Elastomers thermoplastic vulcanizates

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

Thermoplastic polyurethane Thermoplastic rubber (or elastomer) Thermoplastic vulcanizate (aTPE)... 

Thermoplastic polyolefin elastomer/ polyolefin blend elastomer Thermoplastic vulcanizate elastomer TPV TPR, Santo-prene, Geolast, Vyram, Nex-prene, Alcryn... 

The processing technologies for elastomeric blends, thermoplastic elastomer-based on mechanical mixing, and elastomer-plastic vulcanizates are distinctly different. Depending on the type and nature of blend, size, and their final application, a wide range of processing equipment is now in use both industrially as well as in laboratory scale preparation. 

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. 

In this part, we will discuss AFM images and nanomechanical data obtained in smdies of natural and synthetic rubbers, thermoplastic elastomers (TPE), and their vulcanized counterparts— thermoplastic vulcanizates (TPV). 

First report on a conducting polymer, viz oxidised iodine doped polypyrrole by D.E. Weiss et al., a polyactetylene derivative Development of Thermoplastic Vulcanizates, a new class of thermoplastic elastomers by Gessler, Fisher, Coran and Patel. 

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. 

The following TPs are the main thermoforming materials processed high-impact and high-heat PS, HDPE, PP, PVC, ABS, CPET, PET, and PMMA. Other plastics of lesser usage are transparent styrene-butadiene block copolymers, acrylics, polycarbonates, cellulosics, thermoplastic elastomers (TPE), and ethylene-propylene thermoplastic vulcanizates. Coextruded structures of up to seven layers include barriers of EVAL, Saran, or nylon, with polyolefins, and/or styreneics for functional properties and decorative aesthetics at reasonable costs.239-241... 

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. 

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 vulcanizates are a separate class of thermoplastic elastomers (TPEs) with Santoprene as the representative biomedical elastomer. 

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... 

Examples of vulcanizable elastomers include natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), ethylene-propylene-diene monomer-rubber (EPDM), butyl rubber (HR), polychloroprene or neoprene (CR), epichlorohydrin rubber (ECO), polyacrylate rubber (ACM), millable polyurethane rubber, silicone rubber, and flu-oroelastomers. Examples of thermoplastic elastomers include thermoplastic polyurethane elastomers, styrenic thermoplastic elastomers, polyolefin-based thermoplastic elastomers, thermoplastic polyether-ester (copolyester) elastomers, and thermoplastic elastomers based on polyamides. 

Until relatively recently, aU elastomers were vulcanized. However, thermoplastic elastomers were first introduced in 1954 with the introduction of urethane thermoplastic elastomers. Thus, the two major types of elastomers are vulcanizable (conventional) and thermoplastic elastomers. The conventional elastomers are frequently broadly classified as natural and synthetic rubbers. 

Uses of Ethylene-Propylene Rubbers. EPDM and EPR vulcanizates are used in extruded profiles, cable insulation and jacketing, and roofing membranes. There are many automotive uses radiator hose, door and trunk seals, insulation, jacketing, and others. These elastomers are also used in applications such as window and architectural profiles, dock fenders, and washing-machine hoses. In short, their applications are extensive and diverse. Ethylene-propylene rubbers may be the most versatile of general-purpose rubbers. In addition, EP rubbers are added to polyolefin plastics as impact modifiers and as components of certain thermoplastic elastomer compositions (e.g., thermoplastic vulcanizates, which are discussed later in this chapter). 

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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