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Since the introduction of injection moldable Long Fiber Reinforced Thermoplastic (LFRT) composites, continued improvements in both manufacturing technology and processing methods, mechanical performance has dramatically improved. Notably, the step increase in multi- axial impact has significantly differentiated these long glass fiber composites from short glass fiber materials and can place the impact performance commensurate with glass mat thermoplastics (GMTs). This paper will focus on the improvements in mechanical performance of polypropylene, polyamide, and polyphthalamide long glass fiber systems. Specific processing parameters as well as improved screw and tool designs have contributed and will be reviewed. These thermoplastic composites fit many processing modes in addition to injection molding.

A study has proven that by utilizing the injection compression molding (ICM) technique, mechanical properties of long-glass-fiber-reinforced polypropylene (LGFR-PP) are significantly enhanced compared to properties obtained employing standard injection molding (SIM). The ICM technique preserves the initial 11-mm long fiber glass lengths, allows lower injection pressures, reduces molded-in stresses, provides less warpage, and improves weldline strength. This study involved injection compression molding 1.5-mm and 3-mm thick plaques from 30%, 40% and 50% long-glass-fiber-reinforced PP, using SIM as the control. Tensile strength, flexural strength, and flexural modulus values, in both the flow and transverse direction, were generated on specimens cut out and machined from the respective plaques. Falling dart instrumented impact energies were also acquired. Greater benefits were realized at the thinner 1.5-mm substrate thickness. Falling weight impact energies were 25 to 45% higher.