Kuznetsov A.S. 1 , Kornyushko V.F. 2

1 Postgraduate student, 2 Doctor of Technical Sciences, Professor, Head of the Department of Information Systems in Chemical Technology, Moscow Technological University

PROCESSES OF MIXING AND STRUCTURING OF ELASTOMER SYSTEMS AS CONTROL OBJECTS IN A CHEMICAL-TECHNOLOGICAL SYSTEM

annotation

In the article, from the standpoint of system analysis, the possibility of combining the processes of mixing and structuring into a single chemical-technological system for obtaining products from elastomers is considered.

Keywords: mixing, structuring, system, system analysis, management, control, chemical-technological system.

Kuznetsov A. S. 1 , Kornushko V. F. 2

1 Postgraduate stadent, 2 PhD in Engineering, Professor, Head of the department of Informational systems in chemical technology, Moscow State University

MIXING AND STRUCTURING PROCESSES AS CONTROL OBJECTS IN CHEMICAL-ENGINEERING SYSTEM

Abstract

The article describes the possibility of combining on the basis of system analysis the mixing and vulcanization processes in the unified chemical-engineering system of elastomer’s products obtaining.

keywords: mixing, structuring, system, system analysis, direction, control, chemical-engineering system.

Introduction

The development of the chemical industry is impossible without the creation of new technologies, an increase in output, the introduction of new technology, the economical use of raw materials and all types of energy, and the creation of low-waste industries.

Industrial processes take place in complex chemical-technological systems (CTS), which are a set of devices and machines combined into a single production complex for the production of products.

Modern production of products from elastomers (obtaining an elastomer composite material (ECM), or rubber) is characterized by the presence of a large number of stages and technological operations, namely: preparation of rubber and ingredients, weighing solid and bulk materials, mixing rubber with ingredients, molding a raw rubber mixture - semi-finished product, and, in fact, the process of spatial structuring (vulcanization) of the rubber mixture - blanks for obtaining a finished product with a set of specified properties.

All processes for the production of products from elastomers are closely interconnected, therefore, exact observance of all established technological parameters is necessary to obtain products of proper quality. Obtaining conditioned products is facilitated by the use of various methods for monitoring the main technological quantities in production in the central factory laboratories (CPL).

The complexity and multi-stage nature of the process of obtaining products from elastomers and the need to control the main technological indicators imply considering the process of obtaining products from elastomers as a complex chemical-technological system that includes all technological stages and operations, elements of analysis of the main stages of the process, their management and control.

1. General characteristics of mixing and structuring processes

The receipt of finished products (products with a set of specified properties) is preceded by two main technological processes of the system for the production of products from elastomers, namely: the mixing process and, in fact, the vulcanization of the raw rubber mixture. Monitoring compliance with the technological parameters of these processes is a mandatory procedure that ensures the receipt of products of proper quality, intensification of production, and prevention of marriage.

At the initial stage, there is rubber - a polymer base, and various ingredients. After weighing the rubber and ingredients, the mixing process begins. The mixing process is the grinding of the ingredients, and is reduced to a more uniform distribution of them in the rubber and better dispersion.

The mixing process is carried out on rollers or in a rubber mixer. As a result, we get a semi-finished product - a raw rubber compound - an intermediate product, which is subsequently subjected to vulcanization (structuring). At the stage of the raw rubber mixture, the uniformity of mixing is controlled, the composition of the mixture is checked, and its vulcanization ability is evaluated.

The uniformity of mixing is checked by the indicator of plasticity of the rubber compound. Samples are taken from different parts of the rubber mixture, and the plasticity index of the mixture is determined; for different samples, it should be approximately the same. The plasticity of the mixture P must, within the limits of error, coincide with the recipe specified in the passport for a particular rubber compound.

The vulcanization ability of the mixture is checked on vibrorheometers of various configurations. The rheometer in this case is an object of physical modeling of the process of structuring elastomeric systems.

As a result of vulcanization, a finished product is obtained (rubber, an elastomeric composite material. Thus, rubber is a complex multicomponent system (Fig. 1.)

Rice. 1 - Composition of the elastomeric material

The structuring process is a chemical process of converting a raw plastic rubber mixture into elastic rubber due to the formation of a spatial network of chemical bonds, as well as a technological process for obtaining an article, rubber, elastomeric composite material by fixing the required shape to ensure the required function of the product.

1. Building a model of a chemical-technological system
   production of products from elastomers

Any chemical production is a sequence of three main operations: the preparation of raw materials, the actual chemical transformation, the isolation of target products. This sequence of operations is embodied in a single complex chemical-technological system (CTS). A modern chemical enterprise consists of a large number of interconnected subsystems, between which there are subordination relations in the form of a hierarchical structure with three main steps (Fig. 2). The production of elastomers is no exception, and the output is a finished product with desired properties.

Rice. 2 - Subsystems of the chemical-technological system for the production of products from elastomers

The basis for building such a system, as well as any chemical-technological system of production processes, is a systematic approach. A systematic point of view on a separate typical process of chemical technology allows developing a scientifically based strategy for a comprehensive analysis of the process and, on this basis, building a detailed program for the synthesis of its mathematical description for the further implementation of control programs.

This scheme is an example of a chemical-technological system with a serial connection of elements. According to the accepted classification, the smallest level is a typical process.

In the case of the production of elastomers, separate stages of production are considered as such processes: the process of weighing ingredients, cutting rubber, mixing on rollers or in a rubber mixer, spatial structuring in a vulcanization apparatus.

The next level is represented by the workshop. For the production of elastomers, it can be represented as consisting of subsystems for supplying and preparing raw materials, a block for mixing and obtaining a semi-finished product, as well as a final block for structuring and detecting defects.

The main production tasks to ensure the required level of quality of the final product, the intensification of technological processes, the analysis and control of mixing and structuring processes, the prevention of marriage, are carried out precisely at this level.

1. Selection of the main parameters for the control and management of technological processes of mixing and structuring

The structuring process is a chemical process of converting a raw plastic rubber mixture into elastic rubber due to the formation of a spatial network of chemical bonds, as well as a technological process for obtaining an article, rubber, elastomeric composite material by fixing the required shape to ensure the required function of the product.

In the processes of production of products from elastomers, the controlled parameters are: temperature Tc during mixing and vulcanization Tb, pressure P during pressing, time τ of processing the mixture on the rollers, as well as vulcanization time (optimum) τopt..

The temperature of the semi-finished product on the rollers is measured by a needle thermocouple or a thermocouple with self-recording instruments. There are also temperature sensors. It is usually controlled by changing the flow of cooling water for the rollers by adjusting the valve. In production, cooling water flow regulators are used.

The pressure is controlled by using an oil pump with a pressure sensor and appropriate regulator installed.

Establishment of the parameters for the manufacture of the mixture is carried out by the roller according to the control charts, which contain the necessary values ​​of the process parameters.

The quality control of the semi-finished product (raw mixture) is carried out by the specialists of the central factory laboratory (CPL) of the manufacturer according to the passport of the mixture. At the same time, the main element for monitoring the quality of mixing and evaluating the vulcanization ability of the rubber mixture are vibrorheometry data, as well as the analysis of the rheometric curve, which is a graphical representation of the process, and is considered as an element of control and adjustment of the process of structuring elastomeric systems.

The procedure for evaluating the vulcanization characteristics is carried out by the technologist according to the passport of the mixture and the databases of rheometric tests of rubbers and rubbers.

Control of obtaining a conditioned product - the final stage - is carried out by specialists of the department for technical quality control of finished products according to the test data of the technical properties of the product.

When controlling the quality of a rubber compound of one specific composition, there is a certain range of values ​​of property indicators, subject to which products with the required properties are obtained.

Findings:

1. The use of a systematic approach in the analysis of the processes of production of products from elastomers makes it possible to most fully track the parameters responsible for the quality of the structuring process.
2. The main tasks to ensure the required indicators of technological processes are set and solved at the workshop level.

Literature

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References

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4. Novakov I.A., Vol'fson S.I., Novopol'ceva O.M., Krakshin M.A. Reologicheskie i vulkanizacionnye svojstva ehlastomernyh kompozicij. - M.: IKC "Akademkniga", 2008. - 332 s.
5. Kuznecov A.S., Kornyushko V.F., Agayanc I.M. \Reogramma kak instrument upravleniya tekhnologicheskim processom strukturirovaniya ehlastomernyh sistem \ M:. NHT-2015 s.143.
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Technologically, the vulcanization process is the transformation of "raw" rubber into rubber. As a chemical reaction, it involves the integration of linear rubber macromolecules, which easily lose stability when exposed to external influences, into a single vulcanization network. It is created in three-dimensional space due to cross chemical bonds.

Such a kind of "cross-linked" structure gives rubber additional strength characteristics. Its hardness and elasticity, frost and heat resistance improve with a decrease in solubility in organic substances and swelling.

The resulting mesh has a complex structure. It includes not only nodes that connect pairs of macromolecules, but also those that unite several molecules at the same time, as well as cross chemical bonds, which are, as it were, "bridges" between linear fragments.

Their formation occurs under the action of special agents, the molecules of which partially act as a building material, chemically reacting with each other and rubber macromolecules at high temperature.

Material properties

The performance properties of the resulting vulcanized rubber and products made from it largely depend on the type of reagent used. These characteristics include resistance to exposure to aggressive environments, the rate of deformation during compression or temperature rise, and resistance to thermal-oxidative reactions.

The resulting bonds irreversibly limit the mobility of molecules under mechanical action, while maintaining high elasticity of the material with the ability to plastic deformation. The structure and number of these bonds is determined by the method of rubber vulcanization and the chemical agents used for it.

The process is not monotonous, and individual indicators of the vulcanized mixture in their change reach their minimum and maximum at different times. The most suitable ratio of physical and mechanical characteristics of the resulting elastomer is called the optimum.

The vulcanizable composition, in addition to rubber and chemical agents, includes a number of additional substances that contribute to the production of rubber with desired performance properties. According to their purpose, they are divided into accelerators (activators), fillers, softeners (plasticizers) and antioxidants (antioxidants). Accelerators (most often it is zinc oxide) facilitate the chemical interaction of all ingredients of the rubber compound, help reduce the consumption of raw materials, the time for its processing, and improve the properties of vulcanizers.

Fillers such as chalk, kaolin, carbon black increase the mechanical strength, wear resistance, abrasion resistance and other physical characteristics of the elastomer. Replenishing the volume of feedstock, they thereby reduce the consumption of rubber and lower the cost of the resulting product. Softeners are added to improve the processability of processing rubber compounds, reduce their viscosity and increase the volume of fillers.

Also, plasticizers are able to increase the dynamic endurance of elastomers, resistance to abrasion. Antioxidants stabilizing the process are introduced into the composition of the mixture to prevent the “aging” of rubber. Various combinations of these substances are used in the development of special raw rubber formulations to predict and correct the vulcanization process.

Types of vulcanization

Most commonly used rubbers (butadiene-styrene, butadiene and natural) are vulcanized in combination with sulfur by heating the mixture to 140-160°C. This process is called sulfur vulcanization. Sulfur atoms are involved in the formation of intermolecular cross-links. When adding up to 5% sulfur to the mixture with rubber, a soft vulcanizate is produced, which is used for the manufacture of automotive tubes, tires, rubber tubes, balls, etc.

When more than 30% sulfur is added, a rather hard, low-elastic ebonite is obtained. As accelerators in this process, thiuram, captax, etc. are used, the completeness of which is ensured by the addition of activators consisting of metal oxides, usually zinc.

Radiation vulcanization is also possible. It is carried out by means of ionizing radiation, using electron flows emitted by radioactive cobalt. This sulfur-free process results in elastomers with particular chemical and thermal resistance. For the production of special rubbers, organic peroxides, synthetic resins and other compounds are added under the same process parameters as in the case of sulfur addition.

On an industrial scale, the vulcanizable composition, placed in a mold, is heated at elevated pressure. To do this, the molds are placed between the heated plates of the hydraulic press. In the manufacture of non-molded products, the mixture is poured into autoclaves, boilers or individual vulcanizers. Heating rubber for vulcanization in this equipment is carried out using air, steam, heated water or high-frequency electric current.

The largest consumers of rubber products for many years remain automotive and agricultural engineering enterprises. The degree of saturation of their products with rubber products is an indicator of high reliability and comfort. In addition, parts made of elastomers are often used in the production of plumbing installation, footwear, stationery and children's products.

findings

Based on a system analysis of the process of gumming a galvanized strip, models and methods are determined, the application of which is necessary for the implementation of the control method: a simulation model of the polymer coating drying process, a method for optimizing the technological parameters of the polymerization process based on a genetic algorithm, and a neuro-fuzzy process control model.

It has been determined that the development and implementation of a method for controlling the process of vulcanization of a galvanized strip on a polymer coating unit based on neuro-fuzzy networks is an urgent and promising scientific and technical task in terms of economic benefits, cost reduction and production optimization.

It has been established that the process of vulcanization of a galvanized strip in the furnaces of a metal coating unit is a multi-connected object with a distribution of parameters along the coordinate, operating under non-stationary conditions and requires a systematic approach to study.

The requirements for the mathematical support of the control system for multi-connected thermal objects of the metal coating unit are determined: ensuring the functioning in the mode of direct connection with the object and in real time, the variety of functions performed with their relative invariance during operation, the exchange of information with a large number of its sources and consumers in the process of solving the main problems, operability in conditions that limit the time for calculating control actions.

MATHEMATICAL SOFTWARE OF THE NEURO-FUZZY CONTROL SYSTEM FOR MULTIPLE-CONNECTED THERMAL OBJECTS OF A GUDDED METAL COATING UNIT

System Analysis of the Control of Multiconnected Thermal Objects of the Rubberized Coating Unit

Conceptual design is the initial stage of design, at which decisions are made that determine the subsequent appearance of the system, and research and coordination of the parameters of the created solutions with their possible organization are carried out. At present, it is gradually becoming realized that in order to build systems at a qualitatively different level of novelty, and not just their modernization, it is necessary to be armed with theoretical ideas about the direction in which systems develop. This is necessary to organize the management of this process, which will increase both the quality indicators of these systems and the efficiency of their design, operation and operation processes.

At this stage, it is necessary to formulate a control problem, from which we will obtain research problems. After analyzing the process of polymerization of a galvanized strip as a control object, it is necessary to determine the boundaries of the subject area that are of interest when building a process control model, i.e. determine the required level of abstraction of the models to be built.

The most important method of system research is the representation of any complex systems in the form of models, i.e. application of the method of cognition, in which the description and study of the characteristics and properties of the original is replaced by the description and study of the characteristics and properties of some other object, which in the general case has a completely different material or ideal representation. It is important that the model does not display the object of study in the form closest to the original, but only those of its properties and structures that are more of interest to achieve the goal of the study.

The task of control is to set such values ​​of the parameters of the vulcanization process of a galvanized strip, which will allow to achieve the maximum adhesion coefficient with a minimum consumption of energy resources.

A number of requirements are imposed on the quality of pre-painted rolled products, which are described in GOST, listed in section 1.3. The drying process in the ovens of the gum coating unit only affects the quality of adhesion to the substrate. Therefore, defects such as coating unevenness, gloss deviation, and potholes are not considered in this paper.

To carry out the drying process of the polymer coating, it is necessary to know the following set of technological parameters: temperatures of 7 furnace zones (Tz1 ... Tz7), line speed (V), density and heat capacity of the metal substrate (, s), thickness and initial temperature of the strip (h, Tin.) , the temperature range of polymerization of the applied paint ().

These parameters in production are usually called a recipe.

Such parameters as the power of the fans installed in the furnace zones, the volume of clean air supplied, the parameters of the explosion hazard of varnishes are excluded from consideration, since they affect the heating rate of the zones before drying and the concentration of explosive gases, which are not disclosed in this work. Their regulation is carried out separately from the management of the vulcanization process itself.

Let's define the research tasks that need to be performed to achieve the goal of management. Note that the current state of system analysis imposes special requirements on decisions made on the basis of the study of the obtained models. It is not enough just to obtain possible solutions (in this case, the temperatures of the furnace zones) - it is necessary that they be optimal. System analysis, in particular, allows us to propose decision-making methods for the purposeful search for acceptable solutions by discarding those that are obviously inferior to others according to a given quality criterion. The purpose of its application to the analysis of a specific problem is to apply a systematic approach and, if possible, rigorous mathematical methods, to increase the validity of the decision made in the context of analyzing a large amount of information about the system and many potential solutions.

Due to the fact that at this stage we know only the input and output parameters of the models, we will describe them using the “black box” approach.

The first task to be solved is to build a simulation model of the coating drying process, i.e. obtain a mathematical description of the object, which is used to conduct experiments on a computer in order to design, analyze and evaluate the functioning of the object. This is necessary to determine to what extent the temperature of the metal surface (Tp. out.) will increase when leaving the furnace for given values ​​of the strip speed, thickness, density, heat capacity and initial temperature of the metal, as well as temperatures of the furnace zones. In the future, a comparison of the value obtained at the output of this model with the polymerization temperature of the paint will make it possible to draw a conclusion about the quality of adhesion of the coating (Figure 10).

Figure 10 - Conceptual simulation model of the coating drying process

The second task is to develop a method for optimizing the technological parameters of the galvanized strip vulcanization process. To solve it, it is necessary to formalize the control quality criterion and build a model for optimizing technological parameters. Due to the fact that the temperature regime is controlled by changing the temperatures of the furnace zones (Tz1 ... Tz7), this model should optimize their values ​​(Tz1opt ... Tz7opt) according to the control quality criterion (Figure 11). This model also receives vulcanization temperatures as input, since without them it is impossible to determine the quality of paint adhesion to the metal substrate.

Figure 11 - Conceptual model for optimizing process parameters

The main methods of vulcanization of rubbers. To carry out the main chemical process of rubber technology - vulcanization - vulcanizing agents are used. The chemistry of the vulcanization process consists in the formation of a spatial network, including linear or branched rubber macromolecules and cross-links. Technologically, vulcanization consists in processing the rubber compound at temperatures from normal to 220 ° C under pressure and less often without it.

In most cases, industrial vulcanization is carried out with vulcanizing systems that include a vulcanizing agent, accelerators and vulcanization activators and contribute to a more efficient flow of spatial network formation processes.

The chemical interaction between the rubber and the vulcanizing agent is determined by the chemical activity of the rubber, i.e. the degree of unsaturation of its chains, the presence of functional groups.

The chemical activity of unsaturated rubbers is due to the presence of double bonds in the main chain and the increased mobility of hydrogen atoms in -methylene groups adjacent to the double bond. Therefore, unsaturated rubbers can be vulcanized with all compounds that interact with the double bond and its neighboring groups.

The main vulcanizing agent for unsaturated rubbers is sulfur, which is usually used as a vulcanizing system in conjunction with accelerators and their activators. In addition to sulfur, organic and inorganic peroxides, alkylphenol-formaldehyde resins (AFFS), diazo compounds, and polyhaloid compounds can be used.

The chemical activity of saturated rubbers is significantly lower than the activity of unsaturated ones, therefore, for vulcanization it is necessary to use highly reactive substances, for example, various peroxides.

Vulcanization of unsaturated and saturated rubbers can be carried out not only in the presence of chemical vulcanizing agents, but also under the influence of physical influences that initiate chemical transformations. These are high-energy radiation (radiation vulcanization), ultraviolet radiation (photovulcanization), prolonged exposure to high temperatures (thermal vulcanization), shock waves and some other sources.

Rubbers having functional groups can be vulcanized at those groups using substances that interact with the functional groups to form a cross-link.

The main regularities of the vulcanization process. Regardless of the type of rubber and the vulcanizing system used, some characteristic changes in material properties occur during the vulcanization process:

The plasticity of the rubber compound sharply decreases, the strength and elasticity of the vulcanizates appear. Thus, the strength of a raw rubber compound based on NC does not exceed 1.5 MPa, and the strength of a vulcanized material is not less than 25 MPa.

The chemical activity of rubber is significantly reduced: in unsaturated rubbers, the number of double bonds decreases, in saturated rubbers and rubbers with functional groups, the number of active centers. This increases the resistance of the vulcanizate to oxidative and other aggressive influences.

Increases the resistance of the vulcanized material to the action of low and high temperatures. Thus, NC hardens at 0ºС and becomes sticky at +100ºС, while the vulcanizate retains strength and elasticity in the temperature range from -20 to +100ºС.

This character of the change in the properties of the material during vulcanization unambiguously indicates the occurrence of structuring processes, ending with the formation of a three-dimensional spatial grid. In order for the vulcanizate to retain elasticity, cross-links must be sufficiently rare. For example, in the case of NC, the thermodynamic flexibility of the chain is retained if one cross bond occurs per 600 carbon atoms of the main chain.

The vulcanization process is also characterized by some general patterns of changes in properties depending on the vulcanization time at a constant temperature.

Since the viscosity properties of mixtures change most significantly, shear rotational viscometers, in particular Monsanto rheometers, are used to study the vulcanization kinetics. These devices make it possible to study the vulcanization process at temperatures from 100 to 200ºС for 12 - 360 minutes with various shear forces. The recorder of the device writes out the dependence of the torque on the vulcanization time at a constant temperature, i.e. the vulcanization kinetic curve, which has an S-shape and several sections corresponding to the stages of the process (Fig. 3).

The first stage of vulcanization is called an induction period, a scorch stage, or a pre-vulcanization stage. At this stage, the rubber mixture must remain fluid and fill the entire mold well, therefore its properties are characterized by a minimum shear moment M min (minimum viscosity) and a time t s during which the shear moment increases by 2 units compared to the minimum.

The duration of the induction period depends on the activity of the vulcanization system. The choice of a vulcanizing system with one or another value of t s is determined by the mass of the product. During vulcanization, the material is first heated to the vulcanization temperature, and due to the low thermal conductivity of rubber, the heating time is proportional to the mass of the product. For this reason, vulcanizing systems that provide a sufficiently long induction period should be selected for vulcanizing products of large mass, and vice versa for products with low mass.

The second stage is called the main vulcanization period. At the end of the induction period, active particles accumulate in the mass of the rubber compound, causing rapid structuring and, accordingly, an increase in torque up to a certain maximum value M max. However, the completion of the second stage is not the time to reach M max, but the time t 90 corresponding to M 90 . This moment is determined by the formula

M 90 \u003d 0.9 M + M min,

where M – torque difference (M=M max – M min).

Time t 90 is the optimum vulcanization, the value of which depends on the activity of the vulcanizing system. The slope of the curve in the main period characterizes the rate of vulcanization.

The third stage of the process is called the overvulcanization stage, which in most cases corresponds to a horizontal section with constant properties on the kinetic curve. This zone is called the vulcanization plateau. The wider the plateau, the more resistant the mixture to overvulcanization.

The width of the plateau and the further course of the curve mainly depend on the chemical nature of the rubber. In the case of unsaturated linear rubbers, such as NK and SKI-3, the plateau is not wide and then deterioration occurs, i.e. slope of the curve (Fig. 3, curve a). The process of deterioration of properties at the stage of overvulcanization is called reversion. The reason for the reversion is the destruction of not only the main chains, but also the formed cross-links under the action of high temperature.

In the case of saturated rubbers and unsaturated rubbers with a branched structure (a significant amount of double bonds in the side 1,2-units), the properties change insignificantly in the overvulcanization zone, and in some cases even improve (Fig. 3, curves b and in), since the thermal oxidation of the double bonds of the side links is accompanied by additional structuring.

The behavior of rubber compounds at the overvulcanization stage is important in the production of massive products, especially automobile tires, since due to reversion, overvulcanization of the outer layers can occur while undervulcanization of the inner ones. In this case, vulcanizing systems are required that would provide a long induction period for uniform heating of the tire, a high speed in the main period, and a wide plateau of vulcanization during the revulcanization stage.

3.2. Sulfur Vulcanizing Systems for Unsaturated Rubbers

Properties of sulfur as a vulcanizing agent. The process of vulcanization of natural rubber with sulfur was discovered in 1839 by C. Goodyear and independently in 1843 by G. Gencock.

For vulcanization, natural ground sulfur is used. Elemental sulfur has several crystalline modifications, of which only the α-modification is partially soluble in rubber. It is this modification, which has a melting point of 112.7 ºС, and is used in vulcanization. The -form molecules are an eight-membered cycle S 8 with an average activation energy of ring rupture E act = 247 kJ/mol.

This is a rather high energy, and the splitting of the sulfur ring occurs only at a temperature of 143ºС and above. At temperatures below 150ºС, heterolytic or ionic decomposition of the sulfur ring occurs with the formation of the corresponding sulfur biion, and at 150ºС and above, homolytic (radical) decomposition of the S ring with the formation of sulfur diradicals:

t150ºС S 8 →S + - S 6 - S - → S 8 + -

t150ºС S 8 →Sֹ–S 6 –Sֹ→S 8 ֹֹ.

Biradicals S 8 ·· easily break up into smaller fragments: S 8 ֹֹ→S х ֹֹ + S 8-х ֹֹ.

The resulting biions and biradicals of sulfur then interact with rubber macromolecules either at the double bond or at the site of the α-methylene carbon atom.

The sulfur ring can also decompose at temperatures below 143ºС if there are any active particles (cations, anions, free radicals) in the system. Activation occurs according to the scheme:

S 8 + A + →A - S - S 6 - S +

S 8 + B – → B – S – S 6 –

S 8 + Rֹ → R - S - S 6 - Sֹ.

Such active particles are present in the rubber compound when vulcanizing systems with vulcanization accelerators and their activators are used.

To convert soft plastic rubber into hard elastic rubber, a small amount of sulfur is sufficient - 0.10.15% wt. However, the actual dosages of sulfur range from 12.5 to 35 wt.h. per 100 wt.h. rubber.

Sulfur has a limited solubility in rubber, so the dosage of sulfur depends on the form in which it is distributed in the rubber compound. At real dosages, sulfur is in the form of molten droplets, from the surface of which sulfur molecules diffuse into the rubber mass.

The preparation of the rubber mixture is carried out at an elevated temperature (100-140ºС), which increases the solubility of sulfur in rubber. Therefore, when the mixture is cooled, especially in cases of its high dosages, free sulfur begins to diffuse onto the surface of the rubber mixture with the formation of a thin film or sulfur coating. This process in technology is called fading or sweating. Efflorescence rarely reduces the tackiness of the preforms, so preforms are treated with gasoline to freshen up the surface before assembly. This worsens the working conditions of assemblers and increases the fire and explosion hazard of production.

The problem of fading is especially acute in the production of steel cord tires. In this case, to increase the strength of the bond between metal and rubber, the dosage of S is increased to 5 wt.h. To avoid fading in such formulations, a special modification should be used - the so-called polymeric sulfur. This is the -form, which is formed by heating the -form to 170ºС. At this temperature, there is a sharp jump in the viscosity of the melt and polymeric sulfur S n is formed, where n is over 1000. In world practice, various modifications of polymeric sulfur, known under the brand name "cristex", are used.

Theories of sulfur vulcanization. Chemical and physical theories have been put forward to explain the process of sulfur vulcanization. In 1902, Weber put forward the first chemical theory of vulcanization, elements of which have survived to this day. Extracting the product of the interaction of NK with sulfur, Weber found that part of the introduced sulfur is not extracted. This part was called by him bound, and the separated one - free sulfur. The sum of the amount of bound and free sulfur was equal to the total amount of sulfur introduced into the rubber: S total =S free +S bond. Weber also introduced the concept of vulcanization coefficient as the ratio of bound sulfur to the amount of rubber in the composition of the rubber compound (A): K vulk \u003d S bond / A.

Weber succeeded in isolating polysulfide (C 5 H 8 S) n as a product of the intramolecular addition of sulfur to the double bonds of isoprene units. Therefore, Weber's theory could not explain the increase in strength as a result of vulcanization.

In 1910, Oswald put forward a physical theory of vulcanization, which explained the effect of vulcanization by the physical adsorption interaction between rubber and sulfur. According to this theory, rubber-sulfur complexes are formed in the rubber mixture, which interact with each other also due to adsorption forces, which leads to an increase in the strength of the material. However, adsorption bound sulfur should be completely extracted from the vulcanizate, which was not observed in real conditions, and the chemical theory of vulcanization began to prevail in all further studies.

The main proofs of the chemical theory (bridge theory) are the following provisions:

Only unsaturated rubbers are vulcanized with sulfur;

Sulfur interacts with unsaturated rubber molecules to form covalent cross-links (bridges) of various types, i.e. with the formation of bound sulfur, the amount of which is proportional to the unsaturation of the rubber;

The vulcanization process is accompanied by a thermal effect proportional to the amount of added sulfur;

Vulcanization has a temperature coefficient of about 2, i.e. close to the temperature coefficient of a chemical reaction in general.

The increase in strength as a result of sulfur vulcanization occurs due to the structuring of the system, as a result of which a three-dimensional spatial grid is formed. Existing sulfur vulcanization systems make it possible to directionally synthesize practically any type of cross-link, change the vulcanization rate, and the final structure of the vulcanizate. Therefore, sulfur is still the most popular cross-linking agent for unsaturated rubbers.

1. LITERATURE REVIEW

1.1. Development of methods and instruments for determining the degree of vulcanization and vulcanization characteristics

1.2. Vibrational rheometry method

1.3. Possibilities of using the results of rheometric tests

1.4. Improved models of vibrating rheometers

1.5. Mathematical foundations for the interpretation of kinetic curves

2. METHODS AND OBJECTS OF INVESTIGATION

2.1. Software for quantitative interpretation of kinetic curves of the vulcanization process

2.1.1. Table Curve system and its use for quantitative interpretation of kinetic curves

2.1.2. Table Curve 3D system

2.1.3. Characteristics of the MatLab integrated system

2.2. Objects of study 63 f 3. EXPERIMENTAL

3.1. Analysis of the reproducibility of kinetic curves of the vulcanization process

3.2 Analysis of the main empirical models for the quantitative interpretation of the kinetic curves of the vulcanization process

3.2.1. Integral curves

3.2.2. Differential curves 100 ^ 3.2.3. Loss modulus curves

3.3. Kinetic models

3.4. The Influence of Recipe-Technological Factors on the Character of Kinetic Curves of the Vulcanization Process

3.4.1. Temperature dependence of the kinetic curves of the vulcanization process

3.4.2. The Influence of Recipe Factors on the Character of Kinetic Curves of the Vulcanization Process

Recommended list of dissertations

• Study of the kinetics of vulcanization of diene rubbers by complex structuring systems 2000, Candidate of Chemical Sciences Molchanov, Vladimir Ivanovich

• Development of the scientific foundations of technology for the creation and processing of shoe thermoplastic rubbers by dynamic vulcanization 2007, Doctor of Technical Sciences Karpukhin, Alexander Alexandrovich

• Simulation of non-isothermal vulcanization of car tires based on a kinetic model 2009, candidate of technical sciences Markelov, Vladimir Gennadievich

• Algorithmic-information support for system analysis of automated chemical-technological processes of structuring multicomponent elastomeric composites 2017, Candidate of Technical Sciences Kuznetsov, Andrey Sergeevich

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Introduction to the thesis (part of the abstract) on the topic "Quantitative interpretation of the kinetic curves of the vulcanization process in the system of organizing the workplace of a rubber technologist"

In recent years, a whole series of new software products has appeared that allow the technologist to solve problems that were previously impossible to set.

For example, experiment planning methods have long been used in the work of rubber technologists, but the most commonly used methods for describing an almost stationary region were based solely on the construction of polynomials of the second and less often of the third degree. Now such problems can be solved in much more efficient ways, obtaining models whose parameters can be interpreted on the basis of physicochemical concepts.

There was also the possibility of a fundamentally different approach to the formation of databases related to the storage and use of information necessary for the development of vulcanization modes for products and control of technological processes, and primarily the mixing process.

The use of new software products in the work of a rubber technologist practically eliminates the need to store information on paper and can be considered as one of the important components of his workplace.

The purpose of the dissertation work: was the formation of the basic methods for the rational interpretation of the kinetic curves of the vulcanization process and the creation for this complex of software modules that allow the specialist to work at a truly modern level.

To achieve this goal, the following tasks were solved.

Carrying out a statistical analysis of quantitative characteristics obtained by processing the kinetic curves of the vulcanization process.

Development of a method for the most informative presentation of experimental data when processing kinetic curves and writing the corresponding program.

Consideration of possible versions of models for the quantitative interpretation of integral and differential kinetic curves, statistical analysis of these models, development of recommendations on the conditions for their application and methods for constructing models in the presence of secondary processes occurring during vulcanization.

Analysis of the relationship between the parameters of these models and vulcanization characteristics. Based on this, the development of methods for recreating the kinetic curve according to vulcanization characteristics, thereby eliminating the need to store information on paper.

Substantiation of the need to obtain differential kinetic curves (velocity curves), analysis of the possibility of classifying these curves and the effectiveness of using statistical moments to understand the results of kinetic studies.

Carrying out a comparative analysis of rheograms and loss modulus curves, assessing the possibility of predicting vulcanization characteristics from loss modulus curves.

Analysis of the possibility of obtaining a differential equation characterizing the vulcanization process based on the approximation of an integral curve using empirical models. Evaluation of the possibility of calculating the rate constant and the order of the reaction with such an approximation.

Consideration of the influence of recipe-technological factors on the nature of the kinetic curves of the vulcanization process and> evaluation of the advantages of using contour plots for the analysis of this influence.

The development of methods for solving these problems is relevant for rubber industry specialists.

Scientific novelty.

1. For the first time, the relationship between the parameters of models for describing rheograms and kinetic velocity curves and their connection with vulcanization characteristics is shown. Based on this, a method has been developed for constructing kinetic curves according to vulcanization characteristics.

2. Based on the analysis of the influence of recipe-technological factors on the nature of the kinetic curves of the vulcanization process, a method has been developed for constructing contour plots that facilitate decision-making when planning new and evaluating existing vulcanization modes.

3. It is shown that, along with the vulcanization characteristics, it is advisable to calculate the statistical moments of the velocity curves, which characterize the shape of the curve as a whole, and do not fix individual points on this curve.

4. For the first time, the possibility of obtaining a differential equation characterizing the vulcanization process based on the approximation of an integral curve using empirical models has been shown.

Practical significance.

1. On the basis of the developed method for adequate reconstruction of the kinetic curve according to vulcanization characteristics, the need to store information of a kinetic nature (for example, rheograms) on paper is eliminated.

2. The use of contour plots in the coordinates "vulcanization duration - the level of the recipe-technological factor" is necessary for making the right decisions when optimizing the recipe and planning new and evaluating existing vulcanization modes.

3. The expediency of constructing and analyzing differential kinetic velocity curves obtained on new generation rheometers is shown, since the shape of these curves is more (compared to rheograms) sensitive to changes in recipe-technological factors.

1. LITERATURE REVIEW

Similar theses in the specialty "Technology and processing of polymers and composites", 05.17.06 HAC code

• Improving the Efficiency of Heat Exchange Processes in the Heat Treatment of Gumming Coatings Using Microwave Energy 2004, candidate of technical sciences Shestakov, Demid Nikolaevich

• Highly elastic composite materials based on a mixture of rubbers 2000, candidate of chemical sciences Khalikova, Saodathon

• Polyfunctional Ingredients Based on Azomethines for Technical Rubbers 2010, Doctor of Technical Sciences Novopoltseva, Oksana Mikhailovna

• Optimization of thermal states of chemically reacting solid-phase objects 1997, Doctor of Physical and Mathematical Sciences Zhuravlev, Valentin Mikhailovich

• Modeling and calculation of non-stationary thermal processes of induction heating in the production of rubber products 2012, candidate of technical sciences Karpov, Sergey Vladimirovich

Dissertation conclusion on the topic "Technology and processing of polymers and composites", Kashkinova, Yulia Viktorovna

1. Statistical analysis of the quantitative characteristics obtained during the processing of rheograms showed that these characteristics are determined with a large dispersion of reproducibility. This is especially true of the kinetic parameters associated with the magnitude of the degree of vulcanization (minimum torque and its increment), and to a lesser extent, the parameters associated with the duration of the process (vulcanization start time, time of 90 and 50% conversion).

2. For the first time, a method has been developed for constructing contour charts that facilitate decision-making when planning new and evaluating existing vulcanization regimes. The method is based on the creation of models that characterize the dependence of the degree or rate of vulcanization on time; the parameters of these models are arbitrary functions of one or more process-technological factors. A program has been developed to implement this method.

3. A group of models has been proposed for adequate quantitative interpretation of integral and differential kinetic curves; the parameters of these models can be interpreted in terms of physicochemical concepts. In some cases, kinetic curves can be described by summing up such models.

4. The relationship between the parameters of the integral and differential models and their connection with the vulcanization characteristics is shown. On the basis of this, for the first time, a method was developed for adequate reconstruction of the kinetic curve according to vulcanization characteristics. This makes it possible to eliminate the need to store information on paper.

5. The expediency of constructing and analyzing differential kinetic curves for the rate of the vulcanization process is shown. Their shape is more sensitive to changes in recipe-technological factors than in the case of integral curves.

6. On a significant experimental array (88 curves) it is shown that the differential kinetic curves of the vulcanization process, when interpreted as distribution functions, can be attributed to type IV of the family of Pearson curves, but in most cases they are adequately described by the 8062 model from the Table Curve program catalog, which is differential form of the integral model 8092.

7. It is shown that, along with the vulcanization characteristics, it is advisable to calculate the statistical moments of the velocity curves, which characterize the shape of the curve as a whole, and do not fix individual points on this curve.

8. It has been shown that, in the absence of reversion, cure characteristics can be calculated by analyzing the loss modulus curve.

9. For the first time, the possibility of obtaining a differential equation characterizing the vulcanization process based on the approximation of an integral curve using empirical models has been shown. In this case, the rate constant and reaction order can be expressed in terms of model parameters and hence in terms of curing characteristics.

10. The influence of recipe-technological factors on the nature of the kinetic curves of the vulcanization process is considered and the advantages of using contour plots for the analysis of this influence are substantiated. It is shown that the results of kinetic studies of the vulcanization process should be presented as a set of lines of equal level for a number of vulcanization characteristics and kinetic parameters. A classification of vulcanization diagrams based on graph theory has been developed.

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