Effects of Process Parameters on Fiber Length Fiber Orientation Air Trap and Tensile Strength of Injection-Molded Long-Glass-Fiber-Reinforced Polypropylene

Abstract

Long-fiber-reinforced thermoplastics (LFRTs) provide better mechanical performance than their short-fiber-reinforced counterparts However it is not an easy job to injection molding LFRTs since the fibers would be damaged when the LFRTs material is moving through a plastication screw Besides that fibers are also possible to be damaged when polymer melt moving through mold cavities because of gate runner or cavity designs Thus maintaining long fiber during injection molding process is a challenge job This research used a novel design of LFRTs injection molding machine which was developed to have the capability to injection molding LFRTs and maintain fiber length during the molding process However it was found that besides machine and cavity design different molding process parameters would also affect the fiber length fiber orientation air trap and mechanical properties of LFRTs parts Thus this paper is intended to study the influence of key processing parameters such as back pressure screw speed and melt temperature of injection molded LFRTs parts on their mechanical properties Image processing technics such as optical microscope and CT scan were used to identify the fiber length fiber orientation and air traps etc Tensile material test system was used to measure the tensile strength of the parts Different melt paths were designed to count the influence of cavity design on the mechanical performance of the parts The results showed that high screw speed and back pressure could damage and shorten the fiber length in the injection molded parts Higher melt temperature would decrease the viscosity of the polymer melt and increase fluidity thus better the mechanical performance of the parts It was also found that parts at different mold cavity locations would exhibit different mechanical properties Although the prediction of the mechanical properties of LFRTs parts is a complicated job the results obtained from this research can provide a guidance for future development of LFRTs parts

Date of Award	2019
Original language	English
Supervisor	Sheng-Jye Hwang (Supervisor)