Abstract

A glass fiber sizing composition for the reinforcement of resin matrices is provided which comprises a homogeneous aqueous composition of two polyester resins. The first polyester resin is a water solubilized condensation cross-linkable, polyester resin, insoluble in aromatic solvents. The second polyester resin is insoluble but dispersible in water but insoluble in the first polyester resin. Thus, when the second polyester is blended with a water solution of the first polyester, a dispersion is produced. In this dispersion the water and the first polyester form the continuous phase and the second polyester forms the dispersed phase. A plasticizer and two silane coupling agents are also incorporated into the sizing composition. The first coupling agent is provided to promote adhesion between the glass fibers and the resin matrix and the second silane coupling agent is employed in the sizing composition to control the wetting of the glass fibers by the first silane coupling agent. A thermoplastic polymer of sufficiently low molecular weight is employed to impart pressure sensitive adhesive characteristics to the sizing composition. Glass fibers sized with the sizing composition of the invention have found particular utility when incorporated into resin matrices which are utilized as molding compounds.