Nitrile rubber physical properties

Nitrile rubbers are produced over a wide range of monomer ratios and molecular weights, so thek physical constants and basic polymer properties also cover a range of values. Some of the more widely used properties are Hsted ki Table 1. 

Nitrile rubber (NBR) was first commercialized by I.G. Farbindustry, Germany, in 1937, under the trade name of Buna N. Its excellent balance of properties confers it an important position in the elastomer series. Nitrile rubber, a copolymer of butadiene and acrylonitrile, is widely used as an oil-resistant rubber. The acrylonitrile content decides the ultimate properties of the elastomer. In spite of possessing a favorable combination of physical properties, there has been a continuous demand to improve the aging resistance of NBR due to the tougher requirements of industrial and automotive applications. 

Although, the heat resistance of NBR is directly related to the increase in acrylonitrile content (ACN) of the elastomer, the presence of double bond in the polymer backbone makes it susceptible to heat, ozone, and light. Therefore, several strategies have been adopted to modify the nitrile rubber by physical and chemical methods in order to improve its properties and degradation behavior. The physical modification involves the mechanical blending of NBR with other polymers or chemical ingredients to achieve the desired set of properties. The chemical modifications, on the other hand, include chemical reactions, which impart structural changes in the polymer chain. 

This chapter mainly aims at describing the various methods and processes developed for hydrogenation of nitrile rubber. The characterization, physical properties, and application of hydrogenated nitrile rubber are also discussed. Another small section on hydroformylation of nitrile rubber has been included. 

The ductility of GRT-polyethylene blends drastically decreases at ground rubber concentration in excess of 5%. The inclusion of hnely ground nitrile rubber from waste printing rollers into polyvinyl chloride (PVC) caused an increase in the impact properties of the thermoplastic matrix [76]. Addition of rubber powder that is physically modihed by ultrasonic treatment leads to PP-waste ethylene-propylene-diene monomer (EPDM) powder blends with improved morphology and mechanical properties [77]. 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

The carboxylated types (XNBR) contain one, or more, acrylic type of acid as a terpolymer, the resultant chain being similar to nitrile except for the presence of carboxyl groups which occur about every 100 to 200 carbon atoms. This modification gives the polymer vastly improved abrasion resistance, higher hardness, higher tensile and tear strength, better low temperature brittleness, and better retention of physical properties after hot-oil and air ageing when compared to ordinary nitrile rubber. 

Most ABS is made by emulsion polymerization. A polybutadiene or nitrile rubber latex is prepared, and styrene plus acrylonitrile are grafted upon the elastomer in emulsion. The effect of rubber particle size in ABS graft copolymer on physical properties is the subject Chapter 22 by C. F. Parsons and E. L. Suck. Methyl methacrylate was substituted for acrylonitrile in ABS by R. D. Deanin and co-workers. They found a better thermoprocessability, lighter color, and better ultraviolet light stability. 

Chemical modification of polymers continues to be an active field of research [1-5]. It is a common means of changing and optimising the physical, mechanical and technological properties of polymers [5-7]. It is also a unique route to produce polymers with unusual chemical structure and composition that are otherwise inaccessible or very difficult to prepare by conventional polymerisation methods. For example, hydrogenated nitrile rubber (HNBR) which has a structure which resembles that of the copolymer ethylene and acrylonitrile, is very difficult to prepare by conventional copolymerisation of the monomers. Polyvinyl alcohol can only be prepared by hydrolysis of polyvinyl acetate. Most of the rubbers or rubbery materials have unsaturation in their main chain and/or in their pendent groups. So these materials are very susceptible towards chemical reactions compared to their saturated counterparts. 

Oil Resistance The primary property of nitrile rubber is oil resistance and it is this factor, in conjimction with its excellent physical properties, which account for much of its commercial use. Oils generally attack rubbers by causing them to swell. 

Phenolic based adhesives are outstanding in their wetting characteristics and strength. In the unmodified form, however, they tend to be brittle. To overcome this problem, phenolic based adhesives usually contain a rubber modifier to increase the crack resistance of the adhesive. The first modified phenolic contained polyvinyl butyral and was known as the "Redux" adhesive. Many modern phenolic adhesives contain nitrile rubbers (copolymers of acrylonitrile and butadiene) as the modifiers. An example of a phenolic based film adhesive is AF-30 which is listed in Table 1 along with its physical properties. This film... 

Carboxylated nitrile rubber Zn ionomer (90-50)/EAA Zn ionomer (10-50) Physical properties vs. blends of non-ionomeric polymers/FTIR/DMA/also use of recycle Antony et al. 2000... 

Latex adhesives, of which there are many types (Nitrile rubber adhesives (NBR), SBR, Ethylene-vinyl acetate copolymers, acrylics, polyvinylidene chloride, etc.), should ideally be cross-linkable (for wash and dry-clean resistance), preferably with a low cure (reaction) temperature (see Reaction setting adhesives), as some fibres, such as polypropylene, may be damaged by high temperatures. The binder (adhesive) type can markedly affect physical properties and performance the amount of hard and soft polymer in the binder controls the sofmess of the finished product. Most binders impart adequate dry-state adhesion and so the choice of adhesive is usually governed by secondary requirements such as the method and conditions of application and costs. 

Polyblend n. A colloquial term - shortened from polymer blend - used for physical mixtures of two or more polymers, for example, polystyrene and rubber or PVC and nitrile rubber. Such blends usually yield products with favorable properties of both components, sometimes opening markets not available to either of the neat resins. The term alloy is sometimes used for blends. 

Nitrile and Acrylic Rubber. Nitrile rubbers are made by the emulsion copolymerization of acrylonitrile (9-50%) and butadiene (21) and are abbreviated NBR (eq. 11). The ratio of acrylonitrile (ACN) to butadiene has a direct effect on the properties and the nature of the pol5nners. As the ACN content increases, the oil resistance of the poljnner increases (14). As the butadiene content increases, the low temperature properties of the polymer are improved. Nitrile rubber is much like SBR in its physical properties. It can be compoimded for physical strength and abrasion resistance using traditional fillers such as carbon black, silica, and reinforcing clays. The primary benefit of the polymer is its oil and solvent resistance. At a medium ACN content of 34% the volume swell in IRM 903 oil at 70°C is typically 25-30%. Nitrile rubber can be processed on conventional rubber equipment and can be compression, transfer, or injection molded. It can also be extruded easily. Nitrile rubber compoimds have good abrasion and water resistance. They can have compression set properties as low as 25% with the selection of a proper cure system. The temperature range for the elastomers is from -30 to 125°C. The compounds are also plasticized nsing polar ester plasticizers. 

The physical and mechanical properties of the nitrile rubbers are very similar to those of natural rubber. Buna-N does not have exceptional heat resistance. It has a maximum operating temperature of 200°F/93°C and has a tendency to harden at elevated temperatures. The nitrile rubbers will support combustion and burn. NBR has good abrasion resistance and tensile strength. 

Table 4.18 provides the physical and mechanical properties of nitrile rubber. 

Table 4.18 Physical and Mechanical Properties of Nitrile Rubber (NBR, Buna-N)=>...

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