Oscillating knife

The cores are subsequently placed in the sheer, and the slicing procedure is performed by advancing the core over an oscillating knife in a controlled environment (Figure 12.1). Cold (4°C) Krebs-Henseleit buffer (pH = 7.4, saturated with 95% O2 and 5% CO2) supplemented with 25 mM glucose is commonly used in preparing the slices [35,38 0], but Williams medium E [41], Earle s balanced salt solutions [37], Sacks preservation medium [42] and V-7 preservation buffer [43,44] are also used. 

Success in cutting quality with such an oscillating knife is illustrated in Fig. 1.45. A rubber-modified polymer (high-impact polystyrene, HIPS) with so-called salami... 

With axial extruders, it is difficult to cut the extrudates into uniform lengths because the material extrudes faster on the outside of the die plate than nearer to the center (Fig. 8.28). This phenomenon is a result of the complex flow and pressure patterns that are developed in the extrusion zone. A rotating knife or an oscillating wire can be used to separate the extruded strands into pellets but, nevertheless, their length will usually vary considerably. 

Streaks and chatter downweb lines air flow at knife causes oscillations in the upstream bead/distance between the bottom of the air knife and the coating pan edge is too large/inadequate contact angle between the liquid and the web. 

Figure 4.10. Ultrathin sections of polypropylene and polyethylene sectioned at room temperature using a 35° angle diamond knife (A) and sectioned at room temperature using an oscillating diamond knife (B). (From Vastenhout and Gnagi [119] used with permission of Cambridge University Press, courtesy of the Microscopy Society of America.)...

Developments have been made to reduce the compression of ultrathin sections by use of an oscillating diamond knife [118]. A prototype of this oscillating diamond knife was evaluated and tested to prepare ultrathin sections for comparison with the same sample prepared with a 35° angle diamond knife [119], as shown in Fig. 4.10 of a blend of polypropylene and polyethylene. A block face from such sectioning should be flatter and be more useful for AFM imaging as well. 

Sectioning problems, collection, and troubleshooting are all described by Reid [115]. For example, artifacts have been observed in ultra-microtomy of liquid crystal polymers, when compared with x-ray diffraction, due to compression that modified the structure of the polymer [163]. The oscillating diamond knife, discussed earlier, is also intended to reduce compression of ultrathin sections [118]. The list in Table 4.2 is not complete but is intended to provide insight into the cause and potential remedy of sectioning problems [164]. 

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