Aspects of foaming a glass‐reinforced polypropylene with chemical blowing agents

Abstract

This work explores the influence of a chemical blowing agent on different aspects of producing a short glass-fiber-reinforced polypropylene foam, examining the rheology of the system, the developed morphology of the part, and the resulting mechanical properties. Two different forms of an endothermic blowing agent, namely powder versus masterbatch, were compared to determine their effects on the process history and properties of an injection molded part. Samples were produced on an injection molding machine between 230 and 2708C using the low-pressure foaming technique. Rheology of the resulting plasticized melt by the two different blowing agents was measured on an in-line rheometer, showing a greater reduction in shear viscosity for the masterbatch additive, which correspondingly reduced the extent of fiber breakage observed. The final molded samples were analyzed for their foam structure (i.e., cell size, cell density, and skin thickness) as well as the properties of the glass fibers incorporated (namely, fiber length distribution). Tensile properties were found to diminish with increasing blowing agent content, though differences were observed based on the type of CBA used despite the similarities in foam structure produced.

Improved through‐plane electrical conductivity in a carbon‐filled thermoplastic via foaming

“…A low injection flow rate condition likely resulted in foam flow during mold filling (i.e. bubbles were nucleated and grew as the material filled the cavity) [12]. It is thought that the driver for fiber reorientation was the shear forces acting upon a fiber once being pushed out-of-plane by adjacent bubble growth.…”

“…Besides improving through-plane conductivity, foaming offer many advantages and disadvantages which must be considered by the user [11,24]. For filled composites like our material, the plasticizing effect of dissolved gases generated by blowing agents will certainly be viewed as a positive during processing, though the reduction of mechanical properties will need to be considered in material selection [12].…”

“…1, though Wilson never reported experiments to prove his theory. He speculated that bubble growth in close proximity to a fiber would result in outof-plane reorientation; though such circumstances are not easily achieved since it is known that the glass fibers in composite do not act as nucleating sites during foaming [11,12]. Yang et al [13] prepared carbon nanofiber-polystyrene composites by solution casting and found that the foam composite had a similar conductivity and percolation threshold to its solid composite counterpart.…”

Effect of Weld Lines on Injection Moulded Fibreglass Reinforced Structural Foams. 1 - Morphology, Shear and Tensile Properties

“…Several papers have been published on the general subject of composite structural foams (7)(8)(9)(10)(11)(12) . Unfortunately, most of them do not report a complete morphological and mechanical characterisation of the foams produced.…”

Solid‐state foaming of isotactic polypropylene and its composites with spherical or fibrous poly(butylenes terephthalate)

“…To improve the foamability of PP, carbon nanofibers, carbon nanotubes, glass fibers, or wood fibers were added to raise the melt strength and enhance the heterogeneous nucleation during the PP foaming . Much more uniform cells and higher mechanical properties were found in PP foam with carbon nanofibers .…”