THIS METHOD IS CURRENTLY A WORK IN PROGRESS
Here is outlined the method to dry shredded PET in a convection oven at the MOST lab at Michigan Technological University. PET needs to be dried prior to extrusion in a Recyclebot as otherwise it will undergo rapid hyrdolyzation at high temperatures, and reduce the molecular mass. For more information please see the PET Extrusion literature review.
Equipment
- Convection Drying Oven (Any oven will generally work, ovens at home run off the same convection principles of heating and moving air. If using a home oven, be careful of temperatures, and be aware that there could potentially be burning plastic inside of it, if proper precautions are not taken)
- Shredded PET
- Drying tray (Any metal tray to hold the PET shreds)
Procedure
- Turn on the oven
- Evenly distribute the shredded PET in the drying tray. This exposes more surface area to enhance evaporation speed.
- Open the oven by firmly opening the door. It may take a quick jerk, but be careful not to topple it.
- Place the tray inide the oven.
- Close the oven door, firmly.
- Set the temperature on your oven to a value as shown by the table below. This table is a work in progress, please feel free to contribute and check!
- Wait for an amount of time also shown in the table above.
- Switch off the oven then carefully open the door after letting it cool for a few minutes.
- Quickly place the PET in an airtight container, such as inside two (2) layers of plastic bags that are twisted and tied shut. As long as the PET is not allowed to reabsorb water from the air, any arrangement will work.
- Store PET in a cool dry place until it is to be used. One excellent method is to place the dry PET inside a bag, which also has dessicant. This further dries the plastic, and will remove any moisture that may have accrued whilst handling it.
Temperature and Time Table
Important temperatures to be mindful of: 260°C is the melting point at 70-80°C is the glass transition temperature. Because "wet" plastic is being dried, it will likely begin to degrade far below the melting point. For a plastic, the melting point will not signfy much, as the plastic molecules will break apart before the overall material ever reaches that temperature.
| 1 Hour | 2 Hours | 3 Hours | 4 Hours | 5 Hours | 6 Hours | |
|---|---|---|---|---|---|---|
| 82°C
Slightly above Tg |
No Change | No change | ||||
| 100°C | ||||||
| 125°C | ||||||
| 150°C | ||||||
| 175°C | ||||||
| 200°C | ||||||
| 225°C | ||||||
| 250°C | ||||||
| 275°C | ||||||
| 300°C |