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

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n withdrawn slowly.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
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