Synthesis and Characterization of Copolymers and Nanocomposites from Limonene, Styrene and Organomodified-Clay Using Ultrasonic Assisted Method

Abstract

In the present work, we report a simple synthesis method for preparation of copolymers and nanocomposites from limonene and styrene using clay as a catalyst. The copolymerization reaction is carried out by using a proton exchanged clay as a catalyst called Mag-H⁺. The effect of temperature, reaction time and amount of catalyst were studied, and the obtained copolymer structure (lim-co-sty) is characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (¹H-NMR) and differential scanning calorimetry (DSC). The molecular weight of the obtained copolymer is determined by gel permeation chromatography (GPC) and is about 4500 g·mol⁻¹. The (lim-co-sty/Mag 1%, 3%, 7% and 10% by weight of clay) nanocomposites were prepared through polymer/clay mixture in solution method using ultrasonic irradiation, in the presence of Mag-CTA⁺ as green nano-reinforcing filler. The Mag-CTA⁺ is organophilic silicate clay prepared through a direct exchange process, using cetyltrimethylammonuim bromide (CTAB). The prepared lim-co-sty/Mag nanocomposites have been extensively characterized by FT-IR spectroscopy, X-ray diffraction (XRD), scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). TEM analysis confirms the results obtained by XRD and clearly show that the obtained nanocomposites are partially exfoliated for the lower amount of clay (1% and 3% wt) and intercalated for higher amounts of clay (7% and 10% wt). Moreover, thermogravimetric analysis (TGA) indicated an enhancement of thermal stability of nanocomposites compared with the pure copolymer.

1. Introduction

The production of polymers based on renewable monomers has been the subject of several recent research groups around the world. Of the different types of polymers studied, those based on renewable resources have been the most extensively studied [1,2,3]. The most successful studies of terpene reactions in organic chemical synthesis have been published [4], but their applications in polymer science are still few. Limonene is a monocyclic terpene found in many essential oils extracted from citrus peels and has been used as a flavor and green solvent in cosmetics, food and beverages. Limonene is of particular interest in the field of polymerization because it contains double bonds that provide the difunctional groups required for polymerization. Limonene is also an allylic monomer (CH₂=CH–CH₂Y) [5,6]. A literature search reveals that chemists have attempted to develop a substitute for polyterpenes from petroleum distillates [7], but no substitute has yet been developed, as most terpenes are not homopolymerized by bulk steric [8], low stabilization energy between monomers and transition state radicals [9], with the exception of β-pinene and limonene which were polymerized by clay [10,11], Ziegler-Natta [12] as well as Friedel-Crafts catalysts [13]. Limonene is widely used in cosmetics and other products, as a food additive, medicine and even as a green solvent [14].

Styrene is one of the most studied and widely used monomers, both in industry and academia, as its polymerization is used as a model for chain polymerization [15]. Styrene is also utilized as a comonomer in copolymers synthesis, including acrylonitrile butadiene styrene (ABS) [16], rubber or latex based on styrene butadiene (SBS) [17], styrene-acrylonitrile (SAN) [18], acrylonitrile styrene acrylate (ASA) [19] and unsaturated polyesters. During World War II, the production of styrene, in particular, grew rapidly in the United States to meet the army’s demand for synthetic rubber. Styrene is also used in small amounts in perfumes and medications [20], as well as in the manufacture of polyester resins [21].

In recent decades, there has been an increasing interest in nanocomposites, a new class of materials reinforced by nanoparticles. Toyota researchers sparked interest in these novel materials in the early 1990s. In fact, they demonstrated a considerable increase in dimensional stability by dispersing clays in polyamide-6 by in situ polymerization [22]. These findings paved the way for new possibilities for polymer matrix nanocomposites in a variety of domains [23]. Nanocomposites made of toxic polymers have been phased out in favor of those made of green materials in recent years. The addition of a predetermined amount of clay as reinforcement to a polymer matrix improves the physicochemical properties of the resulting nanocomposites [24,25]. Two types of nanocomposites structures, intercalated and exfoliated nanocomposites, can be created based on the interaction strength of the modified polymer/clay. Nanocomposites can be made using different techniques, including in situ polymerization, polymer solution blending and other techniques [26].

Ultrasound is being used to prepare nanocomposites based on polymer and clay in solution, which is highly interesting. This method of production was employed to minimize reaction time and boost nano-filler dispersion in polymer matrix, with the majority of them focused on exfoliating the packed clay layers [27,28,29,30]. Ultrasonication induces acoustic stream and cavitation bubbles, which then undergo an implosion process, releasing heat and energy and resulting in a highly well dispersed reaction medium [31]. The use of ultrasound has an impact on the morphology of the prepared nanocomposites, especially in dispersion, such as in situ polymerization methods [32]. Several nanocomposites based on polymers and clay were created using an ultrasound-assisted technique for these reasons.

According to the literature, nanocomposites based on limonene, including poly (lactic acid)/D-limonene/ZnO bio-nanocomposites [33], Pt, Ru and Ni/graphene nanocomposites [34] and V-MCM-41 nanocomposites [35], but the use of natural clay as a catalyst in the synthesis of copolymers based on limonene and styrene is almost non-existent. The main goal of this research is to look into the catalytic properties of a natural clay (Mag-H⁺) as a new non-toxic catalyst for the copolymerization of limonene and styrene and Mag-CTA⁺ as a new nano-reinforcing filler for the fabrication of nanocomposites based on styrene-limonene copolymer (lim-co-sty) using an ultrasonic assisted approach to improve the copolymer’s thermal and mechanical properties. We previously showed the benefits of various uses of this catalyst type and the kind of nano-reinforcing filler in different polymerization reactions and nanocomposites synthesis in our published work [36,37,38].

2. Materials and Method

2.1. Materials

(R)-(+)-Limonene (97%), styrene (99%), methanol (CH₃OH, 99.9%), dichloromethane (CH₂Cl₂, 99.8%), sulfuric acid (H₂SO₄), sodium chloride (NaCl) and cetyltrimethylammonuim bromide (CTAB) were purchased by Sigma Aldrich (St. Louis, MO, USA) and used as received without further purification. ENOF Bental Spa of the National Company of Nonferrous Mining Products, Maghnia Unit (Algeria), supplies Maghnite (Algerian montmorillonite clay) in its natural state. The ultrasound equipment used to prepare Mag-CTA⁺ and nanocomposites consists of a jacketed glass tank with an ultrasonic horn (13.6 mm diameter, non-replaceable tip composed of Titanium alloy Ti-6Al-4V) and a Sonics VC-750 Vibra 6 Cell generator (Sonics & Materials, Newtown, CT, USA).

2.2. Preparation of Maghnite-H⁺

A procedure identical to that described by Derdar et al. [39] was used to prepare Mag-H⁺. Raw-Mag was activated using a sulfuric acid solution to produce clay that has been exchanged with protons. Crushed raw Maghnite (30 g) was disseminated in distilled water in an Erlenmeyer flask (120 mL). A magnetic stirrer was used to agitate the mixture for 2 h at room temperature. Then a 0.5 M of sulfuric acid solution (100 mL) was added. The resulting mixture was kept under constant stirring for two days. The mineral was filtered and rinsed with distilled water several times until it reached a pH of 7. After filtration, Mag-H⁺ is dried in an oven at 105 °C for 24 h before being crushed.

2.3. Activation of Mag-Na⁺ and Mag-CTA⁺

Derdar et al. [40] established a procedure for preparing Mag-Na⁺. The raw-Mag given by Bental Spa was crushed and finely sieved, and the sodium activation of Maghnite was performed using 1 L of NaCl solution (1 M) and 20 g of raw-Mag (2% by weight), which was combined for 24 h at room temperature before being washed multiple times with distilled water. Ultrasound was used to activate Mag-CTA⁺ for one hour [41]. To begin, place 10 g of Mag-Na⁺ in a 1 L Erlenmeyer flask with the desired concentration (1 CEC). The suspension was filtered and rinsed many times with distilled water at the end of the exchange procedure. Finally, the solid was dried for 24 h at 105 °C and crushed. FT-IR and XRD study establish the structure of the organophylic clay, while SEM and TEM analysis investigate their morphological properties.

2.4. Copolymerization Procedure

The reaction was carried out in solution at room temperature, 0.02 mol of limonene and styrene, are kept under stirring for 2 h in 10 mL of CH₂Cl₂, with 10% by weight of Mag-H⁺ (Scheme 1). Table 1 summarizes the operating conditions of the copolymerization. After 2 h, the reaction mixture was filtered, precipitated in cold methanol and dried under vacuum overnight. The obtained copolymer was a solid product. Regarding the kinetic study, the same procedure described above was repeated by changing the percentage of the catalyst amount, time of the reaction and the temperature, in order to find the optimal reaction conditions.

2.5. Synthesis of Nanocomposites Copolymer/Clay (Lim-co-Sty/Mag)

The polymer/clay mixture in solution synthesis method was used to prepare Lim-co-Sty/Mag nanocomposites. Then, 1 g of the resulting copolymer (Lim-co-Sty) is dissolved in 25 mL of CH₂Cl₂. The copolymer was then thoroughly dissolved by stirring the solution for 15 min. After that, 1% by weight of Mag-CTA⁺ is added to the solution, and the mixture is treated for 3 h using an ultrasonic-assisted technique [42]. The nanocomposite was then precipitated in methanol, filtered and dried under vacuum overnight (Scheme 2). The same process was used by adding different amounts of Mag-CTA⁺ to Lim-co-Sty copolymer 3%, 7% and 10% by weight (see experimental conditions in Table 1).

2.6. Characterization

The functional groups of the resulted copolymer, modified clay and nanocomposites were studied using BRUKER ALPHA Diamond-ATR infrared spectroscopy (Bruker, Billerica, MA, USA) in the range of 4000–360 cm⁻¹. ¹H-NMR analysis in Deuterated Chloroform using Brucker-Avance 300 MHZ equipment, validate the structure of the obtained copolymer. Differential scanning calorimetry (DSC) was also used to study the thermal properties of Lim-co-Sty copolymer, by using calorimetric analysis (DSC) 204 F1, NETZSCH equipment (Selb, Germany), operating at a heating rate of 20 °C/min, from room temperature up to 450 °C under an inert atmosphere with a flow rate of 50 mL/min. The molecular weight of the prepared copolymer was studied by a GPC-PL120 apparatus, using CH₂Cl₂ (1.0 mL/min) as the mobile phase at 27.5 °C. Polystyrene standards are used for calibration. XRD analysis on a Bruker AXS D8 diffractometer (Cu-K radiation) and FEG-SEM on a JEOL 7001F electron microscope (JEOL, Tokyo, Japan) were used to examine the surface morphology of the modified clay and nanocomposites. A Hitachi 8100 (Hitachi, Tokyo, Japan) was used to take transmission electron micrographs. Thermogravimetric analysis (TGA) was performed under nitrogen with a PerkinElmer STA 6000 (PerkinElmer, Waltham, MA, USA) in the temperature range of 30–700 °C and a heating rate of 20 °C/min to determine thermal characteristics of the obtained nanocomposites.

3. Results

3.1. Characterization of the Modified Clay (H⁺, Na⁺ and CTA⁺)

Figure 1 shows the FT-IR spectra of Mag-H⁺, Mag-Na⁺ and Mag-CTA⁺. We see a strong peak at 1057 cm⁻¹ and two bands at 455 cm⁻¹ and 515 cm⁻¹, which correspond to the Si–O–Si and Si–O–Al bonds’ elongation vibrations, respectively [43,44]. Following the modification of Maghnite by CTAB, two additional bands, corresponding to the C–H stretching vibrations of the methyl group, were found in the 2850 cm⁻¹ and 2922 cm⁻¹ areas for Mag-CTA⁺. According to the results of FT-IR analysis, the CTA⁺ alkyl ammonium ions intercalate between the clay sheets.

Raw-Mag, Mag-H⁺, Mag-Na⁺ and Mag-CTA⁺ X-ray diffractograms are shown in Figure 2. We calculated basal spacing (d₀₀₁) from XRD patterns using the Bragg equation (2.d.sinθ = n.λ), which is 1.01 nm for Raw-Mag and 1.45 nm for Mag-H⁺. The substitution of a single water layer between the sheets of Raw-Mag by two interlamellar water layers in Mag-H⁺ explains this increase in basal spacing. Mag-Na⁺ and Mag-CTA⁺ diffractograms have different basal spacing (d₀₀₁), range from d = 1.23 nm for Mag-Na⁺ to d = 1.8 nm for Mag-CTA⁺. The intercalation of the CTAB’s alkyl ammonium ions in the inter-foliar galleries is confirmed by this increase. The influence of ultrasonic irradiation on the preparation of Mag-CTA⁺ can be seen in these data. Aicha Khenif et al. [45] obtained an interlayer distance of 1.98 nm after 24 h of stirring, but in our case, an interlayer distance of 1.8 nm was produced after only 1 h of stirring.

3.2. Characterization of the Obtained Copolymer (Lim-co-Sty)

3.2.1. H-NMR Measurements

¹H-NMR spectrum of the obtained copolymer is shown in Figure 3. The ¹H-NMR spectrum was obtained to further investigate and confirm the proposed structure. ¹H-NMR spectra of (lim-co-sty) clearly show a signal at 0.8 ppm as interfered several peaks corresponding to the protons of the methyl group. There is also the appearance of the peak (d) at 1.16 ppm in the spectrum of the obtained copolymer corresponding to the protons of methylene group (–CH₂–), this peak does not appear in the spectrum of limonene. The peaks (a) and (a’) at 5.15 and 5.66 ppm are the characteristic resonance of the protons resulted by the terminal double bond (–CH=CH–) of the styrene. The peak (b) at 5.32 ppm is the characteristic resonance of the protons resulted by the internal double bond (C=C) of limonene. The comparison of ¹H-NMR spectra of the copolymer (lim-co-sty) with those of limonene in Figure 4 shows that the peak b at 4.6 ppm due to disubstituted olefinic protons (C=CH₂) of limonene has disappeared. These results show, clearly, that the copolymerization of limonene with styrene is successful with Mag-H⁺.

3.2.2. FT-IR Measurements

The structure of the obtained copolymer was also confirmed by FT-IR measurements. FT-IR spectrum of limonene (a) and the obtained copolymer (b) have been shown in Figure 5. It is observed that the peaks at 1309 cm⁻¹, 1217 cm⁻¹, 956 cm⁻¹, 913 cm⁻¹ and 885 cm⁻¹ corresponding to the double bonds in limonene have disappeared in the spectra of the copolymer confirming that the copolymerization has succeeded. It should be noted the presence of characteristic band corresponding to the stretching band of C=C at 1640 cm⁻¹ in the spectra of limonene and at 1600 cm⁻¹ in the spectra of lim-co-sty corresponding to the terminal double bond (–CH=CH–) of the styrene and, also, an intense band at 2930 cm⁻¹ corresponding to the valence vibration of the methylene C–H. The bands at 1456 and 1365 cm⁻¹ are attributed to deformation of C–H bond of the CH₂ and CH₃ groups. A band at 886.38 cm⁻¹ corresponds to the valence vibration C–H bond of CH₂ out-of-plane. The FT-IR spectrum of the obtained copolymer shows, also, the presence of an intense band at 600 cm⁻¹ corresponding to the benzene cycle of styrene which confirms the results obtained by NMR analysis.

3.2.3. Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry (DSC) was used to study the thermal properties of the obtained copolymer. Figure 6 shows the DSC curve of lim-co-sty. The glass transition temperature (Tg) recorded from the DSC curve of the copolymer is observed in the temperature range of 92–98.1 °C. In addition, the comparison of the Tg of the copolymer with those of polystyrene (Tg about 100 °C) [46] and polylimonene (Tg = 116 °C) [47], shows clearly that the copolymerization of limonene with styrene using Mag-H⁺ as a catalyst is successful.

3.2.4. GPC Measurements

The average molecular weight of the obtained copolymer Lim-co-sty was measured by GPC analysis. The results of GPC analysis are presented in Figure 7. GPC chromatogram shows that the molecular weight of the obtained polymer (Mn) is about 4410 g/mol, Mw = 4500 g/mol and Mw/Mn =1.02. This molecular weight is low. Comparing the molecular weight of copolymers based on styrene obtained by radical polymerization [48], but using Mag-H⁺ as a catalyst is still preferred for its many advantages such as very low purchase price compared to other catalysts and the easy removal of the reaction mixture.

3.3. Effects of Various Synthesis Parameters on the Copolymerization Yields

The objective of this part is to study the kinetic of the copolymerization of limonene with styrene by Mag-H⁺, which consists in varying separately different parameters including the catalyst amount, the reaction time and the temperature, in order to study their influence on the yield of the obtained product and to find the optimum conditions of the copolymerization reaction.

3.3.1. Effect of Catalyst Amount

In order to find the optimal conditions for the copolymerization of limonene with styrene and to follow the effect of the quantity of the catalyst on the yield of the copolymerization, on this study we varied the catalyst/monomer (2%, 3%, 5%, 6%, 8% and 10% by weight of Mag-H⁺), this study was carried out at room temperature for 2 h. The obtained results are shown in Figure 8 and show that the yield increases with the increase in the catalyst amount, the best yield (65%) was obtained with 10% of Mag-H⁺. This phenomenon is essentially due to the number of active sites present in the reaction medium because these are proportional to the mass of the catalyst. These active sites are responsible for the initiation and acceleration of the polymerization reaction until there saturation.

3.3.2. Effect of the Temperature

In this study, the copolymerization reactions were carried out for 2 h using 10% by weight of Mag-H⁺. Figure 9 shows the effect of temperature on the yield of the copolymerization. This study is carried out in solution at different temperatures: −15 °C, −5 °C, 0 °C, 15 °C, 15 °C and 25 °C. An interesting result is that Mag-H⁺ is able to initiate the copolymerization even at low temperature with CH₂Cl₂. The yield of the reaction reaches its maximum (80%) for a temperature of −5 °C. The yield decreases with the temperature from 0 to 25 °C. It should be noted that the temperature has a great influence on the yield of the copolymerization reaction.

3.3.3. Effect of Reaction Time

The influence of time on the yield of copolymerization of limonene with styrene was studied at −5 °C in CH₂Cl₂ with 10% Mag-H⁺. Figure 10 shows the effect of reaction time on the yield of the obtained copolymer. As shown in Figure 10 after 6 h, the copolymerization proceeds rapidly and reaches the best yields (89.77%) in the presence of 10 wt% Mag-H⁺ at −5 °C. After this time, the copolymerization gradually slows down and the yield becomes almost constant.

3.4. Characterization of Nanocomposites (Lim-co-Sty-Mag)

Figure 11 shows the XRD patterns of Mag-CTA⁺, obtained copolymer and nanocomposites. We observed that The XRD pattern of the obtained copolymer (lim-co-sty) presents no sharp peak confirming its amorphous structure. In the case of lim-co-sty/Mag 1% and 3%, the characteristic basal diffraction peak of Mag-CTA⁺ at 2θ = 4.9° was nearly disappeared, confirming the exfoliation of the clay, which explains a good diffusion of lim-co-sty copolymer in the clay galleries. The nanocomposites prepared by (7% and 10%) of Mag-CTA⁺ showed a single peak around 2θ = 2° and 3° corresponding to the interlayer distances d₀₀₁ = 4.15 and 3.3 nm, respectively. The interlayer distance of these nanocomposites was increased more than twice compared to the Mag-CTA⁺, which had an interlayer distance of 1.8 nm. This result confirms that the copolymer was well intercalated between the clay galleries. These results are in agreement with those obtained by Hanène Salmi-Mani et al. [49].

The FT-IR spectra of the obtained nanocomposites (lim-co-sty/Mag 1%, 3%, 7% and 10%) are shown in Figure 12. We observed that the obtained nanocomposites are in a good agreement with the pure copolymer structure and have almost the same vibration bands overlapping with the vibration bands of the organo-modified clay (Mag-CTA⁺). The absorption band at 695 cm⁻¹ corresponds to the vibration of the benzyl cycle in styrene and the adsorption band at 1600 cm⁻¹ corresponds to the double bond C=C in the copolymer were observed in the FT-IR spectra of the obtained nanocomposites. The C-H symmetric and asymmetric stretching of the methyl and methylene group was observed at 2921 and 2867 cm⁻¹. Compared with the FT-IR spectrum of the pure copolymer, the spectra of the obtained nanocomposites show the appearance of the intense peak at 1000 cm⁻¹ corresponding to the vibration of Si-O of the Mag-CTA⁺. These results show the intercalation of lim-co-sty copolymer in the interlayer montmorillonite gallery.

Figure 13 shows the SEM images of the Mag-CTA⁺ and the obtained nanocomposites (lim-co-sty/Mag 1%, 3%, 7% and 10%). Comparing the morphology of Mag-CTA⁺ (Figure 13a1,a2) with lim-co-sty/Mag 7% and 10% nanocomposites (Figure 13d,e), we observed a more organized montmorillonite structure in small particles. In the lim-co-sty/Mag 1% and 3% nanocomposites (Figure 13b,c), the observation of nanocomposites at 10 μm, reveals a formation of separated montmorillonite plate, that is a partial exfoliation, also shows a rougher surface and a covering of the montmorillonite surface by the copolymer.

The transmission electron microscopy (TEM) images of Mag-CTA⁺ and the obtained nanocomposites are shown in Figure 14. TEM analysis was used to determine the dispersion of Mag-CTA⁺ in the copolymer matrix and, also, to confirm the results obtained by XRD analysis. For Mag-CTA⁺, it is easy to define the silicate layers by the dark and bright lines. The nanocomposites prepared with 1% and 3% by weight of Mag-CTA⁺ show a partial or total exfoliated structure and the clay nanoparticles are mainly well dispersed in the copolymer matrix. However, the nanocomposites lim-co-sty/Mag 7% and 10% show an intercalated structure of the modified clay. These results confirm the results obtained by XRD analysis.

TGA curves of the obtained nanocomposites and pure copolymer are shown in Figure 15. We observed that all nanocomposites and pure copolymer exhibit a one-step weight loss mechanism. TGA curves show that the Mag-CTA⁺ causes improvement in the thermal stability of the obtained nanocomposites. It can be seen that nanocomposites prepared with 7% and 10% by wt of Mag-CTA⁺ show a high thermal stability up to a degradation temperature about 300 °C, while the degradation temperature of pure copolymer observed at 150 °C, more the nanocomposite is rich in copolymer the more it is degraded quickly. This gain in stability is due, according to previous work [50], to the formation of a protective carbonized layer. The formation of this layer is favored by the fine dispersion of intercalated or exfoliated particles of clay which play an inorganic support role [51]. In general, the degradation temperature of the polymers is increased after the incorporation of exfoliated lamellar silicates [52,53,54], which values these polymers and allows their use at higher temperatures.

4. Conclusions

The copolymerization of limonene with styrene was successfully obtained using Mag-H⁺ as green catalyst and provides excellent results. ¹H-NMR, FTIR and DSC analysis confirm the structure of the obtained copolymer. The copolymerization proceeds via a cationic mechanism due to the presence of intercalated protons in the lamellar structure of Mag-H⁺. According to the study carried out on the operating parameters of the copolymerization reaction we can conclude that the yield achieved is maximum (89.77%) in the presence of 10 wt% of Mag-H⁺ with 6 h of reaction time, wherein the best temperature which promotes copolymerization is −5 °C. The effect of organomodified clay (Mag-CTA⁺), prepared and used with different ratios, on lim-co-sty/Mag nanocomposites properties is also studied. The study shows that the different ratios of the organoclay (Mag-CTA⁺) has an impact in the preparation of nanocomposites copolymer/clay. The FT-IR and XRD results indicate that the nanocomposite prepared with 1% and 3% by weight of Mag-CTA⁺ were exfoliated, and the nanocomposites prepared with 7% and 10% wt of Mag-CTA⁺ were intercalated, leading to an expansion of the interlayer distance between the layers. SEM and TEM analysis confirmed an organization of certain particles, and in other cases a separation in plates made up of montmorillonite layers, this confirms partial or total exfoliation of montmorillonite in the copolymer matrix and formation of the nanocomposites. Thermogravimetric results indicate that the nanocomposites present a higher thermal stability compared with the pure copolymer (T < 300 °C). The objectives of this work are the synthesis of copolymer and nanocomposites out of a green raw material (limonene and clay) by the use of Mag-H⁺ as a catalyst and Mag-CTA⁺ as nano-reinforcing filler. The interesting aspect of clay is the environmentally friendly nature of the reaction because it does not imply the disposal of solvents or metal catalysts.

Author Contributions

Cosnceptualization, H.D., G.R.M., S.C., V.S.M., Z.C., K.B., R.C., F.T., R.M. and M.B.; Synthesis, H.D., S.C. and Z.C.; Characterization, H.D., R.C., K.B. and F.T.; validation, H.D., G.R.M., V.S.M. and R.M.; writing—original draft preparation, H.D. and G.R.M.; supervision, G.R.M., V.S.M., K.B., R.M. and M.B. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not Applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data contained in the paper is available from the authors.

Acknowledgments

We would like to thank the (DGRSDT) Direction générale de la Recherche Scientifique et du développementTechnologique-Algeria, and the CDRSP-IPLeiria (centre for rapid and sustainable product development) for giving us access to their STA device. We also would like to thank M.C. Baghdadli for their help and advices through all the writing process.

Conflicts of Interest

The authors declare no conflict of interest.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures, Schemes and Table

Scheme 1. Copolymerization of limonene with styrene using Mag-H+.

Scheme 2. Synthesis of nanocomposites (Lim-co-sty/Mag) using ultrasonic irradiation.

Figure 1. FT-IR spectra of Mag-H+, Mag-Na+ and Mag-CTA+.

Figure 2. XRD patterns of Raw-Mag, Mag-H+, Mag-Na+ and Mag-CTA+.

Figure 3. 1H-NMR spectrum of the obtained copolymer (lim-co-sy).

Figure 4. 1H-NMR spectrum of limonene.

Figure 5. FT-IR spectra of limonene (a) and lim-co-sty (b).

Figure 6. DSC curve of the obtained copolymer.

Figure 7. GPC chromatogram of the obtained copolymer.

Figure 8. Effect of catalyst amount on copolymerization efficiency.

Figure 9. Effect of temperature on copolymerization efficiency.

Figure 10. Reaction time effect on the copolymerization yield.

Figure 11. XRD patterns of nanocomposites lim-co-sty/Mag, lim-co-sty and Mag-CTA+.

Figure 12. FT-IR spectra of the obtained nanocomposites lim-co-sty/Mag (1%, 3%, 7% and 10%).

Figure 13. SEM images of Mag-CTA+ (a1,a2), lim-co-sty/Mag 1% (b), lim-co-sty/Mag 3% (c), lim-co-sty/Mag 7% (d) and lim-co-sty/Mag 10% (e).

Figure 14. TEM images of Mag-CTA+ (a), lim-co-sty/Mag 1% (b), lim-co-sty/Mag 3% (c), lim-co-sty/Mag 7% (d) and lim-co-sty/Mag 10% (e).

Figure 15. TGA curves of lim-co-sty/Mag nanocomposites and the pure copolymer lim-co-sty.

Table 1

Experimental conditions for the preparation of nanocomposites lim-co-sty/Mag.

Samples	Lim-co-Sty	Mag-CTA+	Time	Frequency	Yield
Lim-so-sty/Mag 1%	1 g	1% (wt)	3 h	20 KHz	100%
Lim-co-sty/Mag 3%	1 g	3% (wt)	3 h	20 KHz	100%
Lim-co-sty/Mag 7%	1 g	7% (wt)	3 h	20 KHz	100%
Lim-co-sty/Mag 10%	1 g	10% (wt)	3 h	20 KHz	100%

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