New types of diblock copolymer silane coupling agents have been investigated as interface modifiers in polymer/inorganic composites. Diblock copolymers composed of polybutadienepolystyrene (PB-PS) and polybutadiene-polydimethylsiloxane (PB-PDMS) have been synthesized with varying molecular mass of the PS and PDMS blocks by living anionic polymerization. The target molecular masses were chosen to be below, around and above the critical molecular mass for formation of entanglements. 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. These analyses showed that the average layer thickness of PDMS block copolymer silanes vary with the molecular mass of the PDMS block when applied to an oxidized silicon wafer from toluene. This variation was not observed for the PS block copolymer silanes. Furthermore atomic force microcopy showed that the PS block copolymer silanes segregate into an island structure on oxidized silicon. 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 which could be below the critical mass for formation of entanglement at the interface. Furthermore microdebond experiments showed that the interfacial adhesion was significantly reduced by exposing glassfiber micro composites to boiling water for 100 hours. 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. The drastic decrease in mechanical properties of the PA66 composites is related to hydrolysis of both the interface region and the PA66 matrix. 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.
|Place of Publication||Roskilde|
|Publisher||Risø National Laboratory|
|Number of pages||161|
|Publication status||Published - 1999|
|Series||Denmark. Forskningscenter Risoe. Risoe-R|