A Rheological Approach to the Analysis of Plastication Influence on Fibers Breakage of LGF-filled Polypropylene

Long glass fiber-filled polypropylene composites are widely used in industry because of their low cost and high performance. To investigate the rheological properties of such composites in the molten state an in-line slit-die rheometer was developed and mounted on an injection molding machine. The shear viscosity of filled PP determined by the in-line rheometer was found to strongly depend on the fiber length distribution. In particular, a linear correlation was determined between the viscosity at a constant temperature and shear rate and the average fiber length equation proposed by Huq and Azaiez. The developed model and the in-line rheometer were then used to assess the effects of the main plastication parameters (i.e. screw rotation speed and backpressure) on fibers damage. The experiments were carried out according to a central composite design and optimal plastication conditions were determined by means of the response surface method.