Polyolefin/layered silicate nanocomposites with functional compatibilizers

Polymer nanocomposites containing layered silicates have been considered as a new generation of composite materials due to their expected unique properties attributed to the high aspect ratio of the inorganic platelets. Nevertheless, addition of layered silicates to polyolefins mostly results in phase separated systems because of the incompatibility of the silicates with the non-polar polyolefins. Functional compatibilizers are required to enhance the interactions and alter the structure from phase separated micro-composites to intercalated and exfoliated nanocomposites. Commercial macromolecular compatibilizers (mainly maleic-anhydride-functionalized polyolefins) are most commonly used to improve the interfacial bonding between the fillers and the polymers whereas specifically synthesized functional homopolymers or copolymers have been utilized as well. In this article, we are reviewing a number of investigations, which studied the influence on the composite structure of various parameters like the compatilizer to inorganic ratio, the type and content of the functional groups and the molecular weight of the functional additive, the miscibility between the matrix polymer and the compatibilizer, the kind of surfactants modifying the inorganic surface, the processing conditions, etc. The most important results obtained utilizing maleic-anhydride-functionalized polyolefins are discussed first, whereas a summary is presented then of the studies performed utilizing other functional oligomers/polymers. X-ray diffraction and transmission electron microscopy studies supported by rheology indicate that the most important factor controlling the structure and the properties is the ratio of functional additive to organoclay whereas the miscibility between the matrix polymer and the compatibilizer is a prerequisite.