Thermoplastic dynamic vulcanizates

Comparing the properties of TPO-0 and TPO-V of the same constituents at the same hardness, the benefits given by the fully cured rubber in TPO-V become clear (improved set properties, fluid and chemical resistance, service temperature and tensile strength). These are achieved, however, at the cost of some other properties (e.g. reduced melt flow, tear 

Irrespective of the high melt viscosity at low shear rates, TDV are available also for processing at low shear rates, such as calendering (see the chapter Calendering of pol) ropylene in this book). 

TPO-V scrap Ccm be easily reprocessed by adding to the virgin material up to 10 wt.% generally no deterioration in the mechanical and rheological properties can be observed. Usually no change in the mechanical properties of TPOV occurs imtil about 5 reprocessing cycles. This is in harmony with the thumbnail rules known for PP. 

The total world demand for thermoplastic elastomers, including cdl types, will reach about 1.5 million tons in the year 2000. The annual growth rate of polyolefin based thermoplastic elastomers was 9.1% between 1985 and 1995, and for the next five years growth of about 7.6%/year was forecast (which may be optimistic) by the Freedonia Group (Cleveland, Ohio, USA). The overall market share of the thermoplastic elastomers is about 10% in the nontyre market. 

(1988) Elastomeric alloy thermoplastic vulcanizates, in Handbook of Thermoplastic Elastomers, 2nd edn. Chap. 4, (eds B.M. Walker and C.P. Rader), Van Nostrand Reinhold, New York, pp. 85-140. 

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In addition to the above-mentioned fields of application, functionahzation of blends of olefin polymers and copolymers has been widely employed in the manufacture of thermoplastic dynamic vulcanizates (71,72). 

Blends of functionalized PO have mostly been used for compatibilization of blended systems based on engineering plastics. They have found applications in the development of thermoplastic dynamic vulcanizates. 

Ke)rwords amorphous polypropylene (aPP), atactic polypropylene (aPP), additives, hot-melt adhesive, rubber extender, bitumen modifier, metallocene synthesis, molecular weight, properties of aPP, applications of aPP, thermoplastic dynamic vulcanizate (TDV). 

Dynamically vulcanized blends ([3, 4] see also the chapter on Thermoplastic dynamic vulcanizates in this book) 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 hlled with high concentration of rubber particles well bonded to the matrix. These blends are usually PP/EPDM (Santoprene ) or PP/polybutadiene (PB), but ex-... 

Keywords blends, processing, elastomer modification, d)mamic vulcanization, morphology, injection molding, extrusion molding, thermoplastic elastomer, thermoplastic dynamic vulcanizates (TDV), application. 

LOW HARDNESS EPDM/POLYPROPYLENE THERMOPLASTIC DYNAMIC VULCANIZATES. I. PREPARATION TECHNOLOGY BY A TWIN-SCREW EXTRUDER... 

Notes Dynamic vulcanizate usually, the EPDM is crosslinked via free radical methods during a shearing action of the blend, often accompanied by a partial phase inversion to dual phase continuity Based on G. Holden, Ch. 16, Table 16.10, in G. Holden, N. R. Legge, R. Quirk, and H. E. Schroeder, Eds., Thermoplastic Elastomers, 2nd Ed., Hanser, Munich, 1996 AES = Advanced Elastomer Systems... 

Table 15.13. Key properties of commercial thermoplastic elastomer blends based on polypropylene/elastomer dynamic vulcanizates...

Sometimes, the elastomer phase is deliberately cross-linked during the intensive mechanical mixing. This is described as dynamic vulcanization [27,34], It produces a finely dispersed, discontinuous, cross-linked elastomer phase (Fig. 5.5). The products are called dynamic vulcanizates or thermoplastic vulca-luzates. This process is more complex than simple mixing, but the products have two important advantages. First, the cross-Unked elastomer phase is insoluble and so oil and solvent resistance is improved. Second, cross-linking reduces or eliminates the flow of this phase at high temperatures and/or imder stress. This improves resistance to compression set. 

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. 

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. 

Keywords Dynamic vulcanization Polymer blends and alloys Reactive processing Thermoplastic elastomers Thermoplastic vulcanizates... 

Two important types of elastomeric polyolefin blends are reactor-made iPP/ EPR blends and postreactor blend iPP/EPDM. The latter is called thermoplastic vulcanizates (TPVs), produced by dynamic vulcanization of blends containing a thermoplastic and an elastomer. To make iPP/EPDM TPV, the two polymers PP and EPDM are mixed with curatives, such as peroxides, phenolic resins, or sulfur with accelerators, and dynamically cured in an extmder resulting in a blend consisting of micrometer-sized elastomer particles dispersed in the PP matrix (20-24). Paraffinic oils are added in the melt mixing process for viscosity control and cost. In iPP/ EPDM TPV, the crystalline iPP resin is normally the minor phase. Recently, polyolefin plastomers have been added to the class of elastomeric polyolefin blends. Polyolefin plastomers are ultralow molecular weight linear low density polyethylenes (ULMW-LLDPE). Nonelastomeric polyolefin blends are blends of polyolefins with mostly nonpolyolefin (other thermoplastic) matrices as mentioned earlier. 

DYNAMICALLY VULCANIZED PP/EPDM BLENDS (OR THERMOPLASTIC VULCANIZATES (TPVs))... 

In addition to EPDM-polyolefln and NBR-nylons combinations, a large number of other rubber-plastic combinations have been used to prepare thermoplastic vulcanizates by dynamic vulcanization (Coran et al., 1982). 

The structure and physical properties of the thermoplastic vulcanizates (TPE-V) produced in the process of the reactive processing of polypropylene (PP) and ethylene-octene elastomer (EOE) in the form of alloy, using the cross-linking system was analyzed. With the DMTA, SEM and DSC it has been demonstrated that the dynamically produced vulcanizates constitute a t5 ical dispersoid, where semicrystal PP produces a continuous phase, and the dispersed phase consists of molecules of the cross-linked ethylene-octene elastomer, which play a role of a modifier of the properties and a stabilizer of the two-phase structure. It has been found that the mechanical as well as the thermal properties depend on the content of the elastomer in the blends, exposed to mechanical strain and temperature. The best results have been achieved for grafted/cross-linked blends with the contents of iPP/EOE-55/45%. 

A thermoplastic vulcanizate (TPV), represented by the lower right quadrant of Fig. 4.38, is a TPE produced by dynamic vulcanization, the process vulcanizing a vulcani-zable elastomer during its intimate mixing with a thermoplastic polymer in the molten state. A TPV comprises finely divided particles of highly cross-linked rubber in a continuous matrix of rigid thermoplastic. 

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