thermal degradation of dna-treated cotton fabrics under different heating conditions

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ARTICLE IN PRESSG ModelAAP-3190; No. of Pages 10

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Journal of Analytical and Applied Pyrolysis

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hermal degradation of DNA-treated cotton fabrics under differenteating conditions

enny Alongia,∗, John Milnesb, Giulio Malucelli a, Serge Bourbigotc, Baljinder Kandolab

Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, sede di Alessandria, and Local INSTM Unit, Viale Teresa Michel 5, 15121 Alessandria,talyInstitute for Materials Research & Innovation, University of Bolton, Deane Road, BL3 5AB Bolton, United KingdomUnité Matériaux et Transformations (UMET) – CNRS UMR 8207, Fire Group – Ecole Nationale Supérieure de Chimie de Lille, BP 90108, F-59652 Villeneuve’Ascq, France

r t i c l e i n f o

rticle history:eceived 28 January 2014ccepted 25 April 2014vailable online xxx

eywords:NA, fabricshermo-oxidation

a b s t r a c t

Our recent work has demonstrated that deoxyribose nucleic acid (DNA) can act as an effective flameretardant when applied to cotton fabrics as a thin coating. DNA acts as a Lewis acid and promotesthe dehydration of cotton cellulose to form char, limiting the production of volatile species. Here, theeffect of heating rates on thermal degradation behaviour has been studied in order to understand thethermo-oxidation behaviour under slow heating and fast (flash) pyrolysis. The low heating rate effecthas been studied using thermogravimetry coupled with infrared spectroscopy and pyrolysis-combustionflow calorimetry, whereas high heating rate effect was obtained by performing thermogravimetry at

◦
hermogravimetryGA–FTIRyrolysis-combustion-flow calorimetry
200–500 C/min and flash-pyrolysis tests coupled with infrared spectroscopy. The information obtainedby the latter has been successfully employed in order to (i) better explain the results collected from com-bustion tests and (ii) demonstrate that the type of the gaseous species and their evolution, as well as thechar formation, as a consequence of the fabric thermo-oxidation, are independent of the adopted heatingrate.

. Introduction

Very recently, the efficiency of bio-macromolecules like pro-eins [1] and nucleic acids [2,3] as novel green flame retardantystems for cellulosic substrates has been investigated and demon-trated. It has been possible to achieve the self-extinguishmentf cotton, when DNA was coupled with chitosan in a Layer-by-ayer (LbL) assembly [4]. This unexpected behaviour has beenscribed to the chemical structure of DNA; its main componentsnamely, nitrogen containing bases, deoxyribose units, and phos-hate groups) act as an intumescent formulation [5–8]. On the basisf the results collected by thermogravimetry at very low heat-ng rates (i.e. 10 ◦C/min), it was possible to assert that the flameetardant feature of DNA mainly consists in its char-forming andhar-promoting character [2,3]; this bio-macromolecule is able toavour the dehydration of cellulose within cotton to form char

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instead of allowing the production of volatile species). In doingo, the formed char behaves like a carbonised replica of the originalabric, which continues to act as a thermal barrier [9].

∗ Corresponding author. Tel.: +39 0131229337; fax: +39 0131229399.E-mail address: [email protected] (J. Alongi).

ttp://dx.doi.org/10.1016/j.jaap.2014.04.014165-2370/© 2014 Elsevier B.V. All rights reserved.

© 2014 Elsevier B.V. All rights reserved.

The behaviour of DNA is similar to that of the most commonlyused phosphorus- and nitrogen-containing flame retardants, whichreduce the formation of volatiles and catalyse the char formation[10,11]. This finding can be ascribed to their Lewis acid properties;upon heating, they release polyphosphoric acid that phosphory-lates the C(6) hydroxyl group in the anhydroglucopyranose moiety,and simultaneously act as an acid catalyst for dehydrating theserepeating units [11]. In this scenario, we have recently studied theeffect of DNA as a char-former for cotton in the condensed phase[2,3]; however, an in-depth investigation of the gas phase, and thuson the release of volatile species has not been carried out yet; thislatter is the focus of this study. Here, pyrolysis-combustion flowcalorimetry and thermogravimetry coupled with infrared spec-troscopy have been employed, aiming to monitor the evolutionof volatile species at very low heating rates (i.e. 10 ◦C/min). How-ever, since in a real fire scenario the heating rate is much higher(∼500 ◦C/min), thermogravimetry and flash-pyrolysis coupled withinfrared spectroscopy tests, both performed at 200 and 500 ◦C/min,have been exploited for better explaining the results previously

of DNA-treated cotton fabrics under different heating conditions,4

collected from combustion tests (horizontal flame spread, limitingoxygen index and cone calorimetry tests [3]).

More specifically, our attention has been focused on per-forming tests that are able to give useful information about the

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2 and Applied Pyrolysis xxx (2014) xxx–xxx

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hermal-oxidation of the materials under investigation duringre-ignition or at least the ignition steps, during which oxygenlays a key role. For this reason, all tests have been performed inn oxidative atmosphere, and not in pure nitrogen. Indeed, theim of the present and of the previous studies was to design aovel flame retardant capable of suppressing cotton combustiony modifying the mechanism through which it degrades in air.

The information obtained has been also used to demonstratehat the type of the gaseous species and their evolution, as well ashar formation, as a consequence of the fabric thermo-oxidation, isn general independent of the adopted heating rate.

. Experimental

.1. Materials

Cotton (COT, 220 g/m2) was purchased from Fratelli Ballesio S.r.l.Torino, Italy).

Herring sperm DNA powder was purchased from Sigma–Aldrich.r.l. (Milano, Italy) and stored at 4 ◦C before its use.

.2. Deposition of DNA-based coatings on cotton fabrics

The DNA solution (2.5 wt.%) was prepared by slowly dissolvinghe DNA powder in acidified distilled water (pH = 5.5) under mag-etic stirring (300 rpm) at 30 ◦C for 30 min. Then cotton fabrics were

mpregnated for 1 min in a climatic chamber (30 ◦C and 30% R.H.);he excess of the solution was then removed with a rotary evapo-ator and the impregnated fabrics were dried to constant weight in

climatic chamber [3].The total dry solids add-on on cotton samples (A, wt.%) was

etermined by weighing each sample before (Wi) and after thempregnation with the suspension and the subsequent thermalreatment at 30 ◦C overnight (Wf), using a Gibertini balance (accu-acy: ±10−4 g). The uptake of samples was calculated according tohe following equation:

= Wf − Wi

Wi100

The untreated and treated samples were coded as COT andOT DNA X, where X is 5, 10 or 19% and stands for the measuredeight percentage add-on on the dried fabric.

.3. Characterisation techniques

Thermogravimetric analysis (TGA) was carried out in air, from0 to 800 ◦C with a heating rate of 10, 100, 200 and 500 ◦C/min. Tohis aim, TAQ500 and TAQ5000IR thermobalances (TA Instruments)ere used (experimental error: ±0.5 wt.%), placing the samples

ca. 6 mg) in open platinum pans, in oxidative atmosphere (air gasow: 100 ml/min). Tonset10% (temperature, at which 10% weight lossccurs), Tmax (temperature, at which maximum weight loss rate ischieved) and the mass of the final residues were evaluated.

Alternatively, TGA (SDT 2960 TA Instruments) was coupled withnfrared spectroscopy (Nicolet iS10 by Thermo-Scientific).

Flash-pyrolysis at 200 and 500 ◦C/min was carried out by using CDS Pyroprobe 2000 with Brill cell FTIR interface.

Isothermal tests at 300, 350 and 440 ◦C were carried out byGA for 1 h and the resulting residues were analysed by FTIR spec-roscopy. The spectra were recorded at room temperature in theange of 650–4000 cm−1 (64 scans and 4 cm−1 resolution), using ahermo Avatar 370 spectrophotometer, equipped with attenuated

Please cite this article in press as: J. Alongi, et al., Thermal degradationJ. Anal. Appl. Pyrol. (2014), http://dx.doi.org/10.1016/j.jaap.2014.04.01

otal reflection accessory (ATR) and a diamond crystal.The data obtained from TGA and TGA-IR were compared with

hose of a pyrolysis-combustion-flow calorimetry (PCFC, FAA Microalorimeter, Fire Testing Technology). This latter was used to assess

Fig. 1. TG, dTG (at 10 and 100 ◦C/min in air) and HRR (at 60 ◦C/min) curves ofuntreated cotton.

the flammability of the formulations, according to ASTM D7309. Indetail, the prepared sample (6.3 ± 0.1 mg) was heated to a specifiedtemperature using a linear heating rate (60 ◦C/min) in a stream ofnitrogen flowing at 80 cm3/min. The thermal degradation productsof the sample in nitrogen were mixed with a 20 cm3/min streamof oxygen prior to entering the combustion furnace (900 ◦C). Thecombustion of fuel gases in the mixture of 20% O2 and 80% N2 at750 ◦C for 10 s is a very conservative condition to ensure completeoxidation of the fuel gases. Tinitial (i.e. the temperature, at whichthe oxidation starts), peak Heat Release Rate (PHRR), correspondingtime-to-peak (tPHRR) and Total Heat Release (THR) were evaluated.The experimental error was ±5%.

3. Results and discussion

3.1. Thermogravimetry and pyrolysis-combustion flowcalorimetry

The thermo-oxidation of untreated cotton has been studiedby using thermogravimetry in air at two different heating rates(10 and 100 ◦C/min). Fig. 1A and B shows the corresponding TGand dTG curves. As already described [12], the overall degrada-tion process of cotton is the result of several competing reactions,which determine the release of volatiles and the thermal stabil-ity of the final char. Usually, cellulose decomposes by three stepsin air, as reported by Price et al. [13 and references quoted in],Kandola et al. [14] and Bourbigot and co-workers [15]. The firststep (located in the range 300–400 ◦C) involves two competitivepathways, which yield aliphatic char and volatile products; in thesecond step (between 400 and 800 ◦C), some aliphatic char con-


verts to an aromatic form, yielding CO and CO2 as a consequenceof simultaneous carbonisation and char oxidation. During the lastdecomposition step at ca. 800 ◦C, the char and any remaining hydro-carbon species are further oxidised mainly to CO and CO2. The

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ig. 2. TG, dTG (at 10 ◦C/min in air) and HRR (at 60 ◦C/min) curves of DNA-treatedotton.

ame mechanism has been also observed at very high heating rates100–300 ◦C/min); but, in these conditions, the char content in thenal residue was found to decrease by increasing the adopted heat-

ng rate [12]. Indeed, when cotton is heated at over 200 ◦C/min inir, depolymerisation of cellulose towards the formation of volatilepecies is favoured and dehydration is inhibited, thus the formationf a thermally stable char does not occur. In addition, comparing theG and dTG curves of cotton heated at 10 and 100 ◦C/min (Fig. 1And B), it is possible to observe that its thermo-oxidation occurs in

similar way. Furthermore, these latter data are consistent withhose collected by PCFC (Fig. 1C), despite the different heatingate (60 ◦C/min) which applies for this process. This finding fur-her confirms a correlation between TGA and PCFC measurements,s already described by Lyon and Walters [16].

In detail, within 10–100 ◦C/min, the thermo-oxidation of cot-on proceeds by two steps, during which the maximum weight lossregistered between 345 and 360 ◦C, Fig. 1B) is accompanied by theubsequent formation of a thermally stable char and volatile speciesFig. 1A). These volatile species are the same as already observedn nitrogen [12] and further confirmed by PCFC (Fig. 1C). On theasis of these results, the effect of the different DNA add-ons onhe cotton thermo-oxidation has been studied by performing TGnalyses at 10 ◦C/min only (Fig. 2A and B). As already pointed out3], by increasing the DNA add-on, cotton degradation is more sen-itised, since it starts at lower temperatures (as demonstrated byhe Tonset10% linear decrease, Table 1), and the maximum tempera-ure of first weight loss (Tmax1) is strongly reduced. This finding isscribed to the phosphate groups of DNA, which behave similarly to



n inorganic phosphate salt like ammonium polyphosphate (APP)hat is itself a common flame retardant system for cellulosic sub-trates. APP acts by favouring the cellulose decomposition towardshar formation, due to the phosphoric acid released at about 260 ◦C.

Fig. 3. Weight loss difference plot between COT DNA 19% and COT.

Thus, analogously, DNA starts to decompose around 200 ◦C, releas-ing the same acid species, and produces a residue thermally stableup to 600 ◦C.

As an example, the weight difference curve between cottontreated with 19 wt.% of DNA and neat cotton (Fig. 3) clearly showsthat the sensitisation exerted by the presence of DNA on cottoncorresponds to 37% weight loss and occurs within the range of200–320 ◦C; meanwhile, at higher temperatures (about 350 ◦C), thepresence of DNA promotes the formation of char, which stabilisesthe fabric (+32% weight gain).

At the same time, a more coherent residue (depending on theDNA add-on) is formed (see residues at Tmax1 in Table 1). Increasingthe temperature, regardless of the DNA add-on, results in residuesthat remain stable up to 600 ◦C (the second step is shifted to highertemperatures; compare Tmax2 values in Table 1). This finding seemsto indicate that DNA is able to promote char formation and to inhibitvolatile production. In order to confirm this hypothesis, TG analyseshave been compared with PCFC measurements (Fig. 2C); duringthese latter tests, the volatile species released during the pyrolysisof a material are completely oxidised [16]; parameters like HRR(peak and time) and THR (heat of combustion) are measured.

As far as untreated cotton is considered, the peak presentedin Fig. 2C can be attributed to its oxidation; the latter proceedswith a maximum PHRR of 290 W/g at 349 ◦C, the same tempera-ture observed in TGA (Fig. 2A and B). Furthermore, the THR valueof 13.7 kJ/g is in agreement with the data published in the litera-ture [16–19]. The presence of DNA anticipates the degradation ofcotton, as evident by the Tinitial values collected in Table 2, which,similar to thermogravimetry (see Tonset10%, Table 1), decrease withincreasing the DNA add-on. As a consequence, the fabric oxidationis anticipated, as evident by comparing the tPHRR values presentedin Table 2. At the same time, DNA strongly decreases PHRR values,the corresponding temperatures and THR, showing that the coat-ing promotes char formation and inhibits volatile production; thelower the volatile amounts, the lower are THR and PHRR. Thesereductions linearly depend on the DNA add-on; the lowest valueshave been registered with an add-on of 19%, as evident by compar-ing THR, PHRR and the corresponding temperature (TPHRR) valuesin Table 2.

3.2. Thermogravimetry coupled with attenuated totalreflectance-infrared spectroscopy


The thermogravimetric data collected up to now have shownthat cotton thermo-oxidation is strongly enhanced by the DNAtreatment and that all reactions occurring between 240 and 500 ◦C

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4 J. Alongi et al. / Journal of Analytical and Applied Pyrolysis xxx (2014) xxx–xxx

Table 1Thermogravimetric data of untreated and DNA-treated cotton fabrics in air (heating rate: 10 ◦C/min) [3].

Sample Tonset10% [◦C] Tmax1 [◦C] Residue at Tmax1 [%] Tmax2 [◦C] Residue at Tmax2 [%] Residue at 600 ◦C [%]

COT 324 348 45.0 492 4.0 0COT DNA 5% 282 313 65.0 506 19.0 8.0COT DNA 10% 263 302 69.0 511 24.0 13.0COT DNA 19% 238 299 68.0 515 29.0 19.0

Table 2Pyrolysis-combustion flow calorimetry data of untreated and DNA-treated cotton fabrics.

Sample Tinitial [◦C] PHRR [W/g] �PHRR [%] tPHRR [s] TPHRR [◦C] THR [kJ/g] �THR [%]

COT 275 290 – 276 349 13.7 –

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COT DNA 5% 194 97 67

COT DNA 10% 191 86 70

COT DNA 19% 150 55 81

re fundamental to explain the experimental results. For thiseason, isothermal TG tests at 300, 350 and 440 ◦C have beenarried out and the resulting residues have been assessed by usingTR-FTIR (Fig. 4). In untreated cotton, the typical vibration modesf cellulose [20] are still detectable when cotton is heated upo 300 ◦C (namely, �(OH) at ca. 3300, �(CH2) at 2900, ı(OH) at630, ı(CH2) at 1430, ı(CH) at 1365, ı(OH) at 1320 and �(C C) at030 cm−1), as reported in Fig. 4A. Only a peak at 1710 cm−1, which

s assigned to the stretching vibration of the carbonyl group (C O),ppears. Hebeish et al. [21] and Kandola et al. [14] ascribed the for-ation of such a band to the different processes occurring at high

emperatures, like: (i) oxidation of the functional end reducing


roups to carboxyl groups, (ii) oxidation of the cellulose hydroxylso aldehyde groups, (iii) hydrolysis of the glucosidic bond of theellulose chains with resultant increase in the aldehyde groups, (iv)

ig. 4. ATR-FTIR spectra of TG residues at 300 ◦C (A), 350 ◦C (B) and 440 ◦C (C) forOT, COT DNA 10% and DNA.

213 288 5.8 58200 277 5.4 61183 256 4.0 71

oxidation of the newly introduced aldehyde group to carboxylgroup, and (v) decarboxylation. In addition, it was observedthat the intensity of the carbonyl peak increases with increasingtemperature.

In the presence of DNA, regardless of its add-on, the ATR spec-trum of cotton completely changes; two main bands appear at 1690and 1580 cm−1 (as an example, Fig. 4B refers to the fabric treatedwith 10 wt.% of DNA). These bands cannot be ascribed to the pureDNA coating (Fig. 4C), as evidenced by comparing the ATR spec-tra of DNA and DNA-treated cotton. In addition, these peaks arenot present at room temperature. This indicates that, upon heat-ing, DNA functional groups react with those of cellulose, generatingchemical species with an aromatic character, bearing C C and C Nbonds [20]. Increasing the temperature up to 350 ◦C (Fig. 4B), cel-lulose decomposes forming both carbonyl-rich and aromatic com-pounds, as well as hydrocarbon species, as confirmed by the threebands at 1710, 1590 and 1190 cm−1, respectively. Furthermore, thepresence of DNA seems to inhibit the formation of hydrocarbonspecies, favouring that of the aromatic counterparts. Indeed, froma qualitative point of view, the band at 1590 cm−1 appears moreintense than that at 1700 cm−1; this finding further confirms whatis observed during thermogravimetric analyses. Chars produced inthe presence of DNA turn out to be thermally stable up to 440 ◦C, asclearly depicted in Fig. 4B; the band at 1590 cm−1 is still detectable,meanwhile that located at 1710 cm−1 is almost negligible.

3.3. Thermogravimetry coupled with infrared spectroscopy

As discussed in the previous section, the data collected by TGAeventually coupled with ATR-FTIR have clearly shown the char-forming feature of DNA; this finding has been further confirmed byPCFC measurements, which, at the same time, have highlighted thatreduced amounts of volatile species are released in the presence ofDNA with respect to the untreated fabric (compare the height ofthe corresponding peaks in Fig. 2C). TGA–FTIR has been employedin order to monitor the evolution of these species. Since in thiswork TGA–FTIR has been carried out in air as opposed to nitrogen(where pure pyrolysis occurs), oxidation of the evolved products ismonitored. This gives more insight into the potential flammabilitybehaviour of the sample, which is the main aim of this work.

Once again, the most interesting temperature range wasbetween 300 and 500 ◦C. Fig. 5A shows the volatile speciesreleased by cotton heated up to 300 ◦C; the characteristicabsorption peaks representing different gases such as watervapour (4000–3500 and 1550–1566 cm−1), CO2 (2270–2385 and


660 cm−1), CO (2053–2211 cm−1), and carbonyl species (i.e. alde-hydes, ketones, carboxylic acids, 1633–1839 cm−1) were identified[22]. The presence of DNA, regardless of its add-on, reduces theintensity of the bands ascribed to hydrocarbons and CO2 and

dx.doi.org/10.1016/j.jaap.2014.04.014

Please cite this article in press as: J. Alongi, et al., Thermal degradation of DNA-treated cotton fabrics under different heating conditions,J. Anal. Appl. Pyrol. (2014), http://dx.doi.org/10.1016/j.jaap.2014.04.014



Fig. 5. FTIR spectra of the volatile species detected by TGA–FTIR at 300 ◦C for COT (A), COT DNA 5% (B), COT DNA 10% (C) and COT DNA 19% (D).


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Please cite this article in press as: J. Alongi, et al., Thermal degradation of DNA-treated cotton fabrics under different heating conditions,J. Anal. Appl. Pyrol. (2014), http://dx.doi.org/10.1016/j.jaap.2014.04.014




Fig. 8. Comparison of FTIR spectra of volatile species detected by TGA–FTIR as a function of time for COT (A), COT DNA 5% (B), COT DNA 10% (C) and COT DNA 19% (D).

dx.doi.org/10.1016/j.jaap.2014.04.014



d DNA

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at 500 ◦C/min (Fig. 10B). It is noteworthy that DNA seems to bemore efficient at 500 ◦C/min with respect to 10 and 200 ◦C/min interms of char formation, as evidenced by comparing the residues

Table 3Thermogravimetric data of untreated and DNA-treated cotton fabrics in air (heatingrates: 200 and 500 ◦C/min).

Sample Tonset10%

[◦C]Tmax1 [◦C] Residue at

Tmax1 [%]Residue at600 ◦C [%]

Heating rate of 200 ◦C/minCOT 337 393 31.0 0COT DNA 5% 254 304 55.0 16.0COT DNA 10% 257 294 59.0 18.0COT DNA 19% 246 289 62.0 22.0

Heating rate of 500 ◦C/min

Fig. 9. TG and dTG curves of COT (A and C) an

lightly increases those of CO (Fig. 5B–D). The same trend has beenbserved when the temperature was increased up to 350 ◦C (Fig. 6)nd 440 ◦C (Fig. 7). The overall evolution of the gaseous species as

function of time is depicted in Fig. 8. From a semi-quantitativeoint of view, it is possible to conclude that a reduction of about0% has been achieved in the CO2 release resulting from employingNA as a coating, regardless of its add-on.

.4. Thermogravimetry and flash-pyrolysis coupled with infraredpectroscopy

As already described [12], thermo-oxidation of cotton dependsn the heating rate; indeed, at very high heating rates (beyond00 ◦C/min), the dehydration of cotton is blocked and the depoly-erisation is favoured. This results in the high flammability

f cotton that is not able to form char, but only to give riseo volatile species able to fuel the combustion. Previous worksave demonstrated that the self-extinguishment of cotton cane achieved employing DNA [2,3]. The same mechanism of char-ormation/promotion already observed at low heating rates (10nd 100 ◦C/min) can be hypothesised also at high heating ratesnamely, hundreds ◦C/min). To this aim, thermogravimetry andash-pyrolysis coupled with FTIR tests at 200 and 500 ◦C/min haveeen carried out.

Fig. 9 plots the TG and dTG curves of untreated COT and pureNA; in both cases, the thermal stability in air decreases from 10

o 200 and 500 ◦C/min. In particular, for cotton, at these high heat-



ng rates, the char formation turns out to be less (Fig. 9A) and theabric residue at Tmax1 decreases with increasing the heating rateTable 3). Further oxidation of the remaining species to give char istill detectable (see Tmax2 and corresponding residues).

(B and D) heated at 10, 200 and 500 ◦C/min.

In the presence of DNA, regardless of its add-on, the thermo-oxidative stability of cotton is significantly enhanced also whencotton is heated at 200 or 500 ◦C/min, as observed in Fig. 10A andB respectively. Table 3 lists the collected data. More specifically,when cotton is heated at 200 ◦C/min (Fig. 10A), the presence of DNAinduces a strong sensitisation of cellulose degradation, as indicatedby Tonset10% and Tmax1 values; however, DNA catalyses the forma-tion of a thermally stable residue (see its corresponding values atTmax1 in Table 3), linearly dependent on the bio-macromoleculeadd-on. The differences observed for these residues are veryremarkable; 31 vs. 62% for COT and COT DNA 19%, respectively.The second step of degradation can be considered negligible.

The same trend has been also observed when cotton was heated


COT 300 375 32.0 0COT DNA 5% 215 270 52.0 19.0COT DNA 10% 207 253 52.0 22.0COT DNA 19% 205 248 62.0 26.0

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n fabr

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Fig. 10. TG curves of COT and DNA-treated cotto

eft at 600 ◦C. As an example, COT DNA 19% leaves a residue of 19,2 and 26% when heated at 10, 200 and 500 ◦C/min, respectivelylast columns of Tables 1 and 3).

In parallel, the evolution of the gases released around cottonmax1 has been monitored by using flash-pyrolysis coupled with


TIR. The samples have been heated up to 400 ◦C with a heat-ng rate of 200 ◦C/min and the FTIR spectra have been acquired.ig. 11A shows the volatile species detected for the untreated fabric;

ig. 11. FTIR spectra of the volatile species detected by flash-pyrolysis at 400 ◦C with

OT DNA 19% (D).

ics heated at 200 ◦C/min (A) and 500 ◦C/min (B).

they correspond to those already observed and discussed duringthermo-oxidation tests performed at 10 ◦C/min (see Section 3.3).More specifically, the characteristic absorption peaks referring towater vapour (4000–3500 and 1550–1566 cm−1), CO2 (2270–2385and 660 cm−1), CO (2053–2211 cm−1), and carbonyl species (i.e.


aldehydes, ketones, carboxylic acids, 1633–1839 cm−1) were iden-tified; furthermore, the formation of hydrocarbons was checkedat 2970, 2910 and 2850 cm−1. Once again, the presence of DNA,

a heating rate of 200 ◦C/min for COT (A), COT DNA 5% (B), COT DNA 10% (C) and

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ig. 12. FTIR spectra of the volatile species detected by flash-pyrolysis at 400 ◦C

OT DNA 19% (D).

egardless of its add-on, reduces the intensity of the bands ascribedo hydrocarbons and CO2 (Fig. 11B–D). The same trend has beenbserved when the heating rate was increased up to 500 ◦C/minFig. 12).

. Conclusions

In this work, the thermo-oxidation of cotton and cotton treatedith DNA at different add-ons (namely, 5, 10 and 19%) has been

horoughly investigated, particularly focusing on the effects of dif-erent heating rates on the fabric degradation. The results collectedy thermogravimetry, pyrolysis-combustion flow calorimetry andash-pyrolysis can be summarised as follows:

i) at very low heating rates (i.e. 10 ◦C/min), the competitionbetween cellulose depolymerisation and dehydration is stillobserved, regardless of the presence of DNA and its add-onon the fabric. However, the dehydration pathway is morefavoured with respect to depolymerisation, due to the char-former/promoter feature of the bio-macromolecule. This findingwas confirmed by the chemical analysis of the TGA residues andof the volatile species released during the thermo-oxidation ofthe fabric.

i) at very high heating rates (i.e. 500 ◦C/min), the char-formingcharacter of DNA seems to be more efficient than that at lowheating rates (i.e. 10 ◦C/min), as revealed by comparing the finalresidues at 600 ◦C in both cases. This finding may explain theefficiency of DNA as a flame retardant for cotton.



cknowledgements

The authors thank the European COST Action “Sustainableame retardancy for textiles and related materials based on

[

[

a heating rate of 500 ◦C/min for COT (A), COT DNA 5% (B), COT DNA 10% (C) and

nanoparticles substituting conventional chemicals” – FLARETEXMP1105 – for having funded a short-term scientific mission forone of the co-authors (J.A.).

Dr. Marco Coletti and TA Instruments are also acknowledged forperforming the thermogravimetric analyses at high heating rates.

References

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thermal degradation of dna-treated cotton fabrics under different heating conditions

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