Subject vulcanizate properties

This analysis of the vulcanization problems that arise when VF2 /mVE/TFB polymers are subjected to conventional curing systems has led to development of specifically peroxide-curable polymers. Thus, the entire prlem of undesirable response to basic curatives has been tqnpassed and excellent vulcanization b tavior and vulcanizate properties, especiidly low temperature service fluid resistance, have been obtained. 

Ultrasonic reclaiming of NR was reported by Okuda and Hatano in 1987, which was also patented. They subjected the NR vulcanizate to 50 kHz ultrasonic energy for 20 min to achieve devulcanization followed by revulcanization and obtained reclaimed rubber with similar properties to those of original rubber. Isayev and coworkers reported in a number of publications the phenomenon of devulcanization by ultrasound energy and they also patented their developments. ... 

The attention of the author has been drawn to an interesting study by Bartenew (Piaste u. Kautschuk, 17, 235 (1970)1 in which the correlation of viscoelastic behaviour and rupture properties is attempted. This deals only with gum elastomers, but when it will be extended to reinforced vulcanizates, it may throw additional light on the subject of this review... 

In considering abrasion, it will be noted that while actual abrasion loss is a phenomenon involving extreme properties at the surface, layers of vulcanizate immediately contiguous are subjected to many cycles of increasing stress before they are abraded, during which chain-length adjustment develops continuously. 

The presence of cross-links also helps in maintaining a desired geometry. Engineering thermoplastics, which contain no cross-hnks, are subject to creep, or cold flow, under load. They also have poor compression set resistance. Set is a permanent deformation that occurs under a load. Cross-linked elastomers can vary significantly in their set resistance. The choice of polymer, vulcanization system, and degree of cross-linking can profoundly affect set resistance (as well as many of the other properties of the vulcanizates). 

ASTM D2137-11 provides Standard Test Methods for Rubber Property -Brittleness Point of Hexible Polymers and Coated Fabrics. Related Methods for Brittleness Point Test are ISO 812, DIN ISO 812 (Germany), and BS 903-A25 (UK). These test methods cover the determination of the lowest temperature at which rubber vulcanizates and rubber-coated fabrics will not exhibit fi actures or coating cracks when subjected to specified impact conditions (ASTM D2137-11). 

Anisometry and fractal dimension are also used as parameters for characterizing fillers, the former to predict various mechanical properties of filled compounds and vulcanizates and the latter to investigate the surface structure. Anisometry, which is always subject to distribution, is found to widen with the fillers investigated, with an increase in the dimensions of the objects detected. 

The first practical systems were based on sulphur. On its own this was not very efficient and it has since been shown that up to 55 sulphur atoms may be combined for every cross-link formed. As the years passed it was found that the use of sulphur in conjunction with certain metal oxides, fatty acids and compounds known collectively as accelerators , gave rise to vulcanizates (the products of vulcanization) with superior properties and which required much shorter vulcanization times. Today the accelerated sulphur systems are still dominant and form the bulk of the subject matter of this chapter. Other methods of vulcanization are however known and several have been, and sometimes still are, of some industrial usage and these will be considered more briefly. 

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