Comparative Study on the Effect of Beta-Cyclodextrin and

Article pubs.acs.org/IECR

Comparative Study on the Effect of Beta-Cyclodextrin and Polypseudorotaxane As Carbon Sources on the Thermal Stability and Flame Retardance of Polylactic Acid Xiaofeng Wang,†,‡ Weiyi Xing,*,† Bibo Wang,† Panyue Wen,† Lei Song,† Yuan Hu,*,†,‡ and Ping Zhang§ †

State Key Laboratory of Fire Science, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, People’s Republic of China ‡ Suzhou Key Laboratory of Urban Public Safety, Suzhou Institute of University of Science and Technology of China, 166 Ren’ai Road, Suzhou, Jiangsu 215123, People’s Republic of China § State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, 59 Qinglong Road, Mianyang 621010, P. R. China ABSTRACT: Polypseudorotaxane (PPR) prepared by the inclusion complex between beta-cyclodextrin (β-CD) and poly(propylene glycol) (PPG) was chosen as a ‘‘green’’ carbon source in intumescent flame retardants (IFRs) and exhibited more effective carbonization and higher degree of graphitic network than that of free β-CD. Its combination with ammonium polyphosphate (APP) and melamine (MA) presented the most excellent char-forming ability whether in nitrogen or in air atmosphere. After blending IFRs into polylactic acid (PLA), the thermal stability was characterized by thermogravimetric analysis (TGA), and their flammability was assessed by limited oxygen index (LOI), vertical combustion, and cone calorimeter. The higher LOI% value and lower total heat release (THR) of PLA2 (which contains 20 wt % APP/MA/PPR mixtures) revealed that it presented more excellent flame retardance. Besides, the results of scanning electron microscopy (SEM) exhibited the existence of more bubbles in the char residue of PLA2.

■

from the ordered arrangement of β-CD on the PPG backbone was chosen to be the carbon source in the IFR system? The answers, however, could not be given until now. The current work attempts to answer this question. Initially, the carbonization mechanism of PPR was investigated by thermogravimetric analysis, scanning electronic microscopy, and Raman spectra. Then the intumescent flame retardant systems containing different carbon sources were blended with PLA resin. After that, their thermal degradation behavior and flammability properties were evaluated by thermogravimetric analysis, limiting oxygen index, UL-94 classification vertical combustion, and cone calorimeter experiments. The residues after combustion were investigated by SEM.

INTRODUCTION The intumescent flame retardancy, since reported in a U.S. patent in 1938,1 has been developed greatly in depth and scope due to its formation of large amount of thermally stable and intumescent char layer acting as a physical barrier, which effectively slows down heat and mass transfer between gas and condensed phases.2 Conventional intumescent flame retardants (IFRs) are composed of three ingredients: acid sources, carbon sources, and the blowing agents.3−8 Many works have focused on searching for new carbon sources. Among them, environmental-friendly and sustainable carbon agents are more and more popular.9−18 Cyclodextrins (CDs), a biobased product, can form inclusion complexes (ICs) with guest molecules due to their structure with the inner hydrophobic cavity and all of the free hydroxyl groups on the outer surface of the ring.19−24 Usually, the thermal stabilities of the ICs are different from that of individual CDs and guest molecules. Some researchers focused on the preparation of β-CD with flame retardant guests and discovered that the ICs containing flame retardants showed much better thermal stabilities than each ingredient.25−27 On the other hand, Song at.al reported the thermal stabilities of ICs at higher temperature could be improved by choosing aliphatic amines with longer chain.28 And they also presented some publications about thermal stability of the ICs between β-CD and poly(propylene glycol).29,30 It was found that the channel arrangements of head-to-head/tail-to-tail could enhance its endurance against the heat shock.30 It has been proved that βCD could be used as a good carbon source in the IFR system.31−33 So what would the result be if polypseudorotaxane © 2013 American Chemical Society

■

EXPERIMENTAL SECTION

Materials. Polylactic acid (PLA) was supplied by Cargill Dow. The commercial products APP (phase II, the degree of polymerization >1000) were obtained from Shandong Shi’an chemical Engineering Corp. Melamine (MA) and betacyclodexrin (β-CD) were purchased from Shanghai Chemical Reagent Corp. Poly(propylene glycol) (PPG, Mn ≈ 1000) were provided by Aladdin Chemical Reagent Corp. Polypseudorotaxane (PPR) was fabricated by the inclusion of β-CD with PPG in water according to previous literature.29,30 All Received: Revised: Accepted: Published: 3287

November 1, 2012 January 21, 2013 January 29, 2013 January 29, 2013 dx.doi.org/10.1021/ie303002b | Ind. Eng. Chem. Res. 2013, 52, 3287−3294

Industrial & Engineering Chemistry Research

Article

Table 1. Formulations of PLA Composites flame retardancy

composition (wt %)

a

sample

PLA

APP

MA

β-CD

PPR

PPG

LOI/%

UL-94 classification

pure PLA PLA1 PLA2 PLA3

100 80 80 80

0 10 10 10

0 5 5 5

0 5 0 4.25

0 0 5 0

0 0 0 0.75

20 30 34 30.5

NCa V0 V0 V0

No classification.

Figure 1. Raman spectra of the char residues of β-CD (a) and PPR (b) under nitrogen at 600 °C for 10 min.

Figure 2. SEM images of the char residues of β-CD (a) and PPR (b) under nitrogen at 600 °C for 10 min.

chemicals were dried in an oven overnight at 100 °C prior to use. Preparation of Flame Retarded PLA Composites. All of the samples were prepared on a two-roll mixing mill (Rheomixer XSS-300, Shanghai Ke Chuang China) at 180 °C, and the roll speed was maintained at 80 rpm. PLA was first added to the mill at the beginning of the blending procedure. After the melting of PLA, the intumescent flame retardants with desired amount were added, and the mixture was processed for about 15 min. The resulting samples were hot-pressed at about 180 °C under 10 MPa for 10 min into sheets with a thickness of 3.0 ± 0.1 mm for UL-94 classification and limiting oxygen index. Other samples were fabricated in the same procedure. The formulations of prepared samples are presented in Table 1. Here PLA1 with the weight ratio of APP/MA/β-CD equal to 2/1/1 has been proved to exhibit the best flame retardancy by previous researchers33 when the total weight percent of IFRs reach 20 wt %. In PLA2, PPR was used to replace β-CD. PPR, prepared according to

previous literature,29,30 has been characterized by 1H NMR measurement, and the result indicated that the host−guest stoichiometric ratio in the complex is 5:1, and therefore, the weight percent of β-CD in PPR can be calculated to be about 85.02%. Measurements. The 1H NMR spectrum was recorded with an Avance 300 Bruker spectrometer using tetramethylsilane as an internal reference and DMSO-d6 as a solvent. Thermogravimetric analysis (TGA) was carried out using a Q5000IR (TA Instruments) thermo-analyzer instrument at a linear heating rate of 10 °C/min under a nitrogen or air flow. The weight of all samples was kept within 3−10 mg in an open Pt pan and heated from room temperature to 800 °C. Scanning electron microscopy (SEM) was performed on the cross sections of the char residues using a Hitachi X650 scanning electron microscope. The specimens were previously coated with a conductive layer of gold. Limiting oxygen index (LOI) was measured according to ASTMD 2863. The apparatus used was an HC-2 oxygen index 3288

dx.doi.org/10.1021/ie303002b | Ind. Eng. Chem. Res. 2013, 52, 3287−3294


Article

meter (Jiangning Analysis Instrument Co., China). The specimens used for the test were of dimensions 100 × 6.5 × 3 mm3. The vertical test was performed on a CFZ-2 type instrument (Jiangning Analysis Instrument Co., China) according to the UL 94 test standard. The specimens used were of dimensions 130 × 13 × 3 mm3. The combustion test was performed on the cone calorimeter (FTT, UK) tests according to ISO 5660 standard procedures, with 100 × 100 × 3 mm3 specimens. Each specimen was wrapped in aluminum foil and exposed horizontally to 35 kW/ m2 external heat flux. Laser Raman spectroscopy (LRS) measurements were carried out at room temperature with a SPEX-1403 laser Raman spectrometer (SPEX Co., USA) with excitation provided in backscattering geometry by a 514.5 nm argon laser line.

Scheme 3. Mechanism of Degradation for MA/PPR System on Heating

■

RESULTS AND DISCUSSION Thermal Degradation Mechanism of PPR. There is no doubt that it is of great importance to understand the thermal against the heat shock, due to the stabilization on β-CD from complexation with PPG.29,30 In order to further investigate the detailed mechanism of this improvement, here Raman spectrum and SEM were chosen to study the ordering degree and the morphology of the char residues, respectively. Figure 1 shows the Raman spectra of the char residues of βCD (a) and PPR (b) under nitrogen at 600 °C for 10 min. There are two prominent peaks at 1364 and 1592 cm−1, which correspond to the D and G bands, respectively. The D band could be assigned to amorphous carbon and lattice defects in the char residue, whereas the G band corresponds to the firstorder scattering of the E2g mode from the sp2 carbon domains.34 The ratio of G to D band intensity is usually employed to estimate the degree of order in the char. The intensity ratio IG/ID of the char from PPR is about 0.380, higher than 0.364 of the char from β-CD, which illustrates that the inclusion complex of β-CD with PPG presents better graphitic sp2 network. Figure 2 presents the morphologies of the residue chars of βCD (a) and PPR (b) collected from nitrogen at 600 °C for 10 min. It could be observed that there are many holes on the char of β-CD. In contrast, as shown in Figure 2b, PPR just has a few holes, much less than that of β-CD, indicating that the PPR could form better char layer compared with β-CD. It has been reported that β-CD could appear intramolecular or intermolecular dehydration by heating,31,33 and there may be a similarity of dehydration for PPR containing several β-CD molecules. The suggested mechanisms for the degradation are proposed in Scheme 1. The hydroxyl groups between the neighboring β-CD molecules in PPR are easier to be dehydrated, and because of the ordered arrangement of β-CD on the PPG backbone, there appeared more effective carbonization, finally leading to the better ordered char residues. Thermal Degradation Behavior and Mechanism of the Flame Retardant Mixtures under Nitrogen Atmosphere. The thermal stabilities of the mixtures of APP/MA with β-CD or PPR or β-CD/PPG under nitrogen at a 10 °C/min heating rate are shown in Figure 3. It can be found that APP/ MA/PPR system produces 60.6% char residue at 400 °C, 44.5% at 600 °C, and 37.6% at 800 °C, respectively. In contrast, there are only 57.6% char residue at 400 °C, 37.1% at 600 °C, and

Scheme 1. Mechanism of PPR Degradation on Heating

Figure 3. TG and DTG curves of flame retardant mixtures under nitrogen.

Scheme 2. Mechanism of Degradation for APP/PPR System on Heating

degradation behavior of PPR for its use as a carbon source in the intumescent flame retardancy system. Until now, there have been some works on the investigation of thermal degradation of PPR.29,30 It has been found that PPR showed higher endurance 3289



Article

Figure 4. SEM images of the char residues of APP/MA/β-CD (a) and APP/MA/PPR (b) under nitrogen at 600 °C for 10 min.

Table 2. TGA Data of Intumescent Flame Retardant PLA Composites under Nitrogen sample

Tmax1 (°C)

Tmax2 (°C)

char (800 °C) (%)


372 286.7 276.6 283.0

363 360 360

1.6 8.6 14.0 10.7

Figure 5. Raman spectra of the char residues of flame retardant mixtures under nitrogen at 600 °C for 10 min.

Figure 8. TG and DTG curves of intumescent flame retardant PLA composites in air.

Table 3. TGA Data of Intumescent Flame Retardant PLA Composites in Air Figure 6. TG and DTG curves of flame retardant mixtures in air.

sample

Tmax1 (°C)

Tmax2 (°C)

char at 400 °C (%)

char at 600 °C (%)

char at 800 °C (%)


365.5 278.0 272.7 280.1

449.2 350.2 350.5 350.7

2.1 15.5 16.1 15.6

0 9.9 9.9 10.0

0 5.8 5.9 5.1

30.2% at 800 °C for APP/MA/β-CD system. As reported previously,29 the residual mass value of PPR at 377 °C is 26.6%, increasing by 3.4% relative to that of free β-CD; when the temperature is elevated to 477 °C, the residual mass of PPR is 18.1%, just higher 0.7% than that of free β-CD. Moreover, the residual mass value of PPR and free β-CD are nearly the same at higher temperature.29 However, the char difference values between APP/MA/PPR and APP/MA/β-CD at 377 and 477 °C are 2.6% and 2.7%, respectively, and the char difference increases to 7.4% at 600 °C and then just stop increasing with further increasing the temperature. The results illustrate that

Figure 7. TG and DTG curves of intumescent flame retardant PLA composites under nitrogen.

3290



Article

previous reports,4,31,33 the suggested mechanisms for the degradation of APP/MA/PPR system, therefore, are proposed in Scheme 2 and Scheme 3. The hydroxyl groups between the neighboring β-CD molecules in PPR could react with APP to form char, and the ordered arrangement of β-CD on the PPG backbone leads to more effective carbonization, finally leaving the more char residues. So the more char residues of the APP/ MA/β-CD/PPG system than that of APP/MA/β-CD system above 550 °C may be due to the fact that there exists a slight inclusion complexation between PPG and β-CD during the simple mechanical grinding.35,36 Figure 4 shows SEM images of the char residues of APP/ MA/β-CD and APP/MA/PPR under nitrogen at 600 °C for 10 min. As shown in Figure 4a, APP/MA/β-CD has the char residue with thin lamellar structures. In contrast, APP/MA/ PPR presents the char residue characteristic of block structures. This may be ascribed to the difference in the mechanism of dehydration and carbonization between β-CD and PPR. Raman spectra of the char residues of APP/MA/β-CD and APP/MA/PPR under nitrogen at 600 °C for 10 min are shown in Figure 5. The intensity ratio IG/ID of the char from APP/ MA/PPR is about 0.301, higher than 0.284 of the char from APP/MA/β-CD, which illustrates that the char of inclusion complex of β-CD with PPG still presents better graphitic sp2 network when catalyzed by APP/MA. Thermal Degradation Behavior of the Flame Retardant Mixtures in Air. The thermal stabilities of the mixtures of APP/MA with β-CD or PPR or β-CD/PPG in air at a 10 °C/ min heating rate are shown in Figure 6. It can be observed that the thermal degradation of all the flame retardant mixtures mainly displays a three-step degradation process over 200 °C in the temperature ranges of 200−450, 450−620, and 620−800 °C, the first process of which is mainly ascribed to the dehydration and carbonization reactions, whereas the latter two processes should be due to the thermal oxidation decomposition of the char layer. It is obvious that there are more char residues left for the APP/MA/PPR system compared to the APP/MA/β-CD system at the first decomposition stage, for instance, the char residue of the APP/MA/PPR mixture at 400 °C is 59.3%, whereas there is 56.9% remains left for the APP/ MA/β-CD system. For the degradation above 450 °C, there are more significant differences. There is an 18% reduction for the the residue of the APP/MA/β-CD system in the temperature range of 460−580 °C, and just an 11.7% decrease for the residue of the APP/MA/PPR mixture appears during this temperature range. Moreover, the temperature of the third maximum weight loss (Tmax3) of APP/MA/β-CD is 650 °C, surprisingly lower 86.5 °C than Tmax3 of APP/MA/PPR system.

Figure 9. HRR curves of intumescent flame retardant PLA composites.

Figure 10. THR curves of intumescent flame retardant PLA composites.

Table 4. Cone Date of Intumescent Flame Retardant PLA Composites sample

TTI (s)

time to PHRR (s)

PHRR (KW/m2)

THR (MJ/m2)

CO (kg/kg)

CO2 (kg/kg)


60 55 45 55

150 90 60 85

658 226 180 203

51.9 49.6 43.1 48.0

0.012 0.025 0.024 0.026

1.519 1.403 1.408 1.412

APP/MA system has more effects on the amount and thermal stability of char residues of PPR than that of free β-CD. Besides this, it needs to be noted that the temperature of the first maximum weight loss (Tmax1) of APP/MA/PPR system decreases by 5.5 °C compared with 289.1 °C of the APP/ MA/β-CD system, contrary to the reported works.29,30 This is possibly because the ordered arrangement of β-CD on the PPG backbone promotes the earlier weight loss of the β-CD in the presence of APP/MA. Based on the combination with the

Figure 11. SEM images of the char residues of the composites: PLA1 (a) and PLA2 (b). 3291



Article

(which contains 20 wt % APP/MA/β-CD/PPG with a weight ratio of 2/1/0.85/0.15), without the beforehand inclusion complexation of β-CD with PPG, presents a little higher LOI value relative to that of PLA1, which may result from the slight inclusion complexation of β-CD with PPG during the melt blending. Measurement of LOI is an easy and useful, small-scale test that ranks flame retardancy in polymers; it is, however, not a reliable indicator of how a material will perform in a real fire. The best method for this is the cone calorimeter, first introduced in 1982 and then developed to predict the flammability behavior of materials in real fire scenarios due to its good correlation with real fire disasters.37 From a cone calorimeter, one can obtain several key parameters like heat release rate (HRR), total heat release (THR), and peak HRR (PHRR), which could be employed to evaluate the developing, spreading, and intensity of fires. Besides, the yields of CO2 and CO can be obtained as well. HRR and THR curves of intumescent flame retardant PLA composites are displayed in Figures 9 and 10, respectively, and the corresponding cone data are shown in Table 4. Pure PLA resin burns very fast once ignited and a sharp PHRR appeared at 658 KW/m2. When 20 wt % IFR was added, the PHRRs of all three flame retardant PLA resins decrease sharply by 1.9−2.7 times and there appear the board HRRs. Among the flame retardant PLA resins, their PHRR values present just slight differences not to assess which one is better considering about 10% deviations. Their differences in THR values, however, are much higher. For example, THR of PLA2 is 43.1 MJ/m2, which is obviously lower than those of other samples. These results indicate that the addition of IFRs can make PLA material much safer in a fire and that inclusion complex of β-CD with PPG may be more effective on the reduction of THR than the individual β-CD. As shown in Table 4, the addition of intumescent flame retardants decreases the release amount of carbon dioxide, but increases the escape of the poisonous CO gas, possibly due to the incomplete combustion of flame retardant PLA composites. Besides, the tiny difference of various flame retardant PLA composites in the yields of CO2 and CO displays that there is little effect of various flame retardant mixtures on the yields of CO2 and CO. Morphologies of the Char Residues of the Flame Retardant PLA Composites. As known to all, the intumescent flame retardants system usually undergoes an intense expansion and protective charred layers formation; thus, the investigation of combustion residues could help to provide a better understanding of the differences in the flame retardancy among the flame retardant PLA systems. Figure 11 shows the morphologies of the residue char for PLA1 and PLA2 collected after cone calorimeter measurements. It could be observed that there are many holes on the char of PLA1 and just a few bubbles were present, indicating that they could not provide a good flame shield for the material beneath. In contrast, the char of PLA2 containing a lot of bubbles makes it clear that much better barrier for the transfer of the heat, combustible gases, and free radicals during fire is formed, which may could be why PLA2 shows lower THR.

These provide enough evidence that the APP/MA/PPR mixture displays more efficient carbonization and its char layer presents higher resistance to the thermal-oxidative degradation, which should be due to the more efficient formation of ordered char residues deriving from the ordered arrangement of β-CD on the PPG backbone. Besides, an intermediate ground of thermal-oxidative stability for APP/ MA/β-CD/PPG mixture should be due to the same reason as the higher thermal stability in nitrogen that there appears a slight inclusion complexation between PPG and β-CD during the simple mechanical grinding. Thermal Degradation Behavior of the Flame Retardant PLA Composites. As shown in Figure 7, the thermal stabilities of all the PLA/IFR systems in nitrogen are inferior to the pure PLA polymer before 380 °C, possibly due to the catalytic degradation of acid species deviating from earlier decomposition of APP on the PLA resin, which contributes to the formation of a char layer so as to improve their thermal stability. This point can be confirmed by the improvement of thermal stability of flame retardant PLA composites at higher temperature. Among all the flame retardant samples, PLA2 has 14.0% char residue at 800 °C, much higher than 8.6% char residue of PLA1 (which contains 20 wt % APP/MA/β-CD mixture with a weight ratio of 2/1/1), indicating that the inclusion complex of β-CD with PPG endows the flame retardant PLA with more char residue than β-CD or the simple mixture of β-CD with PPG above 380 °C. It needs to be noted that the temperature of the first maximum weight loss (Tmax1) of PLA2 as shown in Table 2 decreases by 10.1 °C compared with 286.7 °C of PLA1, which may be resulted from more easier degradation of PPR than free β-CD in the presence of APP/MA. Thermal degradation processes of the PLA composites in air are exhibited in Figure 8 and the corresponding data are collected in Table 3. The degradation of PLA/IFRs composites shows similar trends below 390 °C, i.e., the early degradation of IFRs in the temperature range of 250−300 °C and the catalytic decomposition of acid species on the PLA between 300−390 °C. Above 390 °C, the char residues of PLA composites display higher thermal stabilities than that of neat PLA, for example, the char residue of virgin PLA disappears just above 460 °C, whereas the flame retardant PLA composites still leave above 5.0% residues even at 800 °C. For the PLA/IFRs composites, the temperature of the first maximum weight loss (Tmax1) of PLA2 is about 272.7 °C, lowest among these flame retardant composites, which is the same trend as the degradation of PLA composites in nitrogen. Furthermore, PLA2 has a slightly higher char residue than PLA1 in the temperature range of 380−580 °C. Except these, there are no obvious differences in the thermal oxidation degradation of PLA/IFRs composites. This is quite contrary to the TGA results in nitrogen, and the reason may be because the participation of oxygen in thermal degradation of the flame retardant PLA significantly reduces their differences. Combustion Behavior of the Flame Retardant PLA Composites. The LOI values and the results of UL-94 flame classification of the intumescent flame retardant PLA composites are given in Table 1. Pure PLA exhibits a LOI value of 20.0% and is not classified in the test of UL-94 flame classification. When 20 wt % IFR (APP/MA/β-CD = 2/1/1) is added, the LOI value goes up to 30.0% and passes the V0 rating. While PPR is employed to replace the β-CD, there is a further rise by 4.0% for the LOI value of PLA2, and PLA3

■

CONCLUSION Novel intumescent flame retardant systems had been physically mixed and well characterized by TGA, SEM, and Raman spectra. PPR exhibited more effective carbonization and higher 3292



Article

degree of graphitic network than that of free β-CD. Moreover, the thermal stability of APP/MA/PPR mixture was highest of all the intumescent flame retardant systems no matter what the test was performed in nitrogen or in air. The mechanism was presented and discussed. The APP/MA/PPR systems displayed higher efficiency in enhancing char formation ability and flame retardant properties of PLA. TGA showed that PLA containing APP/MA/PPR had the most char residue in nitrogen and still had the highest char residue in the temperature range of 380− 580 °C in air although just a slight improvement appeared. The higher LOI% value and lower THR of PLA2 using PPR as a carbon source may reveal that it presents more excellent flame retardance. Besides, the existence of more bubbles in the char residue from PLA2 was observed from the SEM image.

■

(10) Nie, S. B.; Hu, Y.; Song, L.; He, Q. L.; Yang, D. D.; Chen, H. Synergistic effect between a char forming agent (CFA) and micro encapsulated ammonium polyphosphate on the thermal and flame retardant properties of polypropylene. Polym. Advan. Technol. 2008, 19, 1077−1083. (11) Yang, G. Z.; Chen, X. L.; Wang, L. M.; Shi, J. G.; Li, C. Z.; Liu, T. X. Synthesis and characterization of fluorene-based rod-coil liquid crystal polymers. Polym. Advan. Technol. 2009, 20, 104−110. (12) Li, B.; Sun, C. Y.; Zhang, X. C. An investigation of flammability of intumescent flame retardant polyethylene containing starch by using cone calorimeter. Chem. J. Chin. U. 1999, 20, 146−149. (13) Nie, S. B.; Song, L.; Guo, Y. Q.; Wu, K.; Xing, W. Y.; Lu, H. D.; Hu, Y. Intumescent Flame Retardation of Starch Containing Polypropylene Semibiocomposites: Flame Retardancy and Thermal Degradation. Ind. Eng. Chem. Res. 2009, 48, 10751−10758. (14) Reti, C.; Casetta, M.; Duquesne, S.; Delobel, R.; Soulestin, J.; Bourbigot, S. Intumescent Biobased-Polylactide Films to Flame Retard Nonwovens. J. Eng. Fiber. Fabr. 2009, 4, 33−39. (15) Wu, K.; Hu, Y.; Song, L.; Lu, H. D.; Wang, Z. Z. Flame Retardancy and Thermal Degradation of Intumescent Flame Retardant Starch-Based Biodegradable Composites. Ind. Eng. Chem. Res. 2009, 48, 3150−3157. (16) Horrocks, A. R.; Zhang, S. Enhancing polymer flame retardancy by reaction with phosphorylated polyols. Part 2. Cellulose treated with a phosphonium salt urea condensate (Proban CC9) flame retardant. Fire. Mater 2002, 26, 173−182. (17) Anna, P.; Zimonyi, E.; Marton, A.; Szep, A.; Matko, S.; Keszei, S.; Bertalan, G.; Marosi, G. Surface treated cellulose fibres in flame retarded PP composites. Macromol. Symp. 2003, 202, 245−254. (18) Li, S. M.; Ren, J.; Yuan, H.; Yu, T.; Yuan, W. Z. Influence of ammonium polyphosphate on the flame retardancy and mechanical properties of ramie fiber-reinforced poly(lactic acid) biocomposites. Polym. Int. 2010, 59, 242−248. (19) Szejtli, J. Introduction and general overview of cyclodextrin chemistry. Chem. Rev. 1998, 98, 1743−1753. (20) Wang, H. M.; Song, L. X. A good linear relationship between the logarithms of formation constants and the stabilization energies of alpha- and beta-cyclodextrin complexes of several phenol and benzoic derivatives. Chem. Lett. 2007, 36, 596−597. (21) Song, L. X.; Wang, H. M.; Xu, P.; Zhang, Z. Q.; Liu, Q. Q. Formation, structure, and stability of alpha- and beta-cyclodextrin inclusion complexes of phenol and benzoic acid derivatives in vacuo and in water. Bull. Chem. Soc. Jpn. 2007, 80, 2313−2322. (22) Hapiot, F.; Tilloy, S.; Monflier, E. Cyclodextrins as supramolecular hosts for organometallic complexes. Chem. Rev. 2006, 106, 767−781. (23) Song, L. X.; Wang, H. M.; Xu, P.; Yang, Y.; Zhang, Z. Q. Experimental and theoretical studies on the inclusion complexation of syringic acid with alpha-, beta-, gamma- and heptakis(2,6-di-Omethyl)-beta-cyclodextrin. Chem. Pharm. Bull. 2008, 56, 468−474. (24) Matsui, Y.; Ono, M.; Tokunaga, S. NMR spectroscopy of cyclodextrin-inorganic anion systems. Bull. Chem. Soc. Jpn. 1997, 70, 535−541. (25) Huang, L.; Gerber, M.; Lu, J.; Tonelli, A. E. Formation of a flame retardant-cyclodextrin inclusion compound and its application as a flame retardant for poly(ethylene terephthalate). Polym. Degrad. Stab. 2001, 71, 279−284. (26) Huang, L.; Allen, E.; Tonelli, A. E. Inclusion compounds formed between cyclodextrins and nylon 6. Polymer 1999, 40, 3211−3221. (27) Alongi, J.; Poskovic, M.; Frache, A.; Trotta, F. Novel flame retardants containing cyclodextrin nanosponges and phosphorus compounds to enhance EVA combustion properties. Polym. Degrad. Stab. 2010, 95, 2093−2100. (28) Song, L. X.; Teng, C. F.; Wang, H. M.; Bai, L. Preparation and spectroscopic study of different stoichiometric solid supromolecular inclusion complexes of beta-cyclodextrin with short chain aliphatic amines. Chin. J. Chem. Phys. 2008, 21, 174−180.

AUTHOR INFORMATION

Corresponding Author

*Fax/Tel: +86-551-3601664. E-mail: (Y.H.) [email protected]. cn; (W.X.) [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The work was financially supported by National Basic Research Program of China (973 Program; 2012CB719701), National Natural Science Foundation of China (Nos. 51036007 and 51203146), China Postdoctoral Science Foundation (2012M511418), and the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials (No. 11ZXFK12).

■

REFERENCES

(1) Tramm H.; Clar C.; Kuhnel P.; Schuff W. Fireproofing of Wood. U.S. Patent No. 2106938, 1935. (2) Bourbigot, S.; LeBras, M.; Delobel, R.; Breant, P.; Tremillon, J. M. 4A zeolite synergistic agent in new flame retardant intumescent formulations of polyethylenic polymers - Study of the effect of the constituent monomers. Polym. Degrad. Stab. 1996, 54, 275−287. (3) Camino, G.; Costa, L.; Trossarelli, L. Study of the Mechanism of Intumescence in Fire Retardant Polymers 1. Thermal-Degradation of Ammonium Polyphosphate Pentaerythritol Mixtures. Polym. Degrad. Stab. 1984, 6, 243−252. (4) Camino, G.; Costa, L.; Trossarelli, L. Study of the Mechanism of Intumescence in Fire Retardant Polymers 3. Effect of Urea on the Ammonium Polyphosphate Pentaerythritol System. Polym. Degrad. Stab. 1984, 7, 221−229. (5) Camino, G.; Costa, L.; Trossarelli, L.; Costanzi, F.; Landoni, G. Study of the Mechanism of Intumescence in Fire Retardant Polymers 4. Evidence of Ester Formation in Ammonium Polyphosphate Pentaerythritol Mixtures. Polym. Degrad. Stab. 1984, 8, 13−22. (6) Camino, G.; Costa, L.; Trossarelli, L.; Costanzi, F.; Pagliari, A. Study of the Mechanism of Intumescence in Fire Retardant Polymers 6. Mechanism of Ester Formation in Ammonium Polyphosphate Pentaerythritol Mixtures. Polym. Degrad. Stab. 1985, 12, 213−228. (7) Riva, A.; Camino, G.; Fomperie, L.; Amigouet, P. Fire retardant mechanism in intumescent ethylene vinyl acetate compositions. Polym. Degrad. Stab. 2003, 82, 341−346. (8) Bourbigot, S.; Lebras, M.; Delobel, R. Carbonization Mechanisms Resulting from Intumescence Association with the Ammonium Polyphosphate-Pentaerythritol Fire-Retardant System. Carbon 1993, 31, 1219−1230. (9) Wang, H. F.; Li, B. Synergistic effects of beta-cyclodextrin containing silicone oligomer on intumescent flame retardant polypropylene system. Polym. Advan. Technol. 2010, 21, 691−697. 3293



Article

(29) Song, L. X.; Guo, X. Q.; Du, F. Y.; Bai, L. Thermal degradation comparison of polypropylene glycol and its complex with betacyclodextrin. Polym. Degrad. Stab. 2010, 95, 508−515. (30) Guo, X. Q.; Song, L. X.; Dang, Z.; Du, F. Y. A Comparative Study on the Formation and Spectral Properties of the Polypseudorotaxanes of beta-Cyclodextrin and Poly(propylene glycol) under Different Conditions. Bull. Chem. Soc. Jpn. 2009, 82, 1209−1213. (31) Trotta, F.; Zanetti, M.; Camino, G. Thermal degradation of cyclodextrins. Polym. Degrad. Stab. 2000, 69, 373−379. (32) Huang, L.; Gerber, M.; Taylor, H.; Lu, J.; Tapaszi, E.; Wutkowski, M.; Hill, M.; Lewis, C.; Harvey, A.; Herndon, A.; Wei, M.; Rusa, C. C.; Tonelli, A. E. Creation of novel polymer materials by processing with inclusion compounds. Macromol. Symp. 2001, 176, 129−144. (33) Feng, J. X.; Su, S. P.; Zhu, J. An intumescent flame retardant system using beta-cyclodextrin as a carbon source in polylactic acid (PLA). Polym. Advan. Technol. 2011, 22, 1115−1122. (34) Kudin, K. N.; Ozbas, B.; Schniepp, H. C.; Prud’homme, R. K.; Aksay, I. A.; Car, R. Raman spectra of graphite oxide and functionalized graphene sheets. Nano Lett. 2008, 8, 36−41. (35) Alongi, J.; Poskovic, M.; Frache, A.; Trotta, F. Role of betacyclodextrin nanosponges in polypropylene photooxidation. Carbohyd. Polym. 2011, 86, 127−135. (36) Alongi, J.; Poskovic, M.; Visakh, P. M.; Frache, A.; Malucelli, G. Cyclodextrin nanosponges as novel green flame retardants for PP, LLDPE and PA6. Carbohyd. Polym. 2012, 88, 1387−1394. (37) Price, D.; Bullett, K. J.; Cunliffe, L. K.; Hull, T. R.; Milnes, G. J.; Ebdon, J. R.; Hunt, B. J.; Joseph, P. Cone calorimetry studies of polymer systems flame retarded by chemically bonded phosphorus. Polym. Degrad. Stab. 2005, 88, 74−79.

3294


Comparative Study on the Effect of Beta-Cyclodextrin and

Recommend Documents