Effects of preferential encapsulation of glass fiber on the properties of ternary GF/PA/PP blends

Long fiber molding materials are expected to play an important role in the near future. This paper describes a series of experiments performed to exam ine properties of ternary blends containing glass fiber (GF), polyamide (PA ), and polypropylene (PP). The continuous glass fiber was impregnated with one of the blend constituent polymers by our specially designed impregnatio n apparatus and cut into chips of 6 mm length. These chips and the other po lymer were used to produce various testing specimens in a twin screw extrud er or in injection molding machine. The results indicated that the effect o f fiber addition on the mechanical and rheological properties is clearly de pendent on the order of impregnation process. In the blends containing the GF/PA + PP, the GFs are preferentially encapsulated with PA, and therefore the mechanical properties are superior to the blends with the GF/PP + PA in which the PP phase is located surrounding the GFs. This improved wetting o f fibers by sequential impregnation not only resulted in better properties but also protected the fibers from shear action of the screw, thereby allow ing significant increase in average fiber length to be achieved in the inje ction molding process.