Adhesion, adhesion (adhesion). Adhesion is an important property of solid and liquid bodies in industrial sectors of the adhesion solution

Determination of the concept of adhesion. Classification of adhesion compounds in dentistry. Mechanisms for the formation of adhesion compounds. The conditions of education and the nature of the destruction of adhesion compounds.

Adhesion- this phenomenon that occurs when connecting heterogeneous materials given in close contact for the separation of which an effort should be applied.When two materials are shown in such a close contact with each other, in which their surface monomolecular layers can interact, the molecules of the same substance determine with the other molecules, experiencing mutual attraction. The forces of this attraction are called forces of adhesionor adhesive forces.Unlike cohesion forces(cohesion forces), which determine the mutual attraction of the molecules of the same substance in its volume.

The material or layer is applied to obtain an adhesive connection, called adhesive. The material on which adhesive is applied is called a substrate.

Adhesion is found in many cases of reducing materials in dentistry. For example, when connecting a seal with the walls of the cavity of the tooth, sealant and lacquer with dental enamel. When fixing fixed dentures cement. In orthodontics on the principles of adhesion, braces are attached to the surface of the teeth. Adhesion is present in combined prostheses, in which they strive to restore the aesthetic and functional properties, namely, when using porcelain and metal in metal-ceramic prosthesis, plastics and metal - in metal plastics.

Scheme 3.1 presents the classification of adhesion compounds used in dentistry.

Scheme 3.1.Classification of types of adhesion compounds in dentistry

It should be emphasized a significant difference between the adhesion compounds of reducing materials with the fabrics of a living organism and compounds of heterogeneous materials that are used in dentures.

There are several mechanisms for the formation of adhesive compound due to various types of adhesive bonds (the classification of types of adhesive links is given in Scheme 3.2).

Mechanical adhesion consists in jamming the adhesive in the pores or irregularities of the substrate surface. It can occur on a microscopic level, as in the case of a compound of a polymer with an etched tooth enamel, or on the macro level, when the plastic cladding is applied to the surface of a metal frame that has special grippers. A visual example of mechanical adhesion can serve as a fixation of fixed dentures inorganic cement, such as zinc phosphate cement.

A more durable and reliable compound can be achieved using chemical adhesion. It is based on the chemical interaction of two materials or phases constituting an adhesive connection. Such type of adhesion is inherent in water cement on polyacryl

Scheme 3.2.Types of adhesion ties *

acid in which there are functional groups that are capable of forming a chemical compound with solid tissues of the tooth, primarily with hydroxylapatitis calcium.

The diffusion compound is formed as a result of the penetration of the structural phase or components of one material into the surface of the other with the formation of a "hybrid" layer, which contains both phases.

In practice, it is difficult to find the case of an adhesive compound, in which any of the listed adhesion mechanisms would be presented in its pure form. In most cases, when using materials of various chemical nature, adhesive interaction and mechanical, and diffusion, and chemical character takes place to restore teeth.

Conditions for creating a durable adhesion connection:

1. Clean the surface on which adhesive is applied. On the surface of the substrate there should be no dust, extraneous particles, adsorbed moisture monolayers and other contaminants.

2. Penetration (penetration) of liquid adhesive into the substrate surface. Penetration depends on the ability of adhesive to make the substrate surface.

Wetting characterizes the ability of a drop of liquid to spread on a solid surface. The material of wetting is the contacting angle of wetting (θ), which is formed between the surfaces of the liquid and solid on the border of their partition (Fig. 3.1).

* Based on the classification WJ. O "Brien" Dental Materials and Their Selection ", Quintessence Publ. Co., Inc, 3 ed., P. 66.

Fig. 3.1.Contact wetting angle

With full wetting, the contact angle is 0 °. Small contact angle values \u200b\u200bcharacterize good wetting. With a bad wetting, the contact angle is greater than 90 °. Good wetting contributes to capillary penetration and indicates a strong mutual attraction of molecules on the surfaces of liquid adhesive and solid substrate.

The formation of strong chemical bonds on the surface of the section will significantly increase the number of places of attaching one material to another. It is assumed that this is exactly what happens between porcelain facing and tin oxide, applied on the surface of alloys with a large content of noble metals.

3. Minimum shrinkage and minimum internal stresses when hardening (curing) adhesive on the substrate surface.

4. Minimal possible thermal stresses. If the adhesive and substrate have different thermal expansion coefficients, then when heating this connection of the glue seam will be tested. For example, a porcelain cladding is applied to the metal frame at a porcelain hiring at a high temperature, and then the metal-ceramic prosthesis was cooled to room temperature. If this pair selected materials with close thermal expansion coefficients, then the voltage arising in the porcelain layer will be minimal.

5. Possible effect of the corrosion environment. The presence of water that contributes to corrosion of liquids or vapor often leads to a deterioration in adhesive connection. The oral cavity environment with its high humidity, the presence of saliva, food products, a variable pH, non-permanent temperature and the presence of microflora is recognized as aggressive. This has a significant impact on the reliability and durability of adhesion compounds of reducing materials in the oral cavity.

The adhesion is usually judged by the magnitude of adhesion strength, i.e. By resistance to the destruction of the adhesion connection. As follows from the definition of adhesion, it suffices to measure the applied force for separating the components of the adhesive pair of materials to determine the strength of this compound. However, it is not so easy to achieve that the measured separation force of the glued pair is numerically corresponded to precisely adhesion strength. Therefore, so many methods are proposed for measuring various adhesion compounds used in dentistry. With all the variety of options, there are only three mechanisms for destruction: when tensile, shift and uneven separation.

When testing the adhesion connection, you must pay attention to the nature of destruction. There are adhesion (adhesive separation) and cohesion destruction. Obviously, the surface of the destruction passes through the weakest link of the compound.

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This clutch of various in its composition and structure of materials, due to their physical and chemical properties. The term adhesion occurred from the Latin word ADHESION - adhesion. In construction, they give a more narrow-controlled and specific designation of what adhesion is the ability of decorative and finishing coatings (LKM, plaster), sealing or adhesive mixtures to a solid and reliable compound with the outer surface of the base material.

Impressive demonstration of the effect of adhesion of modern adhesive compositions

Important! The concepts of adhesion and cohesion should be distinguished. Adhesion connects differentty materials, affecting only the surface layer. For example, paint on a metal surface. Cugezzia is a compound of the same type of materials, as a result of which intermolecular interactions are formed.

Adhesion is one of the key properties of materials in the following areas:

1. Metallurgy - anti-corrosion coatings.
2. Mechanics - Lubrication layer on the surface of machine elements and mechanisms.
3. Medicine - dentistry.
4. Building. In this industry, adhesion is one of the main indicators of the quality of work and reliability of structures.

Almost all stages of construction are controlled by adhesion indicators for the following compounds:

• paints and varnishes;
• plaster mixes, screed and fill;
• adhesive compositions, masonry solutions, sealants, etc.

An example of chemical adhesion - the reaction of the compound of silicone sealant with glass

There are three basic principles of the adhesive connection of materials. In construction and technology, they are manifested as follows:

1. Mechanical - The grip occurs by sticking the material applied to the base. The mechanism of such a compound is to penetrate the applied substance in the pores of the outer layer or compound with the rough surface. An example is the color of the surface of concrete or metal.
2. Chemical - Communication between materials, including different density, occurs at the atomic level. To form such a connection it is necessary for the presence of a catalyst. An example of adhesion of this type is a soldering or welding.
3. Physical - Electromagnetic intermolecular communication occurs on mating surfaces. It may be formed as a result of a static charge or under the influence of a permanent magnetic or electromagnetic field. An example of using technology - staining of various surfaces in an electromagnetic field.

Adhesion properties of construction and finishing materials

The adhesion of construction and finishing materials is carried out mainly, according to the principle of mechanical and chemical compound. The construction uses a large number of different substances, performance characteristics and specific interaction of which differ radically. We divide them into three main groups and characterize in more detail.

paints and varnishes

The adhesion of the LKM to the surface of the base is carried out by a mechanical principle. At the same time, the maximum strength indicators are achieved if the work surface of the material has roughness or porous. In the first case, the area of \u200b\u200bcontact is significantly increasing, in the second, the paint penetrates into the surface layer of the base. In addition, the adhesive properties of the LKM increase due to various modifying additives:

• organosilanes and polyorganosyloxanes have an additional hydrophobic and anti-corrosion action;
• polyamide and polyester resins;
• metallo-organic catalysts of chemical processes of disconcing LKM;
• ballast fine fillers (for example, talc).

Talc filler paint - non-pesticating flame retardant

Construction plaster and dry adhesive mixtures

Until recently, construction and finishing works were conducted using various solutions based on plaster, cement and lime. Often, they were mixed in a certain proportion, which gave a limited change in their main properties. Modern ready-made dry construction mixes: starting, finishing and multifinic plasters and putty, have a much more complex composition. Additives of various origins are widely used:

• mineral - Magnesia catalysts, liquid glass, clamping, acid-resistant or non-shrinkable cement, microsinking, etc.
• polymer - dispersible polymers (PVA, polyacrylates, vinyl acetates, etc.).

Such modifiers significantly change the following main characteristics of building mixtures:

• plastic;
• water-retaining properties;
• thixotropy.

Important! The use of polymer modifiers gives a more pronounced effect of adhesion enhancement. However, the formation of stable compounds of polymer films on the boundary of different type materials (base - hardening plaster) is possible only at a certain temperature. This term is called the minimum fleet of film formation - MTP. In different plasters, it can be different from + 5 ° C to + 10 ° C. To avoid bundle, it is necessary to accurately adhere to the manufacturer's recommendations relative to the temperature, both the environment and the grounds.

Sealants

Sealants used in construction distinguish three different types, each of which requires certain conditions for high-strength adhesion with the base material. Consider each type of Read more.

• Drying sealants. The composition includes various polymers and organic solvents: styrene butadiene or nitrile, chloroprene rubber, etc. As a rule, there are a pasty consistency with a viscosity of 300-550 Pa. Depending on the viscosity, they are applied either with a spatula or brush. After applying them to the surface, a certain time is necessary for drying (evaporation of the solvent) and the formation of a polymer film.

• Sleep sealants. It is usually from rubber, bitumen and various plasticizers. Have limited resistance to high temperature, not more than 70 0 C-80 0 s, after which they begin to deform.

• Cutting sealants. After applying them, under the influence of various factors: moisture, heat, chemical reagents, there is an irreversible polymerization reaction.

Of all these varieties, curable sealants provide maximum clutch reliability with the micronether base of the base. In addition, they are resistant to high temperatures, mechanical and chemical influences. They have an optimal combination of rigidity and viscosity, allowing to maintain an initial form. However, are the most expensive and complex in use.

How is adhesion measured?

Adhesion measurement technology, test methods, as well as all indicators of the strength of the compound of the materials are indicated in the following standards:

• GOST 31356-2013 - Plots and plasters;
• GOST 31149-2014 - Paintwork materials;
• GOST 27325 - LKM to wood, etc.

Information! Adhesion is measured in kgf / cm 2, MPa (megapascular) or KN (kilonutytons) is an indicator of force that must be applied to separate the materials of the base and coating.

If earlier the adhesive characteristics of the materials could be measured only in laboratory conditions, then at the moment there are many devices that can be used directly at the construction site. Most of the methods for measuring adhesion, both "field" and laboratory associated with the destruction of the external covering, layer. But there are several devices, the principle of which is based on ultrasound.

• Knife adhesimetre. Used to determine the adhesion parameters by the method of lattice and or parallel cuts. It is used for paint and varnish coatings with a thickness of up to 200 microns.

• Pulsar 21. The device determines the density of materials. It is used to detect cracks and bundles in concrete both pieces and monolithic. There are special firmware and subprogrammes that in the density of adjustment, allow to determine the strength of the adhesion of the plastecrops of various types to concrete surfaces.

• CM-1U. Used to determine the adhesion of polymer and bitumen insulating coatings by the method of partial destruction - shift. The measurement principle is based on the identification of linear deformations of the insulating material. As a rule, it is used to determine the strength of the insulating coating of pipelines. Use to test the quality of bituminous waterproofing to build structures: walls of basements and basement floors, flat roofs, etc.

Factors that reduce the adhesion of materials

Various physical and chemical factors affect the reduction of adhesion. Physical is the temperature and humidity of the environment at the time of applying decorative and finishing or protective materials. Also reduced adhesion interactions of various contaminants, in particular, the dust covering the base surface. In the process of operation, the effect on the strength of the combination of paints and varnishes may have ultraviolet radiation.

Chemical factors that reduce adhesion are represented by various material pollutants surface: gasoline and oil, fats, acidic and alkaline solutions, etc.

Also adhesion finishing materials can reduce various processes arising in building structures:

• shrinkage;
• stretching and compressive stresses.

Information! The substance applied to the surface to increase the clutch force between the base and finishing material is called adhesive. The basis for which adhesive is applied is called a substrate.

Methods of increasing adhesion

In construction, there are several universal ways to increase adhesion of decorative finishing materials with a base surface:

1. Mechanical - The surface of the base gives roughness to increase the area of \u200b\u200bcontact. To do this, it is treated with various abrasive materials, applied notches, etc.
2. Chemical - The composition of the applied protective finishing materials add various substances. This is, as a rule, polymers forming more durable bonds and give material additional elasticity.
3. Physical and chemical - The base surface is treated with primer changing the main chemical parameters of the material and affects certain physical properties. For example, a decrease in moisture absorption in porous materials, fixing the loose outer layer, and the like.

Ways to increase adhesion to various materials

Let us last in more detail on the methods of improving adhesion for various materials used in construction.

Concrete

Concrete building materials and structures are used everywhere in construction. Due to the high density and smoothness of the surface, their potential adhesion indicators are rather low. To increase the strength of the decoration compounds, the following parameters must be taken into account:

• dry or wet surface. As a rule, adhesion to the dry surface is higher. However, many adhesive mixtures have been developed that require pre-wetting the surface of the base. In this case, you must pay attention to the requirements of the manufacturer;
• ambient temperature and base. Most of the finishing materials are applied to concrete surfaces at an air temperature of at least + 5 ° C ... + 7 ° C. At the same time, the concrete should not be frozen;
• primer. Used in mandatory. For dense concrete, these are compounds with quartz sand fillers (Betonontact), for porous concrete (foam, aerated concrete), these are primer in deep penetration based on acrylic dispersions;
• adding modifiers. Ready dry plaster mixes already have various adhesive additives. If the plaster is mixed alone, it is recommended to add: PVA, acrylic primer, instead of the same amount of water, silicate adhesive, which gives the finishing material additional water-repellent properties.

Metal

A key role in the strength of the combination of paint materials with a metal surface is played by the method and quality of surface preparation. At home, it is recommended to perform the following steps:

• degreasing - Metal processing by various solvents: 650, 646, P-4, White spirit, acetone, kerosene. In extreme cases, the surface is cleaned with gasoline;
• matting - the processing of the base with abrasive materials;
• padding - The use of special paints of primers. They are implemented complete with decorative LCMs of a definite type.

Important! Lead adhesion, aluminum and zinc is much lower than that of cast iron and steel. The reason is that these metals form oxide films on their surface. Therefore, peeling of paint coatings occurs through the oxide layer. Staining these materials is recommended immediately after removing the film with a mechanical or chemical method.

Wood and wood composites

Wood is a porous surface with a lot of irregularities and does not experience special problems with the strength of the compound of finishing materials. But there is no limit to excellence, therefore various technologies have been developed to improve adhesion in combination with the preservation of the protective and decorative properties of the finishing itself. Their use, for example, in combination with acrylic paints, significantly improves weather resistance, resistance to ultraviolet fading, gives biological protection material. The wood surface is treated with a variety of primers, most often, based on borazate compounds and nitrocellulose.

Adhesion when welding

Welding is one of the most durable methods for connecting metal structures. This grip of the molecules of two elements without the use of intermediate or auxiliary substances - glue or solder. This process occurs under the influence of thermal activation. The outer layer of the combined elements is heated above the melting point, after which the intermolecular convergence occurs and the connection of the materials.

The following factors can serve as an obstacle to high-quality adhesion during welding:

• the presence of oxide films. They are removed mechanically or chemically during the preparation of the surface or disappear directly during the welding process under the influence of high temperature or fluxes;
• missing the chemical composition of materials and electrodes. Special attention should be paid to the presence and amount of silicon and carbon in the details connected. To connect steels of different brands, it is recommended to use electrodes with a low content of diffusion hydrogen;
• insufficient propulsion depth, which directly depends on the current strength and speed of the electrode.

Dictionary of medical terms

adhesion (lat. Adhasio sticking, sticking; SIP. adhesive process) in morphology

the battle of serous shells as a result of inflammation.

A new intelligent-word-formational dictionary of the Russian language, T. F. Efremova.

adhesion

g. The adhesion of the surfaces of two inhibited heterogeneous solid or liquid bodies (in physics).

Encyclopedic Dictionary, 1998

adhesion

Adhesion (from Lat. Adhasio - sticking) The grip of the surfaces of heterogeneous bodies. Thanks to adhesion, applying electroplating and paintworks, gluing, welding, etc., as well as the formation of surface films (eg oxide).

Adhesion

(from Lat. Adhasio ≈ adhesion), sticking the surfaces of two heterogeneous solid or liquid bodies. Example A. ≈ Adhesion of water droplets to glass. A. is caused by the same reasons as adsorption. Quantity A. is characterized by a specific work spent on separation of tel. This work is calculated per unit area of \u200b\u200bcontacting surfaces and depends on how their separation is performed: a shift along the surface of the section or a separation in the direction perpendicular to the surface. A. Sometimes it turns out more than a cohesion that characterizes the grip of the particles inside this body. In this case, the gap occurs cohesionly ≈ within the least durable of contacting bodies.

A. solid bodies with an uneven surface is usually small, since they actually come into contact only with separate protruding sites of their surfaces. A. Liquid and solid body and two unsuccessful liquids reaches an extremely high value due to complete contact over the entire area of \u200b\u200bcontact. When the solid body is coated with a polymer in fluctuate condition, the latter penetrates into the recesses and pores. After the polymer harvested, there is a link, sometimes called mechanical A. In this case, for the separation of the polymer film, it is necessary to overcome the cohesion in the solidified polymer. To achieve the limit A. The solid bodies are connected in a plastic or elastic state under pressure, for example, when gluing with rubber glue or with cold welding of metals. Durable A. is also achieved in the formation of a new solid phase on the surface of the section, for example, in the case of galvanic coatings, or in the occurrence of surface chemical compounds (oxides, sulfide, etc. films).

A. polymers are better due to the macromolecule polar and have a large number of chemically active functional groups. To improve A., active additives are introduced into the composition of the glue or film-forming polymer, the molecules of which are strongly binding to the film, to another ≈ with the substrate, forming an oriented adsorption layer. Upon contact of the two volumes of the same polymer, auto-ithesis (self-slope) may occur when the diffusion of macromolecules or their sections from one volume in another occurs. At the same time, the strength of communication over time increases, striving to the limit of ≈ cohesion strength.

A. Phenomenon takes place when welding, soldering, tinning, gluing, in the manufacture of photographic materials, as well as when applying paintwork polymer coatings that protect metal parts from corrosion; The reasons for violations A. In the latter case, there are voltages arising from the shrinkage of the film, as well as the difference in thermal expansion coefficients of film and metal.

A. Not only is the condition for the formation of high-quality coating, binder welded or adhesive seam, but also causes increased wear of rubbing parts. To eliminate A., a lubricant layer is introduced that prevents the contact of the surfaces.

Lit.: Krotova N. A., about gluing and sticking, M., 1956; Wyutsky S. S., Outgeezia and Adhesion of high policies, M., 1960; Dryagin B. V., Krotova N. A., Adhesion, M.Y. L., 1949.

V. I. Shimulis.

Wikipedia

Adhesion

Adhesion In physics, the grip of the surfaces of heterogeneous solid and / or liquid tel. Adhesion is due to intermolecular interactions (van der Wales, polar, sometimes mutual diffusion) in the surface layer and is characterized by the specific work required for the separation of surfaces. In some cases, adhesion may turn out to be stronger than cohesion, that is, the adhesion inside a homogeneous material, in such cases, when applying a tearing force, a cohesive gap occurs, that is, the gap in the volume is less durable of contacting materials.

Adhesion significantly affects the nature of the friction of contacting surfaces: so, when the surface interacts with low adhesion, friction is minimal. As an example, polytetrafluoroethylene (Teflon) can be cited, which, by virtue of adhesion, in combination with most materials, has a low friction coefficient. Some substances with a layered crystal lattice (graphite, molybdenum disulfide), characterized simultaneously low adhesion and cohesion values, are used as solid lubricants.

The most famous adhesion effects are capillary, wettability / non-inspireness, surface tension, menisy of fluid in a narrow capillary, friction of two absolutely smooth surfaces. In some cases, adhesion criterion in some cases can be the time of separation of the layer of material of a certain size from another material in the laminar fluid flow.

Adhesion takes place in the processes of gluing, soldering, welding, coating. The adhesion of the matrix and filler composites is also one of the most important factors affecting their strength.

In biology, cell adhesion is not just a cell connection between themselves, and such a compound, which leads to the formation of certain proper types of histological structures specific to data types of cells. The specificity of cell adhesion is determined by the presence of cell adhesion proteins on the surface of cells - integrins, cadgers, etc. For example, platelet adhesion on the baseal membrane and on collagen fibers of the damaged vascular wall.

In the anti-corrosion protection of the adhesion of the paint and varnish material to the surface, the most important parameter affecting the durability of the coating. Adhesion is the adhesion of paintwork to the painted surface, one of the main characteristics of industrial LKM. The adhesion of paints and varnishes may have a mechanical, chemical or electromagnetic nature and is measured by the power of the parallery coating per unit area of \u200b\u200bthe substrate. The good adhesion of the paint and varnish material to the stained surface can be ensured only with a thorough cleaning of the surface from dirt, fat, rust and other contaminants. Also, to ensure adhesion, it is necessary to achieve a given coating thickness, which is used for the thickness gauge of the wet layer. For evaluation of adhesion / cohesion, criteria were accepted and approved

Examples of the use of the word adhesion in the literature.

Negative ions, accelerating in the cyclotron, acquire a centripetal tendency, that is, they seek more to adhesionthan to dissipation.

Initially, blue plays the role of a passive center adhesionAnd as a result, an agglomerate is formed, which does not have the properties of the codon, but actively collecting those fragments of the charts that we were conventionally called mud.

Cured epoxy resins are distinguished by a small shrinkage, high adhesia, mechanical strength, moisture resistance, good electrically insulating properties.

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First, let's assume that the first condition for adhesion, comply with close contact at the molecular level between the adhesive and the substrate. And now imagine what will happen after the materials come into contact, and how they will interact. Adhesion bond can be mechanical, physical or chemical, but usually it is a combination of these types of communication.

Mechanical adhesion

The simplest type of adhesion is the mechanical adhesion of the adhesive components with the substrate surface. This adhesion is formed by the presence of such surface irregularities such as deepening, cracks, cracks, with the development of which microscopic submutions are formed.

The main condition for the formation of mechanical adhesion is the ability of the adhesive to easily penetrate into the deepening on the surface of the substrate, and then harden. This condition depends on the wetting of the surface of the substrate adhesive, which, in turn, is associated with the ratio of surface energies of materials in contact, which determines the magnitude of the wetting angle. The ideal situation is the complete wetting of the substrate adhesive. To improve contact before applying adhesive, you should get rid of air or steam present in the recesses. If adhesive is able to fill the undercuts and then harden, then, naturally, it is blocked by undercutters (Fig. 1.10.7).

Fig. 1.10.7. Mechanical engagement between the adhesive and substrate on the microscopic level

The degree of adhesive penetration in submution depends on both the pressure that was applied during its application and the properties of the adhesive itself. If you try to tear the adhesive from the substrate, then this can be done only by its gap, since the adhesive cannot be removed from the sublunctions. The concept of mechanical adhesion does not contradict the conditions for fastening or retention of non-removable dentures used in fixing them, with the exception of those phenomena that occur on the microscopic level. An important difference between these concepts is that good wettability is not a prerequisite for macroretia, whereas it plays a decisive role in creating mechanical engagement on the microscopic level.

In general, undercutions often increase the mechanical strength of the compound, but it is usually not enough to ensure that the mechanism of the most (specific) adhesion is involved. There are a number of additional adhesion mechanisms caused by physical and chemical causes. The term true or specific adhesion is usually used to distinguish physical and chemical adhesion from mechanical, however, it is better to abandon such terms, since they are not entirely accurate.

The concept of true adhesion assumes that besides it, there is a false adhesion, but in reality adhesion either exists, or it is not. Physical and chemical differ from mechanical adhesion by the fact that the first involve adhesive and substrate into molecular interaction with each other, while for mechanical such interaction on the surface of the two phases is not required.

Physical adhesion

With close contact of the two planes, secondary bonds are formed due to the dipole-dipole interaction between polarized molecules. The magnitude of the resulting force of attraction is very small, even if they have a high value of the dipole moment or increased polarity.

The magnitude of the communication energy depends on the relative orientation of dipoles in two planes, but usually this value is no more than 0.2 electron-volt. This value is much less than that of primary bonds, such as ionic or covalent, in which bond energy usually ranges from 2.0 to 6.0 electron volts.

Secondary bonds due to the dipole-dipole interaction occur very quickly (since they do not need an activation energy for their occurrence) and are reversible (since molecules on the substance surface remain chemically unaffected). This weak adsorption physical attraction is easily destroyed by increasing the temperature, and it is not suitable for those cases when a permanent connection is required. However, such bonds as hydrogen can be an essential prerequisite for the formation of a chemical bond.

From this it follows that the compound of non-polar liquids with polar solids is difficult, and vice versa, since there will be no interaction at the molecular level between these two substances, even with their close contact. Such behavior is observed in liquid silicone polymers, which are non-polar and therefore do not form secondary ties with solid surfaces. Relations with them are possible only when the chemical stitching reaction is passed, which will create connectivity between the liquid and the solid body.

Chemical adhesion

If, after adsorption on the surface of the molecule dissociate, and then its functional groups, each separately, can be connected with covalent or

ionic connections with a surface, the result is a solid adhesion connection. Such an adhesion form is called chemisorption, and it can be in nature both ion and covalent.

Chemical bond differs from the physical fact that two neighboring atoms jointly possess the same electrons. The surface of the adhesive should be firmly connected to the substrate surface through chemical bonds, so the presence of reactive groups on both surfaces is necessary. In particular, this refers to the formation of covalent bonds, which occurs, for example, when binding to reactive isocyanates with polymer surfaces containing hydroxyl and amine groups (Fig. 1.10.8).

Fig. 1.10.8. The formation of covalent bond between isocyanate and hydroxyl and amine groups on the substrate surface

Unlike non-metallic compounds, metal communication is easily formed between solid and liquid metals - this mechanism is based on a soldering. Metal communication occurs due to free electrons and does not depend on the presence of reactive groups. However, this relationship is possible only if metal surfaces are perfectly clean. In practice, this means that it is necessary to use fluxes to remove oxide films, otherwise these films will prevent contact between atoms of metals.

The only way to separate the adhesive from the substrate is the mechanical gap of chemical bonds, but this does not mean that it is precisely these, and not other valence communications that will be broken. This imposes restrictions on the strength that can be achieved in the connection. If the strength of the gluing or adhesion compound is higher when tensile tensile materials of the adhesive or substrate, then earlier than the adhesive compound is destroyed, the cohesive adhesive or substrate will be destroyed.

Adhesion weave molecules (Diffusion mechanism of adhesion)

So far, we have proceeded from the assumption that there is a clearly pronounced surface of the section between the adhesive and substrate. Usually adhesive is adsorbed by the substrate surface and can be considered as a surfactant substance that accumulates on the surface, but does not penetrate deep into the surface. In some cases, adhesive or one of its components can penetrate inside the surface of the substrate, and not accumulate on it. It should be emphasized that the absorption of molecules occurs as a result of good wetting surface, and is not its reason.

If the absorbed component is a long chain molecule, or forms a long chain molecule after absorbing the substrate, then the resulting molecules or substrate molecules and substrate can occur, which will lead to very high adhesion strength (Fig. 1.10.9).

Fig. 1.10.9. Diffusion transition layer, generated by mutual weakening of molecular fragments of adhesive and substrate

This equality is called the Dupre equation. It means that the adhesion (W) work is the sum of the free surface energy of the solid (y) and the liquid (Y | V) less energy on the surface of the section between the liquid and the solid (YSL).

From the Jung equation should

YSV YSI \u003d YSI COSE

Adhesion will be maximum with full (perfect) wetting, i.e. In the case when Cosq \u003d 1, therefore, the energy of the glued surfaces and the energies of each of these surfaces separately (Fig. 1.10.10).

Fig. 1.10.10. Separation of liquid from a solid surface with the formation of two new surfaces

The surface tension of the liquid hydrocarbon is approximately 30 mJ / m. If we assume that the attraction force is descending to zero at a distance of 3 x 10 ~ meters, the force required in order to separate the liquid from the solid surface is equal to the operation of the adhesion divided by the distance, and is equal to 200 MPa.

In fact, this value is significantly higher.

Thus, adhesives should be highly chemically attracted by the substrates surface to provide high adhesive strength.

Clinical meaning

The doctor needs to know what kind of communication it seeks to get, and this requires an understanding of the stages of creating an adhesive connection. This will avoid errors in work.

Fundamentals of dental materials
Richard Van Nurt.

During the conduct of large-scale or repair concrete work, situations are very often arising when there is no possibility to carry out the simultaneous fill of the entire concrete structure.

As a result, cold seams occur at the point of contact of the concrete layers, which lead to loss of strength, disruption of waterproof, detachment and other "troubles".

In this regard, when repairing concrete and reinforced concrete structures, as well as during the construction of the screeds, it is necessary concrete adhesion to concrete It was as deep and reliable.

The main cause of poor concrete adhesion to concrete and, accordingly, the cause of the formation of cold joints and detachment is the natural process of concrete carbonization.

Free lime, as the main source of functional interaction of concrete layers is practically absent on the surface of the "old" concrete. " Under the influence of CO2 ambient air, active lime enters the calcium carbonate, which is an inert substance that reacts only with acid compounds.

Therefore, a fresh concrete having an alkaline reaction is very bad "clips" with an old carbonized surface, and if you do not take adequate measures in time, it forms cold seams or "departs".

Common case of a set of activities to ensure high-quality adhesion of concrete to concrete

• Mechanical preparation of an old surface: grinding, dedusting, removal of oily spots, etc.;
• Coating with special soil;
• Surface treatment with special compositions "related" to each other chemicals;
• Surface treatment with compositions with high degree of "sticking";
• The use of the compositions of not "related" to each other in chemical composition.

An example of a set of measures to ensure high adhesion of concrete to concrete

• Application of the intermediate adhesion composition of the ASOCRET-KS / HB brand on a pre-treated surface. Provides the required level of adhesion with old concrete;
• Application of the repair sauceproof composition of the high speed of the strength set: ASOCRET-RN - up to 20 mm of adhesion, asocret-GM100 - up to 100 mm of adhesion depth;
• Application of the finishing solution asocret-bs2.

The above materials have a cement-sand base, modified by appropriate additives. The so-called "dry polymers" are used as additives, which are powdered high molecular weight compounds.

When the mixtures of such mixtures are shown, a full-fledged liquid polymer is formed, which gives the composition the required functional property - ensuring a reliable clutch (adhesion) of concrete to concrete.

Adhesion is the relationship between the dissimilar surfaces given into contact. The causes of the occurrence of adhesion bond - the effect of intermolecular forces or forces of chemical interaction. Adhesion determines the gluing of solids - substrates - with the help of adhesive adhesive, as well as the connection of a protective or decorative paint and varnish coating. Adhesion also plays an important role in the dry friction process. In the case of the same nature of contacting surfaces, it is necessary to talk about authezia (authenthesia), which underlies many processing processes of polymer materials. With a long-term contact of the same surfaces and the structure of the structure characteristic of any point in the volume of the body, the strength of the auto-esionic compound is approaching the cohesion strength of the material (see cohesion).

On the interfacial surface of two liquids or liquids and solids, adhesion can achieve an extremely high value, since the contact between the surfaces in this case is full. The adhesion of two solid bodies due to the irregularities of surfaces and contact only in separate points, as a rule, is small.

What is the adhesion of the surface?

However, high adhesion can be achieved in this case if the surface layers of contacting bodies are in plastic or highly elastic state and pressed to each other with sufficient force.

Fluid adhesion

Fluid adhesion to liquid or liquid to solid. From the point of view of thermodynamics, the cause of adhesion is a reduction in free energy on a unit of the surface of the adhesive seam in an isothermally reversible process. The operation of the reversible adhesion separation Wa is determined from the equation:\u003e Wa \u003d σ1 + σ2 - Σ12

where σ1 and σ2 are the surface tension at the phase boundary, respectively, 1 and 2 with the environment (air), and σ12 - the surface tension at the border of phases 1 and 2, between which adhesion occurs.

The adhesion value of two unsuccessful liquids can be found from the equation specified above, according to the easily defined values \u200b\u200bof σ1, σ2 and σ12. On the contrary, the adhesion of the fluid to the surface of the solid, due to the impossibility of directly determining the σ1 of the solid body, can only be calculated by indirectly by the formula:\u003e Wa \u003d Σ2 (1 + COS θ)

where σ2 and θ are the measured values \u200b\u200bof respectively surface tension of the liquid and the equilibrium edge angle of wetting formed by the liquid with the surface of the solid body. Due to the hysteresis of wetting, which does not allow to accurately determine the edge angle, only closely approximate values \u200b\u200bare usually obtained by this equation. In addition, this equation cannot be used in the case of complete wetting when Cos θ \u003d 1.

Both equations applied in the case when at least one phase is liquid is completely inapplicable to assess the strength of the adhesion bond between the two solid bodies, since in the latter case the destruction of the adhesive compound is accompanied by various kinds of irreversible phenomena due to various reasons: inelastic deformations of the adhesive and substrate, Education in the zone of the adhesive seam of the double electric layer, a gap of macromolecules, "pulling out" of the specied ends of the macromolecules of one polymer from the layer of other, etc.

Adhesion polymers

Almost all adhesives used in the practice are represented by polymer systems or form a polymer as a result of chemical transformations occurring after applying adhesive for glued surfaces. Only inorganic substances like cement and soldiers can be attributed to non-polymeric adhesives.

Methods for determining adhesion

1. Method of simultaneous separation of one part of the adhesive connection from another throughout the contact area;
2. The method of gradual separation of the adhesion connection.

Ottay method - adhesion

At the first method, the destructive load can be applied in the direction perpendicular to the surface of the surface contact (tensile test) or parallel to it (shift test). The ratio of force overcome with simultaneous separation throughout the area of \u200b\u200bcontact is called adhesion pressure, adhesion pressure or adhesion bond strength (H / m2, DIN / CM2, kgf / cm2). The separation method gives the most direct and accurate characteristic of the strength of the adhesion compound, however, its use is associated with some experimental difficulties, in particular with the need for a strictly centered load application to the test model and ensuring uniform distribution of voltages on the adhesion seam.

The ratio of forces overcome during the gradual separation of the sample, to the width of the sample is called resistance to peeling or resistance to resolving (N / M, DIN / CM, GS / cm); Often, the adhesion, determined by distinguishing, is characterized by the work that needs to be expensive to the separation of adhesive from the substrate (J / M2, ERG / CM2) (1 J / M2 \u003d 1 N / M, 1 erg / cm2 \u003d 1 din / cm).

Delamination method - adhesion

Definition of adhesion with solidification is more appropriate in the case of measuring the strength of the relationship between thin flexible film and a solid substrate, when, in the conditions of operation, the film peeling comes, as a rule, from edges by slow deepening crack. With the adhesion of two rigid solids, the separation method is more indicative, since in this case, in this case, an almost simultaneous separator can occur throughout the area of \u200b\u200bcontact.

Test methods of adhesion

Adhesion and outgeese when testing for a separation, shift and stratification can be determined on conventional dynamometers or on special adhesiometers. To ensure completeness of the adhesive and substrate contact, the adhesive is used in the form of a melt, a solution in a volatile solvent or monomer, which is polymerized during the formation of the adhesion compound.

However, when cured, drying and polymerization, adhesive, as a rule, undergoes shrinkage, as a result of which tangential voltages arise on the interfacial surface, weakening the adhesive connection.

These voltages may be largely eliminated by the introduction of fillers, plasticizers into adhesive, and in some cases, heat treatment of the adhesion connection.

The strength of the adhesive bond determined when testing, the dimensions and design of the test sample (as a result of the valve of the edge effect), the thickness of the adhesive layer, the prehistory of the adhesion connection, and other factors can be significantly influenced. On the values \u200b\u200bof the strength of adhesion or outgeese, it can be said, of course, only in the case when the destruction occurs on the interfacial boundary (adhesion) or in the initial contact plane (authezia). In the destruction of the adhesive sample, the obtained values \u200b\u200bcharacterize the cohesion strength of the polymer.

Some scientists believe, however, that only the cohesive destruction of the adhesion connection is possible. The observed adhesion nature of destruction, in their opinion, only seemingly, since visual observation or even observation using an optical microscope does not allow to detect the remaining subtle layer of adhesive on the surface of the substrate. However, recently, it was theoretically and experimentally showed that the destruction of the adhesive compound may be the most diverse character - adhesion, cohesion, mixed and micromosaic.

With this process of adhesion, different types of substances are attracted at the molecular level. It may be subject to both solid bodies and liquid.

Definition of adhesion

The word adhesion translated from Latin denotes a clutch. This is a process in which two substances are attracted to each other. Their molecules are connected to each other. As a result, in order to disconnect two substances, it is necessary to produce external impact.

This is a superficial process that is typical of almost all dispersion systems.

Adhesion is what? Adhesion: Definition

This phenomenon is possible between such combinations of substances:

• liquid + liquid,
• solid body + solid,
• liquid body + solid body.

All materials that begin to interact with each other during adhesion are called substrates. Substances that provide substrates dense clutch received the name of adhesives. For the most part, all substrates are represented by solid materials, which can be metals, polymeric materials, plastic, ceramic material. Adhesives are predominantly represented by liquid substances. A good example of adhesive is such a liquid like glue.

This process may be the result:

• mechanical impact on clutch materials. In this case, in order for the substances to be embedded, adding certain additional substances and the use of mechanical clutch methods.
• the appearance of the relationship between molecules of substances.
• The formation of a double electric layer. This phenomenon occurs when the electrical charge is transferred from a single substance to another.

Currently, there are no cases when the adhesion process between substances appears as a result of the influence of mixed factors.

The strength of adhesion

The strength of adhesion is an indicator of how certain substances are tightly connected. To date, the strength of the adhesion interaction of two substances can be determined using three groups of specially developed methods:

1. Methods of separation. They are divided into many ways to determine adhesive strength. To determine the degree of clutch of two materials, it is necessary to try using the external force to break the connection between substances. Depending on the fastened materials, it is possible to use the simultaneous separation method here, or the consecutive separation method.
2. The actual adhesion method without interference in the design created by the clutch of two materials.

When using different methods, various indicators may be obtained, which depend largely on the thickness of two materials. The peeling rate and an angle under which it is necessary to separate separation takes into account.

Adhesion Materials

In the modern world there are various types of adhesion materials. Today, the adhesion of polymers is not a rare phenomenon. When mixing different substances it is very important that their active centers interact with each other. At the border of the interaction of two substances, electrically charged particles are formed, which provide a solid connection of materials.

Adhesion glue is the process of attraction of two substances by mechanical interaction from outside. The glue is used to glue two materials in order to create one item. The strength of the fastening of materials depends on what strength is the glue when contacting with individual types of materials. For gluing materials that poorly interact with each other, it is necessary to strengthen the effect of glue. To do this, you can simply use a special activator. Due to it, durable adhesion is formed.

Very often in the modern world, it is necessary to deal with fastening of materials such as concrete and metals. Concrete adhesion to metal is not enough. More often in construction, special mixtures are used that ensure reliable fastening of these materials. A construction foam, which causes metals and concrete to form a stable system is not rarely applied.

Adhesion method

The methods for determining adhesion are methods that are established by how different materials can interact with each other within a certain specificity. Different construction objects and household devices are made of materials that are fastened with each other. In order for them to function in normal mode and did not harm, it is necessary to carefully monitor the level of adhesion between substances.

The measurement of adhesion is carried out using specialized devices that allow the production stage to determine how firmware are attached to each other after using certain bonding methods.

Adhesion of paints and varnishes

The adhesion of paints and varnishes is a grip of paint with various materials. Most often occurs adhesion of paint and metal and metal. In order to cover metal products with a layer of paint initially, tests of interaction of two materials are initially carried out. It is taken into account how the layer must be applied to the paintwork in order to determine its degree of adsorption. Subsequently, the level of interaction of the coloring film and the material it is covered is determined.

Adhesive property

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Adhesion properties are characterized by the normal voltage of the separation P of the two solid surfaces. The growth of adhesion force increases the intensity of the granuocation, but it makes it difficult to work with the material due to sticking it on the walls of the devices. Upcluding equal conditions / blood pressure, it is essential on the concentration of the binder, and this dependence is extreme.

The adhesion properties of vegetable and animal adhesives are inextricably linked with their chemical nature. However, to identify the immediate link between the chemical nature of the adhesive and the substrate when gluing wood in some cases is difficult not only due to the complexity of the chemical nature of wood, but also because it is susceptible to more significant changes than the adhesive layer. For example, in conditions of high humidity and high temperatures, wood due to swelling and drying is deformed. In addition, wooden structures and products littered with sunlight are absorbed by radiant energy and heat up to a temperature significantly exceeding the ambient temperature. The temperature in the plywood cover of the aircraft, for example, can reach 90 C.

Adhesion properties play a big role in the functioning of the dressings.

On the one hand, the bottom layer of the dressing should be easily saved, providing a dense fitting of the bandage to the wound, on the other, the surface energy at the border of the bandage-wound must be minimal to ensure the smallest injury when removing it from the wound.

Adhesion properties sometimes have a decisive influence on the choice of methods and conditions of manufacture, storage, use and transportation of powdered materials.

Adhesive properties in various high-strength and heating-resistant enamels are about the same and significantly higher than that of the wires of Pal and Pale. When tested, the samples of 50 mm long in accordance with GOST 7262 - 54 must withstand depending on its dimensions of at least 7 - 17 of the circles. In fact, with these tests, higher results are often obtained. Thus, the wires of the Pelr-2 brand with a diameter of 0 55 - 1 20 mm are often kept up to 30 - 24 more circles.

Adhesion properties (stickiness) of synthetic adhesives have been studied not yet enough, but scientists suggest that they depend at least two main factors: the flexibility of the macromolecule links and the presence of polar groups.

Adhesion properties in various high-strength enamels are about the same and significantly higher than that of the wires of Pal and Palo. When testing with twisting, the samples of 50 mm long in accordance with the standard must withstand depending on its dimensions of at least 7 - 17 of the circles. In fact, with these tests, higher results are often obtained. So, with Is - - Pelp tests of Pelr-2 with a diameter of 0 55 - 1 20 mm, samples are often kept up to 30 - 24 dsits.

The adhesion properties of some film-forming materials are dependent on their plastic properties. Since under solidification, a shrinkage of film-forming materials occurs, the voltages developing between film and wood can lead to a significant weakening of the connection of the coating with wood - their lag, and in fragile coatings - to cracking. Therefore, plasticizers that increase the plastic coating properties are introduced into many paints and varnishes. An increase in the thickness of the lacquer film adversely affects the adhesive properties of coatings due to an increase in shrinking stresses.

Adhesion properties can only be manifested in monolayer particles that have been mastered on the walls or filtering surfaces of gas target apparatuses, and due to the very small thickness of such a layer, as a rule, do not affect the operation of the dust and gold systems.

Concrete adhesion to concrete: how, and why?

The adhesive properties of paraffin are most strongly increasing atactic polypropylene and oxidized petrolatum, while their joint presence gives a syner-geographic effect.

The adhesive properties of dust characterize the tendency of dust particles to sticky, which affects the operational parameters of dust collectors.

The adhesive properties of substrates can be changed by vaccination. The vaccination is carried out using high energy sources or in an electric field.

Adhesion properties of bitumen make it valuable material for the production or attachment of many products.

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Fastening types There are many: welding, rivets, connection with fasteners and so on. However, the use of adhesive composition remains one of the most sought-after, as it allows to connect the surfaces of very different materials and without mechanical impact on objects.

Laying glue

One of the fundamental factors of choice is high adhesion of glue.

What it is

Bonding is a way of a permanent connection of any elements, due to the formation of the adhesive bundle between the glued surfaces. The composition used for this is called glue. The substance may have natural or artificial origin, but in any case should have certain properties.

Adhesion is a property that ensures the strength of the compound of materials. After soaring the adhesive layer, items should be as it were. If the compound cannot be fused, we can talk about the high adhesive properties of the substance.

Preparation of adhesive composition

Quality This indicates the ability of the adhesive composition to entrenched on the surface. So, the metal is a substance of low-pore, which indicates its low adhesive properties. Ordinary glue, for example, on the surface of metal or glass, simply will not hold.

Adhesion - what it is in construction

Glue with elevated adhesive properties forms a sufficiently strong connection to connect smooth surfaces.

What is cohesion? The strength provided by the adhesive itself when frozen. For example, plasticine can temporarily consolidate two objects, but under the influence of weight of one of them, the material is easily destroyed. Adhesive composition with good cohesion ensures communication strength.

This is relative, since it depends on the nature and weight of the glued objects. So, the label attached to the bottle has a minimum weight, and to keep it, it is sufficiently mixture with rather low cohesion qualities. But the adhesive tiled with adhesion to the concrete should have increased cheese, since the tile is heavy.

Kneading

Another important parameter of the composition is the ability to maintain the strength of the compound at different temperatures. In everyday life, mixtures that grasp at normal temperature are used, that is, about 20-30 C. However, already in construction work, when fastening stone and ceramics, when fixing metal panels and bricks, this is not enough. We produce different types of products intended for operation at different temperatures.

Adhesion, cohesion, the temperature operating range of the product is regulated by GOST.

Essence bonding

Regardless of the nature of the adhesive mixture, the mechanism of action is the same and determined by 2 main factors.

Glue with good adhesion - tiled, for metal surfaces and so on, comes to the consumer at semicircular form. Its components are mixed, but did not entered the final reaction. When preparing the composition - stirring and mixing dry components with water, a chemical reaction occurs, and the substance begins to polymerize. In this case, the pasty product slowly or quickly goes into a solid state.

In everyday life, this process is called grasp or solidification. It is known that it is possible to glue materials, only as long as the mixture is in a semi-liquid state.

Application of glue

The affinity of materials is understandable that substances close in nature are highly adhesion to each other, only metals are exception. And the ceramic product is a tile, porcelain stoneware, and concrete are compounds complex, the composition of them includes quite a lot of various components. If the solution connecting them has a similar composition, its adhesion properties with respect to these materials will be elevated. Thus, for laying tiles on concrete and brick bases, the compositions include cement are most often used.

How to choose adhesion adhesion glue for tiles

Consider at the same time a fairly decent list of factors:

• Operating conditions - if we are talking about the external finish, it is clear that ceramics will be exposed to low temperatures, and it means that it makes sense only a good special composition resistant to frost. If the case concerns the fireplace cladding, the situation is opposite - we need a material that exists the effect of very high temperatures.
• In addition, it is necessary to take into account humidity. For a raw room, glue will be needed, characterized by elasticity. In the photo - samples of good adhesive mixtures.
• The affinity for the base is concrete, a brick, cement-sandy bundles are considered a simple base when finishing with ceramics, since, firstly, they themselves are quite porous materials, and, secondly, they include a plurality of cement type components, mineral filler, and so on. To connect to metal or glass surfaces, the mixture uses only specialized, with increased adhesion relative to low-porous materials.

Cement glue for tile

Adhesion glue for tile is regulated by GOST. If we are talking about a porous embodiment, conventional mixtures are used, even cement. If it comes to low-porous materials, a special solution is required. In this category, for example, porcelain and clinker, for example,, for example, the porosity of their very low and the usual cement tile makeup does not hold the product on the wall.

GOST 31357-2007

It is used to lay heavy large-format plates and medium-sized plates and weights from marble, natural and artificial stone when conducting internal and external work. The maximum weight of glued slabs is not more than 100 kg / m2 surface.

The glue is recommended for outdoor cladding of bases subject to increased operational loads: socles, columns, external stairs, basements, interior with normal and high humidity: bathrooms, balconies and terraces.

Adhesion coatings

Ideal for facing surfaces of complex bases, such as old tile coatings, heated surfaces, etc.

• For interior and exterior use
• For children's and medical institutions
• Freak and crack resistance
• Application when cladding "complex" grounds
• Plate laying by top-down method
• Use in the system "Warm floor"

Specifications

Temperature of work
The amount of water by 25 kg. Dry mixes
Layer thickness
Consumption when working with a spatula 6x6
Viability of solution
Tile laying time
Tile position adjustment time
Stretch time
Clutch strength with base
Hold the weight of tile
Frost resistance	at least 35 cycles
Operating temperature	from -50 to + 70 ° С
Packaging

The glue has increased strength characteristics, which allows it to be used when laying heavy plates and operate in harsh environments. High adhesive ability allows you to lead the "top-down" method.

The glue is used on heated surfaces (up to + 70c), including in the "Warm floor" system.

The plasticity of the finished solution makes the glue comfortable in the work. After a set of strength, the glue retains its properties with direct contact with water and when exposed to negative temperatures.

Glue is environmentally friendly material. Does not distinguish dangerous to human health and environmental substances in work and operation.