Polar Rubbers

In the rubber industry hydrocarbon oils are often used to reduce the softness and facilitate the processing of hydrocarbon rubbers. These appear to have a small interaction with the polymer but spacing effects predominate. Such materials are generally referred to as softeners. The rubber industry, like the plastics industry, commonly uses the term plasticisers to describe the phthalates, phosphates and sebacates which are more commonly used with the more polar rubbers. 

Nitrile rubber adhesives. The main application corresponds to laminating adhesives. PVC, polyvinyl acetate and other polymeric films can be laminated to several metals, including aluminium and brass, by using NBR adhesives. NBR adhesives can also be used to join medium-to-high polarity rubbers to polyamide substrates. The adhesive properties of NBR rubbers can be further improved by chemical modification using polyisocyanate or by grafting with methyl methacrylate. 

The use of plasticisers, with other than PVC applications, is extensive. Many polar rubber sealants or caulking materials are plasticised in order to make them more pliable, e.g., polysulfides, polychloroprene (Neoprene ), nitrile rubber. Esters, similar to those employed with PVC, are used to render cellulose diacetate ("Acetate") overhead projection sheets more flexible. 

Dithiocarbamates are polar in nature and thus will have a tendency to bloom when used in nonpolar rubbers. The worst bloom problems will be encountered with the dimethyl derivatives higher alkyl chain types have better solubility in non-polar rubbers. Some dithiocarbamates also confer antioxidant protection. 

Fig. 40 WAXD patterns of non-polar rubbers (a) and polar rubbers filled with 20 phr swollen clay (b). All the vulcanized rubbers contain some curing ingredients like organic accelerator, zinc oxide, etc...

It is also interesting to look into the chemical interactions of organoclay (QUAT-modified MMT) with functionally polar rubbers like XNBR, CR, and their mutual blend. The role of layered silicate on the curing process of CR/XNBR blends was investigated through the study of curing kinetics, mechanical properties, WAXS, and DMA [74]. 

In the hard polymer/elastomer combinations, the elastomer is often chosen to be a polar rubber or it is cross-linked in some cases it is both. Either of these features improves the resistance to oils and solvents (44). 

Table 3.2b Peak Assignments for some polar rubbers...

Hence surface oxidation of carbon black leads to a greater extent of bound rubber formation in polar rubbers [152] like ENR. 

Chemical interaction between furnace blacks and rubbers is responsible for the greater extent of reinforcement for polar rubbers [153]. Lately, it has been reported that -OH and -COOH groups of surface oxidised furnace blacks react chemically with functionalised polymers like CSM [154], XNBR [155] and ENR [156], forming a crosslinked vulcanisate in the absence of any crosslinking agent. The mechanism of chemical interactions is supported by IR spectroscopy. 

Fig. 24 TEM micrographs of ternary epoxy, CTBN rubber and octadecyl ammonium-treated montmorillonite nanocomposites which were investigated with different polarity rubbers, (a) shows a broad view of the less polar rubber and the clay tactoids, clearly separated and (b) shows a close up of the more polar rubber close to silicate layers...

Hot vulcanization is carried out in presses heated by steam or by electricity. It can also be done with microwaves, and then it is fast with polar rubbers and slow with apolar rubbers. The rate of this vulcanization is increased by carbon black such an effect by light-colored fillers is not known. 

It is interesting to observe in Fig. 6 that, although the strongly polar ethyl alcohol as a whole is a bad swelling medium, its solvent power on the more polar rubbers is definitely better than that on the less polar ones. The scale of Fig. 6 is too small to demonstrate this clearly and there-... 

The newest vulcanization process under discussion uses microwaves. The heating effect induced by microwaves is rapid with polar rubbers and slow with apolar rubbers. The rate of heating can be increased by the incorporation of carbon black. However, no suitable light-colored filler is known for this microwave heating process. 

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