# Epoxidation of CNSL Mixture, Cardanol, and Cardol: A Sustainable Solution for PVC Plasticization

Adélaïde Gartili, Vincent Lapinte, Sylvain Caillol, Benoit Briou

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Adélaïde Gartili, Vincent Lapinte, Sylvain Caillol, Benoit Briou. Epoxidation of CNSL Mixture, Cardanol, and Cardol: A Sustainable Solution for PVC Plasticization. European Journal of Lipid Science and Technology, 2025, 128 (1), pp.e70084. 10.1002/ejlt.70084. hal-05491997

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RESEARCH ARTICLE

OPEN ACCESS

# Epoxidation of CNSL Mixture, Cardanol, and Cardol:
A Sustainable Solution for PVC Plasticization

Adélaïde Gartili¹,² | Vincent Lapinte¹ | Sylvain Caillol¹ | Benoit Briou²

¹ICGM, Univ Montpellier, CNRS, ENSCM, Montpellier, France | ²Orpia Innovation, Paris/Montpellier, France

**Correspondence:** Benoit Briou (benoit.briou@hotmail.com)

**Received:** 23 April 2025 | **Revised:** 5 November 2025 | **Accepted:** 12 November 2025

**Keywords:** biobased plasticizer | cardanol | cashew nut shell liquid (CNSL) | epoxidation | poly(vinyl chloride) (PVC)

## ABSTRACT

Epoxidation is an effective method for enhancing the plasticizing properties of biobased oils for the plasticization of poly(vinyl chloride) (PVC), among other applications. Epoxy groups not only increase the affinity with PVC but also enhance its thermal and mechanical properties. Cashew nut shell liquid (CNSL), an inedible oil derived from agricultural waste, comprises cardanol, cardol, and anacardic acid. These compounds, phenols with long alkyl chains, contain unsaturation that can be epoxidized. This project aims to evaluate the feasibility of utilizing technical CNSL (80% cardanol and 20% cardol) as a PVC plasticizer. Various plasticizers were synthesized from pure cardanol or technical CNSL through esterification and epoxidation to enhance compatibility with PVC and plasticizing properties. Notably, as far as we know, mixtures of cardanol and cardol derivatives have been epoxidized for the first time. The chemical structures of these plasticizers were fully characterized using ¹H nuclear magnetic resonance (NMR) spectroscopy. Furthermore, the mechanical properties, thermal stability, and chemical resistance of PVC films plasticized with these additives were investigated.

**Practical Applications:** Cardanol, once esterified and epoxidized, has demonstrated good plasticizing capabilities for certain polymers including PVC. This naturally occurring product is obtained after distillation of a crude oil from the shell of cashew nuts, the cashew nutshell liquid (CNSL). Other components present in this oil, such as cardol, have also demonstrated significant pertinence in the plasticization of PVC. Using the crude oil or a mixture of components as precursors for plasticizers for PVC would reduce the cost of the plasticizing agent and avoid possible loss or waste linked to the separation of the raw compounds, currently carried out.

## 1 | Introduction

Because of its outstanding performance and cost-effectiveness poly(vinyl chloride) (PVC) is one of the world's most widely used thermoplastics on the plastics market [1, 2]. It finds numerous applications in the manufacture of a range of products, from rigid to flexible items [3]. However, because of the polarity of the C-Cl bond and robust dipole-dipole interactions, which limit the mobility of the polymer chain, PVC is intrinsically brittle and requires plasticizer to improve the mechanical properties and processability of PVC [4, 5]. Main plasticizers are

phthalic acid esters, such as di(2-ethylhexyl) phthalate (DEHP) [6]. Because external plasticizers leach out over time and with aging, and because phthalates are suspected to have endocrine-disrupting effects in humans and reproductive toxicity, their use is now restricted [7–10]. Besides, phthalates are produced from petroleum which no longer corresponds to the plastics industry's growing demand for renewable plasticizers derived from sustainable raw materials [11–13].

Indeed, recent studies have focused on biobased plasticizers derived from vegetable oils, with the aim of offering sustainable

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.

© 2025 The Author(s). *European Journal of Lipid Science and Technology* published by Wiley-VCH GmbH.
alternatives to phthalates in the plastics industry [14, 15]. Epoxidized linseed oil (ELO) and epoxidized soybean oil (ESBO) are commonly used as nontoxic biological plasticizers for PVC [16, 17]. However, as this could have significant social and economic consequences, care must be taken to ensure that the production of these renewable resources does not compete with food production [18–20]. Intensive soy monoculture requires substantial inputs of industrial chemicals such as fertilizers and pesticides, as well as the need to replant every year, and contributes to deforestation [21].

In an effort to design green plasticizers, sustainable bioresources derived from agro-industrial residues and inedible biomass appear to be more suitable for use as chemical feedstocks for plasticizer synthesis [22]. Recently, attention has focused on a nonedible oil derived from an agricultural waste product, cashew nut shell liquid (CNSL) [23, 24]. This is a by-product of cashew processing in industry, a dark reddish-brown to greenish-yellow viscous liquid contained in the porous lattice structure of the cashew nut shell (CNS) [25, 26]. Although CNS is an agricultural waste product, CNSL is one of the richest natural sources of phenols, consisting of four substituted phenols (anacardic acid, cardanol, cardol, and 2-methylcardol). The valorization of CNSL has given rise to a number of products that rival those derived from fossil fuels [27]. Many of these products are already in use, and ongoing developments are expanding the range [28]. Its applications span a variety of industrial sectors, serving as a raw material in the production of azo compounds/dyes, friction coatings, surface coatings, adhesives, varnishes, resins, rubbers, foundry chemicals, pesticides, larvicides, termite control solutions, pharmaceuticals, and biodiesel [29, 30]. For example, cardanol-based compounds derived from CNSL are aimed to be used for biobased plasticizers for PVC [24]. Indeed, CNSL derivatives are recognized as a promising alternative to phthalates due to their unique natural structure, which is similar to that of phthalates. CNSL's phenol content contributes to thermal stability, whereas its long C-15 aliphatic chain enhances plasticizing effects [15].

Previous researches reveal esterification of cardanol derivatives could increase PVC compatibility as well as epoxidation [23, 24, 31]. Following the work of Neuse et al. [32] and Ghatge et al. [33], in 2010, Greco et al. synthesized cardanol acetate (C2) plasticizers with anhydrous acetic acid and epoxidized these derivatives with chloroperbenzoic acid (m-CPBA) to increase solubility in PVC [23]. PVC films were plasticized with these derivatives used as primary plasticizers at different phr and as secondary plasticizers (6–20 phr) mixed with DEHP phthalate. They showed that the epoxidation of the compounds improved the thermal stability of the PVC film, as well as its resistance to migration, which is desirable. This was further investigated in 2016 when they studied these plasticizers by varying the epoxy rate, synthesized by $H_2O_2$ [34]. Three years later, Briou et al. studied different cardanol esters (C2, C14, C18:1), by Steglich esterification (EDC/DMAP), and epoxidized these plasticizers by $H_2O_2$ [24]. They studied these compounds as primary plasticizers (66 phr) with PVC and as secondary plasticizers (33 phr) with di-isononyl-phthalate (DINP). Epoxidized C14 and C18:1 long-chain ester compounds, used as primary plasticizers, considerably improved the thermal stability of PVC films, and Young's modulus was found to be reduced (4–7 MPa). This appears to have been interpreted as

a low tensile strength of 4–7 MPa according to Yang et al., which is reportedly well below the requirements for practical applications in the food packaging and toy industries (15–20 MPa) [31]. They deduced from this a possible incompatibility between PVC and large quantities of plasticizer. They therefore decided to study C14 and C18:1 cardanol derivatives as secondary plasticizers, this time associated with ESBO, which seemed more relevant, in a sustainable approach, than using phthalates (DEHP, DINP) as in previous studies. They esterified cardanol by Steglich esterification (EDC/DMAP) with C14 and C18:1 esters and epoxidized it with $H_2O_2$. The PVC was then plasticized with 15–40 phr of plasticizers, including 3/5/10 phr of cardanol derivatives.

Observations consistent with prior research on the impact of chain length, epoxidation, and plasticizer content were noted. Specifically, longer chains enhance mechanical and thermal properties, as do epoxidation and a higher plasticizer content. However, these parameters typically increase the glass transition temperature ($T_g$), except for epoxidation, which appears to decrease it. Migration tests revealed that PVC films plasticized with cardanol and ESBO derivatives exhibited more migration compared to those containing DEHP. Shorter-chain compounds (C14) exhibited lower migration rates than even epoxidized C18:1 compounds, and a higher plasticizer content led to greater weight loss during migration tests.

These studies on cardanol derivatives as PVC plasticizers show the complexity of designing a plasticized PVC formulation with the best properties, and many parameters can be studied to assess their influence: esterification and ester chain length, epoxidation and epoxidation rate, primary plasticizer and plasticizer rate, secondary plasticizer and choice of primary plasticizer, and secondary plasticizer rate. Quite apart from the synthesis and formulation processes chosen, often within the limits of the tools available, it is difficult to correlate all the results offered by these studies with one another. However, as detailed above, trends can be seen in the correlation of structure and properties.

As far as we know, the exploration of renewable resources CNSL as a plasticizer for PVC is mainly, if not exclusively, focused on cardanol in academic and industrial research [23, 24, 31, 35]. However, to obtain the desired cardanol, it has to be extracted and separated from other compounds, mainly anacardic acid and cardol [36, 37]. This operation has a significant energy, economic, and time cost, which must be reflected by the biobased aspect sought.

Therefore, the aim of this study is to determine whether it is possible to use technical CNSL as a plasticizer for PVC, in order to avoid the long, energy-intensive, and costly steps linked to the extraction of cardanol. The use of technical CNSL, without isolating pure cardanol or cardol, is a deliberate strategy aimed at simplifying the production process and reducing its environmental and economic impact. By demonstrating that technical CNSL, with its natural cardanol/cardol composition, can be directly used as a PVC plasticizer, this study opens up the possibility for more sustainable and cost-effective formulations. This could facilitate the large-scale development of CNSL-based plasticizers, especially in contexts where minimizing processing steps is crucial for industrial viability and environmental impact.
Thus, it seems interesting to us to conduct experiments on technical CNSL (ratio of cardanol/cardol, 80:20) with different alkyl chain lengths, as it was previously reported to enhance thermal stability for instance and to also investigate epoxidation as epoxidized plasticizers tend to have better plasticizing properties [38]. In this study, plasticizers are synthesized from cardanol, or technical CNSL, through esterification with propylphosphonic acid (T3P), which is a greener reactant than EDC/DMAP, and epoxidized with H₂O₂. The chemical structure of these plasticizers is determined using ¹H nuclear magnetic resonance (NMR) spectroscopy. The resulting PVC films, plasticized with these synthesized compounds as primary plasticizers, undergo an investigation of their mechanical properties, thermal stability, and exudation resistance.

# 2 | Experimental Procedures

## 2.1 | Materials

Cashew nutshells were provided by Orpia Innovation. CNSL was extracted with ethyl acetate by Orpia Innovation. Cardanol NX-2026 was kindly provided by Cardolite. PVC P70 was kindly provided by KemOne in powder form. DINP, di(2-ethylhexyl) phthalate (DEHP), ELO, ESBO, acetic acid, octanoic acid, myristic acid, oleic acid, propylphosphonic anhydride (T3P), sulfuric acid (H₂SO₄), formic acid, and hydrogen peroxide (H₂O₂) were purchased from Sigma-Aldrich. Tetrahydrofuran (THF) and magnesium sulfate (MgSO₄) were purchased from VWR International SAS (Fontenay-sous-Bois, France). Cyclohexane and ethyl acetate were purchased from Analytic Lab. All reagents were used as received.

## 2.2 | Synthesis and Characterization of Epoxy Esters

As in our previous study, cardanol and cardol will be designated by the letter A and B, respectively [39]. Then, the corresponding ratios are indicated by X<sub>A</sub>:X<sub>B</sub>. Esters are designated by their chain length using the letter C, followed by the number of carbons. For instance, a mixture containing naturally 80% of cardanol and 20% of cardol will be noted A_B 80_20 and the corresponding acetate is designated by A_B 80_20 C2.

### 2.2.1 | Synthesis of Ester Derivatives From Cardanol and Cardol

Several acids (acetic, octanoic, myristic, and oleic acids) were used according the same procedure. To a mixture of cardanol, cardol, or a mixture of both (1 eq), acid (1.1 eq), and T3P (1.1 eq) was added. The mixture was stirred at 80°C. The progress of the reaction was monitored by thin layer chromatography (TLC) and ¹H NMR spectroscopy. The reaction was completed before 3 h. The crude product was washed three times by liquid-liquid deionized water-ethyl acetate extraction. The organic phase was dried over anhydrous MgSO₄, separated in the extraction funnel, and ethyl acetate was removed under reduced pressure. The ¹H NMR spectroscopy has been presented in a previous article [38].

### 2.2.2 | Epoxidation of Ester Derivatives From Cardanol and Cardol

The epoxidation was realized on different CNSL derivatives esters. CNSL derivatives esters (1 eq), formic acid (3 eq), and H₂SO₄ (0.01 eq) were mixed and heated at 50°C. H₂O₂ (2 eq/double bond) was drop by drop added to the mixture which was stirred at 65°C. The progress of the reaction was monitored by TLC and ¹H NMR spectroscopy. The reaction was completed after 3 h. The crude product was washed three times by liquid-liquid deionized water-ethyl acetate extraction. The organic phase was dried over anhydrous MgSO₄, separated in the extraction funnel, and ethyl acetate was removed under reduced pressure.

It has to be noted that these plasticizers were epoxidized under identical conditions. However, this does not always result in the same level of epoxidation for both central and terminal unsaturations. This aspect will be further elucidated in the upcoming section.

**A-C2 E:** Isolated yield 95%, central epoxy 100%, terminal epoxy 62%, liquid, light yellow, ¹H NMR (400 MHz, CDCl₃) δ 7.27 (dt, *J* = 7.8, 4.8 Hz, aromatic CH), 7.14–6.99 (m, aromatic CH), 6.97–6.83 (m, aromatic CH), 5.94–5.79 (m, remnants of unsaturated bonds), 5.26–5.06 (m, remnants of unsaturated bonds), 4.17–3.9 (diols), 3.23–3.03 (m, CH₂), 3.03–2.75 (m, CH₂), 2.68–2.52 (m, CH₂), 2.29 (s, CH₃), 2.15–1.79 (m, CH₂), 1.79–0.92 (m, CH₂), and 0.92–0.69 (m, CH₃).

**A-C8 E:** Isolated yield 91%, central epoxy 100%, terminal epoxy 62%, liquid, light yellow, ¹H NMR (400 MHz, CDCl₃) δ 7.31–7.21 (m, aromatic CH), 7.06–6.99 (m, aromatic CH), 6.92–6.84 (m, aromatic CH), 5.96–5.79 (m, remnants of unsaturated bonds), 5.23–5.01 (m, remnants of unsaturated bonds), 4.90–3.25 (diols), 3.23–2.82 (m, CH₂), 2.81–2.75 (m, CH₂), 1.85–1.68 (m, CH₂), 1.68–0.98 (m, 1 CH₂), and 0.95–0.71 (m, CH₃).

**A-C14 E:** Isolated yield 98%, central epoxy 95%, terminal epoxy 15%, paste-like, yellowish, ¹H NMR (400 MHz, CDCl₃) δ 7.35–7.21 (m, aromatic CH), 7.09–6.99 (m, aromatic CH), 6.94–6.81 (m, aromatic CH), 5.99–5.75 (m, remnants of unsaturated bonds), 5.25–4.91 (m, remnants of unsaturated bonds), 3.24–2.79 (m, CH₂), 2.57–2.42 (m, CH₂), 1.84–1.68 (m, CH₂), 1.68–1.13 (m, 1 CH₂), and 0.91–0.74 (m, CH₃).

**A_B 80_20 C2 E:** Isolated yield 81%, central epoxy 60%, terminal epoxy 0%, liquid, orange yellowish, ¹H NMR (400 MHz, CDCl₃) δ 7.31–7.23 (m, aromatic CH of cardanol), 7.04–6.97 (m, aromatic CH of cardanol), 6.93–6.87 (m, aromatic CH of cardanol), 6.85–6.79 (m, aromatic CH of cardol), 6.75–6.71 (m, aromatic CH of cardol), 5.96–5.67 (m, remnants of unsaturated bonds), 5.62–5.25 (m, remnants of unsaturated bonds), 5.25–4.88 (m, remnants of unsaturated bonds), 3.14–2.67 (m, CH₂), 2.64–2.47 (m, CH₂), 2.42–2.15 (m, CH₃), 2.08–1.99 (m, CH₂), 1.82–1.10 (m, CH₂), and 1.06–0.80 (m, CH₃).

**A_B 80_20 C8 E:** Isolated yield 83%, central epoxy 94%, terminal epoxy 42%, liquid, orange yellowish, ¹H NMR (400 MHz, CDCl₃) δ 7.36–7.20 (m, aromatic CH of cardanol), 7.03 (d, *J* = 7.7 Hz, aromatic CH of cardanol), 6.91–6.86 (m, aromatic CH of cardanol), 6.78 (d, *J* = 2.0 Hz, aromatic CH of cardol), 6.73–6.64 (m, aromatic
CH of cardol), 5.95–5.73 (m, remnants of unsaturated bonds), 5.34–4.88 (m, remnants of unsaturated bonds), 3.25–2.73 (m, CH₂), 2.62–2.49 (m, CH₂), 2.44–2.31 (m, CH₂), 1.96–1.88 (m, CH₂), 1.87–1.12 (m, CH₂), and 1.01–0.81 (m, CH₃).

**A_B 80_20 C18:1 E:** Isolated yield 84%, central epoxy 96%, terminal epoxy 79%, liquid, orange yellowish, ¹H NMR (400 MHz, CDCl₃) δ 7.36–7.18 (m, aromatic CH of cardanol), 7.03 (d, *J* = 7.7 Hz, aromatic CH of cardanol), 6.95–6.83 (m, aromatic CH of cardanol), 6.76 (d, *J* = 14.2 Hz, aromatic CH of cardol), 6.71 (s, aromatic CH of cardol), 5.94–5.76 (m, remnants of unsaturated bonds), 5.26–5.06 (m, remnants of unsaturated bonds), 3.27–2.83 (m, CH₂), 2.67–2.18 (m, CH₂), 1.83–1.09 (m, CH₂), and 1.02–0.79 (m, CH₃).

### 2.2.3 | Preparation of Plasticized PVC Films by Solvent Casting Method

PVC films were formulated by mixing PVC with THF (10 mL/g PVC) and with different plasticizers (43 phr) at room temperature. After mixing homogeneously, the solution was poured into an aluminum mold and sealed it with a preservative film, then placed it in the fume hood for 3 days. After that, the films were taken out and dried in and oven at 50°C for 3 h. The thickness of obtained PVC films was around 0.35 mm. No heat stabilizers or other additives have been added.

## 2.3 | Characterization

NMR spectra were conducted on an NMR Bruker Avance I 400 MHz spectrometer at 25°C in CDCl₃. The chemical shifts were in part 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 peak of residual CDCl₃ at 7.26 ppm.

Viscosity experiments were performed on an Anton Paar rheometer, equipped with an oven, by applying a logarithmic increase in shear rate from 0.01 to 100 s⁻¹ at 25°C for 105 s. Cone plate disposable geometries were utilized, with a 25 mm diameter.

Thermogravimetric analyses (TGAs) of plasticizers and PVC films were carried out to determine the thermal stability and were performed on a Netzsch TG 209F1 apparatus under 40 mL/min nitrogen flow. The protective gas used was nitrogen with a 20 mL/min flow. Approximately 10–12 mg of sample was placed in an alumina crucible and heated from room temperature to 580°C with a 10°C/min heating rate.

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 between –150 and 150°C to observe the glass transition temperature.

Elongation at break and Young modulus of the films were measured with an Instron 3366L5885 tensile tester according to ISO 527-3:2018 [40]. Dumbells samples of 12 mm × 2 mm were used for these analyses and mounted between tensile grips with

an initial grip spacing of 0 cm. The tensile speed was set at 200 mm/min. 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.

To further study the thermal performance of plasticized PVC samples, the discoloration was performed at 200°C The plasticized PVC films with 1 cm × 1 cm × 0.35 mm were placed into the aging oven at 200°C and removed at 5, 10, and 60 min.

Volatility properties of the plasticized PVC films were characterized in a convection oven at 80°C for 48 h. The weight loss was calculated according to the following equation:

$$ \text{Volatility} = \left[ 100 - \left( \frac{W1 - W2}{W1} \right) \right] \times 100 \quad (1) $$

where W1 is the weight (g) of the PVC sample before testing and W2 is the weight (g) of the PVC sample after testing.

The leaching tests were carried out. Plasticized PVC samples (1.5 cm × 0.5 cm × 0.35 mm) after weighting were, respectively, immersed in distilled water, petroleum ether, and anhydrous alcohol at 30°C for 48 h. After the solvent was wiped off from the surface of the samples, the weight loss was calculated according to Equation (2). These samples where then dried to 50°C for 24 h. The weight loss was calculated according to the following equation:

$$ \text{Migration rate} = \left[ 100 - \left( \frac{W3 - W4}{W3} \right) \right] \times 100 \quad (2) $$

where W3 is the weight (g) of the PVC sample before testing and W4 is the weight (g) of the PVC sample after testing.

UV–Vis spectrophotometry was performed on a UV–Vis near infrared spectrophotometer (Perkin Elmer, UV–Vis Lambda 365) to determine the transmittance of the plasticized PVC films. The spectrum of each sample was presented in the wavelength range of 200–800 nm.

# 3 | Results and Discussion

## 3.1 | Synthesis and Characterization of CNSL-Based Plasticizers

### 3.1.1 | Esterification and Epoxidation of CNSL-Based Plasticizers

To engineer 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 bonds, electrostatic forces, or van der Waals interactions [15] (Figure 1). 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. In this study, propylphosphonic anhydride reagent (T3P) was used for esterification of pure cardanol or mixture of cardanol and cardol, according
<figure><img src="image_3.png" /><figcaption>**FIGURE 1** | Chemical structure of CNSL-ester derivatives as PVC plasticizer.</figcaption></figure>

the same procedure than presented in a previous article [38]. At no point was pure cardanol mixed with pure cardol. Only mixtures naturally containing both cardanol and cardol were utilized.

The confirmation of the chemical structure for cardanol, cardol, and CNSL derivatives was achieved through ¹H NMR spectroscopy. In Figure 1, the distinctive signals of phenolic protons for cardanol (a–d) shifted from 6.69, 6.80, and 7.14 to 6.96, 7.10, and 7.29 ppm, respectively. The double bond signals between 4.95 and 5.92 ppm remained unaffected by the esterification. Additional aliphatic proton signals corresponding to the grafted alkyl chain were observed at 2.33 ppm. This is in accordance with our previous study [38] (Figure 2).

It is worth noting that literature has previously described only epoxidized cardanol [23, 24, 34]. To the best of our knowledge, no study has yet investigated such modification on cardol.

The epoxidation was investigated in order to add more polar groups into CNSL derivatives to increase the compatibility of the compounds with PVC [24, 34]. Epoxidation was realized on different CNSL derivatives esters. Different methods were investigated. CNSL derivatives are epoxidized by peroxide hydrogen, one of the most conventional method for epoxidation. H₂O₂ (2 eq/double bond) is added and heated at 65°C for 3 h.

The presence of epoxidized groups is shown at 2.76–2.92, 2.93–3.01, and 3.05–3.23 ppm, attributed to g, i, and h protons, respectively (Figure 2). The epoxy ratio was determined by assessing the conversion of signals at positions h, g, and i within the range of 4.93–5.86 ppm. The distinction between terminal protons (Hi and Hg) and ethylenic protons along the alkyl and fatty chains revealed a lower conversion of epoxidation for terminal protons in comparison to internal ones, consistent with prior findings [24].

**3.1.2 | Viscosity and Thermal Stability of CNSL Derivatives**

It is crucial to examine the viscosity of the plasticizers to determine their suitability for PVC plasticization in industrial processes. As depicted in Figure 3a, the introduction of epoxy leads to an increase in the viscosity of the plasticizer. It was observed that A_B 80_20 derivatives exhibit higher viscosity compared to their cardanol counterparts. This may be due to cardol, which has more ester groups and naturally has a higher viscosity than cardanol. Despite epoxidized cardanol/cardol 80:20 C18:1 E, all the plasticizers have lower viscosity compared to both epoxy-modified vegetable oils, ELO and ESBO. For instance, epoxidized A-C2 E is eight times lower than ELO. The viscosity results show that epoxidized plasticizers could be entirely usable in industrial processes.

The thermal stability of plasticizers is also an important parameter to study because they have to remain stable during industrial heat processes, which generally occur around 200°C. From Figure 3b, it is observed that epoxidation contributes to an increase in the thermal stability of the plasticizers of about 11%. The improvement in heat resistance can be ascribed to the formation of more robust bonds between PVC chains and epoxy groups. All plasticizers exhibit a temperature of 5% weight loss within the range of both phthalates and epoxidized vegetable oils (EVOs). These findings confirm that epoxidized plasticizers offer potential advantages in terms of thermal stability, reinforcing their relevance for industrial processes. It can also be observed that CNSL derivatives exhibit higher thermal stability, thanks to the presence of cardol, which can bind more to PVC chains than cardanol.

Moreover, solubility is another parameter to take into account. Although the solubility parameter alone is inadequate for predicting plasticization efficiency, it serves as an efficient method for
<figure><img src="image_4.png" /><figcaption>FIGURE 2 | ¹H NMR spectra of cardanol, A-C2, and epoxidized A-C2 in CDCl₃.</figcaption></figure>

forecasting the solvents in which the polymer will not dissolve, relying on their solubility values. Achieving a significant level of compatibility typically necessitates that the polymer and plasticizer exhibit similar polarity, but polymers and plasticizers with matching solubility may not always be compatible. When there's a significant polarity disparity between the polymer and plasticizer, complete compatibility may not be achieved [15]. It's widely accepted that for good compatibility, the difference in solubility parameters should be <3.7 (J/cm³)¹/². When evaluating the Hansen solubility parameters on CNSL derivatives plasticizers, it appears that the solubility difference with PVC is smaller for epoxidized compounds, indicating improved miscibility (Figure S1).

## 3.2 | Properties of Plasticized PVC Films With CNSL Derivatives

After characterizing CNSL derivatives, these plasticizers were utilized, as primary plasticizers, to produce PVC films, via solvent method. Their plasticizing efficiency was compared with that of both commercial phthalates (DEHP and DINP) and biosourced vegetable oils (ESBO and ELO). No other additives were added. To assess the impact of epoxy groups in the plasticizers on plasticizing efficiency, an analysis of the mechanical properties, thermal features, and leaching behavior has been conducted.

### 3.2.1 | Optical Properties of Plasticized PVC Films With CNSL Derivatives

The PVC thin films obtained demonstrated good transparency and visual transparency. In addition to visual examination, transmittance can be investigated as it plays a pivotal role in assessing PVC films for the packaging industry. Transmittance can be quantified through UV-Vis spectroscopy. An analysis of UV-Vis spectra from plasticized PVC films reveals that blends containing CNSL derivatives effectively block UV rays up to at least 300 nm (Figure S2). No specific influence of epoxy has been identified on UV transmittance. However, it is observable that epoxidation reduces the color of the CNSL derivatives and that the PVC films obtained were less colored than non-epoxidized CNSL ester derivatives (Figure S3).

### 3.2.2 | Mechanical Properties of Plasticized PVC Films With CNSL Derivatives

PVC inherently possesses rigidity and is prone to brittleness, but the addition of a plasticizer can increase flexibility to PVC by increasing the mobility of PVC chains. CNSL derivatives have demonstrated promising plasticizing properties, with elongation at break falling within the same range as traditional phthalate plasticizers (DEHP or DINP) and vegetable epoxidized oils (ESBO and ELO), particularly for cardanol derivatives (Table 1, Figure S4). The elongation at break is slightly lower for CNSL derivatives,
<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /><figcaption>**FIGURE 3** | (a) Viscosity of plasticizers esterified and/or epoxidized. Solid fill: esterified compounds, hatch marks: epoxidized compounds. (b) Temperature at 5% weight loss of different plasticizers. Solid fill: esterified compounds, hatch marks: epoxidized compounds. DINP, di-isononyl-phthalate; ELO, epoxidized linseed oil; ESBO, epoxidized soybean oil.</figcaption></figure>
<table><caption>TABLE 1 | Mechanical and thermal properties of different poly(vinyl chloride) (PVC) films (43 phr of plasticizer).</caption><thead><tr><th rowspan="2">Plasticizer (43 phr)</th><th colspan="3">Tensile properties</th><th colspan="2">Thermal properties</th></tr><tr><th>Young's modulus (MPa)</th><th>Max tensile strength (MPa)</th><th>Elongation at break (%)</th><th>T<sub>gmid</sub> (°C)</th><th>T<sub>5%</sub> (°C)</th></tr></thead><tbody><tr><td>DEHP</td><td>22 ± 2</td><td>22 ± 1</td><td>492 ± 18</td><td>-13</td><td>217</td></tr><tr><td>DINP</td><td>16 ± 3</td><td>18 ± 4</td><td>326 ± 19</td><td>-3</td><td>237</td></tr><tr><td>ELO</td><td>123 ± 19</td><td>26 ± 3</td><td>466 ± 26</td><td>1</td><td>254</td></tr><tr><td>ESBO</td><td>97 ± 12</td><td>23 ± 4</td><td>367 ± 72</td><td>-6</td><td>262</td></tr><tr><td>A-C2</td><td>16 ± 4</td><td>23 ± 4</td><td>566 ± 54</td><td>-35</td><td>221</td></tr><tr><td>A-C2E</td><td>11 ± 4</td><td>22 ± 7</td><td>549 ± 68</td><td>-13</td><td>248</td></tr><tr><td>A-C8</td><td>21 ± 5</td><td>24 ± 7</td><td>405 ± 57</td><td>—</td><td>249</td></tr><tr><td>A-C8E</td><td>24 ± 10</td><td>22 ± 4</td><td>491 ± 65</td><td>-23</td><td>265</td></tr><tr><td>A-C14</td><td>271 ± 14</td><td>23 ± 4</td><td>179 ± 40</td><td>—</td><td>247</td></tr><tr><td>A-C14E</td><td>193 ± 4</td><td>21 ± 2</td><td>347 ± 28</td><td>—</td><td>263</td></tr><tr><td>A_B 80_20 C2</td><td>21 ± 55</td><td>16 ± 8</td><td>291 ± 66</td><td>-35</td><td>234</td></tr><tr><td>A_B 80_20 C2 E</td><td>11 ± 3</td><td>14 ± 4</td><td>319 ± 31</td><td>-10</td><td>251</td></tr><tr><td>A_B 80_20 C8</td><td>100 ± 55</td><td>12 ± 6</td><td>166 ± 68</td><td>—</td><td>246</td></tr><tr><td>A_B 80_20 C8 E</td><td>66 ± 13</td><td>21 ± 2</td><td>395 ± 53</td><td>-23</td><td>261</td></tr><tr><td>A_B 80_20 C18:1</td><td>185 ± 6</td><td>16 ± 2</td><td>274 ± 32</td><td>—</td><td>250</td></tr><tr><td>A_B 80_20 C18:1 E</td><td>150 ± 18</td><td>19 ± 1</td><td>313 ± 77</td><td>—</td><td>262</td></tr></tbody></table>

Note: The symbol “—” indicates that no value was observed.

Abbreviations: DINP, di-isononyl-phthalate; ELO, epoxidized linseed oil; ESBO, epoxidized soybean oil.

attributed to the presence of cardol, which, when isolated, demonstrates lower elongation at break with a higher Young's modulus. Cardol derivatives can act as a pseudo-crosslinker by forming linkages with two or three PVC chains, introducing more rigidity to the material (Figure 4). Once again, a correlation has been observed between shorter chain length and higher elongation for both non-epoxidized and epoxidized compounds.

It was observed that epoxidation decreases the elongation at break for A-C2 plasticized films. This is in accordance with previous works and the study by Greco et al., where an increase in the rate of epoxy led to a decrease in the elongation at break [24, 34]. However, for other PVC films, it is shown that epoxidation results in an increase in elongation at break of the respective PVC films, in accordance with literature for C14 and C18:1 derivatives [31]. This feature is crucial for assessing the material's ability to undergo plastic deformation before breaking. Greater elongation at break indicates that the material can stretch more before breaking, showing improved flexibility and resilience under pressure. This is especially important for plasticizers, as it affects how easily materials can be molded and shaped during manufacturing processes. Epoxidation of CNSL derivatives is therefore beneficial for the resulting PVC material.

Simultaneously, epoxidation leads to a reduction in Young's modulus, indicating a decrease in the material's stiffness (Table 1 and Figure S5). Epoxidation allows for a decrease of approximately 30% in Young's modulus. This was in accordance with literature [41]. For plastic films the reduction in stiffness is as flexibility

and malleability are essential characteristics. It is noteworthy, once again, that the findings underline the importance of chain length in influencing the mechanical properties of the material. For instance, C2 derivatives display a low modulus comparable to phthalates. However, with an increase in the alkyl chain length, Young's modulus becomes higher. Thus, if one intends to use long alkyl chains, it may be advantageous to epoxidized it, which will decrease Young's modulus.

Thus, epoxidation emerges as a promising strategy to tailor the mechanical properties of materials according to specific requirements, thereby contributing to improve the efficiency of plasticizers in modifying the physical characteristics of polymers. Although the mechanical properties of PVC films plasticized with cardanol derivatives are reported, tensile curves are hardly ever presented. Mechanical properties (Young's modulus and elongation at break) are often observed to be similar from one plasticizer to another. Although these parameters do not show major differences, their tensile behavior can be clearly different.

Interestingly, regarding the stress-strain curves (Figure 5), those of C2 derivatives do not exhibit a specific yield point. In contrast, the stress-strain curve of C18:1 derivatives at room temperature shows a yielding point where plastic elongation occurs without an increase in load. The stress-strain curves of C8 derivatives fall somewhere between these two extremes.

This observation suggests that C2 derivatives have a more homogeneous behavior, without a distinct yield point, which may
<figure><img src="image_7.png" /><figcaption>**FIGURE 4** | Possible interactions between plasticizer epoxidized A-C2, epoxidized cardol-C2, and PVC chains. PVC, poly(vinyl chloride).</figcaption></figure>

indicate a more continuous plastic deformation. The absence of a yield point and the continuity of the curve may indicate a reduction in the overall material's stiffness, which is desirable. On the other hand, C18:1 derivatives display a clear yield point, marking the onset of plastic elongation but without a significant increase in load. The mechanical behavior is less homogeneous, and plastic deformation occurs in a less uniform manner. This was also observed for A-C14 derivatives. Finally, C8 derivatives show an intermediate response, suggesting a mechanical behavior that falls between the other two types of derivatives. These variations in the stress-strain curves for plasticized PVC films, depending on the specific derivatives, may be attributed to differences in

molecular structure as the length of alkyl chain. Even epoxidized, the shorter the chain, the more the material will exhibit a more continuous plastic deformation without a specific yielding phase.

From a molecular standpoint, short-chain plasticizers (e.g., C2) are more compatible with PVC due to their better miscibility and lower steric hindrance, which allows for a more intimate interaction with PVC chains. This leads to a more homogeneous dispersion of the plasticizer and thus a more uniform distribution of plasticizing effects within the matrix, resulting in smoother stress-strain curves without abrupt transitions. In contrast, long-chain derivatives (e.g., C18:1) are bulkier and more hydrophobic,

<figure><img src="image_8.png" /><figcaption>**FIGURE 5** | Traction curves of PVC films. Solid line: esterified compounds, short dots: epoxidized compounds.</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**FIGURE 6** | DSC curves of PVC films plasticized. Solid line: esterified compound, dashed lines: epoxidized compounds. DSC, differential scanning calorimetry.</figcaption></figure>

which can hinder their compatibility with the polar PVC matrix. This reduced compatibility can result in less efficient disruption of PVC-PVC interactions, localized deformation zones, and the appearance of yield points. Epoxidation improves polarity and thus enhances the interaction with PVC, but this effect is more pronounced for shorter chains and may not fully compensate the steric effects in longer chains.

### 3.2.3 | Thermal Properties of Plasticized PVC Films

The effectiveness of a plasticizer is primarily determined by its ability to decrease the glass transition temperature ($T_g$) of a polymer. The $T_g$ values for various PVC films were assessed through DSC experiments, as outlined in Table 1 and Figure 6. From DSC experiments, it was not always easy to observe the $T_g$ [24]. However, when observed, only one $T_g$ value was noted, underscoring the favorable miscibility of all plasticizers with PVC [38]. In the literature, it was reported that epoxidation reduces the glass temperature of PVC films [31, 41].

However, in our case, epoxidation was found to moderately elevate the $T_g$. This discrepancy can be explained by the presence of epoxy groups, which are polar and can establish dipole-dipole interactions or even weak hydrogen bonding with the polar sites of the PVC chain (e.g., C-Cl). These interactions may restrict segmental motion of the polymer backbone and thus increase the $T_g$, despite the intrinsic flexibility of the epoxidized side chains. Additionally, the plasticizer content and molecular architecture may play a role. Plasticizer-to-PVC ratio and the structure of the CNSL-based epoxidized compounds differ from those used in studies reporting a decrease in $T_g$, which may also account for the observed differences. Nevertheless, for C18:1 E compounds, the $T_g$ values were lower than those of both phthalates and EVOs

references. Consequently, despite the observed increase in $T_g$ associated with epoxidation, its application is possible.

### 3.2.4 | Thermal Stability of PVC Films Plasticized With CNSL Derivatives

The thermal characteristics of PVC films with 43 phr of plasticizers were evaluated using TGA conducted in an airflow environment. No discernible weight loss was detected in these PVC films prior to 150°C (Figure 7 and Figure S6). All TGA curves exhibited a biphasic degradation pattern. The initial weight loss, observed in the temperature range of approximately 150-325°C, primarily resulted from the plasticizer's decomposition. Furthermore, this weight loss was attributed to the cleavage of hydrogen chloride (HCl), leading to the formation of a PVC polyene structure. Following this phase, a plateau spanning from 325°C to 425°C was consistently observed, irrespective of the plasticizer utilized. The final degradation phase, commencing around 425°C, involved intricate mechanisms such as C=C bond cross-linking and char formation [24].

Importantly, it was demonstrated that epoxidation enhances thermal stability at 5% weight loss by 10-30°C (Figure 7, Table S1). This was in accordance with literature [24, 34, 41]. Several other studies, focusing on the utilization of epoxidized triglycerides as heat stabilizing additives for PVC, assert that their efficacy as stabilizers is linked to the oxirane content [31, 34]. This increase in thermal stability is due to the easy reactions of the epoxide with HCl generated in the early stages of dehydrochlorination, preventing auto-acceleration of the dehydrochlorination process. These epoxides react with labile chlorine atoms in PVC, thereby reducing the polymer's susceptibility to dehydrochlorination [24, 42]. This offers a solution to a prevalent issue in the plastics
<figure><img src="image_10.png" /><figcaption>**FIGURE 7** | TGA curves of PVC films with technical CNSL derivatives. Solid line: esterified compounds, short dots: epoxidized compounds.</figcaption></figure>

industry, wherein the incorporation of Ca/Zn heat stabilizer tends to diminish the mechanical properties of PVC films.

Discoloration tests have also been investigated, in order to evaluate visually the color resistance to heat. As depicted in Figure 8, a progressive coloration phenomenon is observed. The variations in discoloration levels were employed as metrics for assessing

the relative thermal stability of plasticized PVC, a higher degree of discoloration correlates with a more extensive degradation of the sample. Following the exposure of the PVC samples to a 60-min heating period at 200°C, all samples containing plasticizers, excluding epoxidized plasticizers, turned almost black, suggesting diminished thermal stability. On the contrary, PVC samples prepared with epoxidized plasticizers such as ELO or ESBO and epoxidized acetylated cardanol turned orange after the same heating duration [38]. This transformation is attributed to the ability of epoxide groups to catch the HCl generated during PVC degradation, facilitated by the interaction between epoxide groups and labile chlorine atoms within the PVC matrix. This observation is in accordance with literature [31].

### 3.2.5 | Volatility and Migration Resistance of PVC Films Plasticized With CNSL Derivatives

When dealing with leakage issue, it is important to understand that the risk comes from both the harmful substance itself and how much of it is present. To minimize the risk, one effective strategy is to make plasticizers more stable in mixtures, which lowers the chances of them leaking out. As a consequence, achieving lower or suppressed leaching rates proves advantageous in mitigating human exposure, minimizing environmental contamination, and enhancing overall performance. These factors are crucial in the formulation of environmentally friendly plasticizers.

Leaching and volatilization loss are mainly attributed to the compatibility and intermolecular forces between the plasticizer and PVC. In this study, to enhance migration phenomena, samples were selected with a thin thickness and a large contact

<figure><img src="image_11.png" /><figcaption>**FIGURE 8** | The optical images of plasticized PVC films heated at 200°C and taken at 0, 5, 10, and 60 min.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**FIGURE 9** | Chemical resistance in (a) polar solvent and (b) a polar solvent of different PVC plasticized films. Solid fill: esterified compounds, hatch marks: epoxidized compounds.</figcaption></figure>

surface area. The migration of plasticizers from PVC films was assessed by leaching test in distilled water, anhydrous alcohol, and petroleum ether and volatility test in an oven for 48 h.

Plasticizers exhibit minimal leaching in water compared to other solvents (Figure S7a). In anhydrous alcohol tests, it has been observed that the weight loss across most of the samples remains below 20% (Figure 9), which may appear high but is not compared to the literature [39]. It was observed that epoxidation tends to reduce weight loss for CNSL derivatives in both polar and nonpolar solvents, highlighting the advantageous use of epoxidation.

Furthermore, in the volatility test, it was evident that epoxidized derivatives decrease the weight loss comparable to both phthalate and commercially available biobased plasticizers (Figure S7b). These findings highlight the influence of epoxy on chemical resistance and migration behavior, offering valuable insights for the formulation and optimization of plasticizers with enhanced performance characteristics.

## 4 | Conclusion

For the first time, CNSL mixture was epoxidized and used as PVC plasticizer. This study, conducted on different CNSL derivatives with alkyl chains of various lengths, reveals the influence of epoxy on the physicochemical properties of PVC films. To summarize, epoxidation increases the thermal stability and the viscosity of the plasticizer, which does not prevent its use in industrial processes. In addition, epoxidation results in an increase in elongation at break and a significative decrease in Young's modulus, indicating an enhancement in the plasticizing properties of the compounds. Moreover, epoxidation improves thermal stability, by introducing oxirane which captures HCl, and also increases the chemical resistance for CNSL derivatives and volatility, which are sought-after properties. Therefore, epoxidation proves to be a valuable method for enhancing the plasticizing properties of the com-

pounds, even for plasticizers containing long alkyl chains. This study has shown that epoxidation increases the acetate technical CNSL PVC films overall properties and is a promising compound for PVC application. Importantly, this work demonstrates that technical CNSL, without purification into pure cardanol, can be effectively used as a precursor for PVC plasticizers. The performances observed for technical CNSL-based plasticizers are comparable to, and in some cases even superior to, those reported for pure cardanol-based plasticizers in the literature. Thus, the purification step of cardanol can indeed be skipped, allowing for a simpler, more economical, and more sustainable process.

## 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.

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**Supporting Information**

Additional supporting information can be found online in the Supporting Information section.

**Supporting file 1:** ejlt70084-sup-0001-SuppMat.doc