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Improved flame-retardant properties of lyocell fiber achieved by phosphorus compound
Materials Letters 135 (2014) 226–228
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Improved flame-retardant properties of lyocell fiber achieved by phosphorus compound Byong Chol Bai a,b, Eun Ae Kim a,b, Young-Pyo Jeon a,c, Chul Wee Lee a,c, Se Jin In d, Young-Seak Lee b, Ji Sun Im a,c,n a
C-Industry Incubation Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon, 305-600, Republic of Korea Departments of Fine Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon 305-764, Republic of Korea c University of Science and Technology (UST), Daejeon, 305-333, Republic of Korea d Department of Fire and Disaster Protection Engineering, Woosong University, Daejeon 300-718, Republic of Korea b
ar t ic l e i nf o
a b s t r a c t
Article history: Received 4 June 2014 Accepted 19 July 2014 Available online 31 July 2014
The anti-oxidation behavior of Lyocell fibers during flame-retardant treatment as a function of the effects of a phosphorus compound was explored. Di-ammonium-hydrogen phosphate (DAHP) was observed to reduce the thermal degradation rate of the Lyocell fibers and increase the char yield; DAHP also increased the limiting oxygen index via a first-order relationship with the char yield. The integral procedure decomposition temperature (IPDT) increased significantly, and the activation energy increased by a certain factor, indicating a slow degradation pathway involving dehydration, rearrangement, formation of carbonyl groups, evolution of carbon monoxide and carbon dioxide, and formation of a carbonaceous residue for the flame retardancy of Lyocell fibers. & 2014 Elsevier B.V. All rights reserved.
Keywords: Lyocell Flame retardant Thermogravimetric analysis (TGA) Phosphorus compound
1. Introduction Lyocell fibers are produced by dissolving cellulose directly in an N-methylmorpholine-N-oxide/water solution, extruding the obtained solution through an orifice, drawing the material through an air gap, and then precipitating fibers in a coagulation bath [1]. However, Lyocell fibers are often subjected to high temperatures, which can cause degradation. When Lyocell fibers are heated, they undergo a series of interrelated physical and chemical changes. Pyrolysis of Lyocell fibers typically leads to a solid residue (char), high boiling volatiles (tar) and gaseous products. These products are formed by competitive pathways. One of the pathways involves dehydration, rearrangement, formation of carbonyl groups, evolution of carbon monoxide and carbon dioxide, and formation of a carbonaceous residue. These reactions are accelerated in the presence of a variety of organic and inorganic catalysts, particularly Lewis acids, which catalyze dehydration reactions [2,3]. Therefore, the control of reaction pathways during the initial stage of pyrolysis is important for flame-retardant materials. In this study, the effects of a phosphorus compound di-ammoniumhydrogen phosphate (DAHP) treatment on the flame-retardant
n Corresponding author at: C-Industry Incubation Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon, 305–600, Republic of Korea. Tel.: þ 82 42 860 7366; fax: þ 82 42 860 7388. E-mail address: [email protected] (J.S. Im).
http://dx.doi.org/10.1016/j.matlet.2014.07.131 0167-577X/& 2014 Elsevier B.V. All rights reserved.
properties of Lyocell fibers were investigated. The high flameretardant behavior of Lyocell fibers was modified by the treatment, which can be carried out within the span of a few minutes with high modification efficiency. The treatment induces a slow pathway that involves dehydration, rearrangement, formation of carbonyl groups, evolution of carbon monoxide and carbon dioxide, and formation of a carbonaceous residue to enhance flame retardancy. The effect of the flame-retardant treatment was investigated based on the thermal decomposition and thermooxidative reaction of Lyocell fibers.
2. Experimental Materials: In this study, Lyocell fibers (Kolon Industries, Republic of Korea) were cut to a length of 20 cm (approximately 10 g). Diammonium-hydrogen phosphate (DAHP) was selected as an agent for flame-retardant treatment [4]. Chemical treatment of lyocell fibers: For chemical treatment, DAHP was used to induce yield enhancement after heat treatment. First, 10 g of raw Lyocell fibers was immersed in 100 ml of a DAHP solution (concentrations: 1, 3, 5 and 7 wt %) for 30 minutes at 60 1C. Excess solution was removed by centrifugation and dried overnight at 70 1C in vacuum. The five samples were denoted LC, LD-1, LD-3, LD-5 and LD-7 based on their respective DAHP solution concentrations.
B.C. Bai et al. / Materials Letters 135 (2014) 226–228
Test of thermal oxidation resistance: Thermogravimetric analysis (TGA) was carried out on a Shimadzu TGA-50H thermo analyzer at scan rates of 5, 10, 20 and 40 1C/min in air (to investigate the integral procedure decomposition temperature (IPDT)). The char yield was obtained by measuring the residual weight at 1000 1C in nitrogen. Limiting oxygen index (LOI) measurements were conducted using an HC-2-type apparatus in accordance with ASTM D2863-77.
3. Results and discussion Thermal oxidation resistance: The TGA curves in Fig. 1(a) show the effects of DAHP treatment on the thermal oxidation resistance of Lyocell fibers in air at a heating rate of 5 1C. All of the DAHPtreated Lyocell fibers show slight changes in the slopes of their TG curves, which appear as two main shoulder peaks called step 1 and step 2. Step 1, the shoulder peak at approximately 200 1C, is due to the thermal decomposition of DAHP and the release of water and ammonia by the phosphorylation reaction [5]. Moreover, DAHP altered the profile of step 2, which was shifted to a higher temperature and became broader, thus changing the combustion pathway. The char yields of Lyocell fibers modified with DAHP tended to increase with DAHP content. The flameretardant role of DAHP treatment mechanism is presented in Fig. 1(b). The improved char yield was most likely caused by the esterification of phosphoric acid (H3PO4) and primary hydroxyl groups during thermal decomposition following DAHP treatment. This interaction leads to thick and compact char [6]. The increase in char yield implied a greater increase in the fire resistance of the samples because it is proposed that char formation limits the production of combustion gases, inhibits combustion gases from diffusing to the pyrolysis zone and protects the material surface from heat and air [7]. Therefore, the flame-retardant properties of the Lyocell fibers improved with the DAHP treatment.
100
LC LD-1 LD-3 LD-5 LD-7
Weight(%)
80
Step 1
Step 1
20
0
200
400
600
800
1000
Temperature(°c)
Fig. 1. Anti-oxidation properties of Lyocell fibers: (a) assessed by TGA at a heating rate of 5 1C/min, (b) inter-molecular reaction mechanism of flame-retardant treatment.
Step 2
LC
LD-1
LD-3
LD-5
LD-7
LC
LD-1
LD-3
LD-5
LD-7
IDT(1C) 5 1C/min 10 1C/min 20 1C/min 40 1C/min D.S.a
185 205 182 201 16
135 148 156 176 41
130 152 158 169 39
132 148 155 169 37
128 135 146 162 34
385 390 407 433 48
350 370 385 396 46
345 367 379 388 43
341 363 377 380 39
342 374 373 376 34
Tmax(1C) 5 1C/min 10 1C/min 20 1C/min 40 1C/min D.S.b Ea
289 302 315 330 40 145
250 260 265 282 32 156
243 252 252 262 19 241
240 247 243 256 16 282
223 192 213 238 15 290
445 469 479 501 56 165
450 470 485 503 53 176
458 471 488 508 50 190
461 473 498 510 49 195
477 484 506 519 42 235
a b
D.S.: degree of IDT shift (IDT at 40 1C/min - IDT at 5 1C/min). D.S.: degree of Tmax shift (Tmax at 40 1C/min - Tmax at 5 1C/min).
The initial degradation temperature (IDT) and the temperature at the maximum weight loss (Tmax) rate were presented in Table 1. All of the steps of the IDT decreased with the addition of DAHP but increased with the heating rate. This result is attributed to the facilitation of thermal decomposition by the dehydration of Lyocell fibers catalyzed by the byproduct of phosphoric acid, which also enhances the quenching of the pyrolysis system. At low temperature, the decomposition reactions become slow, and thus, more stable char is produced. The degree to which the temperature profiles were shifted decreased with increasing DAHP concentration, indicating that DAHP reduced the effects of the heating rate on the anti-oxidation properties of the samples. Integral procedure decomposition temperature (IPDT): The IPDT was calculated using TGA data (measured under nitrogen flow) via the following equations [8]: IPDT ¼ AnK nðT f T i Þ þT i An ¼ Kn ¼
Step 2
40
0
Table 1 IDT, Tmax and Ea of samples.
S1 þS2 S1 þS2 þ S3
60
227
S1 þ S2 S1
ð1Þ
ð2Þ
ð3Þ
where Ti is the initial experimental temperature and Tf is the final experimental temperature. The terms S1, S2, and S3 are depicted according to Doyle's proposition in Fig. 2(a) [8], and the calculated IPDT is presented in Fig. 2(b). In all samples, the IPDT increased with the heating rate and as a function of the effects of DAHP treatment, indicating that the flame-retardant properties of the fiber samples were improved. Indeed, the IPDT increased by almost 35% relative to that of the LC and LD samples. Char yield and LOI: The char yield and LOI are presented in Fig. 3. The char yield increased from 19.2 to 23.0% due to the effects of DAHP treatment. It is well known that char yield generated on a surface can act as a heat barrier and thermal insulation [9]. The LOI of the samples was investigated to determine the essential oxygen content for ignition. The LOI increased from 21 to 31% due to the effects of DAHP treatment. The char observed on the sample surfaces formed during combustion and acted as a protective layer preventing oxygen from diffusing to the surface of each specimen, increasing the amount of oxygen required for combustion. These results are in good agreement with findings reported for Lyocell fibers modified with DAHP [5]. The relationship between char yield and LOI can also be determined by running a regression between the two factors. In
228
B.C. Bai et al. / Materials Letters 135 (2014) 226–228
was calculated by the following equations derived from the Flynn, Wall, and Ozawa equations [10,11]: R Δ log Φ Ed ¼ C Δð1=T r Þ where Tr is the weight loss temperature and Ф is the heating rate (1C/min). C is a constant equal to 0.4521. The calculated values of Ea are presented in Table 1. All steps of the activation energy increased with increasing DAHP content. The activation energy of sample LD-7 was approximately 100% higher than that of the untreated sample, i.e., 286 versus 145 kJ/mol, respectively. This finding is expected to be due to the formation of thermally stable structures during the initial stages of the thermo-oxidative reactions that occur in step 1. The results also show that under the conditions of step 2, the decomposition of the DAHP-treated samples proceeded at a slightly higher rate, presumably due to a change in the decomposition pathway of the Lyocell fibers.
500
450
400
IPDT
4. Conclusions
350 LC LD-1 LD-3 LD-5 LD-7
300
250
10
20
30
40
o
Heating rate( C/min) Fig. 2. IPDT measured at various heating rates: (a) Doyle's proposition and (b) measured IPDT.
32
LD-7
R=0.9903
Lyocell fibers were treated with phosphorus compounds to determine the corresponding effects on the flame-retardant behavior of the fibers. The flame-retardant properties of the Lyocell fibers tended to increase with increasing DAHP content. Lyocell fibers modified with up to 7 wt% DAHP, sample LD-7, demonstrated the best linear burning rate. DAHP increased the char yield, resulting in a reduced LOI and a lower rate of degradation of the Lyocell fibers by acting as a donor material allowing for the formation of a thick and compact char layer. The IPDT increased significantly and the activation energy increased by a certain factor as a function of DAHP content, indicating that the flame-retardant properties of the Lyocell fibers were improved by the DAHP treatment.
30
LOI(%)
28
LD-5
Acknowledgment
LD-3
26
This work was supported by the Korea Evaluation Institute of Industrial Technology (KEIT) (Grant No. 10045669).
24 LD-1
22 LC
References
20 19
20
21
22
23
Char yield (%) Fig. 3. Relationship between the LOI and char yield of the samples.
this study, LOI increased with char yield, showing first-order behavior with R¼ 0.99. It appears that the char yield generated, especially that on the sample surface, allowed for a higher LOI, hindering the attack of oxygen radicals attack on Lyocell fibers. Activation energy (Ea): The activation energy (Ea) was evaluated to investigate the anti-oxidation behavior of fiber samples. The Ea
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
Loubinoux D, Chaunis S. Text Res J 1987;57::61–5. Thiyagarajan P, Mathur RB, Dhami TL. Carbon Lett 2003;4::117–20. Li XG, Huang MR, Bai H. J Appl Polym Sci 1999;73::2927–36. Tang MM, Bacon R. Carbon 1964;2::211–20. Statheropoulos M, Kyriakou SA. Anal Chim Acta 2000;409::203–14. Gronli MG, Varhegyi G, Di Blasi C. Ind Eng Chem Res 2002;41::4201–8. Nam S, Condon BD, Parikh DV, Zhao Q, Cintron MS, Madison C. Polym Degrad Stabil 2011;96::2010–8. Sponton M, Mercado LA, Ronda JC, Galia M, Cadiz V. Polym Degrad Stab 2008;93::2025–31. Huang MR, Li XG. J Appl Polym Sci 1998;68::293–304. Guo B, Jia D, Cai C. Eur Polym J 2004;40::1743–8. Li XG. J Appl Polym Sci 1999;71::573–8.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Improved flame-retardant properties of lyocell fiber achieved by phosphorus compound Byong Chol Bai a,b, Eun Ae Kim a,b, Young-Pyo Jeon a,c, Chul Wee Lee a,c, Se Jin In d, Young-Seak Lee b, Ji Sun Im a,c,n a
C-Industry Incubation Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon, 305-600, Republic of Korea Departments of Fine Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon 305-764, Republic of Korea c University of Science and Technology (UST), Daejeon, 305-333, Republic of Korea d Department of Fire and Disaster Protection Engineering, Woosong University, Daejeon 300-718, Republic of Korea b
ar t ic l e i nf o
a b s t r a c t
Article history: Received 4 June 2014 Accepted 19 July 2014 Available online 31 July 2014
The anti-oxidation behavior of Lyocell fibers during flame-retardant treatment as a function of the effects of a phosphorus compound was explored. Di-ammonium-hydrogen phosphate (DAHP) was observed to reduce the thermal degradation rate of the Lyocell fibers and increase the char yield; DAHP also increased the limiting oxygen index via a first-order relationship with the char yield. The integral procedure decomposition temperature (IPDT) increased significantly, and the activation energy increased by a certain factor, indicating a slow degradation pathway involving dehydration, rearrangement, formation of carbonyl groups, evolution of carbon monoxide and carbon dioxide, and formation of a carbonaceous residue for the flame retardancy of Lyocell fibers. & 2014 Elsevier B.V. All rights reserved.
Keywords: Lyocell Flame retardant Thermogravimetric analysis (TGA) Phosphorus compound
1. Introduction Lyocell fibers are produced by dissolving cellulose directly in an N-methylmorpholine-N-oxide/water solution, extruding the obtained solution through an orifice, drawing the material through an air gap, and then precipitating fibers in a coagulation bath [1]. However, Lyocell fibers are often subjected to high temperatures, which can cause degradation. When Lyocell fibers are heated, they undergo a series of interrelated physical and chemical changes. Pyrolysis of Lyocell fibers typically leads to a solid residue (char), high boiling volatiles (tar) and gaseous products. These products are formed by competitive pathways. One of the pathways involves dehydration, rearrangement, formation of carbonyl groups, evolution of carbon monoxide and carbon dioxide, and formation of a carbonaceous residue. These reactions are accelerated in the presence of a variety of organic and inorganic catalysts, particularly Lewis acids, which catalyze dehydration reactions [2,3]. Therefore, the control of reaction pathways during the initial stage of pyrolysis is important for flame-retardant materials. In this study, the effects of a phosphorus compound di-ammoniumhydrogen phosphate (DAHP) treatment on the flame-retardant
n Corresponding author at: C-Industry Incubation Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon, 305–600, Republic of Korea. Tel.: þ 82 42 860 7366; fax: þ 82 42 860 7388. E-mail address: [email protected] (J.S. Im).
http://dx.doi.org/10.1016/j.matlet.2014.07.131 0167-577X/& 2014 Elsevier B.V. All rights reserved.
properties of Lyocell fibers were investigated. The high flameretardant behavior of Lyocell fibers was modified by the treatment, which can be carried out within the span of a few minutes with high modification efficiency. The treatment induces a slow pathway that involves dehydration, rearrangement, formation of carbonyl groups, evolution of carbon monoxide and carbon dioxide, and formation of a carbonaceous residue to enhance flame retardancy. The effect of the flame-retardant treatment was investigated based on the thermal decomposition and thermooxidative reaction of Lyocell fibers.
2. Experimental Materials: In this study, Lyocell fibers (Kolon Industries, Republic of Korea) were cut to a length of 20 cm (approximately 10 g). Diammonium-hydrogen phosphate (DAHP) was selected as an agent for flame-retardant treatment [4]. Chemical treatment of lyocell fibers: For chemical treatment, DAHP was used to induce yield enhancement after heat treatment. First, 10 g of raw Lyocell fibers was immersed in 100 ml of a DAHP solution (concentrations: 1, 3, 5 and 7 wt %) for 30 minutes at 60 1C. Excess solution was removed by centrifugation and dried overnight at 70 1C in vacuum. The five samples were denoted LC, LD-1, LD-3, LD-5 and LD-7 based on their respective DAHP solution concentrations.
B.C. Bai et al. / Materials Letters 135 (2014) 226–228
Test of thermal oxidation resistance: Thermogravimetric analysis (TGA) was carried out on a Shimadzu TGA-50H thermo analyzer at scan rates of 5, 10, 20 and 40 1C/min in air (to investigate the integral procedure decomposition temperature (IPDT)). The char yield was obtained by measuring the residual weight at 1000 1C in nitrogen. Limiting oxygen index (LOI) measurements were conducted using an HC-2-type apparatus in accordance with ASTM D2863-77.
3. Results and discussion Thermal oxidation resistance: The TGA curves in Fig. 1(a) show the effects of DAHP treatment on the thermal oxidation resistance of Lyocell fibers in air at a heating rate of 5 1C. All of the DAHPtreated Lyocell fibers show slight changes in the slopes of their TG curves, which appear as two main shoulder peaks called step 1 and step 2. Step 1, the shoulder peak at approximately 200 1C, is due to the thermal decomposition of DAHP and the release of water and ammonia by the phosphorylation reaction [5]. Moreover, DAHP altered the profile of step 2, which was shifted to a higher temperature and became broader, thus changing the combustion pathway. The char yields of Lyocell fibers modified with DAHP tended to increase with DAHP content. The flameretardant role of DAHP treatment mechanism is presented in Fig. 1(b). The improved char yield was most likely caused by the esterification of phosphoric acid (H3PO4) and primary hydroxyl groups during thermal decomposition following DAHP treatment. This interaction leads to thick and compact char [6]. The increase in char yield implied a greater increase in the fire resistance of the samples because it is proposed that char formation limits the production of combustion gases, inhibits combustion gases from diffusing to the pyrolysis zone and protects the material surface from heat and air [7]. Therefore, the flame-retardant properties of the Lyocell fibers improved with the DAHP treatment.
100
LC LD-1 LD-3 LD-5 LD-7
Weight(%)
80
Step 1
Step 1
20
0
200
400
600
800
1000
Temperature(°c)
Fig. 1. Anti-oxidation properties of Lyocell fibers: (a) assessed by TGA at a heating rate of 5 1C/min, (b) inter-molecular reaction mechanism of flame-retardant treatment.
Step 2
LC
LD-1
LD-3
LD-5
LD-7
LC
LD-1
LD-3
LD-5
LD-7
IDT(1C) 5 1C/min 10 1C/min 20 1C/min 40 1C/min D.S.a
185 205 182 201 16
135 148 156 176 41
130 152 158 169 39
132 148 155 169 37
128 135 146 162 34
385 390 407 433 48
350 370 385 396 46
345 367 379 388 43
341 363 377 380 39
342 374 373 376 34
Tmax(1C) 5 1C/min 10 1C/min 20 1C/min 40 1C/min D.S.b Ea
289 302 315 330 40 145
250 260 265 282 32 156
243 252 252 262 19 241
240 247 243 256 16 282
223 192 213 238 15 290
445 469 479 501 56 165
450 470 485 503 53 176
458 471 488 508 50 190
461 473 498 510 49 195
477 484 506 519 42 235
a b
D.S.: degree of IDT shift (IDT at 40 1C/min - IDT at 5 1C/min). D.S.: degree of Tmax shift (Tmax at 40 1C/min - Tmax at 5 1C/min).
The initial degradation temperature (IDT) and the temperature at the maximum weight loss (Tmax) rate were presented in Table 1. All of the steps of the IDT decreased with the addition of DAHP but increased with the heating rate. This result is attributed to the facilitation of thermal decomposition by the dehydration of Lyocell fibers catalyzed by the byproduct of phosphoric acid, which also enhances the quenching of the pyrolysis system. At low temperature, the decomposition reactions become slow, and thus, more stable char is produced. The degree to which the temperature profiles were shifted decreased with increasing DAHP concentration, indicating that DAHP reduced the effects of the heating rate on the anti-oxidation properties of the samples. Integral procedure decomposition temperature (IPDT): The IPDT was calculated using TGA data (measured under nitrogen flow) via the following equations [8]: IPDT ¼ AnK nðT f T i Þ þT i An ¼ Kn ¼
Step 2
40
0
Table 1 IDT, Tmax and Ea of samples.
S1 þS2 S1 þS2 þ S3
60
227
S1 þ S2 S1
ð1Þ
ð2Þ
ð3Þ
where Ti is the initial experimental temperature and Tf is the final experimental temperature. The terms S1, S2, and S3 are depicted according to Doyle's proposition in Fig. 2(a) [8], and the calculated IPDT is presented in Fig. 2(b). In all samples, the IPDT increased with the heating rate and as a function of the effects of DAHP treatment, indicating that the flame-retardant properties of the fiber samples were improved. Indeed, the IPDT increased by almost 35% relative to that of the LC and LD samples. Char yield and LOI: The char yield and LOI are presented in Fig. 3. The char yield increased from 19.2 to 23.0% due to the effects of DAHP treatment. It is well known that char yield generated on a surface can act as a heat barrier and thermal insulation [9]. The LOI of the samples was investigated to determine the essential oxygen content for ignition. The LOI increased from 21 to 31% due to the effects of DAHP treatment. The char observed on the sample surfaces formed during combustion and acted as a protective layer preventing oxygen from diffusing to the surface of each specimen, increasing the amount of oxygen required for combustion. These results are in good agreement with findings reported for Lyocell fibers modified with DAHP [5]. The relationship between char yield and LOI can also be determined by running a regression between the two factors. In
228
B.C. Bai et al. / Materials Letters 135 (2014) 226–228
was calculated by the following equations derived from the Flynn, Wall, and Ozawa equations [10,11]: R Δ log Φ Ed ¼ C Δð1=T r Þ where Tr is the weight loss temperature and Ф is the heating rate (1C/min). C is a constant equal to 0.4521. The calculated values of Ea are presented in Table 1. All steps of the activation energy increased with increasing DAHP content. The activation energy of sample LD-7 was approximately 100% higher than that of the untreated sample, i.e., 286 versus 145 kJ/mol, respectively. This finding is expected to be due to the formation of thermally stable structures during the initial stages of the thermo-oxidative reactions that occur in step 1. The results also show that under the conditions of step 2, the decomposition of the DAHP-treated samples proceeded at a slightly higher rate, presumably due to a change in the decomposition pathway of the Lyocell fibers.
500
450
400
IPDT
4. Conclusions
350 LC LD-1 LD-3 LD-5 LD-7
300
250
10
20
30
40
o
Heating rate( C/min) Fig. 2. IPDT measured at various heating rates: (a) Doyle's proposition and (b) measured IPDT.
32
LD-7
R=0.9903
Lyocell fibers were treated with phosphorus compounds to determine the corresponding effects on the flame-retardant behavior of the fibers. The flame-retardant properties of the Lyocell fibers tended to increase with increasing DAHP content. Lyocell fibers modified with up to 7 wt% DAHP, sample LD-7, demonstrated the best linear burning rate. DAHP increased the char yield, resulting in a reduced LOI and a lower rate of degradation of the Lyocell fibers by acting as a donor material allowing for the formation of a thick and compact char layer. The IPDT increased significantly and the activation energy increased by a certain factor as a function of DAHP content, indicating that the flame-retardant properties of the Lyocell fibers were improved by the DAHP treatment.
30
LOI(%)
28
LD-5
Acknowledgment
LD-3
26
This work was supported by the Korea Evaluation Institute of Industrial Technology (KEIT) (Grant No. 10045669).
24 LD-1
22 LC
References
20 19
20
21
22
23
Char yield (%) Fig. 3. Relationship between the LOI and char yield of the samples.
this study, LOI increased with char yield, showing first-order behavior with R¼ 0.99. It appears that the char yield generated, especially that on the sample surface, allowed for a higher LOI, hindering the attack of oxygen radicals attack on Lyocell fibers. Activation energy (Ea): The activation energy (Ea) was evaluated to investigate the anti-oxidation behavior of fiber samples. The Ea
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
Loubinoux D, Chaunis S. Text Res J 1987;57::61–5. Thiyagarajan P, Mathur RB, Dhami TL. Carbon Lett 2003;4::117–20. Li XG, Huang MR, Bai H. J Appl Polym Sci 1999;73::2927–36. Tang MM, Bacon R. Carbon 1964;2::211–20. Statheropoulos M, Kyriakou SA. Anal Chim Acta 2000;409::203–14. Gronli MG, Varhegyi G, Di Blasi C. Ind Eng Chem Res 2002;41::4201–8. Nam S, Condon BD, Parikh DV, Zhao Q, Cintron MS, Madison C. Polym Degrad Stabil 2011;96::2010–8. Sponton M, Mercado LA, Ronda JC, Galia M, Cadiz V. Polym Degrad Stab 2008;93::2025–31. Huang MR, Li XG. J Appl Polym Sci 1998;68::293–304. Guo B, Jia D, Cai C. Eur Polym J 2004;40::1743–8. Li XG. J Appl Polym Sci 1999;71::573–8.