Non-formaldehyde, crease resistant agent for cotton fabrics based on an organic-inorganic hybrid material

Article abstract of DOI:10.1016/j.carbpol.2014.01.063

1,2,3,4-Butanetetracarboxylic acid (BTCA) was reacted with (3-aminopropyl)triethoxysilane (APTES) to a poly(amic)acid (PAA). The molar ratios of BTCA and APTES were 1/1 (B/A-1/1), 1/2 (B/A-1/2), 1/3 (B/A-1/3), and 1/4 (B/A-1/4). The as-prepared precursor solution was applied to cotton substrates. After thermal treatment (180°C) the physical-mechanical properties of the cotton samples were tested by means of dry crease recovery angle and tensile strength. For B/A-1/1 treated fabrics a significant improvement of the crease resistance was observed. FT-IR spectra revealed the formation of an imide group and an ester linkage, indicating the cross-linking of the cellulosic material. SEM images showed a smooth surface. As evidenced by TGA data the thermal stability of the cotton samples was not increased. No hydrophobicity could be observed. For B/A-1/3 and (B/A-1/4) modified cotton samples no crease resistant properties were detected. However, enhanced contact angle values were measured. A reaction mechanism for the formation of the ladder-like polysilsesquioxane and the cross-linking reaction is proposed.

Full text of DOI:10.1016/j.carbpol.2014.01.063

Accepted Manuscript
Title: Non-formaldehyde, crease resistant agent for cotton
fabrics based on an organic-inorganic hybrid material
Author: Christian Schramm Beate Rinderer Richard Tessadri
PII:
S0144-8617(14)00072-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.carbpol.2014.01.063
CARP 8527
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Received date:
Revised date:
Accepted date:
30-9-2013
16-1-2014
19-1-2014
Please cite this article as: Schramm, C., Rinderer, B., & Tessadri, R.,Non-formaldehyde,
crease resistant agent for cotton fabrics based on an organic-inorganic hybrid material,
Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.01.063
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1
Non-formaldehyde, crease resistant agent for cotton fabrics based on an
organic-inorganic hybrid material
Christian Schramm (corresponding author)
Research Institute of Textile Chemistry and Textile Physics, University Innsbruck
Höchsterstrasse 73, A-6850 Dornbirn, Austria
Phone: ++43(0)5572 28533 582
Fax: ++43(0)5572 28629
E-Mail: christian.schramm@uibk.ac.at
Beate Rinderer
Research Institute of Textile Chemistry and Textile Physics, University Innsbruck
Höchsterstrasse 73, A-6850 Dornbirn, Austria
Phone: ++43(0)5572 28533 582
Fax: ++43(0)5572 28629
E-Mail: beate.rinderer@uibk.ac.at
Richard Tessadri
Institute of Mineralogy and Petrography, University of Innsbruck, Bruno-Sander-Haus,
Innrain 52, A-6020 Innsbruck, Austria
Phone: +43(0)512 507 5509
Fax: +43(0)512 507 2926
E-Mail: richard.tessadri@uibk.ac.at
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Abstract
1,2,3,4-Butanetetracarboxylic acid (BTCA) was reacted with (3-aminopropyl)triethoxysilane
(APTES) to a poly(amic)acid (PAA). The molar ratios of BTCA and APTES were 1/1 (B/A-
1/1), 1/2 (B/A-1/2), 1/3 (B/A-1/3), and 1/4 (B/A-1/4). The as-prepared precursor solution was
applied to cotton substrates. After thermal treatment (180°C) the physical-mechanical
properties of the cotton samples were tested by means of dry crease recovery angle and tensile
strength. For B/A-1/1 treated fabrics a significant improvement of the crease resistance was
observed. FT-IR spectra revealed the formation of an imide group and an ester linkage,
indicating the cross-linking of the cellulosic material. SEM images showed a smooth surface.
As evidenced by TGA data the thermal stability of the cotton samples was not increased. No
hydrophobicity could be observed. For B/A-1/3 and (B/A-1/4) modified cotton samples no
crease resistant properties were detected. However, enhanced contact angle values were
measured. A reaction mechanism for the formation of the ladder-like polysilsesquioxane and
the cross-linking reaction is proposed.
Keywords
Cotton, crease resistance, polyimide, organic-inorganic hybrid, sol-gel
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1.
Introduction
Cellulosic material is chemically modified in an attempt to impart specific properties to cotton
fabrics or garments. Thus, cotton textiles are reacted with crease resistant finishing agents,
which react with the hydroxyl groups of the cellulose to improve the wrinkle resistance and
the dimensional stability. As a consequence the mechanical strength is decreased. The most
widely used crease resistant finishing agent is dimethyloldihydroxyethyleneurea (DMDHEU),
since this finishing chemical is very effective and inexpensive. However, DMDHEU tends to
release the potential human carcinogen formaldehyde during the curing process, the storage
and the consumer use (Bajaj, 2002; Hewson, 1994). Polycarboxylic acids, such as 1,2,3,4-
butanetetracarboxylic acid (BTCA) or citric acid (CA) in conjunction with sodium
hypophosphite (SHP) as appropriate catalyst are considered to be capable of replacing
DMDHEU. At elevated temperatures (180°C, 90s) the carboxyl groups of BTCA react with
the hydroxyl groups of the cellulose via a five-membered cyclic anhydride forming an ester
linkage (Harifi & Montazer, 2012; Welch, 1990; Welch & Andrews, 1989).
Different approaches have been used to substitute SHP as catalyst due to its adverse impact to
the environment (Choi, Li, Goodin & Pratt, 1994; Choi, 1993). A reduction of the
phosphorus-containing catalyst was obtained using nano-TiO2 as co-catalyst (Nazari,
Montazer, Rashidi, Yazdanshenas & Anary-Abbasinejad, 2009; Yuen, Ku, Kan, Cheng, Choi
& Lam, 2007).
To produce a novel formaldehyde-free crease resistant finishing agent BTCA was reacted
with APTES. The latter had been subjected to a hydrolysis reaction according to the sol-gel
process. In general, the sol-gel technology is based on the hydrolysis and the ensuing
condensation of tetraalkoxysilanes Si(OR)4, such as tetraethoxysilane (R = CH2CH3, TEOS)
or of organotrialkoxysilanes R1Si(OR2)3, such as methyltriethoxysilane (R1 = -CH3, R2 =
CH2CH3, MTEOS), thus forming a three dimensional siloxane network (Brinker & Scherer,
1990; Hench & West, 1990; Wright & Sommerdijk, 2001). This sol-gel method is also
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extensively applied to impart new properties to cotton textiles, such as antimicrobial function
(Lee, Broughton, Akdag, Worley & Huang, 2007; Montazer & Afjeh, 2007), flame retardancy
(Blanchard & Graves, 2002; Yang & Wu, 2003), water repellency (Gashti, Alimohammadi &
Shamei, 2012; Wang, Ding, Xue, Wang & Lin, 2011) or other functional properties (Mahltig
& Textor, 2008).
Various studies had been carried out to improve the non-formaldehyde crease resistant
properties of cotton fabrics using sol-gel technology (Ibrahim, Refai, Ahmed & Youssef,
2005; Lam, Kan & Yuen, 2011; Schramm, Binder & Tessadri, 2004).
The major objective of this paper is to present the results that were obtained, when cotton
fabrics were treated with a BTCA/APTES solution. The as-treated cellulosic material was
subjected to a curing process and subsequently evaluated in terms of crease resistant
properties, hydrophobic behavior and thermal stability. This approach had been selected since
a previous investigation has shown that the reaction of BTCA with APTES results in the
formation of a poly(amic) acid, which gives rise to the formation of a cyclic imide when cured
at elevated temperature (Schramm, Rinderer & Tessadri, 2012).
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2.
Experimental
2.1
Materials
Desized, scoured, bleached and mercerized 100% cotton fabric, weighing 109 g/m2, was used
throughout the investigation. The dyes: C.I. Reactive Red 141 and C.I. Reactive Black 5 (Fig.
1) as well as the textile auxiliaries were supplied by BEZEMA AG, Montlingen, Switzerland.
3-Aminopropyltriethoxysilane (100%, APTES, Fig. 1) was obtained from Wacker Silicone,
Burghausen, Germany. 1,2,3,4-Butanetetracarboxylic acid (> 99%, BTCA) (Fig. 1), was
purchased from Merck GmbH, Germany. Deionized water was used throughout the
investigation. The chemicals were used without further purification.
2.2
Preparation of the precursor solution
The standard procedure for the synthesis of a BTCA/APTES solution (molar ratio 1/1) in an
aqueous medium was as follows: APTES (7.07 mL, 30 mmol) was hydrolyzed with HCl (c =
0.05 mol/L, 2.70 mL) in deionized water (20 mL) under magnetic stirring (500 rpm) in a
polyethylene beaker (100 mL) for 15 hours at room temperature (RT). Subsequently, 20 mmol
of BTCA (7.02 g, 30 mmol) were added under vigorous stirring. Stirring was continued for 30
min and the solution was filled to 100 mL with deionized water.
2.3
Finishing of the cotton fabrics
The pre-weighed cotton fabrics (undyed and dyed) were impregnated with the corresponding
BTCA/APTES solution applying a two-roll laboratory padder (HVL 500 Mathis AG,
Niederhasli, Switzerland; air pressure 1 bar, rotary speed 3 m/min). After drying (5 min,
105°C) the as-treated fabric was cured in a lab dryer (LTE, W. Mathis AG, Switzerland) at a
specified temperature and for a specified time.
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2.4
Dyeing procedure
The dyeing process was conducted according to a standard dyeing procedure (Fig. 2). The
dyes were used with 4% on weight of fabric (owf), mass-to liquor ratio 1:15 and 2 hr total
dyeing time. After completion of dyeing, the fabrics were neutralized with acetic acid and
after-treated with anion active soaping product. Standard textile auxiliaries were used for the
process of dyeing: A: Meropan NX, Biavin 109; B: NaCl; C: Na2CO3 5.0 g/L, D: NaOH 38°
Bé, E: acetic acid, F: Cotoblanc NSR.
2.5
Testing methods
Colorimetric data measurements were conducted with the Spectrophotometer CM-3610d from
Konica Minolta, Japan. The color data software CM-S100w Spectra Magic NX V1.9 was
used for data acquisition. The whiteness index (WI) was calculated according to CIE.
Dry crease recovery angle (DCRA) was measured according to ISO 2312: 10 test specimens
were creased and compressed under controlled conditions of time and load. After removal of
the creasing load the angle formed between the two limbs was measured. The DCRA values
render possible the evaluation of a cross-linking reaction between a crease resistant finishing
agent and the cellulosic material.
Washing tests were conducted in accordance with the AATCC Method 61-2009. Abrasion
tests were performed according to DIN EN ISO 12947-3 (Martindale method).
Tensile strength (TS) was determined with the Material Testing System Z010 (Zwick/Roell,
Ulm, Germany) according to DIN EN ISO 13934.
FT-IR spectra were recorded with a Bruker Vector 22 spectrometer using a DTGS detector.
Since the FT-IR/ATR technique provided poor spectra, the KBr method was applied. Prior to
the preparation of the KBr pellets the cotton samples were cut into small pieces and ground
with a rotor mill ZM-1 (Retsch, Haan, Germany). The spectra were the result of 200 scans.
The spectral resolution was 4 cm-1.
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TGA measurements were conducted in air with the thermogravimetric analyzer Linseis STA
PT1000 (heating rate = 10°C/min; scan range = 40°C to 900°C).
The contact angles were measured using a home-made contact angle measuring instrument,
which consists of a digital microscope camera (DigiMicro 2.0 Scale; dnt GMBH,
Dietzenbach, Germany). The data acquisition had been performed by means of the software
Microcapture. A water droplet (15 µL) was deposited on the cotton sample by means of a
microliter syringe (Hamilton, Bonaduz, Switzerland), being placed on a glass slide, which
was mounted on a microscope stage equipped with a double side holder.
The precise contact angle measurement had been conducted using the software ImageJ
(Research Services Branch of the National Institute of Mental Health, Bethesda, Maryland,
USA), and the plugin Drop Analysis (Biomedical Imaging Group, Ecole Polytechnique
Federale de Lausanne, Switzerland) (Stalder, Kulik, Sage, Barbieri & Hoffmann, 2006).
3.
Results and discussion
The organotrialkoxysilane APTES contains the aminopropyl functionality as well as three
ethoxy groups. The latter is capable of reacting with water. As a result, ethanol is released and
silanol groups are formed which condensate to a siloxane network (Brinker & Scherer, 1990).
The amino group of APTES can react with the carboxy groups of BTCA thus forming a PAA.
Since BTCA contains vicinal carboxyl groups a thermal treatment of the PAA results in the
formation of a cyclic imide. This latter functionality can be readily determined by means of
FT-IR (Ahmad, Al Sagheer, Al Arbash & Ali, 2009; Schramm, Rinderer & Tessadri, 2012;
Snyder, Thomson, Bartges, Czerniawski & Painter, 1989; Sroog, 1967). The aqueous reaction
mixtures of BTCA and APTES (molar ratio 1/1 and 1/4) were applied to cotton materials and
treated at elevated temperatures in an attempt to evaluate the surface modification in terms of
the crease resistant properties of the as-treated cotton samples.
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3.1
Application of APTES solution to cotton fabrics
For comparison purposes, the cotton raw material had been impregnated merely with a
solution containing pre-hydrolyzed APTES (30 mmol/2.7 ml HCl/20 ml deionized water).
Thereafter the samples were cured at various elevated temperatures (110°C, 160°C, 180°C,
200°C, and 220°C) for 5 min. The findings are presented in Table 1. The denotations of the
samples are as follow: A-110-5 indicates the cotton samples which had been impregnated
with an APTES solution and which were treated at 100°C for 5 min.
Compared to the untreated cotton fabric no significant improvement of the DCRA values for
the APTES-treated cotton specimens can be observed. The tensile strength is moderately
decreasing as the temperature increases. A significant reduction of the WI can be observed
when the curing temperature increases. This phenomenon can be attributed to decomposition
products originating from the organic group of APTES. The data presented reveal that the
application of APTES to cotton fabrics has no effect on the crease resistant parameters. No
experimental runs had been performed with respect to BTCA, since previous investigations
already have given evidence that the treatment with BTCA solutions without an appropriate
catalyst is not effective in terms of crease resistant properties (Welch, 1988).
3.2
Application of BTCA/APTES solution to cotton fabrics
In an attempt to evaluate the impact of the curing temperature as well as of the curing time on
the physical properties cotton fabrics were impregnated with finishing solutions consisting of
BTCA and APTES with molar ratios of 1/1, 1/2, 1/3 and 1/4. The impregnated cotton samples
were subjected to a drying process (100°C, 3 min) to remove the excess of water and ethanol
which were released during the hydrolysis of APTES. Subsequently, the as-prepared samples
were cured at 110°C, 160°C, 180°C, 200°C and 220°C each for 5 min and 15 min,
respectively. The results of the physical tests (DCRA, TS and WI) are shown in Table 1. The
denotations of the samples are as follow: B/A-1/x-110-5 indicates the cotton samples which
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had been impregnated either with an equimolar solution of BTCA and APTES (x = 1) or a
BTCA/APTES solution with a molar ratio of 1/2, 1/3, 1/4 (x = 2, 3, 4). The second and third
term indicate the curing temperature 100°C and the curing time 5 min.
Compared to the cotton raw material the DCRA values of B/A-1/1-110-5 as well as of B/A-
1/1-110-15 are almost at the same level, indicating that no cross-linking reaction has occurred.
These findings are confirmed by the TS data which have nearly the same values as the
untreated cotton fabrics. These phenomena can also be observed with respect to the other
cotton samples (x = 2, 3, 4). The WI values are moderately lowered when BTCA and APTES
were reacted at the molar ratio of 1/2, whereas a significant reduction of the WI values is
obtained in the case of B/A-1/3-110 and B/A-1/4-110.
An increase of the curing temperature gives rise to a significant improvement of the DCRA
values for cotton fabrics having been treated with B/A-1/1 solutions. This phenomenon
indicates that a cross-linking reaction has taken place under the curing conditions chosen. The
DCRA values of the B/A-1/2 samples are remarkably reduced, whereas the B/A-1/3 and B/A-
1/4 specimens show almost no increase in the DCRA values. The opposite tendency can be
observed with respect to the TS data. The values for the B/A-1/3 and B/A-1/4 fabrics are very
close to those of the raw material. The same trend can be noticed with respect to the WI
values, which were significantly reduced when the curing temperature was increased.
An extension of the curing time from 5 to 15 min brings about a very moderate enhancement
of the DCRA values. The TS values are slightly lower. The same trend applies to the WI
values.
The decrease of the WI is presumably due to the thermo-oxidative instability of the PAA. It is
suggested that the scission of the amide bond results in the formation of species containing the
amine functionality. Under the thermo-oxidative conditions given the latter can be converted
into various organic compounds, such as imines, imides, aldehydes, alkenes etc (El-Mazry,
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Ben Hassine, Correc & Colin, 2013; Richaud, Diogo, Fayolle, Verdu, Guilment & Fernagut,
2013).
B/A-1/1-180-15 had been subjected to a washing test. Five washing cycles had been
performed. Compared to the unwashed specimen the DCRA values were reduced by 5.2 %.
The tensile strength maintained at the same level, indicating that the wrinkle resistance
withstands several washing treatments. The abrasion test was conducted in comparison to the
raw material. After 10000 cycles the B/A-1/1-180-15 modified cotton samples showed
deterioration (hole formation) whereas the raw material was destroyed after 12000 cycles.
These findings give evidence that the chemical modification of the cotton fabric by means of
B/A-1/1 results in a decrease of the abrasion resistance.
To confirm the formation of the imide group the normalized FT-IR spectra of B/A-1/1-180-15
(3a), B/A-1/1-220-15 (3b), and B/A-1/4-220-15 (3c) were recorded (Fig. 3). A comparison of
the normalized spectra 3a-3c at 1771 cm-1 (asymmetric carbonyl stretching mode of imide
group, Imide I) and at 1721 cm-1 (symmetric carbonyl stretching mode of imide group, Imide
I) make evident that an imide functionality is present in B/A-1/1-180-15 as well as in B/A-
1/1-220-15. In this region no absorption band can be observed for B/A-1/4-220-15, indicating
that no cyclic imide ring had been formed during the curing process at 220°C. The spectra 3a
as well as 3b show a shoulder at 1739 cm-1 which can be assigned to a stretching vibration of
an ester carbonyl bond, which proves the cross-linking reaction of the hydroxyl groups of the
cellulose and the carboxyl groups of the organic-inorganic hybrid. An inspection of the
spectrum of B/A-1/4-220-15 (3c) reveals that no absorption band can be observed at 1739 cm-
1, indicating that no ester bond was built.
All the findings mentioned above clearly make evident, that the B/A-1/1 formulation is
capable of endowing cotton fabrics with excellent crease resistant properties. The results of
the physical-mechanical measurements undoubtedly reflect that a cross-linking reaction had
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occurred between the cellulose material and the organic-inorganic hybrid. The inspection of
the FT-IR spectra confirms that the cross-linking reaction is obtained by ester linkages.
No crease resistant performance could be achieved through applying a finishing bath
containing BTCA and APTES with the molar ratio of 1/3 and 1/4. This fact will be explained
in a later section (Mechanism of the cross-linking reaction).
3.3
Morphology of the BTCA/APTES treated cotton fabrics
The morphological structure of cellulose samples which had been treated with BTCA/APTES
solutions were observed using SEM (Fig. 4). Fig. 4a shows the image of untreated cotton
material (4a) for comparison purposes. Fig. 4b shows the morphological characteristics of
B/A-1/1-220-15 and those of BA-1/4-220-15 (4c). The scanning electron micrograms of the
B/A treated cotton samples show that the most part of the surface is smooth. No obvious
difference in shape between the cotton fabric before and after sol-gel treatments can be
observed. No thin coating can be observed on the surface or in the interstices of the cotton
fibers. Therefore, it can be concluded that the PAA having been formed through the reaction
of BTCA with APTES in the finishing solution has penetrated into the cotton fibers. Upon
heating the as-prepared cotton specimen the cross-linking reaction occurred between the
cellulose and the cross-linking agent.
3.4
Thermostability of the BTCA/APTES treated cotton fabrics
Cotton is regarded to be one of the most flammable fibers. Therefore, intensive investigations
have been undertaken in an effort to improve the flame retardancy of cellulosic-based
materials, since they are widely used for apparel (protection clothing), home furnishing (cover
fabrics, upholstery) and technical textiles (Horrocks & Anand, 2004; Tesoro, 1978). Cotton
substrates had been coated with novel materials which were produced by means of the sol-gel
process to improve the thermal stability (Alongi, Ciobanu & Malucelli, 2011).
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Since PI materials are well known for their outstanding properties at elevated temperatures,
the B/A-treated cotton fabrics were tested in terms of their thermal stability by means of
thermogravimetric analysis, which has proven as an excellent analytical tool to estimate the
thermal behavior of materials (Simkovic, 2012; Zhu, Sui, Wang, Sun & Sun, 2004).
Fig. 5 shows the thermograms as well as the corresponding DTG curves of the cellulosic raw
material (TG: 5a, DTG: 5d), B/A-1/1-220-15 (TG: 5b, DTG: 5e), B/A-1/4-220-15 (TG: 5c,
DTG: 5f). An inspection of the curves makes evident, that the treatment of the cotton samples
with a BTCA/APTES solution does not result in an improvement of the thermal stability of
the cotton material. A comparison of the DTG curves of B/A-1/1-220-15 (5e) and of the
untreated cotton fabric (5d) reveals that the DTG maxima temperature of B/A-1/1-220-15 is
reduced. No pristine BTCA is present on the fabric, since no DTG peak at 311°C is visible.
3.5
Contact Angle of the BTCA/APTES treated cotton fabrics
The possibility of imparting multifunctional features to a fabric represents one of the main
goals that the researchers aim to achieve. Therefore, the impact of the BTCA/APTES
treatment on hydrophobicity had been investigated by measuring the contact angle, since
various investigations have shown that cotton material can be endowed with hydrophobicity
using different methods (Bae, Min, Jeong, Lee, Jang & Koo, 2009; Bhat, Netravali, Gore,
Sathianarayanan, Arolkar & Deshmukh, 2011; Gashti, Alimohammadi & Shamei, 2012; Liu,
Chen & Xin, 2008). Fig. 6 shows the water droplet which was deposited on a cotton fabric
treated with B/A-1/4 solution at 220°C for 15 min. Measurable values only could be obtained
when the cotton samples were treated with B/A-1/4 (Table 2). The other cotton samples
showed no improved contact angle values compared to the raw material. This phenomenon
can be explained by the fact that all the carboxyl groups of the BTCA had been converted into
amide groups.
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3.6
Dyeing properties of the BTCA/APTES treated cotton fabrics
A previous study revealed that the application of tetraethoxysilane, triethoxypropylsuccinic
anhydride or APTES did not cause a change of the color properties of cotton samples having
been dyed with C.I. Reactive Red 141 or C.I. Reactive Black 5 (Fig. 1). (Mahltig & Textor,
2006; Schramm & Rinderer, 2011)
To evaluate the impact of the BTCA/APTES treatment on the properties of dyed cotton
fabrics, cotton samples were dyed with 2% owf and 4% owf C.I. Reactive Red 141 (Red) and
2% owf and 4% owf C.I. Reactive Black 5 (RBlack), respectively. Subsequently, all dyed
cotton samples were treated with a B/A-1/1 solution at 180°C for 15 min. The samples are
denoted as follow: RBlack-2-B/A-1/1 indicates the sample having been dyed with 2% owf
C.I. Reactive Black 5. Subsequently, the sample was treated with an equimolar
BTCA/APTES solution and cured at 180°C for 15 min.
The cotton samples were tested with respect to the colorimetric data ! L*, ! a*, ! b* and the
color difference DE* (Table 3). The dyed and untreated samples were applied as references.
Almost no alteration can be observed, when the cotton samples were dyed with C.I. Reactive
Red 141 and C.I. Reactive Black 5. These results give clear evidence that no interaction of the
dyestuffs with the components of the precursor solution takes place during the curing process
at elevated temperatures.
3.7
Successive application of BTCA and APTES to cotton fabric
Firstly, cotton samples were impregnated with a solution containing BTCA and dried at
100°C for 3 min. Subsequently, prehydrolysed APTES solutions (molar ratio B/A-1/1, and
B/A-1/4) were applied to the as-prepared cotton fabrics. The latter were dried again and cured
at 180°C for 15 min. The findings of the physical tests are presented in Table 4 and reveal that
the DCRA values are much lower than those which had been measured when BTCA and
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APTES were applied in a combined solution (Table 4). The higher TS values also confirm the
moderate effect of that treatment. The WI values are almost the same.
These experimental runs make evident that no cross-linking occurs when BTCA and APTES
are applied sequentially.
3.8
Mechanism of the cross-linking reaction
Crease resistant chemicals which are capable of cross-linking cellulose can be divided into
two categories: the reactants which predominately cross-link with the cellulose forming a
covalent bond with the hydroxyl group of the cellulose and the self-cross-linker which
primarily self-polymerize thus forming a three-dimensional network (Harifi & Montazer,
2012).
The present, novel crease resistant agent can be assigned as a reactant, since B/A-1/1 contains
vicinal, free carboxyl groups, as shown in a previous study (Schramm, Rinderer & Tessadri,
2012). These carboxyl groups are capable of reacting with the hydroxyl groups of the
cellulosic material via a five-membered cyclic anhydride intermediate (Gu & Yang, 2000;
Yang, 1993).
Fig. 7 describes the reaction mechanism. APTES is hydrolyzed in an aqueous medium. As a
consequence the ethoxy groups are converted into silanol groups. The addition of a solution
containing an equimolar amount of BTCA results in the formation of an amide functionality.
The as-prepared finishing solution is applied to the cotton fabric. At elevated temperature the
silanol groups condense to siloxane units.
Based on the results which are presented in a previous paper, it can be concluded that a
ladder-like polysilsesquioxane is produced (Schramm, Rinderer & Tessadri, 2012). The
thermal treatment at 220°C results in the production of an imide group as well as of cyclic,
five-membered anhydride functional groups. The latter are assumed to react as an
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intermediate with the hydroxyl groups of the cellulosic material thus forming an ester linkage
which leads to the cross-linking of the cellulose (Gu & Yang, 2000).
When BTCA reacts with APTES at a molar ratio of 1/3, three carboxylic groups of BTCA are
converted to amide functionalities. At a molar ratio of 1/4 all four carboxylic functionalities of
BTCA react to an amide group. As a consequence no imide groups and no cyclic, five-
membered anhydride moieties can be formed. However, the generation of cyclic anhydrides is
necessary to obtain an ester linkage between the ladder-like polysilsesquioxane and the
cellulosic material. This phenomenon explains why B/A-1/3 or B/A-1/4 treated cotton
samples possess very poor crease resistant properties.
Fig. 8 demonstrates potential cross-linkage of the polysilsesquioxane and the hydroxyl groups
of the cellulosic material. The formation of the cross-link as shown in Fig. 8a seems rather
unlikely since the silanol groups will be converted into siloxane entity during the curing
process. The cross-link depicted in Fig. 8b takes into account the formation of a siloxane
network but still contains unreacted, vicinal carboxyl groups, which are capable of reacting
with the hydroxyl groups of the cellulose. Therefore, it can be assumed that each entity
containing vicinal carboxyl groups will be converted to an ester linkage as shown in Fig. 8c.
4.
Conclusions
Cotton fabrics were impregnated with various solutions containing BTCA and APTES using
different molar ratios (1/1, 1/2, 1/3 and 1/4). The as-treated samples were cured at 110°C,
160°C, 180°C, 200°C and 220°C for 5 min and 15 min, respectively, and evaluated in terms
of DCRA, TS and WI. The findings give clear evidence that an improvement of the DCRA
values can be observed when BTCA and APTES were used in the molar ratios of 1/1 and 1/2
and cured at elevated temperatures. An increase of the curing periods resulted in a moderate
improvement of the DCRA values. The increase in the DCRA values resulted in a decrease in
the TS values and WI. In contrast, the B/A-1/3 and B/A-1/4 treated samples showed no
Page 15 of 33

16
improved crease resistant properties compared to the untreated cotton fabric. TG
measurements revealed that no improvement of the thermal stability could be obtained. B/A-
1/4 treated cotton samples were endowed with enhanced hydrophobicity. No phosphorus-
containing catalyst, such as SHP, was applied to impart crease resistant performance.
5.
Acknowledgements
The authors would like to thank the Testing Institute of the HTL Dornbirn (Austria) for
making available textile-physical devices.
Page 16 of 33

17
6.
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7.
Captions of Figures and Tables
Fig. 1
Fig. 2
Formula of substances of interest.
Dyeing procedure. A: Meropan NX, Biavin 109; B: NaCl; C: Na2CO3 5.0 g/L,
D: NaOH 38° Bé, E: acetic acid, F: Cotoblanc NSR.
Fig. 3
Fig. 4
Fig. 5
FT-IR spectra of B/A-1/1-180-15 (3a), B/A-1/1-220-15 (3b), and B/A-1/4-220-
15 (3c).
SEM images of cotton raw material (4a), and BTCA/APTES treated cotton
samples: B/A-1/1-220-15 (4b) and BA-1/4-220-15 (4c).
TG and DTG curves of the cellulosic raw material (TG: 5a, DTG: 5d) and the
BTCA/APTES treated cotton samples: B/A-1/1-220-15 (TG: 5b, DTG: 5e), B/A-
1/4-220-15 (TG: 5c, DTG: 5f).
Fig. 6
Fig. 7
Fig. 8
Water droplet deposited on a cotton fabric treated with B/A-1/4 solution at
220°C for 15 min.
Reaction scheme for the formation of the ladder-like polysilsesquioxane based
on the reaction of APTES and BTCA at elevated temperature.
Potential cross-linkage of the ladder-like polysilsesquioxane with the hydroxyl
groups of the cellulose. (8a) single (8b) partial (8c) complete conversion of the
vicinal carboxyl groups to ester linkages.
Table 1
Physical–mechanical properties of cotton fabrics treated with an APTES solution
(A) and BTCA/APTES solution with different molar ratio (B/A-1/1, B/A-1/2,
B/A-1/3 and B/A-1/4) at various curing temperatures and curing times.
Contact angle values of B/A-1/4 treated at various temperatures.
Table 2
Table 3
Colorimetric data of dyed fabric (C.I. Reactive Red 141: Red-2 and Red-4) and
C.I. Reactive Black 5: RBlack-2 and RBlack-4) which had been treated with a
B/A-1/1 solution at 180°C for 15 min.
Table 4
Physical–mechanical properties of cotton fabrics treated with B/A-1/1 and B/A-
1/4 solutions – successive application of BTCA and APTES.
Page 19 of 33

21
Highlights
A novel non-formaldehyde crease resistant agent has been applied to cotton fabrics
The finishing agent consists of an organic-inorganic hybrid which is prepared by sol-gel
process
No phosphorous containing catalyst is necessary
The treated cotton fabrics show good crease resistant properties.
Page 20 of 33

Table(s)
DCRA (w+f) [°]
Tensile strength [%]
Whiteness index
molar ratio
1/1
1/2
1/3
1/4
1/1
1/2
1/3
1/4
1/1
raw material
A-110-5
A-160-5
A-180-5
A-200-5
A-220-5
190.8
204.4
197.8
191.8
184.6
194.0
100.0
62.4
54.4
34.2
9.9
98.7
97.6
96.6
94.8
-16.6
-32.6
91.7
B/A-1/x-110-5*
B/A-1/x-110-15
214.6
216.2
226.8
227.2
210.4
214.8
175.0
165.2
95.9
97.9
99.4
98.3
98.4
93.5
95.9
65.0
65.2
108.0
B/A-1/x-160-5
B/A-1/x-160-15
258.4
271.4
252.3
260.1
218.3
215.3
180.8
174.8
92.5
85.5
93.8
96.1
94.5
98.3
90.7
50.1
43.0
103.9
B/A-1/x-180-5
B/A-1/x-180-15
274.4
294.2
261.3
268.5
216.5
216.7
180.4
189.2
84.2
73.9
87.4
80.1
96.4
93.4
101.3
92.8
30.9
18.1
B/A-1/x-200-5
B/A-1/x-200-15
287.8
289.6
269.5
273.4
219.5
226.4
181.8
188.4
76.2
68.2
79.4
76.5
93.4
91.8
94.3
92.5
1.9
-6.3
B/A-1/x-220-5
B/A-1/x-220-15
289.4
296.8
269.3
275.4
225.3
228.5
197.8
214.0
63.3
55.6
75.4
73.5
91.6
92.3
99.7
82.9
-14.5
-22.4
* x = 1, 2, 3 or 4
Page 21 of 33

23
table 2
Contact angle [°]
B/A-1/4-110-5
B/A-1/4-160-15
B/A-1/4-180-5
B/A-1/4-180-15
B/A-1/4-200-5
B/A-1/4-200-15
B/A-1/4-220-5
B/A-1/4-220-15
122.9
126.2
123.3
114.8
121.4
123.4
125.6
118.2
Page 22 of 33

24
DE*
! L*!
! a*!
! b*!
Red-2-B/A
Red-4-B/A
0.25
0.27
1.08
0.19
1.66
1.70
2.0
1.7
RBlack-2-B/A
RBlack-4-B/A
-0.93
-1.04
0.67
0.36
-0.50
0.21
1.3
1.1
reference: dyed, untreated raw material
Table 3
Page 23 of 33

25
DCRA (w+f) [°]
Tensile strength [%] Whiteness index
raw material
190.8
243.6
146.6
100.0
78.5
99.5
62.4
17.1
1.7
B/A-1/1-180-15
B/A-1/4-180-15
table 4
Page 24 of 33

Fig 1
BTCA
APTES
R1 =
C.I. Reactive Red 141
C.I. Reactive Black 5
Page 25 of 33

Fig 2
F
100
90
80
70
60
50
40
30
20
10
0
D
E
A B C
0
20
40
60
80
100
120
140
160
180
200
Time [min]
Page 26 of 33

Fig 3
5
4
3
2
1
0
1695
1645
1632
B/A-1/4-220-15
3c
1721
1739
1771
3c
3b
B/A-1/1-220-15
B/A-1/1-180-15
3b
3a
3a
1800
1750
1700
1650
1600
1550
1500
Wavenumber [cm-1]
Page 27 of 33

Fig 4
4a
4b
4c
Page 28 of 33

Fig 5
100
80
60
40
20
5a
5c
5b
0
0,0
-0,1
-0,2
-0,3
-0,4
5e
5d
5f
100
200
300
400
500
600
700
800
Temperature [°C]
Page 29 of 33