Demonstration of the Power Law Model Through Extrusion

For this experiment, a typical thermoplastic copolymer (ExxonMobil Paxon BA50, melt temperature ~204 °C) of high-density polyethylene (HDPE) plus a longer chain olefin will be extruded through a cylindrical die.

1. Initialize the Extruder

1. Turn the exhaust "ON" when you are ready to power up the extruder.
2. Fill the hopper and extruder with polymer pellets.
3. Make sure that the motor switch is "OFF". Then turn the main switch "ON".
4. Set the die temperature between 220 - 250 °C, the zone 1 temperature 5 - 20 °C above the melt temperature, and the zone 2 temperature between the zone 1 temperature and the die temperature using the up/down keys on the panel.
5. After the temperatures of all heated zones reach their set points, wait for a minimum of 1 h to melt the polymer inside the extruder. This is called the "heat-soak", and it is critcally important because any solid left in the melt will exert an excessively high pressure on the die, resulting in unsteady flows.

2. Operating the Extruder

1. Turn the motor "ON" using both switches.
2. Set the desired speed. Start with a low RPM and gradually increase the RPM as the polymer exits the die, until the desired speed is reached. A speed range of 10 - 100 RPM is recommended, but this is highly temperature-dependent. Do not exceed 3,000 psi die pressure under any circumstances. The psi should be <2,500 psi.
3. Run the extruder for ~10 min after reaching the desired speed. Periodically check the hopper to ensure it has resin pellets.
4. Pre-weigh a measuring pan for sample collection.
5. Measure the flow rate by cutting the extrudate with scissors and collecting what exits from the die during measured time intervals in the measuring pan. The die is extremely hot and should not be touched without safety gloves.
6. Weigh the mass of the extrudate and measure the diameter of the extrudate ribbon with a micrometer.
7. Switch the motor to a different speed, and wait ~10 min before collecting data.
8. If working at more than one die temperature, wait 15 min after the new die temperature is reached before collecting data. Lower the speed initially if you raise the die temperature to avoid wasting polymer during the transition.
9. Repeat flow rate measurements for different operating conditions.

3. Shutting down the Extruder

1. After collecting all desired data, turn "OFF" both extruder motor switches.
2. Then turn "OFF" the main switch.