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cotton blend fabrics treated with a hydroxy-functional organophosphorus oligomer
Accepted Manuscript The Chemical Bonding and Fire Performance of the Nylon/Cotton Blend Fabrics Treated with a hydroxy-functional Organophosphorus Oligomer Qin Chen, Charles Q. Yang, Tao Zhao PII:
S0141-3910(16)30066-0
DOI:
10.1016/j.polymdegradstab.2016.03.014
Reference:
PDST 7899
To appear in:
Polymer Degradation and Stability
Received Date: 10 November 2015 Revised Date:
23 February 2016
Accepted Date: 12 March 2016
Please cite this article as: Chen Q, Yang CQ, Zhao T, The Chemical Bonding and Fire Performance of the Nylon/Cotton Blend Fabrics Treated with a hydroxy-functional Organophosphorus Oligomer, Polymer Degradation and Stability (2016), doi: 10.1016/j.polymdegradstab.2016.03.014. 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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The Chemical Bonding and Fire Performance of the Nylon/Cotton Blend Fabrics Treated with a Hydroxyfunctional Organophosphorus Oligomer
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Qin Chen,a,b Charles Q. Yang,a* Tao Zhaob
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Department of Textiles, Merchandising and Interiors, The University of Georgia, Athens, Georgia 30602, U.S.A b College of Chemistry, Chemical Engineering & Biotechnology, Donghua University, Shanghai 201620, China
*Corresponding author. Tel: +1 7065424912; Fax: +1 7065420410; email: [email protected]. 1
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Abstract Nylon/cotton blend fabrics have long been used in military protective clothing. Because
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fire risk has drastically increased in recent warfare, developing flame retarded military nylon/cotton fabrics becomes extremely important for protecting military personnel. It was previously discovered that a hydroxy-functional organophosphorus oligomer (HFPO) was bound to a nylon fabric in the presence of dimethyloldihydroxylethyleneurea (DMDHEU) as a bonding
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agent. In this research, the bonding mechanism of HFPO/DMDHEU on the nylon/cotton blend fabrics was investigated. HFPO was bound to the nylon/cotton blend fabrics by (1) forming
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HFPO/DMDHEU crosslinked polymeric networks on both nylon and cotton and (2) forming a DMDHEU bridge between cellulose and HFPO on cotton. The quantity of the HFPO/DMDHEU crosslinked networks and that of the DMDHEU-bridging formed on the treated blend fabrics was controlled by the HFPO-to-DMDHEU ratio. The HFPO/DMDHEU system was an effective and
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durable flame retarding treatment system for nylon/cotton military blend fabrics. The treated fabrics passed the fabric vertical burning test after 50 home laundering cycles. The fire performance and hydrolysis-resistance of different nylon/cotton blend fabrics treated with
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HFPO/DMDHEU was fully evaluated, and the performance data were analyzed in relation with
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the bonding mechanism.
Key words: Chemical bonding, cotton, cotton/nylon blends, crosslinked polymeric networks, flame retardant finishing, flame retarded textiles, military protective clothing, nylon
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1. Introduction The 50/50 nylon66/cotton blend fabrics, known as “battle dress uniform” fabrics, have long been extensively used to make combat uniforms for the army and marine in the U.S. and in
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more than twenty other countries.1 The major limitation for the nylon/cotton blends is their high flammability. Both nylon66 and cotton are flammable, and the melting of nylon in a blend caused by a fire represents additional risk for burn injuries. In conventional warfare, burn injuries
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caused 5-20% combat casualties.2, 3 A recent study on combat burns occurring in the wars of Iraq
frequency, size and injury severity.4
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and Afghanistan has shown that burn resulted from explosions in combat have increased in
Flame retarded fabrics can be used as barriers to protect military personnel from extremely high temperatures caused by fires and explosions in combat.5, 6 Therefore, developing flame retarded military protective clothing is extremely important for reducing the combat injury
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and mortality caused by fires. Flame retarded textile fibers used for protective clothing include cotton treated by flame retardants and inherently flame retardant fibers.5, 7 Cotton treated with a tetra(hydroxymethylol) phosphonium salt (THPX), urea and ammonia has exceedingly high
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laundering durability and is commercially available for use in industrial fire protection clothing.8 However, low strength and low abrasion resistance of flame retardant cotton fabrics have made
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them not suitable for use in military protective clothing. Inherently flame retardant fibers, such as Nomex®, are currently used by tankers, aviators and submariners of U.S. military services.5, 6, 9 However, high cost of Nomex and similar fibers becomes prohibitive for their use by infantry. Blending cotton with nylon considerably improves affordability and serviceability of the fabrics used by infantry.9 If the nylon/cotton blend fabrics can be treated with an effective flame retardant finishing system, those treated blends will become more affordable. The use of
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additives in the fiber-spinning stage has not been successful to produce flame retardant nylon fibers because adding additives often resulted in forming a separate phase, thus reducing the strength of melt-spun fibers.10 Flame retardant finishing of nylon/cotton blends has only been
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successful when cotton constitutes the overwhelming majority of the blend such as the 88/12 cotton/nylon blend fabrics.6, 11-13 Patent literature indicates that the flame retardant finishing of cotton blends with as much as 35% nylon was possible by treatment with organophosphorus
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compounds.14 As the relative quantity of nylon increases, the flame retardant finishing of the blend fabrics becomes more difficult. The flame retardant finishing of 50/50 nylon/cotton blend
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fabrics is still at the developmental stage today.
Previously, a durable flame retardant finishing system for cotton was developed based on a
hydroxy-functional
organophosphorus
oligomer
(HFPO)
(Scheme
1)
with
dimethyloldihydroxyethyleneurea (DMDHEU) or trimethylolmelamine as bonding agents.15-17 It
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was found that HFPO was bound to nylon66 when DMDUEU was used as a co-additive,18 and the 50/50 nylon66/cotton blend fabric thus treated achieved durable fire resistance.18,
19
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objective of this study was to investigate the bonding mechanism of HFPO/DHDHEU on the
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nylon66/cotton blend fabrics. The fire performance of the treated blend fabrics subjected to
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multiple launderings was also fully evaluated.
H
[ OCH 2 CH 2O
O
O
P ]2X [ OCH 2CH 2 O
P ]X O
OCH 3
CH 3
Scheme 1. Structure of HFPO
4
CH 2
CH 2
OH
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2.
Experimental
2.1.
Materials
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The textile fabrics and chemicals used in this study are listed in Table 1, in which a ripstop fabric is a special light-weight woven fabric with interwoven reinforcement threads in a crosshatch pattern to achieve high resistance to tearing and ripping. 2.2.
Fabric treatment and laundering procedures
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A fabric specimen was first immersed in a solution containing HFPO, DMDHEU and the catalyst. The concentration of the catalyst was 2% of that of DMDHEU (based on 100% active
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reagent). The treated specimen was passed through a laboratory padder with two dips and two nips, dried at 90℃ for 3 min and finally cured in an oven at 165℃ for 2 min. All concentrations were based on weight (w/w, %). The wet pick-up of the 50/50 nylon66/cotton, 30/70 nylon6/cotton and 100% nylon66 was 75±2%, 85±2% and 60±2%, respectively. After curing, the
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treated fabrics were subjected to a specified number of home laundering washing/drying cycles using a reference detergent (“AATCC Standard Detergent 1993”) according to AATCC Test Method 124, and the water temperature of laundering was kept at ~ 46℃. Measurement of “percent fixation”
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2.3.
A fabric specimen was weighed (1) before treatment (W0), (2) after treatment and before
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washing (W1), and (3) after treatment and subsequent washing (W2). All the specimens were weighed after being conditioned for 24 hr. The fabric’s percent fixation was calculated by Equation 1. “Fixation %” represents the weight percentage of the applied (HFPO+DMDHEU) chemically bound to the fabric substrate with respect to their original prewash values. Fixation % = (W2-W0)/(W1-W0) × 100% 2.4.
Quantitative analysis of phosphorus concentrations on the fabrics
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(1)
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Prior to analysis, textile fabric samples were first wet-digested using a procedure described by Feldman.20 Five specimens taken from different areas on a fabric sample were cut and ground into a fine powder in a grinding mill, and the powder was fully mixed in the mill to
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improve homogeneity. The powder was kept under the standard condition for 24 hr before analysis. Approximately 0.1 g of the powder sample was weighted with 4-significant figure precision. The weighed sample was then transferred to a 100 mL glass beaker.
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2 mL of concentrated sulfuric acid was first added to the powder in the beaker. 10 mL 30% H2O2 was then added drop wise into the powder in the beaker, allowing the reactions to
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subside between drops. The reaction mixture was heated up to 250℃ to fully digest the powder and to evaporate water until a dense SO3 vapor appeared and the digested sample became a clear solution. The solution was then transferred to a 50 mL volumetric flask, and finally diluted with deionized water to the mark. The solution thus prepared was analyzed using a Thermo-Farrell-
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Ash model 965 inductively coupled plasma atomic emission spectrometer (ICP/AES) to determine the percent concentration of phosphorus on the fabric (P%, w/w), which was calculated using Equation 2. M (mg/L) was the phosphorus concentration of the sample solution
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generated by ICP/AES and W (g) was the weight of the powder sample in Equation 2. The percent phosphorus retention (%) was calculated by dividing the phosphorus concentration of a
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fabric sample after laundering by that before laundering, and then multiplying by 100%. ()× (
P% (w/w) =
2.5.
()
)
×
× 100 = (
)×10-4
(2)
Evaluation of the fabric fire performance and physical properties Limiting oxygen index (LOI) of fabrics was measured according to ASTM Standard
Method D2863.21 Vertical burning test of fabrics was measured according to ASTM Standard Method D6413.22 Tensile strength was measured according to ASTM Standard Method D5035.23 6
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Fabric stiffness was measured according to ASTM D682824 using a Handle-O-Meter tester (Model 211-300) manufactured by Thwing-Albert Instrument Company, Philadelphia, PA. The slot width in this study was 5 mm and the beam size was 1000 g. The fabric stiffness presented
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was the average of 5 measurements.
Results and Discussion
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3.1. The bonding mechanism of HFPO on the nylon/cotton blends fabrics.
The 50/50 nylon/cotton fabric (ripstop) was treated with DMDHEU at different
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concentrations without HFPO, and it was also treated with combination of 36% HFPO and DMDHEU at different concentrations. The fabrics thus treated were cured at 165℃for 2 min and finally subjected to one home laundering washing/drying cycle. The stiffness of the nylon/cotton fabric before treatment was 264 g as shown in Figure 1. When the fabric was treated with 2%
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DMDHEU, its stiffness increased by 31% to 346 g. Further increasing DMDHEU concentration from 2 to 10% resulted in little change in the fabric stiffness (Figure 1). Without HFPO, DMDHEU reacted with the cotton cellulose to form crosslinking among cellulose molecules.
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The data indicate that crosslinking cotton in the nylon/cotton blend marginally increased stiffness
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of the blend fabric, and the magnitude of the stiffness increase was independent of the DMDHEU concentration.
When the nylon/cotton blend was treated with combination of 36% HFPO and
DMDHEU, however, the stiffness of the treated blend fabric increased considerably (Figure 1). The fabric stiffness increased from 313 to 674 g when DMDHEU concentration was increased from 2 to 10%, respectively. The steady rise in fabric stiffness at higher DMDHEU concentrations shown in Figure 1 was caused by the formation of HFPO/DMDHEU crosslinked
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networks as shown below.18 Figure 1 also shows that the magnitude of the increase in fabric stiffness was dependent on HFPO-to-DMDHEU ratio. O
O C
C N CH2 O HFPO N CH2 O HFPO O CH2 N CH CH OH CH O O HFPO HFPO O O CH OH HC HO CH CH N CH2 O HFPO HFPO O CH2 N N CH2 O HFPO O CH2 N C C O
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O
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HFPO O CH2 N HO CH
Scheme 2. The HFPO/DMDHEU crosslinked polymeric networks
The percent tensile strength retention of the nylon/cotton fabric treated with DMDHEU and that treated with the combination of 36% HFPO and DMDHEU are presented against the
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DMDHEU concentration in Table 2. When the nylon/cotton blend was treated with 2% DMDHEU in the absence of HFPO, its tensile strength retention became 98% at both filling and warp directions. The strength retention gradually decreased to 92 and 90% at the warp and filling
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directions, respectively, as the DMDHEU concentration was increased to 10% (Table 2). It is
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known that crosslinking cellulose reduces tensile strength of cotton fabrics at both warp and filling direction.25-27 The gradual increase in fabric strength loss at higher DMDHEU concentrations shown in Table 2 is due to increasing amount of cellulose crosslinking on cotton at higher DMDHEU concentrations. When 36% HFPO was present for the treatment, the pattern of fabric strength loss became completely different. The strength retention of the fabric treated with combination of 2% DMDHEU and 36% HFPO was 95%, and it remained almost unchanged at both warp and filling
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directions as the DMDHEU concentration was increased from 2 to 10% (Table 2). When the DMDHEU concentration was increased from 2 to 10%, the additional DMDHEU on the fabric apparently did not form more crosslinking among cellulose molecules. It reacted with HFPO to
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form crosslinked polymeric networks instead. Consequently, the additional DMDHEU increased fabric stiffness but caused no further fabric strength loss as shown in Figure 1 and Table 2, respectively. The tensile strength data were consistent with the stiffness data presented in Figure
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1. Both sets of data support the hypothesis that DMDHEU reacts with HFPO to form crosslinked polymeric networks on the treated nylon/cotton blend fabric.
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When HFPO/DMDHEU is applied to the nylon/cotton blend fabric, DMDHEU has three possible reactions on the fabric: (1) forming crosslinking among cellulose molecules on cotton, (2) forming a “bridge” between cellulose and HFPO by its reaction with both HFPO and cotton, and (3) forming HFPO/DMDHEU polymeric crosslinked networks on both nylon and cotton as
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shown in Scheme 2. Forming crosslinking by DMDHEU on cotton only reduces fabric strength and has a marginal effect on fabric stiffness. Forming the HFPO/DMDHEU crosslinked polymeric networks increases both fabric stiffness and phosphorus retention on the fabric.
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Forming a cotton-DMDHEU-HFPO bridge increases phosphorus retention without increasing fabric stiffness. Therefore, the bonding mechanism of HFPO/DMDHEU on the nylon/cotton
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blend can be elucidated based on the changes of strength, stiffness and phosphorus concentration of the nylon/cotton blend fabrics treated with HFPO/DMDHEU under different conditions. Presented in Table 3 are the phosphorus concentrations of the nylon/cotton fabric treated
with the combination of 36% HFPO and DMDHEU at different concentrations. The phosphorus retention (%) of the treated fabric after one washing cycle was presented in Figure 2. It represents the percentages of HFPO bound to the blend with respect to their original prewash
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values. Without the presence of DMDHEU, the nylon/cotton blend treated with 36% HFPO had 0.24% phosphorus on the fabric after one wash (Table 3). Such a small phosphorus concentration was probably due to the physical adsorption of HFPO by the nylon/cotton blend.18 When 2%
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DMDHEU was present, the phosphorus concentration increased to 0.79%, representing 22.5% phosphorus retention. When DMDHEU concentration was increased further from 4 to 10%, the phosphorus retention increased from 45.5 to 71.8%, respectively (Figure 2). Comparison of the
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data for the fabric treated with HFPO/DMDHEU presented in Figures 1 and 2 reveals that the increase in fabric stiffness and increase in phosphorus retention has similar dependency on
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DMDHEU concentration at the 4-10% DMDHEU concentration range. Thus, the data suggest that the majority of HFPO was bound to the nylon/cotton blend by forming a crosslinked polymeric networks under those conditions, which led to the increase in both stiffness and phosphorus retention of the treated fabric. At the 2-4% DMDHEU concentration range, the
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phosphorus concentration appeared to have more significant increase than fabric stiffness as shown in Figures 2 and 1, respectively, indicating that DMDHEU-bridging played a more important role in bonding HFPO to the blend at those low DMDHEU concentrations. Apparently,
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formation of the HFPO/DMDHEU networks requires more DMDHEU than formation of DMDHEU bridging.
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The 50/50 nylon/cotton fabric was treated with the combination of 8% DMDHEU and
HFPO at concentration ranging from 8 to 40%. The treated fabrics were cured at 165
for 2 min
and finally subjected to one home laundering cycle. The phosphorus concentrations of the treated fabric before and after laundering are presented in Table 4. The phosphorus retention (%) of the fabric thus treated is presented as a function of HFPO concentration in Figure 3. The phosphorus concentration on the fabric (after wash) increased as the HFPO concentration was increased
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(Table 4), indicating that the amount of HFPO bound to the fabric increased as the HFPO concentration was increased. However, the phosphorus retention (%) steadily decreased as the HFPO concentration was increased as shown in Figure 3. The data indicate that the effectiveness
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of DMDHEU for bonding HFPO to the blend decreased as HFPO concentration was increased. It is obvious that HFPO-to-DMDHEU ratio is a critical parameter to influence the effectiveness for bonding HFPO to the blend by DMDHEU.
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The stiffness of the nylon/cotton blend fabric thus treated is presented against the DMDHEU concentration in Figure 4. Without HFPO, the fabric treated with 8% DMDHEU had
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stiffness of 345 g. It increased drastically to 892 g when 8% HFPO was present. Fabric stiffness reached its maximum (940 g) when the HFPO concentration was increased to 16%. The fabric stiffness decreased slightly to 921 gram when the HFPO concentration was increased to 22%. Increasing HFPO concentration further to 40% resulted in a significant decline in fabric stiffness
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to 546 g, which represents 42% reduction from its peak at 940 g (Figure 4). The decrease in fabric stiffness was a clear indication of the declining in the formation of the HFPO/DMDHEU crosslinked networks. As the HFPO concentration was increased from 16 to 40%, the phosphorus
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concentration of the fabric increased from 1.38 to 2.74% (Table 4). The simultaneous decrease in fabric stiffness (Figure 4) and increase in the phosphorus concentration on the same fabric (Table
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4) show that formation of HFPO/DMDHEU crosslinked network declined whereas the amount of HFPO bound to the fabric increased as the HFPO concentration was increased from 16 to 40%. Thus, the data show that the increase in phosphorus concentration was a result of increase in formation of cellulose-DMDHEU-HFPO bridging, which increased the phosphorus bound to the blend without increase in fabric stiffness. Since the DMDHEU bridging between cellulose and HFPO can only take place on cotton whereas the HFPO/DMDHEU crosslinked networks can
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form on both cotton and nylon in the blend fabric, the DMDHEU bridging is less effective for bonding HFPO to cotton than the HFPO/DMDHEU crosslinked network. This was demonstrated by the decrease in the phosphorus retention shown in Figure 3.
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The tensile strength retention of the 50/50 nylon/cotton blend fabric treated with the combination of 8% DMDHEU and HFPO at different concentrations are presented in Table 5. Without HFPO, the treated fabric had strength retention of 90 and 86% at the warp and filling
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directions, respectively. DMDHEU’s crosslinking reduced the fabric strength as discussed previously. When the fabric was treated with the combination of 8% DMDHEU and 8% HFPO,
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the fabric strength retention increased to 95 and 91% at the warp and filling directions, respectively. As the HFPO concentration increased further to 16%, the fabric strength retention was increased further to 97 and 93% at the warp and filling directions, respectively. Obviously, DMDHEU reacted with HFPO by forming HFPO/DMDHEU crosslinked networks as well as
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forming bridging between HFPO and cotton, thus reducing the amount of crosslinking among cellulose molecules and consequently increasing fabric strength retention. Further increase in HFPO concentration above 16% caused little change in fabric strength retention.
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3.2. The fire performance of the treated 50/50 nylon/66/cotton blends fabrics. Presented in Table 6 are the LOI and fabric vertical burning test data of the nylon/cotton
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blend fabric (ripstop) fabric treated with 36% HFPO and DMDHEU. The LOI of the nylon/cotton fabric treated with 36% HFPO without DMDHEU was 21.1%, and the fabric failed the fabric vertical burning test. When 2% DMDHEU was present, it still failed the fabric vertical burning test. When the DMDHEU concentration was increased to 4%, the phosphorus concentration on the fabric reached 1.60%, the LOI increased to 27.2%, and the fabric passed the vertical burning test with char length of 89 mm. As the DMDHEU concentration was further
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increased to 6, 8 and 10%, the fire performance of the treated blend fabric steadily improved as indicated by the increasing LOI and declining char length (Table 6). The improving fire performance was attributed to the increasing amount of phosphorus bound to the nylon/cotton
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blend.
The 50/50 nylon/cotton fabric was treated with the combination of 8% DMDHEU and HFPO of different concentrations. The LOI and fabric vertical burning test data are presented in
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Table 7. The fabric treated with 8% DMDHEU without HFPO had LOI of 19.7% and failed vertical burning test. When 8% HFPO was present, the treated fabric contained 0.95%
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phosphorus after one washing cycle. Its LOI increased to 23.7% and the vertical burning char length was 161 mm. As the HFPO concentration was increased further to 34% and the phosphorus concentration became 2.52% accordingly, the LOI increased to 28.2% and the char length decreased to 80 mm (Table 7), indicating high fire-resistant performance.
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We also investigated the hydrolysis-resistance of the two 50/50 nylon/cotton blend fabrics (ripstop and twill) treated with HFPO/DMDHEU. The fabrics were treated with 36% HFPO and 8% DMDHEU, cured at 165℃ for 2 min and subjected to different home laundering cycles. The
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fixation (%) of the two treated fabrics after different number of home laundering cycles is presented in Table 8. The percent fixation was defined as the percentage of the applied
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HFPO/DMDHEU bound to the nylon/cotton blend with respect to its original prewash values. The treated fabric (ripstop) had 69.9% of the HFPO/DMDHEU bound to blend after one washing cycle, and it still had 64.1% of HFPO/DMDHEU on the blend fabric after 40 washing cycles, indicating that 92% of the initially bound HFPO/DMDHEU was retained on the fabric after 40 laundering cycles. The treated fabric (twill) had 65.3 and 53.0% of the initially applied HFPO/DMDHEU “fixed” on the fabric after one and 40 washing cycles, respectively, indicating
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that 81% of the initially bound HFPO/DMDHEU was retained on the fabric after 40 laundering cycles (Table 8). The HFPO/DMDHEU system demonstrates high hydrolysis-resistance on those nylon/cotton blend fabrics.
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The fire performances of the two treated nylon/cotton fabrics thus treated are also shown in Table 8. The treated fabric (ripstop) had LOI of 28.5% after one laundering cycle, and it passed the vertical burning test with char length of 70 mm. Its LOI decreased modestly to 27.8%,
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and it still passed the vertical burning test with char length of 120 mm after 40 laundering cycles. Similarly, the treated fabric (twill) had LOI of 28.1 and 27.4% after one and 40 laundering
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cycles, respectively, and it passed the vertical burning test with char length of 126 mm after 40 laundering cycles. The data presented here undoubtedly indicate that the HFPO/DMDHEU system is effective and hydrolysis-resistant for flame retardant treatment of different 50/50 nylon/cotton military fabrics.
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3.3. The fire performance of the nylon/cotton blend fabrics with different nylon-to-cotton ratios. The 100% nylon66, 50/50 nylon66/cotton and 30/70 nylon6/cotton blend fabrics were treated with 36% HFPO and 8% DMDHEU. The percent fixation of the three treated fabrics is
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presented in Table 9. The 100% nylon had fixation of 55.6% whereas the 50/50 and 30/70 nylon/cotton blends had the fixation of 70.3 and 75.1%, respectively. The low fixation of 100%
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nylon66 was due to the fact that the amount of HFPO/DMDHEU bound to nylon is lower than that bound to cotton. For nylon/cotton blend fabrics, the one with higher cotton-to-nylon ratio (70/30) had higher percent fixation of HFPO/DMDHEU (75.1%). This was primarily because HFPO was bound to cotton by both forming DMDHEU bridging and forming HFPO/DMDHEU crosslinked polymeric networks whereas it was bound to nylon only by forming HFPO/DMDHEU crosslinked networks.
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Also presented in Table 9 are the LOI and char length of the three fabrics treated with the combination of HFPO and DMDHEU and subjected to different number of laundering cycles. When 100% nylon66 fabric was treated with HFPO/DMDHEU and subjected to one laundering
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cycle, its LOI was 25.5% and the fabric vertical burning char length was 186 mm. The LOI decreased to 23.1% and the treated fabric failed the vertical burning test after 10 laundering cycles. The LOI of the nylon fabric thus treated (23.1%) was still significantly higher than the
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control (20-21.6%).
The 50/50 nylon66/cotton and 30/70 nylon6/cotton blend fabrics had LOI of 27.6 and
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28.1%, respectively, and both fabrics passed the vertical burning test after 50 washing cycles (Table 9). The 30/70 nylon6/cotton blend fabric had higher LOI and shorter char length than the 50/50 nylon/cotton blend fabric after 1, 10, 25 and 50 home laundering cycles. The HFPO/DMDHEU bound to the 30/70 nylon6/cotton fabric was higher than that bound to the
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50/50 nylon66/cotton fabric after one wash as discussed above. Moreover, the HFPO/DMDHEU crosslinked networks could react with cotton with its free methylol groups. Such covalent bonding between HFPO and cotton fiber substrate was not possible on nylon. The
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HFPO/DMDHEU crosslinked networks bound to cotton was evidently more hydrolysis-resistant than that formed on nylon. Consequently, an increase in the cotton content in a nylon/cotton
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blend improved flame retarding performance and laundering durability for the treated blend fabrics.
4.
Conclusions (1) When the HFPO/DMDHEU system is applied to the 50/50 nylon66/cotton blend
fabrics, there are three reactions taking place on the fabrics. DMDHEU reacts with cellulose to
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form crosslinking among cellulose molecules on cotton, which reduces fabric strength. DMDHEU reacts with both HFPO and cotton to form a bridge between them, or reacts with HFPO to form polymeric crosslinked networks. Formation of a DMDHEU bridge only takes
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place on cotton whereas a HFPO/DMDHEU networks form on both nylon and cotton. The competition between HFPO and cotton to react with DMDHEU reduces cotton-DMDHEU crosslinking thus increasing fabric strength retention. The formation of the HFPO/DMDHEU
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crosslinked polymeric networks increases stiffness of the treated fabrics. Forming a DMDHEU bridge between cotton and HFPO does not increase fabric stiffness.
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(2) Formation of HFPO/DMDHEU crosslinked networks is more effective in bonding phosphorus onto the nylon/cotton blend than DMDHEU bridging.
(3) The relative quantity of the HFPO/DMDHEU crosslinked network and that of DMDHEU-bridging formed on the treated nylon/cotton blend fabrics were decidedly influenced
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by the HFPO-to-DMDHEU ratio of for the treatment. The HFPO-to-DMDHEU ratio is the most critical parameter for optimizing flame retardant treatment of nylon/cotton blend fabrics in terms of fire performance, laundering durability and stiffness.
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(4) The two 50/50 nylon/cotton blend fabrics and the 30/70 nylon/cotton blend fabric treated with 36% HFPO and 8% DMDHEU demonstrate high flame retarding performance and
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laundering durability by passing the fabric vertical burning test after 50 home laundering cycles. A nylon/cotton blend fabric with higher cotton-to-nylon ratio has more HFPO bound to the blend fabric, better flame retarding performance and higher hydrolysis-resistance.
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http://en.wikipedia.org/wiki/Battle_Dress_Uniform. Cancio LC, Horvath EE, Barillo DJ, Kopchinski BJ, Charter KR, Montalvo AE, et al. Burn support for Operation Iraqi Freedom and related operations 2003 to 2004. J Burn Care Rehabil 2005; 26: 151–161. Champion HR, Bellamy RF, Roberts CP, Leppaniemi A. A profile of combat injury. J Traumas 2003; 54: S13–19. Kauvar DS, Wolf SE, Wade CE, Cancio LC, Renz E M, Holcomb J B. Burns sustained in combat explosions in Operations Iraqi and Enduring Freedom. Burns 2006; 32: 853-857. Nazare S. Fire protection in military fabrics. In Horrocks AR, Price D. editors, Advances in fire retardant materials. Cambridge, UK: Woodhead Publishing, 2008. pp499-504. Gomes CA, Designing military uniforms with high tech materials. In Wilusz E. editor, Military textiles.Cambridge, UK: Woodhead Publishing, 2008. p196. Winterhalter C. Military fabrics for flame protection. In Wilusz S. editor. Military textiles. Cambridge, UK: Woodhead Publishing, 2008. pp327-330. Yang CQ. Flame resistant cotton. In Kilinc FS. Edtor, Handbook of fire resistant textiles. Cambridge, UK: Woodhead Publishing, 2013. pp186-188. Winterhalter CA, Lomba RA, Tucker DW, Martin OD. Novel approach to soldier flame protection. J ASTM Int 2005; 2 (2): 1-8. Weil ED, Levchik S. Current practice and recent commercial developments in flame retardancy of polyamides. J Fire Sci. 2004; 22: 251-264. Smith, GW. Textile treatment, U.S. Pat. 4,909,805 (1990). Fleming, GR, Green, JR. Long wear life flame-retardant cotton blend fabrics. U.S. Pat. 5,468,545 (1995). Fleming, GR, Green, JR. Long wear life flame-retardant cotton blend fabrics. U.S. Pat. 5,480,458 (1996). Johnson, JR. Flame retardant treatments for polyester/cotton fabrics, U.S.Pat. 4,842,609 (1989). Wu WD, Yang CQ. Comparison of different reactive organophosphorus flame retardant agents for cotton: Part I. The bonding of the flame retardant agents to cotton. Polym Degrad Stabil 2006; 91: 2541-2548. Wu WD, Yang CQ. Comparison of different reactive organophosphorus flame retardant agents for cotton. Part II: Fabric flame resistant performance and physical properties. Polym Degrad Stabil 2007; 92: 363-369. Yang CQ, Wu WD, Xu Y. The combination of a hydroxy-functional organophosphorus oligomer and melamine-formaldehyde as a flame retarding finishing system for cotton, Fire Mater 2005; 29: 109-120. Yang H, Yang CQ. 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 2009; 94: 1023-1031. Yang H, Yang CQ. Flame retardant finishing of nylon/cotton blend fabrics using a hydroxyfunctional organophosphorus oligomer. Ind Eng Chem Res 2008; 47: 2160-2165. Feldman C. Perchloric acid procedure for wet-ashing organics for the determination of mercury and other metals. Anal Chem 1974; 46: 1606-1609. ASTM, Standard test method for measuring the minimum oxygen concentration to support
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candle-like combustion of plastics (oxygen index), Book of Standards, vol. 08.01. ASTM, Standard test method for flame resistance of textiles (vertical test), Book of Standards, vol. 07.02. ASTM, Standard test method for breaking force and elongation of textile fabrics (strip method), Book of Standards, vol. 07.02. ASTM, Standard test method for stiffness of fabric by blade/slot procedure, Book of Standards, vol. 07.02 Kang I. Yang CQ, Wei W, Lickfield GC. The mechanical strength of the cotton fabrics crosslinked by polycarboxylic acids: part I. acid degradation and crosslinking of cellulose, Textile Res J 1998; 68: 865-870. Yang CQ, Wei W. The mechanical strength of durable press finished cotton fabrics: part II. comparison of crosslinking agents with different molecular structures. Textile Res J 2000; 70: 143-147. Yang CQ. Wei W. Lickfield GL, Mechanical strength of durable press finished cotton fabric: part III. change in cellulose molecular weight, Textile Res J 2000; 70: 910-915.
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Figure 1. Stiffness of the 50/50 nylon/cotton fabric (ripstop) treated with DMDHEU at different concentrations and that treated with the combination of 36% HFPO and DMDHEU at different concentrations, cured at 165ºC for 2 min and subjected to one home laundering cycle.
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Figure 2. The phosphorus retention (%) of the 50/50 nylon/cotton fabric (ripstop) treated with 36% HFPO and DMDHEU at different concentrations, cured at 165 for 2 min and subjected to one home laundering cycle.
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Figure 3. The phosphorus retention (%) of the 50/50 nylon/cotton fabric (ripstop) treated with combination of 8% DMDHEU and HFPO at different concentrations, cured at 165 for 2 min and subjected to one home laundering cycle.
21
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Figure 4. The stiffness of the 50/50 nylon/cotton fabric (ripstop) treated with the combination of 8% DMDHEU and HFPO at different concentrations, cured at 165 for 2 min and subjected to one home laundering cycle.
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Table 1. A list of all the materials used in the study and their suppliers. Category
Description (1) 50/50 nylon66/cotton military camouflage ripstop fabric weighing 217 g/m2
Mount Vernon Mills, Trion, Georgia
(2) 50/50 nylon66/cotton military camouflage twill fabric weighing 230 g/m2
Same as above
(3) 30/70 nylon6/cotton twill fabric weighing 212 g/m2
Dymatic Chemicals, Guangdong, China
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Textile fabrics
Supplier
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(4) 100% nylon66 plain weave fabric (Style Testfabrics, West 341) weighing 130 g/m2 Pittston, Pennsylvania HFPO (Fyroltex® HP), CAS Registry No. 70715-06-9
Supresta (originally Akzo Nobel), Dobbs Ferry, New York
The bonding agent
DMDHEU (Freerez® 900, 44% active content)
Noveon, Cleveland, Ohio
The catalyst
A NH4Cl-based commercial product (Catalyst Eastern Color & RD®) Chemical, Greenville, South Carolina
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The flame retardant
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Table 2. The tensile strength retention (%) of the 50/50 nylon/cotton fabric (ripstop) treated with DMDHEU and that treated with the combination of HFPO and DMDHEU, cured at 165 for 2 min and subjected to one home laundering cycle.
Warp
0 0 0 0 0 36 36 36 36 36
2 4 6 8 10 2 4 6 8 10
98 96 96 93 92 95 93 95 95 95
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Filling
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DMDHEU (%)
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HFPO (%)
98 93 91 91 90 95 95 95 99 95
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Table 3. The phosphorus concentration of the nylon/cotton fabric (ripstop) treated with HFPO and DMDHEU, cured at 165 for 2 min and finally subjected to one home laundering cycle.
36
0
36
2
－ 6.97
36
4
3.48
36
6
2.32
36
8
1.74
36
10
1.39
Phosphorus (%) before wash
after wash
3.50
0.24
3.51
0.79
3.52
1.60
3.51
2.04
3.51
2.30
3.51
2.52
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DMDHEU (%)
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Molar ratio (HFPO/ DMDHEU)*
HFPO (%)
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* The molecular weight of HFPO was 460 assuming x=1 (Scheme 1). The molecular weight of DMDHEU was 178.
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Table 4. The phosphorus concentration of the 50/50 nylon/cotton fabric (ripstop) treated with DMDHEU and HFPO, cured at 165 for 2 min and finally subjected to one home laundering cycle.
before wash
after wash
8
Molar ratio (HFPO/ DMDHEU)* 0.39
0.99
0.95
16
8
0.77
1.52
1.38
22
8
1.06
2.27
1.80
28
8
1.35
2.83
2.03
34
8
1.64
40
8
1.93
8
Phosphorus (%)
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DMDHEU (%)
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HFPO (%)
3.48
2.52
3.87
2.74
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* The molecular weight of HFPO was 460 assuming x=1 (Scheme 1). The molecular weight of DMDHEU was 178.
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Table 5. The tensile strength retention of the 50/50 nylon/cotton fabric (ripstop) treated with 8% DMDHEU and HFPO at different concentrations, cured at 165 for 2min and subjected to one home laundering cycle*.
0 8 16 22 28 34 40
8 8 8 8 8 8 8
Tensile strength retention (%) Warp Filling 90 86 95 91 97 93 97 94 96 95 97 97 97 94
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DMDHEU
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HFPO (%)
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* The tensile strength of the untreated blend fabric was 634 and 429 N at the warp and filling direction, respectively.
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Table 6. The phosphorus concentration, LOI and char length of the 50/50 nylon/cotton fabric (ripstop) treated with 36% HFPO and DMDHEU at different concentration, cured at 165 for 2 min and finally subjected to one home laundering cycle. Phosphorus (%) 0.24 0.79 1.60 2.04 2.30 2.52
LOI (%) 21.1 24.8 27.2 28.0 28.5 28.6
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Char length mm) ＞300 ＞300 89 76 70 58
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DMDHEU (%) 0 2 4 6 8 10
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HFPO (%) 36 36 36 36 36 36
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Table 7. The phosphorus concentration, LOI and char length of the nylon/cotton fabric (ripstop) treated with 8% DMDHEU and HFPO at different concentration, cured at 165 for 2 min and finally subjected to one home laundering cycle. HFPO (%) DMDHEU (%) Phosphorus (%) LOI (%) Char length (mm) 0 8 19.7 ＞300 8 8 0.95 23.7 161 16 8 1.34 25.9 150 22 8 1.80 27.5 128 28 8 2.03 28.0 103 34 8 2.52 28.2 80 40 8 2.74 28.5 65
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Table 8. The percent fixation, LOI and char length of the two 50/50 nylon/cotton fabrics treated with 36% HFPO and 8% DMDHEU, cured at 165 for 2 min, and subjected to different home laundering cycles. LOI (%)
Char length (mm)
Twill
Ripstop
Twill
1 10 20 30 40
69.9 69.7 68.3 66.9 64.1
65.3 64.6 63.2 57.5 53.0
28.5 28.5 28.2 28.0 27.8
28.1 27.9 27.7 27.6 27.4
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Ripstop
Twill
70 93 97 105 120
78 102 99 107 126
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Ripstop
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Fixation (%)
Home laundering cycles
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Table 9. The percent fixation, LOI and char length of the 100% nylon66, 50/50 nylon66/cotton (ripstop), and 30/70 nylon6/cotton fabrics treated with 36% HFPO and 8% DMDHEU, cured at 165 for 2min and finally subjected to one home laundering cycle. 100% nylon66
50/50 nylon66/cotton
Fixation (%)
1
55.6
70.3
LOI (%)
1 10 25 50 Control
25.5 23.1 − − 20-21.6*
28.4 28.3 28.1 27.6 21.1
Char length (mm)
1 10 25 50 Control
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74 90 112 149 >300
30/70 nylon6/cotton
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No. of launderings
75.1
29.3 28.7 28.5 28.1 19.4
80 85 109 120 >300
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* The LOI of nylon 66 was based on Reference 3.
______________________________________________________________ Note: The reviewers’ comments were received on 01/24/2016; and the revision was completed on 02/14/2006.
31
S0141-3910(16)30066-0
DOI:
10.1016/j.polymdegradstab.2016.03.014
Reference:
PDST 7899
To appear in:
Polymer Degradation and Stability
Received Date: 10 November 2015 Revised Date:
23 February 2016
Accepted Date: 12 March 2016
Please cite this article as: Chen Q, Yang CQ, Zhao T, The Chemical Bonding and Fire Performance of the Nylon/Cotton Blend Fabrics Treated with a hydroxy-functional Organophosphorus Oligomer, Polymer Degradation and Stability (2016), doi: 10.1016/j.polymdegradstab.2016.03.014. 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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The Chemical Bonding and Fire Performance of the Nylon/Cotton Blend Fabrics Treated with a Hydroxyfunctional Organophosphorus Oligomer
a
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Qin Chen,a,b Charles Q. Yang,a* Tao Zhaob
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Department of Textiles, Merchandising and Interiors, The University of Georgia, Athens, Georgia 30602, U.S.A b College of Chemistry, Chemical Engineering & Biotechnology, Donghua University, Shanghai 201620, China
*Corresponding author. Tel: +1 7065424912; Fax: +1 7065420410; email: [email protected]. 1
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Abstract Nylon/cotton blend fabrics have long been used in military protective clothing. Because
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fire risk has drastically increased in recent warfare, developing flame retarded military nylon/cotton fabrics becomes extremely important for protecting military personnel. It was previously discovered that a hydroxy-functional organophosphorus oligomer (HFPO) was bound to a nylon fabric in the presence of dimethyloldihydroxylethyleneurea (DMDHEU) as a bonding
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agent. In this research, the bonding mechanism of HFPO/DMDHEU on the nylon/cotton blend fabrics was investigated. HFPO was bound to the nylon/cotton blend fabrics by (1) forming
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HFPO/DMDHEU crosslinked polymeric networks on both nylon and cotton and (2) forming a DMDHEU bridge between cellulose and HFPO on cotton. The quantity of the HFPO/DMDHEU crosslinked networks and that of the DMDHEU-bridging formed on the treated blend fabrics was controlled by the HFPO-to-DMDHEU ratio. The HFPO/DMDHEU system was an effective and
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durable flame retarding treatment system for nylon/cotton military blend fabrics. The treated fabrics passed the fabric vertical burning test after 50 home laundering cycles. The fire performance and hydrolysis-resistance of different nylon/cotton blend fabrics treated with
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HFPO/DMDHEU was fully evaluated, and the performance data were analyzed in relation with
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the bonding mechanism.
Key words: Chemical bonding, cotton, cotton/nylon blends, crosslinked polymeric networks, flame retardant finishing, flame retarded textiles, military protective clothing, nylon
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1. Introduction The 50/50 nylon66/cotton blend fabrics, known as “battle dress uniform” fabrics, have long been extensively used to make combat uniforms for the army and marine in the U.S. and in
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more than twenty other countries.1 The major limitation for the nylon/cotton blends is their high flammability. Both nylon66 and cotton are flammable, and the melting of nylon in a blend caused by a fire represents additional risk for burn injuries. In conventional warfare, burn injuries
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caused 5-20% combat casualties.2, 3 A recent study on combat burns occurring in the wars of Iraq
frequency, size and injury severity.4
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and Afghanistan has shown that burn resulted from explosions in combat have increased in
Flame retarded fabrics can be used as barriers to protect military personnel from extremely high temperatures caused by fires and explosions in combat.5, 6 Therefore, developing flame retarded military protective clothing is extremely important for reducing the combat injury
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and mortality caused by fires. Flame retarded textile fibers used for protective clothing include cotton treated by flame retardants and inherently flame retardant fibers.5, 7 Cotton treated with a tetra(hydroxymethylol) phosphonium salt (THPX), urea and ammonia has exceedingly high
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laundering durability and is commercially available for use in industrial fire protection clothing.8 However, low strength and low abrasion resistance of flame retardant cotton fabrics have made
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them not suitable for use in military protective clothing. Inherently flame retardant fibers, such as Nomex®, are currently used by tankers, aviators and submariners of U.S. military services.5, 6, 9 However, high cost of Nomex and similar fibers becomes prohibitive for their use by infantry. Blending cotton with nylon considerably improves affordability and serviceability of the fabrics used by infantry.9 If the nylon/cotton blend fabrics can be treated with an effective flame retardant finishing system, those treated blends will become more affordable. The use of
3
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additives in the fiber-spinning stage has not been successful to produce flame retardant nylon fibers because adding additives often resulted in forming a separate phase, thus reducing the strength of melt-spun fibers.10 Flame retardant finishing of nylon/cotton blends has only been
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successful when cotton constitutes the overwhelming majority of the blend such as the 88/12 cotton/nylon blend fabrics.6, 11-13 Patent literature indicates that the flame retardant finishing of cotton blends with as much as 35% nylon was possible by treatment with organophosphorus
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compounds.14 As the relative quantity of nylon increases, the flame retardant finishing of the blend fabrics becomes more difficult. The flame retardant finishing of 50/50 nylon/cotton blend
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fabrics is still at the developmental stage today.
Previously, a durable flame retardant finishing system for cotton was developed based on a
hydroxy-functional
organophosphorus
oligomer
(HFPO)
(Scheme
1)
with
dimethyloldihydroxyethyleneurea (DMDHEU) or trimethylolmelamine as bonding agents.15-17 It
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was found that HFPO was bound to nylon66 when DMDUEU was used as a co-additive,18 and the 50/50 nylon66/cotton blend fabric thus treated achieved durable fire resistance.18,
19
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objective of this study was to investigate the bonding mechanism of HFPO/DHDHEU on the
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nylon66/cotton blend fabrics. The fire performance of the treated blend fabrics subjected to
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multiple launderings was also fully evaluated.
H
[ OCH 2 CH 2O
O
O
P ]2X [ OCH 2CH 2 O
P ]X O
OCH 3
CH 3
Scheme 1. Structure of HFPO
4
CH 2
CH 2
OH
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2.
Experimental
2.1.
Materials
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The textile fabrics and chemicals used in this study are listed in Table 1, in which a ripstop fabric is a special light-weight woven fabric with interwoven reinforcement threads in a crosshatch pattern to achieve high resistance to tearing and ripping. 2.2.
Fabric treatment and laundering procedures
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A fabric specimen was first immersed in a solution containing HFPO, DMDHEU and the catalyst. The concentration of the catalyst was 2% of that of DMDHEU (based on 100% active
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reagent). The treated specimen was passed through a laboratory padder with two dips and two nips, dried at 90℃ for 3 min and finally cured in an oven at 165℃ for 2 min. All concentrations were based on weight (w/w, %). The wet pick-up of the 50/50 nylon66/cotton, 30/70 nylon6/cotton and 100% nylon66 was 75±2%, 85±2% and 60±2%, respectively. After curing, the
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treated fabrics were subjected to a specified number of home laundering washing/drying cycles using a reference detergent (“AATCC Standard Detergent 1993”) according to AATCC Test Method 124, and the water temperature of laundering was kept at ~ 46℃. Measurement of “percent fixation”
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2.3.
A fabric specimen was weighed (1) before treatment (W0), (2) after treatment and before
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washing (W1), and (3) after treatment and subsequent washing (W2). All the specimens were weighed after being conditioned for 24 hr. The fabric’s percent fixation was calculated by Equation 1. “Fixation %” represents the weight percentage of the applied (HFPO+DMDHEU) chemically bound to the fabric substrate with respect to their original prewash values. Fixation % = (W2-W0)/(W1-W0) × 100% 2.4.
Quantitative analysis of phosphorus concentrations on the fabrics
5
(1)
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Prior to analysis, textile fabric samples were first wet-digested using a procedure described by Feldman.20 Five specimens taken from different areas on a fabric sample were cut and ground into a fine powder in a grinding mill, and the powder was fully mixed in the mill to
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improve homogeneity. The powder was kept under the standard condition for 24 hr before analysis. Approximately 0.1 g of the powder sample was weighted with 4-significant figure precision. The weighed sample was then transferred to a 100 mL glass beaker.
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2 mL of concentrated sulfuric acid was first added to the powder in the beaker. 10 mL 30% H2O2 was then added drop wise into the powder in the beaker, allowing the reactions to
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subside between drops. The reaction mixture was heated up to 250℃ to fully digest the powder and to evaporate water until a dense SO3 vapor appeared and the digested sample became a clear solution. The solution was then transferred to a 50 mL volumetric flask, and finally diluted with deionized water to the mark. The solution thus prepared was analyzed using a Thermo-Farrell-
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Ash model 965 inductively coupled plasma atomic emission spectrometer (ICP/AES) to determine the percent concentration of phosphorus on the fabric (P%, w/w), which was calculated using Equation 2. M (mg/L) was the phosphorus concentration of the sample solution
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generated by ICP/AES and W (g) was the weight of the powder sample in Equation 2. The percent phosphorus retention (%) was calculated by dividing the phosphorus concentration of a
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fabric sample after laundering by that before laundering, and then multiplying by 100%. ()× (
P% (w/w) =
2.5.
()
)
×
× 100 = (
)×10-4
(2)
Evaluation of the fabric fire performance and physical properties Limiting oxygen index (LOI) of fabrics was measured according to ASTM Standard
Method D2863.21 Vertical burning test of fabrics was measured according to ASTM Standard Method D6413.22 Tensile strength was measured according to ASTM Standard Method D5035.23 6
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Fabric stiffness was measured according to ASTM D682824 using a Handle-O-Meter tester (Model 211-300) manufactured by Thwing-Albert Instrument Company, Philadelphia, PA. The slot width in this study was 5 mm and the beam size was 1000 g. The fabric stiffness presented
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was the average of 5 measurements.
Results and Discussion
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3.1. The bonding mechanism of HFPO on the nylon/cotton blends fabrics.
The 50/50 nylon/cotton fabric (ripstop) was treated with DMDHEU at different
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concentrations without HFPO, and it was also treated with combination of 36% HFPO and DMDHEU at different concentrations. The fabrics thus treated were cured at 165℃for 2 min and finally subjected to one home laundering washing/drying cycle. The stiffness of the nylon/cotton fabric before treatment was 264 g as shown in Figure 1. When the fabric was treated with 2%
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DMDHEU, its stiffness increased by 31% to 346 g. Further increasing DMDHEU concentration from 2 to 10% resulted in little change in the fabric stiffness (Figure 1). Without HFPO, DMDHEU reacted with the cotton cellulose to form crosslinking among cellulose molecules.
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The data indicate that crosslinking cotton in the nylon/cotton blend marginally increased stiffness
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of the blend fabric, and the magnitude of the stiffness increase was independent of the DMDHEU concentration.
When the nylon/cotton blend was treated with combination of 36% HFPO and
DMDHEU, however, the stiffness of the treated blend fabric increased considerably (Figure 1). The fabric stiffness increased from 313 to 674 g when DMDHEU concentration was increased from 2 to 10%, respectively. The steady rise in fabric stiffness at higher DMDHEU concentrations shown in Figure 1 was caused by the formation of HFPO/DMDHEU crosslinked
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networks as shown below.18 Figure 1 also shows that the magnitude of the increase in fabric stiffness was dependent on HFPO-to-DMDHEU ratio. O
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C N CH2 O HFPO N CH2 O HFPO O CH2 N CH CH OH CH O O HFPO HFPO O O CH OH HC HO CH CH N CH2 O HFPO HFPO O CH2 N N CH2 O HFPO O CH2 N C C O
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HFPO O CH2 N HO CH
Scheme 2. The HFPO/DMDHEU crosslinked polymeric networks
The percent tensile strength retention of the nylon/cotton fabric treated with DMDHEU and that treated with the combination of 36% HFPO and DMDHEU are presented against the
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DMDHEU concentration in Table 2. When the nylon/cotton blend was treated with 2% DMDHEU in the absence of HFPO, its tensile strength retention became 98% at both filling and warp directions. The strength retention gradually decreased to 92 and 90% at the warp and filling
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directions, respectively, as the DMDHEU concentration was increased to 10% (Table 2). It is
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known that crosslinking cellulose reduces tensile strength of cotton fabrics at both warp and filling direction.25-27 The gradual increase in fabric strength loss at higher DMDHEU concentrations shown in Table 2 is due to increasing amount of cellulose crosslinking on cotton at higher DMDHEU concentrations. When 36% HFPO was present for the treatment, the pattern of fabric strength loss became completely different. The strength retention of the fabric treated with combination of 2% DMDHEU and 36% HFPO was 95%, and it remained almost unchanged at both warp and filling
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directions as the DMDHEU concentration was increased from 2 to 10% (Table 2). When the DMDHEU concentration was increased from 2 to 10%, the additional DMDHEU on the fabric apparently did not form more crosslinking among cellulose molecules. It reacted with HFPO to
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form crosslinked polymeric networks instead. Consequently, the additional DMDHEU increased fabric stiffness but caused no further fabric strength loss as shown in Figure 1 and Table 2, respectively. The tensile strength data were consistent with the stiffness data presented in Figure
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1. Both sets of data support the hypothesis that DMDHEU reacts with HFPO to form crosslinked polymeric networks on the treated nylon/cotton blend fabric.
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When HFPO/DMDHEU is applied to the nylon/cotton blend fabric, DMDHEU has three possible reactions on the fabric: (1) forming crosslinking among cellulose molecules on cotton, (2) forming a “bridge” between cellulose and HFPO by its reaction with both HFPO and cotton, and (3) forming HFPO/DMDHEU polymeric crosslinked networks on both nylon and cotton as
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shown in Scheme 2. Forming crosslinking by DMDHEU on cotton only reduces fabric strength and has a marginal effect on fabric stiffness. Forming the HFPO/DMDHEU crosslinked polymeric networks increases both fabric stiffness and phosphorus retention on the fabric.
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Forming a cotton-DMDHEU-HFPO bridge increases phosphorus retention without increasing fabric stiffness. Therefore, the bonding mechanism of HFPO/DMDHEU on the nylon/cotton
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blend can be elucidated based on the changes of strength, stiffness and phosphorus concentration of the nylon/cotton blend fabrics treated with HFPO/DMDHEU under different conditions. Presented in Table 3 are the phosphorus concentrations of the nylon/cotton fabric treated
with the combination of 36% HFPO and DMDHEU at different concentrations. The phosphorus retention (%) of the treated fabric after one washing cycle was presented in Figure 2. It represents the percentages of HFPO bound to the blend with respect to their original prewash
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values. Without the presence of DMDHEU, the nylon/cotton blend treated with 36% HFPO had 0.24% phosphorus on the fabric after one wash (Table 3). Such a small phosphorus concentration was probably due to the physical adsorption of HFPO by the nylon/cotton blend.18 When 2%
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DMDHEU was present, the phosphorus concentration increased to 0.79%, representing 22.5% phosphorus retention. When DMDHEU concentration was increased further from 4 to 10%, the phosphorus retention increased from 45.5 to 71.8%, respectively (Figure 2). Comparison of the
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data for the fabric treated with HFPO/DMDHEU presented in Figures 1 and 2 reveals that the increase in fabric stiffness and increase in phosphorus retention has similar dependency on
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DMDHEU concentration at the 4-10% DMDHEU concentration range. Thus, the data suggest that the majority of HFPO was bound to the nylon/cotton blend by forming a crosslinked polymeric networks under those conditions, which led to the increase in both stiffness and phosphorus retention of the treated fabric. At the 2-4% DMDHEU concentration range, the
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phosphorus concentration appeared to have more significant increase than fabric stiffness as shown in Figures 2 and 1, respectively, indicating that DMDHEU-bridging played a more important role in bonding HFPO to the blend at those low DMDHEU concentrations. Apparently,
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formation of the HFPO/DMDHEU networks requires more DMDHEU than formation of DMDHEU bridging.
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The 50/50 nylon/cotton fabric was treated with the combination of 8% DMDHEU and
HFPO at concentration ranging from 8 to 40%. The treated fabrics were cured at 165
for 2 min
and finally subjected to one home laundering cycle. The phosphorus concentrations of the treated fabric before and after laundering are presented in Table 4. The phosphorus retention (%) of the fabric thus treated is presented as a function of HFPO concentration in Figure 3. The phosphorus concentration on the fabric (after wash) increased as the HFPO concentration was increased
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(Table 4), indicating that the amount of HFPO bound to the fabric increased as the HFPO concentration was increased. However, the phosphorus retention (%) steadily decreased as the HFPO concentration was increased as shown in Figure 3. The data indicate that the effectiveness
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of DMDHEU for bonding HFPO to the blend decreased as HFPO concentration was increased. It is obvious that HFPO-to-DMDHEU ratio is a critical parameter to influence the effectiveness for bonding HFPO to the blend by DMDHEU.
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The stiffness of the nylon/cotton blend fabric thus treated is presented against the DMDHEU concentration in Figure 4. Without HFPO, the fabric treated with 8% DMDHEU had
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stiffness of 345 g. It increased drastically to 892 g when 8% HFPO was present. Fabric stiffness reached its maximum (940 g) when the HFPO concentration was increased to 16%. The fabric stiffness decreased slightly to 921 gram when the HFPO concentration was increased to 22%. Increasing HFPO concentration further to 40% resulted in a significant decline in fabric stiffness
TE D
to 546 g, which represents 42% reduction from its peak at 940 g (Figure 4). The decrease in fabric stiffness was a clear indication of the declining in the formation of the HFPO/DMDHEU crosslinked networks. As the HFPO concentration was increased from 16 to 40%, the phosphorus
EP
concentration of the fabric increased from 1.38 to 2.74% (Table 4). The simultaneous decrease in fabric stiffness (Figure 4) and increase in the phosphorus concentration on the same fabric (Table
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4) show that formation of HFPO/DMDHEU crosslinked network declined whereas the amount of HFPO bound to the fabric increased as the HFPO concentration was increased from 16 to 40%. Thus, the data show that the increase in phosphorus concentration was a result of increase in formation of cellulose-DMDHEU-HFPO bridging, which increased the phosphorus bound to the blend without increase in fabric stiffness. Since the DMDHEU bridging between cellulose and HFPO can only take place on cotton whereas the HFPO/DMDHEU crosslinked networks can
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form on both cotton and nylon in the blend fabric, the DMDHEU bridging is less effective for bonding HFPO to cotton than the HFPO/DMDHEU crosslinked network. This was demonstrated by the decrease in the phosphorus retention shown in Figure 3.
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The tensile strength retention of the 50/50 nylon/cotton blend fabric treated with the combination of 8% DMDHEU and HFPO at different concentrations are presented in Table 5. Without HFPO, the treated fabric had strength retention of 90 and 86% at the warp and filling
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directions, respectively. DMDHEU’s crosslinking reduced the fabric strength as discussed previously. When the fabric was treated with the combination of 8% DMDHEU and 8% HFPO,
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the fabric strength retention increased to 95 and 91% at the warp and filling directions, respectively. As the HFPO concentration increased further to 16%, the fabric strength retention was increased further to 97 and 93% at the warp and filling directions, respectively. Obviously, DMDHEU reacted with HFPO by forming HFPO/DMDHEU crosslinked networks as well as
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forming bridging between HFPO and cotton, thus reducing the amount of crosslinking among cellulose molecules and consequently increasing fabric strength retention. Further increase in HFPO concentration above 16% caused little change in fabric strength retention.
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3.2. The fire performance of the treated 50/50 nylon/66/cotton blends fabrics. Presented in Table 6 are the LOI and fabric vertical burning test data of the nylon/cotton
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blend fabric (ripstop) fabric treated with 36% HFPO and DMDHEU. The LOI of the nylon/cotton fabric treated with 36% HFPO without DMDHEU was 21.1%, and the fabric failed the fabric vertical burning test. When 2% DMDHEU was present, it still failed the fabric vertical burning test. When the DMDHEU concentration was increased to 4%, the phosphorus concentration on the fabric reached 1.60%, the LOI increased to 27.2%, and the fabric passed the vertical burning test with char length of 89 mm. As the DMDHEU concentration was further
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increased to 6, 8 and 10%, the fire performance of the treated blend fabric steadily improved as indicated by the increasing LOI and declining char length (Table 6). The improving fire performance was attributed to the increasing amount of phosphorus bound to the nylon/cotton
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blend.
The 50/50 nylon/cotton fabric was treated with the combination of 8% DMDHEU and HFPO of different concentrations. The LOI and fabric vertical burning test data are presented in
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Table 7. The fabric treated with 8% DMDHEU without HFPO had LOI of 19.7% and failed vertical burning test. When 8% HFPO was present, the treated fabric contained 0.95%
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phosphorus after one washing cycle. Its LOI increased to 23.7% and the vertical burning char length was 161 mm. As the HFPO concentration was increased further to 34% and the phosphorus concentration became 2.52% accordingly, the LOI increased to 28.2% and the char length decreased to 80 mm (Table 7), indicating high fire-resistant performance.
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We also investigated the hydrolysis-resistance of the two 50/50 nylon/cotton blend fabrics (ripstop and twill) treated with HFPO/DMDHEU. The fabrics were treated with 36% HFPO and 8% DMDHEU, cured at 165℃ for 2 min and subjected to different home laundering cycles. The
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fixation (%) of the two treated fabrics after different number of home laundering cycles is presented in Table 8. The percent fixation was defined as the percentage of the applied
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HFPO/DMDHEU bound to the nylon/cotton blend with respect to its original prewash values. The treated fabric (ripstop) had 69.9% of the HFPO/DMDHEU bound to blend after one washing cycle, and it still had 64.1% of HFPO/DMDHEU on the blend fabric after 40 washing cycles, indicating that 92% of the initially bound HFPO/DMDHEU was retained on the fabric after 40 laundering cycles. The treated fabric (twill) had 65.3 and 53.0% of the initially applied HFPO/DMDHEU “fixed” on the fabric after one and 40 washing cycles, respectively, indicating
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that 81% of the initially bound HFPO/DMDHEU was retained on the fabric after 40 laundering cycles (Table 8). The HFPO/DMDHEU system demonstrates high hydrolysis-resistance on those nylon/cotton blend fabrics.
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The fire performances of the two treated nylon/cotton fabrics thus treated are also shown in Table 8. The treated fabric (ripstop) had LOI of 28.5% after one laundering cycle, and it passed the vertical burning test with char length of 70 mm. Its LOI decreased modestly to 27.8%,
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and it still passed the vertical burning test with char length of 120 mm after 40 laundering cycles. Similarly, the treated fabric (twill) had LOI of 28.1 and 27.4% after one and 40 laundering
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cycles, respectively, and it passed the vertical burning test with char length of 126 mm after 40 laundering cycles. The data presented here undoubtedly indicate that the HFPO/DMDHEU system is effective and hydrolysis-resistant for flame retardant treatment of different 50/50 nylon/cotton military fabrics.
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3.3. The fire performance of the nylon/cotton blend fabrics with different nylon-to-cotton ratios. The 100% nylon66, 50/50 nylon66/cotton and 30/70 nylon6/cotton blend fabrics were treated with 36% HFPO and 8% DMDHEU. The percent fixation of the three treated fabrics is
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presented in Table 9. The 100% nylon had fixation of 55.6% whereas the 50/50 and 30/70 nylon/cotton blends had the fixation of 70.3 and 75.1%, respectively. The low fixation of 100%
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nylon66 was due to the fact that the amount of HFPO/DMDHEU bound to nylon is lower than that bound to cotton. For nylon/cotton blend fabrics, the one with higher cotton-to-nylon ratio (70/30) had higher percent fixation of HFPO/DMDHEU (75.1%). This was primarily because HFPO was bound to cotton by both forming DMDHEU bridging and forming HFPO/DMDHEU crosslinked polymeric networks whereas it was bound to nylon only by forming HFPO/DMDHEU crosslinked networks.
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Also presented in Table 9 are the LOI and char length of the three fabrics treated with the combination of HFPO and DMDHEU and subjected to different number of laundering cycles. When 100% nylon66 fabric was treated with HFPO/DMDHEU and subjected to one laundering
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cycle, its LOI was 25.5% and the fabric vertical burning char length was 186 mm. The LOI decreased to 23.1% and the treated fabric failed the vertical burning test after 10 laundering cycles. The LOI of the nylon fabric thus treated (23.1%) was still significantly higher than the
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control (20-21.6%).
The 50/50 nylon66/cotton and 30/70 nylon6/cotton blend fabrics had LOI of 27.6 and
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28.1%, respectively, and both fabrics passed the vertical burning test after 50 washing cycles (Table 9). The 30/70 nylon6/cotton blend fabric had higher LOI and shorter char length than the 50/50 nylon/cotton blend fabric after 1, 10, 25 and 50 home laundering cycles. The HFPO/DMDHEU bound to the 30/70 nylon6/cotton fabric was higher than that bound to the
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50/50 nylon66/cotton fabric after one wash as discussed above. Moreover, the HFPO/DMDHEU crosslinked networks could react with cotton with its free methylol groups. Such covalent bonding between HFPO and cotton fiber substrate was not possible on nylon. The
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HFPO/DMDHEU crosslinked networks bound to cotton was evidently more hydrolysis-resistant than that formed on nylon. Consequently, an increase in the cotton content in a nylon/cotton
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blend improved flame retarding performance and laundering durability for the treated blend fabrics.
4.
Conclusions (1) When the HFPO/DMDHEU system is applied to the 50/50 nylon66/cotton blend
fabrics, there are three reactions taking place on the fabrics. DMDHEU reacts with cellulose to
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form crosslinking among cellulose molecules on cotton, which reduces fabric strength. DMDHEU reacts with both HFPO and cotton to form a bridge between them, or reacts with HFPO to form polymeric crosslinked networks. Formation of a DMDHEU bridge only takes
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place on cotton whereas a HFPO/DMDHEU networks form on both nylon and cotton. The competition between HFPO and cotton to react with DMDHEU reduces cotton-DMDHEU crosslinking thus increasing fabric strength retention. The formation of the HFPO/DMDHEU
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crosslinked polymeric networks increases stiffness of the treated fabrics. Forming a DMDHEU bridge between cotton and HFPO does not increase fabric stiffness.
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(2) Formation of HFPO/DMDHEU crosslinked networks is more effective in bonding phosphorus onto the nylon/cotton blend than DMDHEU bridging.
(3) The relative quantity of the HFPO/DMDHEU crosslinked network and that of DMDHEU-bridging formed on the treated nylon/cotton blend fabrics were decidedly influenced
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by the HFPO-to-DMDHEU ratio of for the treatment. The HFPO-to-DMDHEU ratio is the most critical parameter for optimizing flame retardant treatment of nylon/cotton blend fabrics in terms of fire performance, laundering durability and stiffness.
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(4) The two 50/50 nylon/cotton blend fabrics and the 30/70 nylon/cotton blend fabric treated with 36% HFPO and 8% DMDHEU demonstrate high flame retarding performance and
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laundering durability by passing the fabric vertical burning test after 50 home laundering cycles. A nylon/cotton blend fabric with higher cotton-to-nylon ratio has more HFPO bound to the blend fabric, better flame retarding performance and higher hydrolysis-resistance.
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References
7. 8. 9. 10. 11. 12. 13. 14. 15.
16.
17.
18.
19. 20. 21.
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5.
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4.
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3.
http://en.wikipedia.org/wiki/Battle_Dress_Uniform. Cancio LC, Horvath EE, Barillo DJ, Kopchinski BJ, Charter KR, Montalvo AE, et al. Burn support for Operation Iraqi Freedom and related operations 2003 to 2004. J Burn Care Rehabil 2005; 26: 151–161. Champion HR, Bellamy RF, Roberts CP, Leppaniemi A. A profile of combat injury. J Traumas 2003; 54: S13–19. Kauvar DS, Wolf SE, Wade CE, Cancio LC, Renz E M, Holcomb J B. Burns sustained in combat explosions in Operations Iraqi and Enduring Freedom. Burns 2006; 32: 853-857. Nazare S. Fire protection in military fabrics. In Horrocks AR, Price D. editors, Advances in fire retardant materials. Cambridge, UK: Woodhead Publishing, 2008. pp499-504. Gomes CA, Designing military uniforms with high tech materials. In Wilusz E. editor, Military textiles.Cambridge, UK: Woodhead Publishing, 2008. p196. Winterhalter C. Military fabrics for flame protection. In Wilusz S. editor. Military textiles. Cambridge, UK: Woodhead Publishing, 2008. pp327-330. Yang CQ. Flame resistant cotton. In Kilinc FS. Edtor, Handbook of fire resistant textiles. Cambridge, UK: Woodhead Publishing, 2013. pp186-188. Winterhalter CA, Lomba RA, Tucker DW, Martin OD. Novel approach to soldier flame protection. J ASTM Int 2005; 2 (2): 1-8. Weil ED, Levchik S. Current practice and recent commercial developments in flame retardancy of polyamides. J Fire Sci. 2004; 22: 251-264. Smith, GW. Textile treatment, U.S. Pat. 4,909,805 (1990). Fleming, GR, Green, JR. Long wear life flame-retardant cotton blend fabrics. U.S. Pat. 5,468,545 (1995). Fleming, GR, Green, JR. Long wear life flame-retardant cotton blend fabrics. U.S. Pat. 5,480,458 (1996). Johnson, JR. Flame retardant treatments for polyester/cotton fabrics, U.S.Pat. 4,842,609 (1989). Wu WD, Yang CQ. Comparison of different reactive organophosphorus flame retardant agents for cotton: Part I. The bonding of the flame retardant agents to cotton. Polym Degrad Stabil 2006; 91: 2541-2548. Wu WD, Yang CQ. Comparison of different reactive organophosphorus flame retardant agents for cotton. Part II: Fabric flame resistant performance and physical properties. Polym Degrad Stabil 2007; 92: 363-369. Yang CQ, Wu WD, Xu Y. The combination of a hydroxy-functional organophosphorus oligomer and melamine-formaldehyde as a flame retarding finishing system for cotton, Fire Mater 2005; 29: 109-120. Yang H, Yang CQ. 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 2009; 94: 1023-1031. Yang H, Yang CQ. Flame retardant finishing of nylon/cotton blend fabrics using a hydroxyfunctional organophosphorus oligomer. Ind Eng Chem Res 2008; 47: 2160-2165. Feldman C. Perchloric acid procedure for wet-ashing organics for the determination of mercury and other metals. Anal Chem 1974; 46: 1606-1609. ASTM, Standard test method for measuring the minimum oxygen concentration to support
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1. 2.
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27.
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26.
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25.
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24.
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23.
candle-like combustion of plastics (oxygen index), Book of Standards, vol. 08.01. ASTM, Standard test method for flame resistance of textiles (vertical test), Book of Standards, vol. 07.02. ASTM, Standard test method for breaking force and elongation of textile fabrics (strip method), Book of Standards, vol. 07.02. ASTM, Standard test method for stiffness of fabric by blade/slot procedure, Book of Standards, vol. 07.02 Kang I. Yang CQ, Wei W, Lickfield GC. The mechanical strength of the cotton fabrics crosslinked by polycarboxylic acids: part I. acid degradation and crosslinking of cellulose, Textile Res J 1998; 68: 865-870. Yang CQ, Wei W. The mechanical strength of durable press finished cotton fabrics: part II. comparison of crosslinking agents with different molecular structures. Textile Res J 2000; 70: 143-147. Yang CQ. Wei W. Lickfield GL, Mechanical strength of durable press finished cotton fabric: part III. change in cellulose molecular weight, Textile Res J 2000; 70: 910-915.
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22.
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Figure 1. Stiffness of the 50/50 nylon/cotton fabric (ripstop) treated with DMDHEU at different concentrations and that treated with the combination of 36% HFPO and DMDHEU at different concentrations, cured at 165ºC for 2 min and subjected to one home laundering cycle.
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Figure 2. The phosphorus retention (%) of the 50/50 nylon/cotton fabric (ripstop) treated with 36% HFPO and DMDHEU at different concentrations, cured at 165 for 2 min and subjected to one home laundering cycle.
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Figure 3. The phosphorus retention (%) of the 50/50 nylon/cotton fabric (ripstop) treated with combination of 8% DMDHEU and HFPO at different concentrations, cured at 165 for 2 min and subjected to one home laundering cycle.
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Figure 4. The stiffness of the 50/50 nylon/cotton fabric (ripstop) treated with the combination of 8% DMDHEU and HFPO at different concentrations, cured at 165 for 2 min and subjected to one home laundering cycle.
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Table 1. A list of all the materials used in the study and their suppliers. Category
Description (1) 50/50 nylon66/cotton military camouflage ripstop fabric weighing 217 g/m2
Mount Vernon Mills, Trion, Georgia
(2) 50/50 nylon66/cotton military camouflage twill fabric weighing 230 g/m2
Same as above
(3) 30/70 nylon6/cotton twill fabric weighing 212 g/m2
Dymatic Chemicals, Guangdong, China
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Textile fabrics
Supplier
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(4) 100% nylon66 plain weave fabric (Style Testfabrics, West 341) weighing 130 g/m2 Pittston, Pennsylvania HFPO (Fyroltex® HP), CAS Registry No. 70715-06-9
Supresta (originally Akzo Nobel), Dobbs Ferry, New York
The bonding agent
DMDHEU (Freerez® 900, 44% active content)
Noveon, Cleveland, Ohio
The catalyst
A NH4Cl-based commercial product (Catalyst Eastern Color & RD®) Chemical, Greenville, South Carolina
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The flame retardant
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Table 2. The tensile strength retention (%) of the 50/50 nylon/cotton fabric (ripstop) treated with DMDHEU and that treated with the combination of HFPO and DMDHEU, cured at 165 for 2 min and subjected to one home laundering cycle.
Warp
0 0 0 0 0 36 36 36 36 36
2 4 6 8 10 2 4 6 8 10
98 96 96 93 92 95 93 95 95 95
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Filling
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DMDHEU (%)
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HFPO (%)
98 93 91 91 90 95 95 95 99 95
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Table 3. The phosphorus concentration of the nylon/cotton fabric (ripstop) treated with HFPO and DMDHEU, cured at 165 for 2 min and finally subjected to one home laundering cycle.
36
0
36
2
－ 6.97
36
4
3.48
36
6
2.32
36
8
1.74
36
10
1.39
Phosphorus (%) before wash
after wash
3.50
0.24
3.51
0.79
3.52
1.60
3.51
2.04
3.51
2.30
3.51
2.52
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DMDHEU (%)
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Molar ratio (HFPO/ DMDHEU)*
HFPO (%)
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* The molecular weight of HFPO was 460 assuming x=1 (Scheme 1). The molecular weight of DMDHEU was 178.
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Table 4. The phosphorus concentration of the 50/50 nylon/cotton fabric (ripstop) treated with DMDHEU and HFPO, cured at 165 for 2 min and finally subjected to one home laundering cycle.
before wash
after wash
8
Molar ratio (HFPO/ DMDHEU)* 0.39
0.99
0.95
16
8
0.77
1.52
1.38
22
8
1.06
2.27
1.80
28
8
1.35
2.83
2.03
34
8
1.64
40
8
1.93
8
Phosphorus (%)
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DMDHEU (%)
SC
HFPO (%)
3.48
2.52
3.87
2.74
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* The molecular weight of HFPO was 460 assuming x=1 (Scheme 1). The molecular weight of DMDHEU was 178.
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Table 5. The tensile strength retention of the 50/50 nylon/cotton fabric (ripstop) treated with 8% DMDHEU and HFPO at different concentrations, cured at 165 for 2min and subjected to one home laundering cycle*.
0 8 16 22 28 34 40
8 8 8 8 8 8 8
Tensile strength retention (%) Warp Filling 90 86 95 91 97 93 97 94 96 95 97 97 97 94
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DMDHEU
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HFPO (%)
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* The tensile strength of the untreated blend fabric was 634 and 429 N at the warp and filling direction, respectively.
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Table 6. The phosphorus concentration, LOI and char length of the 50/50 nylon/cotton fabric (ripstop) treated with 36% HFPO and DMDHEU at different concentration, cured at 165 for 2 min and finally subjected to one home laundering cycle. Phosphorus (%) 0.24 0.79 1.60 2.04 2.30 2.52
LOI (%) 21.1 24.8 27.2 28.0 28.5 28.6
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Char length mm) ＞300 ＞300 89 76 70 58
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DMDHEU (%) 0 2 4 6 8 10
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HFPO (%) 36 36 36 36 36 36
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Table 7. The phosphorus concentration, LOI and char length of the nylon/cotton fabric (ripstop) treated with 8% DMDHEU and HFPO at different concentration, cured at 165 for 2 min and finally subjected to one home laundering cycle. HFPO (%) DMDHEU (%) Phosphorus (%) LOI (%) Char length (mm) 0 8 19.7 ＞300 8 8 0.95 23.7 161 16 8 1.34 25.9 150 22 8 1.80 27.5 128 28 8 2.03 28.0 103 34 8 2.52 28.2 80 40 8 2.74 28.5 65
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Table 8. The percent fixation, LOI and char length of the two 50/50 nylon/cotton fabrics treated with 36% HFPO and 8% DMDHEU, cured at 165 for 2 min, and subjected to different home laundering cycles. LOI (%)
Char length (mm)
Twill
Ripstop
Twill
1 10 20 30 40
69.9 69.7 68.3 66.9 64.1
65.3 64.6 63.2 57.5 53.0
28.5 28.5 28.2 28.0 27.8
28.1 27.9 27.7 27.6 27.4
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Ripstop
Twill
70 93 97 105 120
78 102 99 107 126
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Ripstop
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Fixation (%)
Home laundering cycles
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Table 9. The percent fixation, LOI and char length of the 100% nylon66, 50/50 nylon66/cotton (ripstop), and 30/70 nylon6/cotton fabrics treated with 36% HFPO and 8% DMDHEU, cured at 165 for 2min and finally subjected to one home laundering cycle. 100% nylon66
50/50 nylon66/cotton
Fixation (%)
1
55.6
70.3
LOI (%)
1 10 25 50 Control
25.5 23.1 − − 20-21.6*
28.4 28.3 28.1 27.6 21.1
Char length (mm)
1 10 25 50 Control
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74 90 112 149 >300
30/70 nylon6/cotton
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No. of launderings
75.1
29.3 28.7 28.5 28.1 19.4
80 85 109 120 >300
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* The LOI of nylon 66 was based on Reference 3.
______________________________________________________________ Note: The reviewers’ comments were received on 01/24/2016; and the revision was completed on 02/14/2006.
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