Rheological behavior of filled propylene/ethylene copolymers |
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Authors: | Cheng Huang Paula M Wood-Adams Teresa P Karjala Patricia Ansems Jing Li Luminita L Ionescu-Vasii |
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Institution: | (1) Department of Mechanical and Industrial Engineering, Concordia University, 1455 de Maisonneuve Blvd West, EV4.251, Montreal, QC, H3G 1M8, Canada;(2) The Dow Chemical Company, 2301 N. Brazosport Blvd., B-1470D, Freeport, TX 77541, USA |
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Abstract: | A new family of propylene-ethylene copolymers developed by The Dow Chemical Company has narrow molecular weight distributions
for industrial polymers and broad chemical composition distributions. This molecular architecture makes possible high filler
loadings while maintaining good processability. To provide a fundamental understanding of the lower than expected viscosity,
a study of the shear rheological behavior of two series of composites was performed. The composites consist of stearate-coated
calcium carbonate particles suspended in a propylene-ethylene copolymer. The matrix in one series was a new copolymer, and
in the other series, it was a traditional metallocene copolymer. For both systems, the viscosity increases dramatically with
increasing filler loading; however, the viscosity is lower in the case of the composites of the new copolymer. The stearate
coating on the calcium carbonate particles decreases the adhesion of the polymer to the filler surface, allowing particle-matrix
interfacial slip. A high temperature atomic force microscopy study has indicated the existence of ethylene-enriched zones
in the matrix immediately surrounding the particles in the new copolymer. We hypothesize that these high ethylene content
chains around the particle surface enhance particle-matrix interfacial slip resulting in the lower composite viscosity. |
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Keywords: | Multiphase systems Propylene/ethylene copolymers Filled polymers Interfacial slip |
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