# Supercritical CO2 Sorption Within Polymers Used in Medical Devices and Their Packaging

Yasmine Masmoudi, Thierry Tassaing, Daniel Borschneck, Elisabeth Badens

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Yasmine Masmoudi, Thierry Tassaing, Daniel Borschneck, Elisabeth Badens. Supercritical CO2 Sorp-
tion Within Polymers Used in Medical Devices and Their Packaging. Journal of Applied Polymer
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RESEARCH ARTICLE

OPEN ACCESS

# Supercritical CO₂ Sorption Within Polymers Used in Medical Devices and Their Packaging

Yasmine Masmoudi<fnref n="1" /> ID | Thierry Tassaing² ID | Daniel Borschneck³ ID | Elisabeth Badens<fnref n="1" /> ID

**Correspondence:** Yasmine Masmoudi (yasmine.masmoudi@univ-amu.fr)

**Received:** 25 July 2025 | **Revised:** 24 September 2025 | **Accepted:** 2 October 2025

**Funding:** This work was carried out within the framework of the project FASTECO2 funded under the PSPC program (Structuring Projects for
Competitiveness – Regions), with the support of Biffrance, the Sud – Provence-Alpes-Côte d'Azur Region, and the Aix-Marseille-Provence Metropolis.

**Keywords:** biomedical applications | kinetics | packaging | spectroscopy | swelling

## ABSTRACT

Thermodynamic and kinetic aspects of CO₂ sorption and the resulting swelling are investigated in several commercial polymer-based medical devices and packaging materials, using in situ FTIR spectroscopy under mild processing conditions (40°C–50°C and 8–20 MPa). At thermodynamic equilibrium, significant CO₂ uptake (up to 41% w/w) and volume swelling (up to 62%) are observed in silicones and poly(L-lactide-co-ε-caprolactone) copolymers, whereas limited sorption occurs in polyolefins (polypropylene, high-density polyethylene) and in polyester films coated with low-density polyethylene. These differences are attributed to intrinsic polymer properties; sorption and swelling are favored in polymers combining a highly amorphous structure with elevated chain mobility, and the presence of functional groups with chemical affinity for CO₂. Among the studied materials, glycol-modified polyethylene terephthalate exhibits a distinct behavior, characterized by initial CO₂ uptake followed by pressure-induced crystallization after several hours of exposure.

## 1 | Introduction

Polymers are essential in the medical device industry, representing over 70% of components used in devices and packaging [1]. Their versatility, biocompatibility, and cost-effectiveness make them indispensable for applications ranging from implantable or reusable medical devices to packaging, where they ensure product integrity, safety, and performance. Increasing demand for safe and sustainable healthcare solutions highlights challenges in polymer processing, particularly for cleaning, functionalization, and sterilization. Conventional approaches often rely on harsh conditions or organic solvents, which may compromise polymer properties and raise ecological concerns [2, 3].

Supercritical carbon dioxide (scCO₂) is now a well-established and promising solution for polymer processing due to its mild

critical coordinates (31°C, 7.4 MPa), tunable solvent power, and enhanced mass transfer properties [4–6]. These features enable efficient processing of thermosensitive, multi-component and complex structures, including additive-manufactured (3D-printed) medical devices. CO₂ is non-flammable, non-toxic, recyclable, and exhibits biocidal properties making it particularly attractive for industrial-scale applications, including FDA-recognized green sterilization alternatives [7, 8].

Optimizing scCO₂ processes requires understanding polymer behavior under CO₂ exposure. CO₂ diffuses into free volume and sorbs in amorphous domains, plasticizing the polymer, weakening intermolecular interactions, and facilitating chain slippage, acting as a kind of molecular lubricant, thereby enhancing chain mobility, increasing enthalpic state, and inducing swelling. These effects depend on polymer characteristics (chemical nature,

<footnote n="1">¹Aix Marseille University, CNRS, Centrale Med, M2P2, Marseille, France | ²Université de Bordeaux, ISM, UMR CNRS 5255, Talence, France | ³Aix-Marseille
Université, CNRS, IRD, Coll France, INRA, CEREGE, Aix-en-Provence, France</footnote>
crystallinity, free volume, molecular weight, functional groups) and on process conditions (pressure, temperature, exposure time) [9–12]. In addition to plasticization and polymer swelling, scCO₂ shifts thermal transitions. In amorphous polymers, Tg can be depressed by tens of degrees due to increased free volume and segmental mobility [9, 13–17]. In semicrystalline polymers, CO₂ sorbs into amorphous regions, increasing free volume and chain mobility at the crystal and amorphous phase interface. This may enable chain detachment from crystalline lamellae, resulting in thinner or less perfect lamellae and inducing a decrease in Tm according to Gibbs–Thomson relationship. At the same time, the increased chain mobility can also promote lamellar reorganization and thickening, which may partially counteract the Tm depression [17–21]. Hydrostatic pressure from CO₂ can also counteract plasticization, as compression reduces free volume and limits chain mobility [22]. At low to moderate pressures, plasticization dominates and lowers Tg and Tm, whereas at higher pressures or near CO₂ saturation, compression partly offsets this effect, resulting in smaller or even slightly positive shifts [9, 21, 23]. CO₂-induced Selective extraction of oligomers acting as plasticizers by scCO₂ may also counteract Tm depressions [24]. CO₂ not only shifts thermal transitions but also influences crystallization kinetics and crystalline structure, affecting the degree of crystallinity. It may induce crystallization from amorphous regions and trigger solid/solid transitions between different crystalline forms of the polymer [17, 19, 23, 25–27]. Beyond thermophysical properties of polymers, CO₂ sorption impacts their rheological behavior, including viscosity. High CO₂ saturation combined with these thermophysical and rheological property changes, can induce bubble nucleation and growth during depressurization, leading to foaming; this can be mitigated or avoided by regulating the depressurization rate [28–31].

Several techniques can be used to quantify CO₂ uptake in polymers [10]. Among these, spectroscopic techniques, especially Fourier-transform infrared spectroscopy (FTIR) coupled with high-pressure cells, provide in situ and simultaneous quantification of sorption, swelling, and molecular interactions [32–34]. ATR requires films in contact with the crystal and is affected by refractive index changes; transmission mode avoids such corrections [32, 35, 36]. FTIR microscopy in transflection mode allows analysis of thin films or fibers without reshaping, with micrometric resolution [32, 37, 38]. These setups are suitable to monitor sorption kinetics, swelling dynamics, and CO₂-induced crystallization [32, 34, 39, 40].

The present work is part of a broader research initiative aimed at applying scCO₂ technology to various stages in the treatment of already shaped polymer-based medical devices, including implantable ones. This encompasses cleaning, functionalization, and sterilization processes. For the latter, this study also considers polymer pouches, as medical devices are intended to be sterilized within their packaging. For such processes, understanding polymer behavior in scCO₂ is essential, and characterizing sorption and swelling phenomena is a critical step toward optimizing treatment parameters, namely pressure, temperature, and exposure duration.

Within this framework, the present study specifically investigates CO₂ sorption and the resulting swelling in a selection of commercially available polymer-based medical devices and

packaging materials. Experiments were conducted using in situ FTIR spectroscopy in transflection mode, under pressure and temperature conditions representative of industrial scCO₂ treatment. To ensure thermodynamic equilibrium, sorption kinetics were monitored in situ, without prior reshaping of the polymer samples. Among the polymers examined, data on packaging materials widely used for medical devices in industrial applications, such as PETG and Tyvek, remain scarce in the literature. The dimensions studied correspond to those typically used in industrial settings, thereby reinforcing the practical relevance of the findings.

## 2 | Material and Methods

### 2.1 | Chemicals

The behavior of already shaped polymer parts of medical devices and their packaging in a scCO₂ atmosphere was explored in this study.

Poly(L-lactide-co-ε-caprolactone) (RESOMER LC 703 S) made of 70% PLLA and 30% PCL (PLA/PCL) used in Matisse implants, a new generation of 3D-printed absorbable breast implants for reconstructive surgery after breast mastectomy was provided by Lattice Medical (Loos, France). Medical grade silicone wedges (MED-4765) and sheets (MED-4750) and polypropylene (PP) (Bormed HF840MO) meshes used in IntraSPINE lumbar interspinous spinal implant were supplied by Cousin Surgery (Wervicq-Sud, France).

Pouches and blisters suitable for packaging of medical devices, were supplied respectively by Südpack Medica and Oliver Healthcare Packaging. The pouches are composed of one side made of Tyvek (1073B Uncoated 7502916M), a high-density polyethylene (HDPE) resistant to bacterial penetration, and the other side made of a peelable polyester film extrusion-coated with a low-density polyethylene (48 PET/200 LDPE). The same Tyvek was used in one side of blisters sealed together with a blue tinted medical grade glycol-modified polyethylene phthalate (PETG) film.

Some physico-chemical properties of polymers used in the medical devices and packaging are summed-up in Table 1.

### 2.2 | Methods

#### 2.2.1 | High-Pressure Spectroscopy

Carbon dioxide sorption within polymers and the subsequent swelling of the latter were measured in situ using a high-pressure Fourier-transform infrared microscopy (HP-μFTIR) experimental setup (Figure 1), in scCO₂ atmosphere. Experimental conditions ranging from 40°C to 50°C and 8 to 20 MPa, commonly used for scCO₂ processing of medical devices, including cleaning, impregnation and sterilization, and while preserving material integrity, have been investigated [41–45]. For industrial applications, minimizing temperatures and pressures are preferred, as they result in reduced energy consumption of the process while still ensuring effective treatment.
$$S (\%) = 100 \times \left( \frac{A_{\text{Polymer}}^0}{A_{\text{Polymer}}} - 1 \right) \qquad (2)$$

$$w_{\text{CO}_2} = 100 \times \frac{M_{\text{CO}_2}C_{\text{CO}_2} \times 10^{-3}}{M_{\text{CO}_2}C_{\text{CO}_2} \times 10^{-3} + \frac{\rho_{\text{polymer}}}{1+S}} \qquad (3)$$

In these equations, $A_{CO_2}$ is the absorbance of the CO₂ peak at the corresponding selected wavenumber, $\varepsilon$ the molar extinction coefficient at the same wavenumber (L mol⁻¹ cm⁻¹), l the path length (cm) and $M_{CO_2}$ the molar mass of CO₂ equal to 44 g mol⁻¹. $A_{Polymer}^0$ and $A_{Polymer}$ are the spectral band areas of the polymer before and after CO₂ absorption, respectively. $\rho_{polymer}$ is the raw density of the polymer (g cm⁻³).

The extinction coefficients are known from calibration measurements in the literature [32]. For the used setup, the path length is considered twice the distance between the window

<figure><img src="image_3.png" /><figcaption>**FIGURE 1** | HP-μFTIR spectroscopy experimental bench. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

and the mirror (equal to twice the initial polymer thickness) and does not vary during polymer swelling. The wavenumbers and spectral bands selected for CO₂ and polymers are summed up in Table 2.

### 2.2.2 | X-Ray Diffraction (XRD) Analysis

XRD, the traditional technique to identify the crystallized compounds according to their atomic structure, has been used to assess the crystalline or amorphous state of the PETG samples and the crystallinity changes caused by different treatments that have been applied to PETG samples.

XRD was performed with an X-ray diffractometer (X'Pert Pro MPD, Malvern Panalytical) running at 40 kV and 40 mA using a Co Kα radiation (λ=1.79 Å) with a linear detector PIXcel¹⁵. The measurements have been performed in reflection mode to collect the scattered intensity between 10° (2θ) and 40° (2θ) at a step size of 0.026° for a total counting time of 3 h. To improve statistics, samples were spun horizontally at 15 rpm.

XRD analysis were carried out on PETG samples (discs of 3 cm of diameter) that have either been annealed under 150°C at atmospheric pressure for 12 h or treated in scCO₂ under 40°C and 20 MPa for 14 h and compared to raw PETG.

The degree of crystallinity has been determined for each sample following computer calculations as described by Kattan et al. [47]. It was calculated as the ratio of the area of the crystalline peaks to the sum of the areas of the crystalline peaks and the amorphous profile. The contribution of the amorphous phase and the crystalline phase (three main Gaussian curves for PETG) were computed using Fytik 0.9.8 until the sum of these contributions correctly fits the experimental data [48].

## 3 | Results and Discussion

For each material, the absorbance of the selected peaks for CO₂ and the integrated area of the spectral ranges selected for the polymer were recorded as a function of time for the different selected operating conditions (40°C and 50°C under 8, 14, and 20 MPa) as illustrated in Figure 2. An increase in the absorbance of CO₂ peak was observed indicating an increase of CO₂ sorption

<table><caption>**TABLE 2** | Wavenumbers and spectral bands selected for CO₂ and polymers.</caption><thead><tr><th>Polymer</th><th>Polymer wavenumbers and spectral range (cm<sup>-1</sup>)</th><th>Polymer band assignment<sup>a</sup></th><th>CO<sub>2</sub> wavenumbers (cm<sup>-1</sup>)</th><th>CO<sub>2</sub> band assignment</th></tr></thead><tbody><tr><td>Silicone</td><td>[5651, 5990]</td><td>2ν<sub>CH</sub></td><td>4965; 5083</td><td>ν<sub>1</sub> + 2ν<sub>2</sub> + ν<sub>3</sub>; 2ν<sub>1</sub> + ν<sub>3</sub></td></tr><tr><td>PLA:PCL</td><td>4718; [4610, 4806]</td><td>ν<sub>CH</sub> + ν<sub>C=O</sub></td><td>4957; 5076</td><td>ν<sub>1</sub> + 2ν<sub>2</sub> + ν<sub>3</sub>; 2ν<sub>1</sub> + ν<sub>3</sub></td></tr><tr><td>PP</td><td>[4000, 4500]</td><td>ν<sub>CH</sub> + δ<sub>CH</sub></td><td>3590; 3694</td><td>2ν<sub>2</sub> + ν<sub>3</sub>; ν<sub>1</sub> + ν<sub>3</sub></td></tr><tr><td>PET-G</td><td>[5884, 6115]; [4751, 4560]</td><td>ν<sub>CH</sub> + δ<sub>CH</sub>; ν<sub>CH</sub> + ν<sub>C=O</sub></td><td>4949; 5071</td><td>ν<sub>1</sub> + 2ν<sub>2</sub> + ν<sub>3</sub>; 2ν<sub>1</sub> + ν<sub>3</sub></td></tr><tr><td>PET/LDPE</td><td>[3950, 4500]</td><td>ν<sub>CH</sub> + δ<sub>CH</sub></td><td>3692</td><td>ν<sub>1</sub> + ν<sub>3</sub></td></tr><tr><td>HDPE</td><td>[3950, 4500]</td><td>ν<sub>CH</sub> + δ<sub>CH</sub></td><td>3692</td><td>ν<sub>1</sub> + ν<sub>3</sub></td></tr></tbody></table>

<footnote><sup>a</sup>ν = stretching mode; δ = bending mode.</footnote>
<figure><img src="image_4.png" /><figcaption>**FIGURE 2** | Evolution of FTIR spectra of silicone in contact with scCO₂ (40°C–14 MPa) over contact time. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**FIGURE 3** | Illustration of the evolution of the absorbance and integrated area of the selected CO₂ peak and polymer spectral range. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

within the polymer, before reaching a plateau characteristic of the establishment of thermodynamic equilibrium for almost all the studied materials. In parallel, the integrated area of the polymer spectral range decreases, indicating an increase in the volume swelling before stabilizing when the thermodynamic equilibrium is reached (as schematized in Figure 3).

This trend was observed for all the investigated polymers except for PETG for which an increase in the CO₂ peak intensity was observed before it decreased after a certain contact duration with scCO₂.

For all the different materials except for PETG, the duration required ($t_{eq}$) to reach the thermodynamic equilibrium of CO₂ sorption according to the tested thickness was determined. At equilibrium, the CO₂ concentration ($C_{CO2}$), and its corresponding mass fraction in the polymer ($w_{CO2}$) as well as the subsequent volume swelling ($S$) of the latter were quantified and summed up in Table 3. It is noteworthy that for each material, the variation of the time required to reach the thermodynamic equilibrium was not significant in the studied experimental range. For PETG, because a decrease in CO₂ concentration was observed after a certain contact time under each experimental condition, the values reported in Table 3 correspond to the maximum concentrations measured before this decrease occurred.

For all the materials studied, under isobaric conditions, no significant variations were observed in CO₂ sorption or polymer swelling when the temperature was varied from 40°C to 50°C. This is illustrated in Figures 4 and 5, for both silicone wedges and sheets that exhibit the highest values of CO₂ mass uptake (19%–41%) and polymer swelling (25%–62%) among the polymers studied. However, an increase in pressure from 8 to 20 MPa under isothermal conditions was favorable both to CO₂ sorption and polymer swelling in all the studied materials with the effect being more pronounced between 8 and 14 MPa, as illustrated in Figure 6, indicating a saturation of the polymers with CO₂.

Both studied silicone are medical-grade but of different thicknesses, 50 µm-thick sheets and 550 µm-thick wedges. The higher the polymer thickness, the longer the time required for reaching the equilibrium, which is coherent with the characteristic diffusion length being the thickness in thin films. However, at equilibrium, close results in term of CO₂ sorption and polymer swelling were obtained for both silicones. The high values of CO₂ sorption and polymer swelling in silicone are consistent with the behavior of elastomers exhibiting a high chain mobility for elastomers [37]. In addition to being completely amorphous with a relatively low glass transition temperature (<40°C under atmospheric pressure), silyl ether groups in their molecular structure have a good affinity with CO₂ promoting its sorption within the polymer.

The sorption of CO₂ in the MATTISSE implant made of PLA:PCL is also significant varying from 14% to 24% in mass fraction, leading to substantial swelling ranging from 32% to 54% under the tested experimental conditions (8–20 MPa at 40°C and 50°C). Both phenomena are enhanced under higher pressures. PLA:PCL exhibits high chain mobility in the amorphous region, with a low crystallinity rate of 15%. Furthermore, the presence of carbonyl groups which can interact with CO₂ promotes sorption phenomena [9]. Infrared spectroscopy studies have revealed that interactions between CO₂ and carbonyl groups, likely of the Lewis acid-base type, facilitate matrix plasticization by enhancing polymer chain mobility, enabling a greater CO₂ sorption [12, 33].

For PP meshes, as well as Tyvek (HDPE) and PET/PE peels, sorption and swelling phenomena are minimal. The low
<table><caption>**TABLE 3** | Summary of HP-μFTIR results for the different polymers studied at the thermodynamic equilibrium of CO₂ sorption, within a temperature range of 40°C–50°C and a pressure range of 8–20 MPa.</caption><thead><tr><th>Material</th><th>Thickness (μm)</th><th>t<sub>eq</sub><sup>a</sup> (min)</th><th>C<sub>CO2</sub><sup>a</sup> (mol L<sup>-1</sup>)</th><th>S<sup>a</sup> (%)</th><th>w<sub>CO2</sub> (%)</th></tr></thead><tbody><tr><td>Silicone (MED-4765)</td><td>550</td><td>50</td><td>5.3–9.4</td><td>25–62</td><td>19–36</td></tr><tr><td>Silicone (MED-4750)</td><td>50</td><td>20</td><td>6.6–11.4</td><td>31–61</td><td>25–41</td></tr><tr><td>PLA:PCL</td><td>1050</td><td>50</td><td>3.8–5.7</td><td>32–54</td><td>14–24</td></tr><tr><td>PP</td><td>350</td><td>300</td><td>0.2–0.6</td><td>4–8</td><td>1–3</td></tr><tr><td>PET-G<sup>b</sup></td><td>800</td><td>> 500</td><td>2–3</td><td>16–29</td><td>8–11</td></tr><tr><td>PET/LDPE</td><td>64</td><td>250</td><td>0.6–1.5</td><td>2–7<sup>c</sup></td><td>2–6</td></tr><tr><td>Tyvek (HDPE)</td><td>160</td><td>100</td><td>0.1–0.2</td><td>4</td><td>&lt;&lt;</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>**FIGURE 4** | Weight fraction of CO₂ sorbed within silicone wedges (left) and the subsequent polymer swelling (right) at 40°C (gray) and 50°C (black). [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

values for PP and HDPE can be explained, on the one hand, by their high crystallinity (despite their low glass transition temperatures). On the other hand, their structures do not contain functional groups with a specific chemical affinity for CO₂. These results align with the literature which has highlighted the low CO₂ sorption in PP [32, 49, 50]. Champeau et al. [32] characterized in situ CO₂ sorption in PP fibers and the corresponding polymer swelling at 40°C under pressures varying from 2 to 15 MPa in thermodynamic equilibrium conditions. The highest CO₂ mass uptake was of about 7% at 40°C and 15 MPa resulting in low swelling, lower than 5% according to previous literature data. For polyethylene, to the best of our knowledge, literature data of CO₂ sorption in the experimental range of our study are not available, and reported data are mainly at high temperatures (higher than 100°C) or at low pressures (4 or 5 MPa) as detailed in a recent review of Kiran et al. [10].

PET/PE peels present also low CO₂ sorption. On the one hand, polyethylene peel is semi-crystalline and does not contain functional groups with a specific chemical affinity for CO₂. On the other hand, despite the presence of carbonyl moieties in polyethylene terephthalate (PET) as well as phenyl ring presenting good affinity with CO₂, CO₂ sorption is reported to be relatively low in this polymer in pressure and temperature conditions close to our study. Champeau et al. [32] obtained a plateau-like mass uptake close to 10% in mass for pressures ranging from 10 to 15 MPa at 40°C with very low swelling.

<figure><img src="image_7.png" /><figcaption>**FIGURE 5** | Weight fraction of CO₂ sorbed within silicone sheets (left) and the subsequent polymer swelling (right) at 40°C (gray) and 50°C (black). [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

This behavior can be explained by the chain rigidity due to the presence of a phenyl group.

Compared to the other investigated polymers, PETG exhibits a distinct behavior, as previously mentioned. Indeed, a decrease in the concentration of CO₂ sorbed within the polymer was observed after a certain period of contact with CO₂. This behavior was recorded for all the experimental conditions explored, and for two wavenumbers corresponding to CO₂ (4949 and 5071 cm⁻¹) as illustrated in Figure 7. The contact duration before this decrease varies according to the pressure and temperature conditions and was of almost 500 min under 40°C.

Additionally, visual observations of PETG samples exposed to scCO₂ (10 MPa, 35°C) inside a high-pressure cell with a sapphire view window reveal signs of dulling and opacification after approximately 9h of exposure, even before depressurization, as shown in Figure 8.

As far as we know, this behavior has not been observed in literature for PETG polymer in scCO₂. A similar behavior was previously reported for PET [25, 39, 51, 52]. Induced crystallization of initially amorphous PET was observed. This behavior can only occur once a sufficient amount of CO₂ has been sorbed and allowed a depression of the glass transition temperature below the operating temperature, which explains the induction time before crystallization begins [39, 53]. As crystallization occurs, the limited sorption of CO₂ in the crystalline regions leads to a

<footnote><sup>a</sup>Experimental error ±10%.</footnote>

<footnote><sup>b</sup>The highest values revealed before the decrease in CO₂ concentrations.</footnote>

<footnote><sup>c</sup>The density of PET/PLDE was estimated to 1.01 g cm⁻¹ considering a thickness of 12 µm for PET and 50.5 µm for LDPE.</footnote>
<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /><figcaption>**FIGURE 6** | Evolution of weight fraction of sorbed CO₂ (wCO₂) and polymer swelling (S) with the pressure under 40°C (top) and 50°C (bottom) in PP (black), PET/LDPE (dark gray), PETG (light gray), PLA:PCL (white), silicone sheets (dotted), and silicone wedges (hatched). [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

decrease in the CO₂ concentration within the polymer, with CO₂ being progressively expelled as the polymer crystallizes. Similar tendency of an induction time to crystallization was observed in other polymers like polycarbonates [26].

Although PETG and PET polymers have similar chemical structures, their ability to crystallize differs significantly. PET is prone to crystallization, and the recrystallization of its glassy amorphous phase can be induced through thermal treatment, resulting in an isotropic structure, or through drawing, which produces an anisotropic structure [47]. However, PETG is classified as an amorphous copolyester with no ability to crystallize. Indeed, PETG is a polymer derived from PET but modified by the addition of glycol (often cyclohexane dimethanol [CHDM]). The incorporation of a second glycol into the PET structure disrupts its crystallization tendencies by introducing non-crystallizable moieties, resulting in an amorphous polyester [54]. Radhakrishnan and Nadkarni showed that despite the addition of CHDM as a comonomer that can partially inhibit crystallization in PET, it does not entirely prevent it. Crystallinity can develop in the copolymer through annealing at high temperatures or by solvent treatment followed by drying at moderate temperatures [54]. The induced crystallization results in a dulling and opacification of the polymer. Kattan et al. [47] have shown that a crystalline phase could appear in PETG either by an annealing from the glassy state or by a stretching at high draw ratio. Prolonged annealing of undrawn PETG enables crystallization, leading to the formation of a spherulitic superstructure with approximately 11% crystalline phase. This structural

<figure><img src="image_12.png" /><figcaption>**FIGURE 7** | Evolution of the concentration of CO₂ sorbed within PETG under 40°C and 20 MPa calculated from the absorbance of CO₂ peaks at 4949 cm⁻¹ (—) and 5071 cm⁻¹ (—). [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

transformation causes the material to become opaque. Hamonic et al. [55] also investigate the influence of uniaxially drawing of PETG and PET at 100°C. A similar mechanically induced crystalline structure was observed in both polymers, suggesting that crystallization in PETG occurs only in PET-rich regions, where
<figure><img src="image_13.png" /><figcaption>**FIGURE 8** | Photos of PETG sample in contact with scCO₂ (10 MPa and 35°C) for 1 h (left) and for 9 h (right). [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

only a portion of the ethylene-glycol chain segments crystallizes. However, a lower crystalline content was obtained in drawn PETG, likely due to the random distribution of CHDM along the chains, which significantly restricts its ability to crystallize.

XRD analysis of raw PETG and PETG samples that have been submitted to scCO₂ under 40°C and 20 MPa for 14 h were carried out (Figure 9). For comparison with the results obtained by Kattan et al. [47], a PETG sample annealed under 150°C under atmospheric pressure for 12 h was also analyzed.

For raw PETG, only the broad hump characteristic of amorphous polymers is observed. For the sample submitted to scCO₂ under 40°C and 20 MPa, three peaks emerge from the amorphous hump and appear at 2θ of 19.5°, 25.7°, and 29.9°, close to that reported by Kattan et al. [47] for drawn PETG at 20.5°, 25.5°, and 29°. These diffraction peaks are similar to that reported for semicrystalline PET which has undergone thermal crystallization at 20°, 26° and 30° corresponding, respectively, to the planes (010), (110), and (100) of the triclinic lattice structure of crystalline PET [56]. Computer calculations using the broad hump corresponding to the amorphous response of PETG, along with the three main diffraction peaks reported by Kattan et al., allowed estimation of the crystallinity ratio to 23.1%.

For the PETG sample annealed at 150°C under atmospheric pressure for 12 h, although no distinct diffraction peaks are observable by XRD, low-intensity peaks appear in the spectrum at 19.5°, 25.7°, and 29.9° corresponding to a crystallinity ratio of 13%. A close ratio of 11% was reported by Kattan et al. for PETG sample annealed at 120°C under atmospheric pressure for durations above 48 h.

The sorbed CO₂ fractions, observed before the sudden decrease in CO₂ concentrations, potentially due to the induced partial crystallization of PETG as discussed above, ranged from 8% to 11% and resulted in volume swelling between 16% and 29% in the tested conditions of 40°C–50°C and 8 to 20 MPa.

The CO₂ sorption values are consistent with literature. Indeed, Handa et al. [57] measured CO₂ mass uptake in PETG using

gravimetric techniques, reporting up to 16.5% at 35°C and 6.5 MPa. Shieh et al. [58] conducted similar measurements on PETG films (1 and 2.4-mm thick) after 1 h of exposure at various pressures (6.9, 13.8, and 20.7 MPa) and temperatures (25°C, 40°C, and 70°C), followed by depressurization. At 40°C and 13.8 MPa, the highest uptake (5.22%) was observed for the thinner film.

To the best of our knowledge, no literature has reported in situ PETG swelling in a scCO₂ atmosphere. Cejudo-Bastante et al. [59, 60] reported diameter expansion of PETG filaments after supercritical CO₂ treatment or impregnation with Olea EUROPAEA extract using ex situ measurements. Nevertheless, the foaming phenomenon occurring during depressurization influences ex situ measured expansions and a direct comparison with the in situ swelling quantified in this study is therefore not appropriate.

The presence of carbonyl moieties in the ester functionalities of PETG and its amorphous nature are favorable for CO₂ sorption. However, the presence of phenyl groups imparts rigidity to the PETG polymer, as evidenced by a relatively high T<sub>g</sub>, which limits chain mobility.

## 4 | Conclusion

This study provides a comprehensive analysis of CO₂ sorption and swelling behavior in a range of commercial polymers used in medical devices and their packaging, under supercritical CO₂ conditions. Using in situ FTIR spectroscopy, both thermodynamic and kinetic aspects were investigated under mild processing conditions relevant to industrial applications.

Silicones and PLA/PCL copolymers exhibited the highest CO₂ uptake (up to 41% w/w) and volume swelling (up to 62%), attributed to their amorphous structure, high chain mobility, and chemical affinity for CO₂. In contrast, polyolefins (PP, HDPE) and PET/LDPE multilayers showed limited sorption and swelling, due to their high crystallinity and lack of functional groups interacting with CO₂.
<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /><figcaption>**FIGURE 9** | Legend on next page.</figcaption></figure>
**FIGURE 9** | XRD curves of PETG samples from the top to the bottom: Raw PETG, submitted to scCO₂ under 20 MPa and 40°C for 14 h and annealed under 150°C and P_atm for 12 h. [Color figure can be viewed at wileyonlinelibrary.com]

PETG displayed a unique behavior among the characterized polymers, with an initial increase in CO₂ uptake followed by a decline, accompanied by visual opacification. This was attributed to pressure-induced crystallization in PET-rich regions, as confirmed by XRD analysis. Although CO₂-induced crystallization has been previously reported in other polymers such as PET and polycarbonates, this is, to the best of our knowledge, the first time such behavior has been observed and characterized in situ in PETG under supercritical conditions. Despite the amorphous nature of PETG and presence of carbonyl groups, the rigidity imparted by phenyl rings and its relatively high glass transition temperature limit its chain mobility and CO₂ sorption capacity.

This study highlights the importance of understanding polymer and CO₂ interactions for the design of efficient scCO₂-based processes. Ultimately, CO₂ uptake and swelling are favored in polymers that combine low crystallinity, high chain mobility, and functional groups capable of interacting with CO₂. To further improve the applicability of these results, future kinetic studies should be conducted on samples with varying thicknesses and geometries. This would allow the estimation of diffusion coefficients and the modeling of sorption dynamics, providing valuable insight into the time scales required to reach equilibrium under different processing conditions.

Importantly, these findings provide valuable insights for optimizing scCO₂-based processes in medical applications, not only for the functionalization of polymer-based devices, but also for their cleaning and sterilization, including when processed within their final packaging. In such contexts, preserving the structural and functional integrity of materials is critical to ensure safety and performance.

## Author Contributions

**Yasmine Masmoudi:** conceptualization (equal), formal analysis (equal), investigation (equal), methodology (equal), project administration (equal), supervision (equal), validation (equal), writing – original draft (lead), writing – review and editing (lead). **Thierry Tassaing:** data curation (lead), formal analysis (equal), methodology (equal), supervision (equal), validation (equal), writing – review and editing (supporting). **Daniel Borschneck:** investigation (supporting), writing – review and editing (supporting). **Elisabeth Badens:** conceptualization (equal), formal analysis (equal), funding acquisition (lead), methodology (equal), project administration (equal), supervision (equal), writing – review and editing (supporting).

## Acknowledgments

The authors are grateful for the financial support of BPI France and the Région Sud PACA in the framework of the project FASTECO2. They particularly thank Philippine Reymondon and Valentine Pepe (Cousin Surgery, Wervicq-Sud, France) and Megann Le Rest (Lattice Medical, Loos, France) for the fruitful discussions. The authors would also like to acknowledge Moumini Ballo Abdou for the work he carried out during his master's degree internship, which provided a solid foundation for this study.

## Ethics Statement

The authors have nothing to report.

## Conflicts of Interest

The authors declare no conflicts of interest.

## Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## References

1. Fortune Business Insights, “Medical Devices Market Size, Share & Industry Analysis, by Type (Orthopedic Devices, Cardiovascular Devices, Diagnostic Imaging, In-Vitro Diagnostics, Minimally Invasive Surgery, Wound Management, Diabetes Care, Ophthalmic Devices, Dental Devices, Nephrology, General Surgery, and Others), by End-User (Hospitals & ASCs, Clinics, and Others), and Regional Forecast, 2024–2032,” https://www.fortunebusinessinsights.com/industry-reports/medical-devices-market-100085.

2. Fortune Business Insights, “Medical Polymers Market Size, Share & Industry Analysis, by Type (Fibers & Resins, Medical Elastomers, Biodegradable Polymers, and Others), by Application (Medical Device, Medical Packaging, Medical Equipment & Components, Disposables, Implants, and Others), and Regional Forecast, 2024–2032,” https://www.fortunebusinessinsights.com/medical-polymers-markets-109681.

3. European Union, “Regulation (EU) No 2017/745 of the European Parliament and of the Council of 5 April 2017 on Medical Devices, Amending Directive 2001/83/EC, Regulation (EC) No 178/2002 and Regulation (EC) No 1223/2009 and Repealing Council Directives 90/385/EEC and 93/43/EEC (OJ L 117, 5.5.2017, 1),” https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32017R0745&from=EN.

4. International Organization for Standardization, “‘Medical Devices—Quality Management Systems—Requirements for Regulatory Purposes’ (ISO 13485:2016),” 2016, https://www.iso.org/obp/ui/en/#iso:std:iso:13485:ed-3:v1:en.

5. P. Antich-Isern, J. Caro-Barri, and J. Aparicio-Blanco, “The Combination of Medical Devices and Medicinal Products Revisited From the New European Legal Framework,” *International Journal of Pharmaceutics* 607 (2021): 120992.

6. A. White, D. Burns, and T. W. Christensen, “Effective Terminal Sterilization Using Supercritical Carbon Dioxide,” *Journal of Biotechnology* 123, no. 4 (2006): 504–515.

7. G. C. Soares, D. A. Learmonth, M. C. Vallejo, et al., “Supercritical CO₂ Technology: The Next Standard Sterilization Technique?,” *Materials Science & Engineering, C: Materials for Biological Applications* 99 (2019): 520–540.

8. DeviceMed, “Sterilization With EtO: The Inevitable March Towards a Reasoned Use,” https://DeviceMed.fr.

9. S. G. Kazarian, “Polymer Processing With Supercritical Fluids,” *Polymer Science* 42, no. 2 (2000): 78–101.

10. E. Kiran, J. A. Sarver, and J. C. Hassler, “Solubility and Diffusivity of CO₂ and N₂ in Polymers and Polymer Swelling, Glass Transition, Melting, and Crystallization at High Pressure: A Critical Review and Perspectives on Experimental Methods, Data, and Modeling,” *Journal of Supercritical Fluids* 185 (2022): 105378.
11. B. Bonavoglia, G. Storti, M. Morbidelli, A. Rajendran, and M. Mazzotti, "Sorption and Swelling of Semicrystalline Polymers in Supercritical CO₂," *Journal of Polymer Science Part B: Polymer Physics* 44 (2006): 1531-1546.

12. S. G. Kazarian, N. H. Brantley, B. L. West, M. F. Vincent, and C. A. Eckert, "In Situ Spectroscopy of Polymers Subjected to Supercritical CO₂: Plasticization and Dye Impregnation," *Applied Spectroscopy* 51, no. 4 (1997): 491-494.

13. L. Yu, L. Hongsheng, and L. Chen, "Thermal Behaviors of Polystyrene Plasticized With Compressed Carbon Dioxide in a Sealed System," *Polymer Engineering and Science* 49 (2009): 1800-1805.

14. Y. P. Handa and Z. Zhang, "A New Technique for Measuring Retrograde Vitrification in Polymer-Gas Systems and for Making Ultramicrocellular Foams From the Retrograde Phase," *Journal of Polymer Science Part B: Polymer Physics* 38 (2000): 716-725.

15. H. Guo and V. Kumar, "Solid-State Poly(Methyl Methacrylate) (PMMA) Nanofoams. Part I: Low-Temperature CO₂ Sorption, Diffusion, and the Depression in PMMA Glass Transition," *Polymer* 57 (2015): 157-163.

16. H. Guo and V. Kumar, "Some Thermodynamic and Kinetic Low-Temperature Properties of the PC-CO₂ System and Morphological Characteristics of Solid-State PC Nanofoams Produced With Liquid CO₂," *Polymer* 56 (2015): 46-56.

17. Y. Sun, M. Matsumoto, K. Kitashima, M. Haruki, S.-i. Kihara, and S. Takishima, "Solubility and Diffusion Coefficient of Supercritical-CO₂ in Polycarbonate and CO₂ Induced Crystallization of Polycarbonate," *Journal of Supercritical Fluids* 95 (2014): 35-43.

18. K. Kawate, N. Osaka, and H. Saito, "Surface Melting of Crystallized Poly(Vinylidene Fluoride) Under Carbon Dioxide," *Polymer* 54 (2013): 2406-2413.

19. Z. Zhang and Y. P. Handa, "CO₂-Assisted Melting of Semicrystalline Polymers," *Macromolecules* 30 (1997): 8505-8507.

20. Z. Lian, S. A. Epstein, C. W. Blenk, and A. D. Shine, "Carbon Dioxide-Induced Melting Point Depression of Biodegradable Semicrystalline Polymers," *Journal of Supercritical Fluids* 39 (2006): 107-117.

21. S. Takahashi, J. C. Hassler, and E. Kiran, "Melting Behavior of Biodegradable Polyesters in Carbon Dioxide at High Pressures," *Journal of Supercritical Fluids* 72 (2012): 278-287.

22. J. Bicerano, *Prediction of Polymer Properties*, 3rd ed. (CRC Press, 2002).

23. M. A. Fanovich, J. Ivanovic, I. Zizovic, D. Misic, and P. Jaeger, "Functionalization of Polycaprolactone/Hydroxyapatite Scaffolds With Usnea Lethariiformis Extract by Using Supercritical CO₂," *Materials Science and Engineering: C* 58 (2016): 204-212.

24. E. de Paz, Á. Martin, S. Rodríguez-Rojo, J. Herreras, and M. J. Cacerero, "Determination of Phase Equilibrium (Solid-Liquid-Gas) in Poly-(ε-Caprolactone)-Carbon Dioxide Systems," *Journal of Chemical & Engineering Data* 55 (2010): 2781-2785.

25. K. Mizoguchi, T. Hirose, Y. Naito, and Y. Kamiya, "CO₂-Induced Crystallization of Poly(Ethylene Terephthalate)," *Polymer* 28 (1987): 1298-1302.

26. Y. Sun, M. Matsumoto, M. Haruki, S. Kihara, and S.-I. Takishima, "Molecular Weight Dependence of the Crystallization of the Polycarbonate Induced by Supercritical CO₂," *Journal of Supercritical Fluids* 113 (2016): 144-149.

27. R.-H. Zhang, X.-K. Li, G.-P. Cao, et al., "Improved Kinetic Model of Crystallization for Isotactic Polypropylene Induced by Supercritical CO₂: Introducing Pressure and Temperature Dependence Into the Avrami Equation," *Industrial and Engineering Chemistry Research* 50 (2011): 10509-10515.

28. E. Di Maio and E. Kiran, "Foaming of Polymers With Supercritical Fluids and Perspectives on the Current Knowledge Gaps and Challenges," *Journal of Supercritical Fluids* 134 (2018): 157-166.

29. J. A. Sarver and E. Kiran, "Foaming of Polymers With Carbon Dioxide—The Year-In-Review—2019," *Journal of Supercritical Fluids* 173 (2021): 105166.

30. I. Tsivintzelis, A. G. Angelopoulou, and C. Panayiotou, "Foaming of Polymers With Supercritical CO₂: An Experimental and Theoretical Study," *Polymer* 48 (2007): 5928-5939.

31. Y. Masmoudi, L. Ben Azzouk, O. Forzano, J.-M. Andre, and E. Badens, "Supercritical Impregnation of Intraocular Lenses," *Journal of Supercritical Fluids* 60 (2011): 98-105.

32. M. Champeau, J.-M. Thomassin, C. Jérôme, and T. Tassaing, "In Situ FTIR Micro-Spectroscopy to Investigate Polymeric Fibers Under Supercritical Carbon Dioxide: CO₂ Sorption and Swelling Measurements," *Journal of Supercritical Fluids* 90 (2014): 44-52.

33. S. G. Kazarian, M. F. Vincent, F. V. Bright, C. L. Liotta, and C. A. Eckert, "Specific Intermolecular Interaction of Carbon Dioxide With Polymers," *Journal of the American Chemical Society* 118, no. 7 (1996): 1729-1736.

34. A. V. Ewing and S. G. Kazarian, "Current Trends and Opportunities for the Applications of In Situ Vibrational Spectroscopy to Investigate the Supercritical Fluid Processing of Polymers," *Journal of Supercritical Fluids* 134 (2018): 88-95.

35. M. Buback, J. Schweer, and H. Yups, "Near Infrared Absorption of Pure Carbon Dioxide up to 3100 Bar and 500 KI Wavenumber Range 3200 cm⁻¹ to 5600 cm⁻¹," *Zeitschrift für Naturforschung* 41 (1986): 505-511.

36. A. R. C. Duarte, L. E. Anderson, C. M. M. Duarte, and S. G. Kazarian, "A Comparison Between Gravimetric and In Situ Spectroscopic Methods to Measure the Sorption of CO₂ in a Biocompatible Polymer," *Journal of Supercritical Fluids* 36 (2005): 160-165.

37. J. Dubois, E. Grau, T. Tassaing, and M. Dumon, "On the CO₂ Sorption and Swelling of Elastomers by Supercritical CO₂ as Studied by In Situ High Pressure FTIR Microscopy," *Journal of Supercritical Fluids* 131 (2018): 150-156.

38. K. Ongkasin, Y. Masmoudi, T. Tassaing, G. Lebourdon, and E. Badens, "Supercritical Loading of Gatifloxacin Into Hydrophobic Foldable Intraocular Lenses—Process Control and Optimization by Following In Situ CO₂ Sorption and Polymer Swelling," *International Journal of Pharmaceutics* 581 (2020): 119247.

39. N. H. Brantley, S. G. Kazarian, and C. A. Eckert, "In Situ FTIR Measurement of Carbon Dioxide Sorption Into Poly(Ethylene Terephthalate) at Elevated Pressures," *Journal of Applied Polymer Science* 77, no. 4 (2000): 764-775.

40. M. Champeau, J.-M. Thomassin, C. Jérôme, and T. Tassaing, "In Situ Investigation of Supercritical CO₂ Assisted Impregnation of Drugs Into a Polymer by High Pressure FTIR Micro-Spectroscopy," *Analyst* 140 (2015): 869-879.

41. J. C. Bredeau, "Techniques de l'Ingénieur," 2018, MED7700 V1.

42. M. Champeau, J.-M. Thomassin, T. Tassaing, and C. Jérôme, "Drug Loading of Polymer Implants by Supercritical CO₂ Assisted Impregnation: A Review," *Journal of Controlled Release* 209 (2015): 248-259.

43. A. Bernhardt, M. Wehrl, B. Paul, et al., "Improved Sterilization of Sensitive Biomaterials With Supercritical Carbon Dioxide at Low Temperature," *PLoS One* 10, no. 6 (2015): e0129205.

44. G. C. Soares, D. A. Learmonth, M. C. Vallejo, et al., "Supercritical CO₂ Technology: The Next Standard Sterilization Technique?," *Materials Science and Engineering: C* 99 (2019): 520-540.

45. V. Warambourg, A. Mouahid, C. Crampon, A. Galinier, M. Claeys-Bruno, and E. Badens, "Supercritical CO₂ Sterilization Under Low Temperature and Pressure Conditions," *Journal of Supercritical Fluids* 203 (2023): 106084.

46. T. Guadagno and S. G. Kazarian, "High-Pressure CO₂-Expanded Solvents: Simultaneous Measurement of CO₂ Sorption and Swelling of
Liquid Polymers With In-Situ Near-IR Spectroscopy," *Journal of Physical Chemistry. B* 108 (2004): 13995-13999.

47. M. Kattan, E. Dargent, J. Ledru, and J. Grenet, "Strain-Induced Crystallization in Uniaxially Drawn PETG Plates," *Journal of Applied Polymer Science* 81 (2001): 3405-3412.

48. M. Wojdyr, "Fityk: A General-Purpose Peak Fitting Program," *Journal of Applied Crystallography* 43 (2010): 1126-1128.

49. Z. Lei, H. Ohyabu, Y. Sato, H. Inomata, and R. L. Smith, Jr., "Solubility, Swelling Degree and Crystallinity of Carbon Dioxide-Polypropylene System," *Journal of Supercritical Fluids* 40 (2007): 452-461.

50. J. Von Schnitzler and R. Eggers, "Mass Transfer in Polymers in a Supercritical CO₂-Atmosphere," *Journal of Supercritical Fluids* 16 (1999): 81-92.

51. S. M. Lambert and M. E. Paulaitis, "Crystallization of Poly(Ethylene Terephthalate) Induced by Carbon Dioxide Sorption at Elevated Pressures," *Journal of Supercritical Fluids* 4 (1991): 15-23.

52. D. Li, T. Liu, L. Zhao, and W. Yuan, "Controlling Sandwich-Structure of PET Microcellular Foams Using Coupling of CO₂ Diffusion and Induced Crystallization," *AICHE Journal* 58 (2012): 2512-2523.

53. E. J. Beckman and R. S. Porter, "Crystallization of Bisphenol A Poly-carbonate Induced by Supercritical Carbon Dioxide," *Journal of Polymer Science, Part B: Polymer Physics* 25 (1987): 1511-1524.

54. S. Radhakrishnan and V. M. Nadkarni, "Crystallization Behaviour of Aromatic Copolyester Modified With Alicyclic Diol," *European Polymer Journal* 22 (1986): 67-70.

55. F. Hamonic, V. Miri, A. Saiter, and E. Dargent, "Rigid Amorphous Fraction Versus Oriented Amorphous Fraction in Uniaxially Drawn Polyesters," *European Polymer Journal* 58 (2014): 233-244.

56. R. P. de Daubeny, C. W. Bunn, and C. J. Brown, "The Crystal Structure of Polyethylene Terephthalate," *Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences* 226 (1954): 531-542.

57. Y. P. Handa, B. Wong, Z. Zhang, V. Kumar, S. Eddy, and K. Khemani, "Some Thermodynamic and Kinetic Properties of the System PETG-CO₂, and Morphological Characteristics of the CO₂-Blown PETG Foams," *Polymer Engineering and Science* 39 (1999): 55-61.

58. Y.-T. Shieh, J.-H. Su, G. Manivannan, P. H. C. Lee, S. P. Sawan, and W. D. Spall, "Interaction of Supercritical Carbon Dioxide With Polymers. II. Amorphous Polymers," *Journal of Applied Polymer Science* 59 (1996): 707-717.

59. C. Cejudo-Bastante, L. Verano-Naranjo, N. Toro-Barrios, C. Pereyra, C. Mantell, and L. Casas, "Structural Modification of Polymers Functionalized With Mango Leaf Extract by Supercritical Impregnation: Approaching of Further Food and Biomedical Applications," *Polymers* 14 (2022): 2413.

60. N. D. Machado, J. E. Mosquera, C. Cejudo-Bastante, et al., "Supercritical Impregnation of PETG With Olea europaea Leaf Extract: Influence of Operational Parameters on Expansion Degree, Antioxidant and Mechanical Properties," *Polymers* 16 (2024): 1567.