# One step beyond for CNSL-based plasticizers for PVC: Use of cardol

Adélaïde Gartili, Sylvain Caillol, Benoît Briou, Vincent Lapinte

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## To cite this version:

Adélaïde Gartili, Sylvain Caillol, Benoît Briou, Vincent Lapinte. One step beyond for CNSL-based plasticizers for PVC: Use of cardol. European Journal of Lipid Science and Technology, 2024, 126 (11), pp.2400086. 10.1002/ejlt.202400086. hal-04766470

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Submitted on 4 Nov 2024

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Distributed under a Creative Commons Attribution 4.0 International License
RESEARCH ARTICLE

# One step beyond for CNSL-based plasticizers for PVC: Use of cardol

Adélaïde Gartili<fnref n="1" />,<fnref n="2" />

Sylvain Caillol<fnref n="1" />

Benoît Briou<fnref n="2" />

Vincent Lapinte<fnref n="1" />

**Correspondence**

Vincent LAPINTE, ICGM, CNRS, ENSCM, University of Montpellier, Montpellier, France.
Email: Vincent.lapinte@umontpellier.fr

## Abstract

Poly(vinyl chloride) (PVC) is a widely employed plastic across diverse industries and is often associated with plasticizers, additives that decrease the inherent rigidity and brittleness of the material. Conventional phthalate-based plasticizers raise substantial toxicity concerns, encouraging the exploration of bio-based alternatives. One such alternative is the inedible oil, cashew nutshell liquid (CNSL), mainly composed of cardanol and cardol. Recent efforts have focused on developing a cardanol-based PVC plasticizers but the isolation of cardanol involves time-consuming, energy-intensive, and costly steps, limiting its market competitiveness. This study aims to assess for the first time, the efficiency of cardol esters, synthesized using acetic acid and different fatty acids (octanoic acid and myristic acid), in order to evaluate the influence of the alkyl chain on plasticizer properties. The chemical structures of these plasticizers were fully characterized by ¹H NMR spectroscopy, and the mechanical properties and thermal behavior of PVC films plasticized with these additives were investigated. Finally, the endocrine activity was evaluated for cardol and cardanol acetates.

## KEYWORDS

biobased plasticizers, cardanol, cardol, CNSL, fatty acids, nontoxic, PVC

## 1 | INTRODUCTION

PVC stands out as one of the most widely utilized thermoplastics on a global scale within the plastics market.[1,2] Renowned for its outstanding performance and economical nature, PVC is extensively used across various industries such as construction, piping, packaging, wiring, and cables, producing a diverse range of products from rigid to flexible items.[3] The inherent hardness and brittleness of PVC stem from the polarity of the C-Cl bond and strong dipole-dipole interactions, which limit polymer chain mobility.[4] Consequently, a range of plasticizers has been employed to enhance the stretchability and processability of PVC.[4] Historically, phthalic acid esters, particularly diisooctyl phthalate (DEHP), have been prevalent due to their

notable efficiency and affordability.[5] However, conventional plasticizers tend to leach over time and with aging. Phthalates are now subject to restrictions, if not outright prohibitions, due to their potential to act as endocrine disruptors in humans and due to their reproductive toxicity.[6-9] Furthermore, the unsustainable production of phthalates from crude oil no longer aligns with the plastics industry's increasing demand for biobased and renewable plasticizers derived from sustainable feedstocks.[10-12]

In recent years, there has been a notable surge in research focusing on biobased, nontoxic, and low-migration plasticizers derived from vegetable oils.[13-16] These studies aim to provide sustainable alternatives to phthalates, addressing both environmental and health concerns while aligning with the growing emphasis on eco-friendly

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2024 The Author(s). *European Journal of Lipid Science and Technology* published by Wiley-VCH GmbH

<footnote n="1">¹ICGM, CNRS, ENSCM, University of Montpellier, Montpellier, France</footnote>

<footnote n="2">²Orpia Innovation, Paris/Montpellier, France</footnote>
practices within the plastics industry.[17,18] Consequently, epoxidized linseed oil (ELO) and epoxidized soybean oil (ESBO) have become widely used as nontoxic, bio-sourced plasticizers for PVC.[19,20] However, care must be taken to avoid potentially significant social and economic repercussions, which may arise from any unintended impact on food production and land expansion.

Efforts to develop environmentally friendly plasticizers have turned toward the use of renewable resources derived from agro-industrial residues and nonedible biomass as chemical feedstocks.[21] Recently, attention has shifted to cashew nutshell liquid (CNSL), a nonedible oil extracted from agro-waste.[22,23] CNSL is a byproduct of cashew processing, appearing as a viscous dark reddish-brown to greenish-yellow liquid contained within the porous structure of the cashew nutshell (CNS).[24,25] Despite CNS being an agro-waste product, CNSL stands out as one of the richest natural sources of phenols, containing four substituted phenols (anacardic acid, cardanol, cardol, and 2-methylcardol). The valorization of CNSL has led to the development of numerous products that compete favorably with those derived from fossil fuels, across many applications.[25-33] For instance, CNSL has found applications in the field of plasticizers, such as in PVC formulations.[23] CNSL derivatives are increasingly recognized as a promising alternative to phthalates, due to their unique natural structure, which closely resembles that of phthalates. The phenol content in CNSL enhances thermal stability, while its lengthy C-15 aliphatic chain amplifies plasticizing effects.[16]

To date, research into renewable resources, notably CNSL as a plasticizer for PVC, has almost exclusively focused on cardanol in both academic and industrial studies.[22,23,34,35] Most of the research focused on cardanol esters from short alkyl chain (C2) to long alkyl chain (C18:1) in order to increase the free volume between the PVC chains.[23,36] However, acquiring the desired cardanol involves the extraction and separation of other compounds, primarily anacardic acid and cardol.[37,38] This process results in energy, economic, and time costs, which should be reflected in the sought-after biobased aspect. One of the main reasons for the limited studies on cardol is its challenging purification process, making it difficult to produce with a high degree of purity (Figure 1).

By initially avoiding the separation of cardanol and cardol, before esterification, the cost of the raw plasticizer could be significantly reduced, enhancing competitiveness with petroleum-based alternatives. The objective of this study was to evaluate the plasticizing properties of esterified cardol, which have not been thoroughly investigated until now, and compare them to those of esterified cardanol. The esterification of these phenols was conducted using propylphosphonic anhydride reagent (T3P) and carboxylic acids of various lengths in order to evaluate their influence on plasticizer properties. The chemical structures of these plasticizers were determined by ¹H NMR spectroscopy. PVC films were prepared using these plasticizers and their mechanical, thermal properties and endocrine activity were evaluated.

## 2 | EXPERIMENTAL

### 2.1 | Materials

Technical CNSL was obtained by distillation from Orpia Innovation. Cardol was obtained by distillation of technical CNSL followed by its purification through column chromatography over silica, effectively separating it from 2-methyl cardol and cardanol. Cardanol NX-2026 was kindly provided by Cardolite. PVC P70 was kindly provided by KemOne in powder form. Di-isononyl-phthalate (DINP), di(2-ethylhexyl) phthalate (DEHP), epoxidized linseed oil (ELO), epoxidized soybean oil (ESBO), acid acetic, octanoic acid, myristic acid, propylphosphonic anhydride (T3P), and chloride sodium (NaCl) were purchased from Sigma-Aldrich. Tetrahydrofuran (THF), and magnesium sulfate ($MgSO_4$) were purchased from VWR International S.A.S (Fontenay-sous-Bois, France). Cyclohexane and ethyl acetate were purchased from Analytic Lab. All reagents were used as received.

### 2.2 | Synthesis of cardanol and cardol esters

The esterification of CNSL derivatives with various acids (acetic acid, octanoic acid, and myristic acid) were carried out using the following procedure. To a mixture of cardanol, cardol, or a mixture of both (1 eq), acid (1.1 eq), and T3P (1.1 eq) were added. The reaction mixture was stirred at 80°C and the progress of the reaction was monitored by thin layer chromatography (TLC) and ¹H NMR spectroscopy. The reaction was complete in 3 h. The crude product was purified three times by liquid-liquid deionized water-ethyl acetate extraction. The organic phase was dried over anhydrous $MgSO_4$, separated over a filter, and ethyl acetate was removed under reduced pressure.

In this study, cardanol will be designated by the letter A, and cardol will be designated by the letter B. Esters are designated by their chain length using the letter C, followed by the number of carbons added. For instance, cardanol acetate is designated as A-C2. The NMR spectra are presented in Figures S1 to S6.

**A-C2:** quantitative yield, liquid, translucent yellow brownish, ¹H NMR (400 MHz, $CDCl_3$) $\delta$ 7.33-7.19 (m, aromatic CH), 7.03 (d, $J$ = 7.7 Hz, aromatic CH), 6.89 (dd, $J$ = 3.8, 1.8 Hz, aromatic CH), 5.91-5.74 (m, unsaturated bonds CH), 5.52-5.24 (m, unsaturated bonds CH), 5.13-4.85 (m, unsaturated bonds $CH_2$), 2.93-2.72 (m, $CH_2$), 2.71-2.48 (m, $CH_2$), 2.35-2.18 (s, $CH_3$), 2.12-1.87 (m, $CH_2$), 1.70-1.50 (m, $CH_2$), 1.47-1.21 (m, $CH_2$), 1.02-0.78 (m, $CH_3$).

**A-C8:** quantitative yield, liquid, translucent orange yellow, ¹H NMR (400 MHz, $CDCl_3$) $\delta$ 7.34-7.20 (m, aromatic CH), 7.03 (d, $J$ = 7.7 Hz, aromatic CH), 6.89 (dd, $J$ = 3.8, 1.8 Hz, aromatic CH), 5.94-5.70 (m, unsaturated bonds CH), 5.48-5.29 (m, unsaturated bonds CH), 5.15-4.93 (m, unsaturated bonds $CH_2$), 2.92-2.77 (m, $CH_2$), 2.67-2.43 (m, $CH_2$), 2.40-2.26 (m, $CH_2$), 2.09-1.94 (m, $CH_2$), 1.83-1.69 (m, $CH_2$), 1.68-1.52 (m, $CH_2$), 1.49-1.20 (m, $CH_2$), 0.97-0.83 (m, $CH_3$).

**A-C14:** 99% yield, paste-like, cloudy orange yellow, ¹H NMR (400 MHz, $CDCl_3$) $\delta$ 7.30-7.23 (m, aromatic CH), 7.03 (d, $J$ = 7.8 Hz,
<figure><img src="image_3.png" /><figcaption>**FIGURE 1** Schematic pathway from CNSL extraction to cardol purification. Dashed lines represent successive CNSL distillations.</figcaption></figure>

aromatic CH), 6.89 (dd, *J* = 3.7, 1.7 Hz, aromatic CH), 5.93–5.74 (m, unsaturated bonds CH), 5.48–5.27 (m, unsaturated bonds CH), 5.16–4.91 (m, unsaturated bonds CH₂), 2.94–2.79 (m, CH₂), 2.67–2.48 (m, CH₂), 2.39–2.22 (m, CH₂), 2.15–1.93 (m, CH₂), 1.84–1.68 (m, CH₂), 1.68–1.52 (m, CH₂), 1.51–1.19 (m, CH₂), 0.95–0.82 (m, CH₃).

B-C2: 93% yield, liquid, translucent orange-brown,¹H NMR (400 MHz, CDCl₃) δ 6.81 (dd, *J* = 10.6, 1.8 Hz, aromatic CH), 6.74 (t, *J* = 2.1 Hz, aromatic CH), 5.89–5.72 (m, unsaturated bonds CH), 5.54–5.25 (m, unsaturated bonds CH), 5.21–4.91 (m, unsaturated

bonds CH₂), 2.90–2.71 (m, CH₂), 2.66–2.50 (m, CH₂), 2.39–2.21 (m, CH₃), 2.14–1.93 (m, CH₂), 1.69–1.51 (m, CH₂), 1.50–1.18 (m, CH₂), 1.03–0.84 (m, CH₃).

B-C8: 91% yield, liquid, translucent orange-brown,¹H NMR (400 MHz, CDCl₃) δ 6.78 (d, *J* = 2.1 Hz, aromatic CH), 6.71 (t, *J* = 2.1 Hz, aromatic CH), 5.89–5.74 (m, unsaturated bonds CH), 5.54–5.24 (m, unsaturated bonds CH), 5.12–4.94 (m, unsaturated bonds CH₂), 2.89–2.73 (m, CH₂), 2.68–2.42 (m, CH₂), 2.12–1.95 (m, CH₂), 1.90–1.76 (m, CH₂), 1.52–1.16 (m, CH₂), 1.09–0.78 (m, CH₃).
B-C14: 73% yield, liquid, brownish-gray murky yellow, ¹H NMR (400 MHz, CDCl₃) δ 6.78 (d, J = 2.1 Hz, aromatic CH), 6.71 (t, J = 2.1 Hz, aromatic CH), 5.91–5.74 (m, unsaturated bonds CH), 5.49 – 5.28 (m, unsaturated bonds CH), 5.14–4.93 (m, unsaturated bonds CH₂), 2.88–2.71 (m, CH₂), 2.68–2.42 (m, CH₂), 2.40–2.28 (m, CH₂), 2.14–1.92 (m, CH₂), 1.82–1.53 (m, CH₂), 1.53–1.17 (m, CH₂), 1.08–0.79 (m, CH₃).

## 2.3 | Preparation of plasticized PVC films with cardanol and cardol esters

PVC films were formulated by mixing PVC with THF (10 mL g⁻¹ PVC) and different plasticizers at room temperature. The plasticizer content is usually expressed in parts per hundred parts of resin (phr) or in weight/weight (w/w). In the current study, PVC was plasticized with a 70:30, w/w, ratio, which corresponds to approximately 43 phr. After mixing homogeneously, the blend was poured into an aluminum mold, sealed with a plastic film, and placed under the fume hood for three days. Afterward, the films were taken out and dried in an oven at 50°C for 3 h. The thickness of the resulting PVC films was approximately 0.35 mm. No heat stabilizers or other additives were added.

## 2.4 | Characterization

Nuclear magnetic resonance (NMR) spectroscopy was performed on an NMR Bruker Avance 400 MHz spectrometer at 25°C in CDCl₃. The chemical shifts were reported in parts per million (ppm), where (s) means singlet, (d) doublet, (t) triplet, (m) multiplet and (dd) doublet of doublet. For ¹H NMR, chemical shifts were referenced to the signal of residual CHCl₃ at 7.26 ppm.[23]

Thermogravimetric analyses (TGA) were carried out on a Netzsch TG 209F1 apparatus to determine the thermal stability of plasticizers and PVC films. Around 10–12 mg of the sample was placed in an alumina crucible and subjected to heating from room temperature up to 580°C at a rate of 10 °C min⁻¹. The experiments were performed under 40 mL min⁻¹ nitrogen flow and 20 mL min⁻¹ flow of protective gas. Moreover, to further illustrate the thermal stability of these samples, an isothermal test at 200°C was also conducted for plasticized PVC films. The sample was heated from room temperature to 200°C at a heating rate of 20 °C min⁻¹ and held at 200°C for 2 h.[23]

Differential scanning calorimetry (DSC) analyses were carried out using a Netzsch DSC200F3 calorimeter. Nitrogen was used as the purge gas. The thermal properties were analyzed at 20 °C min⁻¹ between –150 and 150°C to observe the glass transition temperature.[23]

Elongation at break and Young modulus of the films were measured with an Instron 3366L5885 tensile tester according ISO 527-3:2018. Dog-bone samples of 12 × 2 mm were used for these analyses and were mounted between tensile grips with an initial grip spacing of 0 cm. The tensile speed was set at 200 mm min⁻¹. The Young modulus, elongation at break and the stress and strain at break were measured on five

samples. The elongation at break was expressed as a percentage of the original length.

Discoloration tests were performed at 200°C to further study the thermal stability of plasticized PVC samples. The plasticized PVC films (1 cm × 1 cm × 0.35 mm) were placed into an aging oven at 200°C and removed at 5, 10, and 60 min intervals.[35]

Estrogenic and androgenic activities were characterized by YES-YAS tests performed by EUROFINS Ecotoxicologie France. YES/YAS—Yeast-based microplate assay for the detection of compounds with estrogenic and androgenic agonistic and antagonistic activities using *Saccharomyces cerevisiae* strains with human estrogen (hERα) and androgen (hAR) receptors.

Genetically modified cultured cells containing the respective hER (YES) or hAR (YAS) receptors are exposed to a range of concentrations of the test sample, positive agonist controls (17β-estradiol for the YES test and 5α-dihydrotestosterone for the YAS test), or positive antagonist controls (4-hydroxytamoxifen in the presence of estradiol for the Anti-YES test and flutamide in the presence of dihydrotestosterone for the Anti-YAS test). Yeasts are then incubated for 48 h at 30°C in the presence of a β-galactosidase substrate. The expression of β-galactosidase is directly proportional to the presence of agonist or antagonist compounds, which leads to the conversion of the yellow substrate into a red degradation product, chlorophenol red. Color development and fungal growth are quantified by spectrophotometry at 570 and 690 nm, respectively.[23]

The evaluation of estrogen-androgen activity for the plasticizers A-C2 and B-C2 was conducted across seven different dilution levels, each assay being replicated three times. A compound under evaluation was classified as having agonistic endocrine activity if its induction reached a minimum of 10% of the disparity between the maximum E2 or DHT response and the solvent control in the agonist assay. Conversely, a sample dilution that suppressed negative control activity (medium with agonist) by a minimum of 50% was deemed to exhibit antagonistic endocrine activity in the antagonist assay.

# 3 | RESULTS AND DISCUSSION

## 3.1 | Extraction of cardol from CNSL: biomass to material

Various extraction methods for CNSL include mechanical, thermal, and chemical extractions.[39,40] Energy consumption is significant, particularly in mechanical and thermal extractions, and must be considered when selecting an extraction method. Depending on the extraction method used, various proportions of anacardic acid, cardanol, and cardol can be obtained in the CNSL. While anacardic acid can be easily separated from cardanol and cardol, the separation of cardol from cardanol is more complex, requiring techniques such as successive distillations or silica column chromatography. Given the cost and complexity of these separation methods, utilizing technical CNSL (a mixture of 80% cardanol and 20% cardol) as a precursor for synthesizing new plasticizers could be advantageous in terms of energy, costs, and time.
In this study, at the laboratory scale, cashew nut shells were crushed using a mixer for a brief duration to prevent heating of the CNSL and its thermal degradation. Subsequently, the CNSL was extracted from the ground shells through solvent extraction. The entire CNSL content can be extracted, resulting in the obtention of natural CNSL amounting to approximately 30% of the weight of the ground shells. The separation of anacardic acid, cardanol, and cardol was carried out in a sequential manner. The initial step focused on precipitating anacardic acid from CNSL, giving 70% anacardic acid and 30% of a cardanol/cardol mixture (20:80).[25] Separation of the cardanol/cardol mixture by column chromatography over silica gel yielded 80% cardol and 20% cardanol. Consequently, the final composition of anacardic acid, cardol, and cardanol accounted for 21%, 7%, and 2%, respectively, of the total CNS weight.

Based on preliminary experiments, the study's focus on cardanol and cardol led to the exploration of an alternative extraction method (Figure 1). Anacardic acid from natural CNSL was converted into cardanol by decarboxylation through heating, resulting in a technical CNSL. This technical CNSL, primarily a cardanol/cardol mixture, was separated by column chromatography over silica gel at the laboratory scale. In larger quantities, the mixture can be distilled. The resulting distillate fraction is rich in cardanol, while the residue fraction, mainly consisting of cardol, retained a minor amount of residual cardanol (< 5%). Purification of the cardol-rich residue was achieved through column chromatography. Through this process, the quantities of cardanol and cardol obtained represented 24% and 6%, respectively, of the total CNS weight. The purity of cardol was verified by ¹H NMR spectroscopy (Figure 2). It is essential to highlight that biobased plasticizers from cardanol entail time-consuming, energy-intensive, and costly processes, primarily due to the requisite separation from cardol. Hence, to determine the potential utilization of the cardanol/cardol mixture as a biobased plasticizer, it is important to assess the plasticizing characteristics of cardol first.

## 3.2 | Synthesis of cardol and cardanol esters

PVC, by its nature, is rigid but brittle. However, a plasticizer can transform a rigid PVC (r-PVC) into a softer (s-PVC) and malleable material by increasing the mobility of PVC chains. Therefore, finding the right plasticizer structure is crucial to enhancing the performance of PVC blends. To design an optimal plasticizer, ester groups have been incorporated to increase cohesive units and enhance stability between the plasticizer and PVC, as they facilitate specific interactions with the polymer, such as hydrogen bonding, electrostatic forces, or van der Waals interactions.[16] In addition to the long aliphatic chain of CNSL derivatives serving as a spacer, various aliphatic chain lengths from acids were explored to strike a balance, ensuring they are neither too short to prevent volatility nor too long to complicate formulation. Indeed, shorter chains are easier to incorporate due to their faster diffusion, but they tend to be more volatile.

Throughout the study, cardanol will be designated by the letter A, and cardol by the letter B. Esters are designated by their chain

length using the letter C, followed by the number of carbons added. For instance, cardanol acetate is designated as A-C2. It is worth noting that cardanol derivatives, such as A-C2, which bear short alkyl chains and exhibit a positive plasticizing effect on PVC materials, have already been described in literature.[22] As far as we know, there are no studies on acetylated cardol or any other cardol esters. The focus of this study is on the esterification of cardol (Figure 3). It is usually achieved through Steglich esterification with EDC/DMAP as reagent.[23,35] However, from an environmental and economic perspective, EDC and DMAP are not suitable reagents. Another esterification method of cardanol derivatives uses anhydrides.[41] However, the lack of commercially available anhydrides of different alkyl chain lengths motivated the use of carboxylic acid to investigate a wider range of alkyl chain such as acetic acid, or fatty acids like octanoic acid and myristic acid. In addition, a greener esterification agent was used, propanephosphonic acid anhydride (T3P) reagent, compared to the conventional EDC/DMAP. According to literature, a convenient aspect of T3P-mediated synthesis is the ease of workup of the reaction. It is reported that residual T3P and any byproducts of T3P degradation are highly water-soluble and therefore easily eliminated through the aqueous phase.[42] With the aim of developing an industrially viable synthesis that is more environmentally friendly, this method has caught our interest. Indeed, this reagent is less toxic and more cost-effective than the previously employed EDC.[23] Additionally, it was intriguing to investigate the reactivity of T3P in the esterification of phenol and carboxylic acid—a topic not extensively explored in the literature, as far as we know.

In this study, propylphosphonic anhydride reagent (T3P) was used as an activator agent for the esterification of phenol and carboxylic acid. T3P-mediated esterification is conducted at low temperatures by mixing the carboxylic acid with the alcohol and 1–2 equivalents of T3P.[43] The reaction takes place in two steps: the activation of the carboxylic acid, followed by nucleophilic substitution with the alcohol to form the corresponding ester. T3P binds to the oxygen of the carboxylic acid functional group of the carboxylic acid, opens the ring, and converts into tripropylphosphonic acid until a global quantitative yield is reached.

The confirmation of the chemical structures of cardol and cardanol esters was achieved through ¹H NMR spectroscopy. In Figure 2 the distinctive signals of the phenolic protons of cardol (Ha and Hc) shifted from 6.19 and 6.27 to 6.75, and 6.80 ppm, respectively. The signals of the unsaturations of the alkyl chain between 4.95 and 5.92 ppm are unaffected by the esterification. Additional aliphatic proton signals corresponding to protons in the alpha position relative to the carbonyl group of the ester formed were observed at 2.29 ppm.

## 3.3 | Properties of PVC plasticized with cardanol and cardol esters

PVC films were produced using the synthesized plasticizers and their plasticizing efficiencies were compared with those formulated with commercial phthalates such as DEHP and DINP. While many studies
<figure><img src="image_4.png" /><figcaption>FIGURE 2 ¹H NMR spectra of cardol and B-C2 in CDCl₃.</figcaption></figure>

include comparisons with one of these references, it seems worthwhile for the ease of comparison to include both of these reference plasticizers in the analysis. Commercially available biobased vegetable oil references were also chosen, such as ESBO and ELO, which are widely used in both industry and academia. This study involved an examination of the mechanical properties and thermal characteristics of various PVC films plasticized with different esters of cardol and cardanol. The plasticizer content in many studies is expressed in phr (parts per hundred parts of resin) or in w/w (weight/weight). To facilitate comparison and standardization, the plasticization ratio is expressed in both ways. In this study, PVC was plasticized with a 70:30, w/w, ratio, equivalent to approximately 43 phr.

### 3.3.1 | Mechanical properties of PVC films

The mechanical properties of PVC films prepared using the solvent casting method were analyzed. The Young modulus, elongation at break and the stress and strain at break are calculated from the average of five samples and presented in Table 1. For cardanol derivatives, the length of the alkyl chain resulted in a decrease in elongation at break, in accordance with the literature.[16,23,44] Indeed, the chain length increases the rigidity of the material. This trend is also observed for B-C2 and B-C14 derivatives while B-C8 derivative surprisingly showed higher elongation at break (Figure 4A).
<figure><img src="image_5.png" /><figcaption>**FIGURE 3** Chemical structure of CNSL-ester derivatives.</figcaption></figure>

<table><caption>**TABLE 1** Mechanical properties of plasticized PVC films.</caption><thead><tr><th>PVC sample</th><th>Young's modulus (MPa)</th><th>Tensile strength (MPa)</th><th>Elongation at break (%)</th></tr></thead><tbody><tr><td>DEHP</td><td>22 ± 2</td><td>22 ± 1</td><td>492 ± 18</td></tr><tr><td>DINP</td><td>16 ± 3</td><td>18 ± 4</td><td>326 ± 19</td></tr><tr><td>ELO</td><td>123 ± 19</td><td>26 ± 3</td><td>466 ± 26</td></tr><tr><td>ESBO</td><td>97 ± 12</td><td>23 ± 4</td><td>367 ± 72</td></tr><tr><td>A-C2</td><td>16 ± 4</td><td>23 ± 4</td><td>566 ± 54</td></tr><tr><td>A-C8</td><td>219 ± 6</td><td>24 ± 7</td><td>405 ± 57</td></tr><tr><td>A-C14</td><td>271 ± 15</td><td>23 ± 4</td><td>179 ± 41</td></tr><tr><td>B-C2</td><td>20 ± 2</td><td>22 ± 3</td><td>440 ± 19</td></tr><tr><td>B-C8</td><td>120 ± 20</td><td>21 ± 0</td><td>483 ± 15</td></tr><tr><td>B-C14</td><td>243 ± 47</td><td>22 ± 2</td><td>79 ± 53</td></tr></tbody></table>

Note: Average ± standard deviation of five repetitive samples

It was also observed that the cardol derivatives B-C2 and B-C14 bearing two alkyl chains demonstrated a lower elongation at break than its counterpart, A-C2 and A-C14 bearing only one alkyl chain. This result was in accordance with literature where it was found that plasticizers bearing three substituents, named three-legged plasticizers (TINTM) represented in Figure 5, reduced elongation at break compared with their two-leg counterparts[45] (DINP) represented in Figure 5. This difference may be explained by the higher concentration

of polar ester groups in B-C2, which increases the polar bonds with the PVC chain. Thus, cardol derivatives may act as pseudo-crosslinkers by interactions with several PVC chains compared to cardanol derivatives (Figure 6). This was in accordance with computational study, where it was reported that polar carbonyl oxygen in three-legged phthalates (TINTM) has similar binding potential with PVC polar groups as their two-legged counterparts[45] (DINP). Due to their more complex structure, they may struggle to fit between polymer segments, leading to potential entrapment within the mixture.[45] It may also be due to their higher molar weight and their bulkiness. Subsequently, PVC films are stiffer but cardol derivatives B-C2 and B-C8 exhibit elongation at break in a range similar to both phthalates and biobased references, highlighting their potential use as plasticizers.

When studying the effect of these parameters on Young's modulus, it appears that increasing the length of the alkyl chain resulted in an increase in Young's modulus for cardol or cardanol esters (Figure 4B), in accordance with literature.[23,44] A-C2 and B-C2 derivatives increase the flexibility of PVC films, as they have the shortest alkyl chains. They are also similar to phthalates, both DEHP and DINP, and A-C8 and B-C8 derivatives fall within the range of ELO and ESBO for cardol ones. Unexpectedly cardol derivatives exhibit lower Young's modulus compared to cardanol derivatives.

As illustrated in Figure 7, the stress-strain curve of B-C14 displays a clear yielding point, indicating plastic elongation without a significant increase in load. On the other hand, PVC films plasticized with

<figure><img src="image_6.png" /><figcaption>**FIGURE 4** (A) Elongation at break and (B) Young modulus of plasticized PVC films with 43 phr of plasticizers.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**FIGURE 5** Chemical structure of DINP and its "three-legged" counterpart plasticizer TINTM, A-C8 and its "three-legged" counterpart B-C8.</figcaption></figure>

B-C2 do not exhibit a distinct yielding point, but produce a smooth curve, demonstrating a more continuous plastic deformation. The stress-strain curve of B-C8 falls between these two extremes. These variations in the stress-strain curves for plasticized PVC films, depending on the specific derivatives, may be attributed to differences in molecular structure, such as the length of the alkyl chain. Regarding

the mechanical properties, B-C2 appears more suitable as a plasticizer design than that with a longer linear chain, such B-C14.

### 3.3.2 | Thermal properties of PVC films plasticized with cardol and cardanol esters

The effectiveness of a plasticizer is first determined by its ability to decrease the glass transition temperature (Tg) of a polymer, in this case PVC, which has an initial Tg around 81°C. The Tg value of PVC films plasticized with cardol or cardanol esters were determined by differential scanning calorimetry (DSC), presented in Figure 8.

When the Tg could be observed, only one Tg was detected, depicting good miscibility between the plasticizer and the PVC. PVC films plasticized with B-C2 (−17°C) showed a lower Tg than both phthalates (−3°C for DINP) and biobased plasticizers (1°C for ELO) (Table S1). This highlights the ability of cardol derivatives to diminish the intermolecular interactions among PVC chains and increase the free volume within the PVC network. PVC plasticized with cardanol derivatives such as A-C2 were also found to exhibit a lower Tg (−35°C) and is lower in comparison to those plasticized with cardol derivatives.

Determining the Tg became more challenging for longer chain lengths because of the melting phenomenon, which hides the amorphous transition. For PVC films plasticized with A-C14, a melting temperature at −16°C was observed while for B-C14 derivatives, two melting temperatures were recorded at −25°C and 38°C (Figure S7). This may lead to an insufficient plasticizing effect.

<figure><img src="image_8.png" /><figcaption>**FIGURE 6** Possible interactions between repetitive units of PVC chains and ester groups of plasticizers A-C2 (left) and pseudo-crosslinking with B-C2 (right).</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**FIGURE 7** Traction curves of PVC films plasticized with cardol derivatives (43 phr).</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**FIGURE 8** DSC curves of PVC films plasticized with cardol and cardanol derivatives, from –150°C to 150°C at 20 °C min⁻¹.</figcaption></figure>

Even though the Tg could not be observed for C8 and C14 derivatives, it is reported that Tg increases with alkyl chain length from A-C14 to A-C18:1 of cardanol derivatives.[23] This behavior was observed on other plasticizers such as acetylated monoglyceride from C8 to C18:1[46] or tartaric acid.[47] However it was also reported that Tg decreases with alkyl chain length from C2 to C8 substitute for succinate acid.[48–50] Another study on cardanol derivatives highlights the influence of alkyl chains on miscibility between the plasticizers and PVC, which decreases, as the alkyl chain length increases.[44] This is attributed to the carbonyl group being responsible for the plasticizers’ miscibility with PVC, while the alkyl chain in diesters is thermodynamically incompatible with the PVC chain. The adjustment of the alkyl chain length of plasticizers leads to notable changes in the miscibility between the plasticizer and PVC, consequently impacting various properties of the final blends. A long alkyl chain provides more free volume compared to shorter ones like C2, thereby enhancing mobility between PVC chains. However, excessively long linear alkyl chains (C14 for instance) decrease miscibility and yield poorer plasticizing properties. Since CNSL derivatives inherently possess a long linear alkyl chain (C15), it already acts as a spacer between PVC chains. Adding a C14 chain increases the free volume excessively, thereby affecting miscibility.

These results were in accordance with other experimental and computational studies.[45] Indeed, plasticizers bearing three long legs have lower compatibility with PVC compared to those with two legs or those with shorter legs. Thus, C2 derivatives seems better designed as efficient plasticizers.

The thermal characteristics of plasticized PVC films were assessed through thermogravimetric analysis (TGA) from room temperature to 580°C. No weight loss was observed in all the PVC films before 150°C and no residual THF was observed (Table S1 and Figure S8). By comparison, we also reported the TGA curves of the plasticizers (Figure S9). It was observed that all TGA curves displayed a diphasic degradation pattern. The initial weight loss, occurring in the temperature range of approximately 150°C to 325°C, is mainly due to the decomposition of the plasticizer. In addition, the weight loss also results from the cleavage of hydrogen chloride (HCl) producing PVC polyene structures.[51,52] Subsequently, a plateau was observed spanning from 325°C to 425°C, regardless of the plasticizer employed. The final degradation phase, starting at approximately 425°C was associated with intricate mechanisms involving C = C bond cross-linking and char formation.[23]

From these results, several key observations have come to light. In the early stages of degradation, a 5% reduction in weight was observed for PVC that had been plasticized, no matter with which compound. The variations observed in the initial degradation phase can be attributed to the well-established thermal stabilizing properties of cardanol[23] (e.g., A-C2). However, the cardol derivatives (e.g., B-C2) are much more stable than the cardanol derivatives (Table S1). The thermal stability of all films is guaranteed up to a minimum of 200°C. Longer chains contribute to delaying degradation processes and is in accordance with literature.[16,23,44,46,47] However, the degradation rate of B-C14 derivatives is slightly higher than that of B-C8 derivatives and could imply a lower compatibility between B-C14 and PVC.[45] Compared to cardanol derivatives, cardol derivatives exhibit greater stability, highlighting their potential in maintaining material stability under thermal stress.

Performing discoloration tests on samples at 200°C provided valuable insights into the thermal stability of plasticized PVC films (Figure 9). This selected temperature exceeds the Tg of PVC, enabling polymers with high mobility to easily reorganize their molecular chain conformation, converting internal thermal energy into kinetic energy. Conversely, for less stable polymers with limited mobility, the conversion of internal energy into kinetic energy is less effective, resulting in the formation of localized hotspots where decomposition and dehydrochlorination reactions take place.[35]

From the TGA isotherms, it is evident that PVC plasticized with cardol derivatives exhibits greater stability compared to cardanol derivatives and DEHP. Furthermore, consistent with literature findings increasing the chain length enhances thermal stability.[23,46,47] C8 derivatives, especially B-C8, have better thermal stability than phthalates (DEHP) and have similar thermal stability to biobased plasticizers. This effect could be attributed to the longer alkyl chains present in B-C8 derivatives and their higher molecular weight compared to their cardanol counterparts. After 60 min of heating at 200°C, all PVC
<figure><img src="image_11.png" /><figcaption>**FIGURE 9** (A) TGA isotherm at 200°C of plasticized PVC films. Dashed line: respective C8 derivatives. (B) Optical images of plasticized PVC films heated for 0, 5, 10, and 60 min at 200°C.</figcaption></figure>

samples containing plasticizer turned black, indicating inferior thermal stability. However, PVC films plasticized with epoxidized plasticizers ELO and ESBO only turned dark orange (Figure 9). This color change is attributed to the epoxide groups' ability to capture the HCl generated during PVC degradation, facilitated by their interaction with labile chlorine atoms within PVC.

PVC plasticized with cardol derivatives demonstrates superior thermal stability compared to A-C2 or commercial plasticizers. However, improving its thermal stability could be achieved by incorporating epoxy groups into the blends, thereby reducing discoloration during thermal degradation. Consequently, further investigation into the epoxidation of cardol derivatives will be conducted and will be discussed in a future article.

## 3.4 | Eco-toxicity tests of A-C2 and B-C2 plasticizer

As outlined by Czernych et al.,[53] evaluating the endocrine potential through in vitro methods has clear constraints, particularly regarding the assessment of plasticizer metabolites' endocrine potency. Nonetheless, the YES/YAS test serves to mitigate uncertainties regarding the endocrine effects of plasticizers. From previous experiment, it was reported that epoxidized A-C18:1 exhibits no agonistic effects on female (YES) or male (YAS hormones, and neither on antagonist effects YES, although DINP have agonist and antagonist YES/YAS effects.[23]

In this study, the endocrine activity was evaluated for A-C2 and B-C2 plasticizers. Based on the YES and YAS tests, no estrogenic or androgenic agonist activity was observed for B-C2 and A-C2 samples. However, the Anti-YES test reveals anti-estrogenic activity for both samples starting from a concentration of 100 µL L⁻¹. Specifically, 1 µL L⁻¹ of sample B-C2 shows anti-estrogenic activity equivalent to 4-hydroxytamoxifen at a concentration of 3.3 × 10⁻⁶ ± 1.19 × 10⁻⁶ g L⁻¹, while 1 µL L⁻¹ of sample A-C2 exhibits anti-estrogenic activity equivalent to 4-hydroxytamoxifen at a concentration of 3.85 × 10⁻⁶ ± 7.07 × 10⁻⁷ g L⁻¹ (Figure S10).

Similarly, the Anti-YAS test indicates anti-androgenic activity for sample B-C2 at the highest concentration (10 000 µL L⁻¹) and for sample A-C2 starting from a concentration of 1000 µL L⁻¹. Specifically, 1 µL L⁻¹ of sample B-C2 demonstrates anti-androgenic activity equivalent to flutamide at a concentration of 1.2 × 10⁻⁶ ± 2.25 × 10⁻⁷ g L⁻¹, while 1 µL L⁻¹ of sample A-C2 exhibits anti-androgenic activity equivalent to flutamide at a concentration of 1.68 × 10⁻⁵ ± 1.05 × 10⁻⁶ g L⁻¹ (Figure S11).

## 4 | CONCLUSION

For the first time, cardol was investigated as a platform molecule for potential plasticizers. While previous literature has explored cardanol, this research reveals significant attraction for the application of cardol derivatives as plasticizers in various flexible PVC products. Cardol esters (B-C2, B-C8, B-C14) demonstrate promising plasticizing properties, including lower Young's modulus compared to cardanol derivatives, similar elongation at break, and improved thermal properties compared to both cardanol and phthalate references. This study reveals that cardol exhibits distinct plasticizing behavior compared to cardanol, attributed to its structure with three pendant alkyl chains and two ester groups. Consequently, cardol does not behave the same way as cardanol derivatives. Better mechanical behavior was observed with esters of shorter length, such as C2, than longer ones, such as C14, although higher chain length increases thermal stability. Additionally, cardol ester B-C2, as well as cardanol ester A-C2, showed no reproductive toxicity and no notable impact on agonistic properties for both female and male hormones, nor antagonistic properties at low concentrations. This suggests that these plasticizers are promising fully bio-based alternatives to phthalate plasticizers or biobased edible oils for PVC films.

## ACKNOWLEDGMENTS

The PVC and cardanol used in this study were provided free of charge by KemOne and Cardolite respectively. The nonendocrine tests were conducted by Eurofins ecotoxicology France.
## CONFLICT OF INTEREST STATEMENT

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.

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## SUPPORTING INFORMATION

Additional supporting information can be found online in the Supporting Information section at the end of this article.

**How to cite this article:** Gartili, A., Caillol, S., Briou, B., & Lapinte, V. (2024). One step beyond for CNSL-based plasticizers for PVC: Use of cardol. *European Journal of Lipid Science & Technology*, 126, e2400086.
https://doi.org/10.1002/ejlt.202400086