Abstract
Poly(butylene succinate) (PBS) films were processed by a radio frequency (RF; 13.56 MHz) low-pressure plasma of oxygen and argon/oxygen, and an oxygen plasma with an argon post-crosslinking plasma to improve their wettability property. Specimens were treated at different times with fixed power processing of 100 W (0.3 W/cm2) and a fixed pressure of 10 Pa. A significant change in hydrophilicity evaluated by the water contact angle was observed. The contact angle of a water drop decreased from 80° for the untreated sample to values lower than 5° for plasma-treated samples. The effect of ageing on the wettability of PBS substrates was also examined, showing a more pronounced trend in the first 4 h and reaching a plateau in the following days. However, partial surface hydrophilicity was maintained for up to 15 days. A practical application of the surface functionalization produced by plasma was obtained via the deposition of SiOx onto PBS surfaces; the study of films’ oxygen permeability demonstrated that the plasma pre-treatment increased the adhesion between PBS and SiOx, resulting in significantly improved oxygen barrier properties. In order to evaluate the morphology and roughness modification caused by plasma exposure, atomic force microscopy characterization was carried out. Chemical information about treated surfaces, such as an increase in oxygen functional groups during plasma exposure, was measured by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Finally, the effects of plasma on crystallinity were investigated by X-ray diffraction.
Highlights
The packaging industry nowadays is dominated by non-degradable petroleum-derived polymers, but in recent decades there has been strong focus on the research and development of environmentally friendly, biodegradable polymers
Poly(butylene succinate) (PBS) films were processed by a radio frequency (RF; 13.56 MHz) low-pressure plasma of oxygen and argon/oxygen, and an oxygen plasma with an argon postcrosslinking plasma to improve their wettability property
A practical application of the surface functionalization produced by plasma was obtained via the deposition of SiOx onto PBS surfaces; the study of films’ oxygen permeability demonstrated that the plasma pre-treatment increased the adhesion between PBS and SiOx, resulting in significantly improved oxygen barrier properties
Summary
The packaging industry nowadays is dominated by non-degradable petroleum-derived polymers, but in recent decades there has been strong focus on the research and development of environmentally friendly, biodegradable polymers. The objective of this work is to analyze the wettability property of PBS substrates when they are subjected to three different plasma processes: oxygen only, oxygen/argon mixture, and oxygen with Ar post-crosslinking, and determine the best treatment to keep the polymeric surface hydrophilic for as long as possible without damaging the sample and without requiring long treatment times in order to keep it scalable from an industrial point of view. Under this perspective it is known that the induced surface properties are not stable over time since the surfaces show a tendency to return to the untreated state to the moment of room storage (hydrophobic recovery). The hexamethyldisiloxane monomer (HMDSO, 99.9%) was an Aldrich product (Merck Life Science, Milano, Italy)
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