PLA is a semicrystalline, hygroscopic thermoplastics resin that will readily absorb moisture from the atmosphere. It is also temperature sensitive. In order to preserve properties and characteristics intended by the resin manufacture, it is important to minimize exposure of PLA to ambient (undried) air and adhere to certain other basic practices during all phases of processing.
PLA is normally crystallized and dried to moisture levels below 400 ppm by the manufacturer prior to shipping. However, if it is not kept in a sealed container, and depending on local conditions, PLA can pick up enough moisture in 5 minutes to defeat most of the benefits of drying. That’s why it is usually delivered in moisture-resistant containers, including foil-lined bags and boxes, which can prevent moisture regain during shipping and storage. Even before it is processed, heat and moisture can degrade PLA, breaking down the polymer chains and resulting in a loss of molecular weight.