Dynamically vulcanized

The more important grades of thermoplastic natural mbber, which fall into the olefinic class of thermoplastic elastomers, are prepared with the natural mbber phase partially cross-linked during blending, a process known as dynamic vulcanization. The hardness of the soft blends is controlled by the natural mbber content, and typical properties of those of 50—90 hardness (Shore A) are shown in Table 7. 

B = Blend of the two components (27) DV = dynamically vulcanized product in which the elastomer has been cross-linked during mixing (30). 

The production of the hard polymer/elastomer combinations is more simple. The two components are mixed together under conditions of intensive shear. In some cases, grafting may occur. In a variation of this technique, the elastomer can be cross-linked while the mixing is taking place, a process described as dynamic vulcanization (32). 

The soft phase is dynamically vulcanized, ie, cross-linked during mixing (32). 

The method of dynamic vulcanization was applied to mixtures of NR with LDPE, PP homopolymer, and PRP... 

Table 14 Properties of Dynamically Vulcanized NR-LDPE (65 35) Blends...

Compatibilization along with dynamic vulcanization techniques have been used in thermoplastic elastomer blends of poly(butylene terephthalate) and ethylene propylene diene rubber by Moffett and Dekkers [28]. In situ formation of graft copolymer can be obtained by the use of suitably functionalized rubbers. By the usage of conventional vulcanizing agents for EPDM, the dynamic vulcanization of the blend can be achieved. The optimum effect of compatibilization along with dynamic vulcanization can be obtained only when the compatibilization is done before the rubber phase is dispersed. 

Dynamic vulcanization as a method to improve the mechanical properties of NR-PE blends has been discussed in detail by Choudhary et al. [30]. The physical properties of unvulcanized and vulcanized NR-HDPE blends are given in Table 7 where notations A, B, and C indicate 70 30, 50 50, 30 70 NR-HDPE blends, respectively. The subscripts C and D denote blends containing DCP and high abrasion furnace (HAF) black (40 phr), respectively. 

In addition to dynamic vulcanization, the technological compatibilization technique was also adopted by Coran and Patel [34] to obtain thermoplastic vulcanizate having good mechanical integrity and elastic recovery. 

Conventional crosslinking agents, such as sulphur, accelerators, and peroxide, etc., used in dynamic vulcanization and melt-mixing of two polymers is the first step in the preparation of an EA. The dynamic vulcanization is done by dynamic shear at a high temperature to activate the process. 

Blend of (1) and (2) type categories mostly include the modification of engineering thermoplastics with another thermoplastic or rubber. PS-EPDM blends using a low-molecular weight compound (catalyst) Lewis acid have been developed [126]. Plastic-plastic blends, alloys of industrial importance, thermoplastic elastomers made by dynamic vulcanization, and rubber-rubber blends are produced by this method. 

Coran and Patel [74] investigated the reactive com-patibilization of PP-NBR and HDPE-NBR blends using phenolic modified polyolefin, maleic anhydride modified polyolefin, and amine terminated nitrile rubber as reactive components. Dynamic vulcanization was also inves-... 

A.Y. Coran s research on the melt-mixed blends of elastomer and thermoplastics with dynamic vulcanization... 

Commercial melt-mixed blends of EPDM and PP, dynamically vulcanized, Monsanto (Santroprene) Polyamide TPE, Atochem (Pebax)... 

For the compatible elastomer-thermoplastic blends, melting of the two polymers is the first step followed by subsequent vulcanization of the elastomeric phase. A typical mixing cycle for dynamically vulcanized NR-PE blend (DVNR) in a Brabender mixer is as follows [58] ... 

Bhowmick A.K. and Inoue T., Stmeture development during dynamic vulcanization of hydrogenated nitrile mbber/nylon blends, J. Appl. Polym. Sci., 49, 1893, 1993. 

Elastomers are often blended with plastics either to improve the impact resistance or to develop new materials having both plastic and elastic behavior. When the elastomer in the blend is dynamically vulcanized, the product is called a thermoplastics vulcanizate (TPV). Blends with unvulcanized mbber phase are usually known as thermoplastic elastomers. TPVs are discussed in another section of this book. This section will deal with recent developments in rubber-plastic blends. 

Prut, E.V. and Erina, N.A., Dynamic vulcanization and thermoplastic elastomers, Macromol. Symp., 170, 73, 2001. 

TPEs from thermoplastics-mbber blends are materials having the characteristics of thermoplastics at processing temperature and that of elastomers at service temperature. This unique combination of properties of vulcanized mbber and the easy processability of thermoplastics bridges the gap between conventional elastomers and thermoplastics. Cross-linking of the mbber phase by dynamic vulcanization improves the properties of the TPE. The key factor that controls the properties of TPE is the blend morphology. It is essential that in a continuous plastic phase, the mbber phase should be dispersed uniformly, and the finer the dispersed phase the better are the properties. A number of TPEs from dynamically vulcanized mbber-plastic blends have been developed by Bhowmick and coworkers [98-102]. 

Dynamic viscometer, 21 736 Dynamic viscosity, 21 723 Dynamic vulcanizates, 24 717 Dynamic vulcanization, 24 700 Dynascone, 24 567 Dynatrol viscometer, 21 739 DynaWave gas cleaning technology, 23 782... 

TPVs, comprising TPEs with a thermoplastic matrix (often polypropylene) and a dynamically vulcanized rubber (often EPDM). 

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