Strengthening of polypropylene–glass fiber interface by direct metallocenic polymerization of propylene onto the fibers

This work deals with the development of a new approach to improve the interfacial adhesion and properties of polypropylene–glass fiber composites. The chemical anchoring of the matrix polymer on glass fibers was improved by direct metallocenic polymerization of propylene onto the fibers surface. The experimental route involves an initial contact with methylaluminoxane (MAO) and hydroxy-α-olefin to generate the anchorage points on the fiber surface, followed by a propylene polymerization catalyzed by EtInd2ZrCl2 (metallocene)/MAO. During the polymerization reaction, polypropylene chains grow on the glass fiber surface. This reaction was studied for different hydroxy-α-olefin concentrations and its effectiveness was characterized by scanning electron microscopy (SEM) with X-ray disperse energy microanalysis. An evaluation of the fiber–matrix interfacial shear strength (ISS) was performed by single-fiber fragmentation tests on model composites. Depending on the hydroxy-α-olefin concentration, the surface treatment induced an increase of the ISS with respect of the untreated fibers by a factor ranging from 1.7 up to 2.1. The improved interfacial adhesion level was also confirmed by SEM observations of the morphology of the fiber–matrix region of cryogenic-fractured surfaces of composites.