ORIGINAL PAPER

Synthesis of Porous Emulsion-Templated Monoliths Usinga Low-Energy Emulsification Batch Mixer

Claire Forgacz • Sylvain Caubet • Yves Le Guer •

Bruno Grassl • Kamal El Omari • Marc Birot •

Herve Deleuze

� Springer Science+Business Media New York 2013

Abstract Emulsion-templated porous monoliths based on

castor oil-in-black liquor emulsions have been prepared

using a low-energy emulsification technique. Lignins from

black liquor polymerize in the continuous phase of the high

internal phase emulsion to obtain highly microcellular

materials with interconnected open porous structures. A

two-step emulsification operating mode was developed in

order to increase the maximum value of the castor-oil

dispersed volume fraction obtained with the one-step

emulsification mode (limited to 53 % of the total emulsion

volume due to the very high viscosities of the fluids). A

rheological study of the black liquor and of the prepared

Medium Internal Phase Emulsions, have been conducted.

Depending on the emulsification operating mode used, the

morphology of the porous monoliths will differ. A rather

low mean droplet size (about 6 lm) is obtained with the

one-step mode, the two-step technique leads to a broader

void size distribution and a further increase of added castor

oil (up to 69 %) do not favor the homogeneity of the

material.

Keywords Kraft black liquor � Lignins � Low-energy

emulsification � Rheological properties � Porous

morphologies

Introduction

Lignin is the second most abundant, renewable macro-

molecule on earth after cellulose. It is found as a cell wall

component in trees and other vascular plants, accounting

for between 15 and 40 % of the dry biomass matter in these

plants. Lignin may be described as a random, amorphous,

complex polyphenolic network [1]. Hydroxyl groups and

free positions on the aromatic ring mainly determine its

reactivity and constitute the reactive sites to be exploited in

macromolecular chemistry. In plants, lignin forms a tridi-

mensional network covalently bonded with cellulose and

hemicellulose and is not directly accessible without major

chemical modifications of its native structure [2]. The main

source of cheap, separated lignin comes from the different

processes employed in the pulp and paper industry to

obtain cellulose [3]. The so-called Kraft process, involving

aqueous solutions of sodium hydroxide and sodium sulfite

to extract cellulose by dissolution of lignin binding the

cellulose fibers together in woody matrix, represents

the major part of the industrial plants presently in use in the

world [4]. The degraded lignin biopolymer thus solubilized

contributes to the dark brown pollution load of the

so-called black liquors [5]. The products coming out of a

Kraft digester are the expected cellulose pulp and the black

liquor considered as a waste. The black liquor chemical

composition depends on the type of raw material pro-

cessed, i.e. softwoods (such as pine), hardwoods (such as

eucalyptus) or fibrous plants (such as bamboo), as well as

on the operational conditions of the pulping stage [6].

C. Forgacz � M. Birot � H. Deleuze (&)

Institut des Sciences Moleculaires, University of Bordeaux,

CNRS-UMR 5255, 351 cours de la Liberation, 33405 Talence,

France

e-mail: h.deleuze@ism.u-bordeaux1.fr

S. Caubet � B. Grassl

IPREM Equipe de Physique et Chimie des Polymeres, Universite

de Pau et des Pays de l’Adour (UPPA), CNRS UMR 5254,

Helioparc, 2 avenue P. Angot, 64053 Pau Cedex 09, France

Y. Le Guer � K. E. Omari

Laboratoire des Sciences de l’Ingenieur Appliquees a la

Mecanique et au genie Electrique (SIAME), Universite de Pau et

des Pays de l’Adour (UPPA), Federation IPRA 2952 CNRS, Bat.

D’Alembert, Rue Jules Ferry, BP 7511, 64075 Pau, France

123

J Polym Environ

DOI 10.1007/s10924-013-0575-1

During the pulping operation, the lignin is fragmented and the

carbohydrates are dissolved and converted into acids of low

molar mass. However, whatever the raw materials and pulping

operational conditions used, black liquor can be considered as

a complex aqueous solution, containing organic materials from

wood or fibrous plants (lignin, polysaccharides and resinous

compounds of low molar mass) and inorganic compounds

(mainly soluble salt ions). This very important amount of

biomass waste, more than 107 tons per year in the European

Union alone, is now merely used as in-house low-grade fuel

[7]. For doing so, two main processes are presently in use. At

most chemical pulp mills today, the black liquor is concen-

trated to a solution of about 80 % solids, and then burned in a

recovery boiler. Steam from the boiler is used to run the pulp

mill. The steam may also be expanded through a steam turbine

before being used at the mill, resulting in some electricity

generation. In addition to energy generation, a critical task of

the recovery boiler is to begin the process of recovering the

pulping chemicals for re-use in pulp production [6]. Black

liquor gasification is an emerging commercial technology.

This technology removes the biomass materials from the black

liquor by gasifying them in a high temperature chamber. The

gasification process converts the complex hydrocarbons mix-

ture into simpler gaseous molecules, primarily hydrogen,

carbon monoxide, carbon dioxide, and methane [8]. The

inorganic pulping chemicals in the black liquor are recovered

for re-use in pulping. For black liquor gasification integrated

with combine cycle electricity generation, the removal of

sulfur (mainly under the form of H2S formed during the gasi-

fication process), from the gasification gas is needed for liquor

recovery and gas turbine protection [9]. In spite of these effi-

cient valorization processes, black liquors still represent a

valuable source of renewable macromolecules for higher value

applications.

After being solubilized in alkali solution by the breakage

of native infinite lignocellulosic network, the damaged

lignin from black liquor must be crosslinked in order to

regenerate a strong, insoluble network. Phenolic molecules

that possess unsubstituted aromatic positions can react at

these positions with formaldehyde and form a network with

trifunctional junctions. Therefore, the most studied appli-

cation of isolated lignin is to replace, at least in part, phenol

in phenol/formaldehyde resins and others thermoset poly-

mers [10]. Radical copolymerizations of black liquors with

poly(vinyl alcohol) (PVA) and polyacrylamide (PAAm)

have recently being reported for the preparation of hydro-

gels [11]. Epichlorohydrin is another potentially useful

crosslinking agent employed in the synthesis of lignin-

epoxy, a well-known compound used, in particular, in the

fabrication of printed circuit boards [12]. Epichlorohydrin

has been recently used for the preparation of ion

exchangers from different black liquors lignins [13]. Fur-

thermore, epichlorohydrin can be seen, in some way, as a

future renewable chemical being produced from glycerol

using the newly developed Epicerol process [14].

Emulsion templating is a simple and versatile method to

prepare highly interconnected microcellular materials (void

size range 2–100 lm, interconnections diameter 0.5–2 lm)

by polymerizing the continuous phase of a High Internal

Phase Emulsion (HIPE), a HIPE being generally defined as

an emulsion having an internal phase ratio higher than 74 %

(for a recent review, see [15]). The obtained materials have

been called polyHIPEs by Unilever researchers [16]. The

historic polyHIPE preparation involves the formation of a

stable, water-in-oil concentrated emulsion using hydropho-

bic monomers as part of the continuous phase (most gener-

ally a mixture of styrene and divinylbenzene with,

optionally, the addition of a functionalized styrene such as

4-vinylbenzyl chloride) and an aqueous phase as the dis-

persed phase. A great deal of work has been devoted to the

study of this particular system. The main topics studied have

been the good control of the porous morphology (voids and

interconnecting windows size dispersion) [17–22] and

attempts to increase the mechanical strength that, in the

native formulation of the materials, is usually considered as

insufficient for practical applications [23–26]. Much less

work has been published on the synthesis of polyHIPE based

on hydrophilic (i.e. water-soluble) monomers emulsified by

a hydrocarbon [27–32] Emulsions less concentrated than

74 % have been called Medium Internal Phase Emulsion

(MIPEs) and gives access to polyMIPEs materials [33].

To disperse a fluid into another immiscible fluid, some

mechanical energy is applied, for example shear, together

with a surfactant to produce a stable dispersion. The two

fluids, the surfactant, and the process conditions (design of

the mixer, mixing rate, and time) all have a critical effect

on the properties of the final emulsion [34].

HIPEs are generally prepared by adding slowly the

dispersed phase (commonly an aqueous solution) into the

stirred organic continuous phase using general purpose

laboratory glassware. This approach is hardly susceptible

to produce monodisperse HIPEs. Surprisingly, almost no

attempt has been reported so far to improve the emulsifi-

cation conditions used in polyHIPE materials preparation

[35]. The droplets size distribution of a HIPE depends on

several factors such as the process, the surfactant, the water

to oil ratio, the type of oil (vegetable, synthetic, bitumen,

etc.), and other formulation and physical parameters used

for the mixing. Typically, the droplets diameter can vary

from one to hundreds of micrometers.

Oil-in-Water (O/W) HIPEs can be prepared with com-

mercially available equipments, for example coaxial mixers

[36], colloid mills [37], high-pressure homogenizers [38], or

static mixers [39]. The production of such emulsions is also

possible by the use of a complex thermodynamic mechanism

based on the phase inversion phenomenon [40].

J Polym Environ

123

We have recently presented a new type of batch mixer

that, contrary to the aforementioned equipment, uses a very

simple geometry (with cylindrical rods and a tank) and that

can be easily extended to a continuous process. This mixer

uses laminar flow with rather moderate rotational speed

that makes it suitable for emulsification of highly viscous

fluids [41].

In the present work, we investigated the use of this low-

energy emulsification device for the preparation of castor

oil-in-black liquor MIPEs in order to prepare polyMIPEs

materials.

Experimental

Materials

The as-received Kraft black liquor comes as a thick, black

liquid (Smurfit Kappa Cellulose du Pin Kraft paper mill,

Facture, France). Its main physico-chemical properties are:

pH = 14 (5 % diluted solution); density q = 1.3 g cm-3;

dry matter amount = 50 wt%. Purified, colorless castor oil,

Cremophor EL and epichlorohydrin were obtained from

Sigma-Aldrich and were used as received. Phenolic group

content (0.5 mmol g-1) and total hydroxyl group content

(0.8 mmol g-1) of black liquor were determined according

to a published procedure [42].

Formulation of Stable Castor Oil-in-Black Liquor

MIPE

Black liquor being an alkaline aqueous solution, the dis-

persed phase of the O/W concentrated emulsion must be a

hydrophobic fluid. In order to avoid the use of organic

solvents, we opted for castor oil, a vegetable oil mainly

constituted of triglyceric esters of ricinoleic acid, a C18-

hydroxylated unsaturated fat acid. This oil cumulates the

advantages to be soluble in ethanol, which will simplify its

extraction from the final monoliths and to be more viscous

and more dense than others common vegetable oils

(g = 1.0 Pa s at 20 �C, q = 0.955 g cm-3). The chosen

surfactant was Cremophor EL, a polyoxyethylene glycerol

triricinoleate (35) derived from castor oil (HLB = 12–14)

[43]. The amount of surfactant used was either 4 or 8 wt%

of the continuous phase and the amount of epichlorohydrin

was set at 10 wt% of the black liquor content.

Emulsions Preparation

The experimental setup used to produce the HIPEs was a

Two-Rod Mixer (TRM) batch device (Fig. 1), whose char-

acteristics have been reported elsewhere [41]. The geomet-

rical parameters were: tank diameter (d0) = 150 mm, large

rod radius (r) = 50 mm, small rod diameter (d00) = 15 mm,

rod–tank gap (e) = 3 mm, rod–rod gap (e0) = 2 mm, and

the angular position of the small rod (h) = 30�. These

parameters remained constant for all the experiments con-

sidered in this study.

Emulsions were prepared at room temperature

(20 ± 1 �C), at no point during the experiments did the

temperature exceed 22 �C.

One-Step Emulsification (Series I)

A mixture of black liquor (94 mL), epichlorohydrin

(7.2 g), surfactant (2.9 or 5.8 g) and castor oil (required

amount for / = 0.53, / represents the weight fraction of

oil inserted in the emulsion) was placed into the TRM

batch device. Then, the large rod was rotated at a constant

rotational speed of 90 rpm. The emulsification duration

was varied (from 15, 30 to 80 min).

Two-Step Emulsification (Series II)

The first step was the same as for series I, but after 80 min, an

additional amount of castor oil was slowly added using a

syringe pump (addition rate 30 mL h-1) in order to increase

the amount of castor oil incorporated into the black liquor

emulsions. For this second step, the rod rotational speed was

fixed at 120 rpm. The emulsification duration of the second

step was varied (from 120 to 200 min).

Characterization of the Fluids and Black Liquor

Emulsions

The rheological properties of the two phases (castor oil and

black liquor) and of black liquor emulsions were measured with

a Malvern Bohlin C-VOR 150 rheometer in controlled stress

mode with a cone-plate configuration. Temperature was con-

trolled with a Peltier plate system and was set at 20.0 ± 0.1 �C.

For the study of viscoelastic properties of the black liquor

emulsions, dynamic frequency sweep tests were recorded in

stress mode at 40 Pa, which was kept constant over the fre-

quency range of 10-4–102 Hz at 20 �C. All the experiments

were performed in the linear viscoelastic regime for which the

storage modulus G0 (i.e. elastic response) and loss modulus G00

(i.e. viscous behavior) are independent of the strain amplitude.

Preparation of the Monoliths

The obtained thick black emulsions were placed in tightly

closed PTFE cylindrical moulds of different sizes and

crosslinked for 48 h at 60 �C in an oven. The resulting

monoliths were extracted by refluxing with ethanol (24 h)

in a Soxhlet apparatus and dried in a vacuum oven at room

temperature to constant weight.

J Polym Environ

123

Characterization of the Monoliths

Porosity Determination

The porosity and the connection size distribution of each

sample were determined by mercury intrusion porosimetry

using a Micromeritics Autopore IV 9500 porosimeter. The

reported average connection size is the maximum of the

pore size distribution of each sample.

Skeletal Density

The skeletal density qs of the materials was determined

using a Micromeritics Accupyc 1330 helium pycnometer.

An average value of qs = 1.55 ± 0.05 g cm-3 was found

for all samples prepared.

Electron Microscopy Investigations

The morphology of the monoliths was observed by scanning

electron microscopy (SEM) in a Hitachi TM-1000 micro-

scope. Micrographs were taken at several different magnifi-

cations between 9500 and 910,000. Pieces of polyHIPEs

(section of about 0.5 cm2) cut from the corresponding

monoliths were mounted on a carbon tab, which ensured a

good conductivity. A thin layer of gold was sputtered on the

polyHIPE fragment prior to analysis. Two-dimensional (2D)

circular cross sections cell diameter was estimated for samples

from SEM micrographs after image processing with ImageJ

freeware (NIH, USA). The experimental data were collected

by manual measurements of diameters from a population of at

least 100 cells. Several methods have been devised to find a

simple factor to convert the mean size of such 2D size dis-

tribution to the actual 3D mean size of the spheres without a

consensus. A standard assumption in the stereology literature

assumes that the distance between the centre of a given sphere

and a random plane that intersects it, has a uniform distribution

on [–x, x], where x is the radius of the sphere [44]. An

approximate solution from this entirely theoretical approach

leads to the result that the ratio of the mean diameter of a set of

spheres (d3D) to that of its 2D intercept (d2D) is: d3D/d2D = 4/

p & 1.27, irrespective of the particular distribution of the 3D

sizes [45]. We will use this correction factor in this work to

estimate the average corrected diameters dm. Therefore, dm

was calculated from the following relations: dm = 1.27 Rnidi/

Rni, where ni is the number of droplets of diameter di.

Results and Discussion

Black Liquor Rheology

Kraft black liquor is a complex aqueous solution that

shows a rheological shear-thinning behavior (i.e. the black

Fig. 1 a Photograph of the two-rod mixer (TRM) batch device b schematic of the TRM batch with the dimensions of the elements

Fig. 2 Castor oil viscosity (round symbols) and black liquor apparent

viscosity (square symbols) at 20 �C as function of the shear rate

J Polym Environ

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liquor apparent viscosity follows a power-law relation with

the shear rate g ¼ 1:41 _c�0:1 Pa.s (Fig. 2).This effect is due

to the detangling of entangled lignin macromolecular

chains at high shear rates [5]. As the apparent viscosity of

the black liquor and the viscosity of the castor oil are very

close in the studied range of shear rate, the emulsification

process will considerably be helped (see Fig. 2).

Black Liquor Crosslinking

We decided, in this work, to use epichlorohydrin as sole

crosslinking molecule. Scheme 1 represents the crosslinking

reaction of lignin with epichlorohydrin. In a previous study

[46], we have established that to obtain the generation of a

satisfactory lignin network, the important parameters to

adjust are: (1) a lignin concentration in the alkali solution no

lower than 40 wt% in order to favor the crosslinking reaction

and, (2) a rather high alkali concentration to ensure the dis-

solution of lignin by generation of a large amount of phenoxy

ions, both conditions being fully completed with the 50 wt%

black liquor used in this work.

Black Liquor Emulsification and Subsequent Monoliths

Preparation

Using the Two-Rod Mixer in its one-step operating mode, the

maximum dispersed phase weight fraction was found limited

to / = 0.53, due to excessive viscosity. An inversion of the

emulsion was observed above this critical oil fraction [47].

Scheme 1 Crosslinking of

Kraft lignin with

epichlorohydrin

Fig. 3 Loss modulus G00 (empty symbols) and storage modulus G0

(filled symbols) as function of the frequency for the black liquor

emulsion (/disp = 0.69). The two-step emulsification mode is used:

sample M280II8 (with a stirring time of 80 min at 90 rpm for the first

step followed by a stirring time of 200 min at 120 rpm for the second

step). The stress applied in the linear domain is 40 Pa. The

temperature during the tests was maintained at 20 �C

Fig. 4 Apparent viscosity as function of the shear rate for the black

liquor emulsion (/disp = 0.69). The same emulsion as that of Fig. 3 is

considered. The black curve represents a power-law fitting for the

shear-thinning behavior. The temperature during the tests was

maintained at 20 �C

J Polym Environ

123

Therefore, a two-step operating mode was developed in

order to increase this value. The first step was the same as

for the one-step operating mode, but after its completion,

an extra amount of castor oil was slowly added using a

syringe pump.

Black Liquor Emulsion Rheology

The linear viscoelastic response of the black liquor emul-

sion is illustrated in Fig. 3. The emulsion is produced using

the two-step emulsification mode. A stirring time of 80 min

at 90 rpm is applied for the first step followed by stirring

time of 200 min at 120 rpm for the second step. Over a

large frequency range (10-4–102 Hz), the storage shear

modulus G0 is a weak function of the frequency and the loss

modulus G00 is always lower than G0 with a maximum

difference of one order of magnitude. The values of G0 and

G00 for the black liquor emulsion (/disp = 0.69) are two

orders of magnitude higher than those obtained for a more

concentrated castor oil-in-water emulsion [41]. This

observed behavior explains the great difficulty to undertake

the emulsification with high dispersed volume fraction of

castor oil in black liquor. It is mainly due to the organic and

inorganic contents of the black liquor that strongly interact

with the oil droplet surfaces and then reduce the mobility of

the emulsion.

The black liquor emulsion rheological shear-thinning

behavior is well demonstrated in Fig. 4 for which a power-

law behavior was established. The apparent viscosity of the

black liquor emulsion is very high in comparison to the

viscosity of the black liquor (see Fig. 2), it decreases by 3

orders of magnitude over the covered range of shear rate

(10-2–101 Hz). It is clearly seen that high shear regions are

needed in the emulsification process in order to avoid an

excessive viscosity during the formation of the black liquor

MIPEs and to facilitate the incorporation of more castor oil

inside.

Monoliths Characterization

The different samples are codified as follows: M is for

monolith, the first number is the mixing time in minutes,

the second letter indicates the formulation used: I for the

one-step emulsification (series I), II for the two-step

approach (series II). The second number indicates the

amount of surfactant used (in percent of the continuous

phase). For example, M280II8 is a monolith prepared using

the series II emulsification procedure with a mixing time of

280 (80 ? 200) min, and 8 wt% of surfactant.

The resulting MIPEs were put into PTFE molds and

heated at 60 �C for 48 h to achieve crosslinking. After

solvent extraction and drying, self-standing brown cylin-

drical monoliths were obtained in every case (Fig. 5).

Experimental porosity (/exp), values of the different

materials were estimated from mercury intrusion porosi-

metry data and are reported in Table 1. /disp is the dis-

persed/continuous phase volume ratio. The total porosity of

the material, /total, can be estimated assuming the complete

removal of all the non-polymerizable components of the

emulsion (dispersed phase, water and surfactant) and in the

absence of any shrinking of the monolith during washing

and drying. /total and /disp were calculated with the

assumption that all the constituents of the emulsion had a

density equal to that of water. Considering the black liquor

used contains about 50 wt% of water, the maximum value

for /total can be estimated to about 0.76 (series I) or 0.83

(series II).Fig. 5 Emulsion-based black liquor monoliths

Table 1 Porosity characteristics of black liquor monoliths

M15I8 M30I8 M80I8 M200II8 M280II8 M200II4

/disp 0.53 0.53 0.53 0.62 0.69 0.64

/expa 0.68 ± 0.03 0.67 ± 0.02 0.74 ± 0.02 0.72 ± 0.01 0.76 ± 0.01 0.69 ± 0.03

Average connection size (lm)b 0.6 ± 0.1 0.60 ± 0.03 0.80 ± 0.04 1.00 ± 0.08 3.8 ± 0.4 0.8 ± 0.1

dm (lm) 12.4 ± 0.5 14.5 ± 0.5 6.6 ± 0.3 9.9 ± 0.6 33 ± 2 18 ± 2

Specific surface area (m2 g-1)b 11 ± 3 8 ± 1 9 ± 1 7 ± 1 5 ± 1 8 ± 1

a Experimental porosity by mercury intrusion porosimetryb Estimated by mercury porosimetry

J Polym Environ

123

Samples prepared with the one-step emulsification

techniques (series I samples) present a similar experimental

porosity /exp closer to the estimated /total value (0.76) than

to the initial / value (0.53). This behavior suggests a low

shrinkage for the monoliths, but mainly indicates a poro-

genic behavior of the water present in the dispersed phase,

leading to the creation of some additional porosity in the

material walls [13, 14].

Supplementary slow addition of dispersed phase (series

II samples) allowed to reach a somewhat higher insertion

value (/disp = 0.69), leading to a low increase of the

experimental porosity.

The morphology of the different samples were observed

using SEM (Fig. 6). Size and size distribution of the voids

have been estimated by image analysis of the SEM

micrographs collected for each sample (Table 1).

Fig. 6 SEM micrographs of samples M15I8 (a); M30I8 (b); M80I8 (c); M200II8 (d); M280II8 (e); M280II4 (f)

J Polym Environ

123

During the one-step emulsification, the droplet size

decreases slowly with the mixing time (M15I8, M30I8 and

M80I8). Thus, it is possible to obtain materials with a

rather low mean droplet size (about 6 lm).

The two-step technique leads to a broader void size

distribution. The amount of surfactant employed appears to

have a low impact on the morphology of the material

(compare M200II4 and M200II8). A further increase of

added castor oil seems to be detrimental to the homoge-

neity of the material, probably due to some destabilization

of the native emulsion.

The average void diameter estimated for M280II8 is

significantly larger than that of M200II8, with a broader

distribution. M280II8 sample comes from an emulsion

having a dispersed oil fraction inserted in the black liquor

phase significantly higher than that of M200II8. For these

high dispersed oil ratio fractions, the viscosity of the

emulsion increases rapidly. Thus, we can postulate that the

TRM system used, with its relatively low rotational speed

(120 rpm), does not produce enough shear efficiency as for

less viscous emulsions. Therefore, the droplets added in the

second step of emulsification have relatively larger

diameters.

Average connections sizes of the different materials

were estimated from mercury intrusion porosimetry data

and are reported in Table 1. The reported average con-

nections size is the maximum of the pore size distribution

of each sample. All samples present rather similar average

connections sizes values (between 0.6 and 1.0 lm),

excepted in the case of M280II8 sample showing an

average connections size significantly higher (3.8 lm). In

that case again, this broadening is probably due to some

destabilization of the native emulsion.

Conclusions

We have used an original two-rod mixer batch process for

the preparation of emulsion-derived materials starting from

highly viscous phases.

In the first method used to create the Medium Internal

Phase Emulsions (MIPEs), all the emulsion components

are placed in the tank before rod activation. Therefore, the

castor oil-in-black liquor MIPE is made in situ without any

intervention, contrary to classical batch method used to

produce HIPEs where the internal phase is added slowly.

However, in that case the dispersed phase weight ratio is

limited to 53 % of the total emulsion volume. Combination

of this technique with a slow addition of supplementary

castor oil allows increasing slightly this value to 69 %. In

all cases, the apparent viscosities of the black liquor

emulsions are very high and show a shear-thinning

behavior that indicates that high shear is necessary during

the laminar emulsification process to reduce the viscosity

of the emulsion and to increase the volume of oil incor-

porated in the black liquor. The first method generates

highly solid porous materials with a relatively low mean

droplet size (until 6 lm) and average connection size

around the micrometer. Applications of this process of

synthesis of porous emulsion-templated monoliths are

envisaged for the development of building materials for

thermal insulation and/or sound absorption.

Acknowledgments This work was supported by two Graduate

Fellowships from the Region Aquitaine (C.F.), and Communaute

d’Agglomeration Pau-Pyrenees (CDAPP), (S.C.).

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