Nitrile chemical resistance

The principal monomer of nitrile resins is acrylonitrile (see Polyacrylonitrile ), which constitutes about 70% by weight of the polymer and provides the polymer with good gas barrier and chemical resistance properties. The remainder of the polymer is 20 to 30% methylacrylate (or styrene), with 0 to 10% butadiene to serve as an impact-modifying termonomer. 

Nitrile mbber finds broad application in industry because of its excellent resistance to oil and chemicals, its good flexibility at low temperatures, high abrasion and heat resistance (up to 120°C), and good mechanical properties. Nitrile mbber consists of butadiene—acrylonitrile copolymers with an acrylonitrile content ranging from 15 to 45% (see Elastomers, SYNTHETIC, NITRILE RUBBER). In addition to the traditional applications of nitrile mbber for hoses, gaskets, seals, and oil well equipment, new applications have emerged with the development of nitrile mbber blends with poly(vinyl chloride) (PVC). These blends combine the chemical resistance and low temperature flexibility characteristics of nitrile mbber with the stability and ozone resistance of PVC. This has greatly expanded the use of nitrile mbber in outdoor applications for hoses, belts, and cable jackets, where ozone resistance is necessary. 

The exceUent chemical resistance of acryhc fibers may stem from its unique lateraUy bonded stmcture. Dipole bonds, formed between nitrile groups... 

A.C7ylonitnk Content. Standard grades available ia the market contain between 15 to 50% acrylonitrile. The acrylonitrile content of nitrile mbber has a significant effect on two properties chemical resistance and low temperature performance. As the acrylonitrile content of the polymer is iacreased, the chemical resistance is improved whereas the low temperature properties are diminished. 

Polyacrylic resins, which have similar chemical resistance to the nitriles, can be used for slightly higher temperature conditions, but because their abrasion resistance is not as good as that of the nitriles, they need continuous lubrication. 

The hydrogenation of unsaturated polymers and copolymers in the presence of a catalyst offers a potentially useful method for improving and optimizing the mechanical and chemical resistance properties of diene type polymers and copolymers. Several studies have been published describing results of physical and chemical testing of saturated diene polymers such as polybutadiene and nitrile-butadiene rubber (1-5). These reports indicate that one of the ways to overcome the weaknesses of diene polymers, especially nitrile-butadiene rubber vulcanizate, is by the hydrogenation of carbon-carbon double bonds without the transformation of other functional unsaturation such as nitrile or styrene. 

Some typical elastomers are natural rubber, which is gathered from trees, SBR rubber, which is used a lot in motorcar tires, neoprene, as in wet suits and oil seals, EPDM, a general purpose rubber, butyl, a heat-resistant rubber with the ability to keep the air in car tires, nitrile for oil seals, silicones for heat resistance, fluoro-elastomers for chemical resistance, and last but not least, polyurethanes, which cover a number of the above fields. Table 1.1 shows some of the advantages of castable polyurethanes over conventional rubbers. 

Nitrile—toughness and peel strength, chemical resistance... 

Epoxy-nitrile Nitrile-epoxy adhesives are composed of solid epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) copolymer. The CBTN is introduced into die epoxy resin at elevated temperatures. The modification provides toughness and high peel strength without sacrificing heat and chemical resistance. The film adhesives are widely used in the aerospace industry in the construction of jetliners. 

However, the single-phase epoxy nitrile adhesive achieves its high peel strength by bulk elongation. Other properties, such as heat and chemical resistance, are generally degraded as they are when other flexibilizers or plasticizers are added to the epoxy. The two-phase version of this adhesive hybrid solves many of these problems. 

The butadiene blocks can be hydrogenated, as mentioned above with hydrogenated nitrile, to form SEBS polymers having better thermal stability and chemical resistance. The EB stands for ethylene-butylene, which are the structures formed after the butadiene segments have been hydrogenated. 

ANs are those that contain a majority of nitrile polymers. They provide good gas barrier, chemical resistance, and low taste and odor transfer with good impact properties when modified with rubber. Extruded sheet is used extensively in food packaging and rigid packaging applications. This crystalline TP is most useful in copolymers. Its copolymer with butadiene is nitrile rubber. Acrylonitrile-butadiene copolymers with styrene (SAN) exist that are tougher than PS. It is also used as a synthetic fiber and as a chemical intermediate. 

After the types of PPE components necessary for protection have been established, one mnst pick specific PPE items that will satisfy the requirements. The task begins by reviewing the information available for chemical resistance and for physical properties. From this information, one selects the materials of constmction for the PPE items. For example, if the need is for hand protection and foot protection for >4 honrs from a pesticide concentrate containing aliphatic petroleum distillates as the carrier solvent, then, with reference to Table 6.6, nitrile might be selected as the material of construction. 

Nitrile (synthetic copolymer) has poor flexibility, but is strong and highly chemical resistant. 

DuPont Performance Elastomers, Chemical Resistance Guide, Version 6.0 (August 2006) Overview of Elastomers and Elastomer Materials, ElastomeFs Characteristics, Fluoroelastomer (Viton. FKM) and Nitrile, hydrogenated Nitrile (NBR, HNBR), Available at http /www.dupontelastomers. com/Tech Info/chemical.asp (accessed October 7, 2006). 

Buna 85 is polybutadiene (the number represents Mooney viscosity), molecular weight -80,000. Hard rubber has high softening point and excellent chemical resistance. The coefficient of vulcanisation to the ebonite stage is 39.3. The coefficient of vulcanisation is the number of unit weight of sulfur combined with 100 units by weight of unsaturated hydrocarbons. Buna S is a butadiene styrene copolymer with 70/30 to 68/32 ratio. Buna SS contains a high proportion of styrene. Perbunan are nitrile rubbers... 

VERs are available as both rigid and flexible epoxy resins. The flexible epoxy resins generally have a depressed glass-transition temperature, Tg, and inferior chemical resistance. Nitrile-rubber-modified VER (I) appeared on the market in the mid- to late 1970s. These elastomer-modified VERs show improved fatigue resistance over unmodified VER (2). 

High nitrile type Oil and chemical resistance seals, gaskets, shoe soles, etc. 

Nitrile rubbers are known for their oil and chemical resistance and addition of PVC improves the ozone resistance. Use of carboxylated NBR is believed to obviate the necessity of vulcanization. 

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