Thermogravimetric analysis during the decomposition of cotton fabrics in an inert and air environment
ABSTRACT The thermal degradation of samples of used cotton fabrics has been investigated using thermogravimetric analysis (TGA) between room temperature and 700 °C. Experiments were carried out with about 5 mg of sample in three different atmospheres: helium, 20% oxygen in helium and 10% oxygen in helium. Three different heating rates were used at each atmosphere condition. A kinetic model for the decomposition of used cotton fabrics explaining the behavior of all the runs performed has been proposed and tested. For the pyrolysis of the cotton, the model comprises two parallel reactions. For the combustion process, one competitive reaction was added to each parallel reaction of the pyrolysis model and four combustion reactions of the different solid fractions to obtain volatiles. One single set of parameters can explain all the experiments (pyrolysis, oxidative pyrolysis and combustion) at the three different heating rates used.
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ABSTRACT: Hierarchical, titania-coated, nanofibrous, carbon hybrid materials were fabricated by employing natural cellulosic substances (commercial filter paper) as a scaffold and carbon precursor. Ultrathin titania films were firstly deposited by means of a surface sol-gel process to coat each nanofiber in the filter paper, and successive calcination treatment under nitrogen atmosphere yielded the titania-carbon composite possessing the hierarchical morphologies and structures of the initial paper. The ultrathin titania coating hindered the coalescence effect of the carbon species that formed during the carbonization process of cellulose, and the original cellulose nanofibers were converted into porous carbon nanofibers (diameters from tens to hundreds of nanometers, with 3-6 nm pores) that were coated with uniform anatase titania thin films (thickness approximately 12 nm, composed of anatase nanocrystals with sizes of approximately 4.5 nm). This titania-coated, nanofibrous, carbon material possesses a specific surface area of 404 m(2) g(-1), which is two orders of magnitude higher than the titania-cellulose hybrid prepared by atomic layer deposition of titania on the cellulose fibers of filter paper. The photocatalytic activity of the titania-carbon composite was evaluated by the improved photodegradation efficiency of different dyes in aqueous solutions under high-pressure, fluorescent mercury-lamp irradiation, as well as the effective photoreduction performance of silver cations to silver nanoparticles with ultraviolet irradiation.Chemistry 07/2010; 16(26):7730-40. · 5.93 Impact Factor
Article: 145 A New High Flux Polysulfone Dialyzer with Waved Fibers Possessing Larger Pores Packed in Lower Fiber Density (Aps-Ea) Is Superior in Eliminating Low Molecular-Weight Proteins as Well as Small Toxins in Comparison to a Conventional Polysulfone Dialyzer with Straight Fibers Possessing Conventional Pores in Popular Fiber Density (Aps-El)American Journal of Kidney Diseases - AMER J KIDNEY DIS. 01/2011; 57(4).
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ABSTRACT: In our previous research (Liu et al., J Anal Appl Pyrol 63:303–325, 2002), the pseudo bi-component separated-stage model (PBSM) was suggested for the kinetic analysis on the decomposition of lignocellulosic materials in air at relatively lower heating rates. As a continuing work, this paper is intended to investigate the applicability of PBSM at different heating rates by experimental analyses. Decomposition of oil tea wood has been studied by means of non-isothermal thermogravimetric analysis in air atmosphere at 10–25 K min−1 heating rates. A two-step parallel reaction kinetic model is used to optimize the kinetic parameters of these materials in air. Meanwhile, an improved PBSM is developed to describe the thermal degradation process of oil tea wood. Furthermore, a comparison between the kinetic results of parallel model and PBSM reveals realistic applicability of PBSM. It is concluded that the PBSM has relatively high accuracy for the first decomposition step in the lower temperature range, while fails to predict the thermal decomposition behavior in the char oxidative process which occurs in the higher temperature range.Journal of Thermal Analysis and Calorimetry 01/2011; 104(3):983-990. · 1.98 Impact Factor
Thermogravimetric analysis during the decomposition of
cotton fabrics in an inert and air environment
Julia Molto ´*, Rafael Font, Juan A. Conesa, Ignacio Martı ´n-Gullo ´n
Chemical Engineering Department, University of Alicante, P.O. Box 99, E-03080 Alicante, Spain
Received 29 November 2004; accepted 4 September 2005
The thermal degradation of samples of used cotton fabrics has been investigated using thermogravimetric analysis (TGA) between room
temperature and 700 8C. Experiments were carried out with about 5 mg of sample in three different atmospheres: helium, 20% oxygen in helium
and 10% oxygen in helium. Three different heating rates were used at each atmosphere condition. A kinetic model for the decomposition of used
cotton fabrics explaining the behavior of all the runs performed has been proposed and tested. For the pyrolysis of the cotton, the model comprises
two parallel reactions. For the combustion process, one competitive reaction was added to each parallel reaction of the pyrolysis model and four
combustion reactions of the different solid fractions to obtain volatiles. One single set of parameters can explain all the experiments (pyrolysis,
oxidative pyrolysis and combustion) at the three different heating rates used.
# 2005 Published by Elsevier B.V.
Keywords: Pyrolysis; Combustion; Cotton fabrics; Kinetics; Thermogravimetry
The growing interest in renewable energies is accompanied
by intensified research and development of technical processes
for the thermal conversion of biomass and wastes. Used cotton
fabrics could be used as biomass, and in this way, offer a valid
alternative to disposal in landfills. Although cotton fabrics are
usually recycled in other ways, thermal decomposition only of
the wastes is interesting for some industries that mainly focus
on obtaining the potential energy by combustion.
requires an optimization of the operating conditions in order
to assure both acceptable gas outlet composition and an energy
recovery, which makes the process economically satisfactory
. A good knowledge of the kinetics of the process is
fundamental for the plant design and scale-up bases on process
Cotton is mainly comprised of cellulose. The pyrolytic
degradationof cellulose hasbeen the subject of extensivestudy,
although in many instances, knowledge of the exact nature of
degradation and decomposition remains incomplete. Chatterjee
and Conrad  studied the kinetics of cellulose decomposition
in the temperature range of 270–310 8C with absorbent cotton,
and proposed two series reactions for the pyrolysis process.
Dollimore and Hoath  used differential thermal analysis
(DTA) to follow the degradation of cellulose in air products and
obtained two and sometimes three exothermic peaks. Antal and
Va ´rhegyi  reviewed the literature of cellulose pyrolysis and
concluded that the pyrolysis of a small sample of pure cellulose
is characterized by an endothermic reaction governed by a first
order rate law with a high activation energy. Vo ¨lker and
Rieckmann  investigated the influence of the final mass on
modelling results and evaluated the applicability of established
kinetic models for engineering purposes.
Cotton fabrics, which have a major share of the textile
market, are highly inflammable and the development of
successful flame retardant systems for cotton is of major
interest. For this reason, many authors have studied the
cotton fabrics. For instance, Faroq et al.  carried out the
thermogravimetric analysis of the mechanism of pyrolysis of
untreated cotton fabrics and cotton fabrics finished with various
flame retardant, considering the fraction decomposed as
between 0.1 and 0.9. These authors evaluated the activation
J. Anal. Appl. Pyrolysis xxx (2005) xxx–xxx
* Corresponding author. Tel.: +34 96 590 34 00x3003; fax: +34 96 590 38 26.
E-mail address: firstname.lastname@example.org (J. Molto ´).
0165-2370/$ – see front matter # 2005 Published by Elsevier B.V.
energies obtaining values of 155–158 kJ mol?1for the thermal
decomposition of untreated cotton. In addition, they proposed a
second order decomposition mechanism as the most suitable.
Wanna and Powell  studied the thermal decomposition of
untreated and treated cotton fabric with selected salts in
oxidative and inert atmospheres using TGA-FTIR. On the other
hand, no papers considering the overall decomposition kinetics
of cotton cellulose or cellulose have been found.
It is clear that the n-th order kinetic model can be correct for
homogeneous gas phase kinetics, in accordance with the
collision theory and the transition state theory developed for
elemental reactions and normally with n = 1, 2 or 3. The
pyrolysis of polymers it is a non-homogeneous reaction and
consequently the n-th model should not be valid. In literature,
we can find mechanisms for the pyrolysis of different polymers
with parallel and series reactions. Considering only one
elemental reaction for the decomposition of a solid, the
proposal ofakineticexpressionbased onthe elementalreaction
is not easy because the decomposition takes place in a solid
phase. Font and Garcı ´a  proposed the application of the
transition state theory to the pyrolysis of biomass considering
the similarity between the pyrolitic reaction that take places in
the outer surface and the first order uni-molecular catalytic
surface reactions. In accordance with the model developed, it is
possible to obtain n-th models as a consequence of the increase
or decrease of the surface with active centres where the
decomposition can take place, and with fractional values of the
reaction order n.
The n-th order reaction has been used extensively by
different researchers when studying the mechanisms of
decomposition of several polymers, no matter the mechanisms
of reactions comprises parallel or series reactions. Never-
theless, in spite of the proposal of a model that could explain
fractional reaction orders, the models obtained from the TG
runs must be considered as correlation ones, and from the
analysis of the activation energy, it can be deduced if the model
is related satisfactorily to a controlling decomposition
elemental step or must be only considered valid for correlation.
The present work, which is included in a wider project
whose objective is to study the combustion of different
industrial and municipal wastes, studies the thermal decom-
position of used and waste cotton fabrics from the thermo-
gravimetric point of view, including the kinetic analysis in a
thermobalance in inert atmosphere and with different amounts
of oxygen, proposing a kinetic model.
2.1. Raw material
Used cotton fabrics were simulated by using a used blue T-
shirt made of 100% cotton. Prior to the runs, the T-shirt was cut
into small pieces with an average size of 1 cm ? 1 cm.
Table 1 shows some characteristics of the material studied.
Elemental analysis of the major components was carried out in
a Perkin-Elmer 2400. The moisture was determined by the
weight loss at 105 8C for 12 h. The calorific valuewas obtained
in an AC-350 calorimetric bomb from Leco Corporation.
Chlorine was measured using an automatic sequential spectro-
meter X-ray Fluorescence model TW 1480. Ash residue was
obtained by calcination at 850 8C.
The thermogravimetric experiments were carried out in a
Setaram thermobalance model DSC92 controlled by a PC
system. The atmosphere used for pyrolysis was helium with a
flowrateof60 ml min?1(STP),accordingtothespecificationsof
the equipment. In the combustion runs, two mixtures of helium
with the same total flow rate. The sample temperature was
measured with a thermocouple directly at the crucible, i.e., very
close to the sample. Because a water-cooled microfurnace was
used, the temperature could be lowered rapidly.
Before the runs with used cotton fabrics, an experiment with
a heating rate of 5 8C min?1usingAvicel PH-105 microcrystal-
line cellulose was done to check the good performance of the
equipment. The results obtained showed good agreement with
the kinetic evaluation of Avicel Cellulose TG curves at this
heating rate presented by Grønli et al.  in their round-robin
study of cellulose pyrolysis kinetics by thermogravimetry.
The experiments were carried out with heating rates of 5, 10
and 20 8C min?1over a variety of temperatures that included
the entire range of solid decomposition, 80–700 8C. Experi-
ments without a sample were carried out, and used as
background in order to subtract the buoyancy effect. The mass
of the samples used was approximately 5 mg, and under these
conditions the heat transfer limitations can be neglected.
3. Results and discussion
3.1. Thermogravimetric study
Figs. 1–3 show in detail the experimental curves for used
cotton fabrics pyrolysis (helium) and combustion (helium:oxy-
gen, 4:1 and 9:1) at different heating rates. The calculated
curves of the kinetic models are also shown. In the figures, w is
defined as the residual mass fraction of the solid (including
residue formed and non-reacted initial solid), i.e., the ratio
(m0). In all the processes, we can be observed the general shift
to higher temperatures when the heating rate is increased.
J. Molto ´ et al./J. Anal. Appl. Pyrolysis xxx (2005) xxx–xxx2
Characteristics of the material used
O% by difference (wt.%)
Ash content (wt.%)
Net calorific value (kJ kg?1)
Fig. 4 compares the results obtained in the different
atmospheres at a constant heating rate. As can be seen, the
at lower temperatures) and a final combustion process is
observed. On the other hand, there is not a great difference
between the runs performed under 10% oxygen and those at
3.2. Kinetics of the process
3.2.1. Pyrolysis model
Most of the papers published corresponding to the
pyrolysis of cellulose and cotton consider only one fraction
when correlating the experimental data of the primary
decomposition, in spite of the parallel and series mechanisms
proposed in literature . In the cotton fabrics used in this
work, and considering that we have extended the tempe-
rature range until high temperatures, a second decompo-
sition process has been considered in order to improve the
The kinetic model proposed for the decomposition of the
used cotton fabrics in an inert atmosphere could be interpreted
considering this waste formed by two independent parts, each
one following an independent reaction, as follows:
where C1and C2refer to different parts of the solid material to
be decomposed (cotton in this case). ‘‘Vi’’ are the gases + vo-
latiles evolved and ‘‘Si’’ are the solid residue formed in the
decomposition. The uncapitalized variables ‘‘cn’’ are the
amount of each material that is in the sample.
It is very useful to introduce the concept of the conversion
degree for each reaction:
ai¼ 1 ?Cn
i ¼ n ¼ 1; 2
(Two different subscripts have been used, because in the
combustion model presented also in this model there are
competitive reactions for the same solid.)
In the previous equations, Vi1represents the maximum
obtainable amount of volatiles via reaction ‘i’ at time infinity,
J. Molto ´ et al./J. Anal. Appl. Pyrolysis xxx (2005) xxx–xxx 3
Fig. 1. Cotton pyrolysis at several heating rates: 5, 10 and 20 8C min?1.
Experimental and calculated curves.
Fig. 2. Cotton combustion at several heating rates and 20% oxygen. Experi-
mental and calculated curves.
Fig. 3. Cotton combustion at several heating rates and 10% oxygen. Experi-
mental and calculated curves.
Fig. 4. Experimental TG plots for pyrolysis and combustion with 20 and 10%
oxygen, all carried out at 20 8C min?1heating rate.
Cnrefers to the non-decomposed material at each time, and Cno
is the initial contribution offraction ‘n’to the total weight.Note
that at t = 0 thevalue of aiis zero, and that V11equals the yield
coefficient v1and that V21equals the yield coefficient v2.
The kinetic equations associated with the parallel reaction
for the pyrolysis runs, taking into account the mass balance
between products and reactants and the degreeconversions, can
be expressed as:
By integration of these reactions it is possible to calculate a1
and a2at each time; the relationship between these two values
and the weight fraction measured in the thermobalance ðwÞ is:
w ¼ 1 ? V ¼ 1 ? ðV1þ V2Þ ¼ 1 ? ðV11a1þ V21a2Þ
The values of V11 and V21 are related with the total
volatiles at time infinity (V1), that is a known amount:
V1¼ V11þ V21
The pyrolysis data and the combustion data have been
correlated together, in order to obtain a single set of parameters
atmospheres: pyrolysis, oxidative pyrolysis and combustion.
3.2.2. Combustion model
Similarly to the kinetic models found in literature to explain
pyrolytic processes, different authors propose different models
to explain decomposition mechanisms under oxidative atmo-
spheres. Obviously, if the model proposed satisfactorily fits
experimental data generated under a wide selection of
conditions, the model can be considered representative of
the process analyzed . However, literature that includes
detailed kinetic studies, fitting experimental curves at different
heating rates and oxygen content is extremely sparse. Different
models have been found in literature, concerning the
decomposition of tannery waste under oxygenated atmosphere
, polycoated materials such as milk cartons ,
polytetrafluoroethylene  and also of tire wastes . No
models for combustion of cotton or used cotton fabrics have
been found, as commented previously.
The kinetic model proposed for the combustion runs could
be interpreted considering, that the presence of the oxygen
introduces a new competitive process for the decomposition of
each fraction and in this way this model explains the fact
observed in Fig. 4, where the first weight loss in combustion
runs reaches a lower value than in pyrolysis runs.
Figs. 5 and 6 show the TG and DSC plots for pyrolysis
and combustion at 5 8C min?1heating rate. As seen in Fig. 5,
an endothermic peak appears for the pyrolysis process
and in the combustion process besides two exothermic peaks
Taking into account the behavior commented above, the
oxygen to be included in the decomposition law has been
considered, as has been done with other materials [15–16].
The following scheme represents the combustion model
proposed to explain the behaviour obtained at two different
helium: oxygen atmospheres and three heating rates:
c1C1þ O2? !
c2C2þ O2? !
J. Molto ´ et al./J. Anal. Appl. Pyrolysis xxx (2005) xxx–xxx4
JAAP 1877 1–8
Fig. 6. Experimental TG and DSC plots for combustion with 20% oxygen at
5 8C min?1heating rate.
Fig. 5. Experimental TG and DSC plots for pyrolysis at 5 8C min?1heating
ki¼ kioexp ?Ei
¼ kið1 ? aiÞni
n;i ¼ 1;2
Reactions 1 and 2 are the same as in pyrolysis. Furthermore,
as a final new process appears in combustion runs, the
combustion reactions to the chars formed has been considered:
siSiþ O2? !
Vcirefers to the volatiles produced through the combustion
reaction with solid Si.
Conversion degrees are considered for each reaction:
i ¼ 1;2;3;4
ai¼ 1 ?ðCnÞreactedbyreactioni
i ¼ 1; 2; 3; 4; n ¼ 1ðfori ¼ 1; 3Þ; n ¼ 2ðfori ¼ 2; 4Þ
i ¼ 1; 2; 3; 4; n ¼ 1ðfori ¼ 1; 3Þ; n ¼ 2ðfori ¼ 2; 4Þ
where Vi1 and Vci1 represent the maximum amounts of
volatiles evolved if the whole solid fraction decomposes only
through the reactions that lead to the corresponding volatiles,
without competitive reaction. Note that in this case Vi1equals
the yield coefficient viand that Vci1equals the yield coefficient
Reactions 1 and 3 are competitive with respect to the same
solid C1, so it is possible that none of the two values of degree
conversion a1and a2can reach the value 1 at time infinity,
although the sum a1and a2logically must be equal to 1, when
the reactant C1is exhausted. In this case, the ratio between the
non-reacted solid C1 and the initial solid C1o, taking into
account the degree conversions a1and a3, can be expressed as:
C1o¼ 1 ? a1? a3
and consequently the kinetic laws for the decomposition of the
solid fraction C1can be written as
¼ kið1 ? a1? a3Þni;
i ¼ 1;3
Similarly for reactions 2 and 4, the following expression can
¼ kið1 ? a2? a4Þni;
i ¼ 2;4
For the combustion of the residue S1(formed by the first
reaction) in accordance with the scheme:
s1S1þ O2? !
The degree conversion ac1is
The kinetic law for the combustion of S1can be written as:
In this way, the kinetic constant of this second decomposi-
tion does not depend on the initial mass fraction, and
consequently the kinetic constant k5 with distinct mass
On the other hand, it can be deduced that:
Consequently, it can be written that:
¼ a1? ac1
¼ k5ða1? ac1Þn5
Another way of obtaining similar expressions can be found
elsewhere . This procedure can be applied to the other three
combustion reactions. Consequently, the reaction model can be
solved considering the following equations:
dt¼ kið1 ? a1? a3Þni;
i ¼ 1;3
dt¼ kið1 ? a2? a4Þni;
i ¼ 2;4
¼ k5ðai? a1iÞn5;
i ¼ 1;2;3;4
v1þ s1¼ v3þ s3
v2þ s2¼ v4þ s4
Note that the same kinetic constant and reaction order are
considered for the decomposition of Si.
The total weight fraction is related to the other variables by:
w ¼ 1 ? V
¼ 1 ? ðV1þ V2þ V3þ V4þ V11þ V12þ V13þ V14Þ
w ¼ 1
? ða1V11þ a2V21þ a3V31þ a4V41 þ ac1Vc11
þ ac2Vc21þ ac3Vc31þ ac4Vc4aÞ
To take into account the effect of the partial pressure of
oxygen (which equals 0.10 and 0.20 atm for helium:oxygen 9:1
and 4:1, respectively), since different behaviour is observed
when comparing corresponding thermograms, the pre-expo-
nential factors for reactions with oxygen have been considered
to consist of two terms, one a typical pre-exponential factor k0
and the other one the partial pressure of oxygen PO2raised to
the power of an order bio:
i ¼ 3;4;5
J. Molto ´ et al./J. Anal. Appl. Pyrolysis xxx (2005) xxx–xxx5