Influence of Reinforcement Volume Fraction on Fibers Length Reduction in Injection Molding of LGFRT

xLong glass fiber-filled polypropylene composites are widely used in industry because of their low material and production cost combined with excellent mechanical performances and lightness. Mechanical properties of the parts, in particular elastic modulus, strength and impact resistance, strongly depend on the volume fraction of the reinforcement, on the average fiber length and on its distribution and orientation. During the processing of fiber-reinforced thermoplastics, such as in extrusion and injection molding, fibers are subjected to breakage, reducing the average fiber length. The phenomena governing the fiber degradation are very complex to analyze since both materials properties and process parameters play a key role in the fiber fracture mechanisms, which can be divided into three categories of interaction: fiber-fiber interactions, fiber – polymer matrix interactions, and fiber collision with the manufacturing system. The aim of this study is to analyze the influence of the reinforcement volume fraction on the residual fibers length during injection molding. Experimental tests in different process condition were conducted on an injection molding machine, in order to determine the lower degradation induced on the fibers with the increasing of the reinforcement volume fraction. The traditional measurement procedure, that is limited by the field of view of the optical CMM used, was improved in order to measure even the longer fibers. The application of image mosaic techniques allowed to merge different images, bypassing the limit imposed by the instrument.