Flame retardant cotton fibers produced using novel synthesized halogen-free phosphoramide nanoparticles

Article abstract of DOI:10.1016/j.carbpol.2014.11.039

Flame retardant cotton fibers were successfully produced using five new nanosized phosphoramide compounds synthesized by ultrasonic method. The ¹H NMR spectra of compounds 1-3 illustrate ³J(H,H)_cis and ³J(H,H)

Full text of DOI:10.1016/j.carbpol.2014.11.039

Carbohydrate Polymers 118 (2015) 183–198
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Flame retardant cotton fibers produced using novel synthesized
halogen-free phosphoramide nanoparticles
Zahra Shariatiniaa,∗, Nasrin Javeria, Shahla Shekarrizb
a Department of Chemistry, Amirkabir University of Technology (Polytechnic), P. O. Box 15875-4413, Tehran, Iran
b Colour and Polymer Research Centre, Amirkabir University of Technology (Polytechnic), P. O. Box 15875-4413, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Flame retardant cotton fibers were successfully produced using five new nanosized phosphoramide com-
pounds synthesized by ultrasonic method. The 1H NMR spectra of compounds 1–3 illustrate 3J(H,H)cis
and 3J(H,H)trans corresponding to the splittings of cis and trans protons present in the CH CH2 bond.
Comparing the char lengths of cotton fibers treated with phosphoramides 1–5 indicates that the samples
with greater degree of grafting (DG) provide smaller char lengths so that the least and the greatest char
lengths are observed for the treated fibers with phosphoramides 1 and 5, respectively. The very close DG
and char lengths of compounds 1 and 2 can be described based on their chemical structures containing 4-
nitroaniline and 4-chloro-3-trifluoromethyl aniline groups that both can release electrons through their
resonance effects to their corresponding P N bonds and enhance the P N system synergistic effect. The
TGA/DSC analyses on the treated fibers revealed that the maximum weight losses at 800 ◦C are occurred
within the range 43.52% (for fiber treated with 1) to 56.37 (for fiber treated with 5) which are all smaller
than that of the raw fiber (56.83%). The in vitro antibacterial activity experiments on phosphoramides
1–5 displayed the greatest and the least antibacterial activities for compounds 2 and 4, respectively. Fur-
thermore, when these phosphoramides are applied on the cotton fibers, they also demonstrate the above
order for the antibacterial activities.
Received 11 September 2014
Received in revised form 31 October 2014
Accepted 14 November 2014
Available online 24 November 2014
Keywords:
Cotton fiber
Flame retardant
Nanoparticle
Phosphoramide
Antibacterial activity
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
and poly phosphates) flame retardants are performed (Edwards,
El-Shafei, Hauser, & Malshe, 2012; Horrocks, 2011). Indeed, the
Cotton is one of the most important natural fibers employed in
the textile industries. However, it is also one of the most flammable
fibers with low limiting oxygen index (LOI = 18.4%) and onset of
pyrolysis at 350 ◦C. Improvement of thermal stability of cellulose
based textiles is still a challenging issue. Numerous investigations
have been conducted in finding innovatory solutions for confer-
ring enhanced and durable flame retardant cotton fibers both at
the academic and the industrial levels to achieve the performances
of the major industrial target compounds known as Proban® and
Pyrovatex® (Alongi et al., 2013a; Weil & Levchik, 2008; Xie, Gao, &
Zhang, 2013). To overcome the thermal instability of cotton, surface
treatment either with durable (e.g. monomers containing phospho-
rus and nitrogen along with reactive moiety) or with non-durable
(usually inorganic salts containing ammonium, urea, phosphate
flame retardants (FRs) are chemicals added to materials both to
prevent combustion and to delay the spread of fire after ignition.
FRs may have different compositions so that they may contain
halogens (bromine and chlorine), phosphorus, nitrogen, metals,
minerals based on aluminum and magnesium, or they may be based
on borax, antimony trioxide, molybdenum, or the FR may be a
nanocomposite.
The most used FRs for rendering cotton fabrics flame retardant
were halogen-containing compounds. However, it was estab-
lished that the halogen-based compounds are not environmentally
friendly because they generate toxic gases, which can be endocrine
disruptive (Legler & Brouwer, 2003; Rahman, Langford, Scrimshaw,
& Lester, 2001), and may cause liver, thyroid, and neuro develop-
mental toxicity. Also, it was demonstrated that they result in liver
cancer in laboratory rats and mice (US EPA, 2012). In addition, it was
evidenced that they persist in the environment and accumulate in
living organisms (Legler & Brouwer, 2003; Rahman et al., 2001; US
EPA, 2012). Therefore, the production of the halogenated FRs were
∗
Corresponding author. Tel.: +98 2164542766; fax: +98 2164542762.
E-mail address: shariati@aut.ac.ir (Z. Shariatinia).
http://dx.doi.org/10.1016/j.carbpol.2014.11.039
0144-8617/© 2014 Elsevier Ltd. All rights reserved.

184
Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
Scheme 1. The proposed mechanisms for the burning/pyrolysis products of cellulose fibers.
banned especially the two major classes including polybrominated
diphenyl ethers (PBDEs) and polybrominated biphenyl (PBB) in EU
and USA (Legler & Brouwer, 2003; US EPA, 2012).
and carbonization of cellulose thereby the amounts of combustible
gases at reduced temperatures are decreasing and the formation of
a carbonaceous replica of the original textile fiber is improved. It
was illustrated that the most effective FRs are those which cause
the transformation of the flammable polymer to a carbonaceous
char (Davies, Horrocks, & Miraftab, 2000). The charred residue not
only reduces the creation of flammable volatiles but also leads in a
flame/heat barrier between the ignition source and the fabric inner
layers (Horrocks, Kandola, Davies, Zhang, & Padbury, 2005). The
enhancement in char formation is feasible both by conventional
intumescents and by increasing thermal barrier properties through
nanoparticles (White, 2004).
After the ban on some brominated flame retardants (BFRs),
phosphorus flame retardants (PFRs), which were responsible for
20% of the flame retardant (FR) consumption in 2006 in Europe,
were replaced as alternatives for BFRs (Andrae, 2007). PFRs can be
divided in three main groups, inorganic, organic and halogen con-
taining PFRs. Most of the PFRs have a mechanism of action in the
solid phase of burning materials (char formation) while some may
also be active in the gas phase. Some PFRs are reactive that are
chemically bound to a polymer, whereas others are additives and
mixed into the polymer.
Functional coating methods are considered as alternative flex-
ible ways to conventional finishing techniques because they are
independent of fabric type and necessitate low amounts of addi-
tives as well as allow incorporation/combination of different
functionalities (Gulrajani & Gupta, 2011). These methods include
layer by layer (LBL) assembly, immobilization of enzymes, nano
coating and using plasma for deposition of functional molecules.
The layer by layer (LBL) assembly was developed to fabricate
thin composite films on solid surfaces by sequential adsorption of
oppositely charged polycations and polyanions to build a series
of polyelectrolyte multilayer films on the substrate (Dvoracek,
Sukhonosova, Benedik, & Grunlan, 2009; Everett, Jan, Sue, &
Grunlan, 2007; Jang, Rawson, & Grunlan, 2008). Both free and
immobilized enzymes can be used to treat the fibers but immobi-
lized enzymes are permanently attached to the textiles. Therefore,
the free enzyme is lost after its first use but the immobilized
enzyme continues to catalyze the anticipated reactions repeat-
edly (Banerjee, Pangule, & Kane, 2011; Tasso et al., 2009). The
nano coatings based on zinc, silver and titanium dioxide nanopar-
ticles have extensively been applied on the fabrics to produce anti
UV, antimicrobial and self cleaning textiles (Kathirvelu, D’Souza, &
Dhurai, 2009). Usually, pad/dry/cure, thermal, radiation or chem-
ical methods have been utilized to fix these nanoparticles on
textiles. It was found that nano coating through LBL is a chemically
mild alternative to other processes in order to produce ultra-
thin, transmissive and stable coatings. Plasma can also be applied
on textiles for surface activation, to perform polymerization on
the surface or for deposition of compounds containing different
functionalities. In the plasma enhanced chemical vapor deposition
(PECV) technique, the plasma functionalizes the substrate surface
before chemical vapor deposition (Alongi, Tata, & Frache, 2011).
In a recent work, LBL assembly of branched polyethylenimine and
Laponite clay was examined and it was shown that these clay-
based assemblies endow flame-resistant behavior to cotton fabric
by creating a protective sheath (∼10 ␮m diameter) around each
individual microfiber (Li, Schulz, & Grunlan, 2009).
Most of the treatments applied in order to confer a flame
retardant behavior to many types of fabrics involved a pad-dry
process containing familiar organophosphorus compounds par-
ticularly those containing P N bonds (Abou-Okeil, El-Sawy, &
Abdel-Mohdy, 2013; Alongi, Colleoni, Rosace, & Malucelli, 2013b;
Maki et al., 2000; Wei et al., 2011). These compounds are the most
commonly used as flame retardants due to their ability to pro-
mote char formation. Many approaches have been developed to
deposit a phosphorus-based flame retardant onto cellulose fiber
such as the pad/dry/cure technique, graft copolymerization to cel-
lulose, or in situ polymerization of monomer which can form three
dimensional network in or on fibers (Horrocks, 1983; Tsafack &
Levalois-Grutzmacher, 2006). The char residue acts as a barrier to
protect the fabric from attack of oxygen and radiant heat of fire and
it can also reduce smoke emission (Duquesne et al., 2004; Granzow,
1978; Green, 2000; Price et al., 2000; Wang, Cheng, Tu, Wang, &
Chen, 2006).
The phosphorous–nitrogen (P N) containing flame retardants
have been widely studied (Hebeish, Waly, & Abou-Okeil, 1999).
Such systems attracted much attention because of their appropriate
thermal stability, low toxicity, and superior performance, due to the
synergistic effect of P N (Lewin, 1999; Pandya & Bhagwat, 1981).
The P N synergism is not a common phenomenon and depends on
the nitrogen containing compound and polymer nature (Levchik,
2006). Some theories have been presented for the P N synergism
(Cullis, Hirschler, & Tao, 1991; Gaan, Sun, Hutches, & Engelhard,
2008) and elucidated that P N compounds reduce the formation
of flammable volatiles and catalyze char formation.
Current industrial flame retardant finishing treatments for
cottonfabricsexploitthe phosphorus–nitrogensynergism(Proban-
Rhodia, Pyrovatex). It was shown that upon cellulose pyrolysis at
high temperatures, phosphorus compounds can phosphorylate the
C(6) of the glucose monomer, avoiding the source of fuel formation
as levoglucosan and promoting the dehydration process that is a
competitive route to depolymerization (Scheme 1) (Broido, Evett,
& Hodges, 1975). In the P N compounds, the FRs may be converted
into phosphorus acid amides that also catalyze the dehydration
In this work, using ultrasonic method, nanoparticles of five
novel phosphoramides were synthesized and characterized by

Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
185
Ar H), 7.91 (d, 3J(H,H) = 9.2 Hz, 2H, Ar H), 8.14 (d, 2J(PNH) = 8.8 Hz,
1H, NHnitroaniline). 13CNMR (75.47 MHz, CDCl3): ı = 42.77 (d,
2J(P,C) = 7.8 Hz, CH2), 114.49 (s, CH2), 116.46 (s, ortho-C),
116.57 (d, 3J(P,C) = 6.8 Hz, ortho-C), 125.02 (s, meta-C), 137.59 (d,
3J(P,C) = 6.8 Hz, CHallylamine), 139.17 (s, meta-C), 150.56 (s, ipso-C),
150.66 (s, para-C). FT-IR (KBr, cm−1): 3483 (NH), 3374, 3154, 2920,
1628 (C C), 1596 (NO2), 1595, 1499, 1477, 1426, 1338 (NO2), 1307,
1178 (P O), 1111, 1037 (P Nallylamine), 995 (P Nnitroaniline), 912,
844, 779, 752, 693, 666, 632, 533, 452, 421. UV–vis (100 ppm in
methanol): ꢀ(max) = 203, 219, 335 nm. Fluorescence (200 ppm in
methanol): ꢀ(max) = 490.5 nm.
multinuclear NMR, FT-IR, fluorescence, UV–vis spectroscopy, XRD
and FE-SEM microscopy. The flame retardancy abilities of these
compounds were evaluated quantitatively by their grafting to the
cotton fibers. Also, the antibacterial properties of the phospho-
ramides and the treated cotton fibers with these phosphoramides
were evaluated against the Gram-positive Staphylococcus aureus
and the Gram-negative Escherchia coli bacteria and greater antibac-
terial effects were observed against Gram-positive bacteria.
2. Experimental
2.1. Materials
2.3.2. N-4-chloro-3-trifluroro-phenyl-Nꢀ,Nꢀꢀ-diallyl phosphoric
All materials were purchased from Merck and Sigma–Aldrich
companies and were used as received. They are phosphorus pen-
tachloride, 4-nitroaniline, 4-chloro-3-trifluroroaniline, benzamide,
allylamine, formic acid, Muller Hinton agar, methanol, CCl4, dis-
tilled water. The mercerized cotton fabrics were prepared from
Yazdbaft textile industries, Yazd, Iran. The two bacteria including
one gram positive S. aureus and one gram negative E. coli were
prepared from Pasteur Institute of Iran.
triamide (2)
To
a solution of N-4-chloro-3-trifluroro-phenyl phospho-
ramidic dichloride [33] (10 mmol, 3.12 g) in acetonitrile, allylamine
(40 mmol, 2.28 g) was added dropwise and the reaction flask
was placed in an ultrasonic bath at 0 ◦C for about 1 h. Then, the
solution was evaporated at room temperature and the precipi-
tate was filtered, washed with distilled water and dried. Yield:
65%. M.p. = 99 ◦C. Anal. calcd. For C13H16N3OPClF3: C, 44.14; H,
4.56; N, 11.88. Found: C, 44.12; H, 4.55; N, 11.87%. 31P { H}
1
2.2. Measurements
NMR (121.49 MHz, d6-DMSO): ı = 9.49 (s). 1H NMR (300.13 MHz,
d6-DMSO): ı = 2.96 (m, 2H, CH), 3.57 (m, 4H, CH2), 5.08 (d,
3J(H,H)trans = 10.2 Hz, 2H, CHtrans), 5.17 (d, 3J(H,H)cis = 18.1 Hz,
2H, CHcis), 5.83 (ddd, 2J(PNH) = 10.6 Hz, 2H, NHallylamine), 6.14
(d, 2J(PNH) = 6.1 Hz, 1H, NHaromatic), 7.20 (d, 3J(H,H) = 8.4 Hz, 1H,
Ar H), 7.29 (d, 3J(H,H) = 8.4 Hz, 1H, Ar H), 7.36 (s, 1H, Ar H).
13C NMR (75.47 MHz, d6-DMSO): ı = 42.86 (s, CH2), 113.95 (s),
114.35 (s, CH2), 115.91 (d, 2J(P,C) = 6.5 Hz, ipso-C), 119.62 (s),
121.91 (d, 3J(P,C) = 6.6 Hz, ortho-C), 131.08 (s), 131.56 (s), 137.70
(d, 3J(P,C) = 6.2 Hz, CHallylamine), 143.02 (s, CF3). FT-IR (KBr): ꢂ = 3408
(NH), 2921 (CH), 2607, 1621 (C C), 1570, 1541 (NO2), 1482, 1437,
1397 (NO2), 1322, 1258, 1206, 1182 (P O), 1134, 1114, 1086,
1038 (P Nallylamine), 991 (P Naromatic), 937, 885, 831, 768, 747,
727, 672, 617, 600, 524, 470 cm−1. UV–vis (100 ppm in methanol):
ꢀ(max) = 205, 248, 298 nm. Fluorescence (200 ppm in methanol):
ꢀ(max) = 492.5 nm.
The 1H, 13C and 31P spectra were recorded on a Bruker Avance
DRS 500 spectrometer. 1H, 13C and 31P chemical shifts were deter-
mined relative to internal Si(CH3)4 and 85% H3PO4 as external
standards, respectively. Fourier-transform infrared (FT-IR) spec-
tra were recorded on a Bruker spectrometer. Elemental analysis
was performed using a Heraeus CHN-O-RAPID apparatus. Melting
points were obtained with an Electrothermal instrument. The field-
emission scanning electron microscopy (FE-SEM) micrographs
were taken from Zeiss instrument, under vacuum, accelerated at
5, 10, 15 kV. To identify the phases and crystallinity of samples,
X-ray diffraction analyses were obtained with an INEL EQUINOX
˚
3000 X-ray diffractometer using Cu K␣ radiation (ꢀ = 1.5406 A) in
the 2ꢁ range of 5–80◦. The thermal stability of the phosphoramide
grafted cotton fibers and raw fiber were evaluated by thermo gravi-
metric analysis (TGA) and differential thermal analysis (DTA) in an
air atmosphere with heating rate of 10 ◦C/min up to 800 ◦C on a
TG-DTA SDTA 851e instrument.
2.3.3. N-benzoyl-Nꢀ,Nꢀꢀ-diallyl phosphoric triamide (3)
To a solution of N-4-benzoyl phosphoramidic dichloride [33]
(10 mmol, 2.38 g) in acetonitrile, allylamine (40 mmol, 2.28 g) was
added dropwise and the reaction flask was placed in an ultrasonic
bath at 0 ◦C for about 1 h. Then, the precipitate was filtered, washed
with distilled water and dried. Yield: 55%. M.p. = 102 ◦C. Anal. Calc.
For C13H18N3O2P: C, 55.91; H, 6.50; N, 15.05%. Found: C, 55.88;
The burning test was used to compare the flammability char-
acteristics of treated and untreated samples. A fabric sample of
size 100 mm × 100 mm was mounted in a sample holder. The flame
from a Terrill burner was placed at a distance of 2 cm from the bot-
tom of sample. The flame was introduced to the sample for 12 s.
After the flame was removed, the sample was observed for char
length for both treated and untreated cotton.
H, 6.49; N, 15.04%. 31P{ H} NMR (121.49 MHz, CDCl3): ı = 10.29
1
(s). 1H NMR (300.13 MHz, CDCl3): ı = 3.43 (m, J = 8.1 Hz, 2H, CH),
3.64 (m, 4H, CH2), 5.04 (d, 3J(H,H)cis = 17.1 Hz, 2H, CHcis), 5.21
(d, 3J(H,H)trans = 10.2 Hz, CHtrans), 5.83 (ddd, 2J(PNH) = 10.0 Hz,
2H, NHallylamine), 7.43 (t, 3J(H,H) = 8.2 Hz, 2H, Ar H), 7.51 (t,
3J(H,H) = 8.2 Hz, 1H, Ar H), 8.00 (d, 3J(H,H) = 8.2 Hz, 2H, Ar H),
9.10 (d, 2J(PNH) = 10.4 Hz, 1H, NHbenzamide). 13C NMR (75.47 MHz,
CDCl3): ı = 42.47 (d, 2J(P,C) = 7.5 Hz, CH2), 114.37 (s, CH2),
127.99 (s, meta-C), 128.29 (s, ortho-C), 132.04 (s, para-C), 133.72
(d, 3J(P,C) = 8.1 Hz, ipso-C), 137.61 (d, 3J(P,C) = 8.1 Hz, CHallylamine),
168.05 (s, C O). FT-IR (KBr, cm−1): 3254 (NH), 3085, 2928 (CH),
2850 (CH), 1647 (C O), 1601 (C C), 1580, 1498, 1455, 1427,
1272, 1205, 1170 (P O), 1124, 1097, 1037 (P Nallylamine), 992,
924 (P Nbenzamide), 893, 850, 794, 710, 670, 534, 466, 420. UV–vis
(100 ppm in methanol): ꢀ(max) = 203, 230, 275 nm. Fluorescence
(200 ppm in methanol): ꢀ(max) = 329.0 nm.
2.3. Synthesis
2.3.1. N-4-nitrophenyl-Nꢀ,Nꢀꢀ-diallyl phosphoric triamide (1)
To a solution of N-4-nitrophenyl phosphoramidic dichloride
(Gholivand, Shariatinia, & Pourayoubi, 2005) (10 mmol, 2.55 g)
in acetonitrile, allylamine (40 mmol, 2.28 g) was added drop-
wise and the reaction flask was placed in an ultrasonic bath
at 0 ◦C for about 1 h. Then, the precipitate was filtered, washed
with distilled water and dried. Yield: 71%. M.p. = 146 ◦C. Anal.
Calc. For C12H17N4O3P: C, 48.65; H, 5.78; N, 18.91%. Found: C,
1
48.64; H, 5.77; N, 18.90%. 31P{ H} NMR (121.49 MHz, CDCl3):
ı = 8.83 (s). 1H NMR (300.13 MHz, CDCl3): ı = 3.43 (m, 4H, CH2),
4.03 (m, 1H, CH), 4.80 (m, 1H, CH), 4.94 (d, 3J(H,H)trans = 10.2 Hz,
1H, CHtrans), 5.11 (d, 3J(H,H)cis = 17.2 Hz, 1H, CHcis), 5.25 (d,
3J(H,H)trans = 10.5 Hz, 1H, CHtrans), 5.34 (d, 3J(H,H)cis = 17.3 Hz, 1H,
CHcis), 5.78 (ddd, 2J(PNH) = 10.5 Hz, 1H, NHallylamine), 5.89 (ddd,
2J(PNH) = 10.7 Hz, 1H, NHallylamine), 6.57 (d, 3J(H,H) = 9.2 Hz, 2H,
2.3.4. N-4-nitrophenyl-dimethyl phosphoramidic acid ester (4)
A solution containing N-4-nitrophenyl phosphoramidic dichlo-
ride [33] in methanol was placed in an ultrasonic bath at

186
Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
Scheme 2. The preparation pathway of phosphoramides 1–5.
0 ◦C for about 1 h. Then, the precipitate was filtered, washed
with distilled water and dried. Yield: 53%. M.p. = 159 ◦C. Anal.
Calc. For C8H11N2O5P: C, 39.03; H, 4.50; N, 11.38%. Found: C,
cotton fabric at pick up of 85–90%. Then, the cotton sample was
dried and padded with a monomer solution. The cotton sample
was allowed to dry and finally, the treated samples were cured at
121 ◦C for 3 min in a muffle furnace with a heating rate of 5 ◦C/min.
The washing durability up to 5 accelerated washes for 30 min was
evaluated using a non-ionic detergent at 35 ◦C. The degree of graft-
ing was calculated using the following formula (1) where Wg and
W0 are the weight of sample after and before grafting, respectively.
1
39.01; H, 4.49; N, 11.37%. 31P{ H} NMR (121.49 MHz, DMSO):
ı = 3.59 (s), 3.49 (s). 1H NMR (300.13 MHz, DMSO): ı = 3.67 (d,
3J(POCH) = 11.4 Hz, 6H, OCH3), 7.17 (d, 3J(H,H) = 9.1 Hz, 2H, Ar H),
8.14 (d, 3J(H,H) = 9.1 Hz, 2H, Ar H). 13CNMR (75.47 MHz, DMSO):
ı = 53.30 (d, 2J(P,C) = 5.4 Hz, OCH3), 116.77 (d, 3J(P,C) = 4.9 Hz, ortho-
C), 116.88 (d, 3J(P,C) = 5.3 Hz, ortho-C), 125.50 (s), 126.40 (s), 140.71
(s), 147.94 (d, 2J(P,C) = 8.8 Hz, ipso-C). FT-IR (KBr, cm−1): 3450 (NH),
3151, 3120, 3035, 2987, 2949, 2919, 2874, 2850, 1781, 1609, 1596
(NO2), 1521, 1498, 1447, 1402, 1383, 1343 (NO2), 1299, 1263, 1229,
1181 (P O), 1123, 1111, 1084, 1045, 957 (P Nnitroaniline), 858 (P O),
819, 749, 690, 659, 624, 589, 538, 518, 498, 432. UV–vis (100 ppm
in methanol): ꢀ(max) = 204, 222, 317 nm. Fluorescence (200 ppm
in methanol): ꢀ(max) = 400.0 nm.
Wg − W0
Degree of grafting(DG) =
× 100
(1)
W0
2.5. In vitro antibacterial activities
The in vitro antibacterial activities of the phosphoramides 1–5
and treated cotton fibers with five different concentrations of
these phosphoramides (25%, 50%, 75% o.w.f.) were evaluated by
the filter paper disk method (Shariatinia & Nikfar, 2013). In these
experiments, the Gram-positive Staphylococcus aureus and the
Gram-negative Escherchia coli bacteria were examined and greater
antibacterial effects were observed against Gram-positive bacte-
ria. The bacteria were cultured in nutrient agar medium and used
as inocula. The phosphoramides were dissolved in ethanol and the
Whatmann filter paper disks (diameter 6.5 mm) were soaked into
the phosphoramides solutions to adsorb them. The disks were then
air-dried to remove the surface solvent and placed on the surface of
a sterilized agar nutrient medium that was inoculated with the test
bacterium. For the phosphoramides treated fibers, 0.004 g of each
sample was directly placed on the agar medium. The thickness of
the agar medium was kept equal in all Petri dishes. Next, the disks
were incubated at 37 1 ◦C for 24 h. The zones of growth inhibitions
were measured indicating the inhibitory activities of the samples
on the growth of the bacterium. The average of three diameters was
calculated for each assay.
2.3.5. N-benzoyl-dimethyl phosphoramidic acid ester (5)
A solution containing N-4-benzoyl phosphoramidic dichloride
[33] in methanol was placed in an ultrasonic bath at 0 ◦C for
about 1 h. Then, the precipitate was filtered, washed with dis-
tilled water and dried. Yield: 49%. M.p. = 117 ◦C. Anal. Calc. For
C9H12NO4P: C, 47.17; H, 5.28; N, 6.11%. Found: C, 47.14; H, 5.28;
1
N, 6.10%. 31P{ H} NMR (121.49 MHz, DMSO): ı = 2.15 (s). 1H NMR
(300.13 MHz, DMSO): ı = 3.73 (d, 3J(POCH) = 11.6 Hz, 6H, OCH3),
7.47 (t, 3J(H,H) = 8.1 Hz, 2H, Ar H), 7.62 (t, 3J(H,H) = 8.1 Hz, 1H,
Ar H), 7.93 (d, 3J(H,H) = 8.1 Hz, 2H, Ar H), 9.99 (d, 2J(PNH) = 9.2 Hz,
1H, NHbenzamide). 13CNMR (75.47 MHz, DMSO): ı = 53.81 (d,
2J(P,C) = 5.7 Hz, OCH3), 128.30 (s), 128.48 (s), 132.58 (s), 132.72
(s), 168.25 (s, C O). FT-IR (KBr, cm−1): 3431 (NH), 3350, 3143,
3053 (CH), 3002, 2952, 2889, 2852, 1793, 1682 (C O), 1646, 1598,
1579, 1502, 1456, 1432, 1277, 1242, 1186 (P = O), 1106, 1043,
938 (P Nbenzamide), 902 (P O), 860, 811, 777, 716, 670, 617, 514,
469, 442, 423. UV–vis (100 ppm in methanol): ꢀ(max) = 203, 231,
274 nm. Fluorescence (200 ppm in methanol): ꢀ(max) = 365.0 nm.
3. Results and discussion
2.4. Application of monomers
3.1. Spectroscopic and microscopic study
In this study, three concentrations of monomers 1–5 (25%, 50%,
75% o.w.f.) were used for grafting to the cotton fabrics. The thermal
initiator was potassium persulphate (KPS) (K2S2O8) 5% along with
Mohr’s salt (ammonium iron(II) sulfate, (NH4)2Fe(SO4)2·6H2O) 1%
for preventing homopolymerization and promoting free radical
graft polymerization of the monomer on the substrate. For each
monomer, the application recipe includes monomer, thermal ini-
tiator (KPS) and Mohr’s salt. Each monomer was dissolved in
methanol (CH3OH). The thermal initiator (5%) and Mohr’s salt (1%)
were dissolved in distilled water separately and the two solutions
were pad applied separately on a 100 mm × 100 mm swatch of
In this study, five new phosphoramides were synthesized
(Scheme 2) and characterized by FT-IR, multinuclear NMR, UV–vis
and fluorescence spectroscopy. A summary of the NMR and FT-IR
data of compounds 1–5 are given in Table 1. The phosphorus chemi-
cal shift, ı(31P), moves to down field from compounds 1 (8.83 ppm)
to 3 (10.29 ppm). This down field shift shows the most electron
withdrawing of substituents on the phosphorus atom in 3 result-
ing in the most deshielded phosphorus atom. Also, comparing the
ı(31P) of molecules 4 and 5 with their analogous phosphoramides
1 and 3 confirms that replacements of allylamine with methoxy
groups lead to much shielded phosphorus atoms. Moreover, the

Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
187
Fig. 1. The 31P NMR spectrum of 4 indicating two peaks in a 1:1 ratio.
31P NMR spectrum of 4 reveals two peaks in a 1:1 ratio reflecting
the presence of two isomers in the solution state for this molecule
(Fig. 1). This can be attributed to the existence of a chiral phospho-
rus center within the molecule due to non symmetrical orientation
of the two OCH3 moieties relative to each other.
The 1H NMR spectra of compounds 1–3 Exhibit 3J(H,H)cis
and 3J(H,H)trans coupling constants about 10.5 and 17.0–18.0 Hz,
respectively. These are produced due to the splittings of cis and
trans protons present in the CH CH2 bond. The 2J(PNH)aliphatic cou-
pling constant within the range 10.0–10.6 Hz are measured for the
splitting of the amino proton of allylamine group with the 31P
nucleus. It is seen in the 1H NMR spectrum of 1 that all of the
protons signals of the two allylamine moieties are appeared sepa-
rately that can be due to the presence of non symmetric P atom in
this molecule. The 2J(PNH)aromatic coupling constants are observed
for the compounds 1–3 and 5 equal to 6.1, 8.8, 10.4 and 9.2 Hz,
respectively. Comparing the 2J(PNH)aromatic of molecules 3 and 5
both containing C6H5C(O)NHP(O) moiety illustrates a smaller value
in 5. This means that substitution of the allylamine with methoxy
results in a less interaction between the NHaromatic proton and the
P atom. The 3J(POCH) coupling constants of 11.4 and 11.6 Hz are
observed for the splittings of the methoxy protons with the P atoms
in compounds 4 and 5, respectively.
The 13C NMR spectrum of 1 indicates six separated signals for
the carbon atoms of nitroaniline ring but one set of peaks for
the two allylamine groups. This splitting pattern in the 13C NMR
spectrum further validates the presence of a chiral phosphorus
in the molecule as mentioned above. The 2J(P,Caliphatic) coupling
constant is measured for the splitting of the CH2 carbon atom
with the P nucleus equal to 7.8 and 7.5 Hz in compounds 1 and
3, respectively. The methoxy carbons in molecules 4 and 5 couple
with their related phosphorus atoms to give 2J(P,Caliphatic) values
of 5.4 and 5.7 Hz, respectively. The 3J(P,Caliphatic) values are also
detected for molecules 1–3 for the splitting of CH2 carbon atom
with the P nucleus equal to 6.8, 6.6 and 8.1 Hz, respectively. The two
3J(P,Caromatic) = 4.9, 5.3 Hz are present in the 13C NMR spectrum of
4 due to the existence of six non equivalent carbon atoms of the
nitroaniline ring. Comparing the 13C NMR spectra of compounds 1
and 4 illustrates that in both of them a similar result is observed
(six non equivalent carbon atoms for the nitroaniline ring) that can
be related to the effect of nitroaniline ring on the molecular spatial
orientation. In molecule 4, the ipso carbon atom also splits with the
P atom with a 2J(P,Caromatic) = 8.8 Hz.

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Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
Fig. 2. The FT-IR spectra of phosphoramides 1–5.
The FT-IR spectra (Fig. 2) demonstrate that the ꢂ(P O) value
decreases from 1, 2 (1178, 1182 cm−1) to 3 (1170 cm−1) exhibiting
almost comparable P O bonds in 1, 2 but its weakening in 3. The
ꢂ(P N)aliphatic values in compounds 1–3 (∼1037 cm−1) are greater
than the ␯(P N)aromatic (∼990, 924 cm−1). Comparing the ␯(C O) of
compounds 3 (1647 cm−1) and 5 (1682 cm−1) displays a stronger
Fig. 3. The (a) UV–vis and (b) fluorescence spectra of phosphoramides 1–5.
C
O bond for 5 that is owing to its stronger PN bond created by
The nanoparticles of compounds 1–5 were prepared by ultra-
sonic irradiation method and their FE-SEM micrographs are shown
in Fig. 4 indicating the spherical morphology for the particles that
are 25–45 nm in size. Comparing the average particle sizes of these
molecules in Table 2 with their related bang gaps reveal that when
the particle size decreases the band gap is increased. The XRD pat-
terns in Fig. 5 reveal sharp peaks due to high crystallinity with the
sharpest peaks for compounds 1, 3–5 appear at 2ꢁ values of 9.62◦,
8.78◦, 14.58◦ and 16.73◦, respectively. The Debye-Scherrer equation
(d = 0.9 ꢀ/ˇ cos ꢁ) (Klug & Alexander, 1954) was used to evaluate the
average crystallite sizes where d is the average crystallite size, ꢀ is
the X-ray wavelength, ˇ is the full width at half maximum (FWHM)
and ꢁ is the diffraction angle. The crystal sizes of these phospho-
ramide were measured from the XRD diagrams within the range
32.8–93.4 nm (Table 2).
the preferred resonance form C(O) P(OH) than C(OH) P(O).
N
N
The P N bond in 4 is stronger than in 5 indicating replacement of
nitroaniline with benzamide causes weakening of the P N bond. An
opposite trend is observed for their P O bonds than is associated
with the effect of the P N bonds.
A summary of the UV–vis and fluorescence spectra of com-
pounds 1–5 and also their crystal/particle sizes are presented
in Table 2. The UV–vis spectra of compounds 1–5 display three
maximum absorption wavelengths at 203–205, 222–248, and
274–335 nm (Fig. 3a) that can be related to the ␲→␲* and n→␲*
transitions. The fluorescence spectra of compounds 1–5 are pre-
sented in Fig. 3b showing the ꢀ(max) of emission signals appear
at ∼490 nm in 1, 2 but it shifts to 329 nm in 3 (blue shift) lead-
ing to increasing the band gap from ∼2.52 eV in 1, 2 to 3.77 eV
in 3. Therefore, replacement of benzamide with both nitroaniline
and 4-chloro-3-trifluoroaniline causes enhanced band gaps for the
phosphoramides. A blue shift is seen for the ꢀ(max) of emission
from 1 to 4 while a red shift is detected from 3 to 5. The band
gaps (Eg) measured for compounds 4 and 5 are 3.10 and 3.40 eV,
respectively. The phosphoramide 2 presents the highest emission
intensity among compounds 1–3. Also, the emission intensities of
molecules 4 and 5 are very much lower than those of their analogs
1 and 3.
3.2. Flame retardancies of phosphoramides grafted cotton fibers
The flame retardant cotton cellulose fabrics treated with phos-
phoramides 1–5 were obtained and their various properties were
evaluated by FT-IR, degree of grafting, vertical burning test, FE-
SEM microscopy, TGA/DSC analyses and antibacterial activities. The
FE-SEM micrographs of the burnt treated cotton fabrics were also

Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
189
Table 2
The summary of the UV–vis and fluorescence spectra of phosphoramides 1–5 and their average crystal/particle sizes from the XRD patterns and FE-SEM images.
Compound
Maximum wavelengths of
absorbtionsa (nm)
ꢀ(max) of
emission (nm)
Max intensity
of emission
ꢃE (eV)
Average particle size
from FE-SEM (nm)
Crystal size from
XRD (nm)
1
2
3
4
5
203 (0.74), 219 (0.41), 335
(0.75)
205 (1.10), 248 (0.92), 298
(0.11)
203 (0.75), 230 (0.55), 275
(0.05)
204 (0.28), 222 (0.21), 317
(0.38)
490.5
492.5
329.0
400.0
365.0
174.84
635.22
131.86
50.52
2.53
2.52
3.77
3.10
3.40
45
40
25
35
30
32.8
–
68.1
53.8
93.4
203 (0.86), 231 (0.80), 274
(0.06)
92.50
a
The numbers in parantheses are the intensities.
Fig. 4. The FE-SEM micrograph of nanoparticles of phosphoramides 1–5.

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Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
Table 3 shows the degree of grafting (DG) obtained for each
monomer at three concentrations. It is seen that the DG is increased
by increasing the monomer concentration. Among monomers 1–3
including allylamine groups connected to the phosphorus atom and
have unsaturated C C bonds with the ability to graft to the cotton
fabrics, compound 1 presents the greatest DG and phosphoramide
3 reveals the least DG. The phosphoramides 4 and 5 that do not
contain unsaturated bonds in their structures for polymerization
and grafting to the fibers were also synthesized and examined on
the cotton fibers to evaluate their ability to make flame retardant
fibers. It is obvious that the DG of compound 4 is greater than that of
compound 5. The DG of compounds 1–5 changes within the order
1 > 2 > 3 > 4 > 5.
Vertical flame test was performed to compare and evaluate
the flammability of the treated and untreated cotton samples. The
results of the char lengths for each of the treated and un-treated
cotton samples are given in Table 3. Fig. 7 exhibits the digital pho-
tographs of vertical burning tests results on cotton fibers treated
with phosphoramides indicating their char lengths. The char length
for the raw cotton fiber was zero while the treated fibers present
measurable char lengths. The reason for such burning behaviors
is linked to the lower decomposition temperatures of the treated
samples. The lower decomposition temperature for the treated cot-
ton is combined with less available fuel due to the presence of flame
retardant material that causes the flame to propagate quickly in
search of combustible fuel (Hobart & Rowland, 1978). This behav-
ior was observed during the burning test for the fabrics treated
with the phosphoramides 1–5. For the treated cotton, the flame
runs through the whole sample very quickly. Nevertheless, the
main discrepancy between the treated and untreated cotton was
the afterglow so that there is no afterglow for the treated sam-
ples at all. The untreated cotton fabric burns vigorously with much
stronger flame and the flame is higher from the surface of the sam-
ple with high heat of combustion and there is absolutely no char.
However, for the treated samples, the flame is weak with very little
heat of combustion and significant char formation. The increase in
the char for the treated cotton fabrics is very high so that the burnt
samples kept their structural integrity.
Fig. 5. The XRD patterns of phosphoramides 1, 3–5.
obtained to compare the effects of different phosphoramides on the
produced flame retardant fibers.
The FT-IR spectra of treated cotton fibers with phosphoramides
1–5 in Fig. 6 evidently reveal that there are some new peaks
around 1600–1750 cm−1 that are related to the existence of car-
bonyl, ester and/or carboxylic acid bonds created upon grafting
the phosphoramides to the fibers. It is well known that the cot-
ton fiber is almost pure cellulose that is a linear polysaccharide
with long chains consisting of ␤-d-glucopyranose units joined by ␤-
1,4-glycosidic linkages (Scheme 3) (Gurgel, Junior, Gil, & Gil, 2008;
Qin, Soykeabkaew, Xiuyuan, & Peijs, 2008). In one repeating unit
of cellulose molecule, there are one methylol and two hydroxyl
groups as functional groups. Therefore, it is seen that the graft-
It is expected that the char lengths of the treated fibers decrease
with increasing in their degrees of grafting. Comparing the char
lengths of cotton fibers treated with phosphoramides 1–5 illus-
trates that the samples with greater DGs provide smaller char
lengths so that the least and the greatest char lengths are measured
for the treated fibers with phosphoramides 1 and 5, respectively.
The reason for the very close DGs and char lengths of compounds 1
and 2 can be described based on their chemical structures contain-
ing 4-nitroaniline and 4-chloro-3-trifluoromethyl aniline groups,
respectively. The two groups can release electrons through their
ing of phosphoramides to the cellulosic fibers can create C O/C
bonds.
O
Table 3
The degree of grafting of cotton fibers treated with three concentrations of phosphoramides and the char lengths of the burnt treated fibers.
Sample
Concentration (% o.w.f.)
Raw fiber
weight (g)
Degree of
grafting (%)
Char length
(mm)
Degree of grafting
after washing (%)
Char length after
washing (mm)
1 + fiber
2 + fiber
3 + fiber
4 + fiber
5 + fiber
1 + fiber
2 + fiber
3 + fiber
4 + fiber
5 + fiber
1 + fiber
2 + fiber
3 + fiber
4 + fiber
5 + fiber
25
25
25
25
25
50
50
50
50
50
75
75
75
75
75
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
11.85
11.57
10.45
9.12
8
9
11
12
14
5
7
8
9
11
3
6.42
5.97
4.52
5.14
3.15
10.62
10.33
9.38
8.97
7.72
16.39
16.14
15.42
14.56
13.24
11
12
14
15
16
7
7.68
16.28
15.97
15.14
14.71
12.35
22.42
21.98
20.92
19.46
17.57
9
10
11
12
5
6
7
4
5
6
8
8
10

Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
191
Fig. 6. The FT-IR spectra of cotton fibers treated with phosphoramides 1–5.
resonance effects to their corresponding P N bonds and enhance
the P N system synergistic effect. The benzamide substituent in
compounds 3 and 5 has a more electron withdrawing property
relative to the 4-nitroaniline and 4-chloro-3-trifluoromethyl ani-
line groups, thus could not strengthen the P N bond similar to
these functionalities. This subject is confirmed by the FT-IR spectra
indicating weaker P Nbenzamide bond than the P Nnitroaniline and
intercalated/entrapped unreacted monomers or even homopoly-
mers (formed during the padding method) within the fibers.
It is known that the chemical action of heat on cotton fibers
plays a key role when their combustion is considered (Horrocks,
1983). In fact, cellulose degrades upon heating by two competitive
routes including depolymerization and dehydration (Scheme 1) so
that the former induces the creation of levoglucosan that subse-
quently pyrolyzes and giving rise mainly to low molecular weight,
highly flammable species. The pyrolysis products are oxidized in
the presence of oxygen and the highly exothermic character of
the combustion causes more cellulose to pyrolyze. On the other
hand, dehydration produces a carbonaceous residue called as char.
The equilibrium between these processes depends on the heat-
ing rate (Alongi, Camino, & Malucelli, 2013c). The roles of any
flame retardant on the cellulosic fabrics are removing the heat,
reducing the gas generation and combustible, promoting the char
formation, preventing oxygen access to the flame and interfering
with the oxidation of flammable species. Consequently, the ideal
flame retardant candidates for cotton are compounds capable of
P
N4-chloro-3-trifluoromethyl aniline. It is noteworthy that the presence
of weaker P Namide bonds than the P Namine has always been con-
firmed by both the FT-IR spectra and X-ray crystallography of the
previously reported phosphoramides (Gholivand et al., 2005).
The char lengths after washing the treated fabrics were
enhanced for all cases and the fibers with higher DGs revealed
smaller increase in the char length. The reduction in the flame
retardancy and DGs of the fibers is also reported by other
researchers (Cheema, El-Shafei, & Hauser, 2013). It is evident
that the covalent bonds formed between the phosphoramide
monomers and cellulose fibers are stable and do not break by
washing. Therefore, the reason can be washing and removing the
Scheme 3. The chemical structure and atom-numbering of cellulose.

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Fig. 7. The digital photographs of vertical burning tests results indicating the increasing in the char lengths of phosphoramides treated cotton fibers. In each series, the
concentration of phosphoramide in increased from 25% to 50% and 75%, o.w.f. from left to right, respectively.

Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
193
Fig. 8. The FE-SEM micrographs of cotton fibers treated with phosphoramides 1–5.

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Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
catalyzing the dehydration and thus to act as char former in the
condensed phase.
Among many examined flame retardants, compounds contain-
ing P N bonds are considered as efficient and non-toxic materials
(Hendrix, Drake, & Barker, 1972a, 1972b). It was suggested that
nitrogen in P N synergistic retardants acts by a nucleophilic attack
on the phosphate, creating polymeric species having P N bonds
that are more polar than the already present P O bonds, and the
enhanced electrophilicity of the phosphorus atom increases its
ability to phosphorylate the C(6) primary hydroxyl group of cel-
lulose (Horrocks, 1983). As a result, the intramolecular C(6)–C(1)
rearrangement reaction forming levoglucosan is blocked. More-
over, the auto-crosslinking of cellulose promotes and consolidates
the char formation caused by the action of the same flame retard-
ants.
Surface morphology can provide useful information for the
substrates undergone any chemical changes on their surfaces. To
address any surface changes following the monomer applications,
FE-SEM analysis was performed on both treated and untreated
cotton samples. The FE-SEM micrographs of treated cotton fibers
with phosphoramides 1–5 are shown in Fig. 8. It is observed
that the FE-SEM micrographs illustrated outstanding differences
in the treated and un-treated cotton samples so that the attach-
ment of phosphoramides 1–3 on treated cotton samples are clearly
approved. It is seen from the FE-SEM images of treated cotton
fabrics with the phosphoramides 4 and 5 that the fabrics have
become much sensitive to the electron beam under the same FE-
SEM imagining conditions and the fibers are destroyed by electron
bombardment.
The FE-SEM images of the charred samples were also analyzed
to determine the efficiency of each monomer as a flame retar-
dant (Fig. 9). It is seen than the raw cotton fibers become almost
completely destroyed by burning but the treated fibers with phos-
phoramides 1–3 maintain their primary forms and do not destroy
entirely. Comparing these figures with the char lengths obtained
from the vertical burning tests demonstrates that the treated cot-
ton fibers with less char lengths are more stable against destroying
than the un-treated fabric. Interestingly, the treated fibers with
phosphoramides 4 and 5 are also more stable against decomposi-
tion relative to the raw cotton fiber. Moreover, the phosphoramide
4 produces more resistant fabric than phosphoramide 5. This may
be described by enhanced interaction of phosphoramide 4 with the
cotton fibers than phosphoramide 5.
The enhancement in char formation for the cotton fabrics
treated with phosphorus-based flame retardants is consistent
with the proposed condensed phase mechanism. The presence of
phosphorus-based flame retardant changes the pyrolysis pathway
of the substrate by lowering the decomposition temperature, ulti-
mately reducing the formation of gaseous combustibles and favors
the formation of char. This can also be confirmed by the TGA/DSC
results. The TGA/DSC plots of raw cotton fiber and phosphoramides
treated cotton fibers are presented in Fig. 10. It was investigated
that the chemical processes happening during the pyrolysis of
untreated and treated cotton fibers are alike (Franklin & Rowland,
1979). It was shown that for flame retardant treated cotton, pyroly-
sis products are formed at lower temperatures so that the presence
of a flame retardant increases all the pyrolysis processes (dehydra-
tion and char formation) at the expense of processes leading to the
formation of flammable volatiles that result in flamed combustion.
Table 4 presents the TGA/DSC results for the raw cotton fiber and
the fibers treated with phosphoramides 1–5. The TGA/DSC thermo-
graphs of raw cotton fabric reveal two decomposition temperatures
at 356.5, 477.2 ◦C with 36.65, 55.51% weight losses, respectively.
Comparing the weight loss percents of un-treated and treated cot-
ton samples with phosphoramids 1–5 in the temperature range
∼310–325 ◦C illustrates that in all treated cotton samples, the
Fig. 9. The FE-SEM micrographs of charred cotton fibers treated with phospho-
ramides 1–5.
weight loss percents change from 22.41% to 31.02% that are smaller
than that of the raw cotton fiber (35.65%). The first degradation
temperatures of treated cotton samples occur at lower tempera-
tures within the range 310.29–328.72 ◦C compared with that of the
un-treated sample (356.5 ◦C). Moreover, it is clearly observed from

Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
195
Table 5
The inhibition zones (mm) measured for the antibacterial activities of phos-
phoramides 1–5, raw cotton fiber as well as cotton fibers treated with these
phosphoramides.a
Sample
Bacterium type
E. coli
S. aureus
1
2
3
4
10.33 0.45
14.57 0.44
12.26 0.50
9.89 0.48
10.53 0.46
0
8.61 0.47
11.69 0.52
9.45 0.47
6.78 0.49
7.32 0.47
18.36 0.49
25.84 0.48
20.75 0.47
15.66 0.43
18.74 0.50
0
16.56 0.47
22.12 0.44
17.23 0.45
12.56 0.51
15.89 0.49
5
Raw cotton fiber
1 + fiber
2 + fiber
3 + fiber
4 + fiber
5 + fiber
a
Mean (n = 3) standard deviation.
5 at 199.04 ◦C can be related to the phosphoramide decomposition.
There are also third decomposition for all of the treated fabrics at
the temperature range 627.02–725.95 ◦C that are probably owing
to the fragmentation of the polymeric bonds within the fabrics.
The maximum weight losses of treated cotton fabrics with phos-
phoramids 1–5 at 800 ◦C were measured within the range 43.52%
(for fiber treated with 1) to 56.37 (for fiber treated with 5) which are
all smaller than that of the raw fiber (56.83%). The greater weight
loss of the untreated cotton fiber is related to the formation of
flammable volatiles but the decrease in the weight losses of treated
cotton fabrics is due to the formation of less volatiles and more char.
Hence, it can be stated that the treatment with phosphoramids 1–5
made cotton fabrics remarkably thermally stable.
Considering the melting points of phosphoramides 1–5 and the
degradation temperatures in the TGA/DSC diagrams, it is found that
for none of the treated fabrics there exist pure phosphoramides
within the fibers. This is due to the formation of covalent bonds
between monomers 1–3 with fibers and entrapments of monomers
4, 5 within them. Therefore, the interactive mechanism proposed
between the intumescents and fibers (Horrocks, Anand, & Hill,
1992; Horrocks, Anand, & Sanderson, 1994) can be accepted here
between phosphoramides 4, 5 and cotton fibers.
Fig. 10. The TGA/DSC plots of raw cotton fiber and cotton fibers treated with phos-
phoramides 1–5.
the DSC plots that the weight losses of all five treated fabrics at
their two main degradation temperatures around 310–330 ◦C and
466–500 ◦C are all about 10% smaller than those of the raw fiber.
The first degradation of sample treated with phosphoramide 4
at 111.06 ◦C can be attributed to the evaporation of water (mois-
ture) within the fabric. The second degradation of this sample at
184.73 ◦C may be due to the decomposition of phosphoramide. Sim-
ilarly, the first degradation of sample treated with phosphoramide
3.3. Antibacterial activity
Table 4
The TGA/DSC results for the raw cotton fiber and the fibers treated with phospho-
ramides 1–5.
The in vitro antibacterial activities of the phosphoramids 1–5
and cotton fibers treated with three different concentrations of
these phosphoramids (25%, 50%, 75% o.w.f.) were performed against
one Gram-positive Staphylococcus aureus bacterium as well as
one Gram-negative Escherchia coli bacterium. Each experiment
was repeated for at least three times. The digital photographs of
the antibacterial effects against Escherchia coli and Staphylococcus
aureus bacteria for the phosphoramids 1–5 and cotton fibers treated
with 75% o.w.f. concentration of phosphoramids are indicated in
Fig. 11. The inhibition zones (mm) measured for the antibacterial
activities of phosphoramides 1–5, raw fibers as well as cotton fibers
treated with these phosphoramides are given in Table 5.
It is well known that although the Gram-positive bacteria have
a thicker peptidoglycan layer in their cell wall that encases their
cell membrane than the Gram-negative bacteria, the Gram-positive
bacteria are more receptive to antibiotics than Gram-negative
bacteria that is due to the latter’s relatively impermeable lipid based
bacterial outer membrane. For this reason, all the samples exhib-
ited the least antibacterial activity against the Gram-negative E. coli
bacterium. Comparing the inhibition zones of five phosphoramides
with each other, it is clear that compound 2 has the greatest antibac-
terial activity. The antibacterial activities change within the order
2 > 3 > 1 > 5 > 4. Moreover, when these phosphoramides are applied
Compound
Raw cotton fiber
1 + fiber
Degradation
T (◦C)
Weight
loss (%)
Weight loss (%)
at 800 ◦
C
356.5
477.2
36.65
55.51
56.83
327.38
494.81
627.02
25.01
38.63
44.40
43.52
43.85
44.00
50.17
324.82
492.87
641.66
22.41
36.19
43.62
2 + fiber
3 + fiber
4 + fiber
321.87
491.51
643.83
23.13
35.91
43.85
111.06
184.73
310.29
500.64
725.95
0.5442
1.58
31.02
41.63
50.17
199.04
328.72
466.41
648.04
4.06
29.09
40.79
55.13
56.37
5 + fiber

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Fig. 11. The antibacterial activities of phosphoramides 1–5, cotton fibers treated with these phosphoramides and raw cotton fiber against (a) Escherchia coli and (b)
Staphylococcus auerus bacteria.

Z. Shariatinia et al. / Carbohydrate Polymers 118 (2015) 183–198
197
on the cotton fibers, their effect become somewhat smaller but they
show the above order for the antibacterial activity. It is also found
that the antibacterial effect is increased by increasing the phospho-
ramid concentration from 25% to 75% on cotton fibers. Therefore,
it can be said that these treated fibers can be used as antibacterial
fibers in producing hygiene related textiles.
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4. Conclusion
Davies, P. J., Horrocks, A. R.,
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In summary, using ultrasonic irradiation, five novel nanosized
phosphoramide compounds were synthesized and fully character-
ized by NMR, FT-IR, fluorescence, UV–vis spectroscopy, XRD and
FE-SEM microscopy. These phosphoramides were pad applied on
cotton cellulose fibers to make flame retardant fabrics. It was found
that among monomers 1–3 including allylamine groups connected
to the phosphorus atom and have unsaturated C C bonds with
the ability to graft to the cotton fabrics, compound 1 indicated the
greatest degree of grafting (DG) but phosphoramide 3 showed the
least DG. The greater DG for phosphoramide 4 relative to its ana-
log 5 (both do not contain unsaturated bonds in their structures for
polymerization and grafting to the fibers) can be related to the effect
of nitroaniline group. The in vitro antibacterial activities against
Gram-positive Staphylococcus aureus and Gram-negative Escher-
chia coli bacteria were enhanced by increasing the phosphoramide
concentration (o.w.f.) from 25% to 75% on cotton fibers. For phos-
phoramides 1–3, the unsaturated C C bonds of allylamine groups
contribute in the formation of covalent C O bonds with the OH
groups present on the cotton fibers but in case of phosphoramides 4
and 5, they are entrapped between the fibers and have electrostatic
interactions with the functional groups of the fibers. The TGA/DSC
analyses revealed lower degradation temperatures for the flame
retardant treated cotton fibers than the raw fiber, thus the mech-
anism of action for the phosphoramides 1–5 as flame retardants is
increasing all the pyrolysis processes (dehydration and char forma-
tion, Scheme 1) at the expense of processes which form flammable
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