Dynamic vulcanization techniques

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. 

The poly(methyl methacrylate) molecules were dispersed in the natural rubber matrix, or vice versa, to form spherical droplets, as observed by optical photographs or scanning electron microscopy. The compatible natural rubber/poly(methyl methacrylate) blends had been made by the addition of the graft copolymer of natural rubber-gr t-poly(methyl methacrylate) as the compatibilizing agent due to its ability to enhance the interfacial adhesion between the two homopolymers. Moreover, Nakasorn and coworkers reported that natural rubber-gr i -poly(methyl methacrylate) could be blended with poly(methyl methacrylate) via a dynamic vulcanization technique with a conventional sulfur vulcanization system. The natural rubber-gra/t-poly(methyl methacrylate) was synthesized by a semi-batch emulsion polymerization technique via different bipolar redox initiation systems, i.e. cumene hydroperoxide and tetraethylene pentamine. ... 

The relative effectiveness of nucleating agents in a polymer can be determined by measuring recrystallization exotherms of samples molded at different temperatures (105). The effect of catalyst concentration and filler content has been determined on unsaturated polyesters by using dynamic thermal techniques (124). Effects of formulation change on the heat of mbber vulcanization can be determined by dsc pressurized cells may be needed to reduce volatilization during the cure process (125). 

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). 

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. 

The dynamically vulcanized blends are melt-processable elastomers, which can be processed by conventional injection molding, blow molding, and extrusion techniques. Some key factors affecting the performance of a TPV are... 

Based on this research work, it is demonstrated that dynamic vulcanization of HDPE/NR/TPS using sulfur and HVA-2 crosslinker was an effective way of improving the properties of the blends. The tensile properties increased with the addition of crosslinkers. All the tested samples displayed significant enhancement in tensile properties and better thermal stability, which could be attributed to crosslink formation in the NR phase. SEM studies of fractured surfaces showed that the vulcanized system had better dispersion of TPS particles and was well embedded in the HDPE/NR matrix. This shows that it could be effectively employed as one of the techniques to improve the homogeneity and tensile properties of HDPE/NR/TPS blends. 

Nowadays, the development of TPEs concern many branches of macromol-ecular chemistry cationic and radical polymerizations, chemical modification, enzymatic catalysis or the use of microorganisms. Their respective contributions are analyzed in Section 2. The elastomers based on halogen-containing polyolefins [37] and those prepared by dynamic vulcanization [38] are also included in the TPE family. More information on these materials and techniques is given in Section 2. 

Several reviews are devoted to SANS applications to TPEs and block copolymers [113,114] and almost 300 reports describe SANS studies of block copolymers. As far as TPEs are concerned, it is a very valuable technique, particularly efficient in the analysis of disorder in the melt [115] or of macroscopic phase separation [116] it is also used in blends [117,118] and in processing operations, such as dynamic vulcanization [119] or co-molding [120]. 

Subsequently, much improved thermoplastic polyolefin rubbers were obtained by invoking a technique known as dynamic vulcanisation. This process has been defined (Coran, 1987) as the process of vulcanizing elastomer during its intimate melt-mixing with a non-vulcanizing thermoplastic polymer. Small elastomer droplets are vulcanized to give a particulate... 

In the past 4-5 years, quite a number of relevant review articles and books have appeared. These included general reviews on NMR of polymers (1 10), reviews on solid state NMR (11-15), solid state multidimensional techniques (16-19), spatially resolved techniques (20), solid state NMR studies of polymer dynamics and structure (21), hydrated polymers (22), vulcanized elastomers (23), crosslinked polymers (24), and polymer networks (25), Reviews have also been written on polymer gels (26-28), polymer colloids (29), polymer-surfactant systems (30), and polymers on surfaces (31). 

Blends of vulcanized rubber particles may be analyzed using dynamic mechanical rheological techniques if the particle size is less than 1/10 of the gap between the plates of the rheometer. If the average particle size approaches the width of the gap, anomalous results may be obtained. More research is needed to establish the optimum conditions for analyzing crumb rubber mixtures. 

Elastomeric systems are one of the most important classes of materials in industry because of their specific dynamic properties. Elastomers are typically crosslinked to a greater or less degree in order to improve their properties. The crosslinking process termed vulcanization prevents permanent deformation under load and ensures elastic recovery on removal of the load. The introduction of crosslinking, however, limits the ability to characterize those systems because of the insolubility of the resulting network. Additionally, the extremely low concentration of the chemically modified structures induced by the vulcanization challenge many of the traditional analytical techniques. Many approaches including physical tests and chemical analysis have... 

Considerable improvements in properties result, compared to RRPP, if cross-linking/curing is introduced into the rubber particles. PR modified, rubber compounds. Such materials may be known as dynamically crosslinked polyolefin elastomer or TPO-XL or, as a d5mamically vulcanized material or, as an elastomeric alloy (EA) or, as an elastomeric alloy thermoplastic vulcanizate (EA-TPV). If enough plastic is present (say 50%), the compound can still be easily processed by thermoplastic techniques. 

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