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cotton blend fabric treated with a crosslinkable organophosphorus flame retardant system
Accepted Manuscript Title: Heat Release Properties and Flammability of the Nylon/Cotton Blend Fabric Treated with a Crosslinkable Organophosphorus Flame Retardant System Author: Qin Chen Charles Q. Yang Tao Zhao PII: DOI: Reference:
S0165-2370(14)00223-X http://dx.doi.org/doi:10.1016/j.jaap.2014.08.021 JAAP 3277
To appear in:
J. Anal. Appl. Pyrolysis
Received date: Revised date: Accepted date:
6-5-2014 25-8-2014 26-8-2014
Please cite this article as: Q. Chen, C.Q. Yang, T. Zhao, Heat Release Properties and Flammability of the Nylon/Cotton Blend Fabric Treated with a Crosslinkable Organophosphorus Flame Retardant System, Journal of Analytical and Applied Pyrolysis (2014), http://dx.doi.org/10.1016/j.jaap.2014.08.021 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Heat Release Properties and Flammability of the Nylon/Cotton Blend Fabric Treated with a Crosslinkable Organophosphorus Flame Retardant System
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Qin Chena,b, Charles Q. Yangb,*, Tao Zhaoa
a
College of Chemistry, Chemical Engineering & Biotechnology, Donghua University, Shanghai 201620, China
b
Department of Textiles, Merchandising and Interiors, The University of Georgia, Athens, Georgia 30602, U.S.A
Corresponding Author *Tel: +1 706 542 4912; Fax: +1 706 542 4890; E-mail address: [email protected]
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Abstract Flame retardant nylon/cotton blend fabrics are widely used in the fields of industrial and military protective uniforms. In this research, we investigate the heat release
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properties and flammability of the 50/50 nylon/cotton blend fabric treated with a
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self-crosslinkable durable organophosphorus flame retardant system. For the
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nylon/cotton blend fabric without treatment, the blend has lower total heat release and higher percent char yield than the arithmetic sum of those of cotton and nylon as
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single fibers. In addition, both the peak heat release rate (PHHR) and the temperature at peak heat release (TPHRR) for cotton increases whereas both PHRR and TPHRR
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decrease for nylon when those two fibers are blended to form a fabric. Thus, the data indicated that interaction takes place between cotton and nylon during the
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decomposition process of the blend. The presence of the organophosphorus flame retardant system reduces PHRR, TPHRR and increases char formation for both cotton
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and nylon as single fibers. When the cotton and nylon are blended and then treated with the flame retardant, the PHRR of the blend becomes even lower and the percent char yield of the blend becomes even higher than those of the treated cotton and nylon as single-fiber fabric. The char length for the treated blend decreases compared with that of the treated cotton and nylon as single-fiber fabrics. We conclude that cotton and nylon interact with each other during the degradation process of the treated nylon/cotton blend fabric and such interaction reduces the flammability of the blend fabric. Key words: nylon/cotton blend, micro-scale combustion calorimeter, flame retardant textiles, flame retardant protective clothing 2
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1. Introduction Cotton blends have become very important fabrics in the apparel market because of the combination of desirable characteristics of the products [1]. Blending cotton
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with nylon improves strength, abrasion resistance, fast-drying property as well as
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wrinkle resistance of the fabrics. Cotton provides the blends with high absorbency and
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soft hand property, thus improving comfortabilty. Nylon/cotton blends have become fabrics of choice for professional work uniforms and military uniforms.
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Thermoplastic polymers, such as polyester, melts upon exposure to high heat, which leads to self-extinguish due to melting. When a polyester/cotton blend is
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ignited upon exposure to high temperatures, it’s flammability becomes more complicated because of so-called “scaffolding effect” [2-3]. The “scaffolding effect”
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for polyester/cotton fabrics has long been discussed and the related literatures was reviewed previously [4-6]. When exposed to high temperature, cotton forms char
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which maintains some degree of integrity. Polyester melts above its melting point (~260ºC) and tends to flow on the cotton char. “Scaffolding effect” refers to the fact that charred cotton in a blend fabric acts as a support for burning of molted polyester in a fire. The molten polyester in the blend does not drip away as it does in a 100% polyester fabric [4-6]. Nylon/cotton blend fabrics are widely used for production of military uniforms and other protective garments [7]. Since nylon also melts like polyester, it is important to know if a nylon/cotton blend also have such flammability-enhancing effect. Flame retardant treatment methods to produce flame retardant nylon/cotton blend
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fabrics include (1) applying organophosphorus flame retardants to the blend if cellulose is the overwhelming fiber; and (2) applying halogen-based back-coatings for blend fabrics with all nylon-to-cotton ratios [2, 8-11]. Flame retardant nylon fibers
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can be produced at the fiber spinning stage using flame retardant additives including
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organophosphorus and halogenated aliphatic/aromatic compounds. The nylon fabrics
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can also be flame retardant finished by a pad-dry-cure process using a number of flame retardants, such as thiourea derivatives, ammonium sulfamate and
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organophosphorus compounds [2]. However, flame retardant finishing has not been successful for most of nylon/cotton blends and new technology is still in the
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developing stage to produce durable flame retardant nylon/cotton blend fabrics. In our previous research, we developed a durable flame retardant finishing
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system for 50/50 nylon/cotton blend fabrics using a hydroxy-functional and self-crosslinkable organophosphorus oligomer (HFPO) [12-15]. We found that the
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HFPO and dimethyloldihydroxyethyleneurea (DMDHEU) form a crosslinked polymeric network on the 50/50 nylon/cotton blend fabrics [16-17]. This HFPO/DMDHEU system has been successfully applied to the 50/50 nylon/cotton fabrics as durable flame retardant finishing system [17]. 1,2,3,4-butanetetracarboxylic acid (BTCA), a formaldehyde-free crosslinking agent for cotton, has been applied to 65/35 nomex/cotton blend military fabric in combination with HFPO as a flame retardant finishing agent [18]. However, HFPO/BTCA showed low laundering durability on cotton [19-20]. It is not suitable for the flame retardant finishing of nylon/cotton blends.
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In this research, we evaluated the heat release properties and flammability of the 50/50 nylon/cotton blend fabric treated with the HFPO/DMDHEU system to determine if interaction between nylon and cotton takes place during the degradation
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of the nylon/cotton blend fabric. Micro-scale combustion calorimetry (MCC) is a
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pyrolysis-combustion flow calorimetry to measure heat release parameters using a
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few milligram sample sizes [21]. In our previous research, we use MCC as an analytical technique to measure the heat release properties of various textile fibers and
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also to differentiate the flame retardant performance of the cotton fabrics with different levels of phosphorus-based flame retardants [22-23]. The heat release
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properties of textiles showed very close correlation with macroscopic flammability parameters such as limiting oxygen index [22-23]. The goal of this research was to
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determine if the two fibers (cotton and nylon) interacts with each other during the thermal decomposition process based on the heat release rate (HRR) vs. temperature
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curve, peak heat release rate (PHRR), temperature at PHRR (TPHRR), total heat release
(THR) and percent char yield of cotton, nylon, and cotton nylon blend. We also measured the flammability parameters including LOI and char length in a vertical fabric burning test and correlated to conform the MCC results.
2. Experimental 2.1. Materials Three woven fabrics were used in this study: (1) a nylon66 woven fabric weighing 130g/m2 (Testfabrics Style 341); (2) a cotton twill woven fabric weighing
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245g/m2 supplied by Milliken, Blacksburg, Sout Carolina; and (3) a 50/50 nylon66/cotton twill woven fabric weighing 256g/m2 supplied by Mount Vernon Mills, Trion, Georgia. HFPO with the commercial name of “Fyroltex HP” (CAS Registry No.
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70715-06-9) was supplied by Supresta (formerly Akzo Nobel), Debbs Ferry, New
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York. DMDHEU was a commercial product (44% solution) under the trade name of
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“Freerez 900” supplied by Emerald Carolina Chemical, Charlotte, NC. The catalyst was an NH4Cl-based commercial product under the trade name of “Catalyst RD”
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supplied by Eastern Color & Chemical, Greenville, SC. 2.2. Fabric treatment
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The three different fabrics (100% cotton, 50/50 nylon/cotton, 100% nylon) were individually immersed in a solution containing flame retardant (HFPO+DMDHEU)
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and the catalyst, passed through a laboratory padder with two dips and two nips. The 100% cotton fabric was treated with 32% HFPO with 8% DMDHEU while other two
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fabrics were treated with 36% HFPO with 8% DMDHEU. All fabrics were dried at
90℃ for 3 min and finally cured in a Mathis oven at 165℃ for 2.5 min. The wet
pick-up of 100% cotton was 82±2%, that of 100% nylon fabrics was 62±2% and that of 50/50 nylon/cotton was 76±2%. After curing, the treated fabrics were subjected to one home laundering washing/drying (HLWD) cycle according to AATCC Test
Method 124-2008 with water temperature at approximately 46℃. All concentrations
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presented in this study were based on weight of bath (w/w, %). 2.3. Fabric weight gain measurement The three untreated fabrics and the treated fabrics (before washing and after one
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HLWD cycle) were weighed after being conditioned for 24 h. The fabric percent
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weight gain and the percent fixation of the flame retardant on the fabric were
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calculated using the following equations where W0, W1, W2 were the weight of the untreated fabric, the treated fabric before washing, and the treated fabric subjected to
Weight gain (%)=(W2-W0)/W0×100%
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one HLWD cycle, respectively.
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Fixation (%) = (W2-W0)/(W1-W0) × 100% 2.4. MCC measurement
(1) (2)
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The MCC measurements of the textile fabric samples were conducted using a micro-scale combustion calorimeter (model “MCC-2”) produced by Govmark,
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Farmingdale, New York, according to ASTM D7309 (Method A). A fabric specimen was first ground in a Wiley mill into a homogeneous powder to ensure sample
uniformity. A sample thus prepared (∼5mg) was loaded to the MCC instrument and
then heated to a specified temperature using a linear heating rate (1℃/s) in a stream of
nitrogen flowing at 80cm3/min. The thermal degradation products of the sample in
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nitrogen were mixed with a 20cm3/min stream of oxygen prior to entering the 900℃
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combustion furnace. Each sample was run in three replicates and the MCC parameters were the averages of the three measurements.
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2.5. DSC and TG measurement
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DSC data was collected using a Mettler Toledo DSC821 differential scanning
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calorimeter. All samples for DSC measurement were analyzed at a rate of 10℃/min
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with a continuous air flow rate of 60 mL/min and heated from 100℃ to 550℃. TG
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data were collected using a Mettler TG50 thermogravimeter. All the samples for TG
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test were heated from 100℃ to 650℃ at a rate of 10℃/min with a continuous air flow
rate of 30 mL/min. The sample size for both DSC and TG was approximately 2 mg. 2.6. Evaluation of the flame retarding performance The fabric vertical burning flammability of was measured according to ASTM
Standard Method D6413-99. The limiting oxygen index (LOI) of the fabrics was measured according to ASTM Standard Method D2863-97.
3. Results and discussion
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3.1. The untreated nylon, cotton and nylon/cotton blend fabrics The HRR versus temperature curves of cotton and nylon were shown in Fig.1.
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For the untreated cotton, the thermal decomposition started at approximately 300℃
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and peaked (274w/g) at 374℃. The decomposition of cotton ended at about 415℃.
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Nylon started to decompose at approximately 375℃, and its HRR reached to
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510℃.
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maximum (565w/g) at 469℃. The decomposition of nylon ended at approximately
We calculated the HHR of the 50/50 nylon/blend based on that of cotton and
nylon as single fibers assuming that no interaction between nylon and cotton takes place during the degradation of the blend. The calculated HRR curve of the nylon/cotton blend shown in Fig. 2 is the arithmetic sum of those of cotton and nylon as single fibers at each temperature multiplied by their weight fraction (0.50) in the blend. Also presented in Fig. 2 was the measured HRR curve of the 50/50 nylon/cotton blend fabric. The measured PHRR of cotton in Fig. 2 (189 w/g) was 48 w/g higher than that of the calculated one (141 w/g). The PHRR of nylon in the
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measured curve (170 w/g), on the contrary, was 113 w/g lower than that of the calculated curve. The TPHRR of cotton shown in the measured curve in Fig. 2 was
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389℃ (15 degree higher than that in the calculated curve) whereas the TPHRR of nylon
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in the measured curve was at 446℃ (23 degree lower than that in the calculated curve).
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Because nylon melts around 256ºC as shown in Fig. 3, the cotton fiber was coated with liquid nylon when cotton’s decomposition started to take place at 320ºC. The
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presence of a layer of liquid nylon on the cotton fiber surface was probably the main reason why cotton’s decomposition temperature increased and its TPHRR was raised by
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When the temperature was increased above 400ºC, nylon’s
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15ºC (Fig. 2).
decomposition took place. At that temperature, the liquid nylon was on the top of a
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char structure formed by the decomposition of cotton. The presence of cotton char was probably the cause for decrease in nylon’s decomposition temperature and decrease of nylon’s TPHRR by 23ºC shown in Fig. 2. The data presented in Fig.2
evidently supported the hypothesis that interaction between nylon and cotton took place during thermal degradation of the blend. Presented in Table 1 are the heat release properties (HRC and THR) and the percent char yield of the untreated cotton, nylon, and 50/50 nylon/cotton blend fabrics. We also calculated the HRC, THR and percent char yield for the nylon/cotton based on the arithmetic sum of those of cotton and nylon as single fibers assuming no
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interaction between the two fibers took place (Table 2). The measured HRC and THR (202 J/[gK]) and 17.9 kJ/g) of the nylon/cotton blend were significantly lower than those calculated (428 J/[gK]) and 19.3 kJ/g) whereas the percent char yield of the
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nylon/cotton blend (9.1%) is 303% of that calculated (3.0%) (Table 2). Thus, the HRC,
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THR and the percent char yield indicated that nylon and cotton in the blend interacted
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in the decomposition process.
We also used thermal analysis techniques to study the untreated cotton, nylon,
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and their 50/50 blend fabrics. The DSC curves of three untreated fabrics were
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presented in Fig.3. The cotton fabric had an endothermic peak at 360℃ in the DSC
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curve related to the heat absorption of the decomposition of cotton. The DSC curve of
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the nylon fabric showed two peaks at 256 and 453℃ corresponding to the melting and
thermal decomposition of nylon, respectively (Fig.3). In the DSC curve of the nylon/cotton blend fabric, nylon had the same melting point, and nylon and cotton in the blend had the two endothermic peaks due to their decomposition at similar temperature. However, the peak area associated with nylon decomposition in the HRR
curve of the blend at 441℃ was only 1/6 of the same peak of nylon as a single fiber,
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and that associated with cotton decomposition of the blend at 335℃ was only 1/15 of
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the same peak area cotton as a single fiber (Fig. 3). The DSC data strongly supported the hypothesis that interaction existed between nylon and cotton in the thermal
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decomposition process the nylon/cotton blend fabric.
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The TG curves of the untreated nylon, cotton and nylon/cotton blend fabrics
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were presented in Fig. 4. Cotton started decomposition at approximately 300℃ and
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the TG curve had a sharp turn with drastically reduced slope at around 380℃. Cotton
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lost 96.0% of its initial weight at 600℃ as a result of decomposition (Fig.4).
nylon, most of its weight loss took place in the 400-500℃ region, which was
consistent with the DSC data in Fig.3. Nylon lost 94.0% of its weight at 600℃. The
50/50 nylon/cotton blend started to lose weight around 320℃ due to the
decomposition of cotton in the blend. It continued its weight loss as the temperature 12
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was increased beyond 400℃ mainly due to the decomposition of nylon as also shown
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in the DSC curve in Fig. 3. The nylon/cotton blend lost 86.0% of its original weight at
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600℃ (Fig. 4). The DSC and the TG data presented here demonstrated that the
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nylon/cotton blend had significantly less weight loss than both nylon and cotton,
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indicated that the decomposition of cotton and nylon interact in the 300-500℃ region.
The TG data is consistent with the MCC data, which showed that the nylon/cotton
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blend had significantly higher percent char yield than both nylon and cotton (Table 1).
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The MCC data also showed that the nylon/cotton blend had significantly lower total
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heat release, thus indicating that more carbon is remained as char. Such a considerable increase in char yield was another piece of evidence to support the hypothesis that cotton and nylon interacted during the thermal decomposition of the nylon/cotton blend.
3.2. The
cotton,
nylon
and
nylon/cotton
blend
fabrics
treated
with
HFPO/DMDHEU The cotton fabric was treated with 32% HFPO with 8% DMDHEU, and the nylon and the nylon/cotton blend fabrics were treated with 36% HFPO and 8%
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DMDHEU. All the fabrics thus treated were cured at 165℃ for 2.5 min. The HRR
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versus temperature curves of the cotton fabric untreated and treated before washing
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were presented in Fig. 5. Cotton started to decompose at approximately 300℃ before
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the treatment, and its decomposition temperature decreased to 200℃ after the
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treatment as shown in Fig. 5. The decrease in the decomposition temperature was due to the catalysis effect of phosphoric acid on cotton for the dehydration of cellulose,
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and the phosphoric acid was formed by decomposition of an organophosphorus flame
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retardant on cotton exposed to elevated temperatures [24]. The PHRR of the cotton
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fabric decreased from 274 w/g before treatment to 174 w/g after treatment whereas
TPHRR decreased from 374℃ before treatment to 277℃ after treatment. All those
changes were due to the HFPO/DMDHEU flame retardant on the cotton fabric [14]. The HRR curve of the cotton treated and subjected to one HLWD cycle was
also included in Fig 5. The PHRR of the treated cotton slightly increased from 174w/g before washing to 187w/g after one wash, and the TPHRR slightly decreased from
277℃ before wash to 272℃ after one wash. The HRC, THR and percent char yield of
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treated cotton fabric (before and after one HLWD cycle) were presented in Table 3. The char yield of the cotton drastically increased from 4.3% before treatment to 29.5% after treatment (before wash). The percent char yield decreased marginally to
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29.0% after one wash. The data indicated that the cotton fabric treated with
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HFPO/DMDUEU and subjected to one HLWD cycle had marginal increase in HRR
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and little decrease in char yield. Therefore, the HFPO/DMDUEU system applied to the cotton fabric was resistant to hydrolysis and durable to home launderings.
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Shown in Fig. 6 were the HRR curves of untreated nylon fabric and the nylon
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fabric treated with 36% HFPO with 8% DMDHEU and cured at 165℃ for 2.5 min. In
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the presence of the flame retardant system, the HRR peaked at 469℃ for the untreated
nylon. It decreased by 77 and 30℃ to become two peaks at 392 and 439℃,
respectively after the treatment as shown in Fig. 6. The PHRR of the untreated nylon
decreased from 565 w/g to 199 and 218 w/g for the two peaks at 392 and 439℃,
respectively, after the treatment. Before the treatment, nylon started to decompose at
approximately 370℃, and the starting temperature decreased to approximately 330℃
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after the treatment (Fig. 6). The THR of nylon decreased from 26.7 to 20.3 kJ/g whereas the percent char yield of nylon increased from 1.6 to 9.0% after the treatment (Tables 1 and 3). Moreover, the one peak in the HRR cure of the untreated nylon
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splitted into two peaks after the treatment, and the HRR curve of the treated nylon
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became broader with a less symmetric shape than that of nylon before treatment. The
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significantly reduction in PHRR, TPHRR and the temperature for the start of the decomposition of nylon, the increase in char yield, and the change in the shape of the
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HRR versus temperature curve in the presence of HFPO and DMDHEU demonstrated
decomposition mechanism of nylon.
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that the phosphorus-based flame retardant system was effective in changing the
It was reported that thermal decomposition of untreated nylon 66 started via a
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hydrogen transfer from carbon(-CH2-) to nitrogen to form compounds having amine and ketoamide end groups, which is followed by further decomposition to form
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cyclopentanone and compounds bearing amine and/or Schiff base groups [25]. Those reactions took place in the 370-509ºC region with a sharp peak at 469ºC in Fig. 6. It was also reported in the literature that ammonium polyphosphate, a phosphorus-based flame retardant, released reactive polyphosphoric acid, which attacked the amide bonds (–CH2–NH–) and alkyl-amide bonds (–CH2–C[O]–) bonds of nylon and
lowered the decomposition temperature by 50–70℃ [26]. Such reactions were
apparently more complex and shown in the 330-490ºC region with two peaks at 392 and 439ºC in Fig. 6. The precise nature of the broadening of the nylon decomposition 16
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temperature range and the two peaks at 392 and 439ºC are the subject of our current research project. The HRR curve of the nylon fabric treated with HFPO/DMDHEU, cured and
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finally subjected to one HLWD cycle was also presented in Fig. 6. As a result of the
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home laundering washing, the two HRR peaks of nylon had a modest decrease and
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TPHRR had a modest increase (Fig. 6), and the percent char yield was marginally reduced from 9.0 to 7.9% (Tables 3) . The shape of the HRR versus temperature curve
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changes little after the washing cycle. Thus, the data indicate that the majority of the HFPO/DMDHEU system still remained on the nylon fabric after the washing cycle.
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The data proves that the HFPO/DMDHEU is a durable flame retardant system for nylon.
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The 50/50 nylon/cotton blend fabric was treated with 36% HFPO and 8%
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DMDHEU, cured at 165℃ for 2.5 min, and was finally subjected to one HLWD cycle.
The HRR versus temperature curve of the nylon/cotton blend thus treated was shown in Fig. 7. For the purpose of comparison, the cotton and nylon treated, cured and washed were also included in Fig. 7. The HRC, THR and percent char yield were
presented in Table 4. The peak at 283℃ in the HRR vs. temperature curve Fig. 7 was
associated to the decomposition of cotton in the blend. The HRR peak of cotton treated with HFPO and DMDHEU as a single fiber appeared at a lower temperature of
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272℃ (Fig. 7). The two peaks at 378 and 442℃ in the curve of the blend in Fig. 7
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were due to the decomposition of nylon in the blend. The HRR peaks of nylon treated
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with HFPO and DMDHEU as a single fiber appeared at higher temperatures (404 and
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443℃) (Fig. 7). The peak at 442ºC in the HRR curve of the treated nylon/cotton blend
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appeared broader than the same peak in the curves of treated cotton and nylon as single fibers (Fig. 7). The measured percent char yield (20.1%) of the treated
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nylon/cotton blend after one wash was significantly higher than that calculated based on the char yield of nylon and cotton as single fibers (18.5%) as shown in Table 4.
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The HRC and THR for the treated blend were significantly lower than that calculated ones. All the data discussed above indicated that nylon and cotton in the blend treated
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with the HFPO/DMDHEU flame retardant system interacted with each other during its thermal decomposition.
In order to evaluate the possible interaction between nylon and cotton during
the thermal decomposition of the 50/50 nylon/cotton blend, we calculated the HRR in
the entire temperature rang (100-550℃) and compared the calculated HRR curve with
the measured one. The calculation was based on the arithmetic sum of the HRR of nylon and cotton discussed previously assuming that both nylon and cotton acted individually as single fibers. Presented in Fig.8 are the calculated and measured HRR 18
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curves of the nylon/cotton blend fabric treated with 36% HFPO and 8% DMDHEU.
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The HRR of the peak at 283℃ associated with the decomposition of cotton in the
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measured curve (64w/g) was 38% lower than that of the same peak in the calculated
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curve. The TPHRR of cotton in the measured HRR curve was 11℃ higher than that in
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the calculated curve. The peak at 442℃, one of the two peaks associated to the
decomposition of nylon, of the measured curve (80w/g) was 37% lower than the same
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peak in the calculated curve. Another peak associated with the decomposition of
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nylon appeared at 378℃ was 26℃ lower than that in the calculated curve (Fig. 8). The
significantly reduced HRR and changed TPHRR in the measured HRR curve was an indication of the interaction of nylon and cotton in the treated nylon/cotton blend during the decomposition of the blend. We applied DSC to study the nylon, cotton, and nylon/cotton blend fabrics
treated with HFPO and DMDHEU, cured at 165℃ for 2.5 min, and subjected to one
HLWD cycle (Fig.9). When nylon was treated with the HFPO, its melting point was
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reduced slighly from 256℃ (Fig. 3) to 249℃ (Fig. 9). Nylon’s single decomposition
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peak at 453℃ in the DSC curve of untreated nylon (Fig. 3) became two peaks at 384
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and 457℃ after the treatment (Fig. 9). Thus, the DSC data indicated that the flame
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retardant system on nylon not only reduced the melting point, but also changed the
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decomposition mechanism of nylon. The untreated cotton showed a symmetric peak
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at 360℃ in the DSC curve (Fig. 3), and it became two asymmetrically overlapped
peaks at much lower temperatures (246 and 265ºC), indicating a different
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decomposition mechanism for the treated cotton (Fig. 9). In the DSC curve of the
treated nylon/cotton blend, the broad cotton decomposition peaks (246-265℃)
became almost invisible, and the first nylon decomposition peak was shifted from 384
to 371℃ and the peak area decreased by 56%, and the area of the second nylon
decomposition peak at 455℃ decreased by 35%. All the DSC data presented in Fig. 9
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indicated considerably reduced heat absorption during the decomposition of nylon in the nylon/cotton blend treated with the flame retardant system, which was consistent with the MCC data discussed above.
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We studied the bonding of the HFPO/DMDHEU system on the nylon/cotton
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blend fabric. We calculated the “percent fixation” of HFPO on cotton, which is the
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percent of the flame retardant covalently bound to the nylon/cotton blend based on the percent weight gain of the treated fabric before and after washing (Table 5). The
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percent fixation of HFPO to the nylon/cotton fabric was 69.9%, which is higher than that onto the nylon fiber and lower than that onto the cotton fiber. This was because
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HFPO can be bound to cotton by a crosslinked HFPO/DMDHEU network and also by
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network [16, 27].
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DMDHEU bridge, but it can only by bound to nylon by a crosslinked polymeric
Presented in Fig.10 is the HRR versus temperature curves of the nylon/cotton
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blend fabric treated with 36% HFPO and 8% DMDHEU before and after one HLWD
cycle. The HRR peak at 281℃ due to cotton decomposition and the two peaks at
373℃ and 440℃ due to nylon decomposition in the HRR curve of the treated
nylon/cotton blend (before washing) increased slightly in both PHRR and TPHRR after the washing procedure, indicating that the overwhelming majority of the HFPO/DMDHEU applied to the blend fabric remained on the fabric after the washing
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procedure. We found that the phosphorus concentration of the nylon/cotton blend was 3.79%, and it decreased to 2.88% after one HLWD cycle, representing 76% of phosphorus retention on the treated blend fabric after the washing procedure. 24%
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reduction in phosphorus concentration resulted modest reduction in PHRR for the
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decomposition of both cotton and nylon.
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The LOI of the nylon, cotton and nylon/cotton blend fabrics treated with HFPO and DMDHEU was shown in Table 6. Before treatment, cotton had the lowest LOI
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(18.2). After the treatment, the LOI of all three fabrics increased significantly and cotton has the highest LOI (31.0). This is probably because phosphorus/nitrogen
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flame retardants are more effective on cellulose than on nylon and nylon blends. After one HLWD cycle, cotton’s LOI was reduced marginally from 31.0 to 30.6 and the
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LOI of the treated nylon decreased modestly from 26.8 to 25.7, indicating the HFPO/DMDHEU system was resistant to hydrolysis on both cotton and nylon. The
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LOI of the nylon/cotton blend decreased slightly from 28.9 before washing to 28.5 after the washing. The data presented here were consistent to the HRR data of the same treated and washed blend fabrics shown in Fig. 10. We found that the 50/50 nylon/cotton military fabric treated with the HFPO/DMDHEU system were able to maintain flame retardancy after 40 HLWD cycles, and the data will be presented in a subsequent paper. The flammability of the nylon, cotton and nylon/cotton fabrics was evaluated using a vertical burning tester (Table 7). Untreated cotton and 50/50 nylon/cotton blend fabrics failed the vertical flammability test (char length ≥300 mm), and the char
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length of nylon was not measured due to the melting of nylon. The nylon, cotton and nylon/cotton blend fabrics treated with HFPO/DMDHEU (before wash) all passed the vertical burning tests, with the treated nylon/cotton blend fabric having the shortest
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char length (68 mm). After one HLWD cycle, the treated nylon/cotton blend fabric
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still had the lowest char length (75 mm). Therefore, the fabric vertical flammability
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data presented in Table 7 clearly indicated that the treated nylon/cotton blend fabric had lower char length that those of the treated cotton and treated nylon as sigle fiber
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fabrics. The interaction between nylon and cotton during the decomposition of the nylon/cotton blend probably was the cause of the lower flammability of the treated
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50/50 nylon/cotton blend fabric than the treated cotton and treated nylon fabrics. The research on scaffolding effect in the past was focused on polyester/cotton
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blends. For example, Tesoro and Meisers presented data to show that the 50/50 polyester/cotton blends had LOI values lower than those of either polyester or cotton
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with similar structure [28]. Miller and coworkers showed that the double-layered polyester/cotton blend fabric ignited and burn faster, but the data appeared to be inconclusive [29]. Hendrix and coworkers measured LOI to investigate the cotton polyester blend and proposed that polyester functioned to furnish additional fuel to the combustion as the temperature was raised by the burning cotton [4]. However, Drews challenged the proposed theory based on his research data using scanning electron microscopy [4]. Our research data on the 50/50 nylon/cotton blend presented above were different from those of polyester/cotton blend in the literature. The nylon/cotton blend, untreated and treated with the HFPO/DMDHEU system, clearly showed that
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the blend had lower heat release rate and high char yield than that nylon and cotton as
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single fibers. The MCC data was consistent with the vertical flammability data.
4. Conclusions
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For the untreated nylon/cotton blend fabric, we observed the following: (1)
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increased PHRR for cotton and decreased PHRR for nylon; (2) changes in TPHRR for both fibers in the blend; (3) increased char yield for the MCC measurement and
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decreased mass lose for TG measurement; and (4) the decreased heat absorption for the decomposition of both fibers for DSC measurement. All the data indicated that the
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nylon and cotton fibers interacted with each other during the thermal decomposition of the nylon/cotton blend.
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The presence of the phosphorus-based HFPO/DMDHEU reduced the PHRR, TPHRR, and the heat absorption for decomposition, and increased char formation for
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nylon, cotton and the 50/50 nylon/blend fabrics. Moreover, the presence of the flame retardant system caused higher reduction in PHRR and heat absorption for decomposition and higher char formation of the nylon and cotton in the blend than those of nylon and cotton as single fibers. Thus, the data indicated that the nylon and cotton fibers in the blend interacted with each other during the decomposition of the nylon/cotton blend treated with the HFPO/DMDHEU system. Consequently the treated nylon/cotton blend fabric had lower flammability than the treated nylon and cotton as fabrics of single fibers as shown by lower char length.
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AUTHOR INFORMATION Corresponding Author *Tel: +1 706 542 4912; Fax: +1 706 542 4890; E-mail address: [email protected]
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References [1] S.P. Charankar, V. Verma and M. Gupta, Growing importance of cotton blends in
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apparel market, J. Textile Assoc. (2007) 201-210.
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[2] A.R. Horrocks, Flame retardant finishes and finishing, in D. Heywood (Ed.), Textile Finishing, Society of Dyers and Colourists, Bradford, UK, 2003, p. 237-238.
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[3] P.J. Wakelyn, Environmentally friendly flame resistant textiles, in A.R. Horrocks
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and D. Price (Eds.), Advances in fire retardant materials, CRC Press, Boca Raton, FL, US, 2008, p. 190-193.
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[4] C.W. Jarvis and R.H. Barker, Flammability of cotton-polyester blend fabrics, in M.
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Lewin, S.M. Atlas and E.M. Pearce (Eds), Flame-Retardant Polymeric Materials,
Ac ce p
Plenum Press, New York, US, 1978, p. 133-158. [5] A.R. Horrocks, Flame-retardant finishing of textiles, Rev Prog Coloration, 16 (1986) 85-89.
[6] A.R. Horrocks, D. Price and M. Tunc, The burning behaviour of textiles and its assessment by oxygen-index methods, Text Prog. 18 (1988) 47-51. [7] H.G. Schutz, A.V. Cardello and C. Winterhalter, Perceptions of fiber and fabric uses and the factors contributing to military clothing comfort and satisfaction, Text Res J. 75 (2005) 223-232. [8] G.R. Fleming, "Long wear life flame-retardant cotton blend fabrics", U.S. Patent 5 480 458, Jan. 2, 1996. 25
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[9] J.R. Green, "Blend of cotton, nylon and heat resistant fibers", U.S. Patent 4 920 000, Apr. 24, 1990. [10] J.H. Hansen, "Flame-resistant nylon/cotton fabric and process for production
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thereof", U.S. Patent 4 812 144, Mar. 14, 1989.
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[11] P.J. Hauser, "Flame-resistant cotton blend fabrics", U.S. Patent 4 732 789, Mar.
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22, 1988.
[12] C.Q. Yang, in F.S. Kilinc (Ed.), Handbook of fire resistant textiles, Woodhead
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Publishing Limited, Cambridge,UK, 2013, p. 186.
[13] C.Q. Yang, W.D. Wu and Y. Xu, The combination of a hydroxy-functional
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organophosphorus oligomer and melamine-formaldehyde as a flame retarding finishing system for cotton, Fire Mater. 29 (2005) 109-120.
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[14] W.D. Wu and C.Q. Yang, Comparison of different reactive organophosphorus flame retardant agents for cotton: Part I. The bonding of the flame retardant agents to
Ac ce p
cotton. Polym Degrad Stabil. 91(2006) 2541-2548. [15] W.D. Wu and C.Q. Yang, Comparison of different reactive organophosphorus flame retardant agents for cotton. Part II: Fabric flame resistant performance and physical properties, Polym Degrad Stabil. 92 (2007) 363-369. [16] H. Yang and C.Q. Yang, The bonding of a hydroxy-functional organophosphorus oligomer to nylon fabric using the formaldehyde derivatives of urea and melamine as the bonding agents. Polym Degrad Stabil. 94 (2009) 1023-1031. [17] H. Yang and C. Q. Yang, Flame retardant performance of the nylon/cotton blend fabric treated by a hydroxy-functional organophosphorus oligomer, Ind Eng Chem
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Res., 47 (2008) 2160-2165. [18] H. Yang and C.Q. Yang, Nonformaldehyde flame retardant finishing of the nomex/cotton blend fabric using a hydroxy-functional organophosphorus oligomer, J
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Fire Sci., 25 (2007) 425-446.
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[19] C.Q. Yang and W. Wu, Combination of a hydroxylalkyl-functional organophorus
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oligomer and a multifunctional carboxylic acid as a flame retardant finishing system for cotton: part I. the chemical reactions, Fire Mater., 27 (2003) 223-237.
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[20] C.Q. Yang and W. Wu, Combination of a hydroxylalkyl-functional organophorus oligomer and a multifunctional carboxylic acid as a flame retardant finishing system
Fire Mater., 27 (2003) 239-251.
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for cotton: part II. Formation of calcium salt during laundering and its suppression,
Pyrol. 71 (2004) 27-46.
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[21] R.E. Lyon and R.N. Walter, Pyrolysis combustion flow calorimetry, J Anal Appl
Ac ce p
[22] C.Q. Yang and Q.L. He, Applications of micro-scale combustion calorimetry to the studies of cotton and nylon fabrics treated with organophosphorus flame retardants, J Anal Appl Pyrol. 91 (2011) 125-133. [23] C.Q. Yang, Q.L. He, R.E. Lyon and Y. Hu, Investigation of the flammability of different textile fabrics using micro-scale combustion calorimetry, Polym Degrad Stabil. 95 (2010) 108-115. [24] M. Lewin, in M. Lewin and S.B. Sello (Eds.), Handbook of Fiber Science and Technology: Chemical processing of fibers and fabrics, Marcel Dekker, New York, US, 1984, p. 38.
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[25] A. Ballistreri, D. Garozzo, M. Giuffrida and G. Montaudo, Mechanism of thermal decomposition of nylon 66, Macromolecules, 20 (1987) 2991-2997. [26] S.V. Levchik, E.D. Weil and M. Lewin, Thermal decomposition of aliphatic
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nylons, Polym Int. 48 (1999) 532-557.
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[27] W.D. Wu and C.Q. Yang, Comparison of DMDHEU and melamine-formaldehyde
agent on cotton, J Fire Sci. 22 (2004) 125-142.
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as the binding agents for a hydroxy-functional organophosphorus flame retarding
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[28] G.C. Tesoro and C. H. Meiser, Some effects of chemical composition on the flammability behavior of textiles, Text Res J., 40 (1970) 430-436.
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[29] B. Miller, J.R. Martin, C.H. Meiser and M. Gargiullo, The flammability of
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polyester-cotton mixtures, Text Res J., 46 (1976) 530- 538.
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Table 1 Heat release properties of the untreated cotton, nylon/cotton blend and nylon.
THR (kJ/g)
Char yield (%)
280 202 576
11.9 17.9 26.7
4.3 9.1 1.6
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cotton nylon/cotton nylon
HRC (J/[gK])
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Fabrics
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Table 2 The measured and calculated HRC, THR and percent char yield of the untreated nylon/cotton blend fabric.
Measured
428 19.3 3.0
202 17.9 9.1
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HRC (J/[gK]) THR (kJ/g) Char yield (%)
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Calculated
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Table 3 Heat release properties and percent char yield of (1) the cotton treated with 32%HFPO and 8% DMDHEU; (2) 50/50 nylon/cotton blend, and (3) nylon. The blend and nylon were treated with 36%
THR (kJ/g)
cotton nylon/cotton nylon cotton nylon/cotton nylon
200 103 216 181 134 262
5.2 12.9 20.3 7.4 13.8 22.3
Char yield (%) 29.5 21.2 9.0 29.0 20.1 7.9
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After one wash
HRC (J/[gK])
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Before wash
Fabrics
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Laundering
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HFPO and 8% DMDHEU. All fabrics were cured at 165℃ for 2.5 min.
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Table 4 The measured and calculated HRC, THR and percent char yield of the nylon/cotton blend
Calculated 221.5 14.9
Char yield (%)
18.5
Measured 134 13.8 20.1
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HRC (J/[gK]) THR (kJ/g)
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one HLWD cycle.
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fabric treated by 36% HFPO and 8% DMDHEU, cured at 165℃ for 2.5 min and finally subjected to
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Table 5 The weight gain and percent fixation of the three fabrics treated with HFPO and
DMDHEU. Fixation (%)
22.9 21.3
81.5 69.9
nylon
20.5
54.2
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Weight gain (%)
cotton nylon/cotton
Fabrics
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Table 6 The LOI (%) of the cotton, nylon/cotton blend and nylon fabrics. The cotton was treated with 32%HFPO and 8% DMDHEU. The nylon/cotton blend and nylon were treated with 36% HFPO and
31.0 28.9 26.8
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18.2 20.1 ─
treated (after one wash) 30.6 28.5 25.7
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cotton nylon/cotton nylon
untreated
treated (before washing)
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Treatment Fabrics
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8% DMDHEU. All fabrics were then cured at 165℃ for 2.5 min.
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Table 7 The char length (mm) of the cotton, nylon/cotton blend and nylon fabrics. The cotton was
Treatment
91 68 250
＞300 ＞300 ─
treated (after one washing) 97 75 279
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cotton nylon/cotton nylon
treated (before washing)
untreated
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Fabrics
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HFPO and 8% DMDHEU. All fabrics were then cured at 165℃ for 2.5 min.
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treated with 32%HFPO and 8% DMDHEU. The nylon/cotton blend and nylon were treated with 36%
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Figure Captions The HRR versus temperature curves of the cotton and nylon fabrics.
Figure 2
The calculated and measured HRR versus temperature curves of the cotton/ nylon fabric.
Figure 3
The DSC curves of the cotton, nylon and 50/50 nylon/cotton blend fabrics.
Figure 4
The TGA curves of the cotton, nylon and 50/50 nylon/cotton blend fabrics.
Figure 5
The HRR curves of (1) untreated cotton fabric, (2) treated cotton fabric (before washing), and (3) treated cotton fabric (after one HLWD cycle).
Figure 6
The HRR curves of (1) untreated nylon fabric, (2) treated nylon fabric (before washing), and (3) treated nylon fabric (after one HLWD cycle).
Figure 7
The HRR curves of (1) the treated cotton fabric, (2) the treated nylon/cotton blend fabric, and (3) the treated nylon fabric. All fabrics were subjected to one HLWD cycle.
Figure 8
The calculated and measured HRR versus temperature curves of the nylon/cotton blend fabric treated and finally subjected to one HLWD cycle.
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Figure 1
Figure 9
The DSC curves of (1) the treated cotton fabric, (2) the treated nylon/cotton blend fabric, and (3) the treated nylon fabric. All fabrics were subjected to one HLWD cycle.
Figure 10
The HRR curves of (1) the treated nylon/cotton (before washing) and (2) the treated nylon/cotton blend (after one HLWD cycle).
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8
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Figure 9
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Figure 10
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Highlights
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We investigated the nylon/cotton blend fabrics used for military protective uniforms. We discovered the interaction between cotton and nylon during the nylon/cotton blend decomposition process. The data showed that the flammability of nylon/cotton blend fabric was lower than that of cotton and nylon as single-fiber fabric.
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S0165-2370(14)00223-X http://dx.doi.org/doi:10.1016/j.jaap.2014.08.021 JAAP 3277
To appear in:
J. Anal. Appl. Pyrolysis
Received date: Revised date: Accepted date:
6-5-2014 25-8-2014 26-8-2014
Please cite this article as: Q. Chen, C.Q. Yang, T. Zhao, Heat Release Properties and Flammability of the Nylon/Cotton Blend Fabric Treated with a Crosslinkable Organophosphorus Flame Retardant System, Journal of Analytical and Applied Pyrolysis (2014), http://dx.doi.org/10.1016/j.jaap.2014.08.021 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Heat Release Properties and Flammability of the Nylon/Cotton Blend Fabric Treated with a Crosslinkable Organophosphorus Flame Retardant System
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Qin Chena,b, Charles Q. Yangb,*, Tao Zhaoa
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College of Chemistry, Chemical Engineering & Biotechnology, Donghua University, Shanghai 201620, China
b
Department of Textiles, Merchandising and Interiors, The University of Georgia, Athens, Georgia 30602, U.S.A
Corresponding Author *Tel: +1 706 542 4912; Fax: +1 706 542 4890; E-mail address: [email protected]
Page 1 of 47
Abstract Flame retardant nylon/cotton blend fabrics are widely used in the fields of industrial and military protective uniforms. In this research, we investigate the heat release
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properties and flammability of the 50/50 nylon/cotton blend fabric treated with a
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self-crosslinkable durable organophosphorus flame retardant system. For the
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nylon/cotton blend fabric without treatment, the blend has lower total heat release and higher percent char yield than the arithmetic sum of those of cotton and nylon as
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single fibers. In addition, both the peak heat release rate (PHHR) and the temperature at peak heat release (TPHRR) for cotton increases whereas both PHRR and TPHRR
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decrease for nylon when those two fibers are blended to form a fabric. Thus, the data indicated that interaction takes place between cotton and nylon during the
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decomposition process of the blend. The presence of the organophosphorus flame retardant system reduces PHRR, TPHRR and increases char formation for both cotton
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and nylon as single fibers. When the cotton and nylon are blended and then treated with the flame retardant, the PHRR of the blend becomes even lower and the percent char yield of the blend becomes even higher than those of the treated cotton and nylon as single-fiber fabric. The char length for the treated blend decreases compared with that of the treated cotton and nylon as single-fiber fabrics. We conclude that cotton and nylon interact with each other during the degradation process of the treated nylon/cotton blend fabric and such interaction reduces the flammability of the blend fabric. Key words: nylon/cotton blend, micro-scale combustion calorimeter, flame retardant textiles, flame retardant protective clothing 2
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1. Introduction Cotton blends have become very important fabrics in the apparel market because of the combination of desirable characteristics of the products [1]. Blending cotton
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with nylon improves strength, abrasion resistance, fast-drying property as well as
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wrinkle resistance of the fabrics. Cotton provides the blends with high absorbency and
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soft hand property, thus improving comfortabilty. Nylon/cotton blends have become fabrics of choice for professional work uniforms and military uniforms.
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Thermoplastic polymers, such as polyester, melts upon exposure to high heat, which leads to self-extinguish due to melting. When a polyester/cotton blend is
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ignited upon exposure to high temperatures, it’s flammability becomes more complicated because of so-called “scaffolding effect” [2-3]. The “scaffolding effect”
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for polyester/cotton fabrics has long been discussed and the related literatures was reviewed previously [4-6]. When exposed to high temperature, cotton forms char
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which maintains some degree of integrity. Polyester melts above its melting point (~260ºC) and tends to flow on the cotton char. “Scaffolding effect” refers to the fact that charred cotton in a blend fabric acts as a support for burning of molted polyester in a fire. The molten polyester in the blend does not drip away as it does in a 100% polyester fabric [4-6]. Nylon/cotton blend fabrics are widely used for production of military uniforms and other protective garments [7]. Since nylon also melts like polyester, it is important to know if a nylon/cotton blend also have such flammability-enhancing effect. Flame retardant treatment methods to produce flame retardant nylon/cotton blend
3
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fabrics include (1) applying organophosphorus flame retardants to the blend if cellulose is the overwhelming fiber; and (2) applying halogen-based back-coatings for blend fabrics with all nylon-to-cotton ratios [2, 8-11]. Flame retardant nylon fibers
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can be produced at the fiber spinning stage using flame retardant additives including
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organophosphorus and halogenated aliphatic/aromatic compounds. The nylon fabrics
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can also be flame retardant finished by a pad-dry-cure process using a number of flame retardants, such as thiourea derivatives, ammonium sulfamate and
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organophosphorus compounds [2]. However, flame retardant finishing has not been successful for most of nylon/cotton blends and new technology is still in the
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developing stage to produce durable flame retardant nylon/cotton blend fabrics. In our previous research, we developed a durable flame retardant finishing
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system for 50/50 nylon/cotton blend fabrics using a hydroxy-functional and self-crosslinkable organophosphorus oligomer (HFPO) [12-15]. We found that the
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HFPO and dimethyloldihydroxyethyleneurea (DMDHEU) form a crosslinked polymeric network on the 50/50 nylon/cotton blend fabrics [16-17]. This HFPO/DMDHEU system has been successfully applied to the 50/50 nylon/cotton fabrics as durable flame retardant finishing system [17]. 1,2,3,4-butanetetracarboxylic acid (BTCA), a formaldehyde-free crosslinking agent for cotton, has been applied to 65/35 nomex/cotton blend military fabric in combination with HFPO as a flame retardant finishing agent [18]. However, HFPO/BTCA showed low laundering durability on cotton [19-20]. It is not suitable for the flame retardant finishing of nylon/cotton blends.
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In this research, we evaluated the heat release properties and flammability of the 50/50 nylon/cotton blend fabric treated with the HFPO/DMDHEU system to determine if interaction between nylon and cotton takes place during the degradation
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of the nylon/cotton blend fabric. Micro-scale combustion calorimetry (MCC) is a
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pyrolysis-combustion flow calorimetry to measure heat release parameters using a
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few milligram sample sizes [21]. In our previous research, we use MCC as an analytical technique to measure the heat release properties of various textile fibers and
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also to differentiate the flame retardant performance of the cotton fabrics with different levels of phosphorus-based flame retardants [22-23]. The heat release
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properties of textiles showed very close correlation with macroscopic flammability parameters such as limiting oxygen index [22-23]. The goal of this research was to
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determine if the two fibers (cotton and nylon) interacts with each other during the thermal decomposition process based on the heat release rate (HRR) vs. temperature
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curve, peak heat release rate (PHRR), temperature at PHRR (TPHRR), total heat release
(THR) and percent char yield of cotton, nylon, and cotton nylon blend. We also measured the flammability parameters including LOI and char length in a vertical fabric burning test and correlated to conform the MCC results.
2. Experimental 2.1. Materials Three woven fabrics were used in this study: (1) a nylon66 woven fabric weighing 130g/m2 (Testfabrics Style 341); (2) a cotton twill woven fabric weighing
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245g/m2 supplied by Milliken, Blacksburg, Sout Carolina; and (3) a 50/50 nylon66/cotton twill woven fabric weighing 256g/m2 supplied by Mount Vernon Mills, Trion, Georgia. HFPO with the commercial name of “Fyroltex HP” (CAS Registry No.
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70715-06-9) was supplied by Supresta (formerly Akzo Nobel), Debbs Ferry, New
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York. DMDHEU was a commercial product (44% solution) under the trade name of
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“Freerez 900” supplied by Emerald Carolina Chemical, Charlotte, NC. The catalyst was an NH4Cl-based commercial product under the trade name of “Catalyst RD”
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supplied by Eastern Color & Chemical, Greenville, SC. 2.2. Fabric treatment
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The three different fabrics (100% cotton, 50/50 nylon/cotton, 100% nylon) were individually immersed in a solution containing flame retardant (HFPO+DMDHEU)
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and the catalyst, passed through a laboratory padder with two dips and two nips. The 100% cotton fabric was treated with 32% HFPO with 8% DMDHEU while other two
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fabrics were treated with 36% HFPO with 8% DMDHEU. All fabrics were dried at
90℃ for 3 min and finally cured in a Mathis oven at 165℃ for 2.5 min. The wet
pick-up of 100% cotton was 82±2%, that of 100% nylon fabrics was 62±2% and that of 50/50 nylon/cotton was 76±2%. After curing, the treated fabrics were subjected to one home laundering washing/drying (HLWD) cycle according to AATCC Test
Method 124-2008 with water temperature at approximately 46℃. All concentrations
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presented in this study were based on weight of bath (w/w, %). 2.3. Fabric weight gain measurement The three untreated fabrics and the treated fabrics (before washing and after one
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HLWD cycle) were weighed after being conditioned for 24 h. The fabric percent
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weight gain and the percent fixation of the flame retardant on the fabric were
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calculated using the following equations where W0, W1, W2 were the weight of the untreated fabric, the treated fabric before washing, and the treated fabric subjected to
Weight gain (%)=(W2-W0)/W0×100%
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one HLWD cycle, respectively.
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Fixation (%) = (W2-W0)/(W1-W0) × 100% 2.4. MCC measurement
(1) (2)
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The MCC measurements of the textile fabric samples were conducted using a micro-scale combustion calorimeter (model “MCC-2”) produced by Govmark,
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Farmingdale, New York, according to ASTM D7309 (Method A). A fabric specimen was first ground in a Wiley mill into a homogeneous powder to ensure sample
uniformity. A sample thus prepared (∼5mg) was loaded to the MCC instrument and
then heated to a specified temperature using a linear heating rate (1℃/s) in a stream of
nitrogen flowing at 80cm3/min. The thermal degradation products of the sample in
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nitrogen were mixed with a 20cm3/min stream of oxygen prior to entering the 900℃
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combustion furnace. Each sample was run in three replicates and the MCC parameters were the averages of the three measurements.
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2.5. DSC and TG measurement
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DSC data was collected using a Mettler Toledo DSC821 differential scanning
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calorimeter. All samples for DSC measurement were analyzed at a rate of 10℃/min
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with a continuous air flow rate of 60 mL/min and heated from 100℃ to 550℃. TG
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data were collected using a Mettler TG50 thermogravimeter. All the samples for TG
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test were heated from 100℃ to 650℃ at a rate of 10℃/min with a continuous air flow
rate of 30 mL/min. The sample size for both DSC and TG was approximately 2 mg. 2.6. Evaluation of the flame retarding performance The fabric vertical burning flammability of was measured according to ASTM
Standard Method D6413-99. The limiting oxygen index (LOI) of the fabrics was measured according to ASTM Standard Method D2863-97.
3. Results and discussion
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3.1. The untreated nylon, cotton and nylon/cotton blend fabrics The HRR versus temperature curves of cotton and nylon were shown in Fig.1.
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For the untreated cotton, the thermal decomposition started at approximately 300℃
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and peaked (274w/g) at 374℃. The decomposition of cotton ended at about 415℃.
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Nylon started to decompose at approximately 375℃, and its HRR reached to
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510℃.
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maximum (565w/g) at 469℃. The decomposition of nylon ended at approximately
We calculated the HHR of the 50/50 nylon/blend based on that of cotton and
nylon as single fibers assuming that no interaction between nylon and cotton takes place during the degradation of the blend. The calculated HRR curve of the nylon/cotton blend shown in Fig. 2 is the arithmetic sum of those of cotton and nylon as single fibers at each temperature multiplied by their weight fraction (0.50) in the blend. Also presented in Fig. 2 was the measured HRR curve of the 50/50 nylon/cotton blend fabric. The measured PHRR of cotton in Fig. 2 (189 w/g) was 48 w/g higher than that of the calculated one (141 w/g). The PHRR of nylon in the
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measured curve (170 w/g), on the contrary, was 113 w/g lower than that of the calculated curve. The TPHRR of cotton shown in the measured curve in Fig. 2 was
cr
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389℃ (15 degree higher than that in the calculated curve) whereas the TPHRR of nylon
us
in the measured curve was at 446℃ (23 degree lower than that in the calculated curve).
an
Because nylon melts around 256ºC as shown in Fig. 3, the cotton fiber was coated with liquid nylon when cotton’s decomposition started to take place at 320ºC. The
M
presence of a layer of liquid nylon on the cotton fiber surface was probably the main reason why cotton’s decomposition temperature increased and its TPHRR was raised by
d
When the temperature was increased above 400ºC, nylon’s
te
15ºC (Fig. 2).
decomposition took place. At that temperature, the liquid nylon was on the top of a
Ac ce p
char structure formed by the decomposition of cotton. The presence of cotton char was probably the cause for decrease in nylon’s decomposition temperature and decrease of nylon’s TPHRR by 23ºC shown in Fig. 2. The data presented in Fig.2
evidently supported the hypothesis that interaction between nylon and cotton took place during thermal degradation of the blend. Presented in Table 1 are the heat release properties (HRC and THR) and the percent char yield of the untreated cotton, nylon, and 50/50 nylon/cotton blend fabrics. We also calculated the HRC, THR and percent char yield for the nylon/cotton based on the arithmetic sum of those of cotton and nylon as single fibers assuming no
10
Page 10 of 47
interaction between the two fibers took place (Table 2). The measured HRC and THR (202 J/[gK]) and 17.9 kJ/g) of the nylon/cotton blend were significantly lower than those calculated (428 J/[gK]) and 19.3 kJ/g) whereas the percent char yield of the
ip t
nylon/cotton blend (9.1%) is 303% of that calculated (3.0%) (Table 2). Thus, the HRC,
cr
THR and the percent char yield indicated that nylon and cotton in the blend interacted
us
in the decomposition process.
We also used thermal analysis techniques to study the untreated cotton, nylon,
an
and their 50/50 blend fabrics. The DSC curves of three untreated fabrics were
M
presented in Fig.3. The cotton fabric had an endothermic peak at 360℃ in the DSC
te
d
curve related to the heat absorption of the decomposition of cotton. The DSC curve of
Ac ce p
the nylon fabric showed two peaks at 256 and 453℃ corresponding to the melting and
thermal decomposition of nylon, respectively (Fig.3). In the DSC curve of the nylon/cotton blend fabric, nylon had the same melting point, and nylon and cotton in the blend had the two endothermic peaks due to their decomposition at similar temperature. However, the peak area associated with nylon decomposition in the HRR
curve of the blend at 441℃ was only 1/6 of the same peak of nylon as a single fiber,
11
Page 11 of 47
and that associated with cotton decomposition of the blend at 335℃ was only 1/15 of
ip t
the same peak area cotton as a single fiber (Fig. 3). The DSC data strongly supported the hypothesis that interaction existed between nylon and cotton in the thermal
cr
decomposition process the nylon/cotton blend fabric.
us
The TG curves of the untreated nylon, cotton and nylon/cotton blend fabrics
M
an
were presented in Fig. 4. Cotton started decomposition at approximately 300℃ and
te
d
the TG curve had a sharp turn with drastically reduced slope at around 380℃. Cotton
For
Ac ce p
lost 96.0% of its initial weight at 600℃ as a result of decomposition (Fig.4).
nylon, most of its weight loss took place in the 400-500℃ region, which was
consistent with the DSC data in Fig.3. Nylon lost 94.0% of its weight at 600℃. The
50/50 nylon/cotton blend started to lose weight around 320℃ due to the
decomposition of cotton in the blend. It continued its weight loss as the temperature 12
Page 12 of 47
was increased beyond 400℃ mainly due to the decomposition of nylon as also shown
ip t
in the DSC curve in Fig. 3. The nylon/cotton blend lost 86.0% of its original weight at
us
cr
600℃ (Fig. 4). The DSC and the TG data presented here demonstrated that the
an
nylon/cotton blend had significantly less weight loss than both nylon and cotton,
M
indicated that the decomposition of cotton and nylon interact in the 300-500℃ region.
The TG data is consistent with the MCC data, which showed that the nylon/cotton
d
blend had significantly higher percent char yield than both nylon and cotton (Table 1).
te
The MCC data also showed that the nylon/cotton blend had significantly lower total
Ac ce p
heat release, thus indicating that more carbon is remained as char. Such a considerable increase in char yield was another piece of evidence to support the hypothesis that cotton and nylon interacted during the thermal decomposition of the nylon/cotton blend.
3.2. The
cotton,
nylon
and
nylon/cotton
blend
fabrics
treated
with
HFPO/DMDHEU The cotton fabric was treated with 32% HFPO with 8% DMDHEU, and the nylon and the nylon/cotton blend fabrics were treated with 36% HFPO and 8%
13
Page 13 of 47
DMDHEU. All the fabrics thus treated were cured at 165℃ for 2.5 min. The HRR
ip t
versus temperature curves of the cotton fabric untreated and treated before washing
us
cr
were presented in Fig. 5. Cotton started to decompose at approximately 300℃ before
an
the treatment, and its decomposition temperature decreased to 200℃ after the
M
treatment as shown in Fig. 5. The decrease in the decomposition temperature was due to the catalysis effect of phosphoric acid on cotton for the dehydration of cellulose,
d
and the phosphoric acid was formed by decomposition of an organophosphorus flame
te
retardant on cotton exposed to elevated temperatures [24]. The PHRR of the cotton
Ac ce p
fabric decreased from 274 w/g before treatment to 174 w/g after treatment whereas
TPHRR decreased from 374℃ before treatment to 277℃ after treatment. All those
changes were due to the HFPO/DMDHEU flame retardant on the cotton fabric [14]. The HRR curve of the cotton treated and subjected to one HLWD cycle was
also included in Fig 5. The PHRR of the treated cotton slightly increased from 174w/g before washing to 187w/g after one wash, and the TPHRR slightly decreased from
277℃ before wash to 272℃ after one wash. The HRC, THR and percent char yield of
14
Page 14 of 47
treated cotton fabric (before and after one HLWD cycle) were presented in Table 3. The char yield of the cotton drastically increased from 4.3% before treatment to 29.5% after treatment (before wash). The percent char yield decreased marginally to
ip t
29.0% after one wash. The data indicated that the cotton fabric treated with
cr
HFPO/DMDUEU and subjected to one HLWD cycle had marginal increase in HRR
us
and little decrease in char yield. Therefore, the HFPO/DMDUEU system applied to the cotton fabric was resistant to hydrolysis and durable to home launderings.
an
Shown in Fig. 6 were the HRR curves of untreated nylon fabric and the nylon
d
M
fabric treated with 36% HFPO with 8% DMDHEU and cured at 165℃ for 2.5 min. In
Ac ce p
te
the presence of the flame retardant system, the HRR peaked at 469℃ for the untreated
nylon. It decreased by 77 and 30℃ to become two peaks at 392 and 439℃,
respectively after the treatment as shown in Fig. 6. The PHRR of the untreated nylon
decreased from 565 w/g to 199 and 218 w/g for the two peaks at 392 and 439℃,
respectively, after the treatment. Before the treatment, nylon started to decompose at
approximately 370℃, and the starting temperature decreased to approximately 330℃
15
Page 15 of 47
after the treatment (Fig. 6). The THR of nylon decreased from 26.7 to 20.3 kJ/g whereas the percent char yield of nylon increased from 1.6 to 9.0% after the treatment (Tables 1 and 3). Moreover, the one peak in the HRR cure of the untreated nylon
ip t
splitted into two peaks after the treatment, and the HRR curve of the treated nylon
cr
became broader with a less symmetric shape than that of nylon before treatment. The
us
significantly reduction in PHRR, TPHRR and the temperature for the start of the decomposition of nylon, the increase in char yield, and the change in the shape of the
an
HRR versus temperature curve in the presence of HFPO and DMDHEU demonstrated
decomposition mechanism of nylon.
M
that the phosphorus-based flame retardant system was effective in changing the
It was reported that thermal decomposition of untreated nylon 66 started via a
te
d
hydrogen transfer from carbon(-CH2-) to nitrogen to form compounds having amine and ketoamide end groups, which is followed by further decomposition to form
Ac ce p
cyclopentanone and compounds bearing amine and/or Schiff base groups [25]. Those reactions took place in the 370-509ºC region with a sharp peak at 469ºC in Fig. 6. It was also reported in the literature that ammonium polyphosphate, a phosphorus-based flame retardant, released reactive polyphosphoric acid, which attacked the amide bonds (–CH2–NH–) and alkyl-amide bonds (–CH2–C[O]–) bonds of nylon and
lowered the decomposition temperature by 50–70℃ [26]. Such reactions were
apparently more complex and shown in the 330-490ºC region with two peaks at 392 and 439ºC in Fig. 6. The precise nature of the broadening of the nylon decomposition 16
Page 16 of 47
temperature range and the two peaks at 392 and 439ºC are the subject of our current research project. The HRR curve of the nylon fabric treated with HFPO/DMDHEU, cured and
ip t
finally subjected to one HLWD cycle was also presented in Fig. 6. As a result of the
cr
home laundering washing, the two HRR peaks of nylon had a modest decrease and
us
TPHRR had a modest increase (Fig. 6), and the percent char yield was marginally reduced from 9.0 to 7.9% (Tables 3) . The shape of the HRR versus temperature curve
an
changes little after the washing cycle. Thus, the data indicate that the majority of the HFPO/DMDHEU system still remained on the nylon fabric after the washing cycle.
M
The data proves that the HFPO/DMDHEU is a durable flame retardant system for nylon.
te
d
The 50/50 nylon/cotton blend fabric was treated with 36% HFPO and 8%
Ac ce p
DMDHEU, cured at 165℃ for 2.5 min, and was finally subjected to one HLWD cycle.
The HRR versus temperature curve of the nylon/cotton blend thus treated was shown in Fig. 7. For the purpose of comparison, the cotton and nylon treated, cured and washed were also included in Fig. 7. The HRC, THR and percent char yield were
presented in Table 4. The peak at 283℃ in the HRR vs. temperature curve Fig. 7 was
associated to the decomposition of cotton in the blend. The HRR peak of cotton treated with HFPO and DMDHEU as a single fiber appeared at a lower temperature of
17
Page 17 of 47
272℃ (Fig. 7). The two peaks at 378 and 442℃ in the curve of the blend in Fig. 7
ip t
were due to the decomposition of nylon in the blend. The HRR peaks of nylon treated
cr
with HFPO and DMDHEU as a single fiber appeared at higher temperatures (404 and
us
443℃) (Fig. 7). The peak at 442ºC in the HRR curve of the treated nylon/cotton blend
an
appeared broader than the same peak in the curves of treated cotton and nylon as single fibers (Fig. 7). The measured percent char yield (20.1%) of the treated
M
nylon/cotton blend after one wash was significantly higher than that calculated based on the char yield of nylon and cotton as single fibers (18.5%) as shown in Table 4.
te
d
The HRC and THR for the treated blend were significantly lower than that calculated ones. All the data discussed above indicated that nylon and cotton in the blend treated
Ac ce p
with the HFPO/DMDHEU flame retardant system interacted with each other during its thermal decomposition.
In order to evaluate the possible interaction between nylon and cotton during
the thermal decomposition of the 50/50 nylon/cotton blend, we calculated the HRR in
the entire temperature rang (100-550℃) and compared the calculated HRR curve with
the measured one. The calculation was based on the arithmetic sum of the HRR of nylon and cotton discussed previously assuming that both nylon and cotton acted individually as single fibers. Presented in Fig.8 are the calculated and measured HRR 18
Page 18 of 47
curves of the nylon/cotton blend fabric treated with 36% HFPO and 8% DMDHEU.
ip t
The HRR of the peak at 283℃ associated with the decomposition of cotton in the
cr
measured curve (64w/g) was 38% lower than that of the same peak in the calculated
an
us
curve. The TPHRR of cotton in the measured HRR curve was 11℃ higher than that in
M
the calculated curve. The peak at 442℃, one of the two peaks associated to the
decomposition of nylon, of the measured curve (80w/g) was 37% lower than the same
te
d
peak in the calculated curve. Another peak associated with the decomposition of
Ac ce p
nylon appeared at 378℃ was 26℃ lower than that in the calculated curve (Fig. 8). The
significantly reduced HRR and changed TPHRR in the measured HRR curve was an indication of the interaction of nylon and cotton in the treated nylon/cotton blend during the decomposition of the blend. We applied DSC to study the nylon, cotton, and nylon/cotton blend fabrics
treated with HFPO and DMDHEU, cured at 165℃ for 2.5 min, and subjected to one
HLWD cycle (Fig.9). When nylon was treated with the HFPO, its melting point was
19
Page 19 of 47
ip t
reduced slighly from 256℃ (Fig. 3) to 249℃ (Fig. 9). Nylon’s single decomposition
cr
peak at 453℃ in the DSC curve of untreated nylon (Fig. 3) became two peaks at 384
us
and 457℃ after the treatment (Fig. 9). Thus, the DSC data indicated that the flame
an
retardant system on nylon not only reduced the melting point, but also changed the
M
decomposition mechanism of nylon. The untreated cotton showed a symmetric peak
te
d
at 360℃ in the DSC curve (Fig. 3), and it became two asymmetrically overlapped
peaks at much lower temperatures (246 and 265ºC), indicating a different
Ac ce p
decomposition mechanism for the treated cotton (Fig. 9). In the DSC curve of the
treated nylon/cotton blend, the broad cotton decomposition peaks (246-265℃)
became almost invisible, and the first nylon decomposition peak was shifted from 384
to 371℃ and the peak area decreased by 56%, and the area of the second nylon
decomposition peak at 455℃ decreased by 35%. All the DSC data presented in Fig. 9
20
Page 20 of 47
indicated considerably reduced heat absorption during the decomposition of nylon in the nylon/cotton blend treated with the flame retardant system, which was consistent with the MCC data discussed above.
ip t
We studied the bonding of the HFPO/DMDHEU system on the nylon/cotton
cr
blend fabric. We calculated the “percent fixation” of HFPO on cotton, which is the
us
percent of the flame retardant covalently bound to the nylon/cotton blend based on the percent weight gain of the treated fabric before and after washing (Table 5). The
an
percent fixation of HFPO to the nylon/cotton fabric was 69.9%, which is higher than that onto the nylon fiber and lower than that onto the cotton fiber. This was because
M
HFPO can be bound to cotton by a crosslinked HFPO/DMDHEU network and also by
te
network [16, 27].
d
DMDHEU bridge, but it can only by bound to nylon by a crosslinked polymeric
Presented in Fig.10 is the HRR versus temperature curves of the nylon/cotton
Ac ce p
blend fabric treated with 36% HFPO and 8% DMDHEU before and after one HLWD
cycle. The HRR peak at 281℃ due to cotton decomposition and the two peaks at
373℃ and 440℃ due to nylon decomposition in the HRR curve of the treated
nylon/cotton blend (before washing) increased slightly in both PHRR and TPHRR after the washing procedure, indicating that the overwhelming majority of the HFPO/DMDHEU applied to the blend fabric remained on the fabric after the washing
21
Page 21 of 47
procedure. We found that the phosphorus concentration of the nylon/cotton blend was 3.79%, and it decreased to 2.88% after one HLWD cycle, representing 76% of phosphorus retention on the treated blend fabric after the washing procedure. 24%
ip t
reduction in phosphorus concentration resulted modest reduction in PHRR for the
cr
decomposition of both cotton and nylon.
us
The LOI of the nylon, cotton and nylon/cotton blend fabrics treated with HFPO and DMDHEU was shown in Table 6. Before treatment, cotton had the lowest LOI
an
(18.2). After the treatment, the LOI of all three fabrics increased significantly and cotton has the highest LOI (31.0). This is probably because phosphorus/nitrogen
M
flame retardants are more effective on cellulose than on nylon and nylon blends. After one HLWD cycle, cotton’s LOI was reduced marginally from 31.0 to 30.6 and the
te
d
LOI of the treated nylon decreased modestly from 26.8 to 25.7, indicating the HFPO/DMDHEU system was resistant to hydrolysis on both cotton and nylon. The
Ac ce p
LOI of the nylon/cotton blend decreased slightly from 28.9 before washing to 28.5 after the washing. The data presented here were consistent to the HRR data of the same treated and washed blend fabrics shown in Fig. 10. We found that the 50/50 nylon/cotton military fabric treated with the HFPO/DMDHEU system were able to maintain flame retardancy after 40 HLWD cycles, and the data will be presented in a subsequent paper. The flammability of the nylon, cotton and nylon/cotton fabrics was evaluated using a vertical burning tester (Table 7). Untreated cotton and 50/50 nylon/cotton blend fabrics failed the vertical flammability test (char length ≥300 mm), and the char
22
Page 22 of 47
length of nylon was not measured due to the melting of nylon. The nylon, cotton and nylon/cotton blend fabrics treated with HFPO/DMDHEU (before wash) all passed the vertical burning tests, with the treated nylon/cotton blend fabric having the shortest
ip t
char length (68 mm). After one HLWD cycle, the treated nylon/cotton blend fabric
cr
still had the lowest char length (75 mm). Therefore, the fabric vertical flammability
us
data presented in Table 7 clearly indicated that the treated nylon/cotton blend fabric had lower char length that those of the treated cotton and treated nylon as sigle fiber
an
fabrics. The interaction between nylon and cotton during the decomposition of the nylon/cotton blend probably was the cause of the lower flammability of the treated
M
50/50 nylon/cotton blend fabric than the treated cotton and treated nylon fabrics. The research on scaffolding effect in the past was focused on polyester/cotton
te
d
blends. For example, Tesoro and Meisers presented data to show that the 50/50 polyester/cotton blends had LOI values lower than those of either polyester or cotton
Ac ce p
with similar structure [28]. Miller and coworkers showed that the double-layered polyester/cotton blend fabric ignited and burn faster, but the data appeared to be inconclusive [29]. Hendrix and coworkers measured LOI to investigate the cotton polyester blend and proposed that polyester functioned to furnish additional fuel to the combustion as the temperature was raised by the burning cotton [4]. However, Drews challenged the proposed theory based on his research data using scanning electron microscopy [4]. Our research data on the 50/50 nylon/cotton blend presented above were different from those of polyester/cotton blend in the literature. The nylon/cotton blend, untreated and treated with the HFPO/DMDHEU system, clearly showed that
23
Page 23 of 47
the blend had lower heat release rate and high char yield than that nylon and cotton as
ip t
single fibers. The MCC data was consistent with the vertical flammability data.
4. Conclusions
cr
For the untreated nylon/cotton blend fabric, we observed the following: (1)
us
increased PHRR for cotton and decreased PHRR for nylon; (2) changes in TPHRR for both fibers in the blend; (3) increased char yield for the MCC measurement and
an
decreased mass lose for TG measurement; and (4) the decreased heat absorption for the decomposition of both fibers for DSC measurement. All the data indicated that the
M
nylon and cotton fibers interacted with each other during the thermal decomposition of the nylon/cotton blend.
te
d
The presence of the phosphorus-based HFPO/DMDHEU reduced the PHRR, TPHRR, and the heat absorption for decomposition, and increased char formation for
Ac ce p
nylon, cotton and the 50/50 nylon/blend fabrics. Moreover, the presence of the flame retardant system caused higher reduction in PHRR and heat absorption for decomposition and higher char formation of the nylon and cotton in the blend than those of nylon and cotton as single fibers. Thus, the data indicated that the nylon and cotton fibers in the blend interacted with each other during the decomposition of the nylon/cotton blend treated with the HFPO/DMDHEU system. Consequently the treated nylon/cotton blend fabric had lower flammability than the treated nylon and cotton as fabrics of single fibers as shown by lower char length.
24
Page 24 of 47
AUTHOR INFORMATION Corresponding Author *Tel: +1 706 542 4912; Fax: +1 706 542 4890; E-mail address: [email protected]
ip t
References [1] S.P. Charankar, V. Verma and M. Gupta, Growing importance of cotton blends in
cr
apparel market, J. Textile Assoc. (2007) 201-210.
us
[2] A.R. Horrocks, Flame retardant finishes and finishing, in D. Heywood (Ed.), Textile Finishing, Society of Dyers and Colourists, Bradford, UK, 2003, p. 237-238.
an
[3] P.J. Wakelyn, Environmentally friendly flame resistant textiles, in A.R. Horrocks
M
and D. Price (Eds.), Advances in fire retardant materials, CRC Press, Boca Raton, FL, US, 2008, p. 190-193.
d
[4] C.W. Jarvis and R.H. Barker, Flammability of cotton-polyester blend fabrics, in M.
te
Lewin, S.M. Atlas and E.M. Pearce (Eds), Flame-Retardant Polymeric Materials,
Ac ce p
Plenum Press, New York, US, 1978, p. 133-158. [5] A.R. Horrocks, Flame-retardant finishing of textiles, Rev Prog Coloration, 16 (1986) 85-89.
[6] A.R. Horrocks, D. Price and M. Tunc, The burning behaviour of textiles and its assessment by oxygen-index methods, Text Prog. 18 (1988) 47-51. [7] H.G. Schutz, A.V. Cardello and C. Winterhalter, Perceptions of fiber and fabric uses and the factors contributing to military clothing comfort and satisfaction, Text Res J. 75 (2005) 223-232. [8] G.R. Fleming, "Long wear life flame-retardant cotton blend fabrics", U.S. Patent 5 480 458, Jan. 2, 1996. 25
Page 25 of 47
[9] J.R. Green, "Blend of cotton, nylon and heat resistant fibers", U.S. Patent 4 920 000, Apr. 24, 1990. [10] J.H. Hansen, "Flame-resistant nylon/cotton fabric and process for production
ip t
thereof", U.S. Patent 4 812 144, Mar. 14, 1989.
cr
[11] P.J. Hauser, "Flame-resistant cotton blend fabrics", U.S. Patent 4 732 789, Mar.
us
22, 1988.
[12] C.Q. Yang, in F.S. Kilinc (Ed.), Handbook of fire resistant textiles, Woodhead
an
Publishing Limited, Cambridge,UK, 2013, p. 186.
[13] C.Q. Yang, W.D. Wu and Y. Xu, The combination of a hydroxy-functional
M
organophosphorus oligomer and melamine-formaldehyde as a flame retarding finishing system for cotton, Fire Mater. 29 (2005) 109-120.
te
d
[14] W.D. Wu and C.Q. Yang, Comparison of different reactive organophosphorus flame retardant agents for cotton: Part I. The bonding of the flame retardant agents to
Ac ce p
cotton. Polym Degrad Stabil. 91(2006) 2541-2548. [15] W.D. Wu and C.Q. Yang, Comparison of different reactive organophosphorus flame retardant agents for cotton. Part II: Fabric flame resistant performance and physical properties, Polym Degrad Stabil. 92 (2007) 363-369. [16] H. Yang and C.Q. Yang, The bonding of a hydroxy-functional organophosphorus oligomer to nylon fabric using the formaldehyde derivatives of urea and melamine as the bonding agents. Polym Degrad Stabil. 94 (2009) 1023-1031. [17] H. Yang and C. Q. Yang, Flame retardant performance of the nylon/cotton blend fabric treated by a hydroxy-functional organophosphorus oligomer, Ind Eng Chem
26
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Res., 47 (2008) 2160-2165. [18] H. Yang and C.Q. Yang, Nonformaldehyde flame retardant finishing of the nomex/cotton blend fabric using a hydroxy-functional organophosphorus oligomer, J
ip t
Fire Sci., 25 (2007) 425-446.
cr
[19] C.Q. Yang and W. Wu, Combination of a hydroxylalkyl-functional organophorus
us
oligomer and a multifunctional carboxylic acid as a flame retardant finishing system for cotton: part I. the chemical reactions, Fire Mater., 27 (2003) 223-237.
an
[20] C.Q. Yang and W. Wu, Combination of a hydroxylalkyl-functional organophorus oligomer and a multifunctional carboxylic acid as a flame retardant finishing system
Fire Mater., 27 (2003) 239-251.
M
for cotton: part II. Formation of calcium salt during laundering and its suppression,
Pyrol. 71 (2004) 27-46.
te
d
[21] R.E. Lyon and R.N. Walter, Pyrolysis combustion flow calorimetry, J Anal Appl
Ac ce p
[22] C.Q. Yang and Q.L. He, Applications of micro-scale combustion calorimetry to the studies of cotton and nylon fabrics treated with organophosphorus flame retardants, J Anal Appl Pyrol. 91 (2011) 125-133. [23] C.Q. Yang, Q.L. He, R.E. Lyon and Y. Hu, Investigation of the flammability of different textile fabrics using micro-scale combustion calorimetry, Polym Degrad Stabil. 95 (2010) 108-115. [24] M. Lewin, in M. Lewin and S.B. Sello (Eds.), Handbook of Fiber Science and Technology: Chemical processing of fibers and fabrics, Marcel Dekker, New York, US, 1984, p. 38.
27
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[25] A. Ballistreri, D. Garozzo, M. Giuffrida and G. Montaudo, Mechanism of thermal decomposition of nylon 66, Macromolecules, 20 (1987) 2991-2997. [26] S.V. Levchik, E.D. Weil and M. Lewin, Thermal decomposition of aliphatic
ip t
nylons, Polym Int. 48 (1999) 532-557.
cr
[27] W.D. Wu and C.Q. Yang, Comparison of DMDHEU and melamine-formaldehyde
agent on cotton, J Fire Sci. 22 (2004) 125-142.
us
as the binding agents for a hydroxy-functional organophosphorus flame retarding
an
[28] G.C. Tesoro and C. H. Meiser, Some effects of chemical composition on the flammability behavior of textiles, Text Res J., 40 (1970) 430-436.
M
[29] B. Miller, J.R. Martin, C.H. Meiser and M. Gargiullo, The flammability of
Ac ce p
te
d
polyester-cotton mixtures, Text Res J., 46 (1976) 530- 538.
28
Page 28 of 47
Table 1 Heat release properties of the untreated cotton, nylon/cotton blend and nylon.
THR (kJ/g)
Char yield (%)
280 202 576
11.9 17.9 26.7
4.3 9.1 1.6
Ac ce p
te
d
M
an
us
cr
cotton nylon/cotton nylon
HRC (J/[gK])
ip t
Fabrics
29
Page 29 of 47
Table 2 The measured and calculated HRC, THR and percent char yield of the untreated nylon/cotton blend fabric.
Measured
428 19.3 3.0
202 17.9 9.1
Ac ce p
te
d
M
an
us
cr
HRC (J/[gK]) THR (kJ/g) Char yield (%)
ip t
Calculated
30
Page 30 of 47
Table 3 Heat release properties and percent char yield of (1) the cotton treated with 32%HFPO and 8% DMDHEU; (2) 50/50 nylon/cotton blend, and (3) nylon. The blend and nylon were treated with 36%
THR (kJ/g)
cotton nylon/cotton nylon cotton nylon/cotton nylon
200 103 216 181 134 262
5.2 12.9 20.3 7.4 13.8 22.3
Char yield (%) 29.5 21.2 9.0 29.0 20.1 7.9
Ac ce p
te
d
M
an
After one wash
HRC (J/[gK])
cr
Before wash
Fabrics
us
Laundering
ip t
HFPO and 8% DMDHEU. All fabrics were cured at 165℃ for 2.5 min.
31
Page 31 of 47
Table 4 The measured and calculated HRC, THR and percent char yield of the nylon/cotton blend
Calculated 221.5 14.9
Char yield (%)
18.5
Measured 134 13.8 20.1
Ac ce p
te
d
M
an
us
HRC (J/[gK]) THR (kJ/g)
cr
one HLWD cycle.
ip t
fabric treated by 36% HFPO and 8% DMDHEU, cured at 165℃ for 2.5 min and finally subjected to
32
Page 32 of 47
Table 5 The weight gain and percent fixation of the three fabrics treated with HFPO and
DMDHEU. Fixation (%)
22.9 21.3
81.5 69.9
nylon
20.5
54.2
Ac ce p
te
d
M
an
us
cr
ip t
Weight gain (%)
cotton nylon/cotton
Fabrics
33
Page 33 of 47
Table 6 The LOI (%) of the cotton, nylon/cotton blend and nylon fabrics. The cotton was treated with 32%HFPO and 8% DMDHEU. The nylon/cotton blend and nylon were treated with 36% HFPO and
31.0 28.9 26.8
us
18.2 20.1 ─
treated (after one wash) 30.6 28.5 25.7
Ac ce p
te
d
M
an
cotton nylon/cotton nylon
untreated
treated (before washing)
cr
Treatment Fabrics
ip t
8% DMDHEU. All fabrics were then cured at 165℃ for 2.5 min.
34
Page 34 of 47
Table 7 The char length (mm) of the cotton, nylon/cotton blend and nylon fabrics. The cotton was
Treatment
91 68 250
＞300 ＞300 ─
treated (after one washing) 97 75 279
Ac ce p
te
d
M
an
cotton nylon/cotton nylon
treated (before washing)
untreated
us
Fabrics
cr
HFPO and 8% DMDHEU. All fabrics were then cured at 165℃ for 2.5 min.
ip t
treated with 32%HFPO and 8% DMDHEU. The nylon/cotton blend and nylon were treated with 36%
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Figure Captions The HRR versus temperature curves of the cotton and nylon fabrics.
Figure 2
The calculated and measured HRR versus temperature curves of the cotton/ nylon fabric.
Figure 3
The DSC curves of the cotton, nylon and 50/50 nylon/cotton blend fabrics.
Figure 4
The TGA curves of the cotton, nylon and 50/50 nylon/cotton blend fabrics.
Figure 5
The HRR curves of (1) untreated cotton fabric, (2) treated cotton fabric (before washing), and (3) treated cotton fabric (after one HLWD cycle).
Figure 6
The HRR curves of (1) untreated nylon fabric, (2) treated nylon fabric (before washing), and (3) treated nylon fabric (after one HLWD cycle).
Figure 7
The HRR curves of (1) the treated cotton fabric, (2) the treated nylon/cotton blend fabric, and (3) the treated nylon fabric. All fabrics were subjected to one HLWD cycle.
Figure 8
The calculated and measured HRR versus temperature curves of the nylon/cotton blend fabric treated and finally subjected to one HLWD cycle.
Ac ce p
te
d
M
an
us
cr
ip t
Figure 1
Figure 9
The DSC curves of (1) the treated cotton fabric, (2) the treated nylon/cotton blend fabric, and (3) the treated nylon fabric. All fabrics were subjected to one HLWD cycle.
Figure 10
The HRR curves of (1) the treated nylon/cotton (before washing) and (2) the treated nylon/cotton blend (after one HLWD cycle).
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ip t cr us an M Ac ce p
te
d
Figure 1
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ip t cr us an M Ac ce p
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d
Figure 2
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ip t cr us an M Ac ce p
te
d
Figure 3
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ip t cr us an M Ac ce p
te
d
Figure 4
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ip t cr us an M Ac ce p
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d
Figure 5
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ip t cr us an M Ac ce p
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d
Figure 6
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ip t cr us an M Ac ce p
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d
Figure 7
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ip t cr us an M Ac ce p
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d
Figure 8
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ip t cr us an M Ac ce p
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Figure 9
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ip t cr us an M Ac ce p
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Figure 10
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Highlights
Ac ce p
te
d
M
an
us
cr
ip t
We investigated the nylon/cotton blend fabrics used for military protective uniforms. We discovered the interaction between cotton and nylon during the nylon/cotton blend decomposition process. The data showed that the flammability of nylon/cotton blend fabric was lower than that of cotton and nylon as single-fiber fabric.
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