**12.1 Stress-strain**

When tested under a tensile stress-strain condition, TPE behave as elastomers until the yield stress after which they can undergo plastic flow, part of which may be viscoelastic (timedependant recovery) and part will be permanent set. The pre-yield region represents an elastomeric response where the physical cross-links are not deformed. The stress-strain curve of SBS is shown in Figure 4.

Fig. 4. The stress-strain curve of SBS

Creep Recovery

0 20 40 60 80 100

**Time (min)**

Stress relaxation is a technique can be used as a physical method to determine the domain structure of the TPEs by studying the time-dependent deformation behaviour of the

At high strain, strain hardening takes place and converts TPE from elastic behaviour to leathery or stiffer characteristic so that elasticity is lost while tensile strength and modulus will be increased. In time, the recovery of the deformation occurs suggesting that the part

Tear strength which describes how well the elastomer resists tearing. TPE is stretched and the amount of force required is recorded. Peel strength is a measure of how well a TPE has

Thermoplastic elastomers have been widely used in automotive sector, medical devices, mobile electronics, household appliance sector and construction to replace conventional

segmented block copolymer. There is no stress relaxation occurs in ideal elastomer.

0.0

**12.4 Stress relaxation** 

**12.5 Strain hardening** 

**12.6 Tear strength** 

**13. Applications** 

vulcanized rubber.

bonded to a rigid substrate.

Fig. 6. The creep and recovery curve of SBS

where deformation occurs is viscoelastic.

0.2

0.4

0.6

0.8

**Strain (%)**

1.0

1.2

1.4

#### **12.2 Dynamic mechanical analysis**

Dynamic mechanical analysis (DMA), uniaxial tensile and microscopic properties were used to observe properties and transitions at lower temperatures to the glass transition of the elastomer phase (Adhikari et al., 2003). Two distinct transitions were detected at the lower temperatures evaluated, an elastomeric to ductile thermoplastic transition, and a thermoplastic to brittle transition. A typical DMA curve of SBS is shown in Figure 5. Scanning electron microscopy (SEM) revealed an associated change in deformation mechanism.

Fig. 5. The storage and loss modulus curves of SBS

#### **12.3 Creep and recovery**

Creep is a problem for TPE because there are only physical crosslinks that can dissociate and flow, chemical crosslinks are permanent and creep will be low. TPEs soften and melt with increasing temperature, showing creep on extended use. Creep resistance and tensile strength are generally directly related. A softer TPE will creep more and have less tensile strength than a harder TPE. Recovery should be elastic with some viscoelasticity, permanent set is not suitable in TPE. The deformation behaviour of TPEs during creep flow can be divided into three strain regimes: linear regime at low strains where the recovery from creep is complete; the transient regime, where the viscosity shows a maximum; flow regime where steady state morphology is formed. Creep and recovery curve of SBS is shown in Figure 6.

Dynamic mechanical analysis (DMA), uniaxial tensile and microscopic properties were used to observe properties and transitions at lower temperatures to the glass transition of the elastomer phase (Adhikari et al., 2003). Two distinct transitions were detected at the lower temperatures evaluated, an elastomeric to ductile thermoplastic transition, and a thermoplastic to brittle transition. A typical DMA curve of SBS is shown in Figure 5. Scanning electron microscopy (SEM) revealed an associated change in deformation

Creep is a problem for TPE because there are only physical crosslinks that can dissociate and flow, chemical crosslinks are permanent and creep will be low. TPEs soften and melt with increasing temperature, showing creep on extended use. Creep resistance and tensile strength are generally directly related. A softer TPE will creep more and have less tensile strength than a harder TPE. Recovery should be elastic with some viscoelasticity, permanent set is not suitable in TPE. The deformation behaviour of TPEs during creep flow can be divided into three strain regimes: linear regime at low strains where the recovery from creep is complete; the transient regime, where the viscosity shows a maximum; flow regime where steady state morphology is formed. Creep and recovery

**12.2 Dynamic mechanical analysis** 

Fig. 5. The storage and loss modulus curves of SBS

**12.3 Creep and recovery** 

curve of SBS is shown in Figure 6.

mechanism.

Fig. 6. The creep and recovery curve of SBS
