Modification and Characterization of the Interface in Polymer/inorganic Composites

Abstract

New types of diblock copolymer silane coupling agents have been investigated as interface modifiers in polymer/inorganic composites. Diblock copolymers composed of polybutadiene-polystyrene (PB-PS) and polybutadiene-polydimethylsiloxane (PB-PDMS) have been synthesized with varying molecular mass of the PS and PDMS blocks by living anionic polymerization. These polymers have been catalyticly hydrosilylated with triethoxysilane to form diblock copolymer silane coupling agents. The investigation has involved a number of surface analytical techniques such as wet chemical analysis, Fourier transformed infrared spectroscopy with different sampling techniques, X-ray photoelectron spectroscopy, ellipsometry, atomic force microscopy and contact angle measurements. Investigations of the interfacial adhesion have been done by JKR-measurements and single fiber microdebond experiments. The investigations showed that the synthesized diblock copolymer silanes perform well as adhesion promoters between SiO2 and a polymer matrix equal to end block of the silane. The measurements showed no increase in interfacial adhesion by increasing the molecular mass of the end block up to 100 kg/mol.

This work also included a study of hydrothermal stability of state of the art glassfiber reinforced polyphenylensulfide (PPS) and Poly(Hexamethylene adipamide) (PA66) composites. The materials were exposed in water at different temperature and pH values up to more than one year. Measurement of various mechanical properties in combination with electron microscopy showed the primary mechanism for reduction of mechanical properties was hydrolysis of the interfacial region. Furthermore gel permeation chromatography showed extensive reduction of the molecular mass of PA66 as a result of exposure in hot water. Hydrolysis of the interface region is still the main problem in thermoplastic glassfiber composites. Diblock copolymer silanes show potential as coupling agents for such systems but they must be optimized for hydrolytic stability. This work presents the tools for such an optimization.