Fibres tend to absorb moisture from the air resulting in a wet fibre. Absorption of even a small amount of moisture by fibres during storage and subsequent 3D printing reduces the final quality of individual parts and causes manufacturing problems.
The wet fibre can be dried but fibre drying is a technical challenge due to the combination of plastic characteristics and conditions required for drying. Commonly available fibre dryers use the form of "hot air drying". Although this approach somewhat reduces the moisture content it does not exclude it. In addition, the high temperatures required for hot air drying can damage the fibres. By using vacuum filament drying the moisture is completely eliminated which reduces manufacturing problems, improves component quality and keeps the fibres intact and undamaged.
This page provides a preview of the moisture related problems for 3D printing and the technical background for fibre drying.
Advantages of vacuum
All drying techniques work with water evaporation. The water is effectively evaporated at a boiling point which is 100 °C at atmospheric pressure. Fibers can not withstand these temperatures and their structure is damaged.
Lower temperatures lead to partial removal of moisture. Traditional techniques are not suitable for drying plastic-based fibres. Vacuum works by reducing the pressure which in turn lowers the temperature required for the water to boil and evaporate. This allows the fibre to be printed without moisture and damage!
Warm air drying
All commercially available fibre dryers use warm air drying which we use in everyday life, such as laundry drying. This method requires three conditions that are critical to its effectiveness. First, the temperature must be high enough for the water to evaporate, the wind blowing, and the humidity to be low.
There are two major challenges to fibre drying. First, the fibres cannot be heated to the desired temperature without degrading their quality and secondly, it is difficult to control the humidity. The 'hot air' method leads to partially dried fibre due to insufficient evaporation and insufficient water migration.
When most of the air is removed from the room a vacuum is generated. This results in low air pressure which leads to improved drying and storage. All water evaporates and is evacuated using a vacuum pump creating a moisture-free space ideal for low temperature drying.
Many common polymers including PLA, PETG, ABS, polycarbonate, cellulose and poly (methyl methacrylate) are hygroscopic which means they have a strong tendency to absorb moisture. The process improvement by vacuum drying of the filaments opens the possibility for printing without moisture with a large number of plastic materials.