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Applied Surface Science 275 (2013) 201– 207

Contents lists available at SciVerse ScienceDirect

Applied Surface Science

j ourna l ho me page: www.elsev ier .com/ locate /apsusc

pplication of fluorinated compounds to cotton fabrics via sol–gel

ranco Ferrero ∗, Monica Periolattoolitecnico di Torino – Dipartimento di Scienza Applicata e Tecnologia Corso Duca degli Abruzzi 24, 10129 Torino, Italy

r t i c l e i n f o

rticle history:eceived 29 September 2012eceived in revised form1 December 2012ccepted 1 January 2013vailable online 11 January 2013

eywords:ottonol–gelluorolink® S10

a b s t r a c t

The aim of this work was the study of the surface modification of cotton fibers to confer hydro and oilrepellency to the fabrics. A surface treatment not involving the bulk of the fibers was chosen, so fabrics canmaintain comfort properties. Moreover the study focused on an economical and environmental friendlyprocess, in order to obtain an effective treatment with good fastness to washing.

A modified silica based film was applied on fibers surface by sol–gel, comparing laboratory gradereagents with a commercial product as precursors and optimizing process parameters.

From obtained results sol–gel can be indicated as a promising process to confer an effective and durablefinishing to cotton fibers with low add-ons. Long impregnation times can significantly improve the treat-ment fastness, while ironing the washed samples can restore, at least partially, hydro and oil repellencylost after the washing. Obtained results were supported by a deep surface characterization of untreated,

OSEOS

treated and washed samples.The best results were obtained using the commercial product as the only precursor. This is interesting

for an industrial application, due to the low cost of this product if compared with the laboratory gradereagents investigated.

Some applications of finished textiles can be for household use, technical garments, umbrellas oroutdoor textiles.

© 2013 Elsevier B.V. All rights reserved.

. Introduction

In the last decades the number of new applications of textileaterials has strongly increased. Especially the market of technical

extiles is showing high rates of economic growth and the demandor materials with new or additional properties is becoming crucial.

ater and soil repellency or superhydrophobicity, in particular, aremong the most desirable textile properties for consumers [1].

In many cases a water barrier is achieved by completely cov-ring the open structure of a textile with a dense polymer layerr by producing laminates by incorporation of certain membranesike Gore-Tex® or Sympatex®. Nevertheless, these treatments canompromise the peculiar characteristics of natural fabrics, such asoftness or breathability. Due to this reason, the surface modifi-ation of fiber materials is an important topic of textile research

orldwide.

The surface modification of textile fibers is carried out by com-only used chemical or electro-chemical application methods.

Abbreviations: TEOS, Tetraethoxysilane; FOS, 1H,1H,2H,2H-luorooctyltriethoxysilane.∗ Corresponding author. Tel.: +39 011 0904653; fax: +39 011 0904699.

E-mail address: franco.ferrero@polito.it (F. Ferrero).

169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.apsusc.2013.01.001

Dyestuffs, polymers or monomers are applied to the fibers and arebonded either in a permanent or often only in a temporary way.

However more recent techniques are applied more and more inaddition to these [2]. Plasma treatment, for instance, can add a hugenumber of functional groups to the polymer surface, depending onthe process gases in the plasma chamber. The literature reports, forexample, the deposition of fluorine rich surfaces, leading to highlyrepellent fabrics [3,4]. Plasma techniques offer far-reaching possi-bilities, but the technical effort is comparatively high due to thefact that the processes often have to be carried out under reducedpressure or at least under oxygen-free atmosphere. Besides plasmatreatments, electron beam technologies as well as different pho-tonic technologies, namely UV-grafting [5–8] or laser treatment,are applied to achieve a specific functionality [9].

In this scenario, nanotechnology shows real and great potentialin the textile industry, especially considering that the conven-tional methods used to impart specific properties to fabric textilesdo not often yield permanent effects against wearing or washing.The application of nanotechnology has been proven to give highdurability to fabric modifications and to improve the overall fab-

ric performance, thanks to the nanomorphology of the fillers used[10].

Among the new approaches, the sol–gel technology is probablyone of the most important developments in material science during

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he last decades. Sol–gel technology enables the possibility to tai-or surface properties to a certain extent, and to combine differentunctionalities in a single material. At the same time, the applica-ion of sols can be carried out with techniques commonly used inhe textile industry [1,11].

An important issue in the application of nanosol coatings to tex-iles is the adhesion to the fiber surface in order to prevent theoating from flaking off during use or washing [12]. In the case ofellulose materials like cotton, the adhesion of the sol–gel coatings easily improved by chemical condensation of silanol groups withhe hydroxyl groups on the textile surface. The chemical condensa-ion of pre-hydrolyzed alkoxysilanes on cellulose is known to occurfter thermal treatment at above 100 ◦C [9,13].

Cotton has always been the principal fiber for clothing due to itsttractive characteristics. However, its high absorbency, as a resultf the high amount of hydroxyl groups on the surface, compro-ises stain-resistance and water repellency. Therefore, additional

nishes are mainly required to impart superhydrophobicity andelf cleaning properties to cotton textiles.

Generally pure laboratory grade alkoxysilanes are used asol–gel precursors. A hybrid framework composite can be obtainedy mixing alkoxysilanes with organic precursors and the final prop-rties of the coating can be tailored on purpose by choosing properrecursors. TEOS is the most widely used precursor in sol–gel pro-esses [14], nevertheless it can be partially or totally replaced byuorinated alkoxysilanes to confer hydro and oil repellency typicalf these compounds [15–19].

In a previous study it was investigated the finishing of cottonabrics by a TEOS nanosol modified with FOS, obtaining quite goodesults [20]. However, pure fluoroalkyl compounds have the signif-cant disadvantage of high cost, making them unsuitable for widendustrial applications.

In the present work, a process improvement is proposed byeplacing FOS with the cheaper commercial product Fluorolink S10,lready used to prepare organic-inorganic hybrid coatings on glassy sol–gel in presence of TEOS [21]. Moreover the possibility tovoid TEOS introduction in the sol–gel process was investigated.

In this way, an improved resistant superhydro and oil repel-ent cotton can be obtained by a cheap and significantly simplifiedrocess.

. Materials and methods

.1. Samples preparation

Tetraethoxysilane (TEOS), 1H,1H,2H,2H-Fluorooctyltrietho-ysilane (FOS), both pure laboratory grade reagent purchased fromigma–Aldrich (Italy), and Fluorolink® S10, commercial productrom Solvay Solexis (Italy) were used as precursors. In Fig. 1 the

olecular structures are reported; in particular that of Fluorolinkas taken from literature [22] and the Mw of the reagent used was

n the range 1750–1950 g/mol.Ethanol 96% vol from Sigma–Aldrich and deionized water were

sed as dilution media while the acidity was adjusted by additionf reagent grade hydrochloric acid.

Three different nanosols were prepared, using FOS or Fluorolinklone or Fluorolink mixed with TEOS as precursors. At first sol–gelrecursors were dissolved in alcoholic media, then aqueous 0.01 Mydrochloric acid was added so that hydrolysis and condensationeactions occurred forming a nanosol by vigorously stirring, for 24 ht room temperature. FOS and Fluorolink nanosols were prepared

oth with 50% w/w of the respective precursor, 46% w/w of ethanolnd 4% w/w of 0.01 M HCl, while that of Fluorolink plus TEOS was7% w/w Fluorolink, 19% w/w TEOS, 58% w/w ethanol and 6% w/w.01 M HCl.

ce Science 275 (2013) 201– 207

The cotton fabric was dipped in the respective suspension,suitably diluted with ethanol (1:2 w/w), in order to adsorb thenanoparticles on the fiber surface; weights on were fixed to about5% or 10% o.w.f. (over weight fiber) and the influence of differentimpregnation times (1 min, 2 h and 24 h) on FOS nanosol was inves-tigated. The best results were obtained with 24 h impregnation,so with Fluorolink only this time was adopted. Finally, drying andcuring were carried out at 120 ◦C for 1 h.

The textile substrate used was Cotton ISO 105-F02 woven fabric,105 g/m2 weight. The area of treated samples was about 100 cm2.

2.2. Samples characterization

Hydro and oil repellency were tested using HPLC grade waterand paraffin oil (Sigma–Aldrich), with surface tension of 72 mN/mand 31.5 mN/m respectively. The wettability of untreated, treatedand washed samples were investigated by a DSA20E “Easydropstandard” drop shape analysis tensiometer from Krüss, (Germany)equipped with DSA software, using the sessile drop method for fit-ting. Measuring liquid drops were deposited from a glass syringeon the fabrics surface by means of the software controlled dosing.The contact angles were the average of at least 5 measurements foreach sample with a standard deviation of about 2–3%.

Moreover, the time necessary for the total absorption of bothwater and oil drops was measured.

Investigation on fastness behavior of treated samples to domes-tic laundering was performed by washing the treated samples at40 ◦C for 30 min using 5 g/l ECE detergent according to ISO 105 C01standard. Contact angles and drop absorption times were measuredafter 5 washing cycles.

FTIR-ATR analyses were performed on a Nicolet FTIR 5700spectrophotometer equipped with a Smart Orbit ATR singlebounce accessory mounting a diamond crystal. Each spectrumwas collected directly on treated samples by cumulating 128scans, at 4 cm−1 resolution and gain 8, in the wavelength range4000–600 cm−1.

Surface chemistry of the fabrics was analyzed before and afterthe treatment by X-ray photoelectron spectra (XPS) with a PHI 5000Versa Probe system (Physical Electronics, MN) using a monochro-matic Al radiation at 1486.6 eV, 25.6 W power, with an X-raybeam diameter of 100 �m. The energy resolution was about 0.5 eV.XPS measurements were performed at a pressure of 1.0 × 10−6 Pa.The pass energy of the hemisphere analyser was maintained at187.85 eV for survey scan and 29.35 eV for high-resolution scanwhile the takeoff angle was fixed at 45◦. Since the samples are insu-lators, an additional electron gun and an Ar+ ion gun were usedfor surface neutralization during the measurements. Binding ener-gies of XPS spectra were corrected by referencing the C1s signal ofadventitious hydrocarbon to 285 eV. XPS data fittings were carriedout with PHI multipakTM software using the Gauss-Lorenz modeland Shirley background.

The surface morphology of the fabrics was examined by SEMwith a Leica (Cambridge, UK) Electron Optics 435 VP scanning elec-tron microscope with an acceleration voltage of 15 kV, a currentprobe of 400 pA, and a working distance of 20 mm. The analy-sis was carried out on the samples treated with 10% Fluorolinkand an impregnation time of 24 h. The samples were mounted onaluminum specimen stubs with double-sided adhesive tape andsputter-coated with gold in rarefied argon using an Emitech K550Sputter Coater with a current of 20 mA for 180 s.

3. Theory

In general, the wettability of solid surfaces is governed by bothchemical composition and topography. Repellent finishes achieve

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F. Ferrero, M. Periolatto / Applied

heir properties by reducing the free energy on fiber surfaces. Waterepellent finishes can be achieved using fluorine-free products suchs alkoxysilanes, but these are unable to repel oils. Therefore theain chemical approach to obtain superhydrophobic and oil repel-

ent substrates is the introduction of perfluorocarbon chains on theurface. Low energy surfaces provide also dry soil repellency byreventing soil particles from strongly adhesion to fiber surfaces.his low interaction allows the soil particles to be easily dislodgednd removed by mechanical action [23].

In order to improve the finishing properties, it can be useful toodify also the microstructure of the fibers surface by applying

fluorine based product in form of a thin film or nanoparticlesurrounding the fibers. For this reason, sol–gel was chosen for theabrics functionalization.

The chemical structure of cotton is based on cellulose macro-olecules, hence it is rich in OH reactive groups on the surface,

hat can be involved in grafting reactions with finishing agents.During acid catalyzed hydrolysis of TEOS or fluorinated alkoxysi-

anes, labile silanol groups are formed, which are enable to promotet first the silane adsorption onto the OH-rich cellulose structure ofotton fibers through hydrogen bonding. Successively, during thehermal curing step, the following condensation reaction can occur:

ell OH + HO Si → Cell O Si + H2O

Moreover, when a fluorinated alkoxysilane, such as FOS or Fluo-olink, is the one precursor, Si OH groups on the silica clusterinked on the fiber surface are partially replaced by hydrolyti-ally stable Si C bonds. In particular Fluorolink has a fairly highw compared to FOS and two silane grafting end groups. These

haracteristics have been recognized to increase the hydropho-ic/oleophobic character of films and resistance to mechanicalemoval from the matrix [22]. However, when TEOS is introduceds co-precursor, O Si(OH)3 groups can be likewise bonded onhe fiber surface and are able to condense with other Si OH orSi O CH2 CH3 groups of the fluorinated alkoxysilane precursor.

Hence when the finishing is applied by sol–gel, besides the reac-ions between the precursors, cotton also is involved in graftingeactions thanks to the hydroxyl groups on the surface that chem-cally bond the finishing product to the substrate in a very durable

ay [24]. In Fig. 2 the possible grafting reactions between the sub-trate and the three investigated nanosols are reported.

In the present work the attention was focused on the wettability

f cotton fabrics, but the study can be extended also to other textileubstrates [25]. In particular, in case of synthetic fibers not so rich inH groups, a pretreatment can be carried out to activate the surface,

uch as low pressure plasma in the presence of oxygen or inert gas,

Fig. 1. Molecular structure of (a) Flu

ce Science 275 (2013) 201– 207 203

in order to improve the wettability and the bonds between coatingand substrate [26].

The final properties of the coating can be tailored on purposeby properly choosing the sol–gel precursors: the presence of tita-nium dioxide can confer antimicrobial and photocatalytic activityor modify the optical properties towards UV light [27,28], phospho-rous compounds can increase the resistance to fire and heat [29,30],nanosol containing dyes or pigments can be used to prepare col-ored textile coatings. Moreover, the preparation of multifunctionalcoatings is possible.

These processes suggest further research work that can be car-ried out on the same topic, i.e. the development of new productsfor high performance textile applications.

4. Results and discussion

4.1. Hydro and oil repellency

From the results reported in Table 1, the conferred hydro and oilrepellency are evident in all cases, with measured contact anglesclearly higher than 90◦. These values have to be compared with the0◦ contact angle shown by untreated cotton, due to the immediateabsorption of the deposited drops.

On samples finished with an impregnation time of 24 h, highervalues of contact angles were measured (169◦) revealing the impor-tance of a deep penetration of the finishing agent inside the fibers.

A better behavior of Fluorolink treated samples, with respectto FOS treated ones, was found: contact angles higher than 150 ◦Cwere measured, typical of super hydro and oil repellent surfacesshowing the so-called “lotus effect”. Moreover, absorption timesof length higher than 2 h were measured with both water and oildrops, while on FOS treated samples the oil drop is absorbed inabout 15 min, a good result but worst than Fluorolink performance.This can be due to the molecular structure of Fluorolink, longer andwith more fluorine atoms than FOS. The presence of TEOS seems tobe ineffective.

4.2. Treatment fastness to washing

The results after treatment to washing are reported also inTable 1. On FOS treated samples prepared with 1 min of impreg-nation time, contact angles lower than 150◦ and water or oil dropabsorption times of few minutes were measured. These values arestill typical of a repellent surface but with a strong worsening with

respect to unwashed samples. A better behavior was obtained with2 h of impregnation on 10% weighted samples and with 24 h ofimpregnation regardless the weight on. These samples showed con-tact angles of 169◦ and oil drop absorption times of about 10 min

orolink®S10, (b) FOS, (c) TEOS.

204 F. Ferrero, M. Periolatto / Applied Surface Science 275 (2013) 201– 207

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Fig. 2. Grafting between cotton and (a) FO

hile the water drop was absorbed in 1 min. Long contact timesean a better interpenetration of the finishing agent inside the cot-

on fibers and higher amount of bonding linkages. It can be statedhat the reduced hydro and oil repellency of FOS treated samplesfter washing is due to a partial loss of finishing agent caused byhe mechanical action of washing and surfactants.

On the contrary, Fluorolink treated samples gave the best per-ormance, without differences ascribable to TEOS presence. On allhese treated samples, contact angles higher than 150◦ were mea-ured on washed samples both with oil and water drops and theermanence time of the oil drop was maintained for 2 h.

The different behavior is ascribable to the different moleculartructure: the FOS chain has a great mobility, while that of Fluo-olink is limited by the steric hindrance of the molecule. Moreoverluorolink molecule can graft to cotton surface on both the tails ofts chain, increasing the bonding stability, while FOS has the half ofonding groups available.

Nevertheless, even on Fluorolink treated samples a strongecrease was revealed in absorption time of water drops afterashing, lowered from 2 h to few min.

It is well known that fluorine-containing polymers are usu-lly quite susceptible to rapid rearrangement when the polymerurface is contacted with water, in particular with short perfluori-

ated side chains (typically n ≤ 8 in CnF2n + 1 groups), to minimizehe interfacial free-energy response to the environmental media.onsequently, high contact angles that are observed on dry sur-

aces can quickly decrease in the wet state, in disagreement with

able 1ydro and oil repellency and treatment fastness evaluated on differently treated samples

Finishing Impregnation time � Contact angle [◦] Abs

Water Oil Wa

5% FOS 1 min 154 149 12010% FOS 1 min 145 139 1205% FOS 2 h 164 135 12010% FOS 2 h 169 168 1205% FOS 24 h 164 147 12010% FOS 24 h 152 165 1205% FS10 24 h 169 169 12010% FS10 24 h 169 169 1205% TEOS + FS10 24 h 169 169 12010% TEOS + FS10 24 h 169 168 120

Fluorolink S10, (c) TEOS+Fluorolink S10.

the aim of creating low-surface-energy materials for long-termuse.

Therefore the strong loss of hydrophobicity after washing can bedue to a rearrangement of the fluorinated chains with an orienta-tion towards the internal part of the fibers. In this way, the hydroxylgroups of cotton surface are unshielded, conferring hydrophilic-ity. The original position can be restored by a heating treatment,at about 80 ◦C, hence an ironing was carried out on the washedsamples in order to test the repellency after it [31].

The influence of ironing and of the different impregnationtimes on finishing fastness of FOS treated samples are reported inFigs. 3 and 4. First of all, the importance of contact time betweennanosol and fabric is shown by the increase of washing fastness.A contact time of 24 h yielded about the same contact angle valueobserved before washing. Moreover, in all the cases, the ironingrestored, at least partially, the hydro and oil repellency lost duringthe washing, confirming our assumption.

4.3. FTIR-ATR results

Treated samples were then characterized by FTIR-ATR spec-troscopy. The presence of the finishing agent is revealed on the

spectra by the presence of the peaks ascribable to fluorinated andsilica groups, in particular at 1150 and 1250 cm−1 related to CFstretching in CF2 and CF3 groups, at 847 cm−1 related to Si C and at1088 cm−1 related to Si O Si groups. The absorbance decrease of

(washed samples measured after 5 washing cycles; FS10: Fluorolink S10).

orption time [min] � Contact angle afterwashing [◦]

Absorption time afterwashing [min]

ter Oil Water Oil Water Oil

9 110 146 <1 <1 14 111 131 <1 1 15 122 139 <1 9 14 169 154 <1 9 12 161 165 <1 13 15 169 168 <1 11 120 169 169 2 120 120 169 169 3 120 120 169 168 2 120 120 169 169 4 120

F. Ferrero, M. Periolatto / Applied Surface Science 275 (2013) 201– 207 205

Fig. 3. Influence of washing and ironing on water contact angles, measured on FOS10% weight on treated samples.

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Fig. 6. FTIR-ATR spectra on FOS 10% weight on treated samples: influence of

ig. 4. Influence of washing and ironing on adsorption times of oil drops, measuredn FOS 10% weight on treated samples.

he hydroxyl peaks at 3340 cm−1 and 1600 cm−1 on treated sampless ascribable to the grafting reactions occurred.

Moreover, the peaks at 2950 cm−1 and 1400 cm−1 are due toH stretching, the peak at 1000 cm−1 to cellulose C O bond whilet 2350 cm−1 there is a peak related to the C O bond more pro-ounced on TEOS treated samples [32].

Comparing the spectra of samples treated with Fluorolink or

ith Fluorolink mixed with TEOS, reported in Fig. 5, a decrease ofydroxyl groups on the surface was revealed showing that TEOSlso is involved in grafting reactions.

ig. 5. FTIR-ATR spectra on Fluorolink S10 (red line) and Fluorolink S10 + TEOSgreen line) treated samples. (For interpretation of the references to colour in thisgure legend, the reader is referred to the web version of this article).

impregnation time (Red: untreated, Blue: 1 min, Green: 2 h, Yellow: 24 h) (For inter-pretation of the references to colour in this figure legend, the reader is referred tothe web version of this article).

The importance of a long impregnation time is confirmed by thecomparison between the spectra of cotton untreated and treatedwith different impregnation times (Fig. 6). Longer impregnationtimes correspond to taller peaks related to functional groups, con-firming a higher amount of finishing agent fixed to the substrate,so a better treatment effectiveness.

On spectra of washed samples the peaks due to the functionalgroups are still present, confirming that the finishing is not totallyremoved by washing. For example, spectra related to a FOS treatedsample are reported in Fig. 7.

4.4. XPS results

Another characterization was carried out by XPS, analyzing thesurface of samples by survey scan and high resolution scan of theC1s orbital [33].

Even in this case the presence of the finishing agent isrevealed by the detection of F and Si on the surface of treatedunwashed samples, as reported in Table 2. The FOS treatedsample shows the higher amount of F, while the presence ofTEOS increases the amount of Si detected with respect to sam-ples without TEOS. Moreover, on Fluorolink treated samples acertain amount of N, present in the finishing molecule, wasdetected.

Fluorine is mainly involved in CF2 and CF3 groups; consider-ing the structure of the molecules of reagents, CF3 refers only toFOS treated samples while CF2 groups are present on both FOSand Fluorolink finished fabrics. The grafting reactions occurred

Fig. 7. FTIR-ATR spectra on FOS 10% weight on treated samples: washing fastness.(Purple: unwashed, Red: washed). (For interpretation of the references to colour inthis figure legend, the reader is referred to the web version of this article).

206 F. Ferrero, M. Periolatto / Applied Surface Science 275 (2013) 201– 207

Table 2XPS analysis on differently treated unwashed samples. Survey scan (a) and High resolution C1s (b). Peak area in %.

Binding energy [eV] Untreated cotton 10% FOS 10% Fluorolink S10 10% Fluorolink S10 + TEOS

(a) C – 60.6 36.2 37 36.1F – – 58.3 38.9 28.6O – 39.4 – 19.8 25.6Si – – 5.5 2.5 8.0N – – <1 1.8 1.8

(b) C C + CH 283–284 27.0 8.7 22.7 2.3C OH 285 62.2 27.0 29.4 31.1O C O 287 10.8 14.5 9.9 18.4C O + CHF 290 – 4.2 7.0 10.1CF2 + CF3 292–293 – 45.5 30.9 38.2

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ig. 8. SEM micrographies: (a) untreated cotton 2070×, (b) Fluorolink S10 10% wefter washing 500×.

etween cotton and finishing agents are revealed by the low-ring of the hydroxyl group content with respect to untreatedotton.

On washed samples the decrease of the amount of fluorine func-ional groups and the increase of hydroxyl groups on the surfaceas confirmed (Table 3).

able 3PS analysis on washed samples. Survey scan (a) and High resolution C1s (b). Peak area in

Binding energy [eV] Untreated cotton

(a) C – 60.6

F – –

O – 39.4

Si – –

N – –

(b) C C + CH 283–284 27.0

C OH 285 62.2

O C O 287 10.8

C O + CHF 290 –

CF2 + CF3 292–293 –

1500×, (c) Fluorolink S10 10% weight on 250×, (d) Fluorolink S10 10% weight on

4.5. SEM analysis

SEM micrographies of untreated cotton showed fibers with a

typically smooth surface (Fig. 8a). On Fluorolink treated samples(Fig. 8b and c), the surface roughness increases and the presenceof a homogeneous thin coating on the single fibers can be noted.

%.

10% FOS 10% Fluorolink S10 10% Fluorolink S10 + TEOS

41.5 38.9 32.453.2 28.3 38.0– 27.2 22.7

5.2 2.7 5.2– 2.2 1.511.4 31.9 16.340.0 40.7 38.5

6.7 11.7 8.06.5 5.3 8.5

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evertheless, the finishing is also present in form of agglomer-tes of higher dimensions, entrapped between the cotton fibersFig. 8c). This can be due to a too high weight on (10%), meaning thathe amount of finishing agent deposited on the fabrics can be fur-her reduced without affecting the conferred properties [34]. Afterashing, these agglomerates break up, spreading on all the fabric

urface but the homogeneous coating on the single fibers is stillresent (Fig. 8d).

Even on FOS treated samples, the presence of a homogeneousoating is revealed by SEM analysis, but after washing the coatinghows some cracks while the fibers remain partially uncovered.he presence of fragments detached from the fibers means that theoating was not so strongly bonded to the cotton surface.

. Conclusions

From the obtained results it can be concluded that the appli-ation of a fluorinated compound to cotton textiles by sol–gel is aromising textile finishing process to confer durable hydro and oilepellency. In fact high contact angle and drop adsorption times val-es were measured on treated cotton with both water and oil andhe deposition of the finishing on textile surface was homogeneous.

oreover, add-ons of 5% o.w.f. are enough to confer the desiredroperty. Such value could not affect the fabrics characteristics.

Concerning the finishing process, 24 h of impregnation time canignificantly improve the conferred properties and the treatmentastness to washing. Moreover, the ironing of the washed sam-les can, at least partially, restore the hydro and oil repellency losturing washing.

The best performances were obtained with the commercialroduct Fluorolink S10, while the presence of TEOS did not affecthe obtained results. This is an interesting result from an economi-al point of view; in fact the prices of FOS, TEOS and Fluorolink S10re 15,000, 40 and 80 euros/kg respectively. Hence Fluorolink S10an be considered a valid candidate for the application of sol–gelrocess also at industrial level. To this purpose, further investiga-ions are necessary to confirm that the functional coating has highong-term stability and to develop an efficient coating technologyeducing the amount of organic solvent needed.

cknowledgements

Authors are grateful to Dr.ssa Raffaella Mossotti, CNR-ISMACf Biella, for SEM analysis and fruitful discussion on the obtainedesults, and to Dr. Salvatore Guastella, Politecnico di Torino DISAT,or XPS analysis.

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