Thermal Properties and Combustion Behaviors of Chitosan Based

Article pubs.acs.org/IECR

Thermal Properties and Combustion Behaviors of Chitosan Based Flame Retardant Combining Phosphorus and Nickel Shuang Hu,† Lei Song,† Haifeng Pan,† and Yuan Hu*,† †

State Key Laboratory of Fire Science, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, PR China ABSTRACT: A renewable carbonization agent based compound nickel chitosan phosphate (NiPCS) has been prepared, which was the combination of flame retardant and synergist. Its effect on thermal properties and flammability of poly(vinyl alcohol) (PVA) has been investigated. Microscale combustion calorimetry (MCC) test proved that NiPCS can decrease the intensities of heat release rate (PHRR) and total heat release rate (THR) greatly. Thermogravimetric analysis (TGA) results indicated that NiPCS possessed a high formation of char. With the increase of the flame retardant, the thermal stability of materials enhanced in high temperature. Real time Fourier transform infrared (RT-IR) data confirmed that the flame retardant can promote the dehydration effect as well as accelerate the char forming. The volatilized products and the synergistic effect of nickel on thermal properties were both investigated with thermogravimetric analysis/infrared spectrometry (TGA-IR) and laser Raman spectroscopy (LRS). The results revealed that nickel restrained the thermal degradation of materials as well as improved the structural organization level of char. synergistic effect.17,18 So, metal ion was introduced in this study to investigate its effect in this novel flame retardant. Poly(vinyl alcohol) (PVA) is widely used in many fields such as home textiles, coating materials, and industrial materials, etc. However, PVA is flammable, resulting in a significant restriction of its fields of application. In this paper, a novel renewable intumescent flame retardant nickel chitosan phosphate (NiPCS) has been prepared with chitosan, phosphorus pentoxide, and nickel(II) nitrate hexahydrate. Its effect on thermal properties and flammability of poly(vinyl alcohol) (PVA) has been investigated. The thermal degradation process was evaluated through thermogravimetric analysis (TGA), real time Fourier transform infrared spectrometry (RT-IR), and thermogravimetric analysis/infrared spectrometry (TGA-IR). Microscale combustion calorimetry (MCC) experiment was used to investigate the flammability performance. The structure of the residual char was investigated with Raman measurement.

1. INTRODUCTION Recently, how to reduce the human impact on the environment has been a focus around the world.1 Special attention has been paid to the replacement of conventional petroleum-based materials by materials based on nature resources.2 Intumescent flame retardant (IFR), first used in the painting industry, has been applied to the fireproofing of polymeric materials for the past thirty years. It has received considerable attention recently because it provides efficient fire protection with minimum of overall health hazard.3−5 The use of IFR which, on heating, forms a char that is able to act as a thermal shield is one of the most promising methods of imparting flame retardant properties to polymers. Carbonization agent is the basic component of intumescent flame retardant, taking an important effect on the formation of char that can be used as a barrier to prevent the combustion of materials. A number of reports investigated different carbonization agents, such as pentaerythrite and polyamide.6−10 However, these carbonization agents root in petroleum that is a limited resource, and its processing procedure is harmful to the environment. Therefore, it is significant that the traditional petroleum-based carbonization agent is replaced by the renewable nature material to prepare a novel flame retardant. Chitosan (CS), the fully or partially deacetylated form of chitin, the principal component of living organisms such as fungi and crustaceans is known to be nontoxic as well as being enzymatically biodegradable.11 Much attention has been paid to its modification on biomedical and ecological application in the past decades.12−15 Moreover, chitosan has the potential to be used as carbonization agent due to the structure of multihydroxyl group. In this research, phosphorylated chitosan was prepared as the basic structure of intumescent flame retardant. Nishi reported that phosphorylated derivatives of chitosan have the metal binding ability.16 It has been proved that metal ion can promote the flame retardancy of materials owing to its © 2012 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Materials. Chitosan (viscosity 50−800 mPa.s, degree of deacetylation 80−95%), phosphorus pentoxide, methanesulfonic acid, and nickel(II) nitrate hexahydrate were all provided by Sinopharm Chemical Reagent Co., Ltd. 2.2. Synthesis of NiPCS. Chitosan (CS, 2 g) and methanesulfonic acid (30 mL) were placed into a three-necked flask with a mechanical stirrer. The flask was put in an ice bath with N2 gas that was aspirated to eliminate residual moisture. Phosphorus pentoxide (10 g) was added, and the reaction went on for 3 h in ice bath. The product was washed with ether, acetone, methanol, and ether and then dried in vacuum oven Received: Revised: Accepted: Published: 3663

October 3, 2011 February 1, 2012 February 6, 2012 February 6, 2012 dx.doi.org/10.1021/ie2022527 | Ind. Eng. Chem. Res. 2012, 51, 3663−3669

Industrial & Engineering Chemistry Research

Article

Scheme 1. Preparation of NiPCS

at 60 °C to obtain phosphorylated chitosan (PCS).19−21 Then, the reaction between PCS and nickel(II) nitrate hexahydrate (weight ratio, 1:10) occurred at 60 °C in ethanol for 1 h. The product was washed by ethanol several times to remove the extra Ni(NO3)2. Finally, the absinthe-green powder can be obtained, after it was dried in vacuum oven at 60 °C. Scheme 1 exhibited the reaction scheme. 2.3. Preparation of NiPCS/PVA Blended Membranes. NiPCS and PVA were mixed in water at room temperature for 1 h. Then, membranes were obtained after the samples were dried at 80 °C for 2 h, 60 °C for 10 h, and 80 °C for 2 h. 2.4. Characterization. FTIR spectroscopy (Nicolet 6700, Nicolet Instrument Company, USA) was employed to characterize samples using thin KBr as the sample holder. NMR measurement was conducted on Avance 300 spectrometer (Bruker Biospin, Switzerland, frequency) at room temperature using CDCl3 as the solvent. Tetramethylsilane (TMS) in CDCl3 was used as internal standard. Atomic absorption spectrometry (Analyst 800, PerkinElmer) was used to test the content of phosphorus and nickel. MCC test were carried out using a Govmak MCC-2 microscale combustion calorimeter; samples were heated to 650 °C at a heating rate of 1 °C/s in a stream of nitrogen flowing at 80 mL/min. The volatile anaerobic thermal degradation products in the nitrogen gas stream were mixed with a 20 mL/min stream of pure oxygen prior to entering a 900 °C combustion furnace. Thermogravimetric analysis (TGA) was carried out using a Q5000IR thermoanalyzer instrument from 50 to 650 °C at a linear heating rate of 20 °C/min under an air flow of 60 mL/min. Real time Fourier transform infrared (RT-IR) method was used Nicolet MAGNA-IR 750 spectrophotometer (Nicolet Instrument Company, USA) to study the thermo-oxidative degradation of the cured film. Powders of the cured sample were mixed with KBr powders, and the mixture was pressed into a tablet, which was then placed into the oven. The temperature of the oven was raised at a heating rate of about 10 °C/min. Thermogravimetric analysis/infrared spectrometry (TGAIR) was performed to analyze the volatilized products after the pyrolysis of samples under a nitrogen flow of 35.0 mL/min. Laser Raman spectroscopy (LRS) was performed with a SPEX-1403 laser Raman spectrometer (USA) at room temperature. It was provided in backscattering geometry by the 514 nm argon laser line. The scanning scope was from 500 to 2000 cm−1.

3. RESULTS AND DISCUSSION 3.1. Characterizations of NiPCS. Figure 1 showed the FTIR spectra of CS, PCS, and NiPCS. After phosphorylation

Figure 1. FTIR spectra of CS, PCS, and NiPCS.

modification, two new peaks appeared at 1050 and 484 cm−1, which can be attributed to the P−O structure, such as P−O−C and P−OH. The peak at 1050 cm−1 overlapped the C−O stretching vibrations in chitosan ether groups at 1100 cm−1.22 The peak at 1200 cm−1 was assigned to PO structure. It indicated that the reaction happened between the OH group of CS and phosphorus pentoxide. The absorption at 1600 cm−1 was replaced by a new absorption at 1634 cm−1, implying that amino groups in chitosan could change into ammonium groups in methanesulfonic acid medium, while some amino groups underwent the reaction to form phosphorylamide groups.23 Then, the reaction between PCS and nickel ion can form phosphate structure. Compared with the FTIR curve of PCS, the FTIR curve of NiPCS showed some changes. The peak assigning to P−O shifted to a higher wavenumber, increasing from 1050 and 484 cm−1 to 1090 and 504 cm−1, respectively. Meanwhile, the band at 1200 cm−1 moved to 1240 cm−1. Figure 2 showed the 31P NMR spectrum of PCS. The peak around 0 ppm indicated that phosphorylation occurred on C-6 hydroxyl groups of chitosan. It was because that the primary hydroxyl groups on the chitosan units were more reactive than the secondary hydroxyl groups.24 The appearance of a small peak at −1 ppm meant that part of the hydroxyl groups on C-3 of chitosan took part in the reaction.23 In addition, atomic absorption spectrometry revealed the weight content of phosphorus and nickel in NiPCS (P 12.2 wt %, Ni 5.9 wt %). 3664

dx.doi.org/10.1021/ie2022527 | Ind. Eng. Chem. Res. 2012, 51, 3663−3669


Article

fire safety, and low values of PHRR were an indication of low flammability and low full-scale fire hazard.25,26 The heat release rate curves of samples demonstrated that with the increase of NiPCS, the intensity of PHRR1 (the first peak of heat release rate) decreased greatly, dropping from 155 W/g to 40 W/g. The results showed that NiPCS exhibited high effectiveness in decreasing heat release rate. Total heat release (THR) is characterized as the total available energy in the material in a fire situation. It is calculated from the area under the HRR curve, which is another important parameter for fire hazard evaluation. Table 1 showed that NiPCS made THR reduce from 18.2 kJ/g to 10.4 kJ/g. It indicated that more volatile products were catalytically carbonized to participate in the charring process, rather than transferred into the MCC combustor.27 Besides, it should be noticed that T1 shifted to lower temperature with the increasing content of NiPCS. It was ascribed to the decomposition of flame retardant, which can be proved from the TGA data. Generally speaking, MCC results demonstrated that NiPCS suppressed the combustion of materials. 3.3. Thermogravimetric Analysis. Thermogravimetric analysis of NiPCS and NiPCS/PVA blended samples were conducted. They were shown in Figure 4, and the related data were listed in Table 2.

Figure 2. P NMR spectrum of PCS.

In summary, the results of FTIR, 31P NMR, and atomic absorption spectrometry confirmed that the phosphorylation modification of chitosan was successful and the nickel ion was bound on the PCS. 3.2. Combustion Properties. MCC is a useful bench scale method for investigating the combustion properties of polymer materials. Oxygen consumption calorimeter is used to measure the rate and amount of heat, producing by complete combustion of the fuel gases generated during controlled heating of a milligram-sized sample. Parameters including peak heat release rate (PHRR), total heat release (THR), and temperature at the first peak heat release rate (T1) can be obtained. Figure 3 showed the heat release rate (HRR) curves of NiPCS/PVA samples, and the corresponding combustion data

Figure 4. Thermogravimetric analysis of samples.

Table 2. TG Curves of Different Ratio NiPCS/PVA samples

Figure 3. HRR curves of NiPCS/PVA.

were presented in Table 1. It was reported that the peak of heat release rate (PHRR) was an important parameter to evaluate

samples

PHRR1 (W/g)

THR (kJ/g)

T1 (°C)

155 60 52 40

18.2 16.1 11.5 10.4

377 318 293 263

T10% (°C)

residual char at 700 °C (wt%)

PVA NiPCS 5 wt % NiPCS/PVA 10 wt % NiPCS/PVA 20 wt % NiPCS/PVA

300 216 260 253 234

0.7 60.4 7.6 12.7 19.5

It can be observed that one obvious stage presented for NiPCS. This section corresponded to the loss of adsorbed and bound water as well as the degradation of organic phosphonate. With the increase of temperature, further decomposition took place very slowly. Thermal degradation of NiPCS/PVA samples showed that the onset temperatures (T10%, the temperature at 10% weight loss) reduced gradually. Specifically, with the increase of NiPCS, T10% decreased from 260 to 234 °C. The phenomenon

Table 1. HRR Curves of Samplesa PVA 5 wt % NiPCS/PVA 10 wt % NiPCS/PVA 20 wt % NiPCS/PVA

samples

a

PHRR1, the first peak heat release rate; THR, total heat release; T1, temperature at the first peak heat release rate. 3665



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Figure 5. Real time FTIR analysis (a: NiPCS; b: PVA; c: NiPCS/PVA).

asymmetric stretching vibration of P−O−P. The bands at 1270 cm−1, 1090 cm−1, and 885 cm−1 were still obvious at 500 °C, indicating that the char contained complex P−O−P and P−O−Φ structures. Besides, nickel ion can produce a bridge between two phosphorus compounds. Such bridges can enhance the stabilization of these phosphorus compounds and decrease the volatility of the phosphorus oxides during the pyrolysis.33 The above results showed that more phosphorus can be available for the char formation. Scheme 2 showed the pyrolysis mechanism of NiPCS.

can be attributed to the decomposition of the flame retardant. However, the flame retardant enhanced the thermal stability of samples after 370 °C, especially at 700 °C, which was clear from Table 2. Compound containing phosphorus accelerated the formation of the char, ascending from 0.7 wt % to 19.5 wt % at 700 °C. It was known to all that char layer had the effect on blocking the transfer of oxygen and heat, retarding thermal decomposition of underlying materials.28−30 Therefore, NiPCS improved the thermal stability of materials in high temperature. 3.4. Real Time FTIR Analysis. Real time FTIR (RT-IR) was used to evaluate the thermal degradation process of NiPCS, PVA, and 20 wt % NiPCS/PVA, showing in Figure 5. Figure 5a described the RT-IR spectra of NiPCS in different pyrolysis temperature. The band at 3420 cm−1 was assigned to the OH group. The peaks at 1220 cm−1 and 1060 cm−1 were ascribed to PO and P−O−C groups, respectively. With the increase of temperature, the peak at 3420 cm−1 disappeared at 180 °C, indicating the loss of adsorbed and bound water. The peak at 1060 cm−1 vanished at 240 °C, implying the break of P−O−C structure. Meanwhile, the peak at 1220 cm−1 shifted to a higher wavenumber (1270 cm−1), which was assigned to the stretching vibration for P−O−Φ structure, where Φ represented the graphite-like poly nuclear aromatic structure.31,32 Two new peaks can be observed at 300 °C. The peaks at 1090 cm−1 and 885 cm−1 were ascribed to symmetric and

Scheme 2. Pyrolysis Mechanism of NiPCS

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Carbonyl compounds, aldehyde and aromatic compounds shared the similar trend. Flame retardant promoted the degradation of materials at a lower temperature. Meanwhile, the flame retardant degraded at low temperature. So the volatilized products come up earlier. TGA data proved that NiPCS promoted the formation of char that was usually used as physical protective barrier to restrain the transfer of mass. So, the intensity of flammable volatilized products decreased extraordinarily, such as carbonyl compounds. In order to investigate the function of nickel, we made a comparison between 20 wt % PCS/PVA and 20 wt % NiPCS/ PVA system using the TGA-IR method. Figure 6 showed that not only the peaks of NiPCS/PVA system appeared later than those of PCS/PVA but also the general intensity of the sample containing nickel was lower. In the previous research, the same phenomenon has also been found.17 The explanation was that nickel ion catalyzed the formation of char that can be used to prevent the transfer of mass and heat. Therefore, NiPCS delayed the thermal degradation of PVA and the general intensity of volatilized products compared with PCS. It implied that nickel in this system further improved the thermal stability of materials. 3.6. Structure Analysis of Char Residue. Raman spectroscopy is a useful tool for the characterization of carbonaceous material. For further understanding the effect of nickel in this system, we used Raman spectroscopy to investigate the structure of char. Samples were collected by burning in a muffle furnace at 600 °C for 10 min. Figure 7 showed the Raman curves of the char from 20 wt % PCS/PVA and 20 wt % NiPCS/PVA. Both curves had two peaks, which were the characteristic of pregraphitic structures. The first peak around 1365 cm−1 was attributed to the E2g vibrational mode, while the second one around 1600 cm−1 represented defects in the structure.36 It can be observed that the intensity of NiPCS/PVA peak was stronger than that of PCS/PVA. This phenomenon can be explained that nickel improved the structural organization level of the carbon.37

It can be observed from Figure 5b that with the increase of temperature, the strength of peaks for pure PVA weakened gradually. By contrast, Figure 5c (NiPCS/PVA) showed that with the addition of NiPCS, the absorption at 3430 cm−1 (OH) vanished suddenly at 220 °C, while the same peak disappeared at 350 °C for pure PVA. The phenomena was because of the effect of catalyzed dehydration by the phosphorus acid. Otherwise, the band at 868 cm−1 assigning to the aromatic ring vibrations appeared at 260 °C, which was of benefit to yield char residues in high temperature.34 The absorption band at 753 cm−1 appeared at 300 °C in the NiPCS/PVA, suggesting that the formation of phosphate-carbon complexes in the carbonized residue, which was propitious to enhance the stability of the char.35 The peak at 1290 cm−1 and 1090 cm−1 were ascribed to complex P−O structure. They still can be found at 550 °C revealing that the residual char contained phosphorus. It implied that phosphorus mainly took effect in condensed phase on char forming, which was useful to improve the thermal stability of materials, just like TGA data showed to us. 3.5. Volatilized Products Analysis. Thermogravimetric analysis/infrared spectrometry (TGA-IR) was performed to analyze the volatilized products after thermal decomposition of samples, which contributed to study the thermal degradation process. In this paper, we used this method to understand the effect of NiPCS. Total and some specific volatilized products were selected to study, concluding H2O (3575 cm−1), aromatic compounds (653 cm−1), aldehyde (1179 cm−1), carbonyl compounds (1773 cm−1), and methyl-terminated polyenes (1391 cm−1). The intensities of absorbance were all normalized to the samples’ content. Figure 6 showed the change of pyrolysis products in different time. For total volatilized curves, it was found that the released peak of NiPCS/PVA appeared at 13 min, which was 2 min earlier than that of pure PVA. On the other hand, the intensity of volatilized product dropped greatly with the presence of NiPCS.

Figure 6. Volatilized products analysis. 3667



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ACKNOWLEDGMENTS

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REFERENCES

Article

The work was financially supported by the National Basic Research Program of China (973 Program) (2012CB719701), National Natural Science Foundation of China (No. 51036007), and the joint fund of NSFC and CAAC (No. 61079015).

(1) Gross, R. A. Biodegradable polymers for the environment. Science 2002, 297, 803−807. (2) Chivrac, F.; Pollet, E.; L. Averous, L. Progress in nanobiocomposites based on polysaccharides and nanoclays. Mater. Sci. Eng., R 2009, 67, 1−17. (3) Riva, A.; Camino, G.; Fomperie, L. Fire retardant mechanism in intumescent ethylene vinyl acetate compositions. Polym. Degrad. Stab. 2003, 82, 341−346. (4) Le Bras, M.; Bourbigot, S.; Fe ĺ ix, E.; Pouille, F.; Siat, C.; Traisnel, M. Characterization of a polyamide-6-based intumescent additive for thermoplastic formulations. Polymer 2000, 41, 5283−5296. (5) Duquesne, S.; Magnet, S.; Jama, C.; Delobel, R. Thermoplastic resins for thin film intumescent coatings-towards a better understanding of their effect on intumescence efficiency. Polym. Degrad. Stab. 2005, 88, 63−69. (6) Shun, Z.; Wang, Z. Z.; Gui, Z.; Hu, Y. Flame retardation an thermal degradation of flame retarded polypropylene comosites containing melamine phosphate and pentaerythritol phosphate. Fire Mater. 2008, 32, 307−309. (7) Mark, T. H. Synergistic effect of the charring agent on the thermal and flame retardant proerties of polyethylene. Plast. Eng. 1993, 11, 29−35. (8) Hu, X. P.; Li, Y. L.; Wang, Y. Z. Synergistic effect of the charring agent on the thermal and flame retardant properties of polyethylene. Mater. Eng. 2004, 289, 208−212. (9) Montaudo, G.; Scamporrino, E. Intumescent flame retardant for polymers. III. The polypropyIene-ammonium poIyphoSphate-polyurethane system. J. Appl. Polym. Sci. 1985, 30, 1449−1460. (10) Almeras, X.; Dabrowski, F.; Le, Bras., M. Using polyamide-6 as chafring agent in intumescent polypropylene fonnulations II. Themal degradation. Polym. Degrad. Stab. 2002, 77, 315−323. (11) Peter, G.; Steinbuchel, A.; Marchessault, R. H. Biopolymers for Medical and Pharmaceutical Applications. Wiley-VCH: Weinheim, 2005; pp 419−512. (12) Silva, S. S.; Ferreira, R. A. S.; Fu, L.; Carlos, L. D.; Mano, J. F.; Reis, L. R.; Rochad, J. Functional nanostructured chitosan−siloxane hybrids. J. Mater. Chem. 2005, 15, 3952−3961. (13) Spagnaa, G.; Barbagalloa, R. N.; Casarinib, D.; Pifferic, P. G. A novel chitosan derivative to immobilize a-L-rhamnopyranosidase from Aspergillus niger for application in beverage technologies. Enzyme Microb. Technol. 2001, 28, 427−438. (14) Lee, E. J.; Shin, D. S.; Kim, H. E.; Kim, H. W.; Koh, Y. H.; Jang, J. H. Membrane of hybrid chitosan−silica xerogel for guided bone regeneration. Biomaterials 2009, 30, 743−750. (15) Liu, Y. L.; Su, Y. H.; Lai, J. Y. In situ crosslinking of chitosan and formation of chitosan−silica hybrid membranes with using gglycidoxypropyltrimethoxysilane as a crosslinking agent. Polymer 2004, 45, 6831−6837. (16) Nishi, N.; Maekita, Y.; Nishimura, S.; Hasegawa, O.; Tokura, S. Highly phosphorylated derivatives of chitin, partially deacetylated chitin and chitosan as new functional polymers: metal binding property of the insolubilized materials. Int. J. Biol. Macromol. 1987, 9, 109−114. (17) Shan, X. Y.; Zhang, P.; Song, L.; Hu, Y.; Lo, S. Compound of Nickel Phosphate with Ni(OH)(PO4)2 -Layers and Synergistic Application with Intumescent Flame Retardants in Thermoplastic Polyurethane Elastomer. Ind. Eng. Chem. Res. 2011, 50, 7201−7209. (18) Nie, S. B.; Song, L.; Hu, Y. Study on a novel and efficient flame retardant synergist-nanoporous nickel phosphates VSB-1 with

Figure 7. Raman curves of the residual char.

Relative intensity ratio between 1596 cm−1 and 1364 cm−1 was inversely proportional to an in-plane microcrystalline size and/ or an in-plane phonon correlation length obtained from Raman spectroscopy.38 The related information was listed in Table 3. Table 3. Raman Curves of Char Residues samples

intensity ratio

PCS/PVA NiPCS/PVA

I1596/1365 = 0.35 I1604/1366 = 0.42

NiPCS/PVA system had a higher intensity ratio (0.42) than that of PCS/PVA system (0.35). Bourbigot reported that higher protective shield efficiency was related to the smaller size of carbonaceous microstructures.39 Hence, nickel made the char more compact containing smaller carbonaceous microstructures, which accorded with the results of MCC and TGA-IR.

4. CONCLUSIONS A renewable carbonization agent based flame retardant NiPCS has been synthesized successfully. The MCC test proved that NiPCS can decrease HRR and THR obviously, indicating that the flammability of PVA reduced. TGA results showed that the flame retardant possessed a high formation of char. With the increase of NiPCS, the thermal stability of materials improved in high temperature. RT-IR results confirmed that the flame retardant can promote the dehydration effect as well as accelerate the char forming. TGA-IR measurement was applied to study the synergistic effect of nickel on thermal properties. It showed that compared with PCS, NiPCS can make samples degrade later and reduce the intensity of combustible volatilized products. LRS results implied that the structural organization level of the carbon increased with nickel. In summary, NiPCS was useful to improve the flammability and thermal properties of materials and the nickel can take its synergistic effect on thermal stability of PVA.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +86-551-3601664. E-mail: [email protected]. Notes

The authors declare no competing financial interest. 3668



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intumescent flame retardants in polypropylene. Polym. Adv. Technol. 2008, 19, 489−495. (19) Nishi, N.; Nishimura, S.; Ebina, A.; Tsutsumi, A.; Tokura, S. Preparation and characterization of water-soluble chitin phosphate. Int. J. Biol. Macromol. 1984, 6, 53−54. (20) Nishi, N.; Ebina, A.; Nishimura, S.; Tsutsumi, A.; Hasegawa, O.; Tokura, S. Highly phosphorylated derivatives of chitin, partaially deacetylated chitin and chitosan as new functional polymers-preparation and characterization. Int. J. Biol. Macromol. 1986, 8, 311−317. (21) Nishi, N.; Maekita, Y.; Nishimura, S. I.; O. Hasegawa, O.; Tokura, S. Highly phosphorylated derivatives of chitin, partaially deacetylated chitin and chitosan as new functional polymers-metalbinding property of the insolubilized materials. Int. J. Biol. Macromol. 1987, 9, 109−114. (22) Amaral, I. F.; Granja, P. L.; Barbosa, M. A. Chemical modification of chitosan by phosphorylation: an XPS, FT-IR and SEM study. Int. J. Biol. Macromol. 2005, 16, 1575−1593. (23) Wang, X. H.; Ma, J. B.; Wang, Y.; He, B. L. Structural characterization of phosphorylated chitosan and their applications as efective additives of calcium phosphate cements. Biomaterials 2001, 22, 2247−2255. (24) Wan, Y.; Creber, K. A. M.; Peppley, B.; Bui, T. Synthesis, Characterization and Ionic Conductive. Macromol. Chem. Phys. 2003, 204, 850−858. (25) Gilman, J. W. Flammability and thermal stability studies of polymer layered-silicate (clay) nanocomposites. Appl. Clay Sci. 1999, 15, 31−49. (26) Zanetti, M.; Kashiwagi, T.; Falqui, L.; Camino, G. Cone Calorimeter Combustion and Gasification Studies of Polymer Layered Silicate Nanocomposites. Chem. Mater. 2002, 14, 881−887. (27) Lu, H. D.; Wilkie, C. A.; Ding, M.; Song, L. Flammability performance of poly(vinyl alcohol) nanocomposites with zirconium phosphate and layered silicates. Polym. Degrad. Stab. 2011, 96, 1219−1224. (28) Horrocks, A. R. Developments in flame retardants for heat and fire resistant textiles-the role of char formation and intumescence. Polym. Degrad. Stab. 1996, 54, 143−154. (29) Bourbigot, S.; Duquesne, S. Fire retardant polymers: recent developments and opportunities. J. Mater. Chem. 2007, 17, 2283− 2300. (30) Laachachi, A.; Ball, V.; Apaydin, K.; Toniazzo, V.; Ruch, D. Diffusion of (26) Polyphosphates into (Poly(allylamine)-montmorillonite) Multilayer Films: Flame Retardant-Intumescent Films with Improved Oxygen Barrier. Langmuir 2011, 27, 13879−13887. (31) Hsiue, G. H.; Shiao, S. J.; We, H. F.; Kuo, W. J.; Sha, Y. A. Novel phosphorus-containing dicyclopentadiene-modified phenolic resins for flame-retardancy applications. J. Appl. Polym. Sci. 2001, 79, 342−349. (32) Bugajny, M.; Bourbigot, S.; Le Bras, M.; Delobel, R. The origin and nature of flame retardance in ethylene-vinyl acetate copolymers containing Hostaflam AP 750. Polym. Int. 1999, 48, 264−270. (33) Lewin, M.; Endo, M. Catalysis of intumescent flame retardancy of polypropylene by metallic compounds. Polym. Adv. Technol. 2003, 14, 3−11. (34) Setnescu, R.; Jipa, S.; Setnescu, T.; Kappel, W.; Kobayashi, S.; Osawa, Z. IR and X-ray characterization of the ferromagnetic phase of pyrolysed polyacrylonitrile. Carbon 1999, 37, 1−6. (35) Lu, H. D.; Wilkie, C. A.; Ding, M.; Song, L. Thermal properties and flammability performance of poly (vinyl alcohol)/a-zirconium phosphate nanocomposites. Polym. Degrad. Stab. 2011, 96, 885−891. (36) Tamor, M. A.; Vassell, W. C. Raman Fingerprinting of Amorphous-Carbon Films. J. Appl. Phys. 1994, 76, 3823−3830. (37) Lespade, P.; Al-Jishi, R.; Dresselhaus, M. S. Model for Raman scattering from incompletely graphitized carbons. Carbon 1982, 20, 427−431. (38) Tuinstra, F.; Koenig, J. L. Raman Spectrum of Graphite. J. Chem. Phys. 1970, 53, 1126−1130. (39) Bourbigot, S.; Le Bras, M.; Delobel, R.; Tremillon, J. M. Synergistic effect of zeolite in an intumescence process. Study of the interactions between the polymer and the additives. J. Chem. Soc., Faraday Trans. 1996, 92, 3435−3444. 3669


Thermal Properties and Combustion Behaviors of Chitosan Based

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