temperature of 70-80 ° C by supplying cooling water to the reactor jacket. After the resin reaches a viscosity in the range of 0.02-0.15 Pa. S, it is cooled to 30-35 ° C, separated from water in a sump and poured into a cooled collection. The finished resin contains up to 20% free phenol and 20-35% water.

Production of phenol alcohols and phenol-formaldehyde concentrates

Phenolic alcohols are intermediate products for the preparation of resole resins and are highly stable during storage. They are used for the preparation of resins, press materials and impregnation of porous fillers such as wood or gypsum.

To obtain phenol alcohols, a reactor of the same type is used as in the production of phenol-formaldehyde resins in a periodic manner (see Fig. 4), into which a 37% aqueous solution is loaded, in which the formaldehyde: phenol ratio is 1.15: 1 and higher. After dissolution of phenol, a concentrated aqueous solution of NaOH is added to the reactor at the rate of 1.5 parts by weight. per 100 parts by weight phenol. The resulting reaction mixture is heated to 40 ° C by supplying steam to the reactor jacket. The mixture is then heated by the heat of the reaction. By supplying cooling water to the reactor jacket, the temperature of the mixture is maintained within the range of 50 - 70 ° C for 5 - 12 hours. The readiness of phenolic alcohols is determined by the content of free phenol (9-15% at the end of the process) or free formaldehyde. At the end of the process, the phenolic alcohol solution is cooled to 30 ° C and poured into aluminum barrels or cans.

Phenol-formaldehyde concentrate also simplifies the transportation and storage conditions with conventional resole resins, since it does not solidify under normal conditions and does not precipitate paraform. On its basis, resole resins and press materials are obtained that are not inferior in quality to ordinary resole resins and press materials obtained from them. At the same time, the water content in the concentrate is 15-20% lower than when using a 37% aqueous solution of formaldehyde and phenol.

Conclusion

From the information presented in the work, it follows that PFRs differ in a wide variety of properties, being thermoplastic or thermosetting and can initially be in a liquid or solid state. PFS are well combined with most polymers, which opens up wide possibilities for obtaining a material that combines the advantages of several polymers.

This largely explains the prevalence of phenol-formaldehyde plastics (phenolic plastics), which are composite materials based on PFS with various fillers. Due to its strength and electrical insulating properties, as well as the ability to operate at high temperatures and in any climatic conditions, pheno-strips are successfully used for the manufacture of structural, frictional and antifriction products, housings and parts of electrical devices, to obtain building materials and products (including in the foamed state), as well as in other industries, replacing steel, glass and other materials.

Raw materials for obtaining PFS and compositions based on them are widespread, and production technologies are relatively simple, which allows them to be obtained in large volumes. The main disadvantage of FFS and compositions based on them, limiting their use, is their relatively high toxicity. However, the production and use of FFS and compositions based on them remains relevant today in connection with the demand for this material, which can be explained not only by its operational properties, but also by its relatively low cost, wear resistance and durability.

Bibliographic reference

Vitkalova I.A., Torlova A.S., Pikalov E.S. TECHNOLOGIES OF OBTAINING AND PROPERTIES OF PHENOLFORMALDEHYDE RESINS AND COMPOSITIONS ON THEIR BASIS // Scientific Review. Technical science... - 2017. - No. 2. - P. 15-28;
URL: https://science-engineering.ru/ru/article/view?id=1156 (date of access: 02/14/2020). We bring to your attention the journals published by the "Academy of Natural Sciences"

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There is a check of the combat readiness of the unit. The generals came in large numbers. We examined the kitchen, parade ground, sorting and sat down under the shade of trees to rest. Suddenly, the unit commander sees a fighter who has just been recruited into the alley walking along the alley. Goes, parasit, just like that, admires the weather. It is clear that a non-working soldier during a check is not an order. The unit commander calls him:
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Human proportions: the size of the nail should correspond to the size of the fingers, occupying about 50% of the area of ​​the upper phalanx of the finger and, at the same time, its length should exceed the width by 10%. On a medium-sized arm, the length of the nail is 12 mm. The growth of a nail in one month ranges from 2.5 to 4 mm and depends on the age and state of health of the person. Full height the nail occurs in 4 - 5 months.

The word "gum" usually means a thick, viscous substance that is sticky to the touch. Resins are natural (for example, resin, rubber, amber) and synthetic. The latter group includes a wide variety of materials produced by industry. They are much cheaper, easy to use, and highly reliable. So, in the 19th century, phenol-formaldehyde resin was first produced, this material still remains at the peak of popularity.

Resin properties

Phenol-formaldehyde resins are synthetic masses from the group of phenolic resins that have the properties of thermosetting plastics. The equation and formula of the material is C6H3 (OH) -CH2-] n. The product was developed by heating a mixture of formaldehyde (formalin) and phenol. The fact that the material is obtained by the reaction of these components was revealed by a scientist from Germany A. Bayer in 1872. As a result of the interaction, water and polymer were formed, however, the latter was rather fragile, and the liquid quickly passed into a gaseous substance. Subsequently, the method of obtaining the product was improved by adding wood flour. Now the finished product includes various fillers that improve its properties.

The characteristics and distinctive qualities of phenol-formaldehyde resins are as follows:

• by structure - liquid or solid oligomers;
• educational environment - acidic, alkaline;
• excellent electrical insulation;
• high resistance to mechanical stress, damage;
• corrosion resistance;
• solubility in hydrocarbons, ketones, chloride solvents, alkalis.

A feature of the material is its transformation into a thick-crosslinked polymer with a microheterogeneous structure after complete curing.

Material application

Phenol-formaldehyde-based resin is used in various spheres of the national economy. Various types of plastic are made from it:

• with sulfonated curing - carbolite;
• when cured with lactic acid - neoleucoric;
• with the participation of hydrochloric acid - resol.

Phenolic resin is used for the manufacture of adhesives and varnishes, including BF brand glue. It is used to create sealants as a structural binder, in the production of plywood, chipboard. Formaldehyde resin is used to make fillings and impregnations for fabrics and other materials.

With the participation of the product, various products for general and special purposes are obtained:

• brake pads for trains, parts for cars, metro escalators;
• abrasive tools;
• plugs, boards, sockets, meters, motors, terminals and other electrical products;
• phone cases, cameras;
• radio products, including capacitors;
• military equipment and weapons;
• unheated elements of kitchen appliances, dishes;
• textolite and getinaks - materials for further processing;
• costume jewelry, haberdashery, souvenirs;
• balls for billiards.

The material is not used for the production of containers in direct contact with food products, especially those intended for heat treatment.

The material belongs to polymers obtained by the polycondensation method. It can be made from methane and methanol by converting it to formaldehyde and then combining it with phenol. The technology is as follows:

• take a solution of formaldehyde 40% in the amount of 3 ml;
• combined with 2 g of crystalline phenol (according to Gosstandart, it can be replaced with 4 ml of carbolic acid solution, it is a liquid concentrated phenol);
• add 3 drops of hydrochloric acid to the mass;
• the mixture will boil, after which it will turn into a transparent mass like glass (resole);
• if you want to slow down the process, then cool the dishes with the mass;
• the resole dissolves easily in alcohol, an experiment can be carried out to clarify the quality of the resulting mass;
• if you leave the product for more long term, it will become viscous, non-flowing and stop dissolving in alcohol - it will turn into more plastic material resitol;
• at the end of the work, the container is placed in boiling water, as a result, the resin hardens, becomes literally stone, acquires a red color.

The finished product does not burn, but is slowly charred. In this case, the fire will turn yellowish, an unpleasant smell of phenol will be felt. Technical conditions to stop the reaction are as follows: at any stage (before the final curing), you can pour in alkali, this will stop the polymerization process.

The state standard also indicates the procedure for obtaining other substances during the production of phenol-formaldehyde resin. So, with an increase in the amount of phenol, novolac can be obtained. Increasing the concentration of formaldehyde makes it possible to make Bakelite. When replacing formalin with acetone with the participation of hydrochloric acid, bisphenol is obtained.

Material harm

Despite the advantages, resins of this type can cause great harm to humans and the environment. Their danger is that toxic components are used in production. Phenol and formalin are poisonous, and the latter is also considered a strong carcinogen. Both substances have the following harmfulness:

• depress the nervous system;
• cause rash, dermatitis;
• provoke allergies and bronchial asthma.

What regulatory documents regulate the production of the product? SanPiN regulates the permissible amounts of migration of these substances into finished goods... They are equal to 0.05 mg / l for phenol, 0.1 mg / l for formaldehyde. The disposal of products made from such resins is also a problem for the environment. Equally important is the protection of workers in the industries where they are produced and processed. In this, phenol-formaldehydes are very different from environmentally friendly epoxy resins.

Phenoplasts

Phenolic plastics are understood to be plastics that are obtained by combining phenol-formaldehyde resins with various fillers. The process takes place at a high temperature, and the type of filler depends on the type of the final product. Phenolic plastics also include phenolic-bakelite adhesive, various plastic products for everyday life and the national economy. Phenoplastics are used to make parts for equipment and cars. Nowadays, production methods are so advanced that in finished products only trace concentrations of harmful substances are present.

 

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