Influence of Discharge Atmosphere on the Ageing Behaviour of Plasma-Treated Polylactic Acid

Abstract

The effect of a plasma treatment on polymers is not permanent, since the treated surfaces tend to recover to the untreated state (ageing process). This paper investigates the influence of discharge atmosphere on the ageing behaviour of plasma-treated PLA foils: these foils are plasma-treated with a DBD in 4 different atmospheres (air, nitrogen, argon and helium) and are subsequently stored in air. Results of contact angle and XPS measurements show that the discharge gas has a significant influence on the ageing behaviour of the PLA foils. This influence can be explained by the different cross-linking degree of the plasma-treated surfaces: helium and argon plasma-treated PLA films have a high cross-linking degree, which limits polymer chain mobility and as a result reduces the ageing process. In contrast, the ageing behaviour of air and nitrogen plasma-treated films is more pronounced due to their low cross-linking degree.

Plasma surface functionalization of biodegradable electrospun scaffolds for tissue engineering applications

“…Many authors experienced an abrupt transfer from superhydrophobic to superhydrophilic nanofibers having a WCA of 0° after plasma treatment [12,145,146]. It is worth mentioning that the plasma activation effect is not permanent over time, a partial hydrophobic recovery occurs by the reorientation of the incorporated groups towards the material bulk and by post-plasma reactions between the modified surfaces and some atmospheric minorities [147,148]. Interestingly, our research group has recently discovered that this hydrophobic recovery is less pronounced for PCL nanofibers compared to PCL films.…”

Plasma Surface Modification of Biodegradable Polymers: A Review

“…These free radicals can subsequently be used for cross‐linking or grafting of oxygen‐containing groups by exposing them to oxygen or air 63, 95. Plasma treatment is mainly applied to increase the surface energy of a polymer, however, it should be noted that the induced surface properties are not permanent since the surfaces tend to partially recover to the untreated state upon storage (hydrophobic recovery) and will undergo post‐plasma oxidation reactions 62, 96, 97…”

“…As previously mentioned, Hirotsu et al102 observed a gradual increase in water contact angle when PLA samples were kept in dry air. This hydrophobic recovery has recently been examined in detail by Morent et al,62 who employed a medium pressure DBD in air, argon, nitrogen and helium for the surface modification of PLA. Figure 10 shows the evolution of the contact angle on the plasma‐treated PLA samples as a function of storage time in air.…”

“…Recently, biodegradable aliphatic polyesters have been extensively studied as scaffold materials for tissue engineering, since they possess good mechanical properties, low immunogenicity, non‐toxicity and adjustable degradation rates 61. However, the hydrophobicity and low surface energy of these polymers lead to inefficient cell attachment, spreading and proliferation 62. As a result, surface modification of these polyesters is usually necessary and several approaches have been developed to improve their cell affinity 63.…”

Low-Pressure Plasma Treatment of Polylactide Fibers for Enhanced Mechanical Performance of Fiber-Reinforced Calcium Phosphate Cements

“…For instance, in Morent et al, [21] PLA films displayed contact angle reductions of around 158 (from 758 to approximately 59-608) after air and argon plasma treatment, which can be considered to generate comparable surface functionalities as the oxygen plasma treatment performed here. This value, apart from its intrinsic relationship with the surface chemistry of the PLA fibers, is relevant with regard to the calcium phosphate cement preparation, as the multifilaments will come in contact with the liquid phase of the cement, and may then absorb water differently after the plasma treatment, slightly modifying the effective L/P ratio of the CPC.…”