2018 Volume 67 Issue 4 Pages 424-429
The purpose of our study is to investigate the influence of fiber breakages of recycled carbon fibers at pelletizing on a tensile strength of the composite. The recycled carbon fibers used in this study were obtained by extracting from a wasted prepreg by pyrolysis method in a muffle furnace under air condition at 600℃ for 30, 90 and 180 min, respectively. It was confirmed, at first, the tensile strength was reduced since tiny flaws on the carbon fiber were induced due to oxidization in a recycling process. Recycled carbon fibers were compounded with PP (polypropylene) resin by twin extruder machine where the conditions of the barrel temperature and screw rotation were changed. A specific mechanical energy (SME) for extruding unit mass of compound was introduced by monitoring the rotational torque and the revolutions of the extruder machine, in order to discuss the changes of residual fiber lengths in pellets. Master curve was prepared to show the relation between residual mean fiber length in the pellet and the SME, considering the change of strength of the single recycled carbon fiber. It seemed that the shift factor was related with the fiber stress on the fiber at the extrusion. Residual mean fiber length in the molded specimen was also predicted where a mechanical model proposed was referred considering the master curve for calculating the strengths of composites with chopped recycled carbon fibers. The estimated strengths in this study well agreed with experimental data.
