Phenol-modified polypropylenes as adhesion promoters in glass fiber-reinforced polypropylene composites

This publication is based on research work done on functional phenol-modified polypropylenes (PPs) as adhesion promoters in glass fiber-reinforced PP composites. The glass fiber roving was first impregnated with different combinations of functional polymers and polypropylene in a melt impregnation die attached to an extruder to obtain prepreg. The prepreg was then tested in many ways both macro- and micromechanically. The tests included notched tensile tests, optical and electron microscopy, and DMTA (dynamic mechanical thermal analyzer) and DSC (differential scanning calorimetry) analyses as well as determination of the glass content. The tests were run on prepregs containing pure PP, PP with a commercial adhesion promoter, and PP with a number of functional, mostly phenol-based, polymers. Also, single-fiber tests were performed on individual glass fibers to test the level of adhesion with the above-mentioned material combinations. With these tests it could be seen that some of the phenol-based functional polymers provided the prepreg with better adhesion between the fibers and the matrix than did the commercial adhesion promoter. Optical and electron microscopy also were used in determining the level of adhesion as well as the deformation and fracture mechanisms of the prepreg.