TY - JOUR

T1 - Morphological characterization of semi-crystalline POM using nanoindentation

AU - Christöfl, Petra

AU - Czibula, Caterina

AU - Seidlhofer, Tristan

AU - Berer, Michael

AU - Macher, Astrid

AU - Helfer, Eric

AU - Schrank, Theresia

AU - Oreski, Gernot

AU - Teichert, Christian

AU - Pinter, Gerald

N1 - Publisher Copyright: © 2021 Taylor & Francis Group, LLC.

PY - 2021

Y1 - 2021

N2 - Nanoindentation (NI) is a contact method to investigate localized micromechanical properties of materials, whereby NI of semi-crystalline polymers is challenging. The influence of morphological structures such as spherulites or crystal-lamellae on localized NI depth-force behavior is discussed controversially in literature. Hence, the main objective of this study is to determine the influence of crystalline zones on NI results. Polyoxymethylene (POM) exhibits high crystallinity with the spherulitic structure on the micrometer scale and was therefore chosen to proof the influence of spherulite distribution on NI results concerning modulus. Furthermore, the correspondence between the mean elastic modulus from different NI experiments and macroscopic compression tests will be demonstrated. A POM tensile bar was investigated by NI with a large sphero-conical and a Berkovich indenter tip at different positions of its cross-section. Here, it was found that regions at the edge of the sample have a lower elastic modulus than regions in the middle of the cross-section. This agrees well with polarized light microscopy results, which reveal a skin layer with less crystallinity close to the sample edge. Therefore, the NI measurements in this edge zone result in a lower elastic modulus compared to the more crystalline middle of the cross-section.In summary, semi-crystallinity influences the NI results obtained for POM and the mean of the elastic modulus distribution over the cross-section of the POM sample is in good agreement with macroscopic compression test results.

AB - Nanoindentation (NI) is a contact method to investigate localized micromechanical properties of materials, whereby NI of semi-crystalline polymers is challenging. The influence of morphological structures such as spherulites or crystal-lamellae on localized NI depth-force behavior is discussed controversially in literature. Hence, the main objective of this study is to determine the influence of crystalline zones on NI results. Polyoxymethylene (POM) exhibits high crystallinity with the spherulitic structure on the micrometer scale and was therefore chosen to proof the influence of spherulite distribution on NI results concerning modulus. Furthermore, the correspondence between the mean elastic modulus from different NI experiments and macroscopic compression tests will be demonstrated. A POM tensile bar was investigated by NI with a large sphero-conical and a Berkovich indenter tip at different positions of its cross-section. Here, it was found that regions at the edge of the sample have a lower elastic modulus than regions in the middle of the cross-section. This agrees well with polarized light microscopy results, which reveal a skin layer with less crystallinity close to the sample edge. Therefore, the NI measurements in this edge zone result in a lower elastic modulus compared to the more crystalline middle of the cross-section.In summary, semi-crystallinity influences the NI results obtained for POM and the mean of the elastic modulus distribution over the cross-section of the POM sample is in good agreement with macroscopic compression test results.

KW - atomic force microscopy

KW - creep

KW - Nanoindentation

KW - polyoxymethylene

KW - semi-crystalline polymer

UR - http://www.scopus.com/inward/record.url?scp=85114405736&partnerID=8YFLogxK

U2 - 10.1080/1023666X.2021.1968122

DO - 10.1080/1023666X.2021.1968122

M3 - Article

AN - SCOPUS:85114405736

VL - 26.2021

SP - 692

EP - 706

JO - International journal of polymer analysis and characterization

JF - International journal of polymer analysis and characterization

SN - 1023-666X

IS - 8

ER -