Methods for improving the performance of silane coupling agents

The use of silane coupling agents in mineral- and glass-reinforced composites is well known. They impart improved initial mechanical properties, but, more importantly, they cause mechanical properties to be retained during the use of the composite. The main cause of loss of mechanical properties is attack of water at the interface. Recent research has focused on imparting more durable bonding of the silane coupling agent to both the polymer and the reinforcement. Improved silane coupling agent systems have been developed by utilizing several techniques: blends of hydrophobic silanes with hydrophilic silanes to give greater hydrophobic character; use of 1,2-bis-(trimethoxysilyl)ethane as an additive to give increased siloxane crosslinking; use of more thermally stable silanes such as phenyltrimethoxysilane and N-[2-(vinylbenzylamino)-ethyl]-3-aminopropyltrimethoxysilane to give increased thermal stability; and the use of a carboxy-functional silane with a carboxy-functional polymer and zinc salt to give ionomer bonds at the interface. The effectiveness of these new coupling agent systems was tested by measuring the flexural strength of composites and the adhesion strength of coatings on inorganic substrates. The results show that composites have increased flexural strength and better strength retention during thermal aging; coatings have greater adhesion strength; there is greater resistance of interfacial bonding to degradation by moisture; and thermoplastic composites have better properties after high shear processing.