Conventional elastomers, TPEs

TPEs from thermoplastics-mbber blends are materials having the characteristics of thermoplastics at processing temperature and that of elastomers at service temperature. This unique combination of properties of vulcanized mbber and the easy processability of thermoplastics bridges the gap between conventional elastomers and thermoplastics. Cross-linking of the mbber phase by dynamic vulcanization improves the properties of the TPE. The key factor that controls the properties of TPE is the blend morphology. It is essential that in a continuous plastic phase, the mbber phase should be dispersed uniformly, and the finer the dispersed phase the better are the properties. A number of TPEs from dynamically vulcanized mbber-plastic blends have been developed by Bhowmick and coworkers [98-102]. 

Thermoplastic elastomers (TPE s) are characterized by the exceptional property that, without vulcanization, they behave as cross-linked rubbers. They are block-copolymers, in which blocks of the same nature assemble in hard domains, acting as cross-links between the rubbery parts of the chain. These hard domains lose their function when they reach their softening temperature, so that the material can then be processed as a thermoplast. One of the oldest member of the family of TPE s is SBS (styrene-butadiene-styrene block copolymer), but several other TPE s have been developed, i.a. on the basis of polyesters, polyurethanes and polyolefins. In their properties these polymers cover a broad range between conventional rubbers and soft thermoplastics. 

There are certain advantages and disadvantages to this type of material compared to conventional elastomers. The advantages concern the existence of reversible physical cross-links. When a TPE is heated, the cross-links disappear if the temperature increases beyond the Tg of the hard phase or above the of the hard domain if it is crystalline. In contrast, conventional elastomers display thermostable structure. The physical nature of... 

Thermoplastic elastomers (TPEs) exhibit properties characteristic of chemically cross-linked elastomers (vulcanized rubbers) at room temperature but, at elevated temperatures, behave as thermoplastics (thermo from the Greek word 0ep x6i , meaning hot). Consequently, they can soften and flow and, thus, can be processed with high speed, efficiency, and economy on conventional thermoplastic equipment. Furthermore, unlike vulcanized mbber, TPEs can be reused. 

More specifically, the dynamic mechanical properties are significantly different in TPEs vs. conventional elastomers. The WLF equation (see Chapter 5) does not generally apply to TPEs since two phases make the material... 

This chapter is a perspective of the science and technology of elastomers and does not include a market analysis. Nevertheless, we must mention that the global market for these materials is large (Fig. 4.1). Global vulcanizable (conventional, vulcanizable) rubber consumption was about 20 million metric tons in 2004, whereas thermoplastic elastomer (TPE) consumption was about 1.5 million metric tons. The consumption of conventional rubbers is growing at a rate of about 3 to 4 percent, whereas the growth of TPE consumption is growing at about twice that rate. 

A thermoplastic elastomer (TPE) is a rubbery material with properties and functional performance very similar to those of a conventional thermoset rubber, yet it can be fabricated in the molten state as a thermoplastic. ASTM D 1566 defines TPEs as a diverse family of rubber-like materials that, unlike conventional vulcanized rubbers, can be processed and recycled like thermoplastic materials. Many TPEs meet the standard ASTM definition of a rubber, since they recover quickly and forcibly from large deformations, they can be elongated by more than 100 percent, their tension set is less than 50 percent, and they are sometimes insoluble in boiling organic solvents. Figure 4.35 indicates hardness ranges for various types of TPEs and conventional elastomers. 

FIGURE 4.36 TPE part fabrication in a single step vs. three or more steps for conventional elastomers. 

Thermoplastic elastomers (TPEs) combine the physical properties of vulcanized rubber with the ease and economy of conventional thermoplastic processing. They are also well suited to reprocessing and recycling and minimize toxicity issues. Many types of thermoplastic elastomers are polymer blends cranprising a thermoplastic continuous phase in combination with a discontinuous vulcanized or unvulcanized elastomeric phase, which in the latter case could also be co-continuous. 

For a long time, the application of thermoplastic elastomers (TPE-0) together with oils was considered impossible, because conventional TPE-0 generally swells strongly when in contact with oily media or oily vapors for an extended period. This swelling may become so significant that it jeopardizes proper service. Therefore, caution is advised for such applications. 

Thermoplastic elastomers (TPEs) are polymeric materials that are processed into fabricated articles in the same manner as a conventional thermoplastic, yet these articles have the properties and functional performance of a thermoset rubber. They have been gaining a significantly larger market share over the past three decades with nontire applications, compared to the conventional thermoset elastomers discussed earlier. 

The thermoplastic elastomers (TPEs) concern large industrial and commercial fields, as well as academic and applied research. Often the TPEs are considered as being only an important part of the block copolymers, but they are present in many other polymeric materials, as clearly shown by Holden et al [1,2] and Rader [3-5]. They are characterized by a set of properties inherent to block and graft copolymers, different blends, and some vulcanized materials. More than 7000 Chemical Abstracts entries directly concern TPEs and in about 12500 other publications they are closely associated to other issues (SciFinderScholar) [6]. Most of these references describe materials, which associate elastomeric recovery and thermoplastic properties however some products exhibit characteristics and properties, which completely differ from those of conventional TPEs. 

Thermoplastic elastomers (TPE) belong to a relatively new and small class of engineering plastics. Nevertheless, they enjoy a steady growth because of their unusual and very important combination of properties. During service, TPE behave as elastomers e.g., as vulcanized natural rubber) but, in contrast to the classical elastomers, they can be processed by means of the conventional techniques and equipment utilized for all thermoplastics. 

It has been noted in several places (Sections 4.6,17.1, and 17.5) that certain thermoplastic polymers can be quite elastic (rubbery) at room temperature. They form a distinct class of materials, the thermoplastic elastomers (TPEs), which have been defined (ASTM D1566) as a family of rubber-like materials that, unlike conventional vulcanized rubber, can be processed and recycled like thermoplastic materials. The typical structure of these materials is the coexistence of soft domains that give rubbery behavior with hard domains that act as heat-labile cross-Unks. Although the thermoplastic elastomers compete in many of the applications traditionally assigned to conventional rubbers, the sensitivity of the cross-links to heat makes them unsuitable for an application such as automobile tires, where the... 

TPEs are materials that possess, at normal temperatures, the characteristic resilience and recovery from the extension of crosslinked elastomers and exhibit plastic flow at elevated temperatures. They can be fabricated by the usual techniques such as blow molding, extrusion, injection molding, etc. This effect is associated with certain interchain secondary valence forces of attraction, which have the effect of typical conventional covalent crosslinks, but at elevated temperatures, the secondary... 

Thermoplastic elastomers are materials that have the properties of vulcanized rubbers but can be processed by techniques associated with thermoplastics. The commercial importance of TPEs is due to their superior processing properties and economic advantages over conventional rubbers and plastics. TPEs from rubber-plastic blends became important because they combine the superior processability of thermoplastics and the... 

---