Entrance flow of long glass fiber reinforced polypropylene through contraction die

Abstract

The entrance flow of long glass fiber reinforced polypropylene has been studied. It is demonstrated that longer glass fibers are easier to break and accumulate at the entrance. As the length of the die and shear rate increase, the fiber breakage increases for long glass fiber reinforced polypropylene. Comparison of fiber breakages of long and short glass fiber reinforced polypropylene indicates that short glass fiber mainly breaks before and at the entrance and remains almost unchanged in the die, while longer glass fibers still break after the entrance within the die. It is demonstrated that fiber accumulation increased when increasing the length of the die and shear rate. The pressure is found to oscillate at the entrance and this pressure accumulation and release should be related to the fiber interactions and fiber breakage at the entrance. It is also found that the presence of long glass fibers would lead to significantly higher viscosity which would decrease when increasing the shear rate.