# Bitumen and Bitumen Modification: A Review on Latest Advances
## 3 Bitumen Chemical Modifiers
### Nanocomposite Modifiers
3) Melt intercalation method: this involves an annealing process, statically or under shear, of a mixture of the polymer and an organically-modified layer silicate (OMLS) above the softening point of the polymer. This method has great advantages over the other two. First, it is environmentally benign due to the absence of organic solvents. Second, it is compatible with current industrial process. The melt intercalation method allows the use of polymers which were previously not suitable for in situ polymerization or solution intercalation. In several studies, clays were used as compatibilizer agents in polymer blends. In this respect, clay localizes at the interfacial bitumen-polymer region reducing the interfacial tension. As a consequence, the \"minor phase-dispersed\" particles lose the typical rounded shape they possess in the pure polymer blends, and a finer dispersion is obtained [204; 205; 206; 207; 208; 209; 210; 211; 212; 213]. Based on this fact, the studies have been focused mainly on their effects on the compatibility between bitumen and polymers. As the results have shown a considerable increase in the bitumen/polymer compatibility, it has been suggested that using ternary bitumen/polymer/clay (BPC) systems, the PmB's performances may be improved. In particular it has been claimed that the use of PLS in PmBs has mainly two effects: (1) improving the aging resistance of PmB with barrier properties of the dispersed clay platelets and (2)  
Figure 10: Illustration of three different types of polymer/layered silicate nanocomposites (reprinted from [199] with the permission of Elsevier). enhancing the storage stability of PmB by decreasing the density difference between polymer modifiers and bitumen [68]. The bitumen-Polymer-Clay Ternary System  
Among the three preparatory methods of PLS described above, melt intercalation is the one that can be easily applied to bitumen modification due to its compatibility with current industrial processes and with all types of thermoplastic polymers. Bitumen, polymer, and clay can be mixed in a single step known as physical mix (PM) (see Figure 11). Otherwise, two consecutive steps could be employed: (1) nano-composite preparation and (2) addition to a bitumen. Globally, the process is known as master batch (MB). The use of one (PM) or the other (MB) method is very important and can give different results. These two methods were applied and studied in different research works, in which different polymers and clays were reported for the production of bitumen/polymer/composites (BPC). SBS and kaolinite [132], SBS and organobertonite [214], poly(styrene-b-ethylene-b-butene-b-styrene) (SEBS) and kaolinite [133], and LDPE or EPDM and silica [134] were the primary compounds which have been studied. In all the previously reported cases, different ratios of polymer-clay nanocomposites were firstly prepared and successively added to bitumen. Storage stability, blend morphology, and mechanical and rheological properties of the BPCs were characterized. Tube tests to evaluate the storage stability of the blend were made. In all cases, storage stability was observed. To justify these results, it has been hypothesized that clays tend to reduce the density gap between the polymer rich phase (PRP) and bitumen asphaltene rich phase (ARP) by locating themselves preferentially in the PRP phase. However, this was not directly supported by experimental evidence. In this respect, the recorded values of softening points are certainly consistent with this interpretation being considered as evidence. [PERSON] et al. [133] lists the softening points of the top and bottom sections of the tube test for the bitumen/SEBS/kaolinite mixes (see Table 3). As can be seen from Table 3, for a given SEBS content, the \(\Delta\)S parameter whose magnitude is indicative of the blend stability (higher magnitude equals lower stability), decreases as clay content increases.