Influence of the Processes Parameters on the Properties of The ...

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Chapter 4. Experimental Procedures and Protocols for Analyses also used during <strong>the</strong> pellet forming process. Without using polyimide film some <strong>of</strong> <strong>the</strong> polylactides stick on <strong>the</strong> stainless steel plunger at elevated temperature. Moreover to make multiple pellets in one batch <strong>the</strong> pellets are separated by polyimide. Body Evacuable base Polyimide film Polyimide circular disk Metallic pellet Polymer powder Plunger Set <strong>of</strong> pellets (a O Ring Kit Polyimide film Metallic pellet (b) (c) (a) Evacuable pellet die accessories (b) Assembled pellet die (c) Schematic representation <strong>of</strong> assembled mould (d) Cross sectional view <strong>of</strong> multi-pellets/batch. Figure 4.7: Schematic diagram to produce pellets in semi-industrial quantities. 1.4.2 Procedure to Prepare Pellets The procedure to process pellets is described stepwise as under shown in Figure 4.8. A B C D E F Insert <strong>the</strong> bottom pellet with <strong>the</strong> polished side facing UP. Pour your powder into <strong>the</strong> bore <strong>of</strong> <strong>the</strong> die barrel. Level <strong>the</strong> sample in <strong>the</strong> bore and wipe <strong>of</strong> any spilled powder. Insert <strong>the</strong> top pellet into <strong>the</strong> die barrel with <strong>the</strong> shiny side DOWN. Put <strong>the</strong> plunger into <strong>the</strong> die barrel on top <strong>of</strong> Center <strong>the</strong> assembled <strong>the</strong> bottom pellet pellet die on <strong>the</strong> platform in <strong>the</strong> press. J I H G K Disassemble <strong>the</strong> pellet die. Invert die assembly, press down gently on <strong>the</strong> piston, bottom pellet and <strong>the</strong> pressed sample disk should pop out. M Remove <strong>the</strong> die base. Pump <strong>the</strong> handle to raise <strong>the</strong> lower platform Irregular disk L Carefully clean all <strong>of</strong> <strong>the</strong> parts with cotton tipped applicators Plane and cleaned disk Gloves Cleaning cutter Figure 4.8: Schematic representation to process pellets by using hydraulic press. - 92 -
Chapter 4. Experimental Procedures and Protocols for Analyses 1.4.2.1 Preparation <strong>of</strong> <strong>the</strong> Die The base must be placed on <strong>the</strong> bench top. It must be carefully checked that <strong>the</strong> bottom O-Ring seal is properly positioned in its groove. The body is assembled on base. One <strong>of</strong> <strong>the</strong> metallic pellets was carefully placed, polished face up and a polyimide circular film was placed in <strong>the</strong> bore <strong>of</strong> <strong>the</strong> body. The evacuation tube was connected to a vacuum pump capable <strong>of</strong> providing a pressure <strong>of</strong> less than two mm Hg. If vacuum setup is not available <strong>the</strong>n manual CARVER hydraulic press is used for compression. 1.4.2.2 Loading <strong>the</strong> Die Using a funnel, <strong>the</strong> powder mixture is poured into <strong>the</strong> bore <strong>of</strong> <strong>the</strong> body. The side <strong>of</strong> <strong>the</strong> die is tapped lightly to be sure that <strong>the</strong> powder is evenly distributed. Completely even powder distribution is accomplished by inserting <strong>the</strong> plunger into <strong>the</strong> bore and rotating it lightly a few times. The plunger is <strong>the</strong>n withdrawn slowly. A second metallic pellet is inserted, polished face down, into <strong>the</strong> upper half <strong>of</strong> <strong>the</strong> bore followed by <strong>the</strong> plunger. If more than one pellet is required, a polyimide film is put on <strong>the</strong> metallic pellet and <strong>the</strong>n powder on it. The procedure is repeated till 3 sample pellets are required. One must be sure that <strong>the</strong> top O-Ring seal is in place around <strong>the</strong> plunger and properly seated in <strong>the</strong> chamber. 1.4.2.3 Processing <strong>the</strong> Pellets The die assembly must be placed in <strong>the</strong> hydraulic press. Without applying pressure, <strong>the</strong> die must be evacuated for 2 - 5 minutes (depending on <strong>the</strong> dryness <strong>of</strong> <strong>the</strong> sample). With continued evacuation, 150 bars pressure is applied to <strong>the</strong> die for 20 minutes and <strong>the</strong> temperature (45−60 o C) is maintained as per requirement. The pressure is released slowly and <strong>the</strong> vacuum removed. 1.4.2.4 Removing <strong>the</strong> Pellets The base is removed from <strong>the</strong> body leaving <strong>the</strong> plunger in position. The assembly is inverted on <strong>the</strong> plate <strong>of</strong> <strong>the</strong> hydraulic press and <strong>the</strong> polycarbonate ring is placed on <strong>the</strong> centre <strong>of</strong> <strong>the</strong> body opposite <strong>the</strong> plunger end. Using <strong>the</strong> hydraulic press, pressure is applied slowly until <strong>the</strong> plunger moves <strong>the</strong> lower pellet and disc clear <strong>of</strong> <strong>the</strong> bore. In <strong>the</strong> preliminary experiments polymer powders <strong>of</strong> ~ 0.150 g <strong>of</strong> weight have been moulded by compression at 150 bars and 60°C for 20 minutes. Our compression moulding setup has initially allowed 3 pellets <strong>of</strong> polymer to be prepared simultaneously. Finally, pellets have a thickness <strong>of</strong> 0.9 − 1.1 mm. In order to prepare pellets in bulk quantity, a modified procedure is fur<strong>the</strong>r adopted. We prepare 12, 15 or 18 pellets, by varying <strong>the</strong> weight <strong>of</strong> polymer powder taken into account, in one batch by using polyimide film as shown in Figure 4.9-d. 1.5 Preparation <strong>of</strong> Pellets by Wet Method In <strong>the</strong> wet method, pellets have been prepared by dissolving composite powder in a good solvent (acetone or chlor<strong>of</strong>orm). Polymer and filler powder have been ground by knife mill, tumbling ball mill and <strong>the</strong>n sieving as described earlier. The solution mixture is heated for minimum 10 minutes in a water bath at temperature 5 o C above <strong>the</strong> polymer or composite T g . When <strong>the</strong> solution mixture becomes homogenous, it is - 93 -
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Institut National Polytechnique de
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Publications and Conferences The wo
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ρ p Pellet density Splitting (Bra
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