Organisch modifizierte Schichtsilicate als thermische Polymerisationsinitiatoren für die Darstellung von Nanokompositen auf Basis von Epoxiden

Abstract

Montmorillonite containing minerals with exchangeable sodium ions are available in large quantities. By exchanging the sodium ions for cationic tensides the surface of the silicate layers becomes organophilic and the distance between the silicate layers the gallery distance increases from 1 nm to about 1.8 nm. Due to this modification the silicate layers can be distributed into a polymeric matrix yielding nanocomposites. If epoxy resins are used as the matrix, the exfoliation of the layered silicate creates polymer clay nanocomposites with improved properties compared to pure epoxy resins or conventional composites. It has been reported in the literature that the diglycidyl ether of bisphenol A undergoes self-polymerization when heated with acidic onium ion exchanged forms of montmorillonite. However nanocomposite formation is accomplished through a dramatic transition from gel state to a dry powder with a very low bulk density. During the thesis two solutions were developed to prevent the rapid liquid to powder transformation and it is now possible to obtain cured transparent epoxy resin based nanocomposites without adding any further hardener. Both methods control the balance between the extragallery reaction rate of the epoxy system and the diffusion rate of monomers into the galleries, which affects the innergallery reaction rate. One possibility is to use the influence of additives for improving the diffusion rate of low viscosity epoxy resins. The other approach leads to a new structure of the ion exchanged montmorillonite. This new structure improves the diffusion of monomers into the galleries and leads to cured and transparent nanocomposites without any further additive or hardener. The organophilic clays and the formed polymers were studied by DSC, TGA, EDX, SEM, XRD and TEM.