Cellulose

, Volume 20, Issue 1, pp 355–364

Hydrorepellent finishing of cotton fabrics by chemically modified TEOS based nanosol

Authors

  • Monica Periolatto
    • Dipartimento di Scienza Applicata e TecnologiaPolitecnico di Torino
    • Dipartimento di Scienza Applicata e TecnologiaPolitecnico di Torino
  • Alessio Montarsolo
    • CNR ISMACIstituto per lo Studio delle Macromolecole
  • Raffaella Mossotti
    • CNR ISMACIstituto per lo Studio delle Macromolecole
Original Paper

DOI: 10.1007/s10570-012-9821-2

Cite this article as:
Periolatto, M., Ferrero, F., Montarsolo, A. et al. Cellulose (2013) 20: 355. doi:10.1007/s10570-012-9821-2

Abstract

Hydrorepellency was conferred to cotton fabrics by an hybrid organic–inorganic finishing via sol–gel. The nanosol was prepared by co-hydrolysis and condensation of tetraethoxysilane (TEOS) and 1H,1H,2H,2H–fluorooctyltriethoxysilane (FOS), or hexadecyltrimethoxysilane (C16), as precursors in weakly acid medium. The application on cotton was carried out by padding with various impregnation times, followed by drying and thermal treatment, varying the FOS add-on from 5 till 30 % on fabric weight or C16 add-on from 5 to 10 %. Treated samples were tested in terms of contact angles, drop absorption times, washing fastness and characterized by SEM, XPS and FTIR-ATR analyses. In the case of FOS modified nanosol applied with an impregnation time of 24 h or C16 modified nanosol, water contact angles values very close or even higher than 150° were measured, typical of a superhydrophobic surface. The application of the proposed sol–gel process yielded also a satisfactory treatment fastness to domestic washing, in particular for FOS modified nanosol.

Keywords

Sol–gelNanosolCottonHydrophobicityHybrid alkoxides

Introduction

Improvement of existing properties and the creation of new material properties are the most important reasons for the functionalization of textiles (Gowri et al. 2010). Recently, as markets in leisure and outdoor sporting textiles have been expanded, the needs for superhydrophobic and self-cleaning fabrics have increased.

Cotton has always been the principal clothing fabric due to its attractive characteristics such as softness, comfort, warmness and biodegradability. However the high concentration of hydroxyl groups on cotton surface makes the fabrics water-absorbent and easily stained by liquids. Therefore, additional finishes are required to impart superhydrophobicity and self-cleaning properties to cotton fabrics.

There have been some reports on the improvement of hydrophobic properties of several kinds of fabrics using nanostructures achieved by nanotechnology (Bae et al. 2009; Liu et al. 2011; Simončič et al. 2012). It was demonstrated that superhydrophobicity depends not only on the surface chemistry but also on the surface topology. Two distinct theoretical models (Wenzel and Cassie–Baxter) have inspired how to engineer superhydrophobic surfaces by either roughening the same through micro- or nano-structures or lowering the surface free energy thanks to waxy materials applied on top of the rough structures, or both. An example is a microprocessing technique to produce rough surface and subsequent chemical treatment with silane or fluoro-containing polymers to reduce the surface free energy (Wang et al. 2008).

Recently, roughened surfaces have been commonly obtained by introducing nano-size particles onto the pristine surface and the sol–gel technique has been reported as a promising tool for preparation of water repellent coatings especially versatile for application on paper, textiles or wood (Tomšič et al. 2008; Cunha and Gandini 2010; Cappelletto et al. 2012). In many research works sol–gel formulations of fluoroalkylsilanes in combination with other silanes to obtain co-condensates are used. These materials are called ORMOCER® (“organically modified ceramics”) or CERAMER (“ceramic polymers”). The solvents are mostly alcohols, but some water-based systems have been described. In these nanocomposites, the organic and the inorganic network are covalently bound and homogeneously intermingled at the nanometer-scale, so that the resulting coatings show enhanced mechanical stability (Pilotek and Schmidt 2003).

These materials have a pronounced gradient structure, with a high concentration of fluoroalkyl groups at the coating-air interface so that only a small amount (1.7 mol %) of fluoroalkyl silane is necessary to obtain an effective repellency (Pilotek and Schmidt 2004). Moreover, it accounts for an excellent adhesion of the coatings on various substrates such as glass, metals and polymers. The gradient is due to the accumulation of surface-active fluorosilanol molecules and condensates at the interface (Tomšič et al. 2008).

The use of nanoparticles together with suitable silane precursors, solvents and additives allows to obtain NANOMERs® (“nano-polymers”) materials with many different additional properties. The homogeneous incorporation of nanoparticles enhances the densification and improves the mechanical scratch resistance and chemical durability of the nanocomposites and may confer additional features such as anti-microbial, UV protection and flame retardant functions (Alongi et al. 2011a). Due to the nanometer size of the particles, the coatings maintain a high transparency between 400 and 1,000 nm. Nanomers can also be tailored by curing at low temperature or even by UV light (Han et al. 2007; Alongi et al. 2011b).

Employing organically modified alkoxysilanes containing long-chained aliphatic or highly fluorinated groups, sol–gel offers far reaching possibilities to prepare water- as well as oil- repellent textiles (Textor and Mahltig 2010). Hydrophobic and oleophobic properties comparable to that of PTFE can be obtained by using fluoroalkyl-substituted alkoxysilanes such as (perfluorooctyl)ethyltrialkoxysilane or (perfluorohexyl)ethyltriethoxysilane (Vilcnik et al. 2009). The high effectiveness of fluorinated polymer coatings for water and oil repellency is associated with their ability to lower the surface energy due to the presence of long perfluoroalkyl chains [-(CF2)n, -CF3] (Satoh et al. 2004; Gowri et al. 2010). In fact superhydrophobic and self-cleaning cotton was prepared by Erasmus and Barkhuysen 2009 using 20 % add-on of 1H,1H,2H,2H-fluorooctyl-triethoxysilane (FOS).

A low required add-on is of great interest for textile applications, because the typical hand and breathability of fabrics are not compromised. Furthermore, most fluorinated materials are very expensive and may often cause serious risks for the human health in case of skin contact and for the environment in case of emissions of fluorine compounds during and after the treatment process. Therefore, it is necessary to minimize the use of fluorinated materials (Bae et al. 2009).

Transparency and durability of surface coatings are particular requirements for textiles. Currently, one major barrier to widespread commercial use of silane chemistry is the poor durability, in terms of washing and abrasion fastness, of the resultant hydrophobic surfaces. The durability of water-repellent coatings after washing, especially for those produced on cotton, remains a challenge, because a post-treatment is usually required to restore the hydrophobic properties. Laundering in fact can reduce the hydrophobicity of treated fabric surfaces by damaging the links formed by silanes and introducing impurities such as residual surfactants and moisture. An additional heat-drying step not only helps to remove residual moisture, but also works to re-crystallize the long-chain alkyl groups on the fabric surface, which enhances the ability of the fabrics to repel water (Roe and Zhang 2009; Daoud et al. 2004).

The formation of highly hydrophobic surfaces on cotton by silica sols from TEOS and hexadecyltrimethoxysilane (C16) was reported by Gao et al. 2009, but in the proposed procedure the fabric was treated in two steps: firstly by impregnation for 20 min with silica sol from hydrolyzed TEOS in basic medium followed by drying at 80 °C; then the fabric was impregnated with hydrolyzed C16 at pH 5, dried at room temperature and finally cured at 120 °C for 1 h. Obviously this procedure is too long for practical purposes. In fact more recently Zhu et al. 2011 proposed a one-step procedure by fabric impregnation for 30 s in silica sol modified, after TEOS hydrolysis in basic medium, by addition of alkyltrialkoxysilanes, followed by drying and curing as before. Moreover the further addition of an epoxy modifier yielded the coatings more durable to multiple launderings.

The aim of the present work was to confer a solid highly hydrophobic behavior to cotton fabrics by one-step deposition of modified silica based coatings by sol–gel technique. These were prepared by co-hydrolysis and condensation in weakly acid medium of TEOS-based sols with low amounts of hydrophobic additives such as C16 or FOS. Textile finishing by C16 can just confer water repellency while FOS enables to confer both water and oil repellency thanks to the fluorine presence, but the work was focused on hydrorepellency and its durability to washing.

Treated fabrics were characterized by SEM, FTIR-ATR and XPS analyses while their wettability was evaluated by measuring the water contact angle and the permanence times of the drops on treated fabrics. These properties were tested also after five washing cycles to asses the durability of the treatments to laundering.

Experimental part

Cotton functionalization

Treated fabrics were EMPA plain-weave pure cotton (105 g/m2) used as received without scouring. In each test, 1 g samples were treated. All chemicals were purchased by Sigma Aldrich.

The sol solution for obtaining silica nanoparticles was prepared by co-hydrolysis and condensation of two silane precursors, tetraethylorthosilicate (TEOS) and 1H,1H,2H,2H–fluorooctyltriethoxy-silane (FOS) or hexadecyltrimethoxysilane (C16) in ethanol-H2O-HCl solution. The preparation was carried out by vigorously stirring, for 24 h at room temperature, of a mixture of 60 ml of ethanol, 15 ml of TEOS, 15 g of FOS or C16 and 4 ml of 0.01 N HCl solution, obtaining sol solutions 17 % w/w of TEOS and 18 % w/w of FOS or C16.

In the sol–gel process, TEOS is hydrolyzed and condensed according to well known reactions. However, using C16 or FOS as a co-precursor in the sol–gel processing stage, the Hs from the OH groups on the silica clusters are partially replaced by the hydrolytically stable ≡Si–C16H33 or ≡Si–C11H10F13 through –O–SiC16H33 or –O–SiC11H10F13 bonds respectively.

During acid catalyzed hydrolysis labile silanol groups are formed, which are enable to promote the silane adsorption onto the OH-rich cellulose structure of cotton fibers through hydrogen bonding. According to the desired water-repellent finishing add-on, proper amounts of nanosol solution were used to impregnate the cotton fabrics: the investigated add-on range of FOS was between 5 till 30 % on fabric weight while C16 add-on was 5 or 10 % on fabric weight .

For each sample the add-on was calculated according to the formula:
$$ m_{sol} = \frac{{\%_{add} \cdot m_{sample} }}{{C_{add} }} $$
(1)
where msol was the amount of nanosol solution (17 % w/w TEOS and 18 % w/w additive) to be taken to obtain the desired add-on percentage (%add), msample the sample mass and Cadd the mass fraction of the additive in the nanosol (0.18). Impregnation was carried out dipping the fabrics in the solution, suitably diluted by ethanol, at ambient temperature, for different times: 1 min, 2 or 24 h.

Then by heat treatment at 120 °C for 1 h silica nanoparticles adhered onto cotton fibers, thanks the formation of siloxane bonds between hydroxyl groups of cellulose and the silanes of modified nanoparticles.

For comparison, two reference samples were also prepared thermally curing fabrics impregnated with FOS or C16 without incorporation into silica nanosol, in order to highlight the nanosol influence on treated fabrics. The add-on was 5 % in both cases and samples were prepared by impregnation of the cotton in an ethanol solution of additive for 2 h at ambient temperature, followed by thermal curing at 120 °C for 1 h.

Characterization

Hydrophobic properties of the cotton fabrics surfaces were estimated by measuring contact angles using a DSA20E “Easydrop standard” drop shape analysis system from Krüss, Germany. The measurements were carried out by the sessile drop method, with Young–Laplace curve fitting, using HPLC grade water (72.8 mN/m surface tension), averaging 5 measures on each fabric side to obtain a representative contact angle value for each sample with standard deviation of about 2°.

Moreover, after the drop deposition, also its permanence time on the fabric before complete adsorption was evaluated. All measurements were carried out at ambient temperature.

On finished fabrics, treatment fastness to domestic washing with standard ECE detergent according to UNI-EN ISO 105-C01 was evaluated measuring the contact angle value and permanence time of the drop after 5 washing cycles. Each sample was treated in a sealed test tube with a solution of 5 g/l of ECE detergent maintaining a fabric to bath mass ratio of 1:50. The tubes were fixed on oscillating plane plunged in a thermostatic bath at 40 °C and agitated for 30 min. Finally the samples were rinsed in cold water and dried in air oven at 80 °C. Each sample was subjected to the same treatment five times.

The surface morphology of the fabrics was examined by SEM with a Leica (Cambridge, UK) Electron Optics 435 VP scanning electron microscope with an acceleration voltage of 15 kV, a current probe of 400 pA, and a working distance of 20 mm. The samples were mounted on aluminum specimen stubs with double-sided adhesive tape and sputter-coated with gold in rarefied argon using an Emitech K550 Sputter Coater with a current of 20 mA for 180 s.

Chemical composition of the fabrics before and after the treatment was analyzed by X-ray photoelectron spectroscopy (XPS) and by FTIR-ATR.

XPS analyses were performed with a PHI 5000 Versa Probe system (Physical Electronics, MN) using monochromatic Al radiation at 1486.6 eV, 25.6 W power, with an X-ray beam diameter of 100 μm. The energy resolution was about 0.5 eV. XPS measurements were performed at a pressure of 1 × 10−6 Pa. The pass energy of the hemisphere analyzer was maintained at 187.85 eV for survey scan and 29.35 eV for high-resolution scan while the takeoff angle was fixed at 45°. Since the samples are insulators, an additional electron gun and an Ar+ ion gun for surface neutralization were used during the measurements. Binding energies of XPS spectra were corrected by referencing the C1s signal of adventitious hydrocarbon to 285 eV. XPS data fittings were carried out with PHI multipack™ software using the Gauss-Lorenz model and Shirley background.

FTIR-ATR analyses were performed on a Nicolet FTIR 5700 spectrophotometer equipped with a Smart Orbit ATR single bounce accessory mounting a diamond crystal. Each spectrum was collected directly on differently treated or untrated samples by cumulating 128 scans, at 4 cm−1 resolution and gain 8, in the wavelength range 4,000–500 cm−1.

Results and discussion

Water repellency

Firstly a test was carried out on a cotton sample treated only with TEOS nanosol, without any additive for its chemical modification. In this case, as expected, no water repellency was conferred as silica is not hydrophobic due to the large amount of hydroxyl groups on its surface.

Water repellency, on the other hand, was conferred to cotton by the nanosol prepared with TEOS and FOS or with TEOS and C16, regardless the process conditions. It is evident by the contact angles measured with water on treated fabrics before washing, reported in Tables 1 and 2, clearly higher than 90°. These values have to be compared with the 0° contact angle measured on untreated cotton, due to the immediate absorption of water drops by the fabric.
Table 1

Water repellency of FOS treated samples before and after washing (CA : contact angle)

FOS on fabric weight (%)

Impregnation time

Water CA before washing (°)

Water CA after washing (°)

Water drop sorption time after washinga

5

1 min

138

139

4  min

10

1 min

137

131

2 h

20

1 min

140

139

90 min

30

1 min

138

136

2 h

5

2 h

138

140

2 h

10

2 h

144

138

>2 h

5

24 h

142

138

>2 h

10

24 h

140

138

>2 h

20

24 h

146

125

>2 h

30

24 h

146

141

>2 h

a Water drop sorption time before washing was in any case higher than 2 h

Table 2

Water repellency of C16 treated samples before and after washing (CA: contact angle)

C16 on fabric weight (%)

Impregnation time

Water CA before washing (°)

Water CA after washing (°)

Water drop sorption time after washinga (min)

5

1 min

147

134

5

10

1 min

169

133

2

5

24 h

169

156

5

10

24 h

157

133

5

a Water drop sorption time before washing was in any case higher than 2 h

In particular, in the case of FOS modified nanosol applied with an impregnation time of 24 h or C16 modified nanosol, values very close or even higher than 150° with water were measured, typical of a superhydrophobic surface. The highest measured value with water was 169°, conferred by C16 modified nanosol with 10 % add-on after 1 min impregnation or with 5 % after 24 h. This result is even higher than that obtained with C16 by Zhu et al. 2011.

Generally an increase in finish add-on should yield higher contact angle values at the same impregnation time. This was observed on samples treated with FOS modified nanosol for long impregnation times and even more on C16 treated for 1 min only.

Another evaluated parameter was the permanence of the drop on the treated fabric, measuring the time till its complete adsorption. In all cases, after 2 h the water drops remained unchanged on the fabric surface; moreover, the same drops rolled away from the textiles without leaving any traces, as typically performed by the so-called Lotus effect.

Water drop contact angle and absorption times were determined also on the reference samples thermally cured after impregnation with FOS or C16 alone without silica nanosol, finding a contact angle value of just 140° and an absorption time lower than 2 h. Hence these results confirmed the importance of the hybrid nanosol on the repellency of the fibers.

Washing fastness

Contact angle and absorption time evaluations were carried out on washed samples differently treated highlighting, in this case, relevant differences as shown also in Tables 1 and 2. A slight decrease of contact angle was measured but the values obtained were still typical of water repellent finishes. Moreover, the sample finished by 5 % C16 modified nanosol with an impregnation time of 24 h showed superhydrophobic behavior, while cotton treated with C16 modified nanosol by Zhu et al. 2011 showed lower water contact angle values. Such difference could be due to the different treatment proposed by Zhu: TEOS hydrolysis in alkaline medium followed by C16 addition and fabric immersion in the modified silica sol for 30 s only.

The importance of a prolonged impregnation time is clear in particular considering the absorption times of water drops. Washed samples treated with the FOS modified nanosol showed absorption times quite comparable with those of the unwashed samples (>2 h), in particular if 24 h of impregnation time was adopted. On the contrary, times evaluated on C16 nanosol treated samples dramatically decreased to few minutes of drop permanence on fabric surface, before its absorption. Evidently the FOS modified silica nanoparticles are involved in stronger bonds with cotton than those modified with C16 which could easier undergo hydrolysis by washing, leaving more free OH groups. This fact could justify the strong decrease of drop adsorption times although the contact angle values were substantially maintained.

Results related to FOS gain even more importance if compared with the reference sample without nanosol. On cotton fabric treated with FOS alone, in fact, the finish is completely lost after washing as denounced by the immediate absorption of the water drop. On C16 reference sample, after washing the water drop stays on the surface for about 30 s with a measured contact angle of 135°, so the nanosol enhances, even if not so strongly as in the case of FOS, the washing fastness of the treatment.

SEM analysis

SEM micrographs at magnification of 1000× on cotton samples treated with FOS or C16 modified nanosol are compared in Fig. 1a–h. The presence of the finishing on treated fibers is evident comparing their images with that of untreated cotton (Fig. 1a). In the samples treated with FOS modified nanosol the roughness of the fiber surface clearly increases the more as higher the add-on. Nevertheless the finish is gradually taking the shape of a coating adherent to the each fiber and even at the highest add-on (30 %) the fibers appear not glued each other and the interfibral holes remain well open so the fabric breathability should be not compromised. However lower add-ons are preferable to obtain fabrics with softer hand.
https://static-content.springer.com/image/art%3A10.1007%2Fs10570-012-9821-2/MediaObjects/10570_2012_9821_Fig1_HTML.jpg
Fig. 1

SEM micrographs at magnification ratio 1000× of cotton: a untreated; b treated with FOS modified nanosol, 5 % FOS add-on, 2 h impregnation; c 10 % FOS add-on, 2 h impregnation; d sample c washed; e 30 % FOS add-on, 24 h impregnation; f sample e washed; g treated with C16 modified nanosol, 10 % C16 add-on, 24 h impregnation; h sample g washed

Comparing washed and unwashed fabrics the additive presence is evident in both cases meaning that the finishing was only partially removed by the mechanical action during washing or by the surfactants. It confirms the results in terms of washing fastness obtained by contact angle evaluation.

XPS analysis

The results of XPS analyses are reported in terms of survey scan and high resolution C1s peak in Tables 3 and 4, referring to FOS modified nanosol and in Tables 5 and 6, referred to C16 modified nanosol.
Table 3

XPS analysis. Survey Scan. FOS modified nanosol

N

FOS add-on

Impregnation time (h)

C (%)

F (%)

O (%)

Si (%)

Ca (%)

C/Si

O/Si

1

Untreated cotton

60.6

39.4

2

5 %

2

36.6

36.6

20.7

6.1

6.0

3.6

3

5 % washed

2

45.5

26.5

22.6

5.0

0.4

6.0

3.4

4

10 %

2

36.6

35.4

21.9

6.1

9.1

4.5

5

10 % washed

2

48.0

23.0

23.4

4.6

0.3

10.4

5.1

6

30 %

24

31.1

40.1

20.4

8.4

3.7

2.4

7

30 % washed

24

39.3

31.8

21.5

7.4

5.3

2.9

Table 4

XPS analysis. C1s peak, high resolution. FOS modified nanosol

N.

FOS add-on

Impregnation time (h)

C–C C–H (%)

C–OH (%)

O–C–O (%)

C=O CHF* (%)

CF2 (%)

CF3 (%)

1

Untreated cotton

27.0

62.2

10.8

2

5 %

2

35.6

22.8

20.4

12.7

6.2

2.3

3

5 % washed

2

57.1

18.7

13.3

4.7

5.2

1.0

4

10 %

2

46.8

31.5

12.7

6.4

2.4

0.2

5

10 % washed

2

38.3

48.7

7.2

3.6

1.5

0.7

6

30 %

24

15.7

38.7

11.2

23.2

7.6

3.6

7

30 % washed

24

33.6

37.9

9.7

6.4

10.4

2.0

* in presence of fluorine

Table 5

XPS analysis. Survey Scan. C16 modified nanosol

N.

C16 add-on

Impregnation time

C (%)

O (%)

Si (%)

Ca (%)

C/Si

O/Si

1

Untreated cotton

60.6

39.4

2

5 %

1 min

71.9

21.1

7.0

10.3

3.0

3

10 %

1 min

66.1

23.7

10.2

6.5

2.3

4

5 %

24 h

61.9

25.7

12.4

5.0

2.0

5

10 %

24 h

62.0

26.2

11.9

5.2

2.2

6

10 % washed

24 h

73.6

19.2

5.8

1.5

12.7

3.3

Table 6

XPS analysis. C1s peak, high resolution. C16 modified nanosol

N.

C16 add-on

Impregnation time

C–C C–H (%)

C–OH (%)

O–C–O (%)

C=O (%)

1

Untreated cotton

27.0

62.2

10.8

2

5 %

1 min

33.9

29.0

30.3

6.8

3

10 %

1 min

23.2

45.0

28.6

3.2

4

5 %

24 h

55.2

30.9

11.8

2.1

5

10 %

24 h

89.9

3.1

5.7

1.3

6

10 % washed

24 h

68.8

22.8

6.0

2.4

On all treated samples the presence of the finishing is revealed by the detection of fluorine and/or silicon on the fiber surface. The detected amounts are higher at higher add-ons while, in accordance with the measured contact angles, decrease after washing on all treated samples. Nevertheless, considering the FOS modified nanosol, this decrease is lower on sample 6, prepared with 24 h of impregnation, confirming the importance of the impregnation time for the treatment fastness. In this case, in fact, more finishing agent is retained after washing, probably thanks to a better penetration of the same inside cotton fibers and an intimate bond on them.

On C16 treated samples, more than 50 % of surface Si was lost after washing. It can be the cause of the low permanence times of the water drop on the fabric surface after washing and of the decrease of the measured contact angle.

Evaluation of the C/Si and O/Si ratios reveals the organic nature of the finishing. From literature data related to pure cellulose, high resolution C1s peak should show only two contributions due to C–OH and O–C–O groups with a relative intensity about 5:1. Nevertheless there is always the presence of C–C and C–H contribute, due to the presence of some surface impurities, even when analyzing pure cellulose paper filters. On a purged cotton the value found for C–C and C–H is usually about 22 % (Mitchell et al. 2005), in good agreement with the value found on our untreated cotton sample.

On all the treated samples an increase of this percentage was found, revealing the presence of the finishing agent. Moreover, the increase was as higher as the measured contact angle.

In particular, from the high resolution C1s peak related to FOS modified nanosol, it can be observed that, on unwashed samples, the presence of fluorine is above all in form of CHF. Nevertheless after washing these groups are lost, leaving just the contribution of C=O to the related peak, while CF2 and CF3 groups are less affected by washing, although the ratio F/C decreased from 1.29 of sample 6 to 0.81 of sample 7.

Sample 6 gave the best performance in terms of contact angles and absorption times before and after washing; these values can be related to the XPS results obtained on the same sample, where the highest fluorine content as CF2 was detected, before and after washing. It means that CF2 together with CF3 are the groups of greater importance to confer water repellency to the substrate rather than CHF group. However it can be observed that CF2 (%) in sample 7 is higher than before washing (sample 6), while CF3 (%), belonging to the same chemical chain, is lower. This variation can be justified by a rearrangement of the residual fluorinated groups which could induce the migration of CF2 groups towards the fabric surface.

Finally, on all C16 treated samples there is a decrease of the C–OH groups detected with respect to untreated cotton, confirming the involvement of these groups on grafting reactions between nanosol and fabric surface.

FTIR-ATR analysis

In Fig. 2 the FTIR-ATR spectra of the fabrics treated with 30 % FOS and 10 % C16 are compared with the spectrum of the untreated cotton in the range 4,000–2,500 cm−1. A significant decrease of the absorbance peak at 3,284 cm−1 assignable to OH groups is observed, clearly indicating the involvement of the OH groups of cellulose in the condensation reactions. Moreover in the spectrum of sample treated with C16 modified nanosol there are two evident peaks at 2,920 and 2,849 cm−1 due to C–H groups, while the same peaks are lower and fused in the spectra of untreated cotton and FOS treated.
https://static-content.springer.com/image/art%3A10.1007%2Fs10570-012-9821-2/MediaObjects/10570_2012_9821_Fig2_HTML.gif
Fig. 2

Comparison between FTIR-ATR spectra of: a untreated cotton, b cotton treated with 30 %FOS modified nanosol, c cotton treated with 10 % C16 modified nanosol

In the range 1,500–650 cm−1 (Fig. 3), the presence of fluorosilane on cotton treated with FOS modified nanosol is indicated by absorbance increase at 1,150–1,250 cm−1 where C–F stretching occurs (Erasmus and Barkhuysen 2009), while a peak at 790 cm−1 is observed in the spectra of samples treated with both modified nanosols and could be due to Si–C stretching according to Gao et al. 2009. However the most significant peaks of the coating are overlapped to those typical of cellulose substrate.
https://static-content.springer.com/image/art%3A10.1007%2Fs10570-012-9821-2/MediaObjects/10570_2012_9821_Fig3_HTML.gif
Fig. 3

Comparison between FTIR-ATR spectra of: a cotton treated with 30 %FOS modified nanosol, b cotton treated with 10 % C16 modified nanosol, c untreated cotton

Conclusions

From the obtained results it can be concluded that the chemical modification of TEOS nanosol by co-hydrolyzed FOS or C16 in weakly acid medium and the following application on textiles substrates is a promising method to confer high hydrophobicity to cotton fabrics. In this way, silica and fluorine based compounds can be homogeneously nano-dispersed on the fabric surface with the consequence of an increase of the surface roughness coupled with the lowering of the surface free energy.

Water contact angles, in many cases close to 150° or even higher, were measured on treated fabrics with an important increase with respect to the C16 or FOS thermally treated samples without nanosol.

The application of the proposed sol–gel process yielded also a satisfactory treatment fastness to domestic washing, in particular for FOS modified nanosol, while that modified with C16 was partially removed from fabric surface by washing, as revealed by XPS analysis.

The water drop absorption times showed the importance of the impregnation time on the durability to washing with the best results (>2 h) after 24 h impregnation in the case of FOS modified nanosol.

Copyright information

© Springer Science+Business Media Dordrecht 2012