No, you should never heat up plastic in a toaster oven. Toaster ovens are designed to cook or toast food items and are not suitable for heating or melting plastic. Heating plastic in a toaster oven can be dangerous and may lead to harmful consequences.
When plastic is heated, it can release harmful chemicals and fumes, some of which may be toxic. These fumes can be hazardous to your health and can potentially contaminate the food you cook in the toaster oven afterward.
If you accidentally place plastic inside a toaster oven and it starts to melt or release fumes, it's essential to turn off the toaster oven immediately, open windows for ventilation, and let the toaster oven cool down before removing the plastic carefully.
To avoid any risk, always ensure that you only use toaster ovens for their intended purpose, which is cooking and toasting food items. Never heat or cook anything in the toaster oven that is not specifically designed for such use, especially plastic or any other non-food items.