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DDC: 530 × Has files: Yes × Type: Article × Subject: Polypropylene × WGL Institute: IPF ×

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    Investigation of transcrystalline interphases in polypropylene/glass fiber composites using micromechanical tests
    (Basel : MDPI, 2018) Brodowsky, Hanna; Mäder, Edith
    In composites, a strong interphase between the components is essential for mechanical properties. By using a suitable sizing (i.e., surface modification) of the fiber, the interphase may be varied, e.g., by suppressing or promoting heterogeneous nucleation of a thermoplastic matrix. In the latter case, three-dimensional transcrystallized interphases with properties differing from those of the bulk matrix are formed. Polypropylene-glass fiber composites are prepared as single-fiber model composites with (a) sizings either inducing or suppressing a transcrystalline interphase, (b) different amounts of modifier maleic acid anhydride grafted polypropylene, and (c) different molecular weights of the matrix polymer. These are studied in quasi-static or cyclic load tests. Static tests permit insights in the interfacial characteristics such as critical interface energy release rate, adhesion strength and frictional stress. Cyclic tests on these model composites can be used to study the nature of dissipative processes and the damage behavior. Atomic Force Microscopy (AFM) investigations of the fiber fracture surfaces provide supplementary information. The transcrystalline layer can indeed improve the mechanical parameters (a 70–100% increase of strength and a 25 or 125% increase in toughness, depending on the molecular weight (MW) of the matrix polymer at low modifier concentration). However, the effect is partially neutralized by an opposing effect: high nucleation in the bulk in samples with commonly used concentrations of modifier.
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    Commingled Yarn Spinning for Thermoplastic/Glass Fiber Composites
    (Basel : MDPI, 2017) Wiegand, Niclas; Mäder, Edith
    Online commingled yarns were spun with three different polymeric matrices, namely polypropylene (PP), polyamide (PA) and polylactic acid (PLA) and glass fibers. Tailored sizings were applied for the three matrices and the resulting mechanical performance of unidirectional composites was evaluated and compared. Significant improvements in the fiber/matrix bonding were achieved by employed sizing chemistry in order to achieve multifunctional interphases. The pure silane coupling agents provide the best performance for all matrices investigated. However, an additional film former has to be added in order to achieve fiber processing. Film formers compatible to the matrices investigated were adapted. The consolidation behavior during isothermal molding was investigated for polypropylene matrix. Different fiber volume contents could be realized and the resulting mechanical properties were tested.