Figures 3D and 4D present the results of P-MAs prepared with either 3 wt% (Fig.
Finally, it was also observed that, regardless the type of polymer (SBS or SEBES), the increase in the polymer concentration from 3 to 10 wt% resulted in the creation of P-MA with an increased polymer-rich phase and higher mechanical resistance, as a result of the compatibility between these polymers and asphalt and the importance of the polymer-rich phase in determining the properties of P-MAs.
The elastic response of the investigated P-MAs is higher than that of NA and depends on the type and amount of the polymer used to produce them.
The rheological behavior of NA and P-MAs was obtained through small-amplitude oscillatory shear flow under linear viscoelastic conditions, and the analysis of their storage G'([omega]) modulus and phase angle [delta]([omega]) master curves led to the following conclusions: (1) SBS-MA and SBEBS-MA exhibited qualitatively similar rheological behavior; (2) for both low-polymer and high-polymer P-MAs, the SBEBS-MA are more elastic thus less responsive toward frequency changes than their SBS-MA analogs; (3) P-MAs prepared with either SBS or SBEBS having the higher molecular weight exhibited higher elastic response; and (4) the thermo-mechanical resistance of SBS-MA and SBEBS-MA can be increased by increasing polymer concentration.
Horizontal shill factor [a.sub.[tau]] of the NA and P-MAs as calculated using data of the storage modulus G' obtained at 50[degrees]C.
Given that the polymer's molecular characteristics, such as molecular weight, chain architecture, and composition of the elastomeric block are important in determining the properties of P-MA, this article presents a study on the morphology and rheological properties of SBS-MA and SBEBS-MA.
Samples of P-MA with 3 and 10 wt% of SBS or SBEBS were produced through high-temperature mixing process, using a stainless steel tank equipped with a thermal jacket and high shear rate stirrer (IKA, Yellow Line OST 20); nitrogen atmosphere blanket was used to minimize polymer degradation.
Characterization of P-MA. Morphology of the P-MA (i.e., shape and distribution of the polymer-rich phase) was observed on images acquired with a Carl-Zeiss KS 300 fluorescence microscope, equipped with a lamp for 390-459 nm wavelength and 20X lens.
The rheological behavior of each P-MA was examined through oscillatory shear flow measurements under linear viscoelastic conditions, as indicated in the NA characterization.
Analysis of the P-MA using fluorescence microscopy gives an idea of the distribution of the polymer-rich phase within the blend.
As a result, the spatial arrangement and interactions of these macro-phases are determined by the asphalt composition, molecular characteristics of the polymer, polymer/asphalt ratio, and mixing conditions; and they are responsible for the morphology and rheological behavior of the P-MA. On the basis of these considerations, it is presumed that the polymer-rich and asphalt-rich phases of SBS-MA can be different from those of SBEBS-MA, thus their morphology and mechanical properties.
Because of its maltenes-swelling, the polymeric phase occupies a volume fraction greater than that of the polymer mass in the P-MA. The spherical shape of the polymer particles indicates that asphalt and polymer are to a large extent immiscible and their interfacial adhesion is low (27-32).