Morphology of thermoplastic elastomers

Pig. 1. Interpenetrating network morphology of thermoplastic elastomer where A = the crystalline domain, B = the junction of crystalline lamellae, and... 

Fig. 2. Spherulitic morphology of thermoplastic elastomer where the heavy lines represent polyester segments (184).

The same approach applied to thermoplastic elastomers of the PEE-type fails to explain the large discrepancy (up to 100 MPa when the measured H values are in the range 20-40 MPa) between the experimental values and those calculated according to eq. (3.4) (Fakirov el al, 1998 Apostolov et al, 1998). For this reason one has to look for other factors which may be responsible for such a discrepancy. Before disclosing these let us recall some of the characteristic features in the structure and morphology of thermoplastic elastomers of PEE-type which are closely related with the problem discussed. 

Schonherr H, Wiyatno W, Pople J, Frank CW, Fuller GG, Gast AP, Waymouth RM. Morphology of thermoplastic elastomers, elastomeric polypropylene. Macromolecules 2002 35 2654-2666. 

Properties such as low permanent set, low creep and low hysteresis are really measures of the efficiency of the heat fugitive network system. This is a complex function of the morphology. As a very general statement, the problem would seem to be less important with the harder grades of thermoplastic elastomer. 

FIGURE 5.12 Change in the morphology of an A-B-A block copolymer as a function of composition. (From Walker, M. and Rader, C.P. (eds.). Handbook of Thermoplastic Elastomers, Van Nostrand Reinhold, New York, 1988.)... 

Akhtar, S. Morphology and Physical Properties of Thin Films of Thermoplastic Elastomers from Blends of Natural Ruhher and Polyethylene, Rubber Chem. Technol. 61, 599-583, 1988. 

A brief review is given of the important qualitative features of thermoplastic elastomers. Particular emphasis is given to the molecular structure, bulk morphology and interfacial character of these materials. Both equilibrium and nonequilibrium structures are discussed... 

Reversible network structure is the single most important characteristic of a thermoplastic elastomer. This novel property generally arises from the presence of a phase-separated morphology in the bulk material which in turn is dictated by the molecular structure, often of a block copolymer nature. A wide variety of synthetic methods can, in principle, produce endless varieties of thermoplastic elastomers this fact coupled with the advantageous processing characteristics of these materials suggest that the use of thermoplastic elastomers will continue to grow in the 1980 s. 

Defined diblocks, triblock or multiblock copolymers find important applications in the areas of thermoplastic elastomers, data storage technology [126], and as compatibilizers (e.g. in polymer blends). In thin films these polymers may display different morphologies than in the bulk, which necessitates an accurate analysis. 

Nanocomposite technology using small amounts of silicate layers can lead to improved properties of thermoplastic elastomers with or without conventional fillers such as carbon black, talc, etc. Mallick et al. [305] investigated the effect of EPR-g-M A, nanoclay and a combination of the two on phase morphology and the properties of (70/30w/w) nylon 6/EPR blends prepared by the melt-processing technique. They found that the number average domain diameter (Dn) of the dispersed EPR phase in the blend decreased in the presence of EPR-g-MA and clay. This observation indicated that nanoclay could be used as an effective compatibilizer in nylon 6/EPR blend. X-ray diffraction study and TEM analysis of the blend/clay nanocomposites revealed the delaminated clay morphology and preferential location of the exfoliated clay platelets in nylon 6 phase. 

FIGURE 4.38 Phase morphology of different types of thermoplastic elastomers. 

Block polymers and polymer blends deserve now a great intere because of their multiphase character and their related properties. The thermodynamic immiscibility of the polymeric partners gives rise indeed to a phase separation, the extent of which controls the detailed morphology of the solid and ultimately its mechanical behavior. The advent of thermoplastic elastomers and high impact resins (HIPS or ABS type) illustrates the importance of the industrial developments that this type of materials can provide. In selective solvents, and depending on molecular structure, concentration and temperature, block polymers form micelles which influence the rheological behavior and control the morphology of the material. 

Muppalla, R. Jewrajka, S. K., Synthesis, Morphology and Properties of Poly(dimethylsiloxane)/Poly(n-butyl acrylate) mixed Soft Block-Based Copolymers A New Class of Thermoplastic Elastomer. Polymer 2012,53, 1453-1464. 

Hemmati M, Narimani A, Shariatpanahi H (2011) Study on morphology, rheology and mechanical properties of thermoplastic elastomer polyolefin (TPO)/carbon nanotube nanocomposites with reference to the effect of polypropylene-grafted-maleic anhydride (PP-g-MA) as a compatibilizer. Int J Polym Mater 60 384—397... 

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