PEREZ Claudio Javier
Injection Molding of Long Sisal Fibers Reinforced Polypropylene. Effects of Compatibilizer Concentration and Viscosity on Fibers Adhesion and Thermal Degradation.
L. M. ARZONDO, C. J PÉREZ, AND J. M. CARELLA
POLYMER ENGINEERING AND SCIENCE
Año: 2005 vol. 45 p. 613 - 613
A two-step process was used to obtain long sisal fiber-polypropylene (SF/PP) reinforced thermoplastic composites, using maleic anhydride grafted polypropylene (MA-g-PP) as a compatibilizer. At a first stage, modified polypropylenes (mPP) were used for an extrusion impregnation process, for the preparation of composite pellets containing about 70 % (w/w) of SF. SF/mPP pellets with large aspect ratio were prepared by continuous extrusion impregnation of a continuous SF yarn, using a single screw extruder and an adequate impregnation die. The mPP used were maleic anhydride grafted polypropylene (MA-g-PP) and regular polypropylene (PP) modified by reaction with different amounts of an organic peroxide. The composite pellets were thus dry blended with regular PP pellets in an injection machine hopper, and injection molded to obtain composite tensile specimens with a minimum quantity of modified polypropylene, minimum fiber breakage and thermal degradation, and excellent mechanical properties. It is shown that the fibers breakage is reduced to a minimum, even for recycled composites, due to the presence of the low-viscosity polymer layer wetting the SF fibers. The bulk composite effective viscosity and the fiber breakage extent and thermal degradation during the injection-molding step are found to be closely related. Blending with much less expensive mPP at the impregnation stage optimizes the amount of expensive MA-g-PP.