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Polymers 2018, 10(10), 1047; https://doi.org/10.3390/polym10101047

Mechanical Behavior—Microstructure Relationships in Injection-Molded Polyamide 66

1
MINES ParisTech, PSL Research University, CEMEF, CNRS UMR 7635, CS 10207, CEDEX, 06904 Sophia Antipolis, France
2
Solvay Engineering Plastics, Technyl Innovation Center, Avenue Ramboz—BP64, 69192 Saint Fons, France
*
Author to whom correspondence should be addressed.
Received: 28 July 2018 / Revised: 10 September 2018 / Accepted: 17 September 2018 / Published: 20 September 2018
(This article belongs to the Special Issue Mechanical Behavior of Polymers)
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Abstract

Clear relationships between the semi-crystalline microstructure of injection molding polymers and their mechanical behavior are not yet totally established for all polymers. Part of this relative lack of understanding is because an unambiguous scientific approach is difficult to build up. The processing of samples promotes a microstructure which is not uniform and can be described in various ways on different scales. This introduces uncertainty in the correlations. Most completed studies were conducted on polyolefin, which exhibits an evolution of microstructure that is quite easy to observe and to correlate to mechanical properties. This paper intends to illustrate a more diffuse case. To achieve this, combined characterizations along the flow path and throughout the thickness of a plaque as well as characterizations of the local microstructure and tensile behavior of polyamide 66 are described. The microstructure was explored in terms of skin-core structure, spherulites sizes, crystallinity ratio and lamellae organization. Mechanical properties were addressed with non-monotonic tests with the use of DIC (Digital Image Correlation) to assess true behavior. The effect of humidity is also accounted for. It is demonstrated that small changes in lamellae or interlamellar amorphous phase are likely to be responsible for non-uniform mechanical properties, whereas more macroscopic levels (skin core structure, spherulites level of crystallinity ratio) appeared to be irrelevant levels of description. Consequently, the usual simplified analyses based on optical microscopy and differential scanning calorimetry (DSC) can be inefficient in improving knowledge in that field. View Full-Text
Keywords: microstructure; mechanical properties; injection molding; polyamide 66 microstructure; mechanical properties; injection molding; polyamide 66
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Billon, N.; Giraudeau, J.; Bouvard, J.L.; Robert, G. Mechanical Behavior—Microstructure Relationships in Injection-Molded Polyamide 66. Polymers 2018, 10, 1047.

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