Scanning electron microscopy of fracture surfaces

The polymers, whose characteristics are summarized in Table 1, were melt mixed in a Brabender-like apparatus at 200 C and at two residence times 6 min, at 2 r.p.m. and further 10 min. at 32 r.p.m. The blend compositions are listed in Table 2. After premixing, cylindrical specimens were obtained directly by extrusion using a melting-elastic miniextruder (CSI max mixing extruder mod. CS-194), Thermal and tensile mechanical tests were performed on these specimens by an Instron Machine (mod. 1122) at room temperature and at cross-head speed of 10 mm/min. Also made were morphological studies by optical microscopy of sections microtomed from tensile samples and scanning electron microscopy of fractured surfaces of samples broken at liquid nitrogen temperature. Further details on the experimental procedures and on the techniques used are reported elsewhere . 

Scanning electron microscopy of fracture surfaces may provide useful information about the super-molecular structure, although artificial structures have been reported. These pseudospherulites arise from fractures initiated at spots in front of the main propagating fracture front. These early fractures propagate in a radial manner outwards from the initiation spots and create a spherulite-like topography which can very easily be mistaken for true spherulites. 

The mode and state of dispersion of the minor component and its volume fraction were determined by scanning electron microscopy on fractured surfaces after metallization with AuPd alloy. A scanning electron microscope (Philips Model 501) was used throughout. 

Trakas and Kortschot [76] used carbon fibre epoxy (AS4/3501-6) specimens modified with Teflon edge delaminations in a study comparing unidirectional and 0°/90° and 90°/90° interfaces under mode 1, mode 11 and mode HI loading. Delamination resistance decreased for all modes when going from unidirectional to cross-ply and 90°/90°. The tests were complemented with scanning electron microscopy of the fracture surfaces, but they did not yield a direct quantitative correlation with the measured values of Gc- It was noted that Gc could be used as a material property for design as long as the layup (ply orientation) and mode of fracmre corresponded to those in the intended use. 

Fig. 7. Fracture surfaces obtained via scanning electron microscopy of the stable crack growth region close to the notch (a) PPO, (b) CR-PP154> (c) CR-PP402 and (d) CR-PP546.

Fig. 17. Fracture surfaces obtained via scanning electron microscopy of (a) the reactor-made copolymer EPBCO-2 and (b) rheology controlled copolymer EPBC-CRIOI. Both materials are characterized by similar structmal properties.

Figure 5.61. Scanning electron microscopy of a fractured, molded POM test bar, containing a high void level shows a skin-core morphology. Elongation of the voids at the skin surface is due to high orientation, whereas the more rounded voids and the semicircular flow front in the core results from less orientation in that region of the mold.

Figure 5.65. Scanning electron microscopy of a molded polyacetal surface shows a smooth texture (A) with little surface detail. Etching for short times results in elongated pits, oriented in the direction of polymer flow (B). Longer etching times result in surface pits deeper below the surface, due to etching larger spheru-lites in the core (C). Fractured cross sections of plated and etched surfaces do not show the structure near the surface (arrows) (D) except in EDS maps of the plating material (E) or at higher magnification (F).

The microstructure of the homopolymers should be examined for comparison with the multiphase polymer. Scanning electron microscopy of an Izod fracture surface of a POM/PP copolymer is shown in Fig. 5.78. The two phases are incompatible (i.e., they are present as two distinct phases). The dispersed phase particles range from less than 0.5 to 2 /im in diameter. The sample fracture path follows the particle matrix interface and holes remain where particles have pulled out of the matrix, showing there is little adhesion between the phases. The shape of dispersed phase particles is determined by the flow field and heat gradients that affect polymer orientation. For instance, the microstructure of copolymers of PE and PP is similar to the skin-core textures described for PE [362]. The orientation of the dispersed phase can affect the mechanical properties of the system. Spherical domains are more commonly formed in systems where phase separation occurs while the polymers are liquid. The SEM image appears to reveal spherical... 

Figure 5.85. Scanning electron microscopy images of liquid nitrogen fractured polyacetal-polyurethane blend show a complex network morphology (A) made more complicated by chemical etching (B). Scanning electron microscopy of the etched fracture surface (B) suggests that the etchant has affected both the dispersed phase and the matrix.

Figure 5.96. Scanning electron microscopy of Izod impact fractured, glass fiber filled thermoplastic text specimens show nonuniform distribution of fibers in the two different specimens (A, C, D and B, D, F). The fibers (A) appear aligned parallel to the skin, and the matrix exhibits brittle failure as hackle marks (arrowheads) are seen. The fibers (B) protruding appear long and poorly wetted with the resin. Hackle or ridged patterns (arrowheads) are observed (C). Resin is also seen on the fiber surfaces in some regions (D and F), whereas cleaner fiber surfaces and less well bonded regions are also observed (E).

Figure 5.97. Scanning electron microscopy of a glass fiber reinforced nylon shows exeellent eompat-ibility between the fiber surfaces and the matrix. Short, nearly lateral failure across the matrix and fiber is observed (A). Some glass fibers exhibit classical brittle fracture (arrow) (B). Adhesion of the matrix resin is seen (arrowheads) at the fiber surfaces (C).

Figure 5.99. Scanning electron microscopy of a fracture surface of a molded sample with a defect particle present (A), found by EDS spectra (C) and map (B) to contain Ti and to likely be an undispersed Ti02 particle.

Figure 5.106. Scanning electron microscopy of a mica filled plastic bottle (A) and a mica-glass fiber composite (B) both show the platy shape of mica. Although the mica fracture surfaces do not appear resin coated, there is good adhesion of these particles with the matrix. The mica is aligned with the oriented polymer (A).

FIGURE 12.11 Scanning electron microscopy (SEM) photomicrographs of the tensile fracture surface of the ethylene-propylene-diene monomer (EPDM) rubber-melamine fiber composites. A, before ageing and B, after ageing at 150°C for 48 h. Test specimen is cut in tbe direction parallel to the milling direction. (From Rajeev, R.S., Bhowmick, A.K., De, S.K., Kao, G.J.P., and Bandyopadhyay, S., Polym. Compos., 23, 574, 2002. With permission.)... 

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