Dynamically vulcanized blends

Fig. 3 Sketch illustrating the deformation and recovery of dynamically vulcanized blends [27]...

Fig. 6 Variation of viscoelastic properties as a function of strain amplitude of uncrosslinked and dynamically vulcanized blends at 180°C (a) storage modulus, (b) loss modulus. CD2 TPV prepared by preblending, PD2 TPV prepared by phase mixing, SD2 TPV prepared by split addition...

Most examples of dynamically vulcanized blends do not involve covalent bond formation between the immiscible phases. However, more recent work has shown that covalent bond formation between phases in conjunction with dynamic vulcanization of one phase can lead to blends with improved properties in certain cases. This is particularly true in blends where certain of Coran s five key requirements above are not met. Examples of dynamically vulcanized blends that also feature copolymer formation between the two immiscible phases are summarized in this review article under the appropriate categories [see also Coran and Patel, 1996]. 

Dynamically vulcanized blends Dynamically vulcanized blends are produced by melt mixing an elastomer phase with a thermoplastic (the elastomer being the major component) and then curing the elastomer during melt mixing. The resulting blend comprises the thermoplastic resin filled with high concentration of rubber particles well bonded to the matrix. Examples include EPDM/PP (Santo-... 

Nitrile rubber/PVC blends have reached a mature stage in their commercial usage. They face increasing competition from other thermoplastic elastomers such as the dynamically vulcanized blends of PP/EPDM and PP/NBR (Santoprene and Geolast , Monsanto-Advanced Elastomer Systems). 

Commercially important elastomeric thermoplastic alloys are dynamically vulcanized blends of polypropylene with high volume fractions of EPDM, polybutadiene rubber, nitrile rubber, and butyl rubber (Santoprene , Vyram , Geolast and Trefsin ) all currently sold by Advanced Elastomer Systems, a joint venture of Monsanto and Exxon. Another recent member of the commercial dynamically cured elastomeric thermoplastic alloys is the blend of PVC and a crosslinked ethylene copolymer (Alcryn , DuPont). The current consumption of all the elastomeric thermoplastic alloys in the USA is over 23 kton/y, with the EPDM/PP blend (Santoprene ) assuming about 90% of the market share. 

Nitrile Rubber/PP, Dynamically Vulcanized Blends (Geolast , AES)... 

Although the dynamically vulcanized blends such as EPDM/PP (Santoprene ) and NBR/PP (Geolast ) have sometimes been referred in the literature as semi-IPNs, we considered them as blends of crosslinked elastomer dispersions in a thermoplastic matrix and as such treated them under the elastomer blends. There is yet another class of thermoplastic/thermoset blend system in which a minor amount of the crosslinkable monomer(s) is allowed to polymerize in the thermoplastic matrix forming a loose network. 

Figure 14.14 shows the SEM micrograph of dynamically vulcanized EPDM/PP (75/25) blend fracture surfaces etched by hot xylene vapor. The microdomains of EPDM have the shape of dumbbell-like microgel of about 0.8-1.0 pm in size, where the dark portions represent the PP phase extracted out by hot xylene vapor. The morphology of the microgel domain of EPDM reveals the reason why the dynamically vulcanized blend can be processed and the dynamic vulcanization prevents the cross-linking of EPDM phase from tmly continuous network (24). 

Dynamically vulcanized blends of PP with EPDM, mineral oil, and PDMS For slush molding large plastic parts Hikasa et ai. 1994... 

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... 

When the crosslinked rubber level in the blend is high, the blends are rubbery with good elastic recovery properties, have low compression set values at elevated temperatures, and are processable as plastics. At low crosslinked rubber levels (<25%), these blends are tough and have very good impact resistance. Dynamic vulcanization was first practiced by Gessler [23] around 1958, when he described the preparation ofhalogenated butyl mbber and polypropylene on a heated roll mill. Most of the blends in the examples had only a small amount of rubber (20 wt%) and the curative used was a metal oxide. The mixing time was about 20 min at 320 ° F. It was shown that the dynamically vulcanized blends had better tensile properties than identical blends vulcanized at 320 °F under static conditions. Fischer [24] prepared... 

Blends comprised of amorphous, low Tg polymers are of primary interest for elastomeric type applications, of which the large tire market commands considerable interest. This section will consider blends of elastomeric polymers, generally low Tg, amorphous blends. In specific cases, low modulus, crystalline polymer blends (such as ethylene copolymers) with other elastomeric materials will be included. Also blends containing crystalline polymer, where the primary component of the blend is the elastomeric component and the blend is considered an elastomeric material, will be discussed. Specifically, dynamic vulcanized blends such as polypropylene/ethylene-propylene rubber blends will be included in this section. 

Eigure 1 Variation of the mixing torque versus time for the preparation of EPDM/PP (60/40) dynamically vulcanized blends, TPVO (blue), TPVNE6 (sky blue). 

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