Polyphosphoric Acid Modification of Asphalt Colloidal Components: Mechanical Responses and Component-Level Effects

To further elucidate the modification effects of polyphosphoric acid (PPA) on different oil-source base asphalts from the perspective of the mechanical properties of asphalt colloidal components, an improved separation device was designed to isolate colloidal components from PPA-modified and unmodified asphalts derived from different oil-source regions. The rheological properties of the maltene components were evaluated across a broad temperature range using a dynamic shear rheometer. The nanomechanical properties of solid-state asphaltenes were examined using atomic force microscopy. The variations in polarity and solubility of resins and aromatics induced by PPA were quantified by thin-layer chromatography with flame-ionization detection (TLC-FID). The results indicated that PPA significantly increased the complex modulus of resins by 2.5 to 3 times. The enhancement effect of 115-grade PPA generally exceeded that of 105-grade PPA. TLC-FID confirmed that PPA simultaneously polymerized rigid aromatic fragments and cyclized alkyl segments in the aromatic and resin fractions. By polymerizing active sites in asphaltenes, PPA introduced a small amount of ultrahard substance into the Derjaguin–Muller–Toporov (DMT) modulus image of the asphaltenes, a phenomenon more pronounced with long-chain PPA. This resulted in increases of 7.4% to 25.6% in the maximum DMT modulus and 10 to 30 MPa in the average DMT modulus of the asphaltenes. This study innovatively investigated the effects of PPA on different oil-source asphalts from the perspective of the mechanical properties of the four components, revealing the material transformation mechanisms within asphalts under the influence of PPA and the reasons for the differences in modification effects among asphalts with different molecular structures. Moreover, the research methodology provides a reference for studies of other chemically modified asphalts.