Chemistry and technology of synthetic rubber. Textbook

The Ministry of Education and Science of Russian Federation Federal State Budget Institution of Higher Education «Kazan National Research Technological University»

I.M. Davletbaeva, O.R. Gumerova,

A.I. Akhmetshina, Ye.I. Grigoryev

CHEMISTRY AND TECHNOLOGY

OF SYNTHETIC RUBBER

Textbook

Kazan

KNRTU Publisher

2014

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UDC 542.97:[54-126]

Davletbaeva I.M.

Chemistry and technology of synthetic rubber : textbook / I.M. Davletbaeva [et al.], Ministry of Education and Science of Russian Federation, Kazan National Research Technological University. – Kazan : KNRTU Publisher, 2014. 92 p.

ISBN 978-5-7882-1673-7

The main purpose of the textbook is to support students with fundamental theoretical knowledge on the course "Chemical technology of synthetic rubber", acquire the experimental skills and form the common cultural and professional competences.

Intended for students of 24050165 "Chemical Technology of HighMolecular Compounds " (24050165-03 specialty "Technology of Synthetic Rubber") and masters of the course 24010068.13 "Chemical Technology and Biotechnology".

Prepared for the Department of Technology of Synthetic Rubber, Kazan National Research Technological University.

Published by the decision of the Editing and Publishing Board of Kazan National Research Technological University

Head of Department of Materials Science and Technology, Kazan National Research Technical University named after A.N. Tupolev, E.R. Galimov, Dr. of Eng., professor

ISBN 978-5-7882-1673-7 © I.M. Davletbaeva, O.R. Gumerova, A.I. Akhmetshina, Ye.I. Grigoryev 2014

©Kazan National Research Technological University, 2014

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INTRODUCTION

The textbook contains theoretical part together with experiments, describing the synthesis, chemical modification and analysis of synthetic rubbers. The main purpose of the textbook is to support students with fundamental theoretical knowledge on the course "Chemical technology of synthetic rubber", acquire the experimental skills and form the common cultural and professional competences:

-principles of thinking, the ability to generalize, analyze, acquire information, goal setting and choosing the ways to achieve it;

-the ability to arrange logically correct, argumentative and clear oral and written speech, the ability to arrange the results of thinking correctly (logically) in written and spoken form;

-the ability and willingness to cooperate with colleagues, work in a team;

-the ability to study the scientific and technical information;

-awareness of the social importance of their future profession;

-technical and technological calculating ability;

-willingness to study the reasons of defects in manufacturing and to develop the suggestions for their prevention and elimination;

-readiness to the development of production rates, technical norms for the materials, feedstocks, fuel and electricity consumption, equipment and production tools selection;

-The ability and willingness to implement the technological process in accordance with the regulations and to use technical tools to measure key process parameters and properties of raw materials and products;

-the ability to justify the specific engineering solution making in the design process, select equipment and technology subject to the environmental impact of their use;

-understanding of safety, industrial hygiene, fire safety;

-the ability to analyze the technological process as a subject to control.

At the beginning of each lab its purpose is formulated, the list of reagents, equipment, and glassware required for the lab, procedure and methods of the lab and the analysis of synthesized polymers, the examples of the data interpreting are given. As a result of the course, students should get an idea about the basic processes of the obtaining and modification of synthetic rubbers, the estimation methods of their physical and chemical properties, and the possibility to control the process and properties of the obtained polymers varying the process parameters.

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1 Safety Rules in the Laboratory of High-Molecular Compounds

The majority of the monomers for rubber production are extremely firehazardous, as they are organic substances and volatile liquids. A lot of operating procedures require the use of solvents such as benzene, toluene, ethyl alcohol, etc. All of these substances can form mixtures with air, exploding upon contact with a source of ignition (spark, flame, heated surface).

It is especially dangerous to use substances that are used as polymerization initiators (benzoyl peroxide, cumene hydroperoxide, etc.). If mishandled they may decompose explosively. Many of the used substances are toxic.

Most accidents that occur in the chemistry laboratory are the result of carelessness, impatience and disregard for safety rules or proper operating procedures.

1.1 Flammable Substances

Getting started with fire hazard substances, you should always consider the possibility of flash or fire. It is necessary to know the properties of substances, the location of fire extinguishers in the laboratory and methods of their using.

Never heat flammable substances with an open flame. Preferred heat sources include steam baths, water baths, oil and wax baths, salt and sand baths, and heating mantles. For uniform boiling in the entire volume the boiling stones should be placed in to the liquid (pieces of pumice stone, unglazed porcelain or capillary of 0.2 - 0.4 mm in diameter, sealed at one end). Heating liquids above their boiling points is acceptable only in the vessels dedicated for this purpose (ampoules, autoclaves).

During distillation of volatile liquids (Tb <50°C) the receiving flask should be placed in a bath of ice water, and the neck of the flask should be closed with cotton. The distillation flask should be heated in water bath.

1.2 Peroxide Compounds

Peroxide compounds are unstable compounds exceptionally prone to explosive decomposition. Peroxides may explode if subjected to heat, mechanical shock or friction, presence of catalysts of their decomposition

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or direct sunlight. The protective equipment should always be worn when handling peroxides and hydroperoxides (face shield, thick rubber gloves, and safety goggles).

Peroxide forming chemicals present a greatest danger because of the possibility of high levels of peroxides forming (e.g. during long-term storage or when a sample containing such chemicals are concentrated using rotary evaporation) which can cause a spontaneous explosion. An activities involving vacuum distillation present the greatest risk of generating dangerous levels of peroxides. Therefore, before the distillation the liquids must be tested for peroxide content using a test tube with a freshly prepared solution of ferrous sulphate, where will be added a few milliliters of ammonium thiocyanate solution.

Before distillation peroxide compounds should be destroyed through heating the material with an alkali solution. Peroxide can be destroyed also by sodium sulfate. 20-25 ml of saturated sodium sulfate solution, diluted with 50 ml of water, is added to 1 liter of solvent. The mixture is put into a separating funnel, shaken and allowed to settle for the complete removal of the peroxide. Freed from the peroxide the substance is dried and distilled, leaving in the distilling flask about a quarter of fluid taken for distillation.

1.3 Pressureand Vacuum Operations

An explosion shield from an organic glass or a metal screen should be used to protect against the hazards of vacuum and pressure procedures.

Precautions to be taken when working with vacuum lines and other glassware used at subambient pressure are mainly concerned with the substantial danger of injury in the event of glass breakage. Glass vessels may collapse violently, either spontaneously from strain or from an accidental blow. So there are used thick-walled round-bottom flasks. Vacuum lines should be separated by explosion shield. Large vessels (receiving flasks, Bunsen flasks, desiccators, etc.) should be wrapped in cloth to prevent glass fragmentation.

1.4 Caustics and Toxic Substances

Safety glasses and rubber gloves must be worn to protect the eyes from the impact of caustics (acids, alkalis). Always use a rubber bulb to fill pipets when handling caustics and toxic substances.

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Toxic substances (methyl alcohol, benzene, toluene, styrene and other aromatic substances) must be poured only inside fume hoods.

Mercury vapors can be quite dangerous. Therefore, mercury containing devices should be handled very carefully, preventing their breaking. If you break some devices, clean up spilled mercury promptly. Large droplets of mercury should be trapped by special amalgamated scoops. For the small ones you should use amalgamated copper or brass plate. Sprinkle 3% solution of KMnO4, Na2S4 or 20% solution of FeCl3 contaminated area to clean it up.

1.5 Electrical Safety

The hazards associated with the use of electricity include an electrical shock and an electrical fire. Fire can be caused by short circuits, over-heated equipment, poor contact, overloaded circuits or wiring.

Lab procedures require using equipment that is in safe, serviceable condition. All equipment (ovens, muffle furnaces, thermostats, etc.) must have safety grounding.

2 Production of Synthetic Rubber by Free Radical Polymerization

Emulsion polymerization is the most common method for synthetic rubber production. Synthetic latex obtained as a result of this process. It is directly used in the rubber and other industries, or is processed into rubber by coagulation and separation of solid polymer.

Emulsion polymerization is characterized by the relative easiness of process control, good heat exchange conditions, the possibility of a wide range of rubbers obtaining, the modifying of the properties of the resulting rubbers, latex filling with oil, carbon black, resins, etc.

Styrene butadiene and butadiene-α-methylstyrene rubbers (SBR), butadiene (BR), chloroprene rubber, etc. are derived by emulsion polymerization.

The emulsion polymerization processes are always proceed via radical mechanism at high (48÷50°C) or low (5°C) temperature and are called as "hot" or "cold" polymerization, respectively.

2.1 Initiation

Polymerization is initiated by free radicals and the macromolecule growth begins with addition of the initiating radical R• to the double bond accompanied by new radical forming.

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CH2CHX

R + CH2CHX R CH2 CHX

R CH2 CHX CH2 CHX

In every act of joining a radical regeneration occurs, and the initiator is involved only in the first act of addition.

Free radicals are produced:

-Using compounds that can decompose to form free radicals;

-By the photochemical and radiation initiation.

Chemical initiation is used for the polymers production on a large scale. The special substances (initiators), capable to decompose more easily than the monomer, are added to the reaction system.

There are two types of chemical initiator for free radical polymerization. They are water-soluble initiators and oil-soluble initiators.

The most widely used initiator system is peroxides. The decomposition of peroxides is as follows:

X O O X' X O + O X'.

Water-soluble initiators include hydrogen peroxide (HO-OH). However, its instability during storage leads to rarely usage for practical purposes. The most popular among the water-soluble initiators are inorganic peroxides - persulphates or perborates. Potassium persulfate (K2S2O8) is the most accessible and wide-spread of them.

The dissolution of potassium persulfate in aqueous phase causes its dissociation accompanied with the formation of cation and anion:

Organic peroxides or hydroperoxides, azoand diazo compounds with covalent bonds easily decomposing being heated, can be used as oilsoluble initiators. However, the high decomposition temperature

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(70 140°C) does not allow to use them as individual initiators for industrial emulsion polymerization.

The redox systems are used in industrial emulsion polymerization to lower the decomposition temperature of hydroperoxides until +5°C. The most widespread ones is the iron-trilon rongalite redox system. Hydroperoxide is used as an oxidizer. Transition metal ions in a lower oxidation state are used as a reducing agent. Iron (Fe+2) addeded to the aqueous phase in the sulfate form FeSO4 is the only practice-relevant among them.

RO–OH + Fe+2 → RO• + Fe+3 + HO–.

Among hydroperoxides isopropylbenzene hydroperoxide (HPIPB) is often used:

ethylenediaminetetraacetate) is used to maintain constant concentration of Fe+2 ions for a long time in the system. Trilon B contains Fe+2 linked by coordination bonds with nitrogen atoms.

Na O C(O) CH2 N CH2 C(O) O

CH2 Fe

CH2

Na O C(O) CH2 NCH2 C(O) O

An additional reducing agent is used to reduce the amount of iron ions in the rubber, trapped in rubber after the latex separating. It is a product of the interaction of formaldehyde with sodium sulfite (rongalite): HO-CH2-S(O)-O-Na.

The rongalite action is shown in Figure:

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