Study of Argon and Oxygen Mixtures in Low Temperature Plasma for Improving PLA Film Wettability

Abstract

Oxygen (O₂) and argon (Ar) plasma give a significant improvement in the wettability of PLA films. This study investigates the effectiveness of plasma activation with a mixture of these two gases. The study includes contact angle measurements with water and diiodomethane and calculation of surface free energy (SFE) together with its polar and dispersion components. In addition, a chemical analysis of the surface, surface roughness, weight loss and the change in tensile strength were examined. As a result of the study, it was found that the use of a mixture of oxygen and argon during the plasma activation of the polylactide film gives better improvement in wettability than the use of pure gases. Moreover, the use of a mixture of these gases in equal proportions turned out to be the most effective, providing the highest value of the SFE and its polar component, as well as the lowest value of the water contact angle. Furthermore, plasma activation with this gas mixture results in reduced surface etching compared to other gas compositions, which manifests itself in lower weight reduction and an insignificant change in tensile strength.

1. Introduction

Polylactide (PLA) is one of the most popular biodegradable plastics [1]. It is a good eco-friendly alternative to traditional plastics, which are currently the source of much debate regarding their use due to the problem of environmental pollution [2]. The question of the use of plastics is no longer just a matter of post-consumer waste or depleting oil resources, but also the threat of microplastics, which are found in the seas, oceans, soil, or in food products, cosmetics and even human blood [3,4]. Therefore, it seems important to replace plastics with biodegradable plastics, which are completely decomposed by microorganisms (bacteria and fungi) through aerobic or anaerobic processes into carbon dioxide or methane, respectively, and water and biomass. Furthermore, polylactide, besides being biodegradable, is produced from renewable raw materials [5]. PLA is mainly used in the production of disposable consumer goods in the packaging industry, e.g., loose-fill packaging, compost bags, food packaging and disposable tableware [6] and in the textile industry, e.g., disposable clothing. It also has biomedical applications such as surgical threads, in the production of implants [7], scaffolds for bone regeneration [8] or drug delivery microsphere [9]. At the same time, the properties of polylactide depend on the constituent isomers, molecular weight, processing temperature and annealing time [10].

Polylactide is a fairly hydrophobic material, as the water contact angle of unmodified PLA is 70–80° [11]. Moreover, PLA films, like all polymeric materials, are non-absorbent materials, which means that they require surface preparation before printing and finishing processes [12,13]. Both effective improvement of wettability and cleaning of the material’s surface are possible through the use of plasma activation processes [14,15,16]. In addition, plasma activation also results in improved adhesion [17], as well as sterilization of the material [18]. Only low-temperature plasma, also called non-thermal, cold, or non-equilibrium plasma, is applicable for modifying polymeric materials due to their thermal sensitivity. Low-temperature plasma activation, depending on the device, can be carried out as low-pressure plasma (pressures in the range of 10–75 Pa are the most commonly used) or atmospheric plasma [18,19]. With low pressures, it is easier to control the plasma reaction because the discharge is more stable [20].

A number of different gases are used for plasma activation of polymers, such as air, oxygen (O₂), helium (He), argon (Ar), nitrogen (N₂), ammonia (NH₃), carbon dioxide (CO₂), tetrafluoromethane (CF₄), etc. The type of gas used during plasma activation determines the physical and chemical properties of the surface being modified [14,16]. At the same time, the use of reactive gases, among which oxygen is the most commonly used, leads to chemical changes, while the use of inert gases, of which argon is a representative, leads mainly to crosslinking [11,12,21]. Previous research [22,23,24,25] demonstrated the beneficial effect of oxygen plasma on PLA films, while other reported works [11,26,27] described the effect of argon plasma on PLA. Considering good results that can be obtained with both gases and taking into account the significant differences in the changes occurring in the material during plasma activation, this scientific work studies the effects of their mixture on polylactide films. Gas mixtures including oxygen and argon have important applications in thermal plasma processes [28]. Moreover, the effect of gas mixtures has been studied for traditional plastics such as low-density polyethylene (LDPE) [29,30], polyethylene terephthalate (PET) [31] and polyethersulfone (PES) [32]. Due to the significant influence of the type of polymer [22] and the parameters of the activation process [33] on the activation efficiency and given the growing importance of PLA for environmental reasons, this study concentrates on cold plasma activation with a mixture of gases for PLA films, which, to the author’s knowledge, has not been studied so far.

Plasma activation of polymers is mainly aimed at changing their wettability, achieving the required adhesion and cleaning the surface, which is achieved by changing the chemical structure through functionalization with oxygen-containing functional groups and changing the roughness through etching or ion bombardment [21,34,35,36]. The type of functional groups generated on the polymer surface depends on the gas used for plasma activation [20,37]). Evaluation of the chemical changes in the surface layer and identification of the types of functional groups that appear is commonly performed by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Oxygen-containing functional groups are highly polar groups, and therefore oxygen-containing polymers will exhibit better wettability than oxygen-free polymers [38].

Wettability, or the ability of a surface to be wetted by various liquids, is one of the most important surface properties determining the ability to further coat, bond, print, laminate or otherwise refine polymeric materials. A common way to determine the wettability of a polymeric material is to measure the contact angle of the polymer using a drop of water planted on its surface [16,39,40].

An important parameter affecting the contact angle is the surface roughness [41], and it has a significant effect if R_a ≥ 100 nm. Moreover, the influence depends on the magnitude of the contact angle, and for hydrophilic surfaces for which it is less than 60°, an increase in roughness will result in a decrease in the contact angle [42]. Atomic force microscopy (AFM) and confocal microscopy can be used to characterize surface topography and roughness.

A parameter closely related to the contact angle is the surface free energy (SFE). Various methods are available for determining SFE values, including Fowkes, Owens–Wendt, van Oss–Chauhury–Good, Neumann, Zisman, for which knowledge of the contact angles of the surface layer of the polymeric material with at least two measuring fluids is required. The Owens–Wendt method is chosen here as being the most applicable [43]. The calculation of SFE and its polar and dispersion components makes it possible to determine the polar or non-polar nature of interactions at the liquid/solid boundary and the hydrophilic or hydrophobic nature of the surface [44]. High values of SFE and its polar component are important for printing, coating, and bonding processes, for example, as proper wetting of a substrate with ink, requires that the substrate’s SFE be much higher than the surface tension of the liquid [45].

The purpose of this research is to determine the effect of a mixture of oxygen and argon on improving the wettability of plasma-activated PLA films and to determine how the gas proportions affect the effects of plasma activation. In addition, the chemical and physical changes occurring during the modification are identified and the optimum proportion of each gas for obtaining the highest hydrophilicity of plasma-activated PLA film is determined.

These studies supplement the state of knowledge in the field of low pressure plasma treated PLA. This work has particular significance due to the fact that PLA is a biodegradable material which is an attractive alternative to currently dominant plastic materials which are increasingly controversial for their environmental impact.

2. Materials and Methods

2.1. Materials

Commercially available, biodegradable and compostable EarthFirst PLA BCP film (Plastic Suppliers, Inc., EarthFirst, Ghent, Belgium) was used for the study. It is a high-gloss transparent film dedicated to packaging purposes with FDA certificates for food contact and compostability certificates in accordance with the EN 13432 standard. The material used was 50 μm thick with the following properties: surface free energy 38 mJ/m², gloss 125 G.U. (60°), haze 7%, oxygen transmission rate O₂TR = 29 cc/100 in²/24 h, moisture vapor transmission rate MVTR = 10 g/100 in²/24 h and ultimate tensile strength MD = TD = 55 MPa. The film was supplied by the manufacturer in the form of A4 sheets, which were cut to 105 mm × 148 mm format before the plasma activation process. The film samples were conditioned in a climatized laboratory room in standard ambient conditions: temp. 23.0 ± 0.5 °C, relative humidity (RH) 50.0 ± 1.5% (ISO 187:1990) before treatment, moreover, all test procedures were carried out under such conditions.

Two pure industrial gases were used in the study: oxygen O₂ (99.8%) and argon (99.998%). The gases were compressed in cylinders at 200 bar, stored and operated in standard ambient conditions.

2.2. Plasma Activation

PLA films were exposed to low-pressure plasma in a half-automated vacuum chamber with a Diener Nano low-pressure plasma system basic unit (Diener Electronic, Altensteig, Germany). Process parameters were as follows: radio frequency 40 kHz, power pressure 0.4 mbar (40 Pa), gas supply process pressure 0.3 mbar (30 Pa), pumping off pressure 0.2 mbar (20 Pa), control pressure via gas, venting time 1 min, gas supply time 2 min and plasma activation time 4 min. The process parameters were selected on the basis of previous studies [25,27,33]. The temperature in the chamber was close to that in a climatized laboratory room, as in this process the plasma temperature hardly rises compared to the non-excited gas. Two gases, oxygen and argon, were used for testing, with different proportions of these gases used during activation, namely: 100% Ar, 75% Ar + 25% O₂, 50% Ar + 50% O₂, 25% Ar + 75% O₂, 100% O₂.

2.3. Contact Angle Measurements and Calculation of Surface Free Energy

The contact angles (CA) were measured with Tangent method 2 [27], using a DSA 100 drop shape analysis system (Krüss, Hamburg, Germany). Two measuring fluids, distilled water and diiodomethane 99% CH₂I₂ (Sigma-Aldrich, Taufkirchen, Germany), were used for the measurements. Sessile drops of the liquids were deposited on the film with needles of 0.5 mm diameter and the drop shape analysis was done 15 s. after the drop deposition. All measurements were done in stable environmental conditions (temp. 23.0 ± 1.0 °C). Fifteen contact angle measurements were made for each sample both before activation and immediately after plasma activation. The surface free energy of PLA film and its polar and dispersive components were calculated with the Owens–Wendt method. Formulas for calculating the SFE (1) and its components (2)–(3) are presented below [46,47].

$${\gamma }_S={\gamma }_S^d+{\gamma }_S^p$$

(1)

$${({\gamma }_S^d)}^{0.5}=\frac{{\gamma }_d\left(cos{\Theta }_d+1\right)-\sqrt{({\gamma }_d^p/{\gamma }_w^p)}{\gamma }_w\left(cos{\Theta }_w+1\right)}{2\left(\sqrt{{\gamma }_d^d}-\sqrt{{\gamma }_d^p({\gamma }_w^d/{\gamma }_w^p)}\right)}$$

(2)

$${({\gamma }_S^p)}^{0.5}=\frac{{\gamma }_w\left(cos{\Theta }_w+1\right)-2\sqrt{{\gamma }_S^d{\gamma }_w^d}}{2\sqrt{{\gamma }_w^p}}$$

(3)

where ${\gamma }_S^d$ is the dispersive component of SFE of the examined films, ${\gamma }_S^p$ is the polar component of SFE of the films, ${\gamma }_d$ is the SFE of diiodomethane, ${\gamma }_d^d$ is the dispersive component of diiodomethane SFE (= 48.5 mJ/m²), ${\gamma }_d^p$ is the polar component of diiodomethane SFE (= 2.3 mJ/m²), ${\gamma }_w$ is the SFE of water, ${\gamma }_w^d$ is the dispersive component of water SFE (= 21.8 mJ/m²), ${\gamma }_w^p$ is the polar component of water SFE (= 51 mJ/m²), ${\Theta }_d$ is the contact angle of diiodomethane and ${\Theta }_w$ is the water contact angle.

2.4. Chemical and Topographic Surface Analysis

Chemical analysis of the surface was carried out by X-ray photoelectron spectroscopy. XPS tests were performed on a 100 SSX ESCA Spectrometer (Surface Science Laboratories Inc., Mountain View, AB, Canada). A monochromatic Al K α radiation was used with energy 9 kV, 19 mA. Measuring spot sizes were appropriately 0.25 mm × 1.0 mm, 0.15 mm × 0.8 mm, 0.15 mm × 0.1 mm. Overview spectra parameters were as follows: passing energy 150 eV, resolution/channel: 0.16 eV, step size/measurement point 0.5 eV, neutralizer energy 0.5 eV. Meanwhile, the binding spectra settings were following: matching energy: 50 eV, resolution/channel: 0.054 eV, step size/measurement point: 0.1 eV, neutralizer energy: 0.5 eV. The decomposition of the carbon and oxygen peak into corresponding components was performed with CASA XPS software (version 2.3.15, Casa Software Ltd., Teignmouth, UK) [27,48].

Surface topographic analysis and roughness measurements were made using the Sensofar Plµ Neox microscope optical profiler (Sensofar-Tech, SL., Terrassa, Spain). Topographic images were taken at three different locations on the sample using the following microscope settings: lens 50 × 0.95 N, white light, measured area 768 × 576 pixels (254.64 × 190.90 μm²), layer thickness 15.2 μm and threshold 15%. The roughness was determined using Sensofar software (Sensofar-Tech, SL., Terrassa, Spain).

2.5. Weight Loss and Change in Mechanical Properties

Weight loss was determined from weight measurements taken immediately before and after plasma activation of the samples using a semi-microbalance Sartorius LE 225D-OCE (Sartorius, Göttingen, Germany). Samples with dimensions of 50 mm × 50 mm were used for the analysis. The weight loss value was calculated from 4 measurements.

The tensile strength of the film was tested using a static testing machine Roell (ZwickRoell GmbH & Co. KG, Ulm, Germany) and testXpert II software. The test was conducted in accordance with ISO 527-3. Measurements were performed on 5 samples per film, both for treated and untreated films.

2.6. Statistical Analysis

Statistical analysis was done using a data analysis toolkit in Excel (Office 365, Microsoft, Redmont, WA, USA). ANOVA test was used to analyze the data. In order to check which group averages differed significantly, a Tukey–Kramer post-hoc test was performed. In addition, as roughness and contact angle are a pair of parameters that can have a significant impact on each other’s values, their correlation was verified using the r-Pearson test. Significant differences were assumed with a significance level greater than 95% (p < 0.05).

3. Results and Discussion

3.1. Analysis of Changes in Water Contact Angle and Surface Roughness

The change in water contact angle (WCA) is the primary parameter used to analyze changes in wettability. As roughness may have a significant effect on WCA values, changes in these two parameters resulting from plasma activation of the PLA film are analyzed together in this chapter. The changes in contact angle and roughness are shown in Figure 1 and Figure 2, respectively.

As a result of plasma activation, a change was observed from a nearly hydrophobic (the value of the contact angle before plasma activation was 72.6°) to a hydrophilic material (the values of the contact angle after plasma activation were in the range of 27.3–39.4°) (Figure 3). Using one-way analysis of variance (ANOVA), a significant effect of plasma activation on the obtained water contact angle values was confirmed. The result of the ANOVA test for contact angle measurements (F(5,84) = 2.323, p = 9.4 × 10⁻⁹¹) indicates significant differences between group averages. At the same time, the best wettability was obtained for the film modified with a mixture of gases, where their proportion was equal, as confirmed by an analysis of the absolute values of the mean differences. Furthermore, the Tukey–Kramer test confirmed statistically significant differences between the averages of all groups with the exception of the activation carried out with 75% O₂ + 25% Ar and 100% Ar plasma. Similar conclusions regarding the positive effect of argon in the gas mixture used for plasma activation were made by Kim et al. [29], Fang et al. [31] and Saxena et al. [32]. However, for other polymeric materials (LDPE film, PET film and PES membranes, respectively), they showed that different proportions of gases in the mixture give the best results (90%, 99.7%–99.8%, and 40% Ar, respectively).

One-way analysis of variance showed no statistically significant differences between group averages for roughness (F(5,12) = 3.106, p = 0.318). However, although the F-test result was not statistically significant, it is worth noting that the plasma-activated film with 50% Ar + 50% O₂ gas had the lowest surface roughness (Figure 2), indicating that the contact angle was indeed the lowest. The remaining samples, especially those modified by plasma with 100% and 75% oxygen, were characterized by high roughness, which theoretically could significantly affect the value of the contact angle by lowering it, but this was not confirmed by the statistical analysis carried out. Verification of whether there was a significant relationship between water contact angle and roughness was carried out using the r-Pearson test. The result obtained, with p = 0.547 (p > 0.05), does not support a statistically significant correlation between the two parameters. Therefore, roughness has no confirmed influence on the contact angle values obtained in the case studied.

Moreover, the topographical changes of the material’s surface prove that plasma activation led not only to the functionalization of the surface and its etching, but also to the cleaning of the surface of impurities formed on the surface of the produced film [16]. Surface topography of the films is presented in Figure 4.

3.2. Analysis of Surface Free Energy and Its Components

Based on measurements of the contact angle with water and diiodomethane, the values of SFE and its components were determined using the Owens–Wendt equation. The results obtained are shown in Figure 5.

Plasma activation resulted in a significant increase in the values of SFE (from 40.1 to a maximum of 65.8 mJ/m²) and its polar component (from 8.8 to a maximum of 38.7 mJ/m²) while slightly reducing its dispersive component (from 31.4 to a maximum of 27.0 mJ/m²). The obtained values of SFE and its polar component confirm that the greatest improvement in hydrophilicity can be achieved using plasma activation with oxygen and argon in equal proportions. Moreover, the results obtained testify to the correct choice of activation process parameters and to high efficiency in improving the wettability of PLA films for both plasma with oxygen, argon and a mixture of these gases.

In comparison, Jordá-Vilaplana et al. [49] obtained similar but still lower SFE values (58.9 mJ/m²) only for air atmospheric plasma activation of PLA film using the most aggressive parameters, while for other parameters the values were much lower. On the other hand, Moraczewski et al. [22] obtained an SFE value slightly higher than ours at over 70 mJ/m² for PLA film activated with pure oxygen, although using an activation time of as much as 30 min, but when the time was reduced to 3 min, the result was already much worse (SFE of about 53 mJ/m²).

3.3. Surface Chemistry Analysis

Although the water contact angle, as mentioned earlier, depends on the surface roughness, it is primarily a function of surface chemistry [34].

XPS analysis was performed for unmodified film, modified with pure argon and pure oxygen, and a mixture of these two gases at 50% Ar and 50% O₂ (Figure 6). Samples activated with a mixture of gases in different proportions were omitted, as their wettability was lower than that of the 50% Ar + 50% O₂ samples. The composition of the surface layer of the samples was determined from the detailed analysis of the Cls and O1s peaks of the XPS spectra (

Table 1. Various components (in area %) of Cls and Ols peaks of XPS spectra of PLA films untreated and plasma treated with different gas compositions.

PLA Films	C1s Components (%)				O1s Components (%)
	C-C/C-H 285 eV	C-O 286.3 eV	C=O 288 eV	O-C=O 289.1 eV	O=C 532.25 eV	O-C 533.66 eV
Without plasma	39.9	24.6	13.8	21.7	34.1	65.9
50% O2 + 50% Ar plasma	15.6	53.3	0	31.1	34.8	65.2
100% Ar plasma	14.6	44.8	9.9	30.7	29.2	70.8
100% O2 plasma	23.8	28.5	22.8	25.0	50.1	49.9

).

The results confirm that plasma activation, regardless of the type of gas or gas mixture used, led to noticeable chemical changes on the sample surface. At the same time, the type of gas had a significant effect on the changes occurring in the surface layer of the polymer. The use of argon during activation led to the breaking of C-C and C-H bonds of the polymer chain and the formation of free radicals. Carbon radicals, as highly unstable elements, can react with one another leading to cross-linking of polymer chains and react with air when the sample is removed from the chamber after modification [11,16]. The results testify to significant oxidation of the sample after modification, both those modified with pure argon and with a mixture of oxygen and argon. Primarily hydroxyl and carboxyl groups were formed on the surface. In contrast, the use of oxygen during activation led to the formation of both hydroxyl, carboxyl and carbonyl groups. The hydroxyl group is polar, which makes it a suitable hydrogen bond donor. Not only does it improve water wettability, but the concentration of OH groups can also have a significant effect on the strength of adhesive bonds [50]. An example is the effect of hydroxyl groups from cellulose nanocrystals [51] on the adhesion properties of composite films [52]. In summary, the formation of polar compounds on the surface of a polymer has a significant impact on its functional properties and thus on its industrial applications, which can be adequately achieved by plasma activation and appropriately selected parameters. A higher number of oxygen-containing functional groups on the sample surface in the case of activation with a non-zero amount of argon is reflected in slightly lower water contact angle values and higher SFE values compared to those modified by pure oxygen plasma.

3.4. Analysis of Changes in Mass and Strength Properties

In addition to the changes in roughness indicative of the surface etching processes occurring during plasma activation, a removal of material from the surface can be identified by changes in mass [35]. Changes in sample mass and tensile strength are shown in Figure 7 and Figure 8. In addition, Figure 9 shows an example of stress-strain carves obtained during PLA film strength tests.

Gas composition has a significant effect on the weight change of plasma-activated PLA film samples, as evidenced by the results of the ANOVA test ((F(4,5) = 5.192, p = 0.016). Furthermore, the Tukey–Kramer test confirmed statistically significant differences between the means of all groups. Moreover, it was observed that the use of oxygen during plasma activation has a significant effect on mass loss (Figure 7). Increasing the proportion of oxygen in the gas mixture during the activation process led to greater mass loss. In the case of activation with pure argon, the mass loss was significantly lower. This is due to the fact that during plasma activation there is etching of the material, while with argon activation it is mainly just cleaning. Nevertheless, the values obtained do not indicate significant degradation of the material, although undoubtedly oxidation is accompanied more by chain scission than crosslinking [12,53]. Results by Kim et al. [29] confirm that cross-linking depends on the ratio of argon to oxygen and that pure argon plasma-treated samples showed the highest degree of cross-linking.

The lack of significant degradation is also confirmed by the tensile strength results (Figure 8). It is true that activation regardless of the type of gas used led to a deterioration of the material’s tensile properties, but these changes were not significant enough to affect the application aspects of the material. The results of the ANOVA test ((F(5,24) = 2.621, p = 0.011) confirm the significant differences in tensile strength values. Moreover, slightly worse resistance was obtained for plasma-activated materials using pure oxygen or mixtures of gases 25% O₂ + 75% Ar compared to pure argon or other mixtures of gases. This is evidenced by the results of the Tukey–Kramer test, which confirmed statistically significant differences only between, first, the averages of non-activated and plasma-activated films involving pure oxygen and, second, non-activated and plasma-activated films involving 25% O₂ + 75% Ar gases. Studies by other researchers [35] confirm the minor effect of cold plasma on tensile strength, where both a slight decrease and a slight increase in tensile strength were recorded depending on the type of plasma and the type of polymer material.

Sample weight loss due to etching accompanying plasma activation of PLA film can be caused by chemical processes such as cleavage of chemical bonds, scission of polymer chains, or chemical degradation of film components by the influence of free radicals, or physical processes which include the removal or re-aggregation of low molecular weight components on the polymer surface [35]. The results obtained (Figure 7) suggest that the weight loss is related to physical processes. The higher weight loss of plasma-modified samples with a higher proportion of oxygen may indicate that during oxygen plasma activation, products poorly bound to the sample surface were formed on the modified PLA surface and were removed [22,25,49].

4. Conclusions and Future Perspectives

The results indicate that the use of a mixture of oxygen and argon during plasma activation of the polylactide film yields a superior improvement in hydrophilicity than the use of pure gases. The use of a 50% O₂ + 50% Ar gas mixture during plasma activation enables the best wettability of PLA films, as evidenced by the highest value of SFE and its polar component and the lowest value of water contact angle. Only slightly worse wettability results were obtained for the gas mixture of 75% O₂ + 50% Ar. Nevertheless, in this case there was a greater negative effect of plasma activation on surface roughness, weight loss and tensile strength.

Moreover, the use of a gas composition of 50% O₂ + 50% Ar during plasma activation results in the lowest surface roughness. In addition, the observed significant improvement in wettability is due to the significant number of highly polar groups, and the number of oxygen-containing functional groups is much higher than for activation with oxygen alone.

In addition, the proportion of oxygen during plasma modification led to increased weight loss compared to modification with argon or its higher proportion in the mixture. However, the use of a mixture of oxygen and argon leads to a reduction in weight loss, as well as a favorable effect on the strength properties of the modified film. Nevertheless, as a result of plasma activation, regardless of the type of gas, a slight reduction in tensile strength was observed, but it was too small to affect the applicability of PLA films.

Polylactide is not only important in medical applications, but it is also a major biodegradable plastic with industrial applications and could become the polymer of the XXI century, once its prices are further aligned with other plastics and when waste regulations are even further tightened. PLA helps reduce the problem of post-consumer waste due to its biodegradability and possibly even compostability in case of some PLA-based plastics. It is now widely used in 3D printing, where its market share is increasing year on year, and is finding growing use in packaging, both in flexible and rigid packaging applications. PLA is an alternative packaging material to PET, polystyrene (PS), polyvinyl chloride (PVC) and cellulosic polymers and has applications in multilayer compositions. In packaging applications, it can be used in the form of films and laminates as well as extruded and thermoformed packaging. Packaging generally requires printing, which involves appropriate wetting of the printing inks and their adhesion to the substrate, while lamination processes require appropriate adhesion as well—thus both printing and lamination require modification of the polylactide. As shown in this work, PLA modification can be efficiently achieved through a low-temperature plasma activation process, which is environmentally friendly—it does not generate chemical waste, allows the desired polymer surface properties to be obtained by adjusting the process parameters, and is useful for temperature-sensitive materials, both in the form of flat films and complex spatial details.