Physico-chemistry control of the linear viscoelastic behaviour of bitumen/montmorillonite/MDI ternary composites: Effect of the modification sequence

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

“…In this regard, as discussed in previous works [15,16], the disappearance of the rubbery plateau region in the 24 h-bitumen/C20A/MDI composite has been attributed to the effects of MDI-related reactions under low shear processing, which, in fact, may promote the agglomeration/re-aggregation of C20A tactoids/platelets through interactions between hydroxyl groups located on the edges of the clay platelets [10,12,[15][16][17]. Moreover, in addition to the reactivity of -NCO groups in MDI with active hydrogen groups in bitumen, isocyanate groups can also react with pendant hydroxyl groups in C20A to form urea/urethane bonds [15], which may further contribute to the agglomeration of clay tactoids/platelets.…”

“…As widely reported for composite materials [10,[12][13][14][15][16][17][22][23][24][27][28][29], a better nanoclay dispersion yields an increase in interfacial area, allowing for optimal mechanical stress transfer between the filler and the matrix and, therefore, an enhancement in mechanical behaviour. In this regard, as discussed in previous works [15,16], the disappearance of the rubbery plateau region in the 24 h-bitumen/C20A/MDI composite has been attributed to the effects of MDI-related reactions under low shear processing, which, in fact, may promote the agglomeration/re-aggregation of C20A tactoids/platelets through interactions between hydroxyl groups located on the edges of the clay platelets [10,12,[15][16][17].…”

“…The complex modulus undergoes an increase of roughly one decade at around 30 ºC (with respect to that of neat bitumen), showing a steady decrease with temperature up to a plateau of G*, reached at approximately 105 ºC. This plateau reveals a higher degree of thermal stability of the system structure, and hints at the hypothesis related to the formation of some kind of reinforcing clay-based network, attributable to the intercalation/exfoliation of clay [15][16][17][22][23][24]. The loss tangent remains almost independent of temperature, with values barely greater than unity up to approximately 60ºC, and then begins to steadily decrease as temperature was raised.…”

“…In previous work with an organo-modified montmorillonite (Cloisite 20A®) [15,16], we reported a remarkable solid-like plateau which extended over a wide interval of high temperatures (100 ─ 165 ºC) for a nanoclay concentration of 10 wt.%. However, further addition of 2 wt.% polymeric MDI, followed by 24 hours of curing, led to the disruption of the above structure and turned the solid-like plateau into a viscous flow region.…”

“…In general, addition of clay to bitumen has yielded nanocomposites characterized by shear thinning behaviour at low shear rates, with noticeably increased viscosities with respect to their parent bitumen [3,11,13,15,16].…”