Clay exfoliation in polymer nanocomposites: Specific chemical reactions and exchange of specialty modifications on clay surface

Abstract

Due the synergistic improvement in properties, which are better than the individual constituents, polymer nanocomposites have been the subject of intensive research. Surface modification of the filler is necessary to enhance its compatibility with the polymer phase and, hence, achieve nanoscale delamination in the polymer matrix. However, conventional alkyl ammonium surface modifications are only suitable for polar polymers and do not lead to exfoliated nanocomposites with non-polar polymers, such as polyolefins. In the absence of any positive interaction between the filler and polyolefin matrices, it is only the higher basal plane spacing of the filler which can lead to its delamination during shearing with the polymer. However, it is not easy to achieve very high basal plane spacing using conventional surface modifications. It requires specific methods or specialty surface modifications, which can lead to a higher amount of organic matter in the clay interlayers and, thus, higher basal plane spacing or reduced forces of attraction. These include synthesis of long chain length surface modifications, chemical reactions with the reactive surface modifications on the filler surface or polymerization reactions on the filler surface to graft polymer chains, etc. In addition, physical adsorption of the polymer chains or other organic molecules on the surface of pre-modified clay can also lead to its uniform organophilization, which again reduces the forces of attraction between the clay platelets.