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\DOI{10.5802/crchim.369}
\datereceived{2024-06-13}
\daterevised{2024-10-22}
\dateaccepted{2024-11-26}
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\dateposted{2025-02-21}
\begin{document}

\begin{noXML}

%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{Materials and Energy Valorization of Biomass and Waste: The Path for Sustainability and Circular Economy Promotion}
%\def\cdr@specialtitle@french{Valorisation \'energ\'etique et mati\`ere de la biomasse et des d\'echets : la voie de la durabilit\'e et de la promotion de l'\'economie circulaire}
%\makeatother

\CDRsetmeta{articletype}{research-article}

\title{Cellulose extraction by biomass valorization of prickly pear seed waste}

\alttitle{Extraction de la cellulose par valorisation de la biomasse des d\'{e}chets de graines de figue de barbarie}

\author{\firstname{Nesrine} \lastname{Ben Ali}\CDRorcid{0009-0002-3853-174X}\IsCorresp}
\address{Research Laboratory of Process Engineering and Industrial Systems, 
National School of Engineers of Gabes, University of Gabes, St Omar Ibn El-Khattab, 6029 Gabes, Tunisia}
\email[N. Ben Ali]{nesrinee.benali@gmail.com}

\author{\firstname{Asma} \lastname{Abdedayem}\CDRorcid{0000-0002-5199-0636}}
\address{Laboratory of Water, Membranes and Environmental
Biotechnologies, Water Research and Technology Center, Technopark
Borj Cedria, PB 273, 8020, Soliman, Tunisia}

\author{\firstname{Hanen} \lastname{Nouri}\CDRorcid{0000-0003-2229-9157}}
\addressSameAs{1}{Research Laboratory of Process Engineering and Industrial Systems, 
National School of Engineers of Gabes, University of Gabes, St Omar Ibn El-Khattab, 6029 Gabes, Tunisia}

\author{\firstname{Samia} \lastname{Ben-Ali}\CDRorcid{0000-0002-9560-4821}\IsCorresp}
\addressSameAs{1}{Research Laboratory of Process Engineering and Industrial Systems, 
National School of Engineers of Gabes, University of Gabes, St Omar Ibn El-Khattab, 6029 Gabes, Tunisia}
\email[S. Ben-Ali]{samia.benali@enig.rnu.tn}

\shortrunauthors

\keywords{\kwd{Biomass valorization}\kwd{Cellulose}\kwd{Extraction}\kwd{Carbon fiber}}

\altkeywords{\kwd{Valorisation des biomasses}\kwd{Cellulose}\kwd{Extraction}\kwd{Fibre de carbone}}

\begin{abstract}
The main objective of this work was the valorization of various
biowastes to extract biocellulose for carbon fiber
synthesis as a subsequent application. The effectiveness of cellulose
extraction was investigated by two methods: maceration extraction
and Soxhlet process. The extracted cellulose was characterized
using a range of analytical techniques: thermogravimetric analysis/differential 
thermal analysis, scanning electron microscopy,
Fourier transform infrared spectroscopy (FTIR), and
energy-dispersive X-ray (EDX) analysis. The purity of extracted cellulose 
was successfully confirmed by FTIR and EDX results, which indicated the
presence of major functional groups characteristic of cellulose
structure. The cellulose extraction yield from prickly pear
seeds was 39.3\% by maceration and 23.18\% using the Soxhlet
extraction method.
\end{abstract}

\begin{altabstract}
L'objectif principal de ce travail \'{e}tait la valorisation de
diverses biomasses pour l'extraction de cellulose en vue de la
synth\`{e}se de fibres de carbone comme application ult\'{e}rieure.
L'efficacit\'{e} de l'extraction de la cellulose a \'{e}t\'{e}
\'{e}tudi\'{e}e par deux m\'{e}thodes : \og Extraction par
mac\'{e}ration \fg{} et le \og Extraction par
Soxhlet \fg{}. La cellulose extraite a \'{e}t\'{e}
caract\'{e}ris\'{e}e \`{a} l'aide d'une gamme de techniques
analytiques, notamment : la thermogravim\'{e}trie et l'analyse
thermique diff\'{e}rentielle (ATG/ATD), le microscope \'{e}lectronique
\`{a} balayage (MEB), la spectroscopie infrarouge \`{a} transform\'{e}e
de Fourier (FTIR) et l'analyse dispersive en \'{e}nergie des rayons X
(EDX). La puret\'{e} de la cellulose extraite a \'{e}t\'{e}
confirm\'{e}e avec succ\`{e}s par les r\'{e}sultats de la FTIR et de
l'EDX, qui ont indiqu\'{e} la pr\'{e}sence de groupes fonctionnels
majeurs caract\'{e}ristiques de la structure de la cellulose. Le
rendement d'extraction de la cellulose obtenu \`{a} partir des graines
de figue de Barbarie (PPS) \'{e}tait de 39,3 \% par mac\'{e}ration et
de 23,18 \% en utilisant la m\'{e}thode d'extraction Soxhlet.
\end{altabstract}

\maketitle
{\vspace*{1pc}}

\twocolumngrid

\end{noXML}

\section{Introduction}

The valorization of agricultural wastes for producing lignocellulosic
fillers (or fibers) is a promising strategy to develop green materials
with appropriate performance and high sustainability from an economic
and an ecological point of view. Biomass wastes were generally incinerated
and discarded instead of being used productively, which intensifies
environmental pollution.\ The growing environmental concerns
and stringent regulations on waste \mbox{dumping} and \mbox{emissions}
have stimulated researchers to valorize material from agriculture waste
and obtain useful industrial substances. Through chemical and
biochemical modification, the carbohydrate polymer from waste can be
treated to obtain fine chemicals that would alleviate various
socioeconomic problems~\cite{1}. Annually, 1.77--2.4 gigatons of
waste from tubers, roots, cereals, and vegetables are produced~\cite{2}.
They can be classified as lignocellulosic waste containing cellulose,
hemicellulose, and lignin. Thus, in recent years, research has focused on
the valorization of these natural and industrial wastes.\ Tunisia has a
vast potential for biomass \mbox{production} from a \mbox{variety} of
sources that can be used for the generation of bioenergy and other
purposes. According to the International Renewable Energy Agency (2021)
report, Tunisia produced approximately 6
million metric tons of biomass in 2019. This comprises 200,000 tons
from wastewater treatment, 400,000 tons from poultry droppings, 2.2
million tons from agriculture and agroindustry, 1 million tons from
olive oil production, and 2.2 million tons from household
waste~\cite{3}. Numerous organic wastes are produced by Tunisia's
agrifood industry, which presents opportunities for the production of
useful materials, the mitigation of environmental issues, and the
enhancement of resource circularity. Prickly pear seeds (PPS) from Tunisia's
agrifood sector offer a promising opportunity among these wastes. 
An often overlooked byproduct of prickly pears arises from their ability 
to be turned into carbon fibers.
This not only makes waste management more
sustainable but also makes it possible to produce materials with
high added value. Interesting characteristics like lightweight,
mechanical strength, and electrical conductivity make carbon fibers
made from leftover PPS valuable in a large range of
industrial applications~\cite{4}. Cellulose extraction represents a
significant opportunity for advancing sustainable and environmentally
friendly solutions. Because of its special properties, including
biodegradability, renewability, and exceptional mechanical strength,
cellulose has attracted a great deal of interest in recent years. These
properties make cellulose a desirable option for a variety of
applications, including paper, textiles, bioplastics, scaffolding for
biomedical procedures, and other advanced materials~\cite{5}, The
employment of cellulose for the production of carbon fibers is a
promising area of research, offering many advantages in terms of
durability and performance. Carbon fibers are highly sought-after
materials in various fields of application (automotive, aeronautics,
space, etc.)~\cite{6}. The advantages of cellulose include its
reasonable budget, durability, and higher carbon content, making it a
dominant precursor~\cite{7}. In this context, this study aims to
extract cellulose from Tunisian lignocellulosic biomass including
industrial biowaste and other waste sources for the potential
application of carbon fiber synthesis. Two different extraction
techniques were investigated: a conventional method using hot water
maceration and a non-conventional method using the Soxhlet process.\ To
assess the \mbox{effect} of the extraction method on the quality of the
extracted cellulose, the extract was finally characterized by various
techniques: scanning electron microscopy (SEM), energy-dispersive
X-ray (EDX) analysis, Fourier transform infrared spectroscopy (FTIR), 
and thermogravimetric analysis (TGA).\looseness=-1

\section{Materials and methods} \label{sec2}
\subsection{Materials} \label{sec2.1}

For cellulose extraction, a variety of biomasses were used, such as
olive stones, straws, palm petioles, sea balls (\textit{Posidonia
oceanica}), allied plants, and more specifically PPS, which were
collected from an experimental plantation of the bioenergy industry in
the Gabes region (Tunisia).\ The reagents utilized were sodium
hydroxide (NaOH) and hydrogen peroxide (H$_2$O$_2$), which were
acquired from the Laboratory of Promosciences, Tunisia.

\subsection{Methods} \label{sec2.2}

In this study, two cellulose extraction methods, maceration and
Soxhlet, were evaluated through continuous chemical treatment to
eliminate lipids, hemicellulose, lignin, and other impurities. Both
methods followed used the same steps shown in Figure~\ref{fig1}. First,
the pretreatment consisted of washing the biomass by distilled water
for 24~h at ambient temperature, sun drying, grinding, and later
storing in sealed plastic bags. Then, samples (25~g) were dewaxed using
ethanol solution (95\%) with a solid--liquid ratio of 1:10 (w/v) for
3~h at 75~{\textdegree}C to remove extractable sugars, fatty acids,
tannins, and wax. The resultant extract was gathered, dried at
60~{\textdegree}C in an oven, and finally weighed. Subsequently,
alkaline treatment was conducted to eliminate lipids, hemicellulose,
lignin, and other impurities present in the raw fiber. The chemical
treatment procedure was assessed three times: prior to treatment
(\%~extractables), following alkaline treatment (\%~lignin), and
following bleaching (\%~hemicellulose). The reaction occurred at a
solid--liquid ratio of 1:10 (w/v), employing a 6\% NaOH (w/w) solution
at 95~{\textdegree}C for 2~h with continuous stirring. The obtained
sample was washed repeatedly with distilled water until attaining
neutral pH and then dried to a constant weight in an oven at
60~{\textdegree}C for 24~h. Finally,
the extracted sample was bleached using 1:40 solid--liquid ratio (w/v)
of a mixture of{\break} 7.5\% hydrogen peroxide (v/v) and 5\% NaOH
(w/w) for 2~h at 75~{\textdegree}C with~stirring. The purified
cellulose at pH 8.4 was rinsed with distilled water and dried at
60~{\textdegree}C in an oven for 24~h. The bleaching treatment was
carried out five times under the same conditions and the samples
weighed.

\begin{figure}
\includegraphics{fig01}
{\vspace*{-.25pc}}
\caption{\label{fig1}Extraction steps of cellulose.}
{\vspace*{-.3pc}}
\end{figure}

The cellulose content from the extraction methods was
estimated by calculating the percentage of cellulose using 
Equation~(\ref{eq1})~\cite{8}:
{\begin{eqnarray}
&amp;&amp;\hspace*{-1pc} 
\%\ \mathrm{Cellulose} = 100
\nonumber\\&amp;&amp;\hspace*{-1pc}\quad 
-\, (\%\ \mathrm{hemicellulose} +
\%\ \mathrm{lignin} + \%\ \mathrm{extractive}) \label{eq1}
\quad 
\end{eqnarray}}\unskip
{\par\vspace*{-.5pc}}

\subsection{Characterization} \label{sec2.3}

The characterization of extracted cellulose was carried out by FTIR
using a Spectrum two FTIR Spectrometer. The spectrum was recorded in
transmittance mode over a range of 4000--400~cm$^{-1}$. Using a SETARAM
thermal analysis system in a dinitrogen environment, the
TGA/differential thermal analysis (TGA/DTA) method was performed 
throughout a temperature range of 30--1000~{\textdegree}C at a heating
rate of 10~{\textdegree}C${\cdot}$min$^{-1}$ and a flow rate of
20~ml/min. The weight loss and thermal properties of the samples were
computed by the associated computer program. Model Tescan
VEGA3 SBH (tungsten filament) equipped with a secondary electron
detector and Bruker Flash 630M EDS
was used to perform elemental analysis using EDX and SEM. Quantifying
the cellulose's carbon, hydrogen, and nitrogen content and examining
the biomass and cellulose morphology are the goals of these analyses.
Ascertaining the ash content of cellulose is essential to evaluate its
purity and appropriateness for different uses. The amount of ash
measures the inorganic residue that remains after burning, which was
mostly made up of minerals and other inflammable materials. The various
percentages of extractives, hemicelluloses, lignin, and ash content
were calculated using Formulas (\ref{eq2}) and~(\ref{eq3}):
{\vspace*{.15pc}}
{\begin{eqnarray}
&amp;\displaystyle 
\% = \frac{m_{i}-m_{f}}{m_{i}} \times 100 \label{eq2}
\Seqnsplit
&amp;\displaystyle 
\text{Ash content}\ (\%) = \frac{\text{Final mass of ash}}
{\text{Initial mass of sample}} \times 100\quad \label{eq3}
\end{eqnarray}}\unskip
where $m_{i}$ is the dried sample weight before extraction (g) and
$m_{f}$ is the dried sample weight after extraction~(g).

\section{Results and discussion} \label{sec3}
\subsection{Characterization of extracted cellulose} \label{sec3.1}
\subsubsection{TGA--DTA analyses} \label{sec3.1.1}

Thermograms of TGA/DTA, presented in Figure~\ref{fig2}, provide a
comparison of the thermal behavior between raw biomasses and extracted
cellulose for different materials, including palm petiole, allied
plant, olive stone, PPS, straw, and sea ball. The TGA curves show mass
loss as a function of temperature while the DTG curves depict the rate
of decomposition. 
For the raw materials, multiple phases of thermal degradation are
observed: an initial phase around 100~{\textdegree}C, corresponding to
moisture removal, followed by significant decomposition between
250~{\textdegree}C and 400~{\textdegree}C due to the breakdown of
cellulose and hemicellulose, with further degradation beyond
400~{\textdegree}C related to lignin.

\begin{figure*}
{\vspace*{.2pc}}
\includegraphics{fig02}
\caption{\label{fig2}TGA/DTA curves of biomasses and their extracted
cellulose: (a)~palm petiole, (b)~allied plant, (c)~olive stone,
(d)~prickly pear, (e)~straw, and (f)~sea ball.}
{\vspace*{.2pc}}
\end{figure*}

The DTA curve showed a slight exothermic reaction at the initial
stage around 100~{\textdegree}C due to sample dehydration. Degradation
of residual cellulose and hemicellulose was indicated by a strong
exothermic reaction between about 270~{\textdegree}C and
375~{\textdegree}C.

According to Safaei et~al.~\cite{9}, heat-induced modifications in
cellulose structure mainly involved depolymerization (starting at
310~{\textdegree}C) as a result of chain breakage at the 1,4 glycosidic
bonds, dehydration (starting at 280~{\textdegree}C), and glucose
formation. According to the literature, the maximum decomposition of
cellulose occurs at 338~{\textdegree}C~\cite{10}, which was verified by
the curves obtained. In fact, the DTG curves showed that a maximum rate
of weight loss occurred between 228~{\textdegree}C and
400~{\textdegree}C. The third stage of degradation happened between 375
and 500~{\textdegree}C, which corresponds to lignin, which was
recognized for having higher thermal stability and resistance to
degradation~\cite{11}. Thermal decomposition is normally deemed to be
finished below 500~{\textdegree}C. In addition, the residue matter,
without impurities at 1100~{\textdegree}C, of different biomasses were
determined as follows: straw, 12.5\%; petiole palm, 17.3\%; PPS, 29\%;
allied plant, 11.6\%; sea ball, 22.5\%; olive stone, 22.3\%. This
observation indicated that PPS had significant cellulosic matter
content, making it a good starting material for cellulose extraction.
Consequently, this biomass was selected for further investigation.

On the other hand, compared to the raw biomass curves, the thermal
analysis (TGA/DTA) curves for the extracted cellulose exhibited
significantly different degradation behavior. The first degradation
process of the extracted cellulose was achieved in only two
samples~\cite{12}.
The first stage involved a minor mass loss around 100~{\textdegree}C,
attributed to the evaporation of moisture. The second stage, in the
temperature range of 300--400~{\textdegree}C, is related to the
decomposition of cellulose, leading to the formation of hydrocellulose
and levoglucosan~\cite{12}.

This also confirmed the effective removal of other components such as
hemicellulose and lignin from the raw biomasses indicating the purity
of the extracted cellulose.

\subsubsection{Fourier transform infrared spectroscopy}
\label{sec3.1.2}

Figure~\ref{fig3}(a) shows the FTIR spectra of the various raw material
samples (untreated) and Figure~\ref{fig3}(b) illustrates the spectra of
prickly pear samples treated and bleached with H$_{2}$O$_{2}$/NaOH. All
spectra (Figure~\ref{fig3}a) show broadly similar peaks, indicating the
existence of the same functional groups. There exist a broad peak
around 3200--3600~cm$^{-1}$, indicating the presence of hydroxyl (OH)
groups due to carbohydrates, organic acids, and water; peaks around
2800--3000~cm$^{-1}$ corresponding to C--H bonds in hydrocarbons; a
sharp peak around 1700~cm$^{-1}$, characteristic of carbonyl groups
(C${=}$O) in organic acids and esters; and peaks around
1000--1300~cm$^{-1}$, often associated with carbohydrates. More
particularly for PPS, the two spectra in Figure~\ref{fig3}(b) show
broadly similar peaks, suggesting the presence of the same functional
groups. This also proves that multi-step treatment does not alter the
cellulose structure in PPS and that cellulose was successfully
extracted after multi-step treatment. The primary peaks indicating the
presence of cellulose are located at 3440~cm$^{-1}$ and 2950~cm$^{-1}$,
and were attributed to the asymmetric stretching vibrations --OH and
--CH, respectively, of the saturated aliphatic C--H group~\cite{13}.
The value of the peak increases with deeper processing but often
becomes sharper as it originates predominantly from the hydroxyl groups
of cellulose, indicating an increase in the amount of cellulose and the
content of --OH groups.

\begin{figure*}
\includegraphics{fig03}
\caption{\label{fig3}FTIR results of (a)~raw material and (b)~cellulose
extracted from prickly pear seeds.}
{\vspace*{.3pc}}
\end{figure*}

The peaks at 1658~cm$^{-1}$ and 1232~cm$^{-1}$ decrease as the
extraction process advances, suggesting that alkaline treatment and
bleaching are the best means of removing hemicellulose and
lignin~\cite{14}.

The stretching vibration of the lignin carbonyl group and the ketone
C${=}$O group is represented by peaks at 1515~cm$^{-1}$. The intensity of this
peak also decreased with time, suggesting that some of the lignin had
been partially removed. As this is the spectral region of 
hemicellulose and lignin fingerprints, the absence of these peaks in
the treated samples verified the total removal of hemicelluloses and
lignin~\cite{15}. The O--H and C--O stretching vibrations of the
polysaccharides present in cellulose were visible in the spectrum at
1024~cm$^{-1}$~\cite{16}. The C$_{1}$--O--C$_{4}$ bending vibration of
the $\upbeta$-glycosidic bond in cellulose was represented by the peak
at 865~cm$^{-1}$~\cite{17}. 

The presence of the cellulose group was strongly guaranteed by all
these observed peaks~\cite{15}.

\subsubsection{Chemical composition and ash content{\hfill\break}
analysis} \label{sec3.1.3}

The chemical composition and ash content of PPS during the extraction
process were determined. \mbox{Table}~\ref{tab1} presents the
significant alterations that were verified through yield computations
for all extraction steps.

\begin{table}[t!]%tab1
\caption{\label{tab1}Chemical\raisebox{.8pc}{} composition and ash
content of prickly pear seeds}
\begin{tabular}{cc}
\thead
Constituents &amp; Percentage (\%)\\
\endthead
\% Extractive &amp; 16\\
\% Lignin &amp; 22.13\\
\% Hemicellulose &amp; 22.57\\
\% Cellulose &amp; 39.3\\
Ash &amp; 0.74
\botline
\end{tabular}
\end{table}

The chemical composition of PPS was investigated to
assess its suitability to produce cellulose fibers for industrial use.
To represent the inorganic impurity in the biomass that does not burn
during the energy conversion process, an analysis of the ash content
was done. In terms of reagent costs and the time needed to evaluate the
purity and suitability of the materials, this approach has proved to be
affordable. Determining the chemical composition of the samples is a
critical step in understanding the organic components of the biomass.
Additionally, analyzing the ash content provides insight into the
amount of mineral matter present, resulting in a complete picture of
the biomass composition. 

\subsubsection{Morphological and elemental composition}
\label{sec3.1.4}

Scanning electron microscopy was used to study the morphology of PPS
pericarp cells. The results revealed that the spindle-shaped
sclerenchyma fibers were arranged in two different orientations. These
tissues usually make up secondary walls. There are also a few
single-helix spiral conducting vessels visible. As demonstrated in
Figure~\ref{fig4}, micrographs of cross-sections of Opuntia
ficus-indica PPS reveal that the seed is composed of two distinct
tissues: the pericarp (P) and the endosperm (E). The percentage of
seeds in an entire Opuntia ficus-indica prickly fruit varies from 30\%
to 40\% dry weight. This is a significant number of seeds, and about
90--95\% of an entire seed is made up of pericarp~\cite{18}.
Table~\ref{tab2} and Figure~\ref{fig5} present the elemental
composition of the biomass, comparing the raw material (PPS) with the
extracted sample.\ The results indicate significant variations in the
content of carbon (C), oxygen (O), sodium (Na), and calcium~(Ca),
underscoring the impact of the extraction process on the chemical
composition of the biomass.

\begin{figure*}
{\vspace*{-2pt}}
\includegraphics{fig04}
{\vspace*{-2pt}}
\caption{\label{fig4}SEM of prickly pear seeds: (a)~raw material and
(b)~treated samples.}
\end{figure*}

\begin{figure*}
\includegraphics{fig05}
{\vspace*{-2pt}}
\caption{\label{fig5}EDX spectra of (a)~raw material of
PPS and (b)~cellulose extracted from PPS.}
{\vspace*{-2pt}}
\end{figure*}

\begin{table}[t!]%tab2
\caption{\label{tab2}Cellulose\raisebox{.8pc}{} and biomass elementary
composition}
\fontsize{9.6}{11.2}\selectfont\tabcolsep3.5pt
\begin{tabular}{ccccc}
\thead
Samples &amp; C (\%) &amp; O (\%) &amp; Na (\%) &amp; Ca (\%)\\
\endthead
{Raw material (PPS)} &amp; 49.97 &amp; 46.15 &amp; - &amp; 3.88\\
{Extracted sample} &amp; \07.65 &amp; 28.64 &amp; 14.38 &amp; -
\botline
\end{tabular}
\end{table}

The carbon content of the raw material decreases substantially from
49.97\% to 7.65\% post-extraction. This reflects a significant removal
of organic matter, likely cellulose or lignin, which are major
components of the biomass. This decrease suggests that the extraction
process effectively removed a large proportion of unwanted organic
compounds, thereby enhancing the purity of the sample.

Additionally, the oxygen content also decreased, albeit less markedly,
from 46.15\% to 28.64\%. Sodium, absent in the raw material, appears in
the extracted sample at a notable concentration of 14.38\%. This can be
attributed to the use of sodium hydroxide (NaOH) during the alkaline
treatment, which is employed to break down lignin or hemicellulose.
Conversely, calcium, initially present at 3.88\% in the raw material,
was completely eliminated in the extracted sample. This suggests
effective demineralization, with the removal of compounds such as
calcium carbonate. The resultant fiber's EDX analysis reveals notable
peaks for oxygen and carbon, pointing to the presence of a
lignocellulosic biomass structure. It also shows that sodium is present
in the cellulose that was extracted from PPS, most likely because of
cations being drawn to negatively charged hydroxide ions during the
bleaching process~\cite{19}. The presence of gold is explained by the
metallic coating that was used to prepare the samples. Most of the
contaminants were eliminated following the bleaching treatment,
indicating that the dewaxing, alkalinization, and bleaching processes
are successful in yielding very pure cellulose with little to no
residual contaminants. The outer layers of cellulose fibers, which
contribute to the protection of cellulose, are composed of
hemicellulose, lignin, pectin, and wax. As a result, untreated
lignocellulose generally exhibits a dense structure.\ As shown in
Figure~\ref{fig3}(a), the waxy and lipidic substances present in PPS,
even in the absence of chemical treatment, contribute to the smoothness
and density of the{\break} fiber surface~\cite{15}.

Figure~\ref{fig3}(b) illustrates that after the dewaxing, alkalinization,
and bleaching treatment with H$_{2}$O$_{2}$/{\ubreak}NaOH on prickly
pear, some waxy and lipidic substances were removed. The dense and
smooth structure of the cellulose surface was disrupted, resulting in
an irregular surface. Hemicellulose, lignin, and pectin, which form the
biomass coating, began to break down. After the alkaline treatment,
part of the hemicellulose disappeared and the fiber surface became
porous and rough. Strongly interwoven fiber bundles can be observed.
The presence of lignin is indicated by the fiber bundles. There are van
der Waals interactions, hydrogen bonds, and O--H covalent bonds between
lignin and cellulose.

Alkaline hydrogen peroxide can act on lignin by penetrating
lignocellulose, leading to the removal of hemicellulose, the formation
of pores, and the complete breakdown of the biomass coating. The
physical barrier of lignin was removed after the alkaline hydrogen
peroxide bleaching treatment, resulting in a more uneven and rough
fiber surface, a more visible pore structure, and a full exposure of
the fiber's internal structure~\cite{17}.

\begin{figure}
\includegraphics{fig06}
\caption{\label{fig6}Yields of cellulose from prickly pear seeds after
extraction with maceration and Soxhlet.}
\end{figure}

\subsection{Cellulose extraction using different methods}
\label{sec3.2}

The extraction of cellulose from PPS was evaluated using maceration and
the Soxhlet method. The extraction yields are summarized in
Figure~\ref{fig6}. Both techniques provided significant extraction
rates. The maceration technique presented a higher extraction yield
equal to 39.3\% compared to 23.14\% obtained by the Soxhlet method.
Maceration improves extraction kinetics because it occurs at a slightly
higher temperature than Soxhlet extraction. Additionally, better
external mass transfer between the solvent and the biomass might be the
result of the direct contact between the two materials made possible by
\mbox{maceration}~\cite{20}.

The results of this study highlighted the importance of selecting the
most appropriate technique for cellulose extraction as well as the
potential for optimizing the extraction process to improve yields.
Additionally, the findings underscored the significance of choosing the
best method for maximizing cellulose extraction yields.

\section{Conclusion} \label{sec4}

An environmentally friendly extraction technique was used in this study
to extract cellulose from Tunisian
industrial waste and other biological wastes such as PPS. Without the use of
chlorine or hard acid, extraction was effectively completed through a
cooperative chemical treatment of dewaxing (ethanol), alkalinization (NaOH),
and bleaching (H$_2$O$_2$). Various characterization analyses were
employed for the identification of extracted cellulose. The TGA analysis
emphasized the stability of cellulose thermal properties and the
composition of lignin and hemicellulose. The FTIR results verified the
cellulose structure in relation to the removal of a significant amount
of hemicellulose and lignin throughout the chemical treatments. The EDX
analysis of crude cellulose and cellulose extracted from PPS proved the
successful extraction of cellulose using H$_2$O$_2$/NaOH with a yield of
39.3\% by maceration and 23.14\% by the Soxhlet method. The results of this
study indicated that PPS represented a good source of high-quality
cellulose and an effective means to produce large amounts of cellulose with
superior thermal properties. Thus, the cellulose extracted from PPS
exhibits a high potential for various sustainable applications.\ 
Because the extracted cellulose is exceptionally strong and light, it is
a good choice for reinforcing composite materials used in 
aerospace, automotive, shipbuilding, and other industries requiring
high-performance structural materials. These crystalline
{nanomaterials} can be utilized to \mbox{produce} \mbox{carbon} fibers used as
reinforcement and energy storage elements as in this work.

\section*{Declaration of interests}

The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

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