# Bitumen and Bitumen Modification: A Review on Latest Advances
## 3 Bitumen Chemical Modifiers
### Nanocomposite Modifiers
Moreover, for the sample of 4% SEBS this difference become negative indicating that the Polymer Rich Phase (PRP) migrates toward the bottom of the tube. At high clay contents, negative values for the \(\Delta\)S were obtained. This could be explained by considering that the polymeric rich phases become heavier than the asphaltenic rich phase (ARP). A balance of PRP and ARP densities obtained at well-defined clay amounts, inducing a storage stability. An LDPE-modified bitumen also has shown a similar effect [134]. However, storage stability is not simply due to a decrease in density difference  
Figure 11: Schematic representation of the two mixing processes: physical mix and master batch (reprinted from [46] with the permission of Elsevier). between the PRP and ARP phases. Several studies have shown that compatibility between bitumen and polymer also plays a fundamental role [215]. Therefore, the improved storage stability can be ascribed mainly to two factors: decrease in density difference between the PRP and ARP phases and, to a greater extent, to a real bitumen/polymer compatibilizing effect. Furthermore, the preparation procedure also plays an important role. As can be seen from Table 3, the only mix found unstable during the high-temperature storage was prepared using the PM method. This, in accordance with the idea that the clay resides preferentially in the PRP leads to a conclusion that only with a pre-formed nanocomposite storage stabilization could it be achieved. This point was confirmed by other researchers who studied different systems, such as a styrene-butadiene rubber (SBR) with a palygorskite- and organo-modified palygorskite clays [216]. This paper studied the storage stability of the blends and the importance of the preparation procedure. [PERSON] et al. [136] investigated the internal structure and nanocomposite nature of the blends. In this research a neat bitumen (NB) and SBS were modified with OMMT (Loisite 20A, referred to simply as 20A) through melt mixing, obtaining two blends of bitumen/clay and polymer/clay: (1) SBS/20A, (2) NB/20A. Ternary blends were then prepared using both PM and MB methods: (3) NB/SBS/20A PM, and (4) NB/SBS/20A MB. Figure 12 reports the X-ray diffractometry (XRD) characterization, which was performed on virgin materials (bitumen, polymer, and clay) and blends. A comparison between the binary blend NB/20A and the 20A alone shows that the clay's interlayer spacing almost doubled. This was attributed to bitumen intercalation. A partial exfoliation of the stacks can also be seen. Moreover, storage tests showed the absence of phase separation, confirming a high degree of interaction between NB and 20A. As shown by the XRD pattern, intercalated nanocomposites were also obtained in the SBS/20A binary blends. The interlayer spacing was found to be independent of the clay quantity, but it was lower than that of NB/20A blends. This suggests that the clay had higher compatibility with the bitumen compared to the polymer. Regarding ternary blends, XRD patterns show that both mixing processes (PM, MB) give intercalation with interlayer spacing equal to that obtained by mixing bitumen and clay without the polymer. This may indicate that the degree of intercalation is substantially determined by the bitumen molecules and is independent of the mixing sequence. This could be explained by considering that the polymer chains are present in a very small amount compared to the bitumen molecules and they interact with a limited amount of clay stacks. Therefore, polymer chains, even if already intercalated between some of the clay platelets, are not expected to inhibit the interactions between clay and the small and abundant bitumen molecules. On the contrary, the ability of the