Multifunctional finishing of cotton fabrics with 3,3′,4,4′- benzophenone tetracarboxylic dianhydride: Reaction mechanism

Article abstract of DOI:10.1016/j.carbpol.2013.02.027

Aqueous solutions of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BPTCD) were successfully employed in treatment of cotton fabrics to bring multiple functions onto the cotton cellulose. The overall reaction mechanism of the chemical finishing process was investigated. Results revealed that the dianhydride groups of BPTCD were hydrolyzed to tetracarboxylic acid groups, and the acid could directly react with hydroxyl groups on cellulose under the catalyst sodium hypophosphite to form ester bonds. Such a mechanism is different from the mostly recognized formation of anhydride from polycarboxylic acid and then esterification between the anhydride with hydroxyl groups. FTIR, DSC and thermogravimetric analyzer (TGA) were employed in the analysis of the reactions, respectively.

Full text of DOI:10.1016/j.carbpol.2013.02.027

Carbohydrate Polymers 95 (2013) 768–772
Contents lists available at SciVerse ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Multifunctional finishing of cotton fabrics with
ꢀ
ꢀ
3
,3 ,4,4 -benzophenone tetracarboxylic dianhydride:
Reaction mechanism
Aiqin Houa,b, Gang Sunb,∗
a
National Engineering Research Center for Dyeing and Finishing of Textiles, Donghua University, Shanghai 201620, PR China
Division of Textiles and Clothing, University of California, Davis, CA 95616, United States
b
a r t i c l e i n f o
a b s t r a c t
ꢀ
ꢀ
Article history:
Aqueous solutions of 3,3 ,4,4 -benzophenone tetracarboxylic dianhydride (BPTCD) were successfully
employed in treatment of cotton fabrics to bring multiple functions onto the cotton cellulose. The overall
reaction mechanism of the chemical finishing process was investigated. Results revealed that the dianhy-
dride groups of BPTCD were hydrolyzed to tetracarboxylic acid groups, and the acid could directly react
with hydroxyl groups on cellulose under the catalyst sodium hypophosphite to form ester bonds. Such
a mechanism is different from the mostly recognized formation of anhydride from polycarboxylic acid
and then esterification between the anhydride with hydroxyl groups. FTIR, DSC and thermogravimetric
analyzer (TGA) were employed in the analysis of the reactions, respectively.
Received 19 January 2013
Accepted 9 February 2013
Available online 21 March 2013
Keywords:
Esterification of cellulose
Catalytic effect
FTIR spectra
©
2013 Elsevier Ltd. All rights reserved.
1
. Introduction
cellulose, and the benzophenone group could introduce photo-
active antimicrobial functions to the products. However, due to
the use of DMF as a solvent, the treatment process is not practi-
cal to textile industry. Since the two anhydride groups in BPTCD
could be hydrolyzed to tetracarboxylic acids, which will make the
compound, benzophenone tetracarboxylic acid (BPTCA), soluble
in hot water, direct use of BPTCD aqueous solutions as finish-
ing baths of cotton fabrics is possible. Thus, a process of using
hydrolyzed BPTCD in aqueous solutions in treatment of cotton
fabrics was developed, and the process was successful and indus-
trially practical. Based on the well-recognized reaction mechanism
of polycarboxylic acids in crosslinking cellulose, the polycarboxylic
acids should form anhydrides on cotton which then can form ester
bonds with cellulose (Yang, 2003; Yang & Wang, 1996). Thus, the
benzophenone tetracarboxylic acid should form BPTCD again on
cellulose, and an esterification reaction should occur between the
anhydride and hydroxyl groups on cellulose consequently under
elevated temperatures. However, the results obtained in this treat-
ment of cotton fabrics revealed that the polycarboxylic acids in
the system could directly react with hydroxyl groups under the
catalyst, sodium hypophosphite, and form ester bonds without
going through the formation of anhydride. To further prove and
understand the overall reactions of the benzophenone tetracar-
boxylic acid on cellulose, FTIR spectrometer, differential scanning
calorimeter (DSC) and thermogravimetric analyzer (TGA) were
employed in the structural analysis of the materials. The reac-
tion condition and potential mechanism are discussed in this
paper.
Wrinkle-free treatment of cotton fabrics is generally achieved
by chemically crosslinking cotton cellulose by using tradi-
tional formaldehyde containing N-methylol compounds or non-
formaldehyde 1,2,3,4-butanetetracarboxylic acid (BTCA) (Hashem,
Ibrahim, El-Shafei, Refaie, & Hauser, 2009; Lam, Kan, & Yuen,
2
011; Yang & Wei, 2000a, 2000b). The ultraviolet (UV) protec-
tive function on the fabrics, which is important for protecting both
materials and wearers (Gouda & Keshk, 2010; Lu, Fei, Xin, Wang,
&
UV blockers onto the fabric (Czajkowski, Paluszkiewicz, Stolarski,
Ka z´ mierska, & Grzesiak, 2006; Hatch & Osterwalder, 2006; Hou,
Zhang, & Wang, 2012; Ibrahim, E-Zairy, & Eid, 2010; Wang & Hauser,
Li, 2006), can be obtained by incorporating UV absorbents or
2
010). To obtain both functions, multi-step chemical treatments of
cotton fabrics should be carried out, which could consume large
quantity of water and energy and consequently increase costs
and environmental impacts. Thus, development of energy efficient
multi-functional finishing processes of textiles is extremely impor-
tant.
In a previous research, 3,3 ,4,4 -benzophenone tetracarboxylic
dianhydride (BPTCD) was directly incorporated to cotton cellu-
lose by using N,N-dimethylformamide (DMF) as a solvent (Hong &
Sun, 2011). The results proved that the BPTCD could crosslink with
ꢀ
ꢀ
∗ Corresponding author. Tel.: +1 530 752 0840; fax: +1 530 752 7584.
E-mail address: gysun@ucdavis.edu (G. Sun).
0
144-8617/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carbpol.2013.02.027

A. Hou, G. Sun / Carbohydrate Polymers 95 (2013) 768–772
769
2
. Experimental
2.1. Materials
Desized, scoured, and bleached pure cotton plain woven fabrics
#400) were purchased from Test Fabrics, Inc. (West Pittston, PA).
(
ꢀ ꢀ
3
,3 ,4,4 -Benzophenone tetracarboxylic dianhydride (BPTCD) and
sodium hypophosphite monohydrate were purchased from Sigma
Chemical Co. (Louis, MO, USA). All other chemicals were purchased
from Fisher Scientific (Pittsburgh, PA, USA). All reagents were used
as received without any further purification.
2.2. Preparation of functional cotton fabrics
BPTCD was dissolved in distilled water in a concentration of 70 g
◦
per liter (70 g/L) at 70–80 C under agitation. Sodium hypophos-
phite monohydrate was added as a catalyst to the BPTCD solution
based on a molar ratio of the catalyst versus BPTCD (Yang, 2003;
Yang & Wang, 1996). The cotton fabric was first impregnated in
the solution containing both BPTCD and the catalyst, then padded
Fig. 1. FTIR spectra of: (a) untreated (control) cotton fabric; (b) fabric treated with
BPTCD solution (70 g/L) and cured at 160 C; (c) cured and after regular washing;
and (d) cured and after alkaline washing.
◦
through two dips and two nips to reach an average wet pickup of
◦
1
20%, dried at 80 C for 5 min, and cured in a curing oven (Roaches
International Ltd., Staffordshire, England) at a specified tempera-
ture for 3 min. And finally the treated fabrics were washed with
water. Additional washing in sodium hydroxide (0.1 N) was per-
formed for FTIR analysis only.
alkaline washing treatment of the fabric also proved durable ester
bond connection between BPTCA and cotton cellulose.
3.2. Whether anhydride is formed first?
2.3. Characterization of treated fabrics
According to the reaction mechanism of butane tetracarboxylic
Fourier transform infrared (FTIR) spectroscopy was performed
acid (BTCA) reaction on cellulose, the polycarboxylic acid groups
will form anhydride, and then the active anhydride will react with
hydroxyl groups of cellulose to form ester bonds under a catalyst,
sodium hypophosphite and an elevated temperature (Yang, 2003;
Yang & Wang, 1996). Such a mechanism was our initial speculation
with a Nicolet 6700 FTIR spectrometer (Thermo Electron Co., USA)
−1
with a resolution of 4 cm , and measurements were carried out
by using KBr pellets. Differential scanning calorimeter (DSC) and
Thermogravimetric analysis (TGA) of samples were carried out
using a Shimadzu DSC-60 and TGA-60 system (Shimadzu Science
ꢀ
ꢀ
on this treatment process. Thus, 3,3 ,4,4 -benzophenone tetracar-
boxylic acid (BPTCA) on the finished cotton fabrics should return
to its original anhydride structure of BPTCD, and then the anhy-
dride group will react with hydroxyl group, during curing. The
formed anhydride group should be observed in the infrared spec-
trum of the treated cotton. However, the FTIR of the treated fabric
◦
Instruments, Inc., USA) at a heating rate of 10 C/min from room
◦
temperature to 500 C under a nitrogen atmosphere.
3
. Results and discussion
◦
3
.1. BPTCD treatment of cotton fabrics
sample (cured at 160 C for 3 min) did not show a clear signal
of the expected anhydride group (Fig. 1b). Instead, strong vibra-
−
1
The anhydride groups in BPTCD are both reactive with water and
tional absorbance at around 1722 cm , representing both ester
and carboxylic acid groups, is shown. This result was unexpected
and consequently raised questions on the reaction mechanism of
BPTCA with cellulose. Thus, a series of experiments were designed
and conducted on the BPTCD treated cotton fabrics to confirm the
observations from FTIR analysis. Fabric samples impregnated in an
aqueous solution containing 70 g/L of BPTCD (catalyst in a molar
ratio of 0.5) were treated in the following steps, (a) only dried at
hydroxyl groups in cellulose structure, and the reactions between
these groups can lead to formations of carboxylic acids and ester
bonds quickly (Yang, 2003; Yang & Wang, 1996). When BPTCD is
added into hot water, the anhydride will be hydrolyzed to polycar-
boxylic acids, making the compound soluble in water. The solution
was applied onto fabrics by a dip-nip-dry-cure process. Fabrics
were treated with a solution of 70 g/L of BPTCD in a wet pick up
◦
◦ ◦
80 C for 5 min and no washing; (b) dried at 80 C for 5 min and
cured at 160 C for 3 min without washing; (c) dried at 80 C for
5 min and cured at 200 C for 3 min without washing. FTIR spectra
rate of 120%, dried at 80 C. The chemical structures of the aqueous
◦
◦
BPTCD solution treated cotton fabrics were examined by using FTIR.
Fig. 1 shows FTIR spectra of the untreated (control) cotton fabric
◦
(
8
Fig. 1a), the fabric treated with the BPTCD solution (70 g/L), dried at
0 C, and cured at 160 C (Fig. 1b), cured and after regular washing
of the samples were carefully taken and are shown in Fig. 2.
The spectrum (a) in Fig. 2 confirmed that the chemical applied
onto the cotton is mostly an acid or polycarboxylic acid not an
◦
◦
(Fig. 1c), and cured and after alkaline washing (Fig. 1d), respectively.
−1
−1
The formation of carbonyl bonds at 1722 cm on the cotton sam-
ple treated with BPTCA is clearly noticeable in Fig. 1b–d. Regular
washing did not remove the incorporated chemical (Fig. 1c). After
alkaline (0.1 N NaOH) washing, the band at 1722 cm weakened
but a strong new band at 1586 cm appeared, which is correspond-
ing to carboxylate ions (COO ), indicating that free carboxylic acids
are converted to the salt of the acid. The vibrational absorbance at
1
anhydride since no characteristic anhydride peaks (1855 cm and
−
1
1778 cm ) are existing in the FTIR spectrum (Fig. 2a). After the fab-
◦
ric was cured at 160 C for 3 min, the FTIR spectrum (Fig. 2b) did not
−
1
show clear signal of anhydride peaks either. However, after cured
−1
◦
at a higher temperature, 200 C, for 3 min, the spectrum revealed
−
quite weak but noticeable anhydride peaks (Fig. 2c), meaning that
◦
anhydride groups were formed at 200 C. Such a result is very inter-
−
1
722 cm in Fig. 1d is a clear signal of formation of ester bonds
esting and different from the literatures (Yang, 2003; Yang & Wang,
◦
between the benzophenone derivative and cellulose, while the
existence of free acid show overlapped band at 1722 cm . The
1996), indicating that at 160 C almost no anhydride group was
−
1
formed but ester bonds between BPTCD and cellulose were indeed

7
70
A. Hou, G. Sun / Carbohydrate Polymers 95 (2013) 768–772
Fig. 4. TGA of pure cotton and TGA and first derivative of TGA of BPTCD treated
cotton with the catalyst: (a) TGA of pure cotton; (b) TGA of BPTCD treated cotton
with the catalyst; and (c) first derivative of TGA of BPTCD treated cotton with the
catalyst.
Fig. 2. FTIR spectra of cotton fabric treated with 70 g/L of BPTCD without washing:
◦
◦
◦
(
a) only dried at 80 C for 5 min; (b) dried at 80 C for 5 min and cured at 160 C for
◦ ◦
min; and (c) dried at 80 C for 5 min and cured at 200 C for 3 min.
3
major weight loss. The addition of the catalyst did not obviously
alter the formation temperature of the anhydride rings and the
decomposition temperature of the compound according to the TGA
(Fig. 3c). The slight loss of weight in the thermogram is caused
by hydrate molecules in the catalyst. However, there is no evi-
dence showing that the addition of the catalyst affected formation
of anhydride structure of this polycarboxylic acid (BPTCA).
established. It suggested that
between polycarboxylic acid and cellulose occurred. FTIR results
also confirmed formation of anhydride of BPTCA on the cellulose
a direct esterification process
◦
under a much higher temperature (200 C), which could cause more
negative impacts on the treated fabrics. However, the newly formed
anhydride groups should be able to react with cellulose to produce
ester bonds or crosslinking cellulose as well.
Then, both pure cotton and a cotton fabric sample impregnated
with a solution containing 70 g/L BPTCD and a catalyst in a molar
◦
ratio of 0.5 and dried at 80 C were subjected to similar TGA tests.
3.3. Catalytic effect of sodium hypophosphite
TGA spectra of the fabric samples are shown in Fig. 4. The TGA of the
treated cellulose shows smooth and continuous weight reduction
(1.44%) in a temperature range of 100–200 C (Fig. 4b), while the
To further confirm the observation from FTIR, BPTCD was
◦
ꢀ
ꢀ
hydrolyzed in hot water again, and its acid derivative, 3,3 4,4 -
benzophenone tetracarboxylic acid (BPTCA), was produced. Pure
BPTCA was heated up to decomposition in both DSC and TGA appa-
ratuses with and without the catalyst, respectively. Based on the
pure cotton exhibited only 0.50% weight loss in the same temper-
ature range (Fig. 4a). First derivative of the TGA curve (Fig. 4b) did
not reveal any peak (Fig. 4c), a sign of continuous dehydration reac-
tion (loss of water) during the temperature range. Both anhydride
formation and direct esterification reactions could release water,
resulting in related weight loss during the heating. Since FTIR of
◦
DSC of BPTCA without the catalyst, an endothermic peak at 234 C
on DSC (Fig. 3a) appeared. Thermogram of BPTCA without the cat-
◦
alyst reveals a major weight loss at around 200 C. The weight
◦
the cotton sample cured at 160 C only showed exclusively ester
◦
loss within this range was 9.28% (200–265 C), equivalent to los-
−
1
bond (1722 cm ) (Fig. 2b), confirming that the direct esterifica-
ing two water molecules from BPTCA (Fig. 3a and b). This is the
formation process of the original anhydride compound, BPTCD.
Afterward, the chemical degradation begins, resulting in another
tion reaction happened, while no anhydride rings were formed, at
◦
1
60 C in this process. Thus, we believe that basically the weight
loss of the samples was the esterification reaction between BPTCA
and cellulose. However, the function of the catalyst in the reaction
should be explored.
To further view the function of the catalyst on the reactions on
cellulose, TGA of cotton fabric samples treated by 70 g/L of BPTCD
◦
in a wet pick up rate of 120%, dried at 80 C without using the
catalyst and with different amounts of the catalyst were carried
out and are shown in Fig. 5. All three TGA thermograms show
similar weight loss patterns without major difference. In fact, the
catalyst itself may also lose water in its monohydrate crystal and
cause weight loss (Brenda & Choi, 1994). The increased amount
of sodium hypophosphite could interfere with the thermogravi-
◦
metric analysis. Thus, a limited temperature range of 100–160 C
was selected since the catalyst weight loss is minimal. The weight
losses of the samples in the temperature range are listed in Table 1,
indicating that the addition of the catalyst indeed have accelerated
the weight loss of the samples during heating, a sign of acceler-
ated reactions. More interestingly, the increased dehydration effect
◦
was more significant at the temperature range of 100–160 C than
1
temperatures.
Fig. 3. TGA and DSC of BPTCA with and without the catalyst: (a) DSC of pure BPTCA;
◦
60–200 C, which could have more impact on selection of curing
(
b) TGA of pure BPTCA; and (c) TGA of BPTCA with catalyst (catalyst molar ratio at
.5).
0

A. Hou, G. Sun / Carbohydrate Polymers 95 (2013) 768–772
771
O
O
O
O
O
O
O
O
O
O
O
O
O
O
o
1
60 C, Catalyst
Cellulose-O
HO
O-Cellulos
OH
H
2
O
HO
HO
OH
OH
+
2 Cellulose
Δ
-H O
2
Crosslinked
Cellulose
O
O
BPTCA
O
BPTCD
Scheme 1. Reaction mechanism of BPTCD with cellulose.
Fig. 5. TGAof cotton fabrics treated with BPTCD70 g/Lwith and withoutthe catalyst:
a) without catalyst; (b) catalyst molar ratio at 0.5; and (c) catalyst molar ratio at 2.
(
Fig. 6. FTIR spectra of cotton treated by BPTCD after washing in 0.1 M NaOH solution:
a) without catalyst; (b) catalyst molar ratio at 0.5; and (c) catalyst molar ratio at 2.
(
3.4. Reaction mechanism
vibrational band of C H of cellulose) was employed as a base,
Based on the above analysis, we would like to propose an over-
all reaction mechanism for this treatment process as the following
Scheme 1). The BPTCD is hydrolyzed to BPTCA in hot water, which
−1
and peak intensities at 1722 cm , representing ester bonds, and
−
1
−
1
586 cm , representing carboxylate, COO bonds, were divided
(
by that of the base peak. The relative intensities, ratios of the
intensities in Table 2, represent the amounts of ester and carbox-
ylate groups on the treated cellulose. Clearly, without the catalyst,
sodium hypophosphite, BPTCA can be incorporated onto cellulose
is then applied onto cellulose together with the catalyst, sodium
◦
hypophosphite. Under an elevated temperature (160 C), BPTCA
could directly react with hydroxyl groups of cellulose to form ester
bonds. Normal esterification reaction of acids with alcohols is slow
and reversible. However, the esterification of BPTCA with cellulose
could be exceptional since the treatment process has the following
features: (1) relatively low pH (2–4); (2) vast majority of hydroxyl
groups in cellulose to react with acid groups; and (3) rapid removal
◦
by directly forming ester bonds. At 160 C, addition of the catalyst
at 0.5 molar ratio to BPTCD increased the intensities of carboxylate
and ester groups 78% (0.42–0.75) and 84% (0.19–0.35), respec-
tively (Table 2). Increase of the catalyst molar ratio from 0.5 to 2
raised more ester intensity (11%, from 0.35 to 0.39) than that of
carboxylate group (4%, from 0.75 to 0.78). The relative amount of
carboxylate groups versus the ester groups decreased from 2.25
to 2.14, and then 2, respectively, indicating that more carboxylic
groups formed ester bonds when the catalyst was increased in the
system.
◦
of water at a curing temperature above 100 C. The removal of water
molecules breaks the balance of the reaction and drives the reaction
forward. The thermograms of three samples (Fig. 5) could partially
prove the proposed mechanism since without catalyst esterifica-
tion also occurred. FTIR spectra of the cotton samples that were
used in the TGA studies were also taken (Fig. 6). The three infrared
spectra are identical, though peak intensities are different at cer-
tain level. This is another solid evidence of esterification reaction
occurred between BPTCA and cellulose with or without any cata-
lyst.
◦
At 200 C, anhydride groups could form (Fig. 2c), which are more
reactive with cellulose than acid groups, thus the esterification
reactions should proceed through two mechanisms, one by direct
esterification and another by reaction of anhydride with hydroxyl
groups. As a result, the relative intensities of ester and carboxyl-
ate groups are increased in most samples, and the relative amount
of carboxylate groups versus ester groups was further reduced to
Obviously, the peak intensities of ester and carboxylate groups
are different from the spectra (Fig. 6). A quantitative analysis of
the peak intensities was carried out, and the results are listed in
1
.80 from 2.14, revealing more ester bonds formed under the higher
−
1
Table 2. The absorbance intensities at 2900 cm
(representing
temperature. And more interestingly, the relative intensity of
Table 1
Table 2
Weight loss of the treated fabrics.
Relative peak intensities of infrared absorbance under different amount of catalyst.
◦
◦
C
Catalyst ratio
Weight loss (%)
Temperature
Catalyst ratio
160
0
C
200
0
◦
◦
100–160
C
160–200
C
0.5
2
0.5
2
−
−
1
−1
−1
−1
0
0.76
0.99
0.88
0.51
0.45
0.48
1586 cm /2900 cm
0.42
0.19
2.25
0.75
0.35
2.14
0.78
0.39
2
0.63
0.29
2.14
0.86
0.43
2
0.74
0.41
1.80
1
0
2
.5
1722 cm /2900 cm
−
1
1586 cm /1722 cm
Note: Catalyst ratio = catalyst molar ratio to BPTCD.
Note: Catalyst ratio = catalyst molar ratio to BPTCD.

7
72
A. Hou, G. Sun / Carbohydrate Polymers 95 (2013) 768–772
carboxylate groups first showed increase and then rapidly
decreased when the catalyst was increased to a molar ratio of 2.
The reduced relative intensity of carboxylic groups was even lower
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4
. Conclusion
ꢀ
ꢀ
3
,3 ,4,4 -Benzophenone tetracarboxylic dianhydride (BPTCD)
ꢀ
ꢀ
was hydrolyzed to its acid derivative, 3,3 ,4,4 -benzophenone
tetracarboxylic acid, BPTCA, and the acid was able to directly
react with hydroxyl groups on cotton cellulose to form ester
bond crosslinkings at an elevated temperature. Direct esterifica-
tion between BPTCA and cellulose was confirmed by using both
thermogravimetric and infrared analyses and could be promoted
by addition of a catalyst, sodium hypophosphite. More catalyst
and higher curing temperature promoted esterification reaction.
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Acknowledgement
Authors would like to acknowledge a scholarship support from
Shanghai Municipal Education Commission to Dr. Aiqin Hou.