Crystallization and Mechanical Properties of Glass Fiber Reinforced Polypropylene Composites Molded by Rapid Heat Cycle Molding

Abstract

The crystalline behavior and mechanical properties of PP/GF (glass fibers) composites molded by rapid heat cycle molding (RHCM) and conventional injection molding (CIM) were compared. SEM, DSC and XRD were utilized to study crystallization behavior of PP and PP/GF composites. Furthermore, universal testing machine was employed to investigate the mechanical properties. Results proved that higher degree of crystallinity and larger crystal size can be obtained in RHCM in comparison to CIM. GF can induce more crystal nuclei and then reduce the crystal size due to shear stress which is generated in polymer matrix around fibers. Nucleating agent (NA) has a positive effect on refine grains. The average crystal diameter of PP/NA/30 %GF is about 1.7 µm which is one-tenth of PP/30 %GF (14 µm) in RHCM. XRD tests illustrated that α-form crystal is the main crystal type for PP and PP/GF composites in RHCM and CIM. However, there is a little β-form crystal in RHCM for PP/GF composites without NA. NA accelerates the formation of α-form crystal and restrains the emergence of β-form crystal. The plastic parts obtained in RHCM exhibited higher strength and modulus compared with that obtained in CIM for both tensile and flexural tests.