Effect of material characteristics of polyolefins on weld line morphology and its correlation to mechanical properties

T. Tjäder, J. Seppälä*, Pirjo Jääskeläinen

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    16 Citations (Scopus)

    Abstract

    The effect of a weld line on the tensile, tensile impact and environmental stress cracking properties of a number of polyethylene (PE) and polypropylene (PP) samples has been investigated. The observed mechanical behaviour has been correlated to material properties, and also to the weld line morphology. PE samples differed in branching, molar mass (Mw) and molar mass distribution (MWD), whereas the PP samples differed in nucleation. The morphology of the weld line formed in injection moulding was analysed by optical microscopy and transmission electron microscopy. The mechanical strength was studied by tensile, tensile impact and constant tensile stress methods. In polyethylene samples with a high Mw, the weld line area was seen through the skin layer to the shear layer, and even down to the beginning of the core layer. The effect of a high Mw on morphological changes was diminished by a broad MWD. Short chain branching limited the morphological change solely to the skin layer. Both PP samples were morphologically rather homogeneous. The weld line created a V-notch on the surface that acted as a crack initiator in mechanical tests and thus reduced the mechanical strength of the weld line samples. The V-notch mainly hid the effect of the morphology on the mechanical properties.

    Original languageEnglish
    Pages (from-to)923-931
    Number of pages9
    JournalJournal of Materials Science
    Volume33
    Issue number4
    DOIs
    Publication statusPublished - 1998
    MoE publication typeA1 Journal article-refereed

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