Processing of bitumens modified by a bio-oil-derived polyurethane

Abstract

Castor oil (CO) functionalized by isocyanate groups (-NCO) is proposed as a novel bio-based reactive polyurethane (PU) for bitumen modification. This work presents a comparative analysis conducted on blends of bitumen and 2 wt.% of a PU prepolymer prepared by NCO-functionalization of castor oil. Four preparation procedures were evaluated, which resulted from the combination of two processing times (1h or 24h, at 90ºC) followed by two different post-treatments (water addition or ambient curing for up to 6 months). It was found that the degree of modification attained after posttreatment depends on the previous processing conditions. Thus, short processing times are required if the binder is further subjected to ambient curing. Instead, the success of the water-addition modification falls on a previous long processing step. As revealed by rheological tests, ambient curing was seen to be by far a more efficient way of modification if compared to direct addition of water, and makes clear that the resulting binder evolves towards a better performance when in service. In that sense, Thin Layer Chromatography tests, Modulated DSC and AFM images demonstrated a more complex microstructure characterized by the presence of a larger content of molecules with higher polarity, size and molecular weight.

Short- and Long-Term Epoxy Modification of Bitumen: Modification Kinetics, Rheological Properties, and Microstructure

“…These results indicate that the esterification and etherification reactions take place between the oxirane groups and high molecular weight molecules found in aromatics and resins that contain carbonyl acid groups. The new bitumen compounds formed would not be eluted during the chromatographic separation, and therefore, they are quantified in the asphaltenes content [33,35,37]. It is evident that the development of more complex structures agrees with the above-commented rheological results.…”

Effect of shear processing on the linear viscoelastic behaviour and microstructure of bitumen/montmorillonite/MDI ternary composites

“…In the low temperature range, the complex modulus increased by two decades with respect to that of neat bitumen, maintaining a monotonic decrease in the entire temperature range examined. At higher temperatures, noticeable lower values than those corresponding to the rest of composites were obtained, seemingly attributable to the effects that the promotion of MDI-related reactive processes exert at longer curing times [7][8][9]25,26]. bitumen yields a system with a mostly elastic response below the crossover frequency (~10 rad/s) at the lowest temperature (30 ºC), shifting towards higher frequencies as test temperature increases, even disappearing at 90 ºC.…”

“…Consequently, MDI content seems to further intensify the improvement derived from the intercalation/exfoliation of clay tactoids when no stirring is applied, which arises from the reactivity between isocyanate groups in MDI and active hydrogen groups, both in bitumen and C20A, yielding urea/urethane bonds [9,15,16,26], and a more complex, reinforced structure. By contrast, and similarly to the previous systems, shear processing continues destabilizing the clay-based network, and its effect is now enhanced, as NCO-involved reactions seemingly promote the agglomeration/reaggregation of clay tactoids/platelets, further reducing their degree of dispersion and the thermo-mechanical stability of the system structure.…”

“…The evolution observed for the different fractions is mainly attributable to the reactive interaction of free -NCO groups in MDI with polar bitumen constituents, and with the hydroxyl groups that MMT clays naturally contain on the edge of the platelets [10,16]. The resulting modified bitumen compounds, with higher molecular weights, either inserted between the clay platelets or attached onto their surface, would not be eluted during the chromatographic separation, giving rise to the observed marked increase in asphaltene content [9,26]. This result points to the strong reactive interaction between the different constituents, yielding notable changes in the bituminous matrix microstructure and composition, in agreement with the results obtained from the rheological and thermal characterization.…”

Development of mechanomutable asphalt binders for the construction of smart pavements

“…Because of the importance of the binder in the mechanical behavior of these infrastructures, modified bitumens are being developed to provide pavements that are sufficiently rigid at high temperatures to reduce the appearance of plastic deformations, and flexible enough at low temperatures to avoid the formation of cracks [1]. The modifiers used to improve the mechanical behavior of these binders are polymers such as thermoplastics, elastomers, and elastomer thermoplastics [2][3][4], which reduce their thermal susceptibility and increase their elastic recovery. Nevertheless, in spite of the fact that these bitumens can improve the performance of asphalt pavements, it is still necessary to develop new binders that can withstand severe climates (which combine low and high temperature periods) and traffic conditions (high loads combined with slow speeds).…”