Blend System Based On NBR Rubber With Natural Rubber

1.4.2.12. Silicone rubber (polydimethyl siloxane)

Silicone rubber (abbreviated as MQ, PMQ, VMQ, PVMQ) or also known as siloxane rubber belongs to the group of organic polymers containing silicon, its main chain is made up of a chain of alternating silicon and oxygen atoms. Currently on the market there are products with trade names such as: Baysilone® by Bayer, KE® by Shincor Silicones, Silastic® by Dow Corning, Silplus® by General Electric and Tufel® by General Electric. Silicone rubber has an average price.

There are two methods of synthesizing silicone rubber: polymerization and condensation polymerization. In industry, people often use the polymerization method based on the Si-O- bond displacement reaction in the siloxane ring. Monomers are commonly used.

The common monomer used in the production of silicone rubber is dimethyldichlorosilane (CH 3 ) 2 SiCl 2 (DDS) with a boiling point of 70 o C. This monomer is obtained by direct synthesis from silicon and methylchloride (CH 3 Cl). DDS must have a purity of not less than 99.96% (by mass). In the presence of a catalyst at high temperature, the siloxane ring

dissociate to form straight chain products:

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R Si OO

R SiO

Si R

H 2 O

COUGH

Si OR

Si OH

R n

Due to the saturated polymer backbone, silicone rubber is resistant to

oxygen, ozone and ultraviolet rays. Silicone rubber is odorless, tasteless, non-toxic and fungus resistant. The material is flexible and compressible.

Silicone rubber is vulcanized with peroxide rather than sulfur.

When replacing part of the methyl groups (-CH 3 ) with phenyl (-C 6 H 5 ), ethyl (-C 2 H 5 ), acrylonitrile (ACN), propyl (-C 3 H 7 ) and other groups, it will affect the properties of silicone rubber. It is also possible to introduce

The main chain of elements (aluminum, titanium, phosphorus, boron, tin, magnesium and nitrogen) will change the properties of the polymer. For example, dimethyl siloxane rubber works in the temperature range from -60 o C to +250 o C, has poor adhesion because the Si-O bond is weakly polar, swells in solvents and grease, has low strength and poor abrasion resistance, and has high air permeability. When we replace the methyl group with vinyl to create methyl vinyl siloxane rubber, the resulting product can work in the temperature range from -55 o C to +300 o C, has good aging resistance and a reduced flow temperature when compressed. Replacing the methyl group with a phenyl group will result in methyl phenyl siloxane rubber that is very cold resistant, from -80 o C to -100 o C, has very good radiation resistance and high mechanical strength. If the methyl group is replaced by a fluorine atom (F) or a cyanide group (-CN), the rubber will have strong polarity and stability in grease and fuel. If boron, phosphorus, etc. atoms are added to the main chain, the rubber's heat resistance will increase to 350  400 o C and its adhesion will be good.

Silicone rubber is used as a special elastic material in many industrial fields. In the electrical, electronic and cable manufacturing industries, this plastic is used to increase the insulation of pipes, cables, motors and generators. In the pharmaceutical and food industries, this material is often used to make heat-resistant and cold-resistant items.

1.4.2.13. Fluorosilicon

Flosilicon (FVMQ) with some commercial products such as Silastic LS®, FSE® is a modified silicone rubber, in which the silicone polymer chain is attached with fluorine. The fluorosilicone molecule is highly polar, so this type of rubber is resistant to grease and fuel. However, this rubber has a high price.

The stable working temperature of fluorosilicone rubber is quite wide, ranging from

-40 o F to 400 o F and has properties similar to silicone rubber (such as very good temperature resistance, ozone, oxygen resistance, weather resistance, excellent resistance to hydrocarbon fuels, mineral oils, silicone fluids and less affected by many other chemicals. However, the tear and abrasion resistance of rubber

Fluorosilicon has poor permeability and high gas permeability. Fluorosilicon is used in sealing systems (gaskets, gaskets) requiring wide temperature exposure and resistance to oil and fuel used in aircraft.

1.4.2.14. Fluorocarbon rubber

Fluorocarbon rubber (FKM) appeared in 1955 as a copolymer of vinylidene fluoride CH 2 = CF 2 and trifluoroethylene chlorine CFCl=CF 2 . These are rubbers that contain only about 50% fluorine. Currently on the market there are fluorocarbon rubber products with trade names such as: Dai-el® by Daikin Industries, Dyneon® (formerly Fluorel®) by Dyneon, Tecnoflon® by Solvay Solexis and Viton® by DuPont Dow. However, because the most famous fluorocarbon manufacturer is DuPont Dow, the name Viton® has become the general term used for FKM products. The original commercial product of DuPont Dow rubber was Viton A and is the most widely used type of FKM. It is a copolymer of vinylidene fluoride (VF 2 ) and hexafluoropropylene (HFP). Because this product contains up to 66% fluorine, Viton has excellent resistance to the impact of specialized fluids, so it is widely used in the automotive and aerospace industries. Viton B is a fluorocarbon rubber compound derived from tetrafluoroethylene (TFE) with VF2 and HFP. Depending on the intended use, it is possible to partially replace TFE or VF2 (this increases the fluorine content to about 68%) or HFP (keeping the fluorine content at 66%). Viton B has better resistance to specialized fluids than Viton A. To date, there are many other types of Viton (Viton GF, Viton GFLT, etc.) with varying fluorine contents to suit the capabilities and application requirements.

Fluorocarbon rubber is also a type of rubber known for its many special properties such as weather resistance, good resistance to high temperatures, ozone, oxygen, mineral oils, fuels, hydraulic fluids, aromatics, organic solvents (except ketones and acetates) and chemicals. The working temperature of the material is in a wide range (from -26 o C to 262 o C) for static applications, although its working temperature can reach

275 o C. In addition to the main properties of fluorocarbon rubber, which are chemical and heat resistance, this material also has resistance to compression deformation and is flexible at low temperatures. The mechanical strength of FKM is average, the elongation is low, but it has very high heat resistance for a long time, so the material has excellent resistance to fire and high temperature, plus good resistance to oil, solvents, chemicals and weather, so it is often used in automobiles, chemical processing, aerospace and many other industries. However, FKM has a relatively high price.

1.4.2.15. Polyurethane

Polyurethane is an ester of dicarbamic acid R(NHCOOH) 2 or its substituted derivatives with glycol. Its composition is similar to polyamide because the peptide group (–CO–NH–) is located in the urethane group (–O–CO–NH–) but there is an additional oxygen atom in the chain, so the molecular chain of polyurethane has high flexibility and the material has a lower melting point than the corresponding polyamide.

There are many methods for synthesizing polyurethanes, the most common is the polymerization of diisocyanate with glycol. The synthesis reaction diagram and structure of polyurethanes are as follows:

The catalysts for the reaction are usually organic compounds of tin and tertiary amines or other acidic and basic compounds.

Polyurethane can also be prepared from the dichlorocarbonic ester of glycol with diamine by condensation polymerization and the reaction is carried out on the molecular surface.

biphasic. When the starting materials are substances with more than 2 functional groups, the synthesized polyurethane will have a spatial structure. Like polyamides, linear polyurethanes are soluble in concentrated inorganic acids, but their hygroscopicity is inferior to polyamides. Both of these polymers are high-grade plastics with high mechanical strength and chemical resistance, especially to acids, light and oxygen. Among the polyurethane resins, the resin prepared from hexamethylenediizocyanate and 1,4-butadiol (also known as Peclon-

U) is used to make faux fur and plastics. Other polyurethanes are used to make varnishes, paints, fabric and paper pastes, foams, and glues. Polyurethane products come in two varieties with varying properties (can be hard or soft) depending on the type of reactant and on their ratio.

Polyurethanes are considered plastics rather than rubbers (elastomers). Linear polyurethanes account for about 1.5% of all polyurethanes and are thermoplastics. Network polyurethanes account for about 98% of all polyurethanes. They are thermosetting and copolymers where one of the two components contains two or more functional groups. These products are produced by casting or by some other special methods. Polyurethanes that have undergone calendering account for only 0.5%. The technological method of calendering is the same as for other types of rubber. People also use organic peroxides or sulfur as curing agents and accelerators. Polyurethanes are used in many applications, such as foam rubber, paints, varnishes, gaskets, metal forming molds, pads, joints, shafts, wheels and conveyor belts. Thermoplastic polyurethanes are used as cable and pipe jackets, textile sheaths, in ski boots and other hard soles, in automobile body components, gears and other machine parts.

1.4.2.16. Butyl rubber

Butyl rubber (IIR) was introduced to the market in 1942 and is currently used in many fields. Butyl rubber is a polymerization product of isobutylene with a small amount (about 1-3%) of diene hydrocarbons, commonly isoprene.

The structure of butyl rubber is shown as follows:

CH 3 CH 3

C CH 2 CH 2 C CH CH 2

CH 3

This is one of the few synthetic rubbers obtained by catalytic polymerization at low temperature using the cationic mechanism. The catalyst used is AlCl 3 . The reaction takes place at a temperature of 100 o C, in which liquid ethylene acts as a refrigerant, and CH 3 Cl is an inert solvent.

There are very few double bonds in the molecule, so the properties of butyl rubber are very different from natural rubber (NR). The density of butyl rubber is 0.92 g/cm3 , odorless, white crepe-like on the outside, less permeable to air and does not absorb water. Butyl rubber has high electrical insulation even in humid environments.

Butyl rubber is also vulcanized with sulfur, but the vulcanization speed is slow, so in practice people often use polysulfide compounds as vulcanization agents, commonly used vulcanization accelerators are tiuram or zinc dibutylditiocarbamate. The vulcanization temperature is above 150 o C. Butyl rubber is often mixed with chloroprene rubber to increase mechanical strength, increase tear resistance and abrasion resistance. Due to its very low air permeability and non-absorption of water, butyl rubber is used to make automobile inner tubes and water-resistant parts. Butyl rubber is resistant to oxygen and ozone, has high chemical stability, so it is used to cover high-voltage electric wires, used

expose parts to concentrated acids and certain other chemicals.

1.4.2.17. Chlorobutyl rubber

Chlorobutyl rubber is a chlorinated product of butyl rubber with a degree of unsaturation of at least 1.8 mol%. In 1960, Standard Oil (USA) produced a new type of butyl rubber, in which 1.2 parts of chlorine were added to one hundred parts of chlorobutyl rubber. The addition of chlorine to butyl rubber was intended to increase the chemical activity of the butyl rubber molecule without increasing its mass, due to

The properties of this rubber are not much different from those of butyl rubber in terms of dynamic properties. The change from elastomer to plastic requires a large number of chlorine atoms in the polymer molecule. The second purpose of adding chlorine to the chain is to increase the vulcanization ability, especially the vulcanization ability of double bonds (using sulfur, accelerators).

Chlorobutyl rubber is produced by continuously passing a stream of chlorine gas into a butyl solution in hexane solvent. For each chlorine molecule that reacts, a HCl molecule and a chlorine atom attached to the rubber molecule chain are released. During the chlorination process, the rubber molecule is broken into smaller pieces (molecular weight decreases from 3 to 9%). However, if the intensity of chlorination is too high (exceeding the ratio of 1 chlorine atom per 1 -C=C- unit), the breakage of the rubber molecule will be very significant.

Since allylic halogens are very active, if exposed to heat (from 175 o C to 200 o C), chlorobutyl rubber will decompose into HCl, so in practice people have to add a stabilizer such as calcium stearate. Under these conditions, chlorobutyl rubber can be stored for a long time without denaturation. Due to the presence of unsaturated olefin groups and active chlorine atoms in the rubber molecular chain, many techniques can be applied to vulcanize this type of rubber such as vulcanization with ZnO or with ZnCl 2 . In these cases, people often add tiourea and TMTD to increase the vulcanization rate. In addition, it is possible to vulcanize with primary amines or with phenolic resins, similar to butyl rubber.

Because the structure of chlorobutyl rubber is similar to butyl rubber, the properties and uses of this rubber are similar to butyl rubber. Chlorbutyl rubber is also a material with low air and moisture permeability, high hysteresis (shock and vibration resistance), good resistance to oxygen, ozone and chemicals. In addition, this material is more heat resistant than butyl rubber vulcanized by a vulcanization system with sulfur. Products made from chlorobutyl rubber do not soften when exposed to heat for a long time and can withstand temperatures up to 193 o C, while under these conditions other types of rubber decompose or soften. Rubber

Chlorobutyl is used to produce inner linings of tires, especially radial tires, heat-resistant tubes, or in the production of technical and medical rubber products.

1.4.3. Some high performance blend rubber systems

1.4.3.1. Blend system based on NBR rubber with natural rubber

Natural rubber (NR) is one of the earliest natural polymers used by humans and to this day it remains an irreplaceable material in many fields. However, products made from NR still have some disadvantages such as poor aging and ozone resistance, low heat resistance, oil resistance and resistance to chemical agents. One of the methods to overcome these disadvantages and increase the value of NR is to mix them with some types of plastic or synthetic rubber.

Chakrit Sirisinha and his colleagues studied the preparation of composite materials of CSTN with nitrile butadiene rubber (NBR). The research results showed that at the CSTN/NBR ratio of 20/80, the oil resistance of the material strongly depends on the morphological structure of the blend. The oil resistance of the blend is higher when the CSTN phase is more dispersed in the NBR phase. In addition, it was found that the properties of the blend when using carbon black filler are better than when using SiO 2 . However, from the studies, it was found that the CSTN/NBR blend system often gives products with some properties worse than each component. The main reason is due to phase incompatibility leading to heterogeneous distribution of filler components and vulcanizing agents [59, 60]. Chakrit Sirisinha and his colleagues also studied the phase morphology and oil resistance of CSTN/NBR 20/80 blends mixed with carbon black fillers N220, N330, N660, SiO 2 and the compatibility when adding ethylene-propylene-dien maleate (EPDM-g-MA) and ethylene copolymer octene maleate (EOR-g-MA). The results showed that blends with SiO 2 had lower oil resistance than blends with carbon black, the compatibility effect of both EPDM-g-MA and EOR-g-MA in the studied system was strongly affected by the total polarity of the blend [61] . In addition to studying the oil resistance

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