Article pubs.acs.org/IECR
Flammability and Char Formation of Polyamide 66 Fabric: Chemical Grafting versus Pad-Dry Process Peng Jiang,†,§ Qian Zhao,†,§ Sheng Zhang,*,† Xiaoyu Gu,† Zhongwu Hu,† and Guozhi Xu‡ †
Key Laboratory of Carbon Fiber and Functional Polymers (Beijing University of Chemical Technology, Ministry of Education), Beijing, 100029, China ‡ School of Material Science and Mechanical Engineering, Beijing Technology and Business University, Beijing, 102488, China ABSTRACT: Chemical grafting and pad-dry physical treatment with maleic anhydride (MA) and 2-hydroxyethyl methacrylate (HEMA) were employed to improve the fire resistance of polyamide 66 (PA 66) fabric, respectively. The flammability characterization demonstrated that chemical grafting could improve the antidripping property of the fabric by the elimination of the melting process which resulted from the so-called “scaffolding effect” during combustion. Pad-dry physical treatment improved the fire performance (including antidripping tendency) of PA 66 fabric through notable molten contraction which could keep the fabric away from the igniting source. It has been suggested that the premature decomposition of the monomers/ graft chains can remove the heat from the fiber and delay the further decomposition of the substrate. The chemical grafting significantly improved the hydrophilicity of the samples, while the physical treatment decreased the hydrophilicity of PA 66 samples.
1. INTRODUCTION Polyamide 66 (PA 66) fabric is one of the most abundantly used fabrics in many areas because of its excellent properties such as easy dyeing, wear resistance, great tenacity, resistance to shrinkage and abrasion, and so on. However, its combustibility and serious dripping problems during burning are inadequate for many industrial applications; moreover, compared with cotton, its inferior hydrophilicity property makes it uncomfortable to be used in civil life, which restricts its application in many cases.1−3 The flame retardancy of PA fabric can be achieved by several methods, which includes the addition of flame retardants to the fabric during fiber spinning, the flame-retardant finishing of fabric by a pad-dry-cure process or back coating, layer-by-layer technique with an intumescent coating of (polyallylaminepolyphosphate)n, and the copolymerization of grafting flameretarding monomers onto the basic fabric, etc.2−11 Flame-retardant finishing has been widely used owing to its simple process and low cost. Our previous study demonstrated that an intumescent flame retardant (IFR) system which included ammonium polyphosphate, melamine, and pentaerythritol could significantly improve the flame resistance of the PA 66 fabric.2 There are some semidurable finishes in the market which will resist a few washing cycles and dry cleaning; however, a durable flame retardant finishing which can withstand at least 50 washing cycles is still not available. A hydroxyl-functional organophosphorus flame-retardant system has been used for the flame retardant finishing of nylon/cotton blend fabric, which exhibited a durable modification through a reaction with the hydroxyl in cotton.12,13 However, this method cannot be employed in PA 66 fabric because PA 66 has no −OH groups, and the −NH2 end groups in PA 66 are in low concentration compared to that in natural fabric.4 Grafting has been reported to be a superior way to achieve a relatively durable modification of fabric because of the covalent © XXXX American Chemical Society
bonds between monomers and chains on a fabric surface. UVinduced grafting, chemical induced grafting, microwave induced grafting, and plasma-induced grafting have been used over the last 10 years to improve hydrophilicity, selective permeability, antistatic property, dyeability, biocompatibility, heat resistance, and antibacterial characteristics of fabric.14−21 Among these methods UV-induced grafting, microwave induced grafting, and chemical grafting have been employed in our laboratory to achieve durable flame retardancy of PA 66 and PET fabric.1,18−21 UV-induced grafting of acrylamide, maleic anhydride, and 2-hydroxyethyl methacrylate phosphate onto PA 66 fabric surfaces can significantly improve the flame retardancy and moisture absorption.1,18,19 Microwave induced grafting of 2-hydroxyethyl methacrylate (HEMA) have been used in our previous research to improve the hydrophilicity and fire performance of PA 66 fabric.21 Chemically induced surface grafting of acrylamide has also been used to enhance the fire resistance and thermal stability of PA 66 fabric.22 This paper reports the introduction of maleic anhydride (MA) and 2-hydroxyethyl methacrylate (HEMA) onto the surface of PA 66 by two different ways: chemical grafting and pad-dry physical process. The fire performance and hydrophilicity of the samples treated with the two methods were investigated and compared. ATR-FTIR, SEM, and TGA were used to characterize the chemical structure and thermal stability of the fabric. The char formation and combustion process of samples were investigated. It suggested that this is the grafting of MA and HEMA onto the surface of PA 66 fabric, which has not been reported so far. It is expected that the comparison of properties and degradation process between the two methods Received: November 6, 2014 Revised: May 18, 2015 Accepted: May 26, 2015
A
DOI: 10.1021/acs.iecr.5b01104 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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heating ramp of 10 °C/min in the temperature range of 45 to 800 °C. The mass of each sample was around 13 mg. FTIR (Thermo-Scientific-Nicolet iS10)-TGA (TA Instruments-Q5000) was used to analyze the decomposed gas of the fabric sample. A transfer line with an inner diameter of 1 mm was used to connect the TGA and the infrared cell. Both the transfer line and the gas cell were heated around 225 °C to avoid the condensation of the decomposition products. The spectra between 400 and 4000 cm−1 were recorded with the accumulation of 8 scans and an optical resolution of 4 cm−1. The mass for each sample was around 13 mg. 2.3.3. Fire Performance and Absorbency Property. The vertical burning test was measured according to GB/T 5455− 1997 by using CZF-3 instrument (Jiangning, China). The sample with the size of 300 × 80 mm2 was fixed a rectangular sample holder to prevent curling of the fabric and keep the sample in vertical position. The ignition time was 12 s, and the flame height was 40 mm. Limiting oxygen index (LOI) tests were carried out on a JF-3 type instrument (Jiangning, China), according to GB/T 2403−1993. The fire testing technology cone calorimeter was also used to evaluate the fire performance of the composites according to the standard IOS 5660 under a heat flux of 50 kW/m2 with a size of 100 × 100 × 1 mm3. The experiments were repeated five times. Absorbency of the fabric sample was evaluated by determining the wetting time according to AATCC test method 79-2007 in order to evaluate the hydrophilicity of fabric surface. Wetting time is defined as the time required for the specular reflection of the distilled water droplets from a fixed height to disappear on the fabric surface.
will provide useful information for understanding the thermal and combustion mechanism of the treated samples.
2. EXPERIMENTAL SECTION 2.1. Materials. PA 66 fabric with an area density of 165 g/ m2 was kindly provided by Chengdu Hairong Special Textile Co. Ltd. (Chengdu, China). Maleic anhydride (MA) was supplied by Fuchen Chemical Engineering Reagent Company (Tianjin, China). Potassium peroxydisulfate (KPS) was supplied by Xilong Chemical Engineering Reagent Company (Beijing, China). The sodium carbonate (Na2CO3), acetone, and 2-hydroxyethyl methacrylate (HEMA) were supplied by the Chemical Reagent Company (Beijing, China). 2.2. Methods. The PA 66 fabric was desized by being immersed in boiling Na2CO3 solution (0.4 wt %) for 30 min and then extracted with acetone for 12 h and dried in vacuum oven to constant weight. 2.2.1. Chemical Grafting. The dried PA 66 fabric was first reacted with potassium peroxy disulfate (KPS 0.5 wt % solution) in a three-necked flask for 1 h (75 °C) to initiate the active radicals on the PA 66 fiber surfaces before being transferred to MA and HEMA solution to undergo the grafting reaction for 2 h. The grafted sample was boiled in water for 20 min to eliminate the homopolymer, and finally dried at 75 °C until a constant weight was achieved. The percentage of grafting (PG%) was calculated according to the following equation: PG% =
W1 − W 100 W
where W is the weight of pure PA 66 sample and W1 is the weight of grafted PA 66 fabric after homopolymer elimination. 2.2.2. Physical Treatment. The pad-dry physical treatment of the PA 66 sample was carried out by two successive dips and nips with a steeping press (ambient temperature). PA 66 fabric were immersed in MA and HEMA (with different ratio) aqueous solution at different concentrations for 1 h and padded through a laboratory padder (0.3 MPa, 1 m/min). The sample then was immersed in the flame retardant solution again for 15 min before being padded for the second time; the treated fabric was then dried at 120 °C until a constant weight was achieved (around 15 min). The percentage of add-on (Ad%) can be calculated according to the following equation: Ad % =
3. RESULTS AND DISCUSSION 3.1. Factors that Affect the Chemical Grafting Reaction and Physical Treatment. Table 1 lists the factors that affect the chemical grafting reaction, which includes the reaction temperature and the ratio of the two monomers (HEMA/MA). Table 1. Effect of Reaction Temperature and Monomer Ratio on Chemical Grafting of PA 66a
W2 − W 100 W
where W is the weight of pure PA 66 sample, and W2 is the weight of treated PA 66 fabric after physical treatment. 2.3. Characterization. 2.3.1. Chemical Structure and Morphology Analysis of the Samples. The chemical structure of the sample was characterized by a Fourier transform infrared (FTIR) (Thermo Nicolet Nexus 670, USA) equipped with an attenuated total reflection (ATR) accessory (PIKE ATR Max II). The surface morphology of fabric samples was observed by scanning electron microscopy (SEM) on a HITA-CHI S4700 instrument at ambient temperature using a 20 kV beam voltage. All the samples were sputtered with platinum to avoid electron penetration. 2.3.2. Thermal Analysis. Thermal behavior of samples was examined on a TA Instruments-Q 5000 under purged air or nitrogen atmosphere with a flow rate of 100 mL/min at a
a
sample
HEMA/MA
reaction time (h)
temp (°C)
PG%
1 2 3 4 5 6
3:7 4:6 5:5 5:5 5:5 5:5
2 2 2 2 2 2
80 80 80 75 80 85
3.5 5.9 6.6 3.1 6.6 5.8
The total monomer concentration was 10 wt %.
One can see from Table 1 (samples 1−3) that the percentage of grafting (PG%) increases gradually with the ratio of HEMA/ MA. It is proposed that the OH groups in HEMA would be attracted to the polarized surface of PA 66, therefore, HEMA more easily immigrates to the fiber surface than MA. a ratio of 5:5 is regarded as the optimal ratio of HEMA/MA because of the relative high PG% as well as a good fire performance, which can be seen in Table 1. Table 1 also indicates PG% (sample 4−6) first increases with the reaction temperature and then decreases when temperature exceeds 80 °C. It is proposed that the chain initiation and propagation can be accelerated rapidly when it is heated, and more initiators and monomers can diffuse to the PA 66 B
DOI: 10.1021/acs.iecr.5b01104 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research macromolecules, thus resulting in the increase of PG%. However, when temperature exceeds 80 °C, the homopolymerization between monomers increases rapidly, and the chain termination rate increases as well, which can result in the decrease of PG%. Table 2 shows the effect of monomer ratio on the percentage of add-on (Ad%) of physically treated samples. It can be seen Table 2. Effect of Monomer Ratio on Ad% of Pad-Dry Physically Treated Samplesa
a
MA/HEMA
10:0
2:1
1:1
1:2
Ad%
6.3 (stiff)
4.1
5.1
3.5
The total monomer concentration was 10 wt %.
that a relative high Ad% can be obtained at the presence of MA only, which can result in stiff hand feeling. The optimal monomer ratio of 1:1 is obtained in terms of the Ad% value and amenity of the fabric. 3.2. Structure Analysis of the Modified Fabric. The ATR-FTIR spectra of PA 66 fabric samples are shown in Figure 1. Peaks at 3294.3, 1626.4, and 1532.8 cm−1 in the curve of
Figure 2. ATR-FTIR spectra of the treated PA 66 fabric after the fabric was washed 20 times.
Figure 3. Outline of grafting process and physical treatment process.
attached on the PA 66 fabric surface. It is proposed that the KPS can initiate free radicals on the backbone of PA 66 and result in the copolymerization of the MA and HEMA monomer. The fabric surface morphology is observed by SEM (Figure 4). It can be seen that the surface of pure PA 66 (Figure 4a) is smooth, and the fiber structure is well organized, while the treated fiber surface is rough with some tight attachment. For the surface of grafted fiber (Figure 4b), the attachment is tightly adhered on the fiber surface, which may be caused by the chemical covalent bonds; but for the physically treated samples in Figure 4c, the attachment is mainly filled in the fiber network, which is not tight enough to withstand the water washing. The SEM images of grafted and physically treated samples after washing with boiled water for 30 min are shown in Figure 4 images d and e, respectively. One can see that the attachments of grafted sample still remaines on the fiber surface, whereas most of the attachments of the physically treated sample have been removed by water washing cycles. 3.3. Thermal Analysis. The thermal stability of treated PA 66 samples has been evaluated by thermogravimetric analysis under nitrogen and air as shown in Figure 5. Figure 5a shows that pure PA 66 fabric in nitrogen undergoes a single-step thermal degradation between 350 to 500 °C, which may be due to the degradation of PA 66 chains. The initial degradation temperature of the grafted sample is around 300 °C which is about 100 °C higher than that of the physically treated sample,
Figure 1. ATR-FTIR spectra of pure PA 66, chemical grafted PA 66, and physically treated PA 66.
pure PA 66 are assigned to −NH−, −CO stretching and the combined absorption of both δ N−H and ν C−N, respectively. Peaks at 2861.6 and 2934.4 cm−1 are assigned to −CH2− stretching of PA 66. New peaks can be observed at 1715.5 cm−1 for treated PA 66 samples, which correspond to CO stretching in HEMA and MA. This demonstrates that the HEMA and MA monomer have been introduced onto PA 66 fabric surface. Figure 2 shows the ATR-FTIR spectra of treated samples after washing in detergent solution for 20 times at ambient temperature. One can see the peak at 1715.5 cm−1 still exists in the grafted sample curve, while it almost disappears in the physically treated sample curve. The result demonstrates that chemical grafting can chemically bond the monomer on the surface of PA 66, and hence can provide a durable treatment. The grafting process and physical treatment process is shown in Figure 3. The grafted PA 66 fabric sample can withstand washing because the monomers are linked with PA 66 by covalent bonds. However, the physical treated sample cannot withstand washing cycles because the monomers are physically C
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the further thermal-oxidative degradation of the small fragments. However, the grafted sample has a much longer thermal degradation period between 280 to 485 °C and 490 to 640 °C than pure PA 66 and physically treated samples. The char residue at 600 °C of physically treated samples did not shown any increase compared with that of pure PA 66 (around 6.3%), while the char residue at 600 °C of grafted samples has increased to 15.4%, indicating the barrier char can be formed by grafting chains. Figure 6 shows the 3D TGA-FTIR spectra of the gas phase during the thermal degradation of pure PA 66 and treated fabric
Figure 4. SEM images of pure PA 66, treated PA 66 fabric samples before and after washing with boiled water for 30 min: (a) pure PA 66, (b) grafted PA 66 (before), (c) physically treated PA 66 (before), (d) grafted PA66 (after), and (e) physically treated PA66 (after)).
Figure 6. 3D TGA-FTIR spectra of gas phase in the thermal degradation of samples: (a) PA 66, (b) PA 66-g-MA and HEMA, (c) PA 66+MA and HEMA.
which indicates the grafting chain is more stable than the physically absorbed compounds. The amount of char residue in nitrogen at 600 °C of physically sample and grafted sample are 4.6% and 10.8% respectively. The TGA curves under air atmosphere are shown in Figure 5b. The temperature of 5% mass loss (T−5%) for grafted and physically treated sample are 280 and 150 °C, respectively, which is caused by the dehydration and the breakage of the grafted HEMA and MA copolymer (PHEMA and MA)/monomer molecules (see Figure 5b). It also shows that a further degradation occurs between 490 to 580 °C for all the samples, which is related to
in air. Pure PA 66 exhibits characteristic bands of −CH2− (2950−2850 cm−1), CO2 (2270−2400 cm−1), carbonyl groups (1760 cm−1), −C-N-(1630 cm−1), and −HCCH− (970, 940, 670 cm−1), and treated samples show similar characteristic bands to that of pure PA 66, which indicates that both chemical grafting and physical treatment by MA and HEMA cannot produce detectable new volatiles during TGA analysis. The absorbance of main pyrolysis products for pure PA 66 and treated PA 66 samples versus time are revealed in Figure 7. It can be seen that pure PA 66 begins to release volatiles at
Figure 5. TGA curves of PA66 and treated PA66 in N2 (a); TGA curves of pure PA 66, treated PA 66 and copolymer of HEMA and HEMA in air (b). D
DOI: 10.1021/acs.iecr.5b01104 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 7. Absorbance of pyrolysis products vs time: (a) −CH2−; (b) CO2; (c) carbonyl groups; and (d) olefin groups.
about 32 min, however, the grafted sample begins to release CO2 and olefin compounds at about 27.5 min, which is caused by the premature degradation of the grafted chains. It is observed in Figure 7 that the absorbance intensities of hydrocarbons, carbonyl groups, and olefin groups of grafted samples are lower than that of pure PA 66, while the absorbance intensity of CO2 of grafted samples is higher than that of pure PA 66. The grafting can extend the release time of CO2 to about 70 min, which may be due to the protection of the char barrier formed by the grafted chains. The physically treated sample begins to produce carbonyl groups at 10 min, and the absorbance intensities of hydrocarbons and carbonyl groups are all higher than that of PA 66, which is due to the early decomposition of the monomer to form hydrocarbons and carbonyl groups. Consequently, the above pyrolysis results correspond well with the TGA results discussed above. 3.4. The Char Residue. The FTIR spectra of the char residue are shown in Figure 8. Char residue samples were obtained from heating the fabric sample in a muffle furnace from ambient temperature to 600 °C for 15 min. It can be seen that peaks of −CH2− (2861.6 and 2934.4 cm−1) and C−N (1532.8 cm−1) in PA 66 disappear, which means the skeleton chains have been disrupted during heating, and this
Figure 8. FTIR spectra of the char residue at 600 °C.
corresponds well to the 3D TGA-FTIR results in section 3.3. A new peak at 1124.5 cm−1 corresponding to C−O−C can also be observed in pure PA 66, demonstrating that some carbon chains have been oxidized. After being heated at 600 °C, the E
DOI: 10.1021/acs.iecr.5b01104 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research intensity of characteristic peaks (range from 2750 to 3000 cm−1 and 1500−1750 cm−1) was greatly reduced in the pure PA 66 sample, while it was slightly changed in the treated samples, indicating that treatment can protect the fabric from degradation. A new peak at 1050.3 cm−1 for the grafted sample corresponds to C−O−C from the oxide products of grafted chains. It can be concluded that the early decomposition of grafted chains can protect the inside substrate from decomposition. The digital images of pure and treated PA 66 char residues are shown in Figure 9 and the degradation processes of the
of the fabric matrix can still be seen even at 510 °C (Figure 9i). It can be concluded that the physically treated samples have a similar decomposition process to that of pure PA 66 sample, while the grafted samples show no molten contraction process because of the “scaffolding effect” caused by grafting chains, which may prevent the inside fabric from further decomposition and eliminate the dripping during burning.21 3.5. Fire Performance and Absorbency Property. The flammability test results and absorbency properties of the treated fabric are listed in Table 4. The LOI values of grafted and physically treated fabric increase from 20.3 to 21.9 and 22.7, respectively, when the PG% is around 5%, which indicate that HEMA and MA can enhance the fire resistance of PA66 fabric and the physical treatment is more effective than the grafting treatment. It can be found from the vertical flammability test that the dripping tendency is greatly reduced for all treated samples. However, the damaged length of grafted samples is 23.4 cm (PG% = 5.8%) which is much longer than the 13.5 cm of pure PA 66 sample, and it is suggested that the grafted chains can cause a “scaffolding effect” to eliminate the molten contraction which is responsible for the increased damaged length. The physically treated sample has a much shorter damaged length of 5.1 cm, and shows much better antidripping performance than pure PA 66, which is caused by the early decomposition of the monomers, and the molten contraction can also enable the sample to shrink away from the igniting source. Table 4 also gives vertical burning test results of treated samples after washing. It can be seen that the flame resistance decreases slightly for grafted samples, while it decreases significantly for physically treated samples; this further demonstrates that only the chemical grafting method can endow a durable modification to the fabric. The absorbency of treated fabric is also listed in Table 4. It is seen that the wetting time is shortened from 417.3 s for PA 66 to 40.8 s for grafted samples. It is suggested that the hydroxyl groups in HEMA and carboxyl in MA can improve the polarity, and hence improve the hydrophilicity of PA 66 fabric surface. The wetting time of the physically treated sample increases to about 1 h, which may be caused by the fact that the monomer has physically filled in the surface cracks and defects of the PA 66 fiber, which can prevent the infiltration of water, and prolongs the wetting time. The HRR curves are shown in Figure 10. It shows that HRR curve of pure PA66 fabric is sharp with a peak value of 351.5 kW/m2, indicating a very fast burning process after ignition. The PHRR values of the grafted and physically treated sample are markedly reduced to 286.7 and 226.7 kW/m2, respectively. The PHRR value of the grafted sample is the lowest, which is reduced by 35.5% compared with that of pure PA66 fabric. This indicates that the flame resistance of grafted HEMA and MA is much more effective than that of physically treated sample. Moreover, the time of ignition was reduced from 26 s for pure PLA to 17 s for the grafted sample. It is suggested that the early
Figure 9. Digital photos of the char residue of pure PA 66, physically treated PA 66 and grafted PA 66. (a) PA 66, 330 °C, (b) PA 66, 420 °C, (c) PA 66, 510 °C, (d) PA66+MA and HEMA, 330 °C, (e) PA 66+MA and HEMA, 420 °C, (f) PA 66+MA and HEMA, 510 °C, (g) PA 66-g-MA and HEMA, 330 °C, (h) PA 66-g-MA and HEMA, 420 °C, (i) PA 66-g-MA and HEMA, 510 °C.
samples are listed in Table 3. It can be seen that pure PA 66 has melted to form a single lump with a smooth surface at 330 °C (Figure 9a), and the surface of the char residue becomes rough and inflated when the temperature reaches 420 °C (Figure 9b), which is due to the decomposition of the fabric surface, while the inside fabric remains as a solidified molten mass. The char residue has decomposed and has inflated with temperature to form a thin and inflated char residue at 510 °C (Figure 9c). Physically treated samples undergo nearly the same meltingdecomposition process as that of the pure PA 66 sample as shown in Figure 9d−f. However, the surface of the char residue is more inflated due to the decomposition of the monomer and the released inflammable gas. The grafted samples (Figure 9g− i) undergo a different combustion process in which the melting process appears to have disappeared, the pyrolysis and combustion have begun with the decomposition of grafted chains on the surface (Figure 9g), and undergoes further decomposition at high temperature (Figure 9h,i), The structure
Table 3. Melting and Degradation Process of PA66 Fabric Samples T/°C
pure PA 66
330
melted to single lump (Figure 9a)
420 510
further melt and shrink (Figure 9b) further melt and decompose (Figure 9e) A thin and fragile char (Figure 9c) Fragile char (Figure 9f)
physically treated PA 66
chemical grafted PA 66
melted to single lump (Figure 9d)
F
no melting process, start to form char layer (Figure 9g), intact fabric structure further decompose, intact fabric structure (Figure 9h) Compact char layer (Figure 9i) DOI: 10.1021/acs.iecr.5b01104 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research Table 4. Vertical Burning Test Results, Wetting Time, and LOI Values of PA 66 Samples before washing samples
after washing
PG%
damaged length/cm
dripping/drop
damaged length/cm
dripping/drop
wetting time
LOI (%)
0 3.1 4.3 5.8 10.1 3.2 4.1 5.0
13.5 11.8 13.6 23.4 7.3 5.8 7.6 5.1
>20 none none 1 1 none 1 none
15.1 20.2 15 27.1 21 30 (all) 30 (all) 30 (all)
>20 3 5 5 9 17 14 9
417.3 s 54.2 s 48.2 s 40.8 s 57.3 s >1 h 48 min 40 min
20.3 20.5 21.3 21.9 21.1 21.3 22.5 22.7
PA 66 grafted
physically treated
■
ACKNOWLEDGMENTS The authors would like to thank the National Natural Science Foundation of China (No.21374004) for financial support.
■
Figure 10. HRR curves for PA66 and its composites.
degradation of grafted HEMA and MA chains is responsible for the easy ignition.
4. CONCLUSIONS MA and HEMA have been successfully introduced on the surface of PA 66 fabric by chemical grafting and pad-dry physical treatment, respectively. The chemical grafting has significantly reduced the dripping tendency and improved absorbency of the PA 66 fabric. It is suggested that the disappearance of the melting process for grafted samples is due to the early decomposition of grafted chains on the fabric surface and the formation of a viscous carbonaceous layer which can reduce the combustible volatile concentration. Physical treatment can also improve the flame retardancy of the fabric in terms of antidripping tendency, damaged length, and LOI results, which is due to the premature decomposition of the monomer molecules and the molten contraction of the fabric during the combustion process. The chemically grafted sample can withstand washing cycles for more than 20 times, while the physically treated sample cannot withstand washing. Efforts to further improve the flame retardancy of PA 66 fabric by synthesizing and selecting more effective flame retardant monomers are underway in our laboratory.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +86 (10) 64436820. Author Contributions §
Peng Jiang and Qian Zhao are joint first authors.
Notes
The authors declare no competing financial interest. G
DOI: 10.1021/acs.iecr.5b01104 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.iecr.5b01104 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
