Page 309 - Handbook of Plastics Technologies

ELASTOMERS

ELASTOMERS 4.101

FIGURE 4.38 Phase morphology of different types of thermoplastic elastomers.

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 continu-
ous matrix of rigid thermoplastic.
Figure 4.39 shows a schematic cost-performance comparison for generic classes of
conventional thermoset rubbers and for TPEs. Very approximately, the properties and per-
formance of a given TPE class are somewhat comparable to those of the thermoset rubber
at the same position on the cost-performance chart. Thus, the styrenics are candidates to
replace NR and styrene-butadiene rubber (SBR), and the TPVs logically replace EPDM
and chloroprene (neoprene) rubber.

4.6.3 Types of Thermoplastic Elastomers
4.6.3.1 Styrenic Block Copolymers. Styrenic TPEs are copolymers whose molecules
have the S-D-S structure, where S is a hard segment of polymerized styrene or styrene de-
rivative, and D is a soft central segment of polymerized diene or hydrogenated diene units.
Polybutadiene (B), polyisoprene (I), and polyethylenebutylene (EB) are the most com-
monly used rubbery segments (D). Structures for these triblock copolymers are repre-
sented as follows:

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