# Controlling stabilization of oil-in-water emulsions with lignins through fractionation, functionalization, and formulation

Caroline Hadjiefstathiou, Audrey Manière, Joan Attia, Florian Pion, Paul-henri Ducrot, Ecaterina Gore, Michel Grisel

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## ► To cite this version:

Caroline Hadjiefstathiou, Audrey Manière, Joan Attia, Florian Pion, Paul-henri Ducrot, et al. Controlling stabilization of oil-in-water emulsions with lignins through fractionation, functionalization, and formulation. Journal of Applied Polymer Science, 2024, 141 (16), pp.e55235. 10.1002/app.55235. hal-04440511

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Submitted on 8 Nov 2024

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# Controlling stabilization of oil-in-water emulsions with lignins through fractionation, functionalization, and formulation

Caroline Hadjiefstathiou<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> ID

Audrey Manière<fnref n="1" />

Joan Attia<fnref n="1" />

Florian Pion<fnref n="2" />

Paul-Henri Ducrot<fnref n="2" />

Ecaterina Gore<fnref n="3" /> ID

Michel Grisel<fnref n="3" /> ID

**Correspondence**

Michel Grisel, Université Le Havre
Normandie Univ, URCOM, 25 Rue
Philippe Lebon, 76600 Le Havre, France.
Email: michel.grisel@univ-lehavre.fr

**Funding information**

Association Nationale de la Recherche et de la Technologie, Grant/Award Number: N°2020_0785

**Abstract**

Lignins, heterogeneous assemblies of polyphenolic oligomers present in lignocellulosic plant biomass, are valorized mainly by combustion because of their low solubility in commonly used solvents. However, in addition to antioxidant, anti-UV and antimicrobial properties, and marked interfacial properties are part of lignins physicochemical properties, thus making them good candidates for sustainable colloids. It is hypothesized that lignins solubility and emulsifying performances could be modulated by fractionation, functionalization, and formulation strategies. The importance of the solvent, and of the pH on lignins solubilization in aqueous phase was investigated. Accordingly, simple O/W emulsions stabilized by different lignins were designed and characterized. The whole results demonstrated that lignins solubility in water can be optimized using appropriate co-solvent and pH readjustment resulting in a homogeneous dispersion with only 7.2 ± 1.8% wt/wt of insoluble lignins. Both fractionation and biocatalytic modification of lignins allowed increasing stabilization of the oil-water interface by limiting coalescence (23%-24% of relative increase of the D90) compared with non-fractionated lignins (32%), thus advocating their potential use as multifunctional emulsion stabilizers. As a result, a direct link between the molar mass profile of lignins and their ability to stabilize the oil-water interface as well as to reduce emulsion's sedimentation could be established.

**KEYWORDS**

bio-based materials, cosmetic applications, emulsifying properties, functionalization, lignins, process optimization

## 1 | INTRODUCTION

An increase in demand for more natural environmentally friendly and sustainable emulsifiers has been imposed to stabilize cosmetic emulsions. Therefore, synthetic

emulsifiers are now replaced by biobased alternatives such as proteins, polysaccharides, phospholipids, or fatty esters.

Despite all the advances made in substituting petroleum-based surfactants with sustainable and

<footnote n="1">¹IFF-Lucas Meyer Cosmetics, Campus Eiffel-Massy - Bat. Edison 13 Rue Ella Maillart, Massy, France</footnote>

<footnote n="2">²Institut Jean-Pierre Bourgin UMR 1318 INRAE-AgroParisTech, INRAE Versailles Grignon</footnote>

<footnote n="3">³Université Le Havre Normandie, Normandie Univ, URCOM, Le Havre, France</footnote>

<footnote>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.</footnote>

<footnote>© 2024 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals LLC.</footnote>
biobased emulsifiers, only rare work has been made on products issued from upcycling, waste recovery and on the diversification of the biomass. Lignocellulosic biomass gives the advantage of being an abundant resource, and its industrial pretreatment allows the separation of lignins, cellulose, and hemicelluloses to use them separately as chemicals.¹ Although the valorization of cellulose and hemicelluloses has been mainly considered and exploited in many fields, such as pharmaceuticals² or cosmetics,³ lignins remain poorly valorized although being the most abundant non-saccharidic polymer⁴ and representing 15%-30% of the organic material in the biosphere.⁵ By the use of technical lignins (TL), the sustainability of biorefineries would be increased through the valorization of the whole biomass⁶,⁷ and new multifunctional properties could emerge, differing from other emulsifiers. Lignins' structure is highly heterogeneous⁸ because they are derived from three different monolignol precursors, coniferyl alcohol, sinapyl alcohol, and para-coumaryl alcohol,⁹ that undergo oxidative oligomerization, forming various interunit linkages. Furthermore, they present structural variability depending on both their botanical origin and the extraction process.

Among the different processes existing for separating cellulose, lignins, and hemicelluloses, the mostly used is the kraft process with more than 35,000 tons of TL extracted per year.¹⁰,¹¹ Another process is the bisulfite process, where TL are extracted as lignosulfonates.¹² Unfortunately, TL resulting from both kraft and sulfite processes do contain sulfur and their general structure is strongly modified by the harsh extraction process conditions.¹¹⁻¹³ A sulfur-free pulping process is also available, so-called the soda pulping, where sodium hydroxide is used and lower molecular mass TL are produced, which are soluble in the alkaline cooking liquor.¹⁴ The resulting TL are less chemically modified in comparison to their raw form,¹⁵ contrary to the kraft and bisulfite process. Therefore, alkali lignins represent a pertinent choice to be used in cosmetic industries, where ingredients containing sulfur are prohibited and where bio-based ingredients should keep at maximum their initial native structure. Even if the field of the use of alkali lignins as emulsifiers arises a lot of interest, there is still some improvement to do to better explore and understand their emulsifying properties. Bertolo et al.,¹⁶ as well as Zhang et al.¹⁷ prepared alkali lignins nanoparticles showing high potential for curcumin encapsulation and for stabilizing Pickering emulsions, respectively. Pang et al.¹⁸ fabricated lignins microcapsules for the encapsulation of hydrophobic substances, whereas Yu et al.¹⁹ used alkali lignins to prepare Pickering emulsions for the protection of a photosensitive pesticide. Furthermore, in the recent work by Álvarez-

Barajas et al.²⁰ the use of native alkali lignins as emulsifiers was explored.

Lignins exhibit many advantageous properties, such as antioxidant,²¹⁻²³ anti-UV,²⁴⁻²⁷ anti-bacterial,²⁸,²⁹ and emulsifying properties³⁰⁻³² due to their specific polyphenolic nature, nevertheless, they have mostly been used in many industries as an alternative material to fossil resources in biofuels.³³,³⁴ Hence, finding new and high value-added applications for lignins represents a key challenge. Because of their complex heterogeneous cross-linked structure, high and polydisperse molecular mass, their solubility remains limited in usual solvents,³⁵ and they show low compatibility with both polar and apolar matrices,³⁶ thus are valorized by combustion. Among other strategies, fractionation has been used by several authors as a promising process to selectively isolate lignins of tailored solubility.³⁷,³⁸ Nevertheless, its impact on the emulsifying capacities of lignins has not been investigated previously. To this end, the molar mass of lignins engaged in the process of emulsification has been investigated to evaluate the value-added of fractionation. Another strategy to improve lignins compatibility with interface is grafting functional moieties on lignins. As examples, chemical modification of alkali lignins with poly(N-isopropylacrylamide) has been conceived to better stabilize Pickering emulsions.³⁹ Furthermore, their sulfo-methylation was studied to overcome their high hydrophobicity and to use them as stabilizers of nanoemulsions.⁴⁰ Nevertheless, functionalizing lignins with chemical catalysts is not selective regarding the hydroxyl groups diversity present on the structure of lignins and knowing that it affects their advantageous antioxidant properties by reducing the amount of free phenols. This is how other methods such as enzymatic modification have been explored because of the low input energy, environmentally friendly, reusability of the enzyme, as well as high specificity and selectivity.⁴¹ It is known that biocatalytic grafting on polymers gives low grafting yield but preserves the overall native structure of polymers; among examples, enzymatic modification of cellulose by Ouajai et al.⁴² gave low grafting yields, nevertheless surface properties improvement were obtained. Furthermore, as demonstrated by Wang et al.⁴³ low rate of grafting of hydrophobic groups on starch improved viscoelastic properties of Pickering emulsions. Nevertheless, the impact of enzymatic modification of lignins on their emulsifying properties has not been described in literature and therefore attempts have been made in this study to investigate the value-added of low-grafted lignins (GLs) within emulsions.

As the goal was the valorization of TL as sustainable resource to conceive new naturally based emulsifiers for industrial applications in the field of cosmetics, the
process used should consider the absence of sulfur, the use of sustainable solvents as well as bio-based ingredients, the prohibition of nanoparticles, and the respect of the human skin pH (between 5 and 6). Therefore, Protobind 1000 grade lignins was selected as a good model of the TL, recovered from an alkali process, that are known to encounter few structural modifications compared to native lignins, thereby being more easily processable than kraft and bisulfite lignins. A novel class of low-grafted bio-based lignins derivatives issued from a biocatalytic process, conducted according to our recent work,⁴⁴ was prepared. The solubility of the resulting lignins derivatives was studied and accordingly, lignins' solubilization in water was modulated through pH adjustment and solvent addition to incorporate them via an aqueous phase in O/W emulsions. Finally, the impact of fractionation and of grafting on the emulsifying capacities of lignins within O/W emulsions was investigated.

## 2 | MATERIALS AND METHODS

### 2.1 | Chemicals

Methyl ethyl ketone (MEK), hexane, and tetrahydrofuran (THF) stabilized with butylhydroxytoluene (BHT) were purchased from Carlo Erba reagents (France) and used as received. Grass (mixture of wheat straw and sarkanda) soda TL (Protobind 1000) were purchased from Green Value LLC (Switzerland). Propanediol (Zemea) was purchased from DuPont (USA) and sweat almond oil from Jan Dekker (France). Ethyl hexanoate was purchased from Sigma Aldrich. Lipase acrylic resin from Candida Antarctica (≥5000 U/g, recombinant, expressed in Aspergillus niger), named CAL-B was purchased from Sigma Aldrich. Solvents and sulfuric acid (96%) were purchased from Carlo Erba and used as received.

### 2.2 | Lignins' modification

#### 2.2.1 | Preparation of fractionated lignins as control lignins (CL)

(TL) were magnetically stirred in MEK (25 g/L) for 2 h at room temperature. The mixture was filtered on glass filter, which was rinsed with MEK, then filtrate was concentrated under reduced pressure and then precipitated in hexane under magnetic stirring to recover a light brown powder. The precipitated lignins were recovered by filtration on glass filter and dried under vacuum overnight to recover fractionated lignins used as a control (CL) as a brown powder with a yield of 61% wt.

#### 2.2.2 | Preparation of grafted lignins

Enzymatic hexanoylation of lignins fractions has been performed according to our recent work⁴⁴ and upon direct treatment of TL. TLs were solubilized in MEK (25 g/L) with ethyl hexanoate (1:1 mass ratio to lignins) and CAL-B (20% mass of lignins) and the enzymatic hexanoylation was conducted for 48 h. The enzymatic hexanoylation could be schemed in Figure 1. The residual ethyl hexanoate was removed by precipitation in hexane and GLs were then recovered (yield of 65%wt). The quantification of the hexanoylation yield has been achieved by transmethylation of GL followed by GC-MS and quantification of the methyl ester obtained gave the % (in wt/wt) of initial hexanoyl moieties grafted on lignins.⁴⁴

### 2.3 | Characterization of lignins fractions by size exclusion chromatography

Size exclusion chromatography (SEC) analyses were performed using an Ultimate 3000 pump (Dionex), an Ultimate 3000 ACC injector (Dionex), a Mixed E column 600 × 7.5 mm, 3 µm (Polymer Laboratories), and an Ultimate 3000 PDA detector at 320 or 280 nm (Dionex). Samples were dissolved at 1 mg/mL in THF containing 1% toluene (internal standard), filtered on PTFE microdisk of 0.45 µm and 10 µL were analyzed using THF (stabilized with BHT) as eluent at 1 mL/min at ambient temperature.

The retention time is linearly correlated with the logarithm of the molar mass of the species, and it is thus possible to estimate the molar mass relatively to polystyrene standards of known molar masses from 100 to 23,000 g/mol (polymer laboratories).

The percentage of each eluted species in the lignins fraction can be extrapolated from the area under curve of their UV absorption peaks obtained in SEC chromatograms, by integration of the corresponding ranges. The percentage of monomers, dimers, and oligomers was calculated according to the area of each pic, and by integrating from 17 to 18.75 min, 16 to 17 min, and 11 to 16 min respectively.

### 2.4 | Solubility testing of lignins

GL was used for solubility trials at 0.5% wt/wt in different solvents: propanediol, water (QSP), propanediol/water with a ratio of 10/90 (P10/W90) under magnetic stirring.

With the aim to control and optimize GL solubility in water, P10/W90 mixture was submitted to alkalization at different pH. Since the present study targets skin care
<figure><img src="image_3.png" /><figcaption>**FIGURE 1** Scheme of the enzymatic acylation reaction of lignins. MEK, methyl ethyl ketone. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

formulations, the respect of the human skin pH should be applied,⁴⁵,⁴⁶ thus a final pH 6 was targeted. Therefore, when pH was above 6, GL dispersions were reacidified up to pH 6 using citric acid.

Three dispersions were prepared. Lignins (0.5% wt/wt) were first pre-solubilized in propanediol (10% wt/wt) and the mixture introduced in water (QSP). A first dispersion with no pH readjustment (pH = 2.9) was prepared corresponding to the initial pH of GL dispersions (pH 3 dispersion). A second dispersion was prepared with alkalization to pH = 6.0 (pH 6 dispersion). A third dispersion was prepared using a back-acid procedure: first pH was alkalized up to 8.5 to avoid hydrolysis of esters bearing the hexanoyl moieties,⁴⁷ and reacidified to 6.0 (pH 8.5–6 dispersion). To evaluate the importance of lignins presolubilization within propanediol prior to incorporation in water, a control dispersion was prepared by introducing lignins (0.5% wt/wt) in water (QSP) and then by using the same back-acid procedure as for pH 8.5–6 dispersion (pH 8.5–6 dispersion without propanediol). Alkalization was performed using NaOH aqueous solution (30 g/L) whereas citric acid aqueous solution (30 g/L) was used for acidification. The volume fraction of water in the propanediol/water mixture considers the volumes of NaOH and citric acid solutions added.

Solubility was characterized by optical microscopy, granulometry analysis and percentage of insoluble lignins after centrifugation. For the latter, centrifugation of each dispersion (pH 3 dispersion, pH 6 dispersion, pH 8.5–6 dispersion, and pH 8.5–6 dispersion without propanediol) at 10,000 RCF, 20°C, 10 min has been performed. The soluble part was removed, and the insoluble part was dried through lyophilization for 48 h. The dried lignins were weighed to calculate the fraction (% wt/wt) of

insoluble lignins within each dispersion and data were presented as means ± standard deviation (SD).

## 2.5 | Emulsions formulation procedure

Lignins (2.5%) were first pre-solubilized in propanediol (10% wt/wt) under mechanical stirring with the bench mixer Turbotest® (VMI, France) equipped with a defloculator turbine of a diameter of 35 mm at 700 rpm during 5 min at ambient temperature (Figure 2). The resulting solution was then gently added in ultrapure water under stirring (550 rpm, 10 min) and the back-acid procedure was performed as described earlier (pH 8.5–6 dispersion preparation in Section 2.4). Finally, emulsification of the aqueous phase in the presence of sweet almond oil (10%) was performed at ambient temperature at 10,000 rpm for 10 min using a T25 digital Ultra-Turrax® (IKA, Germany) equipped with the rotor-stator turbine S25 N-25F. Corresponding resulting emulsions were so-called TL-E, CL-E, and GL-E.

## 2.6 | Characterization of lignins solutions and emulsions

### 2.6.1 | Static light scattering

Droplets or particles size measurements were performed by means of a laser diffraction particle size analyzer SALD 7500 Nano (Shimadzu Co., Ltd., Japan), equipped with a violet semiconductor laser (405 nm) and a reverse Fourier optical system. The dispersions and emulsions were diluted in water (QSP) until reaching an absorption
<figure><img src="image_4.png" /><figcaption>**FIGURE 2** Formulation procedure for incorporating lignins fractions within emulsions. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

value of 0.200 ± 0.10 under continuous stirring in the batch cell (7 cm³). All measurements were made at ambient temperature on at least three separately prepared samples. Data were collected using WingSALD II-7500 software. Data were presented either in the form of qualitative granulometry distributions or as D50 or the D90 numerical data. D50 is the value for which the portion of particles with diameters smaller and larger than this value is 50%, and D90 is the portion of particles with diameters below this value is 90%; both D50 and D90 were presented as means ± SD.

### 2.6.2 | Optical microscopy

A drop of dispersion or emulsion sample was placed on a microscope glass slide covered with a coverslip, and visualized by an optical microscope Nikon (Ni-U NIKON) equipped with a digital camera DS-Fi3 (5,9 MP CMOS 2880 × 2048 at 15 images/s) at different magnifications (×100 or ×400) under the bright field at ambient temperature of storage. NIS-Elements Viewer 5.21 was used to analyze the micrographs.

## 2.7 | Emulsions stability assessment

Emulsions were defined as stable since no coalescence phenomena occurred (merging of droplets inducing an increase of droplets size overtime) and lignins were considered stable within emulsions when exhibiting no or limited sedimentation.

For the stability evaluation, a volume of 10 mL of lignins emulsions was stored at 25°C in 15 mL Eppendorf (Corning Centristar™). Emulsions' stability was monitored over time through visual aspect analysis, optical microscopy observations, and granulometry measurements. Visual aspect stability was studied after preparation at day 1 (D1) and monitored over 3 months (M3) at 25°C. Optical microscopy, and granulometry analysis were performed at D1 and M3 focusing on the concentrated emulsified phase. Both concentrated emulsified phase and sedimented fractions at D1 and M3 were expressed in % vol/vol of emulsion.

## 2.8 | Characterization of the different phases of CL-E

The objective was to characterize the lignins present within the concentrated emulsified phase, and sediments of the emulsion to evaluate the potential privileged lignins type present in these two phases. To achieve that, a methodology for lignins extraction from these different phases was implemented, followed by characterization through SEC analysis. Therefore, the two phases of CL-E were collected separately, then lyophilized and finally dissolved at 100 mg/mL in THF; SEC analysis was performed using the same procedure as described in Section 2.3. For the calculation of percentage of monomers, dimers, and oligomers contained in each of the two phases, integration was performed as described in Section 2.3, and the absolute area of sweet almond oil was subtracted from the absolute area of the concentrated emulsified phase from 11 to 16 min.

# 3 | RESULTS AND DISCUSSION

## 3.1 | Characterization of lignins

Both TL and CL used in the present study were characterized by SEC. Three regions were evidenced on the chromatograms corresponding to low-weight aromatic compounds referred in the following as “monomers”, medium weight aromatic compounds referred as “dimers”, and higher weight aromatic compounds referred as “oligomers”, respectively (Figure 3). The higher hydrodynamic volume polymers corresponding to shorter retention times were eliminated during the filtration. In addition, CL showed a tightening of polydispersity when compared to the starting TL.

In addition, as clearly evidenced in Table 1, when compared with TL, CL showed a decrease of both monomers (partially lost during the precipitation step) and oligomers contents and a relative increased percentage of dimers content. Thus, fractionation process of TL allowed obtaining CL showing reduced PDI (2.15) value along with lower M<sub>w</sub>, M<sub>n</sub>, and M<sub>max</sub>. This aligns with the work of Li and McDonald<sup>48</sup> and Chambon et al.<sup>49</sup> who
<figure><img src="image_5.png" /><figcaption>FIGURE 3 Size exclusion chromatography of technical lignins (TL) compared to control lignins (CL): TL (dotted ---); CL (linear ——); chromatograms are normalized on toluene (internal standard) peak at 20.18 min; eluent: tetrahydrofuran at 1 mL/min; UV detection at 280 nm, ambient temperature.</figcaption></figure>

<table><caption>TABLE 1 Percent ratio of monomers, dimers, and oligomers, M~n~, M~w~, maximum Molar mass (M~max~), and polydispersity Index (PDI) of control lignins (CL) and technical lignins (TL) determined by size exclusion chromatography.</caption><thead><tr><th></th><th>Monomers (%)</th><th>Dimers (%)</th><th>Oligomers (%)</th><th>M<sub>w</sub> (g/mol)</th><th>M<sub>n</sub> (g/mol)</th><th>M<sub>max</sub> (g/mol)</th><th>PDI</th></tr></thead><tbody><tr><td>TL</td><td>9.4</td><td>12.4</td><td>78.2</td><td>1990</td><td>673</td><td>16,000</td><td>2.96</td></tr><tr><td>CL</td><td>7.6</td><td>17.3</td><td>75.1</td><td>1405</td><td>666</td><td>8000</td><td>2.15</td></tr></tbody></table>

obtained low molar mass lignins through fractionation with ethanol or ionic liquids, respectively, as well as with the work of Meng et al.⁵⁰ who demonstrated that lignins fractions obtained with aqueous THF solvent showed relatively low polydispersity.

MEK solvent led to a good removal of the high molar mass oligomers, which aligns with literature.⁵¹,⁵² In addition, the transesterification reaction is conducted in MEK because it is tolerated by the enzyme used and at the same time it affords fractionated GL during the recovery of the enzyme by filtration.

Transmethylation followed by GC-MS of GL inducted a typical hexanoylation yield of 1.2% wt/wt corresponding to 12% mol/mol of transesterification on the aliphatic hydroxyl groups present in the lignin fraction.⁴⁴ The SEC chromatogram of GL showed a SEC profile very similar to CL one (Figure S1), proving that hexanoylation does not have a major impact on the molar mass distributions of lignins.

In this study, fractionation has been performed to eliminate insoluble high molar mass of lignins and hexanoylation to increase amphiphilicity of lignins. Because both fractionation and hexanoylation occur when preparing GL, CL was used as reference to evaluate whether fractionation and/or hexanoylation impact their emulsifying properties on the one hand, and to

investigate the relationship between the structure of lignins and the resulting emulsifying properties on the other hand.

## 3.2 | Investigation of lignins solubility

In a recent review, it has been reported that glycol would be a good solvent for lignins dissolution, more than other alcohols, as well as heterocyclic compounds.⁵³ The use of binary systems, such as ethanol/water⁵³ or butanediol/water⁵⁴ for better dissolution of lignins has also been reported. Therefore, in the present work, the strategy first consisted in focusing on GL solubilization in propanediol, a well-known glycol. Therefore, according to preliminary results, GL solubility in propanediol/water mixture (with an initial non-adjusted pH of 3) was studied at a fixed ratio of 10/90 (wt/wt) (so-called P10/W90) to be in accordance with the ratios of the aqueous phase of the emulsion.

Results evidenced that lignins were not soluble in water, nor in P10/W90 mixture, whereas they were fully soluble in pure propanediol (Table 2a, Table S1). These results were confirmed by optical microscopy and particles size measurements where no particles were identified for lignins/propanediol solutions, whereas the other
<table><caption>TABLE 2 Visual aspect, solubility, optical microscopy photos (G × 400, scale bar 50 µm), and particles size measurements D50 and D90 (dimension of particle amount by volume) of GL dispersions. [Color table can be viewed at wileyonlinelibrary.com]</caption><thead><tr><th>Entry</th><th>A<br>Visual aspect and Solubility</th><th>B<br>Optical microscopy</th><th>C<br>D50 (µm)</th><th>D<br>D90 (µm)</th></tr></thead><tbody><tr><td>Water</td><td>Light brown opaque, non-homogeneous dispersion not soluble, with large lignins aggregates coming to the surface</td><td></td><td>No possible measurements because of completely heterogeneous system</td><td></td></tr><tr><td>Propanediol</td><td>Black opaque homogeneous solution fully soluble</td><td></td><td>No signal (Full solubility)</td><td></td></tr><tr><td>Propanediol/water 10/90</td><td>Light brown opaque moderately homogeneous dispersion not soluble with some aggregated but with more regular and micronized lignins particles</td><td></td><td>32.4 ± 2.0</td><td>84.4 ± 5.8</td></tr></tbody></table>

systems showed large particles clusters. This aligns with the work of Sun et al.⁵⁵ where solubilization of lignins was achieved with the use of ethylene glycol. Similar observations were reported by Wang et al.⁵⁴ with an increased solubility of enzymatically hydrolyzed lignins in 1,4-butanediol/water binary solvent thus illustrating the optimized solubility of lignins in glycol/water mixtures. Based on these results, it was decided to tune GL solubility in aqueous media by first operating a pre-solubilization in pure propanediol and then incorporating the resulting solution in water.

It is well known that lignins obtained using soda process, are more soluble in aqueous phase at alkali pH.⁵⁶

Shulga et al.⁵⁷ reported that alkali pH are more efficient conditions to stabilize lignins emulsions. Tian et al.⁵⁸ showed that system's pH played an important role on lignins-based emulsions' stability. Therefore, to further optimize lignins solubility in water pH readjustment was studied.

Thus, a series of GL dispersions in P10/W90 were prepared and submitted to different pH treatments (pH 3, pH 6, and pH 8.5–6) as described in Section 2.4. A control dispersion, consisting of only solubilizing GL in water and proceeding to the same pH treatment as for pH 8.5–6 dispersion was characterized to evaluate the strategy of presolubilization in propanediol in addition to pH
<table><caption>TABLE 3 Grafted lignins (GL) solubility in P10/W90 depending on pH treatment: visual aspect, optical microscopy photos (G × 100, scale bar 100 µm), and % of insoluble lignins. [Color table can be viewed at wileyonlinelibrary.com]</caption><thead><tr><th>Entry</th><th>A</th><th>B</th><th>C</th></tr><tr><th>GL dispersion</th><th>Visual aspect</th><th>Optical microscopy</th><th>% of insoluble lignins</th></tr></thead><tbody><tr><td>pH 3 dispersion</td><td>Light brown opaque moderately homogeneous dispersion not soluble with some aggregated lignin particles</td><td></td><td>55.1 ± 3.7</td></tr><tr><td>pH 6 dispersion</td><td>Brown opaque homogeneous dispersion not soluble with some very thin lignin particles</td><td></td><td>18.4 ± 0.7</td></tr><tr><td>pH 8.5-6 dispersion</td><td>Dark brown opaque homogeneous dispersion mostly soluble</td><td></td><td>7.2 ± 1.8</td></tr><tr><td>pH 8.5-6 dispersion without propanediol</td><td>Non-homogeneous dispersion, some particles unhomogeneously dispersed ending-up sedimenting</td><td></td><td>29.9 ± 3.9</td></tr></tbody></table>

readjustment. Resulting pH 3 dispersion, pH 6 dispersion, pH 8.5-6 dispersion, and pH 8.5-6 dispersion without propanediol, were characterized by visual aspect,

optical microscopy, and sediment content as detailed in Table 3 and their granulometry distributions are shown in Figure 3.
<figure><img src="image_6.png" /><figcaption>FIGURE 4 Particle size distributions of grafted lignins dispersions with: pH 3 dispersion (in green), pH 6 dispersion (in blue), pH 8.5–6 dispersion (in red), and pH 8.5–6 dispersion without propanediol (in black). [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

Results confirm that lignins solubility depends on the pH history of the dispersion, thus evidencing that the higher the intermediate pH of the dispersion the lower the percentage of insoluble lignins and the lower the particle diameter (Table 3 and Figure 4). Therefore, when back-acid procedure was conducted (pH 8.5–6 dispersion) less undissolved lignins were observed. This could be explained by the use of citric acid, which is regularly employed to adjust pH in skin care formulations,⁵⁹ and known as a chelating agent,⁶⁰,⁶¹ did not induce lignins' sedimentation. Results align with the work of Zhu et al.⁵⁶ as well as Takada et al.¹⁴ who showed that alkali lignins are more soluble in aqueous phase when increasing the pH. pH 8.5–6 dispersion without propanediol showed an unhomogeneous microstructure characterized by both marked aggregates (Table 3) and large particle diameter (Figure 4) compared with pH 8.5–6 dispersion with propanediol. These results undoubtedly allow demonstrating that GL presolubilization in propanediol allows decreasing particles diameter. Thus, the implementation together of the two processes, presolubilization in propanediol followed by pH treatment, are therefore necessary to obtain higher solubility of GL in water.

Based on these results, back-acid strategy (pH 8.5–6) was retained for TL, CL, and GL incorporation in colloidal formulations as a promising route for the use of lignins in applications where pH of 6 is required. Compared to our previous work,⁶² where the objective was to see the influence of pH on the colloidal form of lignins and therefore on their interfacial properties, in this work, the back-acid strategy was retained and the impact of fractionation and acylation on lignins emulsifying capacities was investigated.

## 3.3 | Lignins performance in emulsion

O/W emulsions were prepared to challenge lignins' emulsifying capacities. To evaluate the impact of both fractionation and hexanoylation on lignins emulsifying properties, TL and CL based emulsions were prepared and characterized versus GL-E. Characterization and stability of emulsions were monitored over time by visual aspect, sedimentation amount, optical microscopy, and granulometry analysis. Molar mass distribution of lignins involved in different phases was studied by SEC.

### 3.3.1 | Visual aspect and sedimentation amount of lignins emulsions

The evolution of the visual aspect through photographs of the different emulsions is shown in Figure 5, and Table 4 reports the visual aspect as well as the sedimentation amount of the emulsions stored at 25°C at D1 and M3.

According to both Figure 5 and Table 4, after 1 day all the emulsions exhibit a creaming phenomenon with no oil exudate thus evidencing an emulsifying ability for all the lignins grades but a lack of suspending ability. This aligns with the work of Xiang et al.⁶³ who used alkali lignins for the stabilization of their emulsions and with the work of Yu et al.¹⁹ who demonstrated the high performance of alkali lignins in Pickering emulsions. In any case, two distinct phases were observed: an upper concentrated emulsified phase and a diluted emulsified phase. Such a creaming effect reflects the migration of oil
droplets but still reveals emulsification potential and stability of alkali lignins as this later aspect may easily be solved by the addition of suspending agent. This is consistent with observations by Silmore et al.⁶⁴ who also observed fast creaming of kraft lignins emulsions without affecting stability against coalescence and Ostwald ripening for few months. In addition, TL-E is distinguished by the appearance of a sediment phase already at D1 corresponding to lignins particles (not easily visible on photographs due to very dark color); corresponding sedimentation amount has been reported in Table 4.

Subsequently, there is no evolution, neither for the concentrated emulsified phase nor for the diluted emulsified phase after 3 months of stability. At this stage, TL-emulsion showed a marked level of sedimentation (Table 4), whereas sedimentation appeared limited for CL-E and, to a lesser extent, for GL-E.

<figure><img src="image_7.png" /><figcaption>FIGURE 5 Evolution of the visual aspect of TL-E, CL-E, and GL-E at D1 and M3. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

To sum-up, the monitoring over time demonstrated that fractionated lignins, either grafted or not, were more stable and more compatible within O/W emulsions compared with TL. Compared to CL, hexanoylated lignins GL revealed a limited sedimentation. A more homogeneous system was therefore achieved when lignins were fractionated, with slightly better results when lignins were also hexanoylated.

### 3.3.2 | Characterization of the different phases of CL-emulsion

To apprehend and better understand the mechanism of stabilization of emulsions by lignins molecules, it was envisaged to determine separately the molecular characteristics of the lignins species present in the concentrated emulsified phase and the sediments. To this end, the molar mass of lignins present within each of these two phases of the emulsion was determined by SEC characterization, performed after lyophilization of each phase. Non-emulsified CL were compared to the two different phases of the CL-E. Chromatograms were normalized on lignins signals.

According to Figure 6, one can conclude that the sedimented lignins contained relatively less low molar mass compounds than the concentrated emulsified phase (Table 5). In contrast, concentrated emulsified phase contained a higher ratio of monomers, and dimers as evidenced by Figure 6 and Table 5; therefore, these lignins are mainly responsible for the emulsification of oil droplets. The sedimentation monitored over time, observed for all lignins emulsions, could be induced by the high molar mass lignins that are eliminated during fractionation. These latter lignins possibly tend to interact with each other thus being less available for covering oil-

<table><caption>TABLE 4 Visual aspect and sedimentation amount of TL-E, CL-E, and GL-E at D1 and M3.</caption><thead><tr><th rowspan="2">Emulsion</th><th>D1</th><th colspan="3">M3</th></tr><tr><th>Visual aspect stability</th><th>Sedimentation (% vol/vol of emulsion)</th><th>Visual aspect stability</th><th>Sedimentation (% vol/vol of emulsion)</th></tr></thead><tbody><tr><td>TL-E</td><td>Light brown concentrated emulsified phase (15% vol/vol of emulsion) dark brown diluted emulsified phase</td><td>Sedimentation</td><td>No evolution</td><td>6</td></tr><tr><td>CL-E</td><td>Light brown concentrated emulsified phase (15% vol/vol of emulsion) brown diluted emulsified phase</td><td>No sedimentation</td><td>No evolution</td><td>0.6</td></tr><tr><td>GL-E</td><td>Light brown concentrated emulsified phase (15% vol/vol of emulsion) brown diluted emulsified phase</td><td>No sedimentation</td><td>No evolution</td><td>0.2</td></tr></tbody></table>
<figure><img src="image_8.png" /><figcaption>FIGURE 6 Size exclusion chromatography of each phase of CL-E: non-emulsified CL (black), concentrated emulsified phase (blue), sedimented lignins (pink); chromatograms are normalized on lignins signals, eluent: THF at 1 mL/min, ambient temperature; UV detection at 320 nm. [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

<table><caption>TABLE 5 Ratio of monomers, dimers, and oligomers in each phase of CL-E (in %).</caption><thead><tr><th></th><th>Monomers (%)</th><th>Dimers (%)</th><th>Oligomers (%)</th></tr></thead><tbody><tr><td>Non-emulsified CL</td><td>7.6</td><td>17.3</td><td>75.1</td></tr><tr><td>Concentrated emulsified phase</td><td>20.2</td><td>19.7</td><td>60.1</td></tr><tr><td>Sedimented lignins</td><td>2.8</td><td>10.0</td><td>87.2</td></tr></tbody></table>

water interface and, finally, sediment. Their lower amount in CL and GL led to more acceptable emulsions with less sedimentation. It must be considered that some high molar mass lignins also participate in the emulsification of oil droplets as shown in Table 5 and Figure 6. Nevertheless, the retention time in SEC is not an absolute characterization; species eluted at a given time might differ by their chemical functionalities and so their surface properties. Furthermore, some artifacts could occur due to the branched structure of lignins.

### 3.3.3 | Microstructure and granulometry characterization of the concentrated emulsified phase of lignins emulsions

For the characterization of lignins emulsions, only the concentrated emulsified phase was considered since the lower diluted emulsified aqueous phase mainly consisted of only few oil droplets (Table S2). Optical microscopy images and droplets' diameter evolution and

distributions of the concentrated emulsified phase are shown in both Table 6 and Figure 7.

Optical microscopy images of the concentrated emulsified phase of TL-E, CL-E, and GL-E, as reported on Table 6a and Table 6b allow evidencing a high concentrated network of oil droplets.

After 1 day of aging, both Table 6 and Figure 7 evidence a similar microstructure and a similar granulometry for the TL-E and CL-E whereas GL-E showed a slight shift of distribution to smaller particle sizes. In all cases, two main populations of droplets are observed: one between 0.5 and 2 µm and the other from 5 up to 40–50 µm (Figure 7a). One can hypothesize that the similarities observed in microstructure and granulometry distribution after 1 day of aging for both TL-E and CL-E could be explained as the result of similar molar mass lignins molecules involved in the stabilization of oil droplets. Meanwhile, the major part of sediments consists of high molar mass lignins, as evidenced in Section 3.3.2. Consequently, these latter high molar mass lignins, which are more present in TL fraction, are less involved in the
<table><caption>TABLE 6 Optical microscopy images (G × 400, scale bar 50 µm) and evolution of the droplets diameter (D90 in µm) of the concentrated emulsified phase of technical lignins (TL)-emulsion, control lignins (CL)-emulsion, and grafted lignins (GL)-emulsion after 1 day and after 3 months of stability. [Color table can be viewed at wileyonlinelibrary.com]</caption><thead><tr><th rowspan="3">Entry</th><th>A</th><th>B</th><th>C</th><th>D</th><th>E</th></tr><tr><th colspan="2">Optical microscopy</th><th colspan="2">D90 (µm)</th><th rowspan="2">Relative increase<br>between D1 and<br>3 months</th></tr><tr><th>D1</th><th>M3</th><th>D1</th><th>M3</th></tr></thead><tbody><tr><td>TL-emulsion</td><td></td><td></td><td>26.9 ± 0.1</td><td>35.6 ± 0.7</td><td>32%</td></tr><tr><td>CL-emulsion</td><td></td><td></td><td>26.9 ± 0.1</td><td>33.4 ± 0.4</td><td>24%</td></tr><tr><td>GL-emulsion</td><td></td><td></td><td>23.9 ± 1.0</td><td>29.4 ± 1.1</td><td>23%</td></tr></tbody></table>

emulsification of oil droplets. Finally, if considering emulsions prepared with GL, hexanoylated lignins lead to slight reduction of initial droplets size compared with the other lignins, namely TL and CL.

Emulsions stability was monitored over a period of 3 months at 25°C to evidence and, as far as possible, understand the mechanisms responsible for the emulsions' stabilization or destabilization. For the three systems, Figure 7b and Table 6b evidence a tendency to coalescence for all preparations as distribution curves shift to larger particle size when compared with initial ones; corresponding microscope images show larger objects and aggregated structures for both TL and CL systems and, in a lesser extent, for GL. According to Figure 7b the distributions of both fractionated lignins emulsions appear more polydisperse when compared with the initial one, with the occurrence of objects with sizes ranging from 2 to 8 µm that were not initially evidenced or in a very low amount (Figure 7a). This may be

explained by the fact that the population of 0.5–2 µm (Figure 7a) has coalesced. At the same time, D90 after 3 months of aging significantly increased for the three emulsions, with a higher increase for TL compared with the other two emulsions (Table 6d and Table 6e). CL fraction being composed of a higher ratio of lignins dimers (39% of high molar mass of lignins being removed by fractionation), compared with TL fraction (Section 3.1), and both being at 2.5% within emulsion, not enough lignins dimers are present in TL fraction, which are one of the main lignins molecules responsible for oil droplets stabilization (Section 3.3.2), thus oil droplets coalesce. Both fractionated lignins emulsions showed a lower relative increase of D90 between day 1 and 3 months of stability with 24% and 23% respectively compared with TL-E with 32% of relative increase (Table 6e).

All the results exposed in Section 3.3, establish that both fractionated lignins, either grafted or not, appear better systems for preparing more homogeneous O/W
<figure><img src="image_9.png" /><figcaption>**FIGURE 7** Particles size distribution of the concentrated emulsified phase of lignins emulsions: (a) after 1 day of aging and (b) after 3 months of aging: TL-E (in blue); CL-E (in red); GL-E (in green). [Color figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

When emulsified at 2.5%, fractionated lignins, grafted or not, are characterized by a higher ratio of dimers, which have more affinity with the interface and therefore fractionated lignins sediment much less if compared with TL. Thus, corresponding CL and GL molecules diffuse more easily and reach the interface. Nevertheless, GL leads to limited sedimentation and coalescence, possibly as the result of acylated hexanoyl moieties leading to more favorable physico-chemical interactions at O/W interface. It is important to underline that the impact of fractionation on improving TL emulsifying ability is significantly greater than that of hexanoylation. In addition, it must be considered that for the same molar masses, functional groups present on the lignins structure, such as hydroxyls and carbonyls, necessarily play a significant role on their physico-chemical properties and therefore play an important role in the mechanisms of interface stabilization.

4 | CONCLUSIONS

The main objective being the valorization of alkali lignins within cosmetic O/W emulsions, a process had to be

implemented to maximize compatibility of lignins dispersion and solubility in cosmetic grade solvent. First, the study of lignins solubility confirmed the high solubility of alkali lignins in glycols such as propanediol. An appropriate glycol-water mixture was conceived to disperse lignins to allow monitoring the pH. Both pH control, either alkaline or acidic, to reach a final pH of 6, as well as lignins presolubilization in propanediol before their incorporation in water showed a great impact on the solubility of lignins. With those results, an optimal strategy to incorporate lignins within simple emulsions was developed, consisting of incorporating lignins/propanediol solution in water and then pH adjustment by applying a back-acid procedure.

More narrow-dispersed molecular mass profile of alkali lignins have been isolated by means of a solvent fractionation, which provides better features for solubilizing and emulsifying sweet almond oil O/W emulsions. Emulsions containing fractionated lignins, grafted or not, were more stable and more homogeneous systems with less sedimentation and lower evolution of the droplets size in time. The whole results show that fractionation of lignins has a major impact and hexanoylation has a minor impact on improving stability of lignins within
O/W emulsions. According to our findings, lignins responsible for the stabilization of oil droplets are composed of a higher ratio of low molar mass compounds (monomers and dimers types). To conclude, the whole results demonstrate the ability to modulate lignins solubility and lignins emulsifying performances by combining accurate lignins modification strategies and formulation procedure. The whole results described in the present paper allowed opening very promising prospects for industrial exploitation, especially in cosmetics, of these biobased materials.

According to results exposed in this article, lignins dispersion used for emulsification contains few undis- solved lignins, therefore different states of solubility may impact their interfacial properties and Pickering emul- sions could be formed. In addition, emulsification through mechanical mixing, is in many cases not sufficient to result in small enough droplets for stable emulsions. Alternative methods like sonication or high- pressure homogenization could be performed to decrease emulsions droplets size. Therefore, understanding the stabilization mechanism of lignins at the interfaces, iden- tifying all the phenomena involved for their emulsifying capacities as well as optimizing their emulsification pro- cess need further investigation for deeper insights, which are under investigation and part of our perspectives.

AUTHOR CONTRIBUTIONS

**Caroline Hadjiefstathiou:** Conceptualization (equal); data curation (lead); formal analysis (lead); investigation (lead); methodology (equal); visualization (lead); writing – original draft (lead). **Audrey Manière:** Conceptualization (equal); funding acquisition (lead); methodology (equal); resources (lead); supervision (equal); writing – review and editing (equal). **Joan Attia:** Funding acquisition (lead); supervision (supporting). **Florian Pion:** Conceptualization (equal); methodology (equal); resources (equal); supervision (equal); writing – review and editing (equal). **Paul-Henri Ducrot:** Conceptualization (equal); methodology (equal); resources (equal); supervision (equal); writing – review and editing (equal). **Ecaterina Gore:** Conceptualization (equal); methodology (equal); resources (equal); supervision (equal); writing – review and editing (equal). **Michel Grisel:** Conceptualization (equal); funding acquisition (supporting); methodology (equal); resources (equal); supervision (equal); validation (lead); writing – review and editing (equal).

FUNDING INFORMATION

This work was funded by the National Association of Research and Technology (ANRT) (N°2020_0785).

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

DATA AVAILABILITY STATEMENT

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

ORCID

Caroline Hadjiefstathiou https://orcid.org/0009-0006-1674-847X

Ecaterina Gore https://orcid.org/0000-0002-3494-9981

Michel Grisel https://orcid.org/0000-0003-0480-8747

REFERENCES

[1] D. Shen, W. Jin, J. Hu, R. Xiao, K. Luo, *Renewable Sustainable Energy Rev.* **2015**, *51*, 761.

[1] H. C. Arca, L. I. Mosquera-Giraldo, V. Bi, D. Xu, L. S. Taylor, K. J. Edgar, *Biomacromolecules* **2018**, *19*, 2351.

[3] R. T. Bianchet, A. L. Vieira Cubas, M. M. Machado, E. H. Siegel Moecke, *Biotechnol. Rep.* **2020**, *27*, e00502.

[4] C. Vasile, M. Baican, *Polymer* **2023**, *15*, 3177.

[5] J. P. Jyothibasu, R.-H. Wang, Y.-C. Tien, C.-C. Kuo, R.-H. Lee, *Polymer* **2022**, *14*, 3106.

[6] D. S. Argyropoulos Ed., *Materials, Chemicals, and Energy from Forest Biomass*. ACS Symposium Series, Vol. 954, American Chemical Society, Washington, DC **2007**. https://doi.org/10.1021/bk-2007-0954

[7] Z. Usmani, M. Sharma, A. K. Awasthi, T. Lukk, M. Tuohy, L. Gong, P. Nguyen-Tri, A. D. Goddard, R. M. Bill, S. C. Nayak, V. K. Gupta, *Renewable Sustainable Energy Rev.* **2021**, *148*, 111258.

[8] Sharma, S.; Sharma, A.; Mulla, S. I.; Pant, D.; Sharma, T.; Kumar, A. In *Lignin*; Sharma, S., Kumar, A., Eds.; Springer Series on Polymer and Composite Materials, Springer International Publishing: Cham, **2020**; 1–15. https://doi.org/10.1007/978-3-030-40663-9_1

[9] E. Ten, W. Vermerris, *J. Appl. Polym. Sci.* **2015**, *132*, 42069.

[10] F. S. Chakar, A. J. Ragauskas, *Ind. Crops Prod.* **2004**, *20*, 131.

[11] G. Gellerstedt, *Ind. Crops Prod.* **2015**, *77*, 845.

[12] A. Duval, S. Molina-Boisseau, C. Chirat, *Ind. Crops Prod.* **2013**, *49*, 66.

[13] D. M. Miles-Barrett, J. R. D. Montgomery, C. S. Lancefield, D. B. Cordes, A. M. Z. Slawin, T. Lebl, R. Carr, N. J. Westwood, *ACS Sustainable Chem. Eng.* **2017**, *5*, 1831.

[14] M. Takada, R. Chandra, J. Wu, J. N. Saddler, *Bioresour. Technol.* **2020**, *302*, 122895.

[15] B. Xiao, X. F. Sun, R. Sun, *Polym. Degrad. Stab.* **2001**, *13*, 307.

[16] M. R. V. Bertolo, L. B. Brenelli de Paiva, V. M. Nascimento, C. A. Gandin, M. O. Neto, C. E. Driemeier, S. C. Rabelo, *Ind. Crops Prod.* **2019**, *140*, 111591.

[17] W. Zhang, J. Shen, P. Gao, Q. Jiang, W. Xia, *Ind. Crops Prod.* **2022**, *188*, 115651.

[18] Y. Pang, Y. Sun, Y. Luo, M. Zhou, X. Qiu, C. Yi, H. Lou, *Ind. Crops Prod.* **2021**, *167*, 113468.

[19] X. Yu, S. Chen, W. Wang, T. Deng, H. Wang, *J. Cleaner Prod.* **2022**, *339*, 130769.
[20] R. Álvarez-Barajas, A. A. Cuadri, F. J. Navarro, F. J. Martínez-Boza, P. Partal, *Polymer* **2021**, *13*, 2703.

[21] C. Pouteau, P. Dole, B. Cathala, L. Averous, N. Boquillon, *Polym. Degrad. Stab.* **2003**, *81*, 9.

[22] A. Majira, B. Godon, L. Foulon, J. C. Putten, L. Cézard, M. Thierry, F. Pion, A. Bado-Nilles, P. Pandard, T. Jayabalan, V. Aguié-Béghin, P. Ducrot, C. Lapierre, G. Marlair, R. J. A. Gosselink, S. Baumberger, B. Cottyn, *ChemSusChem* **2019**, *12*, 4799.

[23] M. P. Vinardell, V. Ugartondo, M. Mitjans, *Ind. Crops Prod.* **2008**, *27*, 220.

[24] P. Widsten, *Cosmetics* **2020**, *7*, 85.

[25] Y. Qian, X. Zhong, Y. Li, X. Qiu, *Ind. Crops Prod.* **2017**, *101*, 54.

[26] Y. Qian, X. Qiu, S. Zhu, *ACS Sustainable Chem. Eng.* **2016**, *4*, 4029.

[27] Y. Qian, X. Qiu, S. Zhu, *Green Chem.* **2015**, *17*, 320.

[28] A. G. Morena, A. Bassegoda, M. Natan, G. Jacobi, E. Banin, T. Tzanov, *ACS Appl. Mater. Interfaces* **2022**, *10*, 37270.

[29] A. J. Basbasan, B. Hararak, C. Winotapun, W. Wanmolee, W. Chinsirikul, P. Leelaphiwat, V. Chonhenchob, K. Boonruang, *Polymer* **2023**, *15*, 989.

[30] K. M. Perkins, C. Gupta, E. N. Charleson, N. R. Washburn, *Colloids Surf. A* **2017**, *530*, 200.

[31] A. Czaikoski, A. Gomes, K. C. Kaufmann, R. B. Liszbinski, M. B. De Jesus, R. L. da Cunha, *Ind. Crops Prod.* **2020**, *154*, 112762.

[32] N. Ghavidel, P. Fatehi, *ChemSusChem* **2020**, *13*, 4567.

[33] H. Chen, J. Liu, X. Chang, D. Chen, Y. Xue, P. Liu, H. Lin, S. Han, *Fuel Process. Technol.* **2017**, *160*, 196.

[34] S. Li, D. Ogunkoya, T. Fang, J. Willoughby, O. J. Rojas, *J. Colloid Interface Sci.* **2016**, *482*, 27.

[35] J. H. Lora, W. G. Glasser, *J. Polym. Environ.* **2002**, *10*, 39.

[36] O. A. T. Dias, M. Sain, I. Cesarino, A. L. Leão, *Polym. Adv. Technol.* **2019**, *30*, 70.

[37] H. Jin, H. Shi, W. Jia, Y. Sun, X. Sheng, Y. Guo, H. Li, H. Sun, *Int. J. Biol. Macromol.* **2022**, *207*, 531.

[38] H. Li, G. Sivasankarapillai, A. G. McDonald, *J. Appl. Polym. Sci.* **2015**, *132*, 41389.

[39] L. Dai, Y. Li, F. Kong, K. Liu, C. Si, Y. Ni, *ACS Sustainable Chem. Eng.* **2019**, *7*, 13497.

[40] L. B. Brenelli, L. R. B. Mariutti, R. Villares Portugal, M. A. De Farias, N. Bragagnolo, A. Z. Mercadante, T. T. Franco, S. C. Rabelo, F. M. Squina, *Ind. Crops Prod.* **2021**, *167*, 113532.

[41] Z. Shokri, F. Seidi, M. R. Saeb, Y. Jin, C. Li, H. Xiao, *Mater. Today Chem.* **2022**, *24*, 100780.

[42] S. Ouajai, A. Hodzic, R. A. Shanks, *J. Appl. Polym. Sci.* **2004**, *94*, 2456.

[43] P.-P. Wang, Z.-G. Luo, Chun-Chen, Xiong-Fu, T. M. Tamer, *Carbohydr. Polym.* **2020**, *228*, 115389.

[44] A. Sarieddine, C. Hadjiefstathiou, A. Majira, F. Pion, P.-H. Ducrot, *Front. Chem.* **2023**, *11*, 1239479.

[45] E. Gore, C. Picard, G. Savary, *Biotribology* **2018**, *16*, 17.

[46] J. R. Sharpe, K. L. Harris, K. Jubin, N. J. Bainbridge, N. R. Jordan, *Br. J. Dermatol.* **2009**, *161*, 671.

[47] E. Humeres, N. A. Debacher, E. P. De Souza, *Can. J. Chem.* **2005**, *83*, 10.

[48] H. Li, A. G. McDonald, *Ind. Crops Prod.* **2014**, *62*, 67.

[49] C. L. Chambon, V. Fitriyanti, P. Verdía, S. M. Yang, S. Hérou, M.-M. Titirici, A. Brandt-Talbot, P. S. Fennell, J. P. Hallett, *ACS Sustainable Chem. Eng.* **2020**, *8*, 3751.

[50] X. Meng, A. Parikh, B. Seemala, R. Kumar, Y. Pu, C. E. Wyman, C. M. Cai, A. J. Ragauskas, *Bioresour. Technol.* **2019**, *272*, 202.

[51] Y. Lu, L. Joosten, J. Donkers, F. Andriulo, T. M. Slaghek, M. K. Phillips-Jones, R. J. A. Gosselink, S. E. Harding, *Sci. Rep.* **2021**, *11*, 13937.

[52] C. Allegretti, S. Fontanay, K. Rischka, A. Strini, J. Troquet, S. Turri, G. Griffini, P. D'Arrigo, *ACS Omega* **2019**, *4*, 4615.

[53] T. Rashid, F. Sher, T. Rasheed, F. Zafar, S. Zhang, T. Murugesan, *J. Mol. Liq.* **2021**, *321*, 114577.

[54] Q. Wang, K. Chen, J. Li, G. Yang, S. Liu, J. Xu, *BioResources.* **2011**, *6*, 3034.

[55] J. Sun, T. Dutta, R. Parthasarathi, K. H. Kim, N. Tolic, R. K. Chu, N. G. Isern, J. R. Cort, B. A. Simmons, S. Singh, *Green Chem.* **2016**, *18*, 6012.

[56] H. Zhu, Y. Li, B. Pettersson, L. Zhang, M. Lindström, G. Henriksson, *J. Adhes. Sci. Technol.* **2014**, *28*, 490.

[57] G. Shulga, S. Livcha, B. Neiberte, A. Verovkins, S. Vitolina, E. Zhilinska, *IOP Conf. Ser. Mater. Sci. Eng.* **2019**, *500*, 012011.

[58] J. Tian, J. Chen, J. Guo, W. Zhu, M. R. Khan, Q. Fu, Y. Jin, H. Xiao, J. Song, O. J. Rojas, *Colloids Surf. A* **2023**, *670*, 131503.

[59] S. Nangare, Y. Vispute, R. Tade, S. Dugam, P. Patil, *Futur. J. Pharm. Sci.* **2021**, *7*, 54.

[60] M. M. Fiume, B. A. Heldreth, W. F. Bergfeld, D. V. Belsito, R. A. Hill, C. D. Klaassen, D. C. Liebler, J. G. Marks, R. C. Shank, T. J. Slaga, P. W. Snyder, F. A. Andersen, *Int. J. Toxicol.* **2014**, *33*, 16S.

[61] C. R. Soccol, L. P. S. Vandenberghe, C. Rodrigues, A. Pandey, *Food Technol. Biotechnol.* **2006**, *44*, 141.

[62] C. Hadjiefstathiou, A. Manière, J. Attia, F. Pion, P.-H. Ducrot, E. Gore, M. Grisel, *J. Mol. Liq.* **2023**, *390*, 123030.

[63] H. Xiang, A. Zhong, H. Wang, L. Xiao, T. Deng, T. Hu, P. Wen, *Int. J. Biol. Macromol.* **2022**, *218*, 739.

[64] K. S. Silmore, C. Gupta, N. R. Washburn, *J. Colloid Interface Sci.* **2016**, *466*, 91.

## 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:** C. Hadjiefstathiou, A. Manière, J. Attia, F. Pion, P.-H. Ducrot, E. Gore, M. Grisel, *J. Appl. Polym. Sci.* **2024**, *141*(16), e55235. https://doi.org/10.1002/app.55235