Can the aging process of PLA be frozen?

PLA has been the most popular material used in 3D printing for many years. In addition to the obvious advantages over other filaments in the form of negligible shrinkage or no harmful odor during 3D printing, it has several disadvantages. The best known are low temperature resistance (PLA becomes plastic already at 60 ° C) and brittleness, however, the material also has another, often overlooked disadvantage – physical aging of polylactic acid (PLA) is a phenomenon that changes the properties of this material over time.

The aging process is highly dependent on environmental variables such as temperature and humidity. In the case of PLA, aging is noticeable even at room temperature, and the process is commonly called natural aging. Researchers from the Universidad Politécnica de Madrid in Spain conducted research in which they tried to check whether the aging process and degradation of PLA can be stopped by… freezing it?

Stopping the aging process by freezing the filament or finished 3D prints can help preserve the properties of PLA and stabilize them at any time during storage until it is required for testing. A study by Spanish scientists analyzed four different methods of stopping aging – all based on freezing and thawing PLA samples.

The temperature and the influence of water vapor from the environment during the freezing and thawing process with the use of desiccant and ziplock bags were determined. PLA print samples were printed at 190°C and had diameters ranging from 400 to 550 µm, and then were frozen at -24°C with or without a desiccant.

The influence of the processes on the aging and mechanical integrity of PLA has been investigated in terms of thermal, mechanical and fractographic properties. As a result, the anti-aging process has been defined to effectively stop the natural aging of PLA indefinitely. The material freezing process does not affect the mechanical properties or structural integrity of the PLA.

According to the results presented, it is possible to stop the aging of PLA by freezing it at -24°C or lower for up to nine months without damaging it. Additionally, it can be safely stored without a desiccant inside the zipper bags, which simplifies the process, making the anti-aging procedure cheap, simple and effective.

The main conclusions of the study are as follows:

• aging was completely stopped by freezing the PLA at -24°C
• there were no mechanical damages in the frozen PLA
• the presence or absence of a desiccant during the freezing or thawing process does not introduce measurable changes in the final state, properties and behavior of PLA
• PLA can be safely frozen at -24°C inside PET zipper bags without a desiccant to stop aging.

Source: www.mdpi.com

Natural Ageing of PLA Filaments, Can It Be Frozen?
Jaime Orellana-Barrasa, Ana Ferrández-Montero, Begoña Ferrari, José Ygnacio Pastor
Centro de Investigación en Materiales Estructurales (CIME), Universidad Politécnica de Madrid
Instituto de Cerámica y Vidrio (CSIC), Campus de Cantoblanco, 28049 Madrid, Spain