Ultra-Dispersed Powders Produced by High-Temperature Shear-Induced Grinding of Worn-Out Tire and Products of Their Interaction with Hot Bitumen

Abstract

Structural features of crumb rubber (CR) particles obtained by grinding on rollers and ultra-disperse powder elastomeric modifiers (PEM) obtained by high-temperature shear-induced grinding (HTSG) of CR or co-grinding with butadiene styrene thermoplastic elastomer (SBS) have been studied by electron and optical microscopy methods. Samples of modified bitumen were obtained at different mixing times (1–40 min) in a wide temperature range (120–180 °C). The products of interaction of PEM with hot bitumen precipitated on filters when washed with solvent from modified bitumen (MB) were studied by scanning electron microscopy (SEM). The self-similarity PEM particles and PEM breakdown fragments in bitumen up to the size of 100–200 nm were noted. The rapid (for 1 minute) decomposition of PEM particles into fragments is shown, which is due to the specific structure formed as a result of HTSG. It has been suggested that this fragmentation may be caused by bitumen penetrating deep into the porous particle and breaking it, due to differently directed swelling pressure and precede the classical swelling associated with the penetration of solvent between rubber macromolecules, or occur concurrently with it.

Mechanism of Multi-Stage Degradation in Hot Bitumen of Micronized Powder Elastomeric Modifiers from Worn-Out Tire’s Rubber

“…In our opinion, the separation of such films occurs as a result of multidirectional swelling forces from the surface of microblocks with a denser structure than others. In our opinion, these images have similarities with the fragments of APDDR particles in the form of films observed earlier using electron scanning microscopy [ 17 ]. Figure 6 b shows a three-dimensional image of the MB surface, from which we can see that the film is partially located on the bee structure.…”

“…One such fragment is shown in Figure 5 c,d. The appearance of these fragments correlates very well with SEM images of the APDDR fragments [ 17 ]. Elements of an agglomerative structure are also traced.…”

“…Smaller fragments of the original APDDR particles of 100÷1000 nm are clearly visible in Figure 3 . Similar particles of the same size and similar (self-similar) agglomerative structure were observed in SEM images after washing the MB with solvent [ 17 ].…”

“…According to electron microscopy data, a PEM particle is an agglomerate of micron- and submicron-size blocks, connected by strands of different thickness (from several nanometers to several microns). According to atomic force microscopy data, the structure of PEM particles can be defined as having a strong phase heterogeneity (at the level of 0.1–0.2 μm or even less) [ 16 , 17 ].…”

“…Previously, the method of electron scanning microscopy (SEM) showed that after the solvent washing of binders prepared by mixing bitumen with PEM for 1–40 min in the temperature range 120–180 °C, fragments of PEM in the form of particles up to 100–200 nm or in the form of micron-sized thin films were observed [ 17 ]. However, it is important to test the presence of such fragments in the modified bitumen.…”