Effect of CEC coverage of hexadecyltributylphosphonium modified montmorillonite on polymer compatibility

Abstract

The present work was aimed to investigate polymer compatibility of hexadecyltributylphosphonium bromide (HDTBPh) modified Na-montmorillonite (Na-Mt) at different cation exchange capacity (CEC) coverages. The Na-Mt was modified at five different CEC coverages in the range of 60%-150%. The morphology, porosity, and thermal and surface properties of HDTBPh in Na-Mt interlayer were investigated. The intercalation behavior of HDTBPh investigated by X-ray diffractometry showed that the door-value reached a maximum of 23.4 angstrom at 125% CEC coverage. The specific surface area (SSA) and porosity were investigated by N-2 adsorption at -197 degrees C temperature. The SSA decreased from 57.19 m(2)/g to 24.11 m(2)/g at 150% CEC coverage, as opposed to the porosity which increased upon interaction with HDTBPh and led to a more open structure. The thermal stability, investigated by themogravimetry (TGA), slightly decreased with increasing CEC coverage. The CEC coverage of HDTBPh was found to play an important role in the clay-polymer compatibility. A simple acid-base approach involving the calculation of total energy of interaction between Na-Mt surface and polymer surface (Delta G(clay)(IF)/(poiymer/clay)) was developed to evaluate the clay-polymer compatibility. While the positive value of Delta G(clay/Polymer/Clay)(IF) indicated the clay-polymer compatibility, the negative value was ascribed to no polymer compatibility. The calculated value of Delta G(clay/Polymer/Clay)(IF) was critical for proper selection of CEC coverage for each polymer.