Blends of bitumen with polyethylenes

Blends of a 100 penetration grade bitumen with four different polyethylenes having up to 40 pph or 29% of polymer by weight were prepared using a Z-bl ade mixer at more than 160 degrees C. The blends were studied by fluorescen ce optical microscopy, differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The optical measurements indicated the presence of bitumen-rich and polymer-rich phases. The DSC showed that the m elting point of the crystallites was lowered and within the polymer-rich ph ases, the extent of crystallinity reduced by the presence of the bitumen. A nnealing made significant changes to crystallite size, suggested by the rai sing of the melting point of the polymer crystallites. The DMTA measurement s show that these polymers lower the temperature at which the glass transit ion softens the material, but raises the temperature at which the blend und ergoes viscous flow. When the polymer fraction is over 20% to 28% the flow starts only when the crystallites melt, so the polymer then provides an ass ociating junction network. (C) 1999 Elsevier Science Ltd. All rights reserv ed.