Studies on Blends of Acetate and Acrylic Functional Polymers with Bitumen

Blends with a 100 penetration grade bitumen from Venezuela have been made with five commercial polar polymers in up to 40 parts per hundred (29%) proportions, and examined by fluorescence optical microscopy, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA), to reveal developments in the performance of the colloid, a readily-made nanocomposite. The low temperature stiffness of the bitumen was enhanced by two orders of magnitude whatever polymer or its quantity used, but the ionomer additive was more effective than this when its proportion was low, indicating a specific organisation of the asphaltenes. All the polymers dispersed in and lowered the glass transition of the bitumen-rich phase, and all raised the modulus at high temperatures, some copolymers of ethylene doing this by creating within the polymer-rich phase – when this was extensive – a network which failed only when the crystallite crosslinks melted. Blends of the EVA with 28% ester groups almost lacked such crystallinity but had a second tanδ process and enhanced high temperature stiffness, perhaps caused by the polar groups bonding to the asphaltenes, the highly anisotropic nanoparticulates. Phase inversion – the development of an extensive polymer-rich phase – was demonstrated by the two EVA systems and the EAA polymer in the fluorescence photomicrographs, and by the resolution of a clear peak at the glass transition in the tan δ plot, but the DMTA plots of the blends of PMMA and the ionomer lacked such features. The PMMA was present mainly as a dispersed phase, for its Tg was hardly depressed by any component of the bitumen, but the latter, according to the fluorescence photomicrographs, did have an extensive polymer-rich phase. Activation energies from the E″ measurements were about 150 to 200 kJ·mol–1 for the glass transition, in keeping with the absence of extensive crystalline regions. Several polymers caused the Tg of the material to fall by up to 24°C when in small proportions (the EAA being most effective), but to rise upon further additions. The 9% EVA and the ionomer were the least effective plasticisers. Polymers with a cohesive energy density of more than 17 (J/cm3)0.5 caused blends to adhere to glass, whatever their proportion.