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Chapter

Cellulose as a Natural Emulsifier:

From Nanocelluloses to
Macromolecules
Carolina Costa, Bruno Medronho, Björn Lindman,
Håkan Edlund and Magnus Norgren

Abstract

During the last decade, cellulose structural features have been revisited, with
particular focus on its structural anisotropy (amphiphilicity) and interactions
determining its recalcitrance to dissolution. Evidences for cellulose amphiphilicity
are patent, for instance, in its capacity to adsorb at oil–water interfaces, thus being
capable of stabilizing emulsions. This behavior is observable in all its forms, from
cellulose nanoparticles to macromolecules. This chapter is divided into two main
parts; first, the fundamentals of emulsion formation and stabilization will be intro-
duced, particularly focusing on the role of natural emulsifiers. Secondly, the emerg-
ing role of cellulose as a natural emulsifier, where the ability of cellulose to form and
stabilize emulsions is revisited, from cellulose nanoparticles (Pickering-like effect)
to macromolecules (i.e., cellulose derivatives and native molecular cellulose).

Keywords: Nanocelluloses, regenerated cellulose, cellulose derivatives,

native molecular cellulose, amphiphilicity, oil–water interface, emulsifiers,
adsorption, emulsions, stabilization

1. Introduction

Every year, hundred billion tons of cellulose are produced by nature from various
biomass sources, making this biopolymer an ultimate platform for developing
sustainable applications on an industrial scale [1]. The increased environmental
awareness due to global climate changes has pushed cellulose science to advance
rapidly, and thus cellulose is expected to continue playing a central role in the
emergent bio-economies and biorefineries. Cellulose extraction and purification
rely on fairly simple, scalable, and efficient isolation techniques, and cellulose can
be further modified and shaped into different colloidal and macroscopic forms,
showing very different features [2–5].
Emulsions are among the most important colloids in everyday life, and have
multiple uses, from technical applications, such as paints and coatings, to life
science applications, such as foods, pharmaceuticals, and cosmetics. Emulsions
can encapsulate and protect sensitive ingredients, adjust appearance, taste and
sensorial properties, and facilitate application, spreading and drying. They can also
serve as an intermediator for efficient oil extraction, polymerization reactions, and
the production of microcapsules and lightweight foams [6]. Their structural and

1
Cellulose Science and Derivatives

functional properties are vast and therefore, the emulsifiers and stabilizers must
be carefully selected according to the needs. With the growing global demand for
sustainable and “clean-label” products, industries are actively seeking to replace
synthetic emulsifiers by new alternatives. Finding natural ingredients, with mini-
mal modification requirements (without compromising environment and human
health) and still being capable of achieving a competitive performance to the opti-
mized synthetic options is highly desirable but challenging. In this respect, cellulose
has the potential to become a key star player in emulsion systems. In addition to its
natural, non-toxic, biodegradable, and renewable nature, it is also a versatile source
of natural emulsifiers. From cellulose derivatives, used since the early 20th century,
to the more recently explored native forms of cellulose, including nanocelluloses,
and the native cellulose itself, either molecular or in the form of polymeric particles
and microgels, all its different morphological forms have shown an intrinsic amphi-
philic character by self-assembling at oil–water interfaces.

2. Emulsion formation and stabilization by natural polymers and

particles

Emulsions are multiphasic systems of at least three main components, the oil
phase, the water phase, and the emulsifier. One of the phases is dispersed into the
other in the form of droplets that are stabilized by a key compound, an emulsifier.
Depending on the dispersed phase, we can have either oil-in-water (o/w) or water-
in-oil (w/o) emulsions, and the type of emulsion formed mainly depends on the
solubility properties of the emulsifier. According to Bancroft’s rule, o/w emulsions
are formed when the emulsifier has a preference for water whereas the opposite
applies for w/o emulsions [7]. When an emulsion is formed, a large interfacial area
is created between the two phases, generating an increased energy in relation to the
interfacial tension between oil and water. Therefore, emulsions seek to minimize
the energy used to create such large interfacial area and break down over time by
the combination of different instability mechanisms, such as, creaming, floccula-
tion, coalescence and Ostwald ripening [7]. The role of the emulsifier is to reduce
the interfacial tension and form a “protective layer” through its adsorption on the
droplets surface, thus facilitating not only the formation of the droplets but also
preventing/minimizing their re-association. Amphiphilic molecules and insoluble
particles have both been employed as emulsifiers (Figure 1). Small surfactant
molecules are usually good emulsifiers. Nevertheless, they are often not particularly
well suited to provide long-term stability; this is because they are in dynamic equi-
librium with the bulk medium. In this case, often, a stabilizer is required to achieve
sufficient kinetic stability for the required shelf-life of a certain product. Polymers

Figure 1.
Emulsifiers: Surfactants, polymers and particles. Differences in scaling are not considered.

2
Cellulose as a Natural Emulsifier: From Nanocelluloses to Macromolecules
DOI: http://dx.doi.org/10.5772/intechopen.99139

are often applied as stabilizers in oil-in-water (o/w) emulsions, and they can act
either via the reinforcement of the stabilizing layer, co-acting with the emulsifier at
the interface, or via the viscosity enhancement of the continuous phase, thus reduc-
ing droplet mobility [8]. Certain amphiphilic polymers and particles may act as
both emulsifiers and stabilizers. Good examples are surface-active polysaccharides,
such as gum Arabic, pectin, galactomannans and modified starches and celluloses
[8–11]. These polymers provide strong steric repulsions driven by the entropic
penalty when polymer segments from two droplets start to entangle, since confor-
mational rearrangements are hindered due to their high molecular weight [12].
Another type of stabilization is provided by insoluble particles, often called
Pickering stabilization; rigid particles, Janus particles and microgels, have been
described as Pickering emulsifiers [13–15]. The amphiphilicity of a typical
Pickering emulsifier (rigid particles) is usually described in terms of surface wet-
tability, which is measured by the three-phase contact angle of a particle adsorbed
at an oil–water interface. Both o/w and w/o emulsions can be formed depending
on the particle wettability and whether the particles are predominantly hydro-
philic or hydrophobic [13]. In agreement with Bancroft’s rule, the interface tends
to bend towards the more poorly wetted liquid, and this becomes the dispersed
phase. Pickering particles adsorb irreversibly at the oil–water interfaces due to the
high-binding energy per particle, forming an effective mechanical barrier against
coalescence; they may also inhibit lipid oxidation due to the thick interfacial layers
formed [10, 11]. This is an important feature in what concerns food and pharmaceu-
tical applications where polyunsaturated lipids are involved. Their double bonds are
prone to oxidation leading to the deterioration of the products by the formation of
rancid flavors and, eventually, toxic by-products [16]. The most widely used biopar-
ticles are derived from biopolymers, such as cellulose, chitin and chitosan, starch
and modified starches, lignin and proteins [17–21]. Bioparticles may vary widely in
shape, size, aspect ratio and morphology, implying that their mechanistic behavior
considerably deviates from that of both the solid sphere and the flexible polymer
[22]. Nevertheless, particles with an irregular shape and higher aspect ratios have
been found to have a greater ability in stabilizing emulsions and foams (and at lower
concentrations) compared to synthetic particles of spherical shape [19].
A special type of particles that display some similarities to surfactants and
polymers are known as Janus particles. These are amphiphilic particles, composed
of two or more regions with distinct physicochemical properties, that can self-
assemble in bulk media and readily adsorb to fluid interfaces, remarkably lowering
the interfacial tension; for this reason, they are also called “colloidal surfactants”
[14, 23, 24]. They can be synthesized in geometrically different shapes and chemical
compositions with high uniformity and precision [14]. Polysaccharides, such as,
alginates, chitosan, pectin, cellulose and heparin, have been used to produce bio-
based Janus particles [25, 26].
Another interesting type of emulsifying particles are microgels, which are
soft deformable gel-like particles made up of aggregated or cross-linked polymer
networks [22]. These microgels can swell in aqueous solvents and rearrange at the
oil–water interface, resulting in thick and mechanically resilient layers. Owing
to the amphiphilic character of their polymeric constituents, most microgels are
inherently surface active at oil–water and air-water interfaces and, as rigid particles,
they also irreversibly adsorb at the interfaces [22]. Synthetic microgels offer an
additional feature that arises as a direct consequence of their combined polymeric
and particulate character. They have the potential to effectively stabilize water-in-
water emulsions, which are mixed solutions of thermodynamically incompatible
polymers, producing two immiscible aqueous phases, and where the effective
thickness of the interface is defined on a length scale considerably greater than the

3
Cellulose Science and Derivatives

molecular dimensions of a conventional emulsifier [22, 27]. However, microgels

based on physical cross-linking of biopolymers are rather novel and much of their
behavior at interfaces remains unclear [15]. Two examples of natural ingredients
that exhibit microgel-like characteristics are casein micelles (in their native form)
and whey proteins and gelatinized starch granules (upon heat treatment). However,
in order to mimic the special features of the synthetic microgels, these traditional
food-grade microgels need more pronounced long-term structural stability under
conventional processing and storage conditions, which typically requires the intro-
duction of additional covalent cross-links within the aggregated biopolymer-based
entity [22].

3. Cellulose: a versatile source of emulsifiers

3.1 Physicochemical characteristics of cellulose and the various morphological

forms

Cellulose is a polysaccharide composed of glucose monomers, the anhydro-

glucose units (AGUs), linked by β -(1–4) glycosidic bonds. These β-linked AGUs
adopt the 4C1 chain conformation, which is the conformation with the lowest free
energy of the molecule. Consequently, the three polar hydroxyl groups in each AGU
are located on the equatorial positions of the rings, and the hydrogen atoms of the
non-polar C–H bonds are located on the axial positions [1]. This structural anisot-
ropy is what gives cellulose its amphiphilic nature [28]. Due to the large number of
hydroxyl groups within a cellulose molecule, both intra- and intermolecular hydro-
gen bonding occur and various types of supramolecular semi-crystalline structures
can be formed. It is believed that intramolecular hydrogen bonding is responsible
for the single-chain conformation and stiffness, while the intermolecular hydrogen
bonding would be responsible for the sheet-like arrangement of the native polymer
[1]. However, the stacking of these sheets into the three-dimensional crystalline
supramolecular structures must involve hydrophobic interactions, as it was shown
trough molecular dynamic simulations, and moreover was observed, many years
ago, in native cellulose biosynthesis [1, 29, 30].
Hydrophobic interactions between cellulose molecules make, in combination
with favorable packing conditions (and thus a low energy) in the crystalline state,
cellulose insoluble in water [31]. Solubility can be achieved by ionizing cellulose,
which occurs at extreme pH’s. Solubility in water can also be aided by addition of
co-solutes that weaken hydrophobic interactions. Derivatization of cellulose is also
found to generally enhance solubility strongly, which can be referred to packing
constraints in the solid state. Thus, to make cellulose soluble in aqueous solutions,
the crystalline packing has to be disrupted, and this can be achieved, for example,
by chemical modifications via etherification reactions in alkaline media, result-
ing in water-soluble cellulose ethers [32, 33]. These cellulose derivatives keep the
amphiphilic properties of cellulose, as can be seen from their association with
surfactants and their adsorption at the air-water and oil–water interfaces [34–39].
A fairly simple way of converting cellulose into a versatile class of new materials
is through a dissolution-regeneration process. The regeneration of cellulose occurs
when a coagulant (“anti-solvent”) gets in contact with a cellulose solution or dope,
leading to a solvent exchange and subsequent aggregation of the cellulose chains.
The organization of the molecules in the regenerated materials (e.g., fibers, films,
foams, particles) and their properties are strongly influenced by the dissolution
state of cellulose (molecular cellulose, partially dissolved, crystalline or amorphous
aggregates), as a well as the nature of the coagulant used [40, 41].

4
Cellulose as a Natural Emulsifier: From Nanocelluloses to Macromolecules
DOI: http://dx.doi.org/10.5772/intechopen.99139

Cellulose can also be shaped into micro- and nanoparticles of different col-
loidal structure. Acid or mechanical treatments are usually applied to deconstruct
the cellulose fibers into crystalline or semi-crystalline nanocelluloses [20, 42–44].
Partial decomposition of cellulose fibers, by acid treatment and cellulase-catalyzed
hydrolysis, yields powdery microcrystalline cellulose (MCC), such as commercial
Avicel®, with DP values between 150 and 300 [45]. Avicel® still contains both
amorphous and crystalline portions. On the other hand, nanocrystalline cellulose
(NCC) is obtained by strong acid hydrolysis. During the chemical process, the
more readily accessible amorphous regions are completely disrupted deliberating
rod-like crystal sections, whose sizes are dependent on the time and temperature
of the reaction. The dimensions of the isolated NCC are also found to be strongly
influenced by the degree of crystallinity of cellulose, which, in turn, is dependent
on the natural source. Cotton, wood and Avicel® usually yield highly crystalline
nanorods (90% crystallinity) with a narrow distribution of sizes (5–10 nm in width
and 100–300 nm in length), whereas sources, such as tunicin (extracted from
the tunicates), bacteria and algae, yield crystals with higher polydispersity and
larger dimensions [42]. NCC forms stable suspensions in water by application of a
mechanical force, typically sonication. Its surface properties are determined by the
mineral acid and the reaction conditions used during its extraction. NCC prepared
with hydrochloric acid (HCl) is weakly negatively charged, while it exhibits a strong
repulsive character if prepared with sulfuric acid (H2SO4), since approximately one
tenth of the glucose units is functionalized with the anionic sulfate ester groups.
Thus, NCC prepared with H2SO4 give suspensions with higher colloidal stability
than NCC prepared with HCl.
Micro- and nanofibrillated (MFC/NFC) celluloses are obtained by extruding
wood pulp suspensions trough mechanical devices (high-pressure homogenizers),
which results in fiber delamination and deliberation of the fibrils, usually being
tens of nanometers wide and lengths ranging from several nanometers to several
micrometers (i.e., 5–60 nm in width and 100 nm to several micrometers in length)
[42]. This type of nanocelluloses are usually less crystalline than NCC, since they
still own part of the amorphous domains, and have higher aspect ratios [5, 46]. In
aqueous solutions, the fiber-like morphology and high aspect ratio, typically drive
gel-like behavior due to entanglements between the microfibrils.

3.2 Nanocelluloses at interfaces

Several researchers have demonstrated the ability of cellulose particles to

self-assemble at oil–water interfaces and to stabilize o/w emulsions without the
aid of classical surfactants [47–49]. It is believed that the amphiphilic character of
nanocellulose resides in its crystalline organization at the elementary “brick” level,
and thus, cellulose nanocrystals have both hydrophilic and hydrophobic edges that
are preferentially wetted by water and oil phases, respectively [49]. The wettability
properties of cellulose particles may be tuned by surface hydrophobization, due to
the presence of many reactive hydroxyl groups, and w/o emulsions can be formed
[50–52]. Most of the particles from biological origins, such as cellulose, chitosan,
or starch, show an irregular shape and are polydisperse in size and morphology.
However, this structural anisotropy may be very beneficial for emulsion formation
and stability. Particles with high aspect ratios are capable of stabilizing biphasic
systems at lower concentrations compared to systems containing spherical particles
[53]. Particles with such a well-defined shape are usually derived from inorganic
materials, like silica and these have been extensively studied because of their
availability in different sizes with narrow size distributions and chemical surface
tunability. However, their lack of biocompatibility and biodegradability restricts

5
Cellulose Science and Derivatives

their use in food and pharmaceutical applications [54]. For this reason, the study
and characterization of materials from biological origins have gained increas-
ing attention, and many efforts have been made in the food and pharmaceutical
industries in order to develop new food-grade particles [19, 55]. It was early noticed
that MCC particles have the ability to stabilize conventional o/w emulsions, and
multiple emulsions systems of w/o/w type, with the aid of a hydrophobic surfactant
for the stabilization of the internal w/o interface [56, 57]. These MCC particles
form a network around the emulsified oil droplets that provides a mechanical
barrier against coalescence, and, beyond that, the non-adsorbed particles may act
as thickener agents in the continuous aqueous phase. MCC particles have also the
ability to reduce lipid oxidation, one of the major concerns among food manufac-
turers due to its negative effects on food quality [55]. More recently, nanocelluloses,
such as MFC/NFC and NCC, have been increasingly in focus for having a better
performance than MCC, owing their smaller sizes and more regular shapes [58].
NCCs with low aspect ratios (shorter) have a dense organization at the interface
and cover better the oil surface, while NCCs with high aspect ratios (longer) typi-
cally form a network around the droplet with relatively low coverage. Therefore,
shorter NCCs have better emulsification efficiency and long-term stability, since
higher droplet coverage usually means smaller droplet size [59, 60]. On the other
hand, long nanofibrils (NFC) with a high aspect ratio also tend to form bigger
droplets resultant from a lower surface coverage, but the fibers protrude in the
continuous phase forming a strong network that is able to physically hinder droplet
coalescence [59]. As mentioned, the colloidal stability of NCC is controlled by their
surface charge resulting from the acid hydrolysis with various acids (e.g., H2SO4
or HCl). The higher the charge density the better their colloidal stability, but their
ability to efficiently stabilize emulsions is reduced. Thus, the anionic charges on
the surface of the nanocrystals control their tendency to be dispersed in water in
relation to being adsorbed at the oil–water interface and, therefore, the particle
polarity must be confined to a limited range. A surface charge density lower than
ca. 0.03 e/nm2 is ideal for the effectiveness of NCC as an emulsifier and stabilizer,
usually achieved by HCl hydrolysis. NCC with sulfate groups, resultant from the
hydrolysis with H2SO4, possess a high surface charge density (e.g., 0.123 e/nm2),
and the charges may undergo desulfation or may be screened by salt addition, to
tune their amphiphilicity [49, 61]. Nanocellulose-stabilized emulsions are generally
thermally stable, but in the presence of charges their stability against pH and ionic
strength may decrease [58, 62]. NCC are able to form stable o/w high internal phase
emulsions (HIPEs) containing volume fractions of oil as high as 0.9, at very low
NCC concentrations (< 0.1 wt.%) [61]. Hydrophobized nanocellulose has been also
explored to form w/o HIPEs [51]. Double emulsions of both o/w/o and w/o/w have
been prepared by using a combination of native and hydrophobized NCC and NFC
[63, 64]. Apart from the outstanding physical stability against coalescence, nanocel-
luloses also afford oxidative stability and lipid digestion control due to the dense
interfacial layer formed [60].

3.3 Cellulose derivatives at interfaces

Cellulose derivatives produced by etherification reactions are generally

water-soluble and surface-active. Therefore, cellulose ethers are a major class of
commercially important water-soluble polymers, from construction products,
ceramics, and paints to foods, cosmetics, and pharmaceuticals [32, 33, 65, 66].
Cellulose ethers are commonly made by reacting alkali cellulose with the appropri-
ate reagents to substitute the hydroxyl groups of the AGU monomers by either
alkyl, hydroxyalkyl or carboxyalkyl groups [66]. Methyl cellulose (MC), ethyl

6
Cellulose as a Natural Emulsifier: From Nanocelluloses to Macromolecules
DOI: http://dx.doi.org/10.5772/intechopen.99139

cellulose (EC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), and

their derivatives, are common products of those reactions. Their functionality and
solubility in water depend on the type of substituent, degree and pattern of substi-
tution, and molecular weight [33, 67]. The non-ionic cellulose ethers, such as, MC,
HPMC and EHEC and their hydrophobically modified versions, have been mostly
used to produce o/w emulsions due to their water-solubility [68–71], but EC can
be used to stabilize w/o emulsions [72]; this change-over from MC to EC illustrates
the subtle role of polarity and illustrates the applicability of Bancroft’s rule. The
emulsion stabilization due to cellulose ethers is the result of the combined effects
of: a) reduction of the interfacial tension, arising from the balance between polar
and non-polar groups; b) adsorption of thick layers, forming a physical barrier
with strong steric repulsion; and c) the viscosity increase of the continuous phase,
constraining droplet dynamics [7, 71, 73]. Cellulose derivatives often show a dual
effect, as stabilizing and emulsifying agents [73]. However, carboxymethyl cel-
lulose (CMC) which is an anionic polymer, cannot efficiently stabilize emulsions by
itself due to its highly polar character. However, it can assist emulsion stabilization
by controlling the viscosity of the continuous medium [5, 16]. In general, cellulose
ethers provide good stability against droplets aggregation due to the strong steric
repulsions between the adsorbed polymer layers of two approaching droplets, and
due to the increased viscosity of the systems. One of the main advantages of using
non-ionic polysaccharides, such as the cellulose ethers in this specific case, is their
high stability against environmental stresses, such as, pH, ionic strength, and tem-
perature. This is particularly important in food and pharmaceutical applications,
where complex environments are encountered. Cellulose ethers also provide good
oxidative stability to the core materials and delay lipid digestion of o/w emulsions,
provided that the physical barrier and thickened aqueous phase slows down the dif-
fusion of pro-oxidants and lipases [71, 74]. Lipid digestion is even further reduced
using cellulose ethers when compared to calcium-caseinate, a common food
emulsifier. Additionally, the thermo-gelling ability of cellulose ethers, in particular
HMC, makes it possible to obtain emulsions with high consistency during gastric
digestion, contributing to slow down the gastric digestion and increase fullness and
satiety perceptions [71].

3.4 Molecular and regenerated cellulose at interfaces

The behavior of molecularly dissolved cellulose at interfaces is expected to

resemble that of typical cellulose derivatives or any semiflexible amphiphilic
polymer that shows interfacial activity, i.e., the tendency to adsorb at oil–water
interfaces and reduce the free energy between the two phases. However, due to
its dissolution limitations, the properties of molecularly dissolved cellulose and
its potential in emulsions formation and stability are clearly much less explored.
Nevertheless, recent studies have confirmed the stated hypothesis. Molecular
dynamics simulations indicate that molecularly dispersed cellulose gradually
assembles at the oil–water interface eventually surrounding the oil droplet [75].
Experimentally, molecular cellulose dissolved in H3PO4 (aq.) was found to adsorb at
the oil–water interface and decrease the interfacial tension (IFT) between the two
phases (Figure 2).
The decrease in IFT is similar in magnitude to that of the non-ionic cellulose
derivatives MC and HPMC, for the same polymer concentration (0.1 wt.%) and
same type of oil (liquid paraffin) [34]. Yet, cellulose-stabilized emulsions formed
in H3PO4 (aq.) were found to be short-lived, as oil was separating from the emul-
sions and floating to the top within 24 h. However, by subsequently adding water
to the dispersions during emulsification, the properties of the emulsions changed

7
Cellulose Science and Derivatives

Figure 2.
Effect of dissolved cellulose on the interfacial tension oil-aqueous medium.

dramatically, and there was no evidence of oil separation over one year of storage
(Figure 3). This effect was attributed to a decrease in cellulose solvency in H3PO4
(aq.) by the addition of an anti-solvent (water), which promoted a greater affinity
for the oil–water interface, leading to the outstanding stability against macroscopic
phase separation of the oil.
There are two ways of using native cellulose to stabilize o/w emulsions without
the need of further modifications. One, is by following the dissolution-regeneration-
emulsification approach, resulting in Pickering emulsions of solid or soft cellulose
particles (microgels), since the oil is either dispersed in a water suspension of cel-
lulose particles or in a water suspension of cellulose microgels, respectively [76–83].

Figure 3.
Two step emulsification procedure for cellulose dissolved in phosphoric acid solvent.

8
Cellulose as a Natural Emulsifier: From Nanocelluloses to Macromolecules
DOI: http://dx.doi.org/10.5772/intechopen.99139

Another way, is to follow the dissolution-emulsification-(“in situ”)regeneration

approach, where the oil is directly dispersed in the cellulose solution, and regenera-
tion takes place at the oil–water interface (“in situ”) [34, 84]. This way, the oil drop-
lets seem to be stabilized by a “cellulose film” with a smooth appearance, contrasting
with the rough networks and particulate appearances of Pickering emulsions
(Figure 4) [7, 84]. Another fundamental difference between the two described
approaches is related to the existence of dissolved cellulose during the oil emulsi-
fication, which acts as a polymeric surfactant by decreasing the IFT, and possibly
contributing for a reduction in droplet size. Overall, the emulsions produced by both
methods display very good stability against droplet coalescence which can be referred
to the irreversible adsorption of cellulose onto the droplet surfaces [34, 78, 79, 85].
Soft cellulose microgels also impart an outstanding stability against flocculation
because of the thick viscoelastic layers formed at the interface [15]. The mechanism
behind droplet stabilization in emulsions prepared with cellulose particles is similar to
that operating for nanocelluloses as described above, i.e., a combination of Pickering
adsorption and network stabilization, often showing gel-like characteristics upon a
concentration increase of cellulose [79, 82–84].
Moreover, the resulting emulsions are remarkably stable against environmental
changes, such as, pH, ionic strength, and temperature, which makes them good
candidates for target delivering [80, 82, 86]. Cellulose regenerated particles have
also been shown to improve the physical stability of emulsions stabilized by
sodium-caseinate, a milk-protein commonly used as a food emulsifier, promoting
adsorption of the protein and thickening the continuous phase [87]. Very little has
been done regarding the stabilization of w/o emulsions since cellulose particles are
better wetted by water than oil. However, it has been suggested that the presence of
a water–oil interface when regenerating cellulose affects the conformation of the
cellulose molecules and so the way they reassemble. Therefore w/o emulsions are
possible to form, but they have poorer stability compared to o/w emulsions [78].
More recently, a “hydrophobic” cellulose microgel was developed to stabilize w/o
emulsions, by coagulating cellulose in the presence of a coagulant and sunflower

Figure 4.
Different morphologies of cellulose-stabilized emulsions. Particle-stabilized emulsions by longer NCC
(bacterial cellulose) (a), shorter NCC (b), and regenerated cellulose (dissolution-regeneration-emulsification
approach) (d). Emulsions prepared from molecular solutions of cellulose (dissolution-emulsification-”in-situ”
regeneration approach) (c and e). Reprinted (adapted) with permission from Ref. [49, 77, 80, 84].

9
Cellulose Science and Derivatives

oil [88]. The resultant microgels were more easily dispersed in oil than water, and
stable emulsions w/o emulsions were formed. The simplicity and versatility of the
dissolution-regeneration approaches open many new possibilities for the function-
alization of cellulose and its applicability in both o/w and w/o emulsions.

4. Conclusions

The list of emulsion formulations having a remarkable impact in our lives is

vast, and therefore, it is not surprising that natural molecules have been emerging
as important players to partially or completely replace the available non-sustainable
options. The future leading role of cellulose as an effective stabilizing agent is
unquestionable and opens a new era of sustainable, biocompatible, and value-
added functional materials. Surfactant-free emulsions have recently been developed
using all forms of cellulose (crystalline, fibrillated, molecular and regenerated),
providing a strong support for the vision of cellulose as an amphiphilic molecule,
capable of acting as a polymeric surfactant and a Pickering stabilizer. Structural dif-
ferences and mechanisms of emulsion stabilization between the different cellulose
forms have been presented in this chapter. In general, and given the right condi-
tions, cellulose coatings are a powerful mechanical barrier against coalescence, lipid
oxidation and lipid digestion. Non-adsorbed cellulose forms a 3D network in the
continuous phase, that constrains droplet movements and enhances kinetic stabil-
ity. The colloidal assembly of cellulose particles when liquid interfaces of notably
different polarities are present might serve as a template for the synthesis of new
functional microcapsules. The dissolution-regeneration process is highlighted as an
important approach of making cellulose-based emulsions, whose hydrophilic–lipo-
philic balance can be simply tuned by playing with solvent quality and regeneration
coagulant(s). Furthermore, the exceptional stability against environmental stresses
(pH, ionic strength and temperature) makes the cellulose regenerated coatings
potential candidates for target delivery in complex conditions.

Acknowledgements

This research was funded by the Swedish Research Council (Vetenskapsrådet),

grant number 2015-04290. Bruno Medronho acknowledges the financial support
from FCT via the projects PTDC/ASP-SIL/30619/2017, UIDB/05183/2020, and the
researcher grant IF/01005/2014. Björn Lindman acknowledges the support from
the Coimbra Chemistry Centre (CQC), funded by FCT through the Project UID/
QUI/00313/2020. The authors also acknowledge the support from Treesearch.se.

Conflict of interest

The authors declare no conflict of interest.

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Cellulose as a Natural Emulsifier: From Nanocelluloses to Macromolecules
DOI: http://dx.doi.org/10.5772/intechopen.99139

Author details

Carolina Costa1*, Bruno Medronho2, Björn Lindman3,4, Håkan Edlund1

and Magnus Norgren1

1 FSCN, Surface and Colloid Engineering, Mid Sweden University, Sundsvall,

Sweden

2 Faculty of Sciences and Technology, MED (Mediterranean Institute for

Agriculture), Environment and Development, University of Algarve, Faro, Portugal

3 Physical Chemistry, University of Lund, Lund, Sweden

4 Coimbra Chemistry Center (CQC), Department of Chemistry, University of

Coimbra, Coimbra, Portugal

*Address all correspondence to: carolina.costa@miun.se

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms
of the Creative Commons Attribution License (http://creativecommons.org/licenses/
by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,
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Cellulose Science and Derivatives

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