Blends of Bitumen with Various Polyolefins

Abstract Blends of a 100 penetration grade bitumen have been prepared at 180°C with five different polyolefins, each in four different proportions (10, 20, 30 and 40  pph). They have been examined by fluorescence microscopy at ambient temperatures, and by DSC and DMTA over a wide temperature range. DSC indicated that the melting points of crystallites formed on cooling the blends were about 10°C lower than for the pure polymer, for the crystallites were smaller in size. The stiffness of the bitumen was enhanced at low temperatures by 100 fold and at high temperatures to an even greater extent by the polymers, the sole exception being blends of an atactic polypropylene, whose moduli at low temperatures were the same as the bitumen. Loss processes were seen with all the polymers, the temperature falling from about 55°C for the isotactic polypropylene blends to about −30°C for the ethylene–propylene rubber. Their Arrhenius activation energies fell from 1300 to about 160 kJ mol−1 with temperature and as the crystallinity fell in the blend. The 40 pph blend of the isotactic polymer may have extensive lamellar morphology, for it was as stiff at 150°C as the bitumen at −20°C. Several of the other polymers formed an amorphous and extensive polymer-rich phase. In general, the blends lost modulus suddenly when the temperature rose above the melting points of the crystallites, which, until then, served to crosslink the polymer to form a gel.