Polylactic Acid (PLA) is the most popular material used in desktop 3D printing due to its ease of use and plant-derived origins. This thermoplastic is highly hygroscopic, meaning it readily absorbs and retains moisture from the surrounding air. When a PLA spool is left exposed, water molecules infiltrate the polymer structure, severely compromising the filament’s quality and causing print failure. Managing this absorption process is necessary to ensure consistent, high-quality results.
The Hygroscopic Nature of PLA
The root of PLA’s moisture problem lies in its chemical composition as a polyester. The polymer chains contain polar ester groups, which have a strong affinity for water molecules present in the atmosphere. This attraction draws water into the filament, where it bonds with the polymer structure and becomes trapped.
Once absorbed, the water initiates hydrolysis, a destructive chemical process, especially when the filament is subjected to the high temperatures of the printer’s hot end. During hydrolysis, water molecules break the long polymer chains into shorter, weaker segments. This breakdown reduces the material’s molecular weight, compromising the filament structure before it is extruded.
The weakening of the polymer chains degrades the filament’s mechanical properties, causing poor flow characteristics and reduced tensile strength in the printed part. Maintaining a dry state is necessary to preserve the filament’s original quality and performance.
Identifying the Symptoms of Wet Filament
The most immediate sign of wet PLA is auditory, manifesting as distinct popping, sizzling, or crackling sounds emanating from the hot end during printing. This noise occurs because the absorbed water instantly turns into steam when it reaches the high temperature of the nozzle, rapidly expanding. Observing steam or smoke visibly rising from the hot end confirms that trapped moisture is vaporizing.
Visually, the surface quality of the print will suffer noticeably, often displaying a rough or porous texture. The rapid expansion of steam creates micro-voids, bubbles, and inconsistent extrusion, which can appear as blobs or zits scattered across the print surface. This erratic flow decreases the strength and accuracy of the printed object, as layers do not bond cleanly.
Excessive stringing and oozing are also common indicators, as the steam pockets disrupt the controlled flow of the material. Furthermore, wet filament can become significantly more brittle before it reaches the hot end, often snapping suddenly when bent or under tension.
Effective Methods for Drying PLA
To restore printability, trapped moisture must be removed through a controlled heating process. The most effective method is using a dedicated filament dryer box, designed to maintain a precise, consistent temperature around the spool. These devices often include a fan to circulate warm air and vent the released moisture, creating an ideal drying environment.
A modified food dehydrator is another practical option, providing the necessary low, stable heat and sufficient space for a standard filament spool. For PLA, the ideal drying temperature range is between 40°C and 55°C, with a duration of four to six hours typically recommended. For severely wet filament, the drying time may need to be extended up to 12 hours.
Using a conventional oven is possible but requires caution due to the poor temperature calibration of many household units. PLA has a low glass transition temperature, meaning it will soften and deform if the heat exceeds a certain point, potentially ruining the spool. Temperatures should never exceed 60°C, and an external thermometer is necessary to monitor the chamber temperature and prevent warping.
Long-Term Storage and Moisture Prevention
Once a spool has been dried, the focus shifts to maintaining that dry state to prevent future moisture absorption. Long-term storage involves using airtight containers, such as sealed plastic bins or vacuum-sealed bags, to create a barrier against ambient air. These containers should hold the spool comfortably without stressing the filament.
The inclusion of desiccants, most commonly silica gel packets, within the sealed container is necessary to absorb residual moisture. Silica gel acts as a moisture sponge, helping to maintain a low-humidity environment for the stored PLA. These packets can often be regenerated by heating them in an oven to drive off the absorbed water, making them reusable.
For preservation, the storage area should be cool and dry, ideally maintaining relative humidity below 20%. Avoiding direct sunlight is important, as UV light can degrade the PLA polymer, contributing to brittleness and color change. Removing the filament from the printer and placing it back into sealed storage immediately after a print is the simplest prevention method.