A dynamic mechanical and thermal study of various rubber-bitumen blends

Blends of a Nynas 100 penetration-grade bitumen with a cis-polybutadiene, a butyl rubber, three polyisobutylenes of different molecular weights, a chl orinated-polyethylene, polychloroprene in latex form, and a polyurethane ru bber (scrap Lycra) were prepared using a Z-blade masticator mixer at a temp erature of about 180 degrees C. The blends contained between 10 and 40 pph (i.e., 9 and 29%) by weight of rubber. They were characterized by fluoresce nce optical microscopy, differential scanning calorimetry, and dynamic mech anical thermal analysis. The bitumen rich phases provided the matrix in mos t of these systems, polymer rich extensive phases being formed with butyl r ubber, and low- and moderate-molecular-weight poly(isobutylenes) when the p roportion rose above 30 pph, and for the poly(cis-butadiene) and chlorinate d polyethylene system only when the proportion rose above 40 pph, according to the tan delta plots. Only glass transitions were associated with polyme r-rich phases, and there were some melting transitions from paraffinic wax components ejected from the bitumen-rich phases. Below room temperature the modulus of blends of polybutadiene, chlorinated polyethylene, and the poly urethane rubber were similar to that of the bitumen; but those of the other polymers were stiffer by a factor of 50, perhaps because of a rearrangemen t of the asphaltenes. The softer blends, particularly the first two named a bove, had loss processes (with tan delta > 0.5) ranging over 200 degrees C or more. (C) 2000 John Wiley & Sons, Inc.