e-Polymers 2006, no. 041 http://www.e-polymers.org ISSN 1618-7229 Modification of NR/BR blend with unsaturated thermo plastic polyurethane; polyurethane synthesis, blend morphology, vulcanization, and vulcanizate properties Urška Šebenik, Ida Poljanšek, Matjaž Krajnc* University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškerčeva 5, P. O. Box 537, SI-1001 Ljubljana, Slovenia; Fax +386 1 2419 541; matjaz.krajnc@fkkt.uni-lj.si (Received: 13 October, 2005; published: 21 July, 2006) Abstract: The unsaturated polyurethane (PU) was synthesized, characterized, and used in rubber compound. To study the effect of PU incorporation in the blend a systematic approach was used where PU was added to the natural rubber (NR), butadiene rubber (BR), and NR/BR blends. Different un-vulcanized and vulcanized compounds were characterized and the vulcanization process was investigated. It was observed that the synthesized PU was able to crosslink with the rubber compounds during the vulcanization process. The lowered temperature of melting indicated a better processability of the composites containing thermoplastic PU which melted at processing temperature, thereby allowing improvement in blend viscosity mold flow and to some extent in its homogeneity, although the mechanical properties such as hardness, tensile strength, modulus, and elongation at break did not differ significantly from the properties of elastomer blends without PU. The thermal stability of compounds with PU did not significantly worsen. Introduction Blending of elastomers is carried out for three main reasons: improvement of the technical properties of the original elastomer, achievement of better processing behaviour, and lowering of compound cost. All elastomers have deficiencies in one or more properties and blending is a way of obtaining optimum all-around performance. Compounds with good properties also need to be capable of factory processing without difficulty and of providing uniformity in behaviour [1-2]. Blends occur at different hierarchical scales in the material range employed in the industry. Composite products such as tires, hoses, belts, and air springs are composed of metal wire, textile cord, and elastomeric compounds, which form a rubber matrix. The rubber matrix itself is a compound of elastomer, filler, and plasticizer. The elastomer phase can also be a blend of different elastomers [1]. However, there are technological problems arising from some types of mutual immiscibility which can exist between dissimilar elastomers. Three main types of immiscibility have generally been noted; the thermodynamic immiscibility, immiscibility due to viscosity mismatch, and immiscibility due to the cure rate mismatch [3]. The commercially useful polymer-polymer combination is linked by intermolecular forces such as van der Waals forces or dipole moments and exhibits 1