Nitrile PVC blends

Since the original hot polymerized NBRs there have been many improvements and expansion of the types and ranges of properties available to the mbber industry. Cold polymerization is the predominant process for the emulsion polymerization of NBR with Acrylonitrile (ACN) contents now ranging from 18%-50% and Mooney viscosity going from 25 to 120. In addition, modifications now include carboxylated, precrosslinked, ACN/isoprene/butadiene, liquid, carbon black masterbatches, plasticizer extended, and nitrile/pvc blends (with and without plasticizer). Nitrile latices, powdered and crumb will not be covered in this book. Hydrogenated NBR is dealt with in a separate chapter. 

A 70/30 fully fluxed nitrile-PVC blend. Provides outstanding ozone resistance. Used in cable jackets, hose, and shoe soles... 

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. 

Carboxylated nitriles, hydrogenated nitrile, liquid nitriles and blends with PVC are also commercially available. 

PVC decomposition products as health hazard, 25 677 PVC fusion/gelation, 25 663-664 PVC-nitrile rubber blends, 24 717. See also Poly(vinyl chloride) (PVC)... 

Apex N PVC blend with nitrile rubber Teknor Apex... 

S—EB—S (compounds) polyurethane/elastomer block copolymers polyester/elastomer block copolymers polyamide/elastomer block copolymers polyetherimide/polysiloxane block copolymers polypropylene/EPDM or EPR blends polypropylene/EPDM dynamic vulcanizates polypropylene/butyl rubber dynamic vulcanizates polypropylene/natural rubber dynamic vulcanizates polypropylene/nitrile rubber dynamic vulcanizates PVC/ nitrile rubber blends... 

Humes. [Hules Mexicanos] Nitrile elastomer or NBR/PVC blends used for molded parts, mech. goods subjected to oils and fuels, wire and cable jackets, soles, hoses. 

PB2. [Zeon] Hydrogenated nitrile rub-ber/PVC blends elastomer fm fuel hose, fuel diaphragms. 

Several investigators have looked at PVC blends with nitrile-butadiene rubber (6, 8), and, although compatibility increased with acrylonitrile content (up to about 40 wt %), micro-heterogeneity was still evident in electron photomicrographs. 

In PVC/nitrile rubber blends, PVC is added more as an ozone resistant additive. In these ther-moplastically processable blends, PVC is flexibil-ized enough to be used for soft goods, wire jacketing, hoses, gaskets and seals. When the NBR contains >25% acrylonitrile, it becomes miscible with PVC and at < 20% acrylonitrile level, it is fairly compatible due to partial miscibility [Matso et al., 1969]. 

Blends of butadiene-acrylonitrile copolymer rubber (nitrile rubber or NBR) and PVC are among the oldest known examples of commercial elastomer/ thermoplastic blends. The shortage of natural rubber during World War II stimulated research in the USA on the compounding and modification of synthetic polymers to produce rubber-like materials. An outcome of this research was the commercial introduction of NBR/PVC blends by B.F. Goodrich in 1947 under the trade name of Geon Polyblends [Pittenger and Cohan, 1947]. The blend showed improved ozone resistance and melt processability compared to the nitrile rubber (Table 15.12). 

Ingredients and Machinery for Rubber, published annually by Bill Communications, Inc. Currently, the PVC/nitrile rubber blends worldwide consumption is estimated to be 30 kton/y. 

Nitrile rubber/PVC blends have reached a mature stage in their commercial usage. They face increasing competition from other thermoplastic elastomers such as the dynamically vulcanized blends of PP/EPDM and PP/NBR (Santoprene and Geolast , Monsanto-Advanced Elastomer Systems). 

Weather Resistance Many rubbers are affected adversely by outdoor exposure, particularly by the traces of ozone, which are always present in the atmosphere and which cause rapid cracking of lightly stressed rubber articles. Nitrile rubber is no exception and thus it is not suitable for use in exposed conditions. However, the incorporation of a proportion of PVC (Polyvinyl chloride) into the nitrile compound results in improved resistance until, with a blend of 70/30 nitrile/PVC, a material with almost complete resistance to ozone attack is produced. The presence of PVC produces stiffer compounds, with lower resiliance and inferior low temperature properties, but the oil and solvent resistance is enhanced. 

Fire Resistance Nitrile rubbers are not flame resistant, but by special compounding a useful degree of resistance can be obtained using PVC blends. 

Table 19.16 Typical properties of nitrile rubber/PVC blends vs. nitrile rubber ...

SBR/PVC blends with nitrile rubber (NBR) as a compatibilizer show improved mechanical properties at lower cost than NBR/PVC. i This was the conclusion of studies using a divinylbenzene cross-linked, hot-polymerized emulsion polymer with 30% bound styrene and a cold-polymerized emulsion polymer with 23% boimd styrene PVC with inherent viscosity from 0.86 to 1.4 NBR with Mooney viscosity from 30 to 86 acrylonitrile content of 23.5, 32.6, and 39.7% and ZnO, stabilizers, sulfur, and accelerators. ... 

The most prominent application end-uses for PVC blends require permanent plasticisation. Butadiene/acrylonitrile copolymers have been compounded as permanent plasticisers for PVC wire and cable insulation, applications requiring food contact, and in pond liners used for oil containment [21]. Compounding with nitrile rubbers in plasticised PVC provides improved ozone, thermal ageing and chemical resistance for applications such as fuel hose covers, gaskets,... 

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