Surface modification of polylactic acid (PLA) by air atmospheric plasma treatment

• The atmospheric plasma treatment improves the wettability of PLA substrates.
• Best wettability for a 10 mm nozzle–substrate distance and a 100 mm s−1 advance rate.
• PLA plasma surface energy gets values over 60 mJ m−2 twice the untreated sample value.
• Polar contribution is important in surface wettability, increasing up to 32.8 mJ m−2.
• Increase surface roughness and polar groups after treatment with atmospheric plasma.

The main objective of this experimental study is the validation of the technique of atmospheric plasma with the aim of improving the surface energy of the polylactic acid (PLA) for further adhesion uses. The wettability of PLA has been improved with the application of an atmospheric plasma surface treatment. This method provides good adhesion properties with the optimizing the process parameters in terms of the nozzle–substrate distance and sample advance rate. In order to achieve that goal, a new and environmentally friendly technology has been used which is based on the use of air atmospheric plasma. The effects of the surface treatment on this type of substrates have been analyzed. The macroscopic effects of the process parameters have been determined using contact angle measurements and subsequent surface free energy (SFE) calculation. In addition, the chemical changes at the topmost layers have been studied using X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared spectroscopy (FTIR). Surface topography changes due to the plasma-acting mechanisms have been evaluated with scanning electron microscopy (SEM) and atomic force microscopy (AFM). The obtained results show a remarkable increase in surface free energy from 37.1 mJ m−2 up to values of 60 mJ m−2 thus indicating the effectiveness of the air plasma treatment. The main advantage of this technology is that the industrial process is continuous, it is easy to establish in current production systems and it does not generate wastes.

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