Fine cut resins

Pelletized granular resins can be obtained by agglomeration of fine-cut resins. The agglomeration process increases the powder flow and apparent density. The goal of this process is to make the small PTFE particles adhere together. Essentially, there are two processes of agglomeration namely, dry and wet techniques [24]. 

Polytetrafluoroethylene selection. Polymer selection for compounding granular PTFE is relatively straightforward. Fine cut resins are used as a starting point to produce filled compounds. These powders have relatively small particle size and form the most uniform compounds. Typically, smaller particle size resins produce compounds with higher physical properties. 

Resin flow is a function of the apparent density of the resin. Resins with an apparent density of >500 g/1 are usually obtained by pelletizing fine cut resins and are known as free flow (Fig. 5.1a). The consistency of these resins is similar to granulated sugar in contrast to fine cut resins (with apparent density of <500 g/1) which have a consistency close to that of flour. 

Fine-cut granular resins resnlting from size redaction of the snspension polymer have a typical average particle size 20 pm to 40 pm. The small particle size of hne-cnt PTFE imparts the highest possible mechanical properties to articles made from grannlar resins. Fine-cnt resins (powders) have poor flow and low apparent density... 

Filling the mold must be done uniformly because uneven filling leads to nonuniform density in the preform and cracking. Charging the mold is much simpler with a free flow resin than a fine cut powder. Free flow resins more or less assume the shape of the mold and require little distribution. 

Of course, in order to vary the mass transport of the reactant to the electrode surface, the radius of the electrode must be varied, and this unplies the need for microelectrodes of different sizes. Spherical electrodes are difficult to constnict, and therefore other geometries are ohen employed. Microdiscs are conunonly used in the laboratory, as diey are easily constnicted by sealing very fine wires into glass epoxy resins, cutting... 

Figure 13.3.7 shows scanning electron microscopy (SEM) photographs of the surface of the polyethylene particle after the silica particles were peeled off. The specimen was prepared in the following way. After the composite particles were potted in epoxy resin, the dried resin block was cut using a microtome to produce fine sections. The fracture surface appearance of the polyethylene was then observed under a microscope. The mean depth penetration into the surface of the core particles could be measured using the SEM photographs. Silica 0.3 pan in diameter was embedded in the surface of the polyethylene particles at a depth of 0.03 xm. In... 

Figure A. The distribution of optically distinct materials in the cut-back and straight-distilled refractory pitches are different. The strongly anisotropic materials (oil phase) (A) contrast with the fine solids (S) in an amorphous resin from the original pitch and with the material which is more isotropic (I). At 450°C. another distinct isotropic phase (H) exists in the straight-distilled pitch, Reflected light...

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