Controlled morphology evolution of PLA via rapid heat cycle molding

Thomas Hutterer

    Research output: ThesisMaster's Thesis

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    Abstract

    Due to the ever-growing demand of biobased polymers, ways to increase their applicability as technical parts need to be established. Poly (lactic acid) is by now the most widely used biopolymer, but its improper crystallization behaviour when processed via injection molding limits its usefullness to a great degree. In this work, two approaches to increase the degree of crystallinity of PLA parts with state of the art injection moulding equipment are being proposed. First, compounds of PLA and nucleating agents, specifically talc and layered silica, were made, and secondly, specimens were manufactured from those compounds using Rapid Heat Cycle Molding (RHCM) process control during injection molding. The injection moulding experiments were carried out according to a full factorial Design of Experiments (DOE) for every compound. The manufactured specimens were then analysed with Differential Scanning Calorimetry (DSC) in order to obtain the achieved degree of crystallinity by the different compounds and DOE settings. Furthermore, polarized optical micrographs were made to investigate the distribution of crystallites across the diameter of the samples. Lastly, hardness measurements were carried out. The results of the DSC measurements were then statistically analysed and models were fit to the data. The fits of the different materials were then compared to analyse the effect of nucleation separately from the effectiveness of the RHCM process. Those results were then linked to the polarized optical micrographs and hardness measurements. It was shown that adding talc to PLA can increase the degree of crystallinity achieved during injection moulding considerably, even at low RHCM temperatures. Furthermore, talc greatly enhances the distribution of crystallites across the part diameter as opposed to the raw material, which only shows crystallites close to the heated cavity walls. Furthermore, Shore D Hardness measurements proved to be a quick and easy method to compare the different degrees of crystallinity within the same material.
    Translated title of the contributionGezielte Beeinflussung der Morphologie von PLA mittels variothermer Prozessführung
    Original languageEnglish
    QualificationDipl.-Ing.
    Supervisors/Advisors
    • Berger, Gerald, Co-Supervisor (internal)
    • Pacher, Gernot, Co-Supervisor (external), External person
    • Friesenbichler, Walter, Supervisor (internal)
    Award date21 Oct 2016
    Publication statusPublished - 2016

    Bibliographical note

    embargoed until 05-09-2021

    Keywords

    • PLA
    • Poly(lacitic acid)
    • nucleation
    • compounding
    • talc
    • layered silica
    • rapid heat cycle molding
    • DSC

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