Drying the Plastic

PET plastic must be dried before extrusion. Any residual water can lead to hydrolysis during extrusion. Hydrolysis in turn causes the melt viscosity to drop. Low viscosity PET is difficult to make into quality filament.

To dry the flake, it should be heated to around 175 deg C for 4 hours.

Note: A drying hopper has been incorporated into the design. This allows for continuous drying of the flake before extrusion.

It is possible to do this in a bench top oven in a well ventilated area. Air circulation will probably not be the greatest, and pre-dried air isn't being used, so the results will not be as good as what is achieved in industry. It does help considerably when compared to plastic that isn't dried at all. WARNING - Putting plastic in an oven can be a fire hazard and can produce toxic fumes. Take the appropriate safety precautions. You are responsible for your own safety. After removing the plastic from the oven, it will cool and begin adsorbing moisture again. Keep the plastic in the hopper covered at a minimum.

We have developed a Drying Hopper that continuously blows 175 deg C air through the plastic while it is in the hopper. It has yet to be fully documented.

In industry, air is blown through desiccant, then heated before going through the flakes. After that, it is cooled and recirculated. This may be challenging to do on a budget and at small scale.