Rheological Comparison of Chemical and Physical Blowing Agents in a Thermoplastic Polyolefin

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This article describes an investigation into the effects of foaming on the electrical conductivity for a carbon-filled cyclic olefin copolymer (COC) composite incorporating both chopped carbon fibers (cCF) and carbon black (CB). Foamed and solid samples were injection molded and then analyzed for cell size, fiber length, fiber orientation, and electrical conductivity. Foamed samples exhibited higher electrical conductivity in the through-plane direction for materials containing only CB or composites containing both filler types, and reduced electrical conductivity in the cCFfilled composites. The increased electrical property gained by foaming was attributed to multiple percolation with CB aggregates forming more effective conductive clusters and networks in the continuous polymer phase during growth of the gas domains. A mechanism for the phenomenon was proposed based on these experimental observations.

Section: Hybrid Carbon Fiber/cb-coc Compositementioning

confidence: 71%

Multiple percolation in a carbon‐filled polymer composites via foaming

Thompson

Motlagh

Oxby

et al. 2009

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“…Since gas is dissolved in the melt the flow behavior is positively influenced which is reflected by a reduction of the melt viscosity by 50% and more, depending on materials, gas content, and conditions. [5][6][7] At the same time, the engineering effort for process management is increased. Numerous properties of foamed parts can be improved (e.g., thermal 8,9 or acoustic 10 insulation, shrinkage and warpage 11 etc.)…”

Section: Introductionmentioning

confidence: 99%

Influence of process parameters on mechanical properties of physically foamed, fiber reinforced polypropylene parts

Kastner

Steinbichler

Kahlen

et al. 2018

Due to the high complexity of the foaming technology, the relationship between processing and final properties of parts produced is not completely understood. Investigating the causality chain Processing–Morphology–Properties is of great importance, especially for the automotive industry, in order to be able to tailor the mechanical properties of foamed parts. This article examines and qualifies the effects of seven process parameters (melt/mold temperature, degree of foaming, injection speed, delay time, gas content, and back pressure) on biaxial bending and flexural behavior—the predominant deformation mechanisms in interior automotive applications—of foamed plaques, using the MuCell process. The results clearly show that three major factors (mold temperature, degree of foaming, and delay time) have significant impact on the mechanical properties of the foamed parts. For a clear understanding of these interactions, computed tomography scans of certain plaques are correlated to process parameters and mechanical performance. This article should forge a bridge between production and performance. © 2018 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47275.

“…Looking at the highest flow rate where the differences are most clearly seen in the figure, the powder CBA demonstrated only a weak concentration effect while the masterbatch CBA yielded a stronger influence on the pressure drop as its concentration was increased. The difference in the pressure drop gradient shown by the glass‐fiber‐filled polypropylene when compared with the pure polymer could not be attributed directly to the foaming additive, since the phenomenon was not previously observed with either a homogeneous LDPE16 or a heterophasic TPO18 using the same masterbatch CBA. Rather, we suggest that the variation observed for the rheological behavior of the composite is attributed to the impact that the CBA had on the mechanism of glass fiber breakage, an influence which was different based on the type of CBA used.…”

Section: Resultsmentioning

confidence: 86%

“…Both the gas and carrier resin have been shown to lower the shear viscosity of the melt, which would lower the shear stresses transmitted to the fibers during processing and reduce the extent of fiber breakage 6. The plasticizing effect of dissolved gas in a molten polymer has been repeatedly reported7, 16, 18, 20, 21 (also evident in Fig. 1); however, the fact that fiber breakage occurred to almost the same extent for any concentration of the powder CBA as the nonfoamed sample suggests that the influence of the gas was minor in comparison with the lubricating effect of the carrier resin or possibly there was a synergistic interaction between the gas and carrier.…”

Section: Resultsmentioning

confidence: 99%

“…It has been shown in earlier studies16–18 that the plasticizing effect of a blowing agent on a polymer reduces the viscosity without affecting other material behavior such as its shear‐thinning nature. However, for the present gas–polymer solutions which included glass fibers, the above‐mentioned description does not appear to properly fit the observed rheology.…”

Section: Resultsmentioning

confidence: 99%

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

Thompson

Zhang

Hrymak

2006

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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.