Exploring the Effect of Annealing on PLA/Carbon Nanotube Nanocomposites: In Search of Efficient PLA/MWCNT Nanocomposites for Electromagnetic Shielding.

In this research, poly(lactic acid) (PLA) nanocomposites with multi-walled carbon nanotubes (MWCNT) were produced by extrusion, injection, and compression molding, focusing on electromagnetic shielding. Various amounts of carbon nanotubes (MWCNTs) were tested in PLA matrix, specifically ranging from 1 to 4 parts per hundred resin (phr). The resulting nanocomposites were analyzed before and after undergoing annealing heat treatment. It was observed that as the MWCNT content increased, the melt flow index of PLA decreased. This reduction indicates that the nanotubes were effectively accommodated into the PLA chain. The PLA/MWCNT (2 phr) formulation presented the greatest balance of properties, with potential for electromagnetic shielding application. Scanning electron microscopy (SEM) demonstrated that incorporating 2 phr of carbon nanotubes in PLA promoted good distribution, favoring high electrical conductivity and electromagnetic shielding between 20-22 dB (8.2-18 GHz), corresponding to approximately 99% attenuation. Furthermore, its properties, such as elastic modulus (3156 MPa), tensile strength (65.1 MPa), hardness (77.8 Shore D), and heat deflection temperature (55.3 °C), increased compared to pure PLA. After annealing, the PLA/MWCNT (2 phr) nanocomposite underwent a molecular reordering, resulting in an increased crystalline fraction, as confirmed by X-ray diffraction (XRD). However, the electrical conductivity maintained the same order of magnitude, while the electromagnetic shielding varied from 19.7 to 20 dB. The results indicate that these nanocomposites are promising for electromagnetic shielding applications and can be manufactured in the molten state.