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In a paper entitled “3D Printing of PLA/clay Nanocomposites: Influence of Printing Temperature on Printed Samples Properties,” a group of researchers investigate the possibility of using a layered silicate-reinforced PLA in 3D printing applications. In particular, they examine the influence of printing temperature in 3D printing clay/PLA nanocomposites.

“For this reason, two PLA grades (4032D and 2003D, D-isomer content 1.5 and 4, respectively) were melt-compounded by a twin screw extruder with a layered silicate (Cloisite 30B) at 4 wt %,” the researchers explain. “Then, PLA and PLA/clay feedstock filaments (diameter 1.75 mm) were produced using a single screw extruder.”

The researchers 3D printed dog-bone-shaped and prismatic specimens using FDM 3D printing at three different temperatures, which were progressively increased from the melting temperature (185–200–215 °C for PLA 4032D and 165–180–195 °C for PLA 2003D). The PLA and PLA/clay specimens were characterized using thermogravimetric analysis (TGA) dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and tensile tests.

The morphology of the 3D printed specimens was also investigated using optical microscopy and contact angle measurements. DMA on the PLA/clay filaments showed an increase in storage modulus both at ambient temperature and above the glass transition temperatures compared to regular PLA filaments. The presence of nanoclay also increased thermal stability, demonstrated by TGA, and acted as a nucleating agent, which was observed by the DSC measurements.

“Finally, for 3D printed samples, when increasing printing temperature, a different behavior was observed for the two PLA grades and their nanocomposites,” the researchers state. “In particular, 3D printed nanocomposite samples exhibited higher elastic modulus than neat PLA specimens, but for PLA 4032D+C30B, elastic modulus increased at increasing printing temperature while for PLA 2003D+C30B slightly decreased. Such different behavior can be explained considering the different polymer macromolecular structure and the different nanocomposite morphology (exfoliated in PLA 4032D matrix and intercalated in PLA 2003D matrix).”

One of the reasons the researchers give for conducting the study is that PLA, while a popular 3D printing material, has several issues including low thermal stability, crystallization ability, and drawability. A possibility for overcoming these drawbacks is to reinforce PLA with nanofillers such as layered silicates, carbon nanotubes, and so on. The use of filler at the nanoscale allows for improvement of both the materials’ properties and processability. Few scientific studies have looked at the printability of PLA/clay nanocomposites, however.

In addition to the increase of the elastic modulus with the increase of the printing temperature, the researchers found that the properties of the 3D printed specimens were strongly affected by the different polymer matrices and the resulting nanocomposite morphologies. The different macromolecular architecture of the two matrixes affected the polymer’s ability to orient or not. The printing temperature also had an effect on the 3D printed specimen transparency – the higher the printing temperature, the higher the transparency.

“This study demonstrated that printing temperature should be chosen considering not only melting temperature, but also polymer architecture and/or nanocomposite morphology in the case of nanocomposite systems,” the researchers conclude. “Therefore, potential applications could be found in both considering the improvement in mechanical properties, if the correct temperature is used, and physical/aesthetical properties such as different degree of transparency.”

Authors of the paper include Bartolomeo Coppola, Nicola Cappetti, Luciano Di Maio, Paola Scarfato and Loredana Incarnato.

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