XNBR rubber

Table II Glass transition temperature of self-crosslinked CR/XNBR rubber blends...

XNBR rubbers are used primarily in nonalkaline service. Refer to Table 5.9 for the compatibility of NBR with selected corrodents. 

XNBR carboxylic-nitrile butadiene rubber (carboxynitrile rabber)... 

Bhattacharjee et al. [79] introduced another new catalyst based on a Pd complex containing both acetate and benzoyl pyridine ligands (Table 6). This was developed to hydrogenate liquid carboxylated nitrile rubber (L-XNBR) [80]. Selective hydrogenation of C=C in L-... 

Figure 25 Variation of apparent viscosity with the percent polyurethane rubber in XNBR-AU blends.

The important factors that affect the rubber toughening are (1) interfacial adhesion, (2) nature of the matrix, (3) concentration of the rubber phase, and (4) shape and size of the rubber particles. In the PS-XNBR blend containing OPS, due to the reaction between oxazoline groups of OPS and carboxylic groups of XNBR, the interfacial adhesion increases and as a result, the minor rubber phase becomes more dispersed. The immiscible blend needs an optimum interfacial adhesion and particle size for maximum impact property. In PS-XNBR, a very small concentration of OPS provides this optimum interfacial adhesion and particle size. The interfacial adhesion beyond this point does not necessarily result in further toughening. 

Blends of carboxylated nitrile rubber (XNBR) with EPDM are likely to provide an attractive combination of properties including oil resistance, heat and ozone resistance, high tensile strength, modulus, and hardness. However, the polar curing ingredients often diffuse from the nonpolar to polar component, thereby producing cure rate mismatch and inferior properties. Three different measures have been used to overcome the cure rate mismatch [29] ... 

FIGURE 11.9 Tensile fractured samples show the texture of XNBR vulcanizates (a) 75 25 EPDM/XNBR (b) 75 25 EPDM/XNBR (c) 50 50 EPDM/XNBR (one stage) (d) 50 50 EPDM/XNBR (two stage) (e) 25 75 EPDM/XNBR (one stage) (f) 25 75 EPDM/XNBR (two stage). (From Naskar, M., Debnath, S.C., and Basu, D.K. Rubber Chem. TechnoL, 75, 309, 2002.)... 

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. 

Zinc peroxide is used as the curative for carboxylated acrylonitrile-butadiene rubber (XNBR) compounds. It confers better scorch safety than does zinc oxide. It is usually added in a masterbatch form. 

Carboxylated nitrile rubber (XNBR), a high-performance elastomer, is remarkable for providing vulcanizates that exhibit enhanced tensile strength, elastic modulus, hardness, and improved resistance to tear, abrasion, and the deleterious action of... 

Fig. 5 Stress-strain diagram of rubber composite mixed at different temperatures containing 5 phr organoclay in a XNBR matrix. Circles indicate crossover points...

Fig. 13 Variation of 200% modulus (a), tensile strength (b), and elongation at break (c) with the amount of organoclay and XNBR. Stress-strain diagram of the organoclay-rubber composites (d)...

S-SBR, and organoclay it can be assumed that the surface silanol groups of the layered silicates react with the carboxyl groups of the XNBR and, thus, direct rubber-filler bonds are formed. In this way, the high elongation properties can be explained. 

It is observed from this figure that there are a lot of small dark lines preferably oriented in a north-south direction. Here, the organoclay is distributed evenly in the whole rubber matrix. Some small dark clusters are shown enlarged in Fig. 29b. These structures are formed due to the separation of the polar XNBR phase from the nonpolar S-SBR matrix. Furthermore, exfoliated layers of organoclay are visible in the interface between the two polymer phases, which obviously promotes a better compatibility between XNBR and S-SBR phases. Figure 29c displays the ... 

However, such spectroscopic techniques are sometimes used to more fully understand rubber-clay interaction. For example, XNBR filled with organoclay gave very interesting results with IR studies. 

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