Modification by thermoplastic elastomers

Bitumen modification with elastomers is currently the most common method for producing paving modified bitumen. The bitumen produced is often called elastomer bitumen. 

Thermoplastic elastomers or elastomers are designated as elastic polymers, which, after polymerisation, can be extended under the influence of a tensile force, and by removing the force, they can quickly revert to their initial length. The elastic behaviour of these polymers is due to the fact that parts of the macromolecular chains at ambient temperatures not only can be moved under the influence of a force but also revert back to their initial position after removing the force, provided the glass transition temperature (Tg) is lower than the usual ambient temperatures. 

According to the International Union of Pure and Applied Chemistry (lUPAC), the polymer is defined as a substance composed of molecules characterized by the multiple repetition of one or more species of atoms or groups of atoms (constitutional units) linked to each other in amounts sufficient to provide a set of properties that do not vary markedly with the addition or removal of one or a few of the constitutional units (lUPAC 1974). 

The category of elastomers includes a wide range of products, such as natural rubber (NR), styrene-butadiene rubber (SBR), styrene-butadiene-styrene copolymer (SBS known as thermoplastic rubber), styrene-isoprene-styrene copolymer (SIS), polyurethane rubber, polyether-polyester copolymer, olefinic copolymers, ethylene-propylene rubber (EPR) and so on (see also Table 3.16). 

From the abovementioned elastomers, those widely used today for the production of elastomer bitumen are SBS, SBR elastomer, SIS and, to a smaller extent, NR. It should be stated here that crumb rubber from used tyres is also indirectly classified into this category. 

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