Mechanical and Gas Barrier Properties of Polypropylene Layered Silicate Nanocomposites: A Review

Polypropylene owing to its apolar nature suffers from compatibility problems with clay, which is partially polar even after the surface modification with alkyl ammonium ions. To circumvent this limitation, polypropylene nanocompo- sites have been synthesized by using two methodologies: a) partial polarization of the matrix by the addition of low mo- lecular weight compatibilizer which owing to its amphiphilic nature acts towards compatibilizing the polymer and inor- ganic phases and b) by completely organophilizing the clay surface by using filler surface modification with long alkyl chains and with higher chain density. The addition of compatibilizer leads to better filler delamination and better me- chanical performance, however, the modulus decreases after a certain extent of compatibilizer owing to plasticization of matrix. The permeation properties were observed to be affected negatively owing to mismatch of the polar compatibilizer chains with apolar surface modification chains. The second methodology, on the other hand, leads to simultaneous im- provement of mechanical and gas barrier properties. Better organophilization of the filler surface reduces the attractive forces between the platelets further and increases their potential of exfoliation in the polymer matrix. Other advanced sur- face modifications dealing with chemical reactions on the surface of the filler have also been reported to increase the basal plane spacing.