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

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Chapter 4. Experimental Procedures and Protocols for Analyses depressurizing valves or by <strong>the</strong> combination <strong>of</strong> both types <strong>of</strong> valves. The dP/dt procedure is quite tricky and requires great skill. CO 2 is supplied by Air Liquid and is 99.5% pure. 2.1.2 Setup One: Filling <strong>the</strong> Chamber with Teflon ® In this setup, three pellets are placed in <strong>the</strong> pressure chamber on perforated metal stages which are encircled by a Teflon ® isolation material (cf. Figure 4.12-a). The pellets <strong>of</strong> upper, centre and bottom compression moulding position (A, B and C) are placed in <strong>the</strong> upper, centre and bottom position in <strong>the</strong> pressure chamber (A, B and C), respectively. Teflon ® material is placed into <strong>the</strong> pressure chamber in order to decrease <strong>the</strong>ir volume which facilitates <strong>the</strong> depressurization rate. 2.1.3 Setup Two: Filling <strong>the</strong> Chamber with Glass Beads The second procedure consists <strong>of</strong> filling <strong>the</strong> pressure chamber (until <strong>the</strong> ~ 1/3 or ~ 2/3 <strong>of</strong> <strong>the</strong> height <strong>of</strong> <strong>the</strong> pressure chamber) with small glass balls (diameter 3 mm) and <strong>the</strong>n a perforated grill (hole diameter 2 mm) is placed above <strong>the</strong>m. After that, <strong>the</strong> pellet is placed on <strong>the</strong> grill. This setting was adopted to study <strong>the</strong> pore size difference at <strong>the</strong> top <strong>of</strong> <strong>the</strong> chamber as compared to three different points in <strong>the</strong> chamber (cf. Figure 4.12-b). Figure 4.12: Schematic representation <strong>of</strong> <strong>the</strong> cross section <strong>of</strong> <strong>the</strong> supercritical CO 2 chamber with two different configurations. For both procedures, after placement <strong>of</strong> <strong>the</strong> pellets, <strong>the</strong> temperature and pressure have been raised to <strong>the</strong> required value. Then, pellets have been saturated with supercritical CO 2 during a desired time. After that, <strong>the</strong> chamber has been depressurized with a given depressurization rate. 2.2 SEPAREX SFC6 scCO 2 Laboratory Plant 2.2.1 Experimental Device The bigger volume <strong>of</strong> <strong>the</strong> chamber (6 L) allows increasing <strong>the</strong> number <strong>of</strong> samples (up to 15) in one batch (cf. Figure 4.13). The process flow diagram is given in Figure 4.14. 2.2.2 Experimental Procedure To begin experimentation <strong>the</strong> system is started four hours before <strong>the</strong> foaming process so that <strong>the</strong> entire system might attain an equilibrium temperature. Sub-cooled liquid CO 2 is pumped by a volumetric membrane pump (Milton Roy, maximum 5 kg/h), <strong>the</strong>n heated until <strong>the</strong> desired temperature and continuously introduced into <strong>the</strong> mixing chamber. Experiments can be carried out in open-loop or closedloop configuration, in which case, after condensation, CO 2 is recycled to <strong>the</strong> pump. Normally open loop experimentation is carried out in this pilot plant. Temperatures and pressures are controlled, pressure being - 96 -
Chapter 4. Experimental Procedures and Protocols for Analyses limited to 300 bars and temperature around 60°C. Before starting an experiment, <strong>the</strong> pilot is filled with CO 2 at bottle pressure (about 5.5 MPa) and air is flashed out. Autoclave with top Autoclave Temperature and pressure monitor board scCO 2 heat exchanger Foam after process Perforated stage with pellets Digital vernier Caliper SEPAREX Pilot SFC 6 Two plate stage Five plate stage Pressure regulating and venting valves CO 2 pump Foams after measurement Figure 4.13: Details <strong>of</strong> equipment (SEPAREX Pilot SFC-6). Figure 4.14: SEPAREX Pilot SFC-6 process flow diagram. 2.2.2.1 Initial Filling <strong>of</strong> Chamber with CO 2 Polymer/composite pellets are placed in <strong>the</strong> chamber upon a perforated plate. Then, CO 2 is pumped and heated into <strong>the</strong> chamber. Temperature <strong>of</strong> CO 2 is adjusted by <strong>the</strong> heating fluid circulation in <strong>the</strong> jacket <strong>of</strong> <strong>the</strong> mixing chamber. At t 0 <strong>the</strong> pressure <strong>of</strong> <strong>the</strong> chamber is at <strong>the</strong> atmospheric pressure. CO 2 pump is started and <strong>the</strong> flow rate is maintained at 0.5 bar/s. To equalize <strong>the</strong> pressure <strong>of</strong> chamber and line, it takes approximately 2.5 − 3 minutes and at that time <strong>the</strong> pressure <strong>of</strong> <strong>the</strong> whole system is about 60 bars. Then flow - 97 -
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