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montmorillonite composite on cotton fabric
Composites Part B 77 (2015) 329e337
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Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Flammability, thermal and physical-mechanical properties of cationic polymer/montmorillonite composite on cotton fabric Dangge Gao a, *, Rui Li a, Bin Lv a, b, Jianzhong Ma a, b, Fen Tian a, Jing Zhang c a
College of Resources and Environment, Shaanxi University of Science & Technology, Xi'an 710021, China Shaanxi Research Institute of Agricultural Products Processing Technology, Xi'an 710021, China c College of Culture and Communications School, Shaanxi University of Science & Technology, Xi'an 710021, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 December 2014 Received in revised form 18 February 2015 Accepted 17 March 2015 Available online 24 March 2015
The flammability, thermal and mechanical properties on cotton fabric were improved by being finished with the composite containing montmorillonite. To this aim, polymer dimethyl diallyl ammonium chloride-allyl glycidyl ether (PDMDAAC-AGE) was prepared and its structure characterized by Fourier transform infrared (FT-IR) and Nuclear magnetic resonance (1H NMR). The quaternary ammonium salt copolymer/montmorillonite composite (PDMDAAC-AGE/MMT) was obtained by polymer intercalation method. The X-ray diffraction (XRD) indicated that the MMT interlayer spacing increased after the polymer intercalation. Composite materials were loaded onto the cotton fabrics by a dip-pad-dry method. The thermo gravimetric analysis (TGA), vertical flame test and limiting oxygen index (LOI) results showed that the thermal and flammability properties of the cotton fabric were improved after it was finished with the composite. Tensile testing revealed an increase on mechanical properties of the finished fabric, but the physical properties hardly changed from the bending length and whiteness results. Scanning electron microscope (SEM) and energy disperse X-ray spectroscope (EDX) results verified the improvement of those properties due to the presence of montmorillonite in the composite. © 2015 Elsevier Ltd. All rights reserved.
Keywords: A. Fabrics/textiles A. Polymer-matrix composites (PMCs) B. Mechanical properties B. Thermal properties
1. Introduction In recent years, the accidents caused by fire have become more and more serious and has caused huge personnel loss of property. According to not complete count, direct property loss caused by fire is estimated at $1.5 billion and more than three thousand casualties yearly in our country. There are 5e6 million each year in global that result in that economic loss reached 0.2% of global social GDP, and 0.1 million civilian deaths. So, Fire prevention has been one of the serious problems that public care most [1,2]. Cotton is one of the most important natural textile fibers used in a large range of textile applications with a unique combination of properties, including high strength, durability, softness, good dyeability and biodegradability [3,4]. However, this cellulosic material has a low LOI (18.4%) and combustion temperature (350 C) that make it highly flammable [5]. Once ignited, cotton textiles burn rapidly, and the flame spreads quickly. As a consequence, the industrial and academic research activities are currently being
* Corresponding author. Tel./fax: þ86 (0) 29 86132559. E-mail address: [email protected] (D. Gao). http://dx.doi.org/10.1016/j.compositesb.2015.03.061 1359-8368/© 2015 Elsevier Ltd. All rights reserved.
exploited for developing efficient flame retardant systems for cotton fabric, since this issue is also of very considerable economic importance [6]. At present, many studies have focused on enhancing the flame retardant behavior of cotton using chemical modification. By changing the nature of burning from flash to steady, charring, or glowing, these flame resistant additives can slow burning and improve safety [7e9]. Halogenated additives and boron containing additives are widely used in flame retardant research for generating large volume of nonflammable gases and forming a glass coating during thermal decomposition [10]. However, the halogenated flame retardant is likely to release the gas that is harmful to human bodies and the environment [11], and the use of boron containing flame retardant for the unwashed fabric is restricted because of its lack of durability [12]. For this reason, there is an urgent need to develop an environmentally friendly and effective approach to flame retardant finishing of cotton fabrics. Clays are natural and environmentally friendly materials with high specific surface area [13] and they are widely applied in many fields such as polymer nanocomposites, coating, ceramics, etc [14]. For years, Polymer/layer silicate nanocomposite material (PLSN) with nanostructure has attracted many researchers because of its
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good mechanical properties, thermal stability and flame retardant properties [15e18]. Montmorillonite (MMT) is inorganic mineral clay, and it does not demonstrate any adverse effects in animals or humans [19]. Therefore, the flame retardant study of MMT applied to textile fiber has attracted much attention in recent years. And the studies reported that the introduction of MMT clay can improve the flammability, thermal and mechanical properties of the cotton fabric, but not diminish those properties [13,20,21]. The reason for the improvement is that the well dispersed MMT platelets in a polymer matrix form a barrier layer in the combustion process and slow the volatilization of combustible gas and blocked the penetration of oxygen, and then cut off the heat transfer and restrained degradation [22e24]. In the present work, MMT was intercalated with cationic polymer PDMDAAC-AGE, which was prepared by radical polymerization reaction, to generate nanocomposite (PDMDAAC-AGE/MMT) assemblies on cotton fibers with polymer intercalating method, and this method was not mentioned in previous studies. The aim of the assemblies on cotton fibers with the composite was to improve the flame retardancy, thermal and mechanical properties on cotton fabrics. Innovation of the paper is pointed on Scheme 1: a film formed on the surface of the cotton fabric after it was finished with the composite, and the MMT platelets were coated in the fabric surface by the polymer. It is worth mentioning that the chemical interactions took place between the epoxy group of the polymer and the eOH on cotton fibers, which to reinforce the fastness between the composite material and cotton fiber.
reflux condenser in a water bath at 80 C. After being stirred for 15 min, one of the six KPS solution and one-half of AGE (4.8 g) were added into the flask. After being stirred for 15 min, the remaining KPS solution and AGE were added into the flask. Finally, the solution which formed with above methods was being stirred for 3.5 h, and cooled down to room temperature. 2.3. Synthesis of PDMDAAC-AGE/MMT Under continuous stirring with 550 rpm, 1%e5% to total system MMT (1 g, 2 g, 3 g, 4 g or 5 g) and 98 g deionized water were poured into a 250 mL three-necked flask equipped with a digital agitator and a reflux condenser. After being stirred for 30 min, PDMDAAC-AGE (CEC ¼ 90 mmol/100 gMMT, 0.36 g, 0.72 g, 1.09 g, 1.45 g or 1.82 g) was added into the flask. The above-mentioned mixture solution reacted for 4 h at 90 C. Then, the products were washed thoroughly with deionized water in a centrifuge machine, and dried for 24 h at 120 C. 2.4. Application to cotton fabric
2. Experimental section
2.4.1. Finishing process As shown in Fig. 1, a typical sample finishing process was as follows: the substrate, a piece of cleaned cotton fabric (259 g/m2) was dipped in the PDMDAAC-AGE solution or PDMDAAC-AGE/MMT solution for 30 s, the dipping process was repeated four times. After each immersion step, the substrate was padded with the pickup 70% using an automatic padder at a nip pressure. Then, the padded samples were dried at 90 C for 6 min in a preheated oven to drive off solvent and finally cured at 150 C for 6 min in a curing oven.
2.1. Materials
2.4.2. Fabric properties determination
Sodium montmorillonite (Na-MMT) was purchased from Zhangjiakou Qinghe Chemical Factory, Hebei, China. Dimethyl Diallyl Ammonium Chloride (DMDAAC) and Allyl Glycidyl Ether (AGE) were received from Sloan Materials Science and Technology Limited Company, Hangzhou, China. Methacrylic acid (MAA) was provided by Tianjin Fuchen Chemical Reagent Factory, Tianjin, China. Potassium Persulfate (KPS) was obtained from Hongyan Rergent Hedong District, Tianjin, China. 2.2. Preparation of PDMDAAC-AGE The synthetic route of PDMDAAC-AGE was presented in Scheme 2. Initiator solution was prepared with KPS (3.6 g) dissolved in 48 g deionized water. Then, under continuous stirring at 350 rpm, DMDAAC (60%, 92 g) and two thirds KPS solution were poured into a 250 mL three-neck-flask equipped with a digital agitator and a
(1) Vertical Flame Test Vertical Flame Tests were performed according to ISO1210, using a vertical burning tester (CZF-4, Nanjing Shangyuan Analytical Instrument Limited Company, China). The samples (300 mm 76 mm, the thickness of sample is 0.59 mm), held 125 mm over the Bunsen burner, were first exposed to the flame for a period of 10 s and then removed rapidly. The test was repeated five times for each formulation. (2) Oxygen Index Test Oxygen Index Detector (HC-2C, Nanjing Shangyuan Analytical Instrument Limited Company, China) was employed to investigate the flammability of fabric samples (150 mm 58 mm). The sample was placed in the center of a glass chimney where the oxygen/nitrogen gas mixture flows upward. After a 30 s purge of the chimney with the mixture gas, the top of the specimen was ignited using a diffusion pilot flame, the burning of the sample was observed until it stop as the oxygen concentration decreased and the minimum oxygen volume concentration, which so-called limiting oxygen index (LOI) was obtained. The test was repeated three times for each formulation. (3) White Degree Test The fabric samples before and after finishing were detected by WS-SDD/O Chromaticity White Degree Program (Wenzhou Instrument Limited Company, China). Each sample was detected keeping the direction of different parts 3 times at least.
Scheme 1. Scheme of PDMDAAC-AGE/MMT composite on the surface of the cotton fiber.
(4) The breaking strength of fabric
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Scheme 2. The reaction scheme of DMDAAC and AGE.
Fig. 1. Finishing process of cotton fabric.
The breaking strength of fabric samples (30 cm 6 cm) was measured with a PT-1080 electronic fabric strength tester (Perfect International Instruments CO., LTD.). (5) The bending length of fabric The bending length of fabric samples (2.5 cm 20 cm) was measured according to ZBWO4003-87 using a YG(B)022D stiffness tester (Wenzhou great glory textile instrument co., LTD). 2.5. Characterization The PDMDAAC-AGE solution and PDMDAAC-AGE/MMT composite material were washed with acetone and ethanol three times and then dried at 105 C. The structure of PDMDAAC-AGE was studied using Fourier Transform Infrared Spectroscopy (FT-IR; VECTOR22, Nicole, the frequency region of 4000e500 cm1 at a 1 cm1 resolution) and Hydrogen Nuclear Magnetic Resonance (1H NMR; ADVANCE III, bruker, 400 MHz, D2O). Number average (Mn) and weight average (Mw) molecular weight and polydispersity index (PDI) of PDMDAACAGE were obtained via gel permeation chromatography (GPC; Water e2695-2414, America). The samples of PDMDAAC-AGE/MMT were investigated using X-ray diffraction instrument (XRD; D/ Max2200PC, RigakU, Cu Ka X-ray source, q ¼ 1.5e10 , scanning rate of 2 /min). The morphologies of the unfinished and finished cotton fabrics, along with the char residue after vertical flame tests, were observed using scanning electron microscope (SEM, Hitachi S4800, operated at 5 kV) which is equipped with energy disperse X-ray spectroscope (EDX) for the composition analysis. The thermal and thermo oxidative stabilities of the fabrics were evaluated by TGA, (Q500 TA), The measurements were performed placing the samples in open alumina pans in nitrogen atmosphere (gas flow, 60 mL/min) from 20 to 600 C with a heating rate of 10 C/min.
3. Results and discussion 3.1. Characterization results of PDMDAAC-AGE 3.1.1. FT-IR analysis FT-IR curve of PDMDAAC-AGE is presented in Fig. 2. The peaks around 3300e3600 cm1 were corresponded to free water, adsorbed water, crystallization water and structure water of eOH group stretching vibrations. The peaks at 2950, 2890 and 1314 cm1 corresponded to the symmetric and asymmetric stretching vibrations of CH3e, eCH2e, and CHe groups. The bands at 1590 cm1 and 620 cm1 were characteristic to the CeN groups, which caused by the presence of the heterocycle in the polymer [25]. The peak at 1130 cm1 was the stretching vibration of the CeOeC, furthermore,
Fig. 2. FT-IR curve of PDMDAAC-AGE.
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the spectral bands from 980 to 850 cm1 were assigned to stretching and deformation vibrations characteristic of epoxy group [26]. On the other hand, the peak of C]C at 1640 cm1 disappeared, which indicated there was no unreacted monomers. From the above, it can be seen that the copolymer was successfully prepared. 3.1.2. 1H NMR analysis The 1H NMR spectrum of PDMDAAC-AGE is illustrated in Fig. 3. The bend at 4.700 ppm was the peak of the solvent D2O. Due to the influence of the dimensional structure of five heterocyclic and oxygen and nitrogen atoms which high electronegativity, the chemical shift of eCHe was appears at 0.937 ppm (h), while eCH3 and eCH2eCH2e appeared at 1.159 ppm (g) and 1.362 ppm (g). The chemical shift of eCH2e next to Nþ appeared at 2.121 ppm (f) and 2.536 ppm (e) because of the dimensional structure of five heterocyclic and the high electronegativity of nitrogen atom. But for the bends at 3.080 ppm (c) and 2.974 ppm (d) attributed to the eCH and eCH2 due to the epoxy group. The reason for the increase of chemical shift of eCH (c) was synergistic effect of the ether bond and epoxy group. The bends at 3.669 ppm (a) and 3.417 ppm (b) were the peaks of hydrogen proton of eCH2e on the two sides of ether bond, respectively. In addition, no peak appeared more than 5 ppm in Fig. 3 clearly, which indicated that there was no double bond in the polymer. 3.2. X-ray diffraction (XRD) analysis of PDMDAAC-AGE/MMT According to some research works [27,28], the flammability, thermal and physical-mechanical properties depend on the degree of intercalation or exfoliation of MMT. These properties improved finely when the MMT dispersed in polymer with laminated. Therefore, the intercalation of polymer in MMT is important. Actually, montmorillonite was modified by cation exchange with Nþ of polymer PDMDAAC-AGE in the present paper (Scheme 3). Fig. 5 shows the XRD patterns of Na-MMT and PDMDAAC-AGE/ MMT. As reported earlier, when d001 peak shift to a lower angle, the interlayer of the MMT or OMMT will be widen [13]. The interlayer
spacing can be calculated according to the Bragg law (2dsinq ¼ l). It can be found that the crystalline peak of the Na-MMT was at 2q ¼ 6.98 (d001 ¼ 1.26 nm), and it was at 2q ¼ 6.05 (d001 ¼ 1.467 nm) in the PDMDAAC-AGE/5%MMT, and the detailed information about other PDMDAAC-AGE/MMT is given in Table 1. From Fig. 5 and Table 1, we can conclude that the cationic polymer PDMDAAC-AGE was intercalated into the MMT gallery and interaction between montmorillonite and PDMDAAC-AGE led to a shift of the d diffraction peak of montmorillonite toward lower 2q values, implying the expansion of the interlayer space due to the polymer PDMDAAC-AGE intercalation. The Mw of PDMDAAC-AGE was found to be 1496 (with a PDI of 1.04) in Fig. 4. 3.3. Performance of fabric 3.3.1. Thermal properties The thermal stability of unfinished and PDMDAAC-AGE/MMT finished fabrics was assessed by TGA in nitrogen. TGA and derivative thermo gravimetric (DTG) curves are plotted in Fig. 6 and the collected data are listed in Table 2. The control fabric and PDMDAAC-AGE finished fabric decomposed in a single step between 250 and 500 C. With inclusion of MMT, the decomposition behaviors changed unremarkable. From TGA and DTG curves, the 5 wt % weight loss temperature (T5%) and maximum weight loss temperature (Tmax) were observed. Compared to the control fabric, T5% and Tmax of fabric finished with PDMDAAC-AGE decreased obviously due to the presence of organic polymer, and the residue amount at T5% and Tmax gave the similar results. On the contrary, T5% and Tmax of fabrics finished with PDMDAAC-AGE/MMT were higher than that of the control fabric. Additionally, the residue amount of fabric finished with PDMDAACAGE/5%MMT was higher than that of the control fabric at Tmax although that of the fabric finished with PDMDAAC-AGE/1%MMT and PDMDAAC-AGE/3%MMT was lower, because the residue amount depends on the content and the intercalation degree of montmorillonite as well [27]. At the end of the tests, the final residue turned
Fig. 3. 1H NMR curve of PDMDAAC-AGE (D2O, 400 Hz).
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Scheme 3. Schematic diagram of MMT modified by polymer PDMDAAC-AGE.
out to be depending on montmorillonite content. The finished fabrics left 12.17e16.36 wt% residue, and the residue weight percentage increased with the increase of MMT amount within the composite. It suggested that the PDMDAAC-AGE/MMT composite, especially the montmorillonite enhanced the thermal stability of cotton fibers and char was formed at high temperature. As for the mechanism, some studies showed that the flame retardant role of PLSN was principally caused by physical blocking effect of nano clay layer [29]. When the fabric was burning, montmorillonite platelet
Table 1 Interlayer spacing of Na-MMT and PDMDAAC-AGE/MMT. Sample
2q ( )
d (nm)
Na-MMT PDMDAAC-AGE/1%MMT PDMDAAC-AGE/2%MMT PDMDAAC-AGE/3%MMT PDMDAAC-AGE/4%MMT PDMDAAC-AGE/5%MMT
6.98 6.18 6.18 6.06 6.16 6.05
1.26 1.429 1.429 1.453 1.434 1.467
Fig. 4. GPC curve of PDMDAAC-AGE (0.1 M NaNO3, 40 C, flow rate of 1 mL/min).
within the composite materials gradually gathered to the material surface and formed compact blocking layer. The blocking layer cut off the heat transfer and material exchange from the outside to surface, and restrained degradation [30].
3.3.2. Flammability properties In order to assess the flammability properties of the finished fabrics, we first took the vertical flame test on the control fabric and fabrics finished with PDMDAAC-AGE/MMT proceed under the same conditions. Time to ignition did not increase upon the fabrics, but the more rapid burning was observed on the control fabric and PDMDAAC-AGE finished fabric compared to that of the fabric finished with PDMDAAC-AGE/MMT. After being burned, no control fabric and PDMDAAC-AGE finished fabric were left on the sample holder, but the significant residue of fabric finished with PDMDAAC-AGE/MMT was left, as shown in Fig. 7. In addition, with the increasing mass of MMT, the PDMDAAC-AGE/MMT finished fabrics were consumed by the same flame more and more slowly, while the collected char residue
Fig. 5. XRD of (a) Na-MMT, (b) PDMDAAC-AGE/1%MMT, (c) PDMDAAC-AGE/2%MMT, (d) PDMDAAC-AGE/3%MMT, (e) PDMDAAC-AGE/4%MMT, (f) PDMDAAC-AGE/5%MMT.
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Fig. 6. TGA and DTG of fabrics unfinished and finished with PDMDAAC-AGE/MMT: TGA curves (a), DTG curves (b).
Table 2 Thermogravimetric data of control fabric and fabrics finished with PDMDAAC-AGE/ MMT. Sample
Control PDMDAAC-AGE PDMDAAC-AGE/1%MMT PDMDAAC-AGE/3%MMT PDMDAAC-AGE/5%MMT a
T5% ( C)
283 260 290 292 284
Tmaxa ( C)
348 320 360 360 350
Residue at Tmaxa (%)
590 C (%)
47.81 44.35 38.14 39.24 50.20
10.29 0.25 12.17 13.54 16.36
From derivative TG curves.
was heavier and heavier. It can be concluded that the flammability properties of fabric was improved. Flammability properties of the fabrics were further assessed by the oxygen index test. Limiting oxygen index (LOI) is the minimum fraction of oxygen in a mixture of oxygen and nitrogen in which one sample will just sustain burning [31]. From the data in Table 3, it can
Fig. 8. X-ray diffraction patterns of control fabric and fabric finished with PDMDAAC-AGE/ 5%MMT.
Fig. 7. Images of control fabric and fabrics finished with PDMDAAC-AGE/MMT following the vertical flame test.
Table 3 The Breaking strength, bending length, whiteness and LOI of different fabric samples. Sample
Breaking strength (KG)
Bending length (mm)
Whiteness (%)
LOI (%)
Control PDMDAAC-AGE PDMDAAC-AGE/1%MMT PDMDAAC-AGE/2%MMT PDMDAAC-AGE/3%MMT PDMDAAC-AGE/4%MMT PDMDAAC-AGE/5%MMT
950.6 948.9 960.4 1019.2 960.4 999.6 1009.4
26.5 26.9 28.0 29.3 30.2 31.8 32.5
75.13 74.24 74.34 74.74 75.29 74.9 74.55
20.45 20.40 20.70 20.85 21.45 21.75 21.85
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Fig. 9. SEM and EDX images: unfinished fabric before (a) and after (b) the vertical flame test, fabric finished with PDMDAAC-AGE/5%MMT before (c) and after (d) the vertical flame test.
be obtained that the limiting oxygen index (LOI) increased with the increase of the MMT amount. In other words, flame retardancy of the fabrics enhanced with the introduction of MMT. The reason for this conclusion can be summarized as follows. When the fabric
burning, the silicate slices which arranged in the surface of the finished fabrics resist the diffusion of small molecules derived from combustion products, then slow down the migration rate of outside oxygen and play the role of flame retardant.
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3.3.3. Physical-mechanical properties The breaking strength, bending length and whiteness of the fabrics unfinished and finished with PDMDAAC-AGE and PDMDAAC-AGE/ MMT are listed in Table 3. The breaking strength of the fabrics finished with PDMDAAC-AGE/ MMT was superior to those of the unfinished fabric and PDMDAACAGE finished fabric, which were 950.6 and 948.9 KG separately. It embodied the function that nanoparticles could improve the strength of material adequately. The bending length of the finished fabric demonstrates the extent of stiffness in the fabric. The bending length of finished fabrics was slightly higher than that of unfinished fabric. It indicated that the handle feeling was not affected adversely by the composite finishing [32]. Compared to the control sample, the whiteness of fabrics finished with PDMDAAC-AGE and PDMDAAC-AGE/MMT hardly changed, and the results showed that the composite materials have no effect on the whiteness of fabric.
Thermal and flammability properties of cotton fabric were characterized by TGA, vertical flame test and oxygen index test. TGA analysis showed that the finished cotton with composite left a higher amount of char residue than the control fabric. The composite enhanced the thermal stability of cotton fibers and char was formed at high temperature. The flame retardancy of the fabrics was enhanced with the introduction of MMT, and the minimum oxygen consumption of the fabrics was increased. Physicalmechanical properties, such as tensile strength, stiffness and whiteness, were studied. Tensile strength of finished fabrics was superior to that of unfinished fabric. The composite did not have obvious influence on the blending length and whiteness of the cotton fabric. From SEM-EDX results, the structure of the ashes from finished fabrics was well preserved, whereas the scant ashes from the control fabric showed little structure due to the presence of montmorillonite in composite.
3.4. XRD analysis The XRD pattern in Fig. 8 provides additional evidence of coating on the fabric. Compared with the control fabric, the finished fabric showed an additional peak at 6.20 clearly, which was attributed to the PDMDAAC-AGE/5%MMT based on the X-ray pattern in Fig. 5. This results suggest that PDMDAAC-AGE/5%MMT existed on the surface of fabric successfully. 3.5. SEM analysis Fabrics before and after flame testing were imaged by scanning electron microscopy to observe the surface morphology and fabric structure. The control fabric left only ashes after flame exposure, so the ashes were used for imaging. Meanwhile finished fabric images were more representative from the charred remains. In Fig. 9(a) and (c), the unfinished and PDMDAAC-AGE/5%MMT finished fabrics are shown prior to the flame test. The fiber surface of unfinished fabric appeared very clean and smooth compared to that of the finished fabrics. While some montmorillonite aggregates can be seen on the fibers of the finished fabrics. From the EDX result, C and O elements were examined in unfinished fabric. Cotton fiber is a group of naturally occurring proteins. The main element components of cotton fiber contain C and O. Compared with EDX result of unfinished cotton fibers, the C, O, Mg, Al and Si elements can be detected in finished fabric. MMT was a kind of layer silicates composed of Mg, Si and Al elements. It revealed that the composite PDMDAAC-AGE/ 5%MMT was successfully adhered on the surface of cotton fibers. After flame testing, the ashes from the unfinished fabric and the residue from finished fabric were imaged under the same condition. Fig. 9(b) very clearly shows that the ashes of the control fabric no longer had the same structure and shape as the original fiber. Broken pieces and holes in the fiber illustrated the complete destruction occurred during burning of unfinished fabric. But for the finished fabric in Fig. 9(d), the fiber structure was maintained and the fiber was relatively intact. It is possible that the presence of montmorillonite platelets in the fabric fiber contributed to the formation of a protective char layer acting as a barrier to the combustion process. In addition, the speculation was verified by EDX, which Mg, Al and Si elements exist in the fabric before and after the vertical flame test. 4. Conclusion Cotton fabric was finished with a series of PDMDAAC-AGE/MMT composite with different MMT amount which was prepared by polymer intercalation method.
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[26] Bhalchandra KV, Ganesh CI, Ponrathnam S, Sanjay NN. Poly(allyl glycidyl etherco-ethylene glycol dimethacrylate) copolymer beads as support for covalent immobilization of L-aminoacylase. React Polym 2012;72(10):687e94. [27] Guo BC, Jia DM, Cai CG. Effects of organo-montmorillonite dispersion on thermal stability of epoxy resin nanocomposites. Eur Polym J 2004;40(8): 1743e8. [28] Bee ST, Hassan A, Ratnam CT, Tee TT, Sin LT, Hui D. Dispersion and roles of montmorillonite on structural, flammability, thermal and mechanical behaviours of electron beam irradiated flame retarded nanocomposite. Compos Part B Eng 2014;61:41e8. [29] Liu JC, Chen Q, Jing MM, et al. Fire performance and flame-retardant mechanism of organic montmorillonite/polystyrene composites. Acta Mater Compos Sin 2011;28(6):50e8. [30] Nihat AI, Cevdet K. Nanostructure of montmorillonite barrier layers: a new insight into the mechanism of flammability reduction in polymer nanocomposites. Polym Degrad Stab 2011;96(12):2284e9. [31] Willard JJ, Wondra RE. Quantitative evaluation of flame-retardant cotton finishes by the limiting-oxygen index (LOI) technique. Text Res J 1970;40: 203e10. [32] Gupta D, Haile A. Multifunctional properties of cotton fabric treated with chitosan and carboxymethyl chitosan. Carbohydr Polym 2007;69(1):164e71.
Contents lists available at ScienceDirect
Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Flammability, thermal and physical-mechanical properties of cationic polymer/montmorillonite composite on cotton fabric Dangge Gao a, *, Rui Li a, Bin Lv a, b, Jianzhong Ma a, b, Fen Tian a, Jing Zhang c a
College of Resources and Environment, Shaanxi University of Science & Technology, Xi'an 710021, China Shaanxi Research Institute of Agricultural Products Processing Technology, Xi'an 710021, China c College of Culture and Communications School, Shaanxi University of Science & Technology, Xi'an 710021, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 December 2014 Received in revised form 18 February 2015 Accepted 17 March 2015 Available online 24 March 2015
The flammability, thermal and mechanical properties on cotton fabric were improved by being finished with the composite containing montmorillonite. To this aim, polymer dimethyl diallyl ammonium chloride-allyl glycidyl ether (PDMDAAC-AGE) was prepared and its structure characterized by Fourier transform infrared (FT-IR) and Nuclear magnetic resonance (1H NMR). The quaternary ammonium salt copolymer/montmorillonite composite (PDMDAAC-AGE/MMT) was obtained by polymer intercalation method. The X-ray diffraction (XRD) indicated that the MMT interlayer spacing increased after the polymer intercalation. Composite materials were loaded onto the cotton fabrics by a dip-pad-dry method. The thermo gravimetric analysis (TGA), vertical flame test and limiting oxygen index (LOI) results showed that the thermal and flammability properties of the cotton fabric were improved after it was finished with the composite. Tensile testing revealed an increase on mechanical properties of the finished fabric, but the physical properties hardly changed from the bending length and whiteness results. Scanning electron microscope (SEM) and energy disperse X-ray spectroscope (EDX) results verified the improvement of those properties due to the presence of montmorillonite in the composite. © 2015 Elsevier Ltd. All rights reserved.
Keywords: A. Fabrics/textiles A. Polymer-matrix composites (PMCs) B. Mechanical properties B. Thermal properties
1. Introduction In recent years, the accidents caused by fire have become more and more serious and has caused huge personnel loss of property. According to not complete count, direct property loss caused by fire is estimated at $1.5 billion and more than three thousand casualties yearly in our country. There are 5e6 million each year in global that result in that economic loss reached 0.2% of global social GDP, and 0.1 million civilian deaths. So, Fire prevention has been one of the serious problems that public care most [1,2]. Cotton is one of the most important natural textile fibers used in a large range of textile applications with a unique combination of properties, including high strength, durability, softness, good dyeability and biodegradability [3,4]. However, this cellulosic material has a low LOI (18.4%) and combustion temperature (350 C) that make it highly flammable [5]. Once ignited, cotton textiles burn rapidly, and the flame spreads quickly. As a consequence, the industrial and academic research activities are currently being
* Corresponding author. Tel./fax: þ86 (0) 29 86132559. E-mail address: [email protected] (D. Gao). http://dx.doi.org/10.1016/j.compositesb.2015.03.061 1359-8368/© 2015 Elsevier Ltd. All rights reserved.
exploited for developing efficient flame retardant systems for cotton fabric, since this issue is also of very considerable economic importance [6]. At present, many studies have focused on enhancing the flame retardant behavior of cotton using chemical modification. By changing the nature of burning from flash to steady, charring, or glowing, these flame resistant additives can slow burning and improve safety [7e9]. Halogenated additives and boron containing additives are widely used in flame retardant research for generating large volume of nonflammable gases and forming a glass coating during thermal decomposition [10]. However, the halogenated flame retardant is likely to release the gas that is harmful to human bodies and the environment [11], and the use of boron containing flame retardant for the unwashed fabric is restricted because of its lack of durability [12]. For this reason, there is an urgent need to develop an environmentally friendly and effective approach to flame retardant finishing of cotton fabrics. Clays are natural and environmentally friendly materials with high specific surface area [13] and they are widely applied in many fields such as polymer nanocomposites, coating, ceramics, etc [14]. For years, Polymer/layer silicate nanocomposite material (PLSN) with nanostructure has attracted many researchers because of its
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good mechanical properties, thermal stability and flame retardant properties [15e18]. Montmorillonite (MMT) is inorganic mineral clay, and it does not demonstrate any adverse effects in animals or humans [19]. Therefore, the flame retardant study of MMT applied to textile fiber has attracted much attention in recent years. And the studies reported that the introduction of MMT clay can improve the flammability, thermal and mechanical properties of the cotton fabric, but not diminish those properties [13,20,21]. The reason for the improvement is that the well dispersed MMT platelets in a polymer matrix form a barrier layer in the combustion process and slow the volatilization of combustible gas and blocked the penetration of oxygen, and then cut off the heat transfer and restrained degradation [22e24]. In the present work, MMT was intercalated with cationic polymer PDMDAAC-AGE, which was prepared by radical polymerization reaction, to generate nanocomposite (PDMDAAC-AGE/MMT) assemblies on cotton fibers with polymer intercalating method, and this method was not mentioned in previous studies. The aim of the assemblies on cotton fibers with the composite was to improve the flame retardancy, thermal and mechanical properties on cotton fabrics. Innovation of the paper is pointed on Scheme 1: a film formed on the surface of the cotton fabric after it was finished with the composite, and the MMT platelets were coated in the fabric surface by the polymer. It is worth mentioning that the chemical interactions took place between the epoxy group of the polymer and the eOH on cotton fibers, which to reinforce the fastness between the composite material and cotton fiber.
reflux condenser in a water bath at 80 C. After being stirred for 15 min, one of the six KPS solution and one-half of AGE (4.8 g) were added into the flask. After being stirred for 15 min, the remaining KPS solution and AGE were added into the flask. Finally, the solution which formed with above methods was being stirred for 3.5 h, and cooled down to room temperature. 2.3. Synthesis of PDMDAAC-AGE/MMT Under continuous stirring with 550 rpm, 1%e5% to total system MMT (1 g, 2 g, 3 g, 4 g or 5 g) and 98 g deionized water were poured into a 250 mL three-necked flask equipped with a digital agitator and a reflux condenser. After being stirred for 30 min, PDMDAAC-AGE (CEC ¼ 90 mmol/100 gMMT, 0.36 g, 0.72 g, 1.09 g, 1.45 g or 1.82 g) was added into the flask. The above-mentioned mixture solution reacted for 4 h at 90 C. Then, the products were washed thoroughly with deionized water in a centrifuge machine, and dried for 24 h at 120 C. 2.4. Application to cotton fabric
2. Experimental section
2.4.1. Finishing process As shown in Fig. 1, a typical sample finishing process was as follows: the substrate, a piece of cleaned cotton fabric (259 g/m2) was dipped in the PDMDAAC-AGE solution or PDMDAAC-AGE/MMT solution for 30 s, the dipping process was repeated four times. After each immersion step, the substrate was padded with the pickup 70% using an automatic padder at a nip pressure. Then, the padded samples were dried at 90 C for 6 min in a preheated oven to drive off solvent and finally cured at 150 C for 6 min in a curing oven.
2.1. Materials
2.4.2. Fabric properties determination
Sodium montmorillonite (Na-MMT) was purchased from Zhangjiakou Qinghe Chemical Factory, Hebei, China. Dimethyl Diallyl Ammonium Chloride (DMDAAC) and Allyl Glycidyl Ether (AGE) were received from Sloan Materials Science and Technology Limited Company, Hangzhou, China. Methacrylic acid (MAA) was provided by Tianjin Fuchen Chemical Reagent Factory, Tianjin, China. Potassium Persulfate (KPS) was obtained from Hongyan Rergent Hedong District, Tianjin, China. 2.2. Preparation of PDMDAAC-AGE The synthetic route of PDMDAAC-AGE was presented in Scheme 2. Initiator solution was prepared with KPS (3.6 g) dissolved in 48 g deionized water. Then, under continuous stirring at 350 rpm, DMDAAC (60%, 92 g) and two thirds KPS solution were poured into a 250 mL three-neck-flask equipped with a digital agitator and a
(1) Vertical Flame Test Vertical Flame Tests were performed according to ISO1210, using a vertical burning tester (CZF-4, Nanjing Shangyuan Analytical Instrument Limited Company, China). The samples (300 mm 76 mm, the thickness of sample is 0.59 mm), held 125 mm over the Bunsen burner, were first exposed to the flame for a period of 10 s and then removed rapidly. The test was repeated five times for each formulation. (2) Oxygen Index Test Oxygen Index Detector (HC-2C, Nanjing Shangyuan Analytical Instrument Limited Company, China) was employed to investigate the flammability of fabric samples (150 mm 58 mm). The sample was placed in the center of a glass chimney where the oxygen/nitrogen gas mixture flows upward. After a 30 s purge of the chimney with the mixture gas, the top of the specimen was ignited using a diffusion pilot flame, the burning of the sample was observed until it stop as the oxygen concentration decreased and the minimum oxygen volume concentration, which so-called limiting oxygen index (LOI) was obtained. The test was repeated three times for each formulation. (3) White Degree Test The fabric samples before and after finishing were detected by WS-SDD/O Chromaticity White Degree Program (Wenzhou Instrument Limited Company, China). Each sample was detected keeping the direction of different parts 3 times at least.
Scheme 1. Scheme of PDMDAAC-AGE/MMT composite on the surface of the cotton fiber.
(4) The breaking strength of fabric
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Scheme 2. The reaction scheme of DMDAAC and AGE.
Fig. 1. Finishing process of cotton fabric.
The breaking strength of fabric samples (30 cm 6 cm) was measured with a PT-1080 electronic fabric strength tester (Perfect International Instruments CO., LTD.). (5) The bending length of fabric The bending length of fabric samples (2.5 cm 20 cm) was measured according to ZBWO4003-87 using a YG(B)022D stiffness tester (Wenzhou great glory textile instrument co., LTD). 2.5. Characterization The PDMDAAC-AGE solution and PDMDAAC-AGE/MMT composite material were washed with acetone and ethanol three times and then dried at 105 C. The structure of PDMDAAC-AGE was studied using Fourier Transform Infrared Spectroscopy (FT-IR; VECTOR22, Nicole, the frequency region of 4000e500 cm1 at a 1 cm1 resolution) and Hydrogen Nuclear Magnetic Resonance (1H NMR; ADVANCE III, bruker, 400 MHz, D2O). Number average (Mn) and weight average (Mw) molecular weight and polydispersity index (PDI) of PDMDAACAGE were obtained via gel permeation chromatography (GPC; Water e2695-2414, America). The samples of PDMDAAC-AGE/MMT were investigated using X-ray diffraction instrument (XRD; D/ Max2200PC, RigakU, Cu Ka X-ray source, q ¼ 1.5e10 , scanning rate of 2 /min). The morphologies of the unfinished and finished cotton fabrics, along with the char residue after vertical flame tests, were observed using scanning electron microscope (SEM, Hitachi S4800, operated at 5 kV) which is equipped with energy disperse X-ray spectroscope (EDX) for the composition analysis. The thermal and thermo oxidative stabilities of the fabrics were evaluated by TGA, (Q500 TA), The measurements were performed placing the samples in open alumina pans in nitrogen atmosphere (gas flow, 60 mL/min) from 20 to 600 C with a heating rate of 10 C/min.
3. Results and discussion 3.1. Characterization results of PDMDAAC-AGE 3.1.1. FT-IR analysis FT-IR curve of PDMDAAC-AGE is presented in Fig. 2. The peaks around 3300e3600 cm1 were corresponded to free water, adsorbed water, crystallization water and structure water of eOH group stretching vibrations. The peaks at 2950, 2890 and 1314 cm1 corresponded to the symmetric and asymmetric stretching vibrations of CH3e, eCH2e, and CHe groups. The bands at 1590 cm1 and 620 cm1 were characteristic to the CeN groups, which caused by the presence of the heterocycle in the polymer [25]. The peak at 1130 cm1 was the stretching vibration of the CeOeC, furthermore,
Fig. 2. FT-IR curve of PDMDAAC-AGE.
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the spectral bands from 980 to 850 cm1 were assigned to stretching and deformation vibrations characteristic of epoxy group [26]. On the other hand, the peak of C]C at 1640 cm1 disappeared, which indicated there was no unreacted monomers. From the above, it can be seen that the copolymer was successfully prepared. 3.1.2. 1H NMR analysis The 1H NMR spectrum of PDMDAAC-AGE is illustrated in Fig. 3. The bend at 4.700 ppm was the peak of the solvent D2O. Due to the influence of the dimensional structure of five heterocyclic and oxygen and nitrogen atoms which high electronegativity, the chemical shift of eCHe was appears at 0.937 ppm (h), while eCH3 and eCH2eCH2e appeared at 1.159 ppm (g) and 1.362 ppm (g). The chemical shift of eCH2e next to Nþ appeared at 2.121 ppm (f) and 2.536 ppm (e) because of the dimensional structure of five heterocyclic and the high electronegativity of nitrogen atom. But for the bends at 3.080 ppm (c) and 2.974 ppm (d) attributed to the eCH and eCH2 due to the epoxy group. The reason for the increase of chemical shift of eCH (c) was synergistic effect of the ether bond and epoxy group. The bends at 3.669 ppm (a) and 3.417 ppm (b) were the peaks of hydrogen proton of eCH2e on the two sides of ether bond, respectively. In addition, no peak appeared more than 5 ppm in Fig. 3 clearly, which indicated that there was no double bond in the polymer. 3.2. X-ray diffraction (XRD) analysis of PDMDAAC-AGE/MMT According to some research works [27,28], the flammability, thermal and physical-mechanical properties depend on the degree of intercalation or exfoliation of MMT. These properties improved finely when the MMT dispersed in polymer with laminated. Therefore, the intercalation of polymer in MMT is important. Actually, montmorillonite was modified by cation exchange with Nþ of polymer PDMDAAC-AGE in the present paper (Scheme 3). Fig. 5 shows the XRD patterns of Na-MMT and PDMDAAC-AGE/ MMT. As reported earlier, when d001 peak shift to a lower angle, the interlayer of the MMT or OMMT will be widen [13]. The interlayer
spacing can be calculated according to the Bragg law (2dsinq ¼ l). It can be found that the crystalline peak of the Na-MMT was at 2q ¼ 6.98 (d001 ¼ 1.26 nm), and it was at 2q ¼ 6.05 (d001 ¼ 1.467 nm) in the PDMDAAC-AGE/5%MMT, and the detailed information about other PDMDAAC-AGE/MMT is given in Table 1. From Fig. 5 and Table 1, we can conclude that the cationic polymer PDMDAAC-AGE was intercalated into the MMT gallery and interaction between montmorillonite and PDMDAAC-AGE led to a shift of the d diffraction peak of montmorillonite toward lower 2q values, implying the expansion of the interlayer space due to the polymer PDMDAAC-AGE intercalation. The Mw of PDMDAAC-AGE was found to be 1496 (with a PDI of 1.04) in Fig. 4. 3.3. Performance of fabric 3.3.1. Thermal properties The thermal stability of unfinished and PDMDAAC-AGE/MMT finished fabrics was assessed by TGA in nitrogen. TGA and derivative thermo gravimetric (DTG) curves are plotted in Fig. 6 and the collected data are listed in Table 2. The control fabric and PDMDAAC-AGE finished fabric decomposed in a single step between 250 and 500 C. With inclusion of MMT, the decomposition behaviors changed unremarkable. From TGA and DTG curves, the 5 wt % weight loss temperature (T5%) and maximum weight loss temperature (Tmax) were observed. Compared to the control fabric, T5% and Tmax of fabric finished with PDMDAAC-AGE decreased obviously due to the presence of organic polymer, and the residue amount at T5% and Tmax gave the similar results. On the contrary, T5% and Tmax of fabrics finished with PDMDAAC-AGE/MMT were higher than that of the control fabric. Additionally, the residue amount of fabric finished with PDMDAACAGE/5%MMT was higher than that of the control fabric at Tmax although that of the fabric finished with PDMDAAC-AGE/1%MMT and PDMDAAC-AGE/3%MMT was lower, because the residue amount depends on the content and the intercalation degree of montmorillonite as well [27]. At the end of the tests, the final residue turned
Fig. 3. 1H NMR curve of PDMDAAC-AGE (D2O, 400 Hz).
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Scheme 3. Schematic diagram of MMT modified by polymer PDMDAAC-AGE.
out to be depending on montmorillonite content. The finished fabrics left 12.17e16.36 wt% residue, and the residue weight percentage increased with the increase of MMT amount within the composite. It suggested that the PDMDAAC-AGE/MMT composite, especially the montmorillonite enhanced the thermal stability of cotton fibers and char was formed at high temperature. As for the mechanism, some studies showed that the flame retardant role of PLSN was principally caused by physical blocking effect of nano clay layer [29]. When the fabric was burning, montmorillonite platelet
Table 1 Interlayer spacing of Na-MMT and PDMDAAC-AGE/MMT. Sample
2q ( )
d (nm)
Na-MMT PDMDAAC-AGE/1%MMT PDMDAAC-AGE/2%MMT PDMDAAC-AGE/3%MMT PDMDAAC-AGE/4%MMT PDMDAAC-AGE/5%MMT
6.98 6.18 6.18 6.06 6.16 6.05
1.26 1.429 1.429 1.453 1.434 1.467
Fig. 4. GPC curve of PDMDAAC-AGE (0.1 M NaNO3, 40 C, flow rate of 1 mL/min).
within the composite materials gradually gathered to the material surface and formed compact blocking layer. The blocking layer cut off the heat transfer and material exchange from the outside to surface, and restrained degradation [30].
3.3.2. Flammability properties In order to assess the flammability properties of the finished fabrics, we first took the vertical flame test on the control fabric and fabrics finished with PDMDAAC-AGE/MMT proceed under the same conditions. Time to ignition did not increase upon the fabrics, but the more rapid burning was observed on the control fabric and PDMDAAC-AGE finished fabric compared to that of the fabric finished with PDMDAAC-AGE/MMT. After being burned, no control fabric and PDMDAAC-AGE finished fabric were left on the sample holder, but the significant residue of fabric finished with PDMDAAC-AGE/MMT was left, as shown in Fig. 7. In addition, with the increasing mass of MMT, the PDMDAAC-AGE/MMT finished fabrics were consumed by the same flame more and more slowly, while the collected char residue
Fig. 5. XRD of (a) Na-MMT, (b) PDMDAAC-AGE/1%MMT, (c) PDMDAAC-AGE/2%MMT, (d) PDMDAAC-AGE/3%MMT, (e) PDMDAAC-AGE/4%MMT, (f) PDMDAAC-AGE/5%MMT.
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Fig. 6. TGA and DTG of fabrics unfinished and finished with PDMDAAC-AGE/MMT: TGA curves (a), DTG curves (b).
Table 2 Thermogravimetric data of control fabric and fabrics finished with PDMDAAC-AGE/ MMT. Sample
Control PDMDAAC-AGE PDMDAAC-AGE/1%MMT PDMDAAC-AGE/3%MMT PDMDAAC-AGE/5%MMT a
T5% ( C)
283 260 290 292 284
Tmaxa ( C)
348 320 360 360 350
Residue at Tmaxa (%)
590 C (%)
47.81 44.35 38.14 39.24 50.20
10.29 0.25 12.17 13.54 16.36
From derivative TG curves.
was heavier and heavier. It can be concluded that the flammability properties of fabric was improved. Flammability properties of the fabrics were further assessed by the oxygen index test. Limiting oxygen index (LOI) is the minimum fraction of oxygen in a mixture of oxygen and nitrogen in which one sample will just sustain burning [31]. From the data in Table 3, it can
Fig. 8. X-ray diffraction patterns of control fabric and fabric finished with PDMDAAC-AGE/ 5%MMT.
Fig. 7. Images of control fabric and fabrics finished with PDMDAAC-AGE/MMT following the vertical flame test.
Table 3 The Breaking strength, bending length, whiteness and LOI of different fabric samples. Sample
Breaking strength (KG)
Bending length (mm)
Whiteness (%)
LOI (%)
Control PDMDAAC-AGE PDMDAAC-AGE/1%MMT PDMDAAC-AGE/2%MMT PDMDAAC-AGE/3%MMT PDMDAAC-AGE/4%MMT PDMDAAC-AGE/5%MMT
950.6 948.9 960.4 1019.2 960.4 999.6 1009.4
26.5 26.9 28.0 29.3 30.2 31.8 32.5
75.13 74.24 74.34 74.74 75.29 74.9 74.55
20.45 20.40 20.70 20.85 21.45 21.75 21.85
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Fig. 9. SEM and EDX images: unfinished fabric before (a) and after (b) the vertical flame test, fabric finished with PDMDAAC-AGE/5%MMT before (c) and after (d) the vertical flame test.
be obtained that the limiting oxygen index (LOI) increased with the increase of the MMT amount. In other words, flame retardancy of the fabrics enhanced with the introduction of MMT. The reason for this conclusion can be summarized as follows. When the fabric
burning, the silicate slices which arranged in the surface of the finished fabrics resist the diffusion of small molecules derived from combustion products, then slow down the migration rate of outside oxygen and play the role of flame retardant.
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3.3.3. Physical-mechanical properties The breaking strength, bending length and whiteness of the fabrics unfinished and finished with PDMDAAC-AGE and PDMDAAC-AGE/ MMT are listed in Table 3. The breaking strength of the fabrics finished with PDMDAAC-AGE/ MMT was superior to those of the unfinished fabric and PDMDAACAGE finished fabric, which were 950.6 and 948.9 KG separately. It embodied the function that nanoparticles could improve the strength of material adequately. The bending length of the finished fabric demonstrates the extent of stiffness in the fabric. The bending length of finished fabrics was slightly higher than that of unfinished fabric. It indicated that the handle feeling was not affected adversely by the composite finishing [32]. Compared to the control sample, the whiteness of fabrics finished with PDMDAAC-AGE and PDMDAAC-AGE/MMT hardly changed, and the results showed that the composite materials have no effect on the whiteness of fabric.
Thermal and flammability properties of cotton fabric were characterized by TGA, vertical flame test and oxygen index test. TGA analysis showed that the finished cotton with composite left a higher amount of char residue than the control fabric. The composite enhanced the thermal stability of cotton fibers and char was formed at high temperature. The flame retardancy of the fabrics was enhanced with the introduction of MMT, and the minimum oxygen consumption of the fabrics was increased. Physicalmechanical properties, such as tensile strength, stiffness and whiteness, were studied. Tensile strength of finished fabrics was superior to that of unfinished fabric. The composite did not have obvious influence on the blending length and whiteness of the cotton fabric. From SEM-EDX results, the structure of the ashes from finished fabrics was well preserved, whereas the scant ashes from the control fabric showed little structure due to the presence of montmorillonite in composite.
3.4. XRD analysis The XRD pattern in Fig. 8 provides additional evidence of coating on the fabric. Compared with the control fabric, the finished fabric showed an additional peak at 6.20 clearly, which was attributed to the PDMDAAC-AGE/5%MMT based on the X-ray pattern in Fig. 5. This results suggest that PDMDAAC-AGE/5%MMT existed on the surface of fabric successfully. 3.5. SEM analysis Fabrics before and after flame testing were imaged by scanning electron microscopy to observe the surface morphology and fabric structure. The control fabric left only ashes after flame exposure, so the ashes were used for imaging. Meanwhile finished fabric images were more representative from the charred remains. In Fig. 9(a) and (c), the unfinished and PDMDAAC-AGE/5%MMT finished fabrics are shown prior to the flame test. The fiber surface of unfinished fabric appeared very clean and smooth compared to that of the finished fabrics. While some montmorillonite aggregates can be seen on the fibers of the finished fabrics. From the EDX result, C and O elements were examined in unfinished fabric. Cotton fiber is a group of naturally occurring proteins. The main element components of cotton fiber contain C and O. Compared with EDX result of unfinished cotton fibers, the C, O, Mg, Al and Si elements can be detected in finished fabric. MMT was a kind of layer silicates composed of Mg, Si and Al elements. It revealed that the composite PDMDAAC-AGE/ 5%MMT was successfully adhered on the surface of cotton fibers. After flame testing, the ashes from the unfinished fabric and the residue from finished fabric were imaged under the same condition. Fig. 9(b) very clearly shows that the ashes of the control fabric no longer had the same structure and shape as the original fiber. Broken pieces and holes in the fiber illustrated the complete destruction occurred during burning of unfinished fabric. But for the finished fabric in Fig. 9(d), the fiber structure was maintained and the fiber was relatively intact. It is possible that the presence of montmorillonite platelets in the fabric fiber contributed to the formation of a protective char layer acting as a barrier to the combustion process. In addition, the speculation was verified by EDX, which Mg, Al and Si elements exist in the fabric before and after the vertical flame test. 4. Conclusion Cotton fabric was finished with a series of PDMDAAC-AGE/MMT composite with different MMT amount which was prepared by polymer intercalation method.
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