# Centrifugal partition chromatography approach to separate additives from PVC resin to support recycling processes

Noemie Auchere, Alexandra Berlioz-Barbier, Agnès Le Masle, Olivier Boyron, Alexandra Chaumonnot

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## To cite this version:

Noemie Auchere, Alexandra Berlioz-Barbier, Agnès Le Masle, Olivier Boyron, Alexandra Chaumonnot. Centrifugal partition chromatography approach to separate additives from PVC resin to support recycling processes. Journal of Chromatography A, 2025, 1761, pp.466337. 10.1016/j.chroma.2025.466337. hal-05409629

HAL Id: hal-05409629

https://ifp.hal.science/hal-05409629v1

Submitted on 10 Dec 2025

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# Centrifugal partition chromatography approach to separate additives from PVC resin to support recycling processes

Noemie Auchere<sup>a,*</sup> <sup>●</sup>, Alexandra Berlioz-Barbier<sup>a</sup>, Agnès Le Masle<sup>a</sup>, Olivier Boyron<sup>b,●</sup>,
Alexandra Chaumonnot<sup>a</sup>

## ARTICLE INFO

### Keywords:

Plastic characterization

Centrifugal partition chromatography

Solvent system development

High resolution mass spectrometry

Polyvinyl chloride

Recycling support

## ABSTRACT

Plastics are widely used materials composed of polymers and various additives to achieve specific properties. Their composition is often highly complex, particularly in post-consumer plastic waste. As mechanical recycling faces increasing limitations, chemistry-driven strategies are attracting growing interest to improve plastic recovery. Among these, dissolution recycling offers the possibility of selectively recovering pure polymers free from additives and contaminants. However, the absence of efficient methods to separate and analyze the different components of plastics remains a major bottleneck to evaluate recycling processes efficiency. Here, we report the first application of Centrifugal Partition Chromatography (CPC) to address this challenge using polyvinyl chloride (PVC) as a model material. A biphasic solvent system based on heptane, dimethyl sulfoxide (DMSO), and 3-pentanone (DEK) (25/45/30 w/w/w) was developed, guided by Hansen solubility parameters. CPC enabled the separation of the polymer from organic additives and contaminants, as well as the fractionation of additives into distinct groups, facilitating their subsequent identification and potential quantification. Moreover, CPC allows the recovery of sufficient amounts of purified polymer, enabling detailed spectroscopic characterization to assess its structural integrity and purity. After fractionation, additives were identified by reverse phase liquid chromatography coupled with tandem high resolution mass spectrometry (RPLC—HRMS/MS), while the recovered polymer was analyzed using nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). Overall, these results demonstrate that CPC is a promising tool to fractionate complex plastic matrices, offering new opportunities for advanced material characterization and supporting the development of more efficient recycling processes.

## 1. Introduction

Plastics are widely produced and used across various industries, including construction, food packaging, and automotive manufacturing. In 2022, global plastic production reached 400.2 million tons, with polyvinyl chloride (PVC) ranking second after polyolefins, accounting for 50.84 million tons [1]. Since the 1970s, PVC production has grown steadily, leading to significant challenges in waste management. Recycling has emerged as a key solution following prior sorting steps [2,3], with two primary approaches: mechanical recycling and physico-chemical recycling.

Mechanical recycling, the most common approach, involves washing and shredding waste with similar formulations. However, it is not well suited for complex materials like PVC, which often contain high levels of

additives - particularly legacy additives that may have been used decades ago and are now subject to strict regulations - making their identification and removal particularly challenging [4,5]. Solvent-based recycling, an advanced physico-chemical recycling method, has been gaining interest as a complementary solution. This approach employs solvent systems to selectively dissolve and separate polymers from additives, contaminants, and impurities. It not only enables the recovery of high-purity polymers but also facilitates the identification and potential reuse of extracted additives, making it particularly well suited for PVC and other complex plastics. PVC is highly versatile, encompassing a broad range of formulations for various applications. As a composite material, it combines a polymer base with additives, which can account for up to 70 % of the weight in soft PVCs. Furthermore, some PVC-based products have lifespans of several decades, during which additive

<footnote><sup>a</sup> IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, 69360 Solaize, France</footnote>

<footnote><sup>b</sup> Université Lyon 1, CPE Lyon, CNRS, UMR 5128, CP2M, Equipe PCM, 69100 Villeurbanne, France</footnote>

<footnote>* Corresponding author at: IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, 69360 Solaize, France.</footnote>

<footnote>E-mail address: noemie.auchere@ifpen.fr (N. Auchere).</footnote>
regulations may evolve. For instance, certain additives historically approved, such as specific phthalates, are now restricted. For example, di(2-ethylhexyl) phthalate (DEHP), a commonly used plasticizer in PVC, has been regulated since 2011 and must not exceed 0.1 % by weight of the plastic.

The development of efficient recycling processes, particularly for complex materials like PVC, relies heavily on advanced analytical methodologies. Analytical techniques enable the precise characterization of waste streams, ensuring the identification and quantification of additives and contaminants. This information is essential for optimizing recycling processes, such as solvent-based approaches. Moreover, analytical monitoring supports compliance with evolving regulations and guarantees the quality of recycled materials, making it a key element in advancing sustainable solutions for plastic waste management.

Today, methods to characterize plastic waste, including their aging, are limited due to the complexity of the matrix. The two parts of plastics (polymer and additives) are characterized differently and by consequence, their separation is required. In literature, different solid/liquid extraction methods exist, as microwave assisted extraction, accelerated solvent extraction, ultrasonic assisted extraction, soxhlet, etc [6]. The dissolution-precipitation method is also well known as a purification method and continue to be developed [7]. However, this method presents limits as capture of additives during reprecipitation or degradation of polymer with high temperature involved [8]. In particular, multiple steps are required to fully recover additives with dissolution-precipitation and obtain a purified polymer. For instance, one study demonstrated that at least seven purification steps are necessary to separate DEHP from PVC resin [9]. The difficulty in separating PVC resin from its additives arises from their high chemical affinity, which is reflected in their very close Hansen solubility parameters [10]. These parameters – describing dispersive, polar, and hydrogen-bonding interactions – are widely used to predict solubility and miscibility between polymers and additives. The closer the Hansen parameters, the stronger the interaction, and the more challenging the separation.

In general, all methods described in literature are useful to extract one additive or additive families. However they are not associate to exhaustive extraction methods of additives [11]. The literature lacks fractionation methods to recover both the purified polymer and the additives to characterize or quantify them. In one hand, the polymer is characterized chemically by size exclusion chromatography (SEC) [12–14] or by Fourier transform infra-red spectroscopy (FTIR) [15,16]. In the other hand, organic additives and their respective potential degradation products are often characterized by gas chromatography coupled with mass spectrometry (GC-MS) for volatiles [17–19] and liquid chromatography coupled with mass spectrometry (LC-MS) for semi-volatiles and non-volatiles [20–23].

Centrifugal partition chromatography (CPC) is a well-established method for purifying natural materials. It can also be used to purify macromolecules such as proteins or to fractionate some complex mixtures such as lignocellulosic hydrolysates [24–27]. This type of chromatography involves two immiscible liquid phases, similar to liquid-liquid extraction: one serves as the stationary phase and the other as the mobile phase. The compounds in the sample are distributed between the two phases according to their affinity for each. Their separation depends on their partition coefficients, defined as the ratio of solute concentrations in the stationary and mobile phases. A low partition coefficient indicates a high affinity of the solute for the mobile phase. During CPC, the mobile phase flows through the stationary phase, which is retained in the CPC cells by centrifugal force. Compounds with higher affinity for the mobile phase elute more quickly, corresponding to higher partition coefficients. One major advantage of CPC is its versatility: a tailored biphasic solvent system can be designed to match a specific sample matrix, provided the two phases remain immiscible. Moreover, both the mobile and stationary phases can be recovered,

enabling complete recovery of the sample without loss.

This study presents the first application of CPC on plastic materials. It purposes a methodology to separate additives and polymers from plastic without degrading them, focusing on PVC-based materials. Inspired by the use of CPC as a purification technique for natural products, the methodology aims to extract and purify molecules of interest – specifically additives such as phthalates – and the polymer itself from a complex matrix. The main advantages of CPC, as previously discussed, include its versatility, complete sample recovery, and suitability for preparative-scale applications. In the context of plastic characterization, separating additives from the polymer is essential to facilitate accurate analysis. CPC is therefore employed to recover all organic additives in one phase while the polymer remains in the other, enabling its total purification and recovery. The initial step consisted of identifying a biphasic solvent system adapted to the PVC matrix, using Hansen solubility parameters and refining it through the UNIFAC method to ensure stability. The CPC method was then developed using a model feedstock containing a plasticizer from a regulated family (phthalates), and the additive fractions were characterized by liquid chromatography coupled with electrospray ionization high-resolution mass spectrometry (LC-ESI-HRMS) to confirm complete additive removal. The polymer resin was finally characterized by SEC and FTIR to assess its purity and potential degradation.

## 2. Material and methods

### 2.1. Chemicals and reagents

3-pentanone (DEK), dimethylsulfoxide (DMSO) and n-heptane were HPLC grade purchased from Fisher Scientific (France). Ultrapure water (18.2 MΩ-cm) was produced by a Milli-Q water purifier (Millipore SAS, France). Methanol (MeOH), acetonitrile (MeCN), isopropanol (IPA) and formic acid (FA) were LC-MS grade Optima from Fisher Scientific (France). Tetrahydrofuran (THF) was HPLC grade from Fisher Scientific (France). Filters was produced by Interchim (France). Phthalates standards (dibutyl phthalate (DBP), di(2-ethylhexyl) phthalate (DEHP) and diisodecyl phthalate (DIDP)) were purchased by Sigma-Aldrich (France). The sodium formate was home-made with NaOH at 0.1 mol, IPA, water and FA.

### 2.2. Sample of interest

The matrix used in this study was a soft PVC specifically formulated to mimic a commercial formulation (Table 1). The resin K75 was also supplied in its pure form (without any additives) and used as standard.

The soft PVC corresponds to one of difficult PVC to recycle due to its high phthalate content.

### 2.3. Sample preparation

The PVC based plastic of interest was weighed in a mixture of heptane/DMSO/DEK (7.7/61.4/30.9 w/w/w). An amount of 300 mg of the PVC compound was solubilized in 10 mL of the solvent mix for 5 h at 60 °C to accelerate the solubilization. Then the mixture was centrifugated during 15 min at 5300 rpm and filtrated through a 4.5 µm PTFE filter to

<table><caption>**Table 1**
PVC model feedstock composition.</caption><thead><tr><td>Name</td><td>Weight %</td></tr></thead><tbody><tr><td>PVC resin K75</td><td>55.3</td></tr><tr><td>Plasticizer DIDP</td><td>24.3</td></tr><tr><td>Co-stabilizer Epoxidized Soybean Oil (ESO)</td><td>3.3</td></tr><tr><td>Lubricant Wax (Oxidized polyethylene)</td><td>3.3</td></tr><tr><td>Stabilizer and mineral charge</td><td>16.8</td></tr><tr><td>Coloration</td><td>0.1</td></tr></tbody></table>
remove insoluble particles, mainly due to fillers. This step provided to keep in solution only the organic part of plastic (resin, plasticizer, co-stabilizer and lubricant).

## 2.4. CPC fractionation

CPC experiments were performed on a SCPC100 associated to a Spot Prep II (Gilson Purification, USA). The column used has a volume of 131 mL and the apparatus had a total dead volume of 20 mL. The system was equipped with a quaternary pump, an automatic sample injection valve with a 5 mL sample loop and a fraction collector. Experiments were conducted at room temperature (20 ± 2 °C). The solvent system consisted of heptane/DMSO/DEK (0.25/0.45/0.30 w/w/w). Ascending elution mode was used, allowing the use of the DMSO-enriched phase as the stationary phase and the heptane-enriched phase as the mobile phase. The stationary phase (A) is a ratio of heptane/DMSO/DEK (7.7/61.4/30.9 w/w/w) and the mobile phase (B) a ratio of heptane/DMSO/DEK (62/7.8/30.2 w/w/w). Each phase was prepared in a separate bottle.

The Table 2 shows the different parameters used to prepare the column and carry out the separation. The stationary phase ratio was measured at 50 %. It corresponds to the ratio of stationary phase and mobile phase present in CPC cells after equilibration. Fractions were collected every 10 mL during the 70 min of the elution part and numbered consequently from 1 to 49.

Then they are collected every 55 mL for 10 min during the extrusion part, ie the recovery of the stationary phase.

### 2.4.1. Determination of partition coefficient

The partition coefficient K corresponds to the ratio of the solute concentrations [S] in the upper and in the lower phases (Eq. (1)):

$$K_D = \frac{|S|\text{lower}}{|S|\text{upper}} \qquad (1)$$

K<sub>D</sub> was measured on model molecules in the heptane/DMSO/DEK system. The biphasic system was prepared as described in part 2.4. 5 mL of each phase and approximately 100 mg of analytical standard (phthalates or pure PVC resin) were added to a 20 mL flask. After vigorous shaking and 5 min of equilibration, 1 mL of each phase was transferred into vials. The upper phase was evaporated under nitrogen flux and 1 mL of methanol was added to the vials. Upper and lower phase were analyzed by SEC-RID-UV (method described in 2.7 (1)).

## 2.5. RPLC-ESI-HRMS analysis

Reversed-phase liquid chromatography (RPLC) analyses were performed on an Agilent 1290 composed of a high-speed pump, a 1290 autosampler (thermostated at 15 °C), a 1290 MCT column oven and a 1290 DAD UV detector. The injection volume was 1 µL. Separation was achieved on a Macherey-Nagel Nucleoshell biphenyl C18 column (150 × 3 mm, 2.6 µm) at 40 °C. Mobile phases used were water (A1) and MeCN/MeOH (50:50 v:v) (B1) both acidified with 0.05 % (v:v) of formic acid. The separation was performed at 0.6 mL/min with the following elution gradient: 0 – 17 min (from 30 % B1 to 100 % B1), 17 – 21 min (100 % B1), 21 – 21.01 min (from 100 % B1 to 30 % B1) and 21.01 – 25 min (30 % B1). The chromatographic system was hyphenated to a trapped ion

<table><caption>**Table 2**
CPC method.</caption><thead><tr><th>Step</th><th>Start (min)</th><th>End (min)</th><th>Rotational speed (rpm)</th><th>Flow rate (mL/min)</th><th>% A</th><th>% B</th></tr></thead><tbody><tr><td rowspan="2">Equilibration</td><td>0</td><td>10</td><td>500</td><td>30</td><td>100</td><td>0</td></tr><tr><td>10</td><td>30</td><td>2000</td><td>7</td><td>0</td><td>100</td></tr><tr><td>Elution</td><td>0</td><td>70</td><td>2000</td><td>7</td><td>0</td><td>100</td></tr><tr><td>Extrusion</td><td>70</td><td>80</td><td>2000</td><td>30</td><td>100</td><td>0</td></tr></tbody></table>

mobility quadrupole-time-of-flight mass spectrometer (timsTOF, Bruker Daltonics, Germany) through an electrospray ionization (ESI) interface (Apollo II, Bruker Daltonics, Germany) for analyte detection.

The ESI polarity, *m/z* scan range, spectra rate, capillary voltage, nebulizer pressure, dry gas flow rate and dry gas temperature were set to positive (ESI +), 50–1200 Th, 4 Hz, 4000 V, 55 psi, 9 L/min and 250 °C, respectively. HRMS/MS and trapped-ion mobility was not used in this study; the cell was only used as an ion guide. Data acquisitions were carried by HyStar version 6.2.1.13 and treatment were managed with Bruker Data Analysis version 6.1.119.

## 2.6. Data processing for RPLC-ESI-HRMS data

An automatic mass calibration using sodium formate clusters between 90–1200 *m/z* is ensured by the high-precision calibration algorithm (HPC) during the 0.5 first minutes of each run. The analytical sequence comprises 49 fractions from the CPC fractionation of the model PVC and 49 fractions from the CPC fractionation of a sample containing only the solvent system in order to have a CPC extraction blank.

Data processing was performed on DataAnalysis® (Bruker Daltonics, Germany). For each fraction, the signal of the correspondent blank was subtracted. It provided to deduce the ions of interest. For each feature, an extracted ion chromatogram (EICs) was built based on the most intense adduct ([M + H]<sup>+</sup>, [M + Na]<sup>+</sup> or [M + NH<sub>4</sub>]<sup>+</sup>). It gives a certain number of compounds of interest for each fraction. EICs were added with a home-made software and a “remastered chromatogram” was obtained for each elution fraction (Figure S1).

## 2.7. SEC analysis

Two different SEC systems were used to fulfill complementary analytical objectives. A UV-RI SEC system was employed to determine the partition coefficients of the polymer and associated additives (1), while a multi-detection SEC setup enabled in-depth characterization of the polymer fractions collected after CPC extrusion, including molecular weight distribution and intrinsic viscosity (2).

(1) SEC analysis was performed on an Agilent 1260 system composed of a pump, an autosampler (15 °C), a column over (50 °C), a UV detector and a refractive index (RI) detector. The mobile phase was THF. The injection volume was 5 µL. Separation was achieved on 3 columns Waters Acquity APC XT 150 × 4,6 mm (45 Å, 125 Å and 450 Å). The flow was set at 0.6 mL/min. The signal of polymer was measured with the RI detection, while the phthalates signal was measured at 226 nm using UV detection. A calibration curve of DBP, DEHP, DIDP and PVC K75 was associated to determine the exact concentration of the samples.

(2) SEC analyses were carried out using a Viscotek TDA 305 system equipped with an autosampler, a column oven, and a triple detection system (RALS-LALS, refractive index, and viscometer detectors), all thermostatted at 40 °C. Injections of 100 µL were performed on a set of three Mixed-C columns from Agilent operated at 40 °C. The mobile phase was tetrahydrofuran (THF), delivered in isocratic mode at a flow rate of 1.0 mL/min. The system was calibrated using a universal calibration method based on PS standards, and a refractive index increment (dn/dc) value of 0.105 was applied [28].

## 2.8. Infra-Red spectroscopy of recover polymer

IR spectra were collected with a Nicolet™ iS50 FTIR Spectrometer from ThermoFisher Scientific equipped with an attenuated total reflection (ATR) diamond.

Background and sample spectra were collected with 32 scans at a spectral resolution of 4 cm<sup>-1</sup>, covering the range from 4000 to 400 cm<sup>-1</sup>. Spectral data were acquired and analyzed using OMNIC software
(Thermo Fisher Scientific).

# 3. Results and discussion

## 3.1. Optimization of CPC operational parameters

This study presents a method for separating a polymer from additives using a model formulation. The objective is to identify a solvent system that retains the polymer in one phase while extracting and recovering the additives in the other. To achieve this, the system must satisfy four key criteria:

(1) both the polymer and the additives must be soluble in the solvent system without any precipitation, to avoid damaging the CPC equipment and to enable their separation.

(2) the solvent system must form two immiscible liquid phases.

(3) effective separation in CPC requires the additives to partition between the two phases, while the polymer remains exclusively in one (Figure S2). This behavior is reflected in the polymer's partition coefficient, which should ideally approach infinity, indicating complete retention in a single phase –unlike the additives.

(4) lastly, the two phases must separate (demix) within 30 s to ensure stable operation of the CPC system.

### 3.1.1. Selection of biphasic solvent systems

The key to selecting an effective solvent system lies in its ability to solubilize compounds and separate them without causing precipitation.

In CPC, three commonly used biphasic solvent systems are: the ARIZONA system (heptane, ethyl acetate, methanol, water), the OKA system (hexane, ethyl acetate, n-butanol, methanol and water) and the acetone scale (heptane, toluene, acetone and water) which together cover most cases in natural product purification [24]. When these solvents are incompatible with the samples – resulting in precipitation – alternative approaches using ‘good’ solvents can be considered [29]. This is referred to as the good solvent approach for CPC solvent system selection, which has been described in the literature when standard systems are ineffective [25,30,31]. In this study, the ‘good’ solvent approach is applied using HSPs as a guiding tool.

HSPs are used to characterize the solubility of a polymer in a solvent. They are three parameters: $\delta_D$ (quantify the strength of dispersion interactions), $\delta_P$ (quantify the dipole-dipole interactions) and $\delta_H$ (quantify the hydrogen bonding interactions). These parameters are determined theoretically or experimentally for a solvent or a solute and can be represented on a 3D diagram with the three parameters as coordinates.

For polymers, an additional parameter is introduced, represented by a sphere centered at the point corresponding to the polymer’s Hansen Solubility Parameters (HSPs) in the three-dimensional HSP space. The radius of this sphere ($R_0$) defines the boundary for “good” solvents. The geometric distance ($R_a$) between a solvent and the polymer in the 3D HSP space indicates how compatible they are. If the ratio $R_a/R_0$ is greater than one - meaning the solvent lies within the polymer’s solubility sphere - the solvent is considered “good” [10].

The same goes for additives, the geometric distance $R_a$ can be used to determine which solvent is the most likely compatible with them. The smaller $R_a$ is, the more compatible they are:

$$Ra^2 = 4(\delta D1 - \delta D2)^2 + (\delta P1 - \delta P2)^2 + (\delta H1 - \delta H2)^2$$

If a solvent blend is considered, to estimate solubilities, parameters of each solvent ($\delta_D$, $\delta_P$, $\delta_H$) are added relatively to their percentage $\varphi$ in the blend:

$$(\delta D, \delta P, \delta H)_{\text{blend}} = \sum \varphi_{n.\text{comp}} (\delta D, \delta P, \delta H)_{n.\text{comp}}$$

HSPs offer insights into the solubility behavior of components in

various solvents. A model PVC formulation was selected as a reference matrix, primarily composed of PVC and DIDP, a widely used plasticizer.

DIDP is part of the phthalate family, a group of additives often present in high concentrations in soft PVC formulations, some of which are subject to strict regulatory oversight. Therefore, the selected solvent system will also be evaluated with regulated phthalates to validate its broader applicability.

#### 3.1.1.1. Solvent system selection using Hansen parameters.
The selection of solvents is based on their affinity for model plastic using HSPs [32]. More generally, all the solubility parameters were founded in the literature, Vebber et al. quote HSPs for 100 common solvents and Hansen gives HSP for phthalates [32,33]. Then, Table 3 gives HSPs of the various compounds studied (polymer, DIDP, the selected solvents), as well as the associated $R_a$ values, and the representation of these data in a 3D diagram is also available in Fig. 1. The criteria for the selection of each solvent are detailed below.

The first step involves selecting the most suitable solvent for dissolving PVC. DEK was chosen for this purpose, with $R_a$ values (distance in Hansen space) of 2.4 MPa$^{1/2}$ from PVC and 3 MPa$^{1/2}$ from DIDP, indicating it is likely a good solvent for both the polymer and the plasticizer. Next, heptane was selected for its ability to dissolve the phthalate ($R_a = 7.2$ MPa$^{1/2}$) while being a poorer solvent for PVC. This is reflected by its location at the edge of the PVC solubility sphere in the HSP diagram, suggesting limited compatibility with the polymer. Finally, DMSO was chosen as a third solvent to establish a biphasic system. In the HSP space, it is positioned opposite to heptane, promoting phase separation. However, DMSO still lies within the PVC solubility sphere ($R_a = 9.6$ MPa$^{1/2}$), ensuring that the polymer remains dissolved and does not precipitate. (Table 2)

To create a stable bi-phasic system for CPC separation, the ratio of solvent was determined with a ternary diagram (Fig. 2). This diagram was built with the software ASPEN V11 and based on UNIFAC theory [34].

The solvent ratios were selected to ensure compatibility with both the polymer and the additive. PVC should not be exposed to excessive amounts of heptane (e.g., 50 %), as this may lead to precipitation of the resin. Conversely, the phthalate additive (DIDP) should not be in contact with high concentrations of DMSO (e.g., 50 %) to avoid immiscibility issues. As previously mentioned DEK is not considered a limiting solvent, due to its good compatibility with both components. In this study, a heptane/DMSO/DEK (w/w/w) ratio of 0.25/0.45/0.30 was used. This solvent system proved to be stable, with a phase separation time (also called demixing) of less than 30 s after shaking. The upper phase consisted of 62.0 % (w) heptane, 7.8 % (w) DMSO, and 30.2 % (w) DEK, while the lower phase consisted of 7.7 % (w) heptane, 61.4 % (w) DMSO, and 30.9 % (w) DEK.

The sharing of components between phases is represented by partition coefficients, as compiled in Table 4. These partition coefficients are initially estimated using HSPs and then confirmed experimentally by SEC analysis of each phase. For the HSP estimation, the lower the $R_a$ value, the higher the affinity of the solute for the phase. This estimation helps determine whether the CPC method, along with the identified solvent system, can effectively separate plasticizers from the PVC polymer.

Table 4 displays the theoretical distribution, represented by the $R_a$

<table><caption>**Table 3**
HSP values and HSP distances ($R_a$) relative to PVC and DIDP.</caption><thead><tr><th>Chemical</th><th>δ<sub>D</sub></th><th>δ<sub>P</sub></th><th>δ<sub>H</sub></th><th>R<sub>a</sub> PVC</th><th>R<sub>a</sub> DIDP</th></tr></thead><tbody><tr><td>DEK</td><td>15.8</td><td>7.6</td><td>4.7</td><td>2.4</td><td>3.0</td></tr><tr><td>DMSO</td><td>17.5</td><td>1.8</td><td>9</td><td>9.6</td><td>13.2</td></tr><tr><td>Heptane</td><td>15.3</td><td>0</td><td>0</td><td>11.3</td><td>7.2</td></tr><tr><td>DIDP</td><td>16.6</td><td>6.2</td><td>2.6</td><td>4.6</td><td>/</td></tr><tr><td>PVC</td><td>16.0</td><td>10.0</td><td>5.0</td><td>/</td><td>4.6</td></tr></tbody></table>
<figure><img src="image_5.png" /><figcaption>**Fig. 1.** HSP sphere of PVC with DMSO, heptane, DEK and DIDP. Illustration of distances R<sub>a</sub> between compounds in pairs.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Ternary diagram of mixture DMSO, heptane and DEK. The diagram shows the two-phase zone and the single-phase zone of the mixture delimited by the blue parabola curve at 25 °C. The star symbol (★) corresponds to the ratio chosen in this study.</figcaption></figure>

<table><caption>**Table 4**
Estimation of R<sub>a</sub> (between solutes and two phases) and experimental sharing for PVC and phthalates.</caption><thead><tr><th>Component</th><th>R<sub>a</sub> in Upper phase (in MPa<sup>1/2</sup>)</th><th>R<sub>a</sub> in Lower phase (in MPa<sup>1/2</sup>)</th><th>Experimental sharing in upper phase (%w)</th><th>Experimental sharing in lower phase (%w)</th><th>Partition coefficient K<sub>D</sub></th></tr></thead><tbody><tr><td>DBP</td><td>6.8</td><td>5.3</td><td>18</td><td>82</td><td>4.5</td></tr><tr><td>DEHP</td><td>4.0</td><td>7.3</td><td>44</td><td>56</td><td>1.3</td></tr><tr><td>DIDP</td><td>3.2</td><td>8.2</td><td>56</td><td>44</td><td>0.8</td></tr><tr><td>PVC</td><td>7.3</td><td>3.6</td><td>0</td><td>100</td><td>∞</td></tr></tbody></table>

values, between solutes and the two solvent blends corresponding to the upper and lower phases. The experimental distribution is represented by the weight percentage of each solute in each phase. Additionally,

partition coefficients for two other phthalates, DEHP and DBP, were estimated and included in the analysis. These two phthalates are here presented to demonstrate that the solvent system is not only applicable to DIDP, but also to other REACH regulated phthalates. HSP affinities indicate that the phthalates will be distributed between the two phases, while PVC will predominantly prefer the lower phase. Experimentally, the phthalates are effectively split between the two phases, with the PVC resin remaining in the lower phase. The experimental results confirm the potential for CPC separation of each phthalate tested.

The partition coefficient (K<sub>D</sub>) governs the CPC separation process: the higher the K<sub>D</sub> value, the faster the solute will be eluted from the CPC column, as shown in Fig. 3.

Consequently, the study predicts the following elution order for the phthalates in CPC: DIDP, followed by DEHP and DBP. The polymer, however, does not partition between the two phases.

In the end, the four prerequisites for developing a suitable solvent system were validated: the organic fraction of the plastic (polymer and organic additives) is totally soluble, the system is biphasic and stable, the polymer remains in the lower phase and the additives of interest are shared between the 2 phases.

## 3.2. CPC method development: elution-extrusion

The CPC method is divided in two parts: the elution and the extrusion. After the equilibration of the two phases in the CPC cells at a given flow, the solute is injected. The mobile phase flows through the stationary phase and is recovered during the elution part. The stationary phase is then extruded (pushed out) from cells, it corresponds to extrusion part.

The choice of the solvent system leads to the polymer being present in the lower phase, while the additives are distributed between both phases. The mobile and stationary phases are then selected to promote the partitioning of the different sample components according to the separation objectives. To enable the separation of the additives from each other and from the polymer, the upper phase is selected as the mobile phase. Since the polymer is expected to elute with the extrusion fractions, it should preferentially remain in the stationary phase.

This choice determines the direction of flow (ascending or descending). In this case, the upper phase (used as the mobile phase) must pass through the lower phase. Therefore, an ascending mode is selected.

In practice, the sample is dissolved in the stationary phase and can be concentrated until 12 % of polymer weight in solvent. Above this concentration, the solubility's limit of the sample leads to an increase in viscosity, making the solution incompatible with CPC conditions. At 12 % of weight, the concentration of the sample in the solution does not disturb the equilibrium of the bi-phasic system.

To maintain the stability of mobile phase and stationary phase in

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Schema of theoretical phthalates elution in CPC with a solvent system Heptane/DMSO/DEK based on their partition coefficients.</figcaption></figure>
CPC's cells and avoid band boarding, the injection volume is set as 5 mL [35].

### 3.3. Elution fractions: recovery of PVC additives

The CPC was then applied to a plastic from a model feedstock. This part will purpose method to ensure total recovery of PVC resin and the different additives after CPC fractionation. The solvent system was developed using phthalates as a model, given their high concentration in PVC formulations. However, this approach also ensures the complete recovery of other organic compounds present in the plastic. To rule out the presence of residual polymer in the elution fractions, these were characterized by size exclusion chromatography prior to this analysis.

To characterize the elution fractions with potential additives, a RPLC-HRMS method is used. The RPLC provides another dimension of separation while HRMS enables a supervised screening. The Fig. 4 shows the two-dimensional separation obtained, with the CPC separation as a function of the LC separation. This cartography was built from the Extract Ion Chromatograms (±0.005 Da). Principal organic components present in the PVC model sample were annotated according to mass accuracy (< 2 ppm) and isotopic pattern accuracy. Specifically, the phthalate DIDP and its isomers were found in the fractions 11 and 13 between 17.4 and 18 min. ESO, chemically corresponding to epoxidized triglycerides, was found in different fractions (10 to 40) and the wax, identified as oxidized polyethylene, was found in fractions 10, 11, 12, 16, 17 and 18.

This cartography allows for conclusions about the recovery of each soluble organic additive from soft PVC in the CPC elution fractions, with these additives being separated into distinct elution fractions. This separation is driven by the interactions of each component with the two phases, governed by HSPs, including dipole-dipole interactions, hydrogen bonding, and dispersion forces. In this study, the objective was to separate the polymer from its organic additives, and CPC successfully facilitated this separation.

### 3.4. Extrusion fractions: recovery of PVC resin

At the end of the previous additive separation and their total recovering, the extrusion step is done. The extrusion fractions are combined. They contained the polymer dissolved in a solvent incompatible with subsequent analyses. Then to recover polymer, 500 mL of MeOH are added to the 300 mL collected during CPC extrusion for polymer precipitation. The solution was filtered on Büchner with

cellulose filter. The powder was recovered and dried at 70 °C in oven for 4 h. SEC analysis was then performed to characterize the resin fraction recovered after CPC separation. This analysis yields multiple pieces of information: the refractive index (RI) signal allows quantification of the PVC resin using the appropriate *dn/dc* value, while molar mass and intrinsic viscosity measurements, obtained via universal calibration, provide insights into potential polymer degradation [36]. A quantitative analysis by weight confirms the total recovery of the resin.

The PVC resin purified with the CPC has been compared to the original resin PVC K75 used to formulate the model compound of this study. On Table 5, SEC results for each resin are shown. They show similar size distributions for both, and a quantification analysis confirms the recovery of all the polymer injected in CPC. In addition, the polymer was not degraded by CPC. Indeed, molar masses are the same before and after CPC as previously shown. If the polymer was degraded, chains scissions should happen and lower molar mass average compared to resin before CPC should be measured [37]. The Mark-Houwink coefficient can also help to determine if some branching occur. During its oxidation, PVC polymer can create branches by which increase its viscosity [38,39]. In fact, this coefficient is given by the Mark-Houwink formula which link the molar mass with the viscosity. Here the two Mark-Houwink coefficients are similar before and after CPC analysis: according to SEC results, PVC polymer was not modified by the CPC extraction process [40].

SEC results were confirmed by FTIR analysis. The FTIR is used to determine chemicals functions present in the sample and, in case of PVC, the degradation can also be characterized [15]. On Fig. 5, are shown FTIR results for a pure PVC resin without additives and the resin recovered after CPC. Both spectra present the classical bands for PVC as 606, 633 and 688 cm⁻¹ corresponding to the stretching of C—Cl bond, bands 1331 and 1253 cm⁻¹ corresponding to C—H bond deformation of CHCl and the band at 2970 cm⁻¹ corresponding to the C—H bond stretching of CHCl [16]. Chemically, the FTIR spectra of recovered PVC does not present additional structures which mean that no degradation

<table><caption>**Table 5**
Molar masses and Mark-Houwink coefficient for PVC resin before and after CPC.</caption><thead><tr><th>PVC resin</th><th>Mn (kg/mol)</th><th>Mw (kg/mol)</th><th>Dispersity</th><th>Mark-Houwink coefficient α</th></tr></thead><tbody><tr><td>After CPC</td><td>47.2</td><td>138.2</td><td>2.9</td><td>0.55</td></tr><tr><td>Before CPC</td><td>47.7</td><td>126.0</td><td>2.6</td><td>0.58</td></tr></tbody></table>

<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Two-dimensional cartography of elution fractions corresponding to PVC additives without polymer. It represents the separation with CPC in y-axis and the LC separation in x-axis. The colors correspond to the intensity of mass signal. To build the cartography, Extracted Ions Chromatograms, corresponding to all component's signals, have been extracted for each elution fraction (figure S1).</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Fig. 5.** Infra-Red spectra. The sample of pure polymer (resin PVC K75) was analyzed (blue). The resin was formulated and became a compound which was purified by CPC (red). On this figure, the resins before formulation and after purification are presented.</figcaption></figure>

occurred. Usually, degradations of PVC resin, by dechlorination or oxidation, are visible on FTIR spectra, with some characteristic bands respectively for carbon double bonds (3020 cm⁻¹, 1470–1520 cm⁻¹) and carbon-oxygen bonds (1720 cm⁻¹) [16].

Both SEC and FTIR methods confirmed the absence of polymer chains degradation and demonstrated that all additives were removed using CPC technique. As a last verification, a ¹H NMR spectrum was recorded for both resins and the results confirmed their purity (Figures S3 and S4).

To compare results with current literature: S. Wagner and M. Schlummer employed the dissolution-precipitation method – currently considered the reference technique for PVC resin purification – to remove phthalate-type plasticizers from post-consumer flooring materials [9]. The authors report a reduction in DEHP concentration from 100,000 ppm to 60 ppm. However, the dissolution-precipitation process, as currently described in the literature, focuses primarily on the removal of phthalate plasticizers, with a particular emphasis on DEHP, while other additives such as stabilizers are not addressed. In contrast, the CPC-based approach enables the removal of all organic additives regardless of their chemical nature or functional role. Furthermore, CPC allows for the recovery of pure PVC resin in a single step, compared to the seven purification steps required for dissolution-precipitation.

## 4. Conclusion

The lack of techniques for separating polymers from all additives and recovering them for characterization remains a major obstacle to the development of physical recycling processes. CPC, typically used for purifying natural products, is applied here for the first time to plastics fractionation. The selection of the two-phase solvent system is critical to the performance of this technique and often requires numerous laboratory tests. In this study, a more theoretical approach based on HSPs is proposed. This approach facilitates solvent selection with fewer experimental tests by providing insights into the parameters governing the solubility of both the polymer and representative additives, such as phthalates.

For a soft PVC the DMSO/heptane/DEK system proved effective, enabling the complete recovery of the polymer while removing all soluble organic additives and offering a first dimension of additive separation. These results were validated using RPLC–HRMS analysis of the

additive fractions, and FTIR and SEC analyses of the polymer fractions. Importantly, the recovered polymer was pure and remained structurally unaffected by the CPC fractionation process. This method demonstrates its effectiveness in simplifying complex plastic formulations by fully isolating soluble organic additives, making it a valuable tool for characterizing materials such as PVC.

CPC can also be used as a quality assessment method during recycling, allowing the characterization of plastics through the detection of polymer degradation and the quantification of regulated additives (such as phthalates) and impurities prior to processing. The flexibility of the technique supports its application across a wide range of thermoplastics and polymer-based materials. Moreover, by adjusting the solvent system ratios, CPC can be adapted to achieve tailored separations according to specific objectives – whether focused on time efficiency, solvent usage, or targeting compounds for removal. This adaptability highlights CPC’s strong potential for broad applications in plastic analysis and recycling.

### CRediT authorship contribution statement

**Noemie Auchere:** Writing – original draft, Project administration, Methodology, Investigation, Data curation, Conceptualization. **Alexandra Berlioz-Barbier:** Writing – review & editing, Validation, Supervision, Conceptualization. **Agnès Le Masle:** Writing – review & editing, Validation, Supervision, Conceptualization. **Olivier Boyron:** Writing – review & editing, Validation, Supervision. **Alexandra Chaumonnot:** Writing – review & editing, Validation, Supervision, Conceptualization.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgment

The authors would like to thank Laurent Lemaitre and Florent Moreau for NMR analysis.
## Supplementary materials

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.chroma.2025.466337.

## Data availability

Data will be made available on request.

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