Thermoplastic vulcanizate blends

Recent work on thermoplastic vulcanizates (TPVs) will not be included in this chapter since it is being reviewed elsewhere in the book. Abbreviations for some mbbers and accelerators will be used throughout in place of their full names as shown in Table 11.1. Acronyms for other polymers and additives wUl be provided in the text as required. A short discussion of polymer miscibility and compatibUization of polymer blends will be provided for better appreciation of the subject. 

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. 

Anandhan, S., De, P.P., Bhowmick, A.K., Bandyopadhyay, S., and De, S.K., Thermoplastic elastomeric blend of nitrile rubber and poly(styrene-co-acrylonitrile). n. Replacement of nitrile rubber by its vulcanizate powder, J. Appl. Polym. Set, 90, 2348, 2003. 

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

TPOs are basically two-component elastomer systems consisting of an elastomer finely dispersed in a thermoplastic polyolefin (such as polypropylene). The thermoplastic polyolefin is the major component. Thermoplastic elastomers (TPEs) include TPOs, TPVs (thermoplastic vulcanizates), etc. Properties of TPOs depend upon the types and amounts of polymers used, the method by which they are combined, and the use of additives such as oils, fillers, antioxidants, and colors. Blends and reactor-made products compete primarily with other TPEs and metals. There are vulcanizates (TPVs) that have higher elastomeric properties. They compete primarily with TS elastomers. 

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

Results given in Table VII show that the viscosity versus shear rate variation of these three Santoprene grades fits the power law over the entire range from 10 to 5200 s . Both the viscosity and the extrudate swell at constant shear rate increase with decreasing rubber particle content (or increasing hardness). Thus, these olefinic thermoplastic vulcanizates essentially behave like highly filled fluids in flow. When compared with unvulcanised rubber (see previous sections) or polypropylene - EPDM blends (32), the extrudate swell appears low and there is no Newtonian viscosity plateau. 

Nakason, C., Pechurai, W., Sahakaro, K., and Kaesaman, A. 2005. Rheological, mechanical and morphological properties of thermoplastic vulcanizates based on NR-g-PMMA/PMMA blends. Polymers for Advanced Technologies 16(8) 592-599. 

Nakason, C., Tobprakhon, A., and Kaesaman, A. 2005. Thermoplastic vulcanizates based on poly(methyl methacrylate) /epoxidized natural rubber blends Mechanical, thermal, and morphological properties. Journal of Applied Polymer Science 98 3) 1251-1261. 

The structure and physical properties of the thermoplastic vulcanizates (TPE-V) produced in the process of the reactive processing of pol5rpropyl-ene (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 d5mamically produced vulcanizates constitute a typical 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%. 

Thermoplastic elastomer (TPE) blends have been broadly studied as a new class of materials. TPEs offer various advantages and require no state-of-the-art processing machinery, while scrap and rejects are recyclable. Blends can be homogeneous, phase separated or both. TPEs are multi-phase polymer systems consisting of hard and soft domains that can be copolymers or mechanical blends. This phase separation leads to materials having unique and viable commercial physical properties. TPEs exhibit the thermoplastic characteristics of the hard thermoplastic phase, and resilience as a result of the rubbery domains. TPEs based on natural rubber (NR) and thermoplastic blends are known as thermoplastic natural rubber (TPNR) blends. There are two types of TPNR, namely thermoplastic polyolefin (TPO) and thermoplastic vulcanizate (TPV).3... 

In contrast to the rigid TPOs described above, low-modulus/flexible grades of TPO blends are also produced commercially. In flexible TPOs, the rubber content can be as high as 60 %, and in some cases, the dispersed rubber may also be partially cross-linked during the mixing without losing the thermoplastic character of the matrix. However, the latter type of dynamically vulcanized elastomeric alloys or thermoplastic vulcanizate rubbers (TPVs) are considered as a separate class of elastomeric materials and hence will be discussed under elastomer blends. On the other hand, the soft TPO blends discussed here contain a low-modulus olefln copolymer elastomer as the major component with some polypropylene added to impart melt processability. 

Dynamically vulcanized, elastomeric thermoplastic alloys or TPVs display properties as good as or even better than the block copolymers, viz., a high degree of rubber elasticity yet good melt processability. The main advantages of the thermoplastic vulcanizate elastomer blends over the uncured thermoplastic/elasto-mer blends are... 

Addresses phase morphology in polymer/polymer micro and nano blends, thermoscts/thermoplastics blends, and thermoplastic vulcanizates... 

TPEs which are prepared by physical blending of an elastomer with a thermoplastic. Such TPEs are categorized into two types depending on rubber vulcanization (i) thermoplastic olefins (TPOs) or thermoplastic elastomer polyolefins (TEOs) (ii) thermoplastic vulcanizates (TPVs). 

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