Nanocomposites of comb-like ionic complexes of bacterial poly(glutamic acid) with nanoclays

Nanocomposites made from stoichiometric complexes of bacterial polyglutamic acid with alkyltrimethyl ammonium surfactants and Cloisite 30B were prepared for a wide range of compositions spanning from 3% to 90% of inorganic contents. The TGA analysis ascertained the compositions of the nanocomposites and revealed that their thermal decomposition proceeded through a mechanism similar to that of the complexes. Their structure and nanomorphology were examined by DSC, XRD and TEM which evidenced an exfoliated structure for low contents in Cloisite (less than 10%). Nanocomposites with high Cloisite compositions consisted of mixtures of isolated clay lamellae with stacks of intercalated polyacid-Cloisite layers heterogeneously dispersed in a disordered complex matrix. Both thermal and mechanical properties of the surfactant complexes changed steadily with the increasing amount of added nanoclay. An exceptional mechanical tensile behavior was however observed for the composite containing 3% of Cloisite, which was associated to the occurrence of a fully exfoliated structure.