Flow marks in injection molding of polypropylene and ethylene-propylene elastomer blends: Analysis of morphology and rheology

Bhaskar Patham, Paul Papworth, Krishnamurthy Jayaraman, Chichang Shu, Michael D. Wolkowicz

Research output: Contribution to journalArticle

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Abstract

This paper reports an investigation of asynchronous flow marks on the surface of injection molded parts and short shots made from two different blends of polypropylene and ethylene-propylene random copolymer elastomers. Flow marks were observed on the surface with both blends; the spatial frequency of flow marks on the surface was greater in the blend B1, which also exhibited a greater contrast between the surface regions. The same blend was distinctly faster in the linear viscoelastic tests of shear creep recovery and shear viscosity growth. The degree of contrast between the flow-mark regions and the out-of-flow-mark regions was examined with a detailed analysis of SEM micrographs of the surface regions as well as the near wall regions from short shots. This revealed that the dispersed phase was highly stretched to cylindrical strands in the glossy surface regions of both blends and retracted in the dull regions to different extents in the two cases. A comparison of the particle size distributions and aspect ratio distributions in different regions established that rapid retraction of the suspended elastomer phase was the dominant cause of changes in particle shape between surface regions. Nonlinear shear creep and creep recovery curves of the two elastomer components showed that at a time of 1 s, the fractional strain recovery of the elastomer in B1 was much higher than that of the elastomer in B2. Hence, the nonlinear elastic recovery of the elastomer phase at short times is an important factor in flow mark formation with blends of polypropylene and olefinic elastomers.

LanguageEnglish (US)
Pages423-434
Number of pages12
JournalJournal of Applied Polymer Science
Volume96
Issue number2
DOIs
StatePublished - Apr 15 2005

Profile

Elastomers
Polypropylenes
Rheology
Injection molding
Propylene
Ethylene
Recovery
Creep
Shear viscosity
ethylene
propylene
Particle size analysis
Aspect ratio
Copolymers
Scanning electron microscopy

Keywords

  • Blends
  • Injection molding
  • Morphology
  • Polyolefins
  • Rheology

ASJC Scopus subject areas

  • Polymers and Plastics

Cite this

Flow marks in injection molding of polypropylene and ethylene-propylene elastomer blends : Analysis of morphology and rheology. / Patham, Bhaskar; Papworth, Paul; Jayaraman, Krishnamurthy; Shu, Chichang; Wolkowicz, Michael D.

In: Journal of Applied Polymer Science, Vol. 96, No. 2, 15.04.2005, p. 423-434.

Research output: Contribution to journalArticle

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