PSI - Issue 43

Komal P. Malla et al. / Procedia Structural Integrity 43 (2023) 71–76 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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Fig. 2 shows the stress – strain curves of polymer scaffolds as a function of the volume fraction percentage of filler used. The scaffolds of pure blend without any filler exhibit very brittle performance with unstable crack growth, while all filler composite scaffolds (filler fraction: 2 – 12 %) became ductile with no unstable crack growth. This is a clear correlation with the change in the micromechanical deformation mechanisms that will be discussed below. The brittle-to-ductile transition seems to be triggered by the incorporation of filler particles, which can be confirmed by the strain at break as a function of filler percentage (Fig. 3c). The strain at break of the pure polymer blend without filler is very low at only 2 %. However, the strain at break of all composites is much higher (18 – 37 %). Additionally, the tensile strength increases from 0.7 MPa for the pure polymer blend via 1.5 MPa of the composite containing 6 % filler to 5.6 MPa of the composite containing 12 % filler (Fig. 3b). Interestingly, the elastic modulus is first nearly constant at 0 – 6 % filler (about 44 MPa); afterwards, the modulus jumps to 199 MPa at 12 % filler (Fig. 3a). The same jump can be observed for the tensile strength, probably due to the high-volume fraction of filler percentage in the scaffold fibers. The incorporation of the filler into the fibers improves not only the biocompatibility of the scaffolds but also their ductility, which is essential for easy handling during practical applications. This is in contrast to the general brittle behavior of solution cast films where the strain at break (about 1.3 %) remains at the low level of the pure blend (Fig. 3c).

Fig. 3. Tensile properties of the nanofibrous scaffolds as a function of the filler fraction: elastic modulus (a), tensile strength (b) and strain at break (c); the lines are visualizing the trend only. 4. Microdeformation of the Scaffolds at Tensile Loading The scaffold containing no filler exhibits highly brittle behavior in the tensile test as discussed in Section 3 (see Fig. 3). This behavior is clearly reflected in local low-deformation structures of the fibers. For the scaffold with low filler percentage the representative SEM image (SEM – scanning electron microscopy) after the tensile test visualizes the microdeformation (Fig. 4a). Several modulated craze marks in the fibers, which might be the effect of filler addition as well as local deformation and nanophase separation of each polymer.

Fig. 3. SEM micrographs after tensile test of the nanofibers for the neat polymer blend (a) and the polymer blend with 12 % filler (b).