Gas-assisted Injection Molded Polypropylene/Glass Fiber Composite: Foaming Structure and Tensile Strength

Abstract

Tensile strength of isotactic polypropylene (iPP)/glass fiber (GF) composites and neat iPP molded respectively by gas-assisted injection molding (GAIM) was examined. For comparison, tensile strength of the counterparts, which were molded by conventional injection molding (CIM) under the same processing conditions but without gas penetration, was also examined. Tensile strength of the CIM parts steadily increases with the increase of the GF content. For neat iPP molded by GAIM, as the gas pressure increases the tensile strength increases. However, for the iPP/GF composites, the tensile strength generally decreases when the gas pressure increases. And, at a given content of GF, tensile strength of the parts molded by GAIM is unexpectedly lower than that of the counterparts molded by CIM. At a given gas pressure, the higher the fiber content, the lower the tensile strength. In addition, scanning electron microscope (SEM) results show that foaming structure should be responsible for the poor tensile strength of the composites molded by GAIM. The poor adhesion between the glass fibers and the matrix and the unique properties of the gas used in GAIM process are the substantial factors in the formation of foaming structure.

Microcellular injection molding of polypropylene and glass fiber composites with supercritical nitrogen

“…13,14 Gas-assisted injection molding, as a ripe technology, has been used in producing molded parts of PP-GF composites. [15][16][17] Gas channel provides the possibility for the structural reinforcement, which is an effective improvement of the mechanical properties of molded parts.…”

Simulation of the gas-assisted injection moulding process using a viscoelastic extension to the Cross-WLF viscosity model

“…where is density, C p the specific heat capacity, and the thermal conductivity. Concentration convects with the flow according to equation (2). As the concentration, c, progresses, it is normally clipped to 0 or 1 (whichever is nearest) except in the case when the contour of 0.5 passes through the element is considered; this case is easy to identify for linear elements as there will be at least one nodal value of concentration above 0.5 and at least one below 0.5.…”

“…Structural rigidity and dimensional stability are also good compared with conventional injection moulding (CIM) [1]. Tensile strength has been shown to benefit from low gas pressures (GPs) [2] and the factors affecting gas penetration have been analysed [3]. Many attractive features of GAIM in polymer processing has led to the development of GAIM for rubber processing [4].…”