Hysteresis copolymers

Short fiber reinforcement of TPEs has recently opened up a new era in the field of polymer technology. Vajrasthira et al. [22] studied the fiber-matrix interactions in short aramid fiber-reinforced thermoplastic polyurethane (TPU) composites. Campbell and Goettler [23] reported the reinforcement of TPE matrix by Santoweb fibers, whereas Akhtar et al. [24] reported the reinforcement of a TPE matrix by short silk fiber. The reinforcement of thermoplastic co-polyester and TPU by short aramid fiber was reported by Watson and Prances [25]. Roy and coworkers [26-28] studied the rheological, hysteresis, mechanical, and dynamic mechanical behavior of short carbon fiber-filled styrene-isoprene-styrene (SIS) block copolymers and TPEs derived from NR and high-density polyethylene (HOPE) blends. 

It was the objective of this work to investigate the effect of variation in block architecture (number and the order of the blocks) on the crystallinity level, morphology, the stress-strain and hysteresis behavior of this series of polymers. In addition, the composition ratio of the two block types is expected to play a crucial role in determining the bulk material properties of the block copolymers. This is related to the fact that the mechanical properties of block copolymer are typically influenced more substantially by the behavior of the continuous phase, as will be demonstrated.(1,22)... 

Hysteresis Behavior. The hysteresis behavior of the HBIB triblock copolymers are given in Figure 13A and of that of the inverted HIBI block copolymer is given in Figure 13B. The difference in the behavior of these two series of block copolymers is tremendous. The origin of these differences are again directly related to the morphology and the architecture of the polymers. 

The hysteresis behavior of the diblock copolymer HBI-50 is not shown but is very similar to that of HIBI-49. In summary then, the difference in hysteresis behavior of the HBIB series to that of HIBI and HBI is related to the ability of the members of the first series to form permanent entanglements, by entrapment of the end blocks in the semicrystalline domains, whereas no such arrangment is possible for neither HIBI nor HBI series. The permanent entanglement serves as a physical crosslink which promotes recovery of the polymer after the deforming stress has been removed. At the same time, much less energy is lost as heat. 

Another graft copolymer having the same composition, but presumably a somewhat greater density of PEO side chains, had the same transparent appearance and low Tg. Modulus as well as dilatometric data exhibited a hysteresis loop between — 20° and 60°C. These results along with x-ray measurements indicate presence of some crystallinity in contrast to the first completely amorphous copolymer. For given composition the relation between the size and distribution of the side chains, and their ability to crystallize is not yet clear. 

Fig. 21. Electric displacement, D, versus electric field, E, hysteresis loop of the 55/45 copolymer at 20 °C (Figure from Ref. [8])...

Styrene butadiene rubber (SBR) is, quantitatively, the most important synthetic rubber. It is a copolymer of styrene and butadiene in such a ratio that its rubbery nature predominates, vulcanization is carried out with sulphur, reinforcement with carbon black. It is used at a very large scale in tyres for passenger cars, thanks to its excellent combination of abrasion resistance and friction on the road. In large tyres it can not replace natural rubber because of its heat development (hysteresis losses). 

Kaelble has developed a model137) to relate mechanical properties of SBS and SIS copolymers to their interfacial morphology. The adsorption-interdiffusion model for the interfacial phase defines the size, shape, and connectivity of microdomains. Kaelble has applied his model to the interfacial morphology in order to explain the initial tensile yielding, cold drawing, and subsequent hysteresis in recovery of Kraton 101138,139). 

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