Formulation of Intumescent Flame Retardant Coatings Containing

Feb 27, 2015 - ... flame retardant formulations as blowing agent and carbon source. ... In addition, the smoke release of TS-IFRCs was also studied, w...
5 downloads 0 Views 3MB Size
Download PDF
Article pubs.acs.org/JAFC

Formulation of Intumescent Flame Retardant Coatings Containing Natural-Based Tea Saponin Wei Qian,†,§ Xiang-Zhou Li,*,†,‡ Zhi-Ping Wu,† Yan-Xin Liu,†,# Cong-Cong Fang,⊥ and Wei MengΔ †

School of Materials Science and Engineering, Central South University of Forestry and Technology, Changsha 410004, Hunan, People’s Republic of China ‡ State Key Laboratory of Ecological Applied Technology in Forest Area of South China, Changsha 410004, Hunan, People’s Republic of China § Guangdong Vocational College of Environmental Protection Engineering, Foshan 528216, Guangdong, People’s Republic of China # School of Chemistry and Bioengineering, Changsha University of Science and Technology, Changsha 410114, Hunan, People’s Republic of China ⊥ Business School, Central South University of Forestry and Technology, Changsha 410004, Hunan, People’s Republic of China Δ School of Chemistry and Environment Engineering, Hunan City University, Yiyang 413000, Hunan, People’s Republic of China ABSTRACT: Natural product tea saponin (TS), extracted from the nutshell of camellia (Camellia oleifera Abel, Theaceae), was introduced into intumescent flame retardant formulations as blowing agent and carbon source. The formulations of the flame retardant system were optimized to get the optimum proportion of TS, and intumescent flame retardant coatings containing tea saponin (TS-IFRCs) were then prepared. It was found that TS can significantly affect the combustion behavior and the thermal stability of TS-IFRCs evaluated by cone calorimetry and simultaneous thermal analyzer, respectively. It was shown that TS, degraded to water vapor and carbon at high temperatures, can combine with other components to form a well-developed char layer. The char layer was supposed to inhibit erosion upon exposure to heat and oxygen and enhance the flame retardancy of TSIFRCs. In addition, the smoke release of TS-IFRCs was also studied, which provided a low amount of smoke production. KEYWORDS: tea saponin, intumescent flame retardant coatings, formulation, flame retardancy, thermal analysis

■

hydrophobins15) as novel green flame retardants for cotton fabrics was recently proposed by Jenny Alongi and her group. In addition, chitosan, a biobased carbohydrate, can act as both carbon source and foaming agent in the flame retardant coatings for polyester−cotton fabrics;4furthermore, biobased chitin derivatives can be used in flame retardant biobased coatings of cotton fabrics,16 and starch and lignin are applied in intumescent PLA for flame retardance.17 Tea saponin (TS), an important class of natural byproduct from processed camellia, is extracted from Camellia oleifera seeds or C. oleifera cakes (about 10−15% content of TS) by using ultrasound, supercritical carbon dioxide, and solvent, with widely different yields of about 7−96%.18,19 Tea saponins comprise a family of natural compounds with the structure of a pentacyclic triterpene as shown in Figure 120,21 and have many biological activities.22−24 TS is also a natural nonionic surfactant, which can be easily transformed into nontoxic compounds by enzymolysis, and is free of pollution to the environment. Also, TS can be used as the blowing agent of foam rubber and foam fire extinguishers to produce aerated concrete and fiberboard due to its strong absorption properties of CO2.25 In this study TS is used to substitute for melamine as blowing agent and carbon source in intumescent flame

INTRODUCTION Intumescent flame retardant coating technology had been commonly used in material science for providing an efficient flame retardancy to matrix material formulations including steels,1 woods,2,3 and polymers4 in the past several decades. Usually, the intumescent flame retardant coatings, mainly consisting of resin matrix and flame retardant components, that is, an acid source, a carbon source (or char forming agent), and a gas source (or a blowing agent),5 can expand upon contact with fire or at a high temperature to form various spongiform porous structure char layers to effectively isolate heat and oxygen as a barrier and exhibit outstanding efficiency of heat and flame resistance.1,6,7 Typically, traditional intumescent flame retardants in intumescent flame retardant coatings consist of ammonium polyphosphate (APP), pentaerythritol (PER), and melamine (MEL).2,8 However, with the ever-increasing environmental protection awareness, some additives with a potential pollution risk such as melamine, halogens, and halogen derivatives are not welcomed to be applied in coatings. In recent years the invention of green flame retardant technology has caught the eye of people and researchers significantly. Green carbohydrate has been used in flame retardant technology, such as the study of cyclodextrin nanosponges as novel green flame retardants for PP, LLDPE, PA6,9 and EVA,10 and β-cyclodextrin as a char source of flame retardant system in polylactic acid (PLA)11 and low-density polyethylene (LDPE)-based formulations12 was demonstrated. Also, the use of DNA13 or protein (whey protein,14 caseins, and © 2015 American Chemical Society

Received: Revised: Accepted: Published: 2782

December 5, 2014 February 25, 2015 February 27, 2015 February 27, 2015 DOI: 10.1021/jf505898d J. Agric. Food Chem. 2015, 63, 2782−2788

Journal of Agricultural and Food Chemistry

Article

representative, many screening experiments were also conducted on the basis of previously studied works26,27 to determine the weight ratio among APP:PER:MEL of MEL-IFRC to be 12:7:1.5 or 24:14:3. In this case, the comparison showed good flame retardancy. Residue and Expansion Rate Measurement. Residue and expansion rate of the TS-IFRCs with various contents of TS were measured to determine the best formulation of the TS-IFRCs. Liquid flame retardant coatings were poured into the mold and cured at 23 ± 2 °C for 15 days in a ventilated environment. The samples for the test were prepared by cutting cured coatings into pieces of the size of 30 mm × 10 mm × 3 mm (about 1.5 g, accurate to 0.1 mg). Then the samples were placed in an SX-12-10 type box resistance furnace at a constant temperature of 400 °C for 10 min to measure the residue (g carbon/g sample) and expansion rate (mL/g). The residue and expansion rate of coatings were calculated according to the following formulas, respectively.

Figure 1. Chemical structural formula of tea saponin.

retardant systems. Using TS in intumescent flame retardant coatings could provide a new idea for the research and development of green flame retardant coatings as well as open up new avenues for its utilization. On the other hand, there could be a potential application and economic prospect of TSIFRCs because TS has the advantages of being rich, renewable, biodegradable, and environmentally friendly. The coatings were formulated based on TS, APP, and PER. The flame retardant properties of TS-IFRCs were evaluated by limited oxygen index (LOI), smoke density (SDR), and ignition temperature (IT), and the combustion characteristics of TS-IFRCs were tested by cone calorimetry (CONE). Thermal analysis and scanning electron microscopy observations were also conducted.

■

residue =

wt of carbon residue after heating (G2) wt of sample (G1)

expansion rate =

vol changes before and after heating (ΔV ) wt of sample (G1)

Flame Retardancy and Smoke Suppression Tests. The effect of TS on flame retardancy and smoke suppression in the TS-IFRCs was evaluated by means of limiting oxygen index (LOI), ignition temperature (IT), and smoke density measurement (SD). The test samples were prepared in the same way of painting the liquid TSIFRCs on three-layer plywood twice; the coated plates were dried at 23 ± 2 °C for 15 days in a ventilated environment. The coated weight was about 500 g/m2, and total thickness of dry film was 1 mm. The LOI tests of the coated plates (140 mm × 6.5 mm × 3 mm) were performed by a JF-3 type oxygen index apparatus (ISO 4589 standard). A JCY-1 material smoke density tester was employed to measure smoke density (coated plates, 30 mm × 30 mm × 3 mm). The ignition temperature was tested on a DW-02 ignition temperature tester (curing coating after crushing and sieving, D = 0.5−1.0 mm). Analysis of Cone Calorimetry. The combustion behavior of the coated plates (wood boards, 100 mm × 100 mm × 10 mm, coated 500 g/m2) was investigated by cone calorimetry according to the ISO 5660-1 standard. The test samples were prepared in a similar way as above with regard to painting the liquid TS-IFRCs on wood boards twice; the coated plates were dried at 23 ± 2 °C for 15 days in a ventilated environment. The coated weight was about 500 g/m2, and total thickness of dry film was 1 mm. The test coated plates were heated after being wrapped in aluminum foil with the upper surface exposed. The measurements were conducted for three replicates per sample under an irradiative heat flow of 50 kW/m2 horizontally, following the procedure described by Alongi.9,28 Parameters such as total heat release (THR, kW/m2), heat release rate (HRR, kW/m2), effective heat of combustion (EHC, kJ/kg), mass loss rate (MLR, g/s), and total smoke release (TSR, m2/m2) were measured. For comparisons, the plates were coated with alkyd varnish and MEL-

MATERIALS AND METHODS

Materials. Ammonium polyphosphate (APP, n > 1000, industrial) was provided by Zhejiang Longyou Gede Chemical Corp. Alkyd varnish (commercial product), with a medium oil length and solid content of 48.26%, was produced by Hunan Xiangjiang Coating Group. Pentaerythritol (PER, AR) was provided by Kermel Tianjin Chemical Reagent Development Center. Tea saponin (TS, industrial) is a kind of saponin mixture extracted from C. oleifera cake, and the content of TS is approximately 60%. Melamine (MEL, CP) was produced by Sinopharm Chemical Reagent Co., Ltd. Three-layer plywood and wood board (Chinese fir) were used as substrates for painting. Preparation of TS-IFRCs. The TS-IFRCs were prepared by compounding intumescent flame retardants containing APP, PER, and TS (with weight ratios of 15:4:1, 15:7:3, and 15:7:1, respectively) with alkyd varnish; the weight ratio of intumescent flame retardants and alkyd varnish was 3:2. Dispersing agents and other additives were also introduced to improve the overall properties of the coatings. Figure 2 shows the preparation process of TS-IFRCs. In addition, the traditional intumescent flame retardant coatings containing melamine (MEL-IFRC) were selected as a comparison. To make the comparison

Figure 2. Process flow of the preparation of TS-IFRCs. 2783

DOI: 10.1021/jf505898d J. Agric. Food Chem. 2015, 63, 2782−2788

Journal of Agricultural and Food Chemistry

Article

second stage ranging from 276 to 392 °C, the serious weight loss stage was monitored with a weight loss of 31.6%. At this stage APP, TS, PER, and alkyd resin pyrolyzed severely, and a large amount of gas was generated to form a rich intumescent char layer with catalysis by APP, hindering the decomposition of the TS-IFRCs. The temperature of the third thermal degradation stage was from 392 to 600 °C, and the weight loss was 13.3%. On the other hand, the thermal degradation curves of TS-IFRCs were basically consistent with the curves of MELIFRC, whereas the weight loss rate was lower than that of MEL-IFRC; the residue weight of TS-IFRCs during the degradation process was obviously higher than that of MELIFRC, and the final weight residual was 39.0%, much higher than the 31.1% of MEL-IFRC and 11.1% of alkyd resin, which indicated that TS combined with other components had a good influence on thermostability. The thermal degradation was weakened, and the carbon residue and thermal stability of the flame retardant coatings were improved effectively. DSC curves in Figure 3b revealed that there are mainly two endothermic regions and two exothermic regions during the whole degradation process. At the first endothermic region of the temperature ranging from 160 to 200 °C, there was a sharp endothermic peak at 189 °C, which can be interpreted as the amount of heat needed to be concentrated for the preliminary decomposition of volatile substance released from TS-IFRCs. The temperature ranging from 200 to 320 °C was the second endothermic region, in which there were three small continuous endothermic peaks at temperatures of 245, 300, and 323 °C, respectively. At this region, the TS-IFRCs system continued to absorb heat to concentrate energy for the decomposition of TS-IFRCs and charring, which corresponded to early in the second stage of thermal degradation. Although with the temperature increasing, the flame retardant coating system was decomposed, a lot of heat was released to form the first exothermic region from 330 to 380 °C with a sharp exothermic peak at 349 °C. The second exothermic region was around the temperature of 444 °C, with a wide exothermic peak, owing to the continuous heat released from the decomposition of flame retardant intumescent char layer with the temperature increasing, which corresponds with the third stage of thermal degradation. On the other hand, at the high temperature of 587 °C, it is evident that there was also a sharp endothermic peak, which may be interpreted as a phase change occurring for a sublimation of residue char within a large amount of heat. Compared with the heat release process of the MEL-IFRC, the endothermic peak at 253 °C and the exothermic peak at 358 °C of TS-IFRCs were shifted to the low-temperature area, which was beneficial to the formation of intumescent char layer at low temperature. Furthermore, during the thermal decomposition process, the levels of heat absorption and heat release of TS-IFRCs were larger than those of alkyd resin, but were significantly smaller than those of MEL-IFRC. It was demonstrated that TS-IFRCs had less dependence on heat demand or contribution from outside, which was conducive to slowing the rate of the pyrolysis process and was crucial to the flame retardancy of TS-IFRCs. From the above, the degradation mechanism can be simply interpreted as APP and PER having nearly no weight loss before 200 °C, whereas TS decomposed with a small weight loss of about 10% at the range from 80 to 190 °C, which mainly eliminated a lot of water vapor to retard oxygen gas and heat. Therefore, we consider this stage as a gas phase flame retardant mechanism before 200 °C. With the decomposition of TS-

IFRC with the weight ratio among APP, PER, and MEL of 24:14:3, respectively. Simultaneous Thermal Analysis of TS-IFRCs. The thermal stability of TS-IFRCs was evaluated by thermogravimetric analyses (TG) and differential scanning calorimetry (DSC) analyses using a NETZSCH STA 449 F3 Jupiter simultaneous thermal analyzer according to the ISO 11357 standard. The measurements were performed for three replicates per sample by placing the samples in open alumina pans (ca. 8.0 ± 0.5 mg) under nitrogen purge (20 cm3/ min) over the whole range of temperature from 40 to 800 °C at a heating rate of 10 °C/min. TG, DTG, and DSC analyses were obtained by using Origin Software 8.0. Scanning Electron Microscopy (SEM) Observations. SEM observations of the char layer of TS-IFRC sample after being heated at 400 °C for 10 min were performed by a FEI Quanta 450 scanning electron microscope operated at 15 kV and 200× and 1000× levels of magnification.

■

RESULTS AND DISCUSSION Thermal Analysis of TS-IFRCs. As seen from the TGDTG curves in Figure 3a, the thermal degradation process of TS-IFRCs can be broadly divided into three stages. The temperature ranging from 177 to 276 °C is the minor weight loss stage for the total weight loss of 10.4%, which may be caused by the initial thermal decomposition reaction of TSIFRCs, including the deamination of APP and dehydration of TS to generate noncombustible gas NH3 and H2O.6 In the

Figure 3. TG-DTG (a) and DSC (b) curves of TS-IFRCs. 2784

DOI: 10.1021/jf505898d J. Agric. Food Chem. 2015, 63, 2782−2788

Journal of Agricultural and Food Chemistry

Article

IFRCs, APP began to decompose at about 300 °C, eliminating ammonia and water, and interacted with PER to form the char structure, whereas TS involved a key weight loss ranging from 200 to 500 °C, eliminating water and carbon dioxide, which could blow the char formed by APP, PER, and itself to form a uniform and compact intumescent charring layer, which is effective for good thermal and oxygen blockage. We consider this stage as a condensed phase flame retardant mechanism. Effects of TS on Residue and Expansion Rate of TSIFRCs. The effects of TS on the performance of TS-IFRCs were studied by fixing the weight ratio of APP and PER in flame retardant systems of TS-IFRCs. The effects of the content of TS on residue and expansion properties of TS-IFRCs are shown in Table 1.

Table 2. Flame Retardant Performance Indices of TS-IFRCs samplea A1* A2* B1* B2* B3*

flame retardant coating formulation m(APP):m(PER):m(TS)

residue at 400 °C (g/g)

expansion rate (mL/g)

A1 A2 A3 A4 A5 B1 B2

alkyd varnish + 40% IFR (12:7:1) alkyd varnish + 40% IFR (12:7:3) alkyd varnish + 40% IFR (12:7:6) alkyd varnish + 40% IFR (12:7:9) alkyd varnish + 40% IFR (12:7:12) alkyd varnish + 40% IFR (24:14:3) alkyd varnish

0.477 0.511 0.353 0.332 0.348 0.359 0.906

12 10 9 4 6 8 3

IT (°C)

± ± ± ± ±

305 ± 2.9 310 ± 2.9 305 ± 2.9

43.8 38.8 38.6 38.0 24.2

0.06 0.12 0.06 0.12 0.12

245 ± 2.9

SDR (g/m3) 60.47 26.61 53.21 42.25 9.61

± ± ± ± ±

2.42 1.81 2.49 2.19 0.38

A1* and A2* refer to TS-IFRC plates, with the flame retardant formula APP:PER:TS = 15:4:1, 15:7:3, respectively; B1* refers to MEL-IFRC plate as a comparison, with the flame retardant formula APP:PER:MEL = 24:14:3; B2* refers to flame retardant coating plate without TS, with the flame retardant formula APP:PER:TS = 12:7:0; B3* refers to alkyd varnish coating plate as a comparison. a

proportions are quite different. When the weight ratio of APP, PER, and TS was 15:7:3 in the TS-IFRCs system, the smoke density with only 26.61 g/m3 was far lower than those of MELIFRC plate and flame retardant coating plate without TS, which greatly reduced the potential danger of the combustion of flame retardant coating plates, whereas when the weight ratio of APP, PER, and TS was 15:4:1, the smoke density was 60.47 g/m3. In addition, as seen from SEM micrographs of the outer surface of char layer of TS -IFRC plates at 200× and 1000× magnification, respectively, in Figure 4, at high temperature the

Table 1. Effects of Tea Saponin on Performance of TSIFRCs samplea

LOI (%)

B1 refers to melamine comparison, with the flame retardant formula APP:PER:MEL = 24:14:3; B2 refers to alkyd varnish comparison. a

It was shown that TS as blowing agent and carbon source with a different weight ratio in intumescent flame retardant systems can obviously affect the residue and expansion rate of coatings. For A1 and A2 with weight ratios of 12:7:1 and 12:7:3 in the TS-IFRC system, the char residues were 0.477 and 0.511 g/g, respectively, higher than the 0.359 g/g of B2, which contains MEL as blowing agent. The expansion rates of A1 and A2 (12 and 10 mL/g, respectively) were also significantly superior to those of alkyd varnishes and MEL-IFRC (B2 and B1). The well-developed intumescent char layer could decrease the destruction of gas flow and heat flow and isolate the oxygen, which was effective in retarding the tendency of the fire. However, with the weight ratio of TS increased, the residue and expansion rate of TS-IFRCs decreased. This could possibly be explained by the fact that TS was rich in carbon and hydroxyl groups; as a result, it could promote the formation of char layer during heating and release H2O, CO2, and other nonflammable gas to protect the intumescent char layer. However, when the content of TS was too high, as observed in the test, the gas released in the process of thermal decomposition was too much and resulted in the burst of the expanding bubble in char layer, so the quality of the fire retardant char layer was reduced, and, as a result, the effects of flame retardancy and heat insulation were reduced. Flame Retardant Performance Analysis of TS-IFRCs. As seen from Table 2, when a certain amount of TS was contained in the coatings, the limited oxygen index and ignition temperature were substantially improved: the LOI increased from 24.2 to 43.8%, and the ignition temperature increased from 245 to 310 °C. Compared with the MEL-IFRC plate with a LOI of 38.6%, TS-IFRC plates had some obvious advantages, and the ignition temperature was also slightly higher. It was found that the smoke densities of TS-IFRC plates of different

Figure 4. SEM micrographs of intumescent char layer of TS-IFRCs.

surface of flame retardant coating plates formed a welldeveloped intumescent char layer with a lot of expanding bubbles, and the structure of the intumescent char layer was dense and uniform, which was conductive to decreasing the thermal conductivity coefficient between the intumescent char layer and the substrate; the intumescent char layer effectively prevents oxygen flow and heat flux from eroding into the matrix. It could be explained that TS, being rich in carbon source, can cooperate with PER to play a key role in strengthening the quality of the char layer and preventing the intumescent char layer from being damaged by air flow and heat to decrease the efficiency of flame retardant coatings. Combustion Performance Analysis of TS-IFRCs. At present, the cone calorimeter test is considered to be an effective way to simulate actual fire burning behavior due to its good correlation with large-scale combustion experiments, which can accurately measure the mass loss rate, heat release rate, smoke production rate, content of toxic gases, and other parameters of materials in the event of burning. Therefore, it was not surprising that the cone calorimeter was increasingly found to be a characterization tool in the research and development of flame retardant materials internationally.29−32 Heat release rate (HRR) is an important parameter indicating the spread trends of a fire and the degree of fire 2785

DOI: 10.1021/jf505898d J. Agric. Food Chem. 2015, 63, 2782−2788

Journal of Agricultural and Food Chemistry

Article

Figure 5. Cone calorimetery test curves of TS-IFRC plates: (a) heat release rate curves; (b) total heat release curves; (c) mass residual curves; (d) total smoke release curves.

hazard. The greater the value of HRR is, the greater the degree of fire risk.33 The peak heat release rate (pk-HRR), the maximum value of HRR, determines the scale of the fire greatly.28 The heat release rate curves of different formulations of TS-IFRC plates under the thermal radiation power of 50 kW/m2 are shown in Figure 5a. Table 3 and Figure 5a show that the pk-HRR of TS-IFRC plates (190.62 kW/m2) was significantly lower than that of flame retardant coating plate without TS (227.52 kW/m2) and MEL-IFRC plate (231.57 kW/m2). At the same time, the mHRR of TS-IFRC plates was lower by 25.16 and 6.5% than those of flame retardant coating plate without TS and MELIFRC plate, respectively. It was also illustrated that there were two pk-HRR in the combustion process of the flame retardant coating plates. The first pk-HRR came almost at the time of about 25−30 s; subsequently, the HRR of TS-IFRC reduced significantly at a certain degree. Particularly after the first pkHRR, the A2* and A3* plates coated with TS-IFRCs smoldered for 55 and 165 s, respectively, the HRR of which almost decreased to 0, which successfully limited the growth of the fire. Specifically, the HRR of TS-IFRC plates was always obviously lower than those of MEL-IFRC plate and flame retardant coating plate without TS in the entire combustion process, which indicated that the addition of TS can inhibit the HRR of

TS-IFRC plates, slow the process of the combustion, and effectively reduce the risk of fire. From Table 3 and Figure 5b, it is shown that the THR values of TS-IFRC plates were much lower than those of MEL-IFRC plate and the flame retardant coating plate without TS in the entire combustion process. In addition, the THR values of A3* were reduced by 68.42 and 27.88%, respectively, compared with the alkyd varnish and flame retardant coating plate without TS, which is a key factor to control the scale and spread of the fire.31 The mean effective heats of combustion (m-EHC) of the TSIFRC plates shown in Table 3 were much superior to those of MEL-IFRC plate and flame retardant coating plate without TS. Especially, the values of A3* being 9.95 KJ/kg decreased by 33.78%, compared with that of the flame retardant coating plate without TS. It could be explained that the addition of the blowing agent (TS) played an extremely important role in making the formation of the intumescent protective char layer rapid, which successfully slowed the accumulation of the heat in the system. The mass loss of TS-IFRC plates is shown in Table 3 and Figure 5c. The mean mass loss rates (m-MLR) of A1* and A3* were slightly higher than those of MEL-IFRC plate and flame retardant coating plate without TS, but the m-MLR of the A2* 2786

DOI: 10.1021/jf505898d J. Agric. Food Chem. 2015, 63, 2782−2788

Article

was much lower than those of any other coatings, only 0.0405 g/s. Figure 5d shows that the mass residue of TS-IFRC plates was relatively higher than that of other coatings throughout the combustion process. At the time of 600 s the mass residue of A1* was 57.91%, higher than the 53.37% of MEL-IFRC plate and 53.59% of flame retardant coating plate without TS, and much higher than the 26.59% of alkyd varnish coating plate. In addition, after the combustion, the mass residue of A1* was still the highest at 33.41%, and the mass residues of the other TSIFRC plates (A2* and A3*) were also quite high at 28.17 and 28.61%, respectively. Furthermore, the properties of smoke release of TS-IFRC plates were studied by analyzing total smoke release (TSR), specific extinction area (SEA), CO yields (COY), and CO2 yields (CO2Y) collected by a cone calorimeter. The values of TSR, mean-SEA, mean-COY, and mean-CO2Y are shown in Table 3, and the total smoke release curve is described in Figure 5d. From Table 3 and Figure 5d, it was concluded that there was a big difference among the TSR values of TS-IFRC plates with different flame retardant formulations; for example, the TSR values of A1* and A2* were always lower than the values of MEL-IFRC plate and flame retardant coating plate without TS in the early stage of combustion, but the TSR value of A3* was the highest. As far as the mean-SEA was concerned, the SEA values of all TS-IFRC plates were decreased significantly, compared with those of flame retardant coating plate without TS and alkyd varnish coating plate, which indicated that TS was conducive to a small SEA value and a low smoke production of TS-IFRC plates during the combustion. In addition, the values of mean-COY and mean-CO2Y showed that the decrease of CO yields of TS-IFRC plates was not apparent; only the COY value of A1* was much less than those of the other flame retardant coating plates. The COY values of A2* and A3* were similar to that of MEL-IFRC plate, but were much higher than those of flame retardant coating plate without TS and alkyd varnish coating plate. At the same time, the CO2Y values of TSIFRC plates were approximate to each other among the flame retardant coating plates, but much lower than that of alkyd varnish coating plate, which can be explained by the incomplete combustion of TS-IFRCs, releasing more CO and less CO2. In this study, it was confirmed that the natural product tea saponin (TS) used in a dual role of blowing agent and carbon source in TS-IFRCs can play an important role in improving the flame retardancy, smoke release, and thermostability of TSIFRCs. When the weight ratio of APP, PER, and TS is 15:4− 7:1−3 for a certain addition in TS-IFRCs, the TS-IFRCs exhibited a pretty good flame retardancy, which effectively inhibited the heat release of TS-IFRC plates and reduced heat release rate, effective heat, and smoke release. Absolutely on the basis of this work, the mechanism of action of tea saponin in flame retardant coatings will be the focus of future study.

a A1*, A2*, and A3* refer to TS-IFRC plates, with the flame retardant formulas APP:PER:TS = 15:4:1, 15:7:3, 15:7:1, respectively; B1* refers to MEL-IFRC plate as a comparison, with the flame retardant formula APP:PER:MEL = 24:14:3; B2* refers to flame retardant coating plate without TS as a comparison, with the flame retardant formula APP:PER:TS = 12:7:0; B3* refers to alkyd varnish coating plate as a comparison. Cone calorimeter test was carried out at a thermal radiation power of 50 kw/m2.

0.0039 0.0017 0.0012 0.0006 0.0019 0.0015 ± ± ± ± ± ± 1.0014 1.0176 0.9145 1.0019 1.0873 1.4594 0.0013 0.0021 0.0013 0.0022 0.0025 0.0017 ± ± ± ± ± ± 0.0588 0.0782 0.0727 0.0725 0.0668 0.0406 6.50 8.19 6.24 4.43 8.54 13.37 ± ± ± ± ± ± 125.18 209.89 145.83 79.00 296.08 436.11 10.15 7.55 13.10 8.02 7.00 7.94 ± ± ± ± ± ± 337.59 302.46 397.36 363.91 313.22 197.37 0.0012 0.0005 0.0006 0.0020 0.0014 0.0009 ± ± ± ± ± ± 0.0467 0.0405 0.0442 0.0430 0.0412 0.0484 0.36 0.22 0.49 0.36 0.41 0.36 ± ± ± ± ± ± 10.75 10.87 9.95 10.84 13.31 16.05 190.62 218.37 206.94 231.57 227.52 470.62

6.23 5.09 7.55 3.61 8.61 11.14 ± ± ± ± ± ± A1* A2* A3* B1* B2* B3*

53.52 49.81 49.90 53.03 62.34 87.91

2.39 1.10 2.05 1.73 2.65 2.18

52.45 50.32 49.90 48.29 63.81 84.04

1.50 1.33 1.73 1.54 2.65 2.39 ± ± ± ± ± ± ± ± ± ± ± ±

m-EHC (kJ/kg) THR (kJ/m2) m-HRR (kW/m2) pk-HRR (kW/m2) samplea

Table 3. Combustion Performance Parameters of Cone Calorimeter Test

m-MLR (g/s)

TSR (m2/m2)

m-SEA (m2/kg)

m-COY (kg/kg)

m-CO2Y (kg/kg)

Journal of Agricultural and Food Chemistry

■

AUTHOR INFORMATION

Corresponding Author

*(X.-Z.L.) Phone: +86 073185623038. Fax: +86 073185623096. E-mail: [email protected]. Funding

The work is supported by the National Key Technology R&D Program in the 11th Five year Plan of the People’s Republic of China (2009BADB1B0303), the Program of Education and Research of Guandong Province and Ministry of Education (2011B090400333), the Program of Hunan Provincial Innovation Foundation for Postgraduate (CX2012B324), and 2787

DOI: 10.1021/jf505898d J. Agric. Food Chem. 2015, 63, 2782−2788

Journal of Agricultural and Food Chemistry

Article

(15) Alongi, J.; Carletto, R. A.; Bosco, F.; Carosio, F.; Blasio, A.; Di Cuttica, F.; Antonucci, V.; Giordano, M.; Malucelli, G. Caseins and hydrophobins as novel green flame retardants for cotton fabrics. Polym. Degrad. Stab. 2014, 99, 111−117. (16) Pan, H. F.; Wang, W.; Pan, Y.; Song, L.; Hu, Y.; Liew, K. M. Formation of self-extinguishing flame retardant biobased coating on cotton fabrics via layer-by-layer assembly of chitin derivatives. Carbohydr. Polym. 2015, 115, 516−524. (17) Réti, C.; Casetta, M.; Duquesne, S.; Bourbigot, S.; Delobel, R. Flammability properties of intumescent PLA including starch and lignin. Polym. Adv. Technol. 2008, 19, 628−635. (18) Zhou, H.; Wang, C. Z.; Chen, H. X.; Gong, K. Research progress on chemical structure and separation of theasaponin from Camellia oleifera Abel. For. Prod. Chem. Ind. 2009, 29 (10), 233−237. (19) Zhao, P.; Gao, D. F.; Xu, M.; Shi, Z. G.; Wang, D.; Yang, C. R.; Zhang, Y. J. Triterpenoid saponins from the genus Camellia. Chem. Biodivers. 2011, 8 (11), 1931−1942. (20) Yang, F.; Shi, H.; Zhang, X.; Yu, L. L. Two novel antiinflammatory 21-nordammarane saponins from tetraploid Jiaogulan (Gynostemma pentaphyllum). J. Agric. Food Chem. 2013, 61 (51), 12646−12652. (21) Song, B. L.; Shang, S. B.; Song, Z. Q.; Li, M. H. Preparation of deestered tea saponin and its properties. Biomass Chem. Eng. 2011, 45 (3), 8−10. (22) Kuo, P. C.; Lin, T. C.; Yang, C. W.; Lin, C. L.; Chen, G. F.; Huang, J. W. Bioactive saponin from tea seed pomace with inhibitory ef fects against Rhizoctonia solani. J. Agric. Food Chem. 2010, 58 (15), 8618−8622. (23) Li, S. X.; Mu, Y.; Zheng, F. Y. Influence of gastrointestinal digestion and edible plant combination on oral bioavailability of triterpene saponins, using a biomimetic digestion and absorption system and determination by HPLC. J. Agric. Food Chem. 2013, 61 (44), 10599−10603. (24) Yang, X. P.; Zhang, H. Q. Synergistic interaction of tea saponin with mancozeb against Pestalotiopsis theae. Crop Prot. 2012, 40, 126− 131. (25) Jiang, H. P.; Sun, L. F. Progress on the research fields on the extraction and application of tea saponin. Jiangxi Chem. Ind. 2003, 4, 52−57. (26) Gu, J. W.; Zhang, G. C.; Dong, S. L.; Zhang, Q. Y.; Kong, J. Study on preparation and fire-retardant mechanism analysis of intumescent flame-retardant coatings. Surf. Coat. Technol. 2007, 201, 7835−7841. (27) Shan, Y. Y.; Jiao, B. X. Exploitation of ultra-thin intumescent fireproof coating for wood structure. New Chem. Mater. 2010, 38 (7), 112−115. (28) Tata, J.; Alongi, J.; Carosio, F.; Frache, A. Optimization of the procedure to burn textile fabrics by cone calorimeter: Part I. Combustion behavior of polyester. Fire Mater. 2011, 35, 397−409. (29) Park, H. S.; Kim, D. W.; Hwang, K. H.; Yong, B. S.; Wu, J. P.; Park, J. W.; Hahm, H. S.; Im, W. B. Preparation and characterization of polyurethane flame-retardant coatings using pyrophosphoric lactonemodified polyesters/isophorone diisocyanate−isocyanurate. J. Appl. Polym. Sci. 2001, 80, 2316−2327. (30) Wang, D. Y.; Cai, X. X.; Qu, M. H.; Liu, Y.; Wang, J. S.; Wang, Y. Z. Preparation and flammability of a novel intumescent flameretardant poly(ethylene-co-vinyl acetate) system. Polym. Degrad. Stab. 2008, 80, 2186−2192. (31) Schartel, B.; Bartholmai, M.; Knoll, U. Some comments on the use of cone calorimeter data. Polym. Degrad. Stab. 2005, 88, 540−547. (32) Lorenzetti, A.; Besco, S.; Hrelja, D.; Roso, M.; Gallo, E.; Schartel, B.; Modesti, M. Phosphinates and layered silicates in charring polymers: the flame retardancy action in polyurethane foams. Polym. Degrad. Stab. 2013, 98, 2366−2374. (33) Biswal, M.; Mohanty, S.; Nayak, S. Thermal stability and flammability of banana-fiber-reinforced polypropylene nanocomposites. J. Appl. Polym. Sci. 2012, 125, 432−443.

the Program of Scientific Innovation Fund for Graduate of Central South University of Forestry and Technology (2010sx05). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We acknowledge the support of Wen-Sheng Li, from the College of Chemistry and Chemical Engineering of Hunan University, and Sheng Zhang, from the School of Materials Science and Engineering of Central South University of Forestry and Technology.

■

ABBREVIATIONS USED TS, tea saponin; APP, ammonium polyphosphate; PER, pentaerythritol; MEL, melamine; TS-IFRCs, tea saponin intumescent flame retardant coatings; MEL-IFRC, intumescent flame retardant coating containing melamine

■

REFERENCES

(1) Yew, M. C.; Ramli Sulong, N. H. Fire-resistive performance of intumescent flame-retardant coatings for steel. Mater. Design 2012, 34, 719−724. (2) Gu, J. W.; Zhang, G. C.; Dong, S. L.; Zhang, Q. Y.; Kong, J. Study on preparation and fire-retardant mechanism analysis of intumescent flame-retardant coatings. Surf. Coat. Technol. 2007, 201, 7835−7841. (3) Chou, C. S.; Lin, S. H.; Wang, C. I. Preparation and characterization of the intumescent fire retardant coating with a new flame retardant. Adv. Powder Technol. 2009, 20 (2), 169−176. (4) Carosio, F.; Alongi, J.; Malucelli, G. Layer by layer ammonium polyphosphate-based coatings for flame retardancy of polyester− cotton blends. Carbohydr. Polym. 2012, 88 (4), 1460−1469. (5) Bourbigot, S.; Le Bras, M.; Duquesne, S.; Rochery, M. Recent advances for intumescent polymers. Macromol. Mater. Eng. 2004, 289 (6), 499−511. (6) Duquesne, S.; Magnet, S.; Jama, C.; Delobel, R. Intumescent paints:fire protective coatings for metallic substrates. Surf. Coat. Technol. 2004, 180, 302−307. (7) Wang, Z. Y.; Han, E. H.; Ke, W. Influence of nano-LDHs on char formation and fire-resistant properties of flame-retardant coating. Prog. Org. Coat. 2005, 53, 29−37. (8) Ma, Z. L.; Zhao, M.; Hu, H. F.; Ding, H. T.; Zhang, J. Compatibilization of intumescent flame retardant/polypropylene composites based on α-methacrylic acid grafted polypropylene. J. Appl. Polym. Sci. 2002, 83, 3128−3132. (9) Alongi, J.; Poskovic, M.; Frache, A.; Malucelli, G. Cyclodextrin nanosponges as novel green flame retardants for PP, LLDPE and PA6. Carbohydr. Polym. 2012, 88 (4), 1387−1394. (10) 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. (11) Feng, J. X.; Su, S. P.; Zhu, J. An intumescent flame retardant system using β-cyclodextrin as a carbon source in polylactic acid (PLA). Polym. Adv. Technol. 2011, 22, 1115−1122. (12) Le Bras, M.; Bourbigot, S.; Le Tallec, Y.; Laureyns, J. Synergy in intumescence-application to β-cyclodextrin carbonisation agent in intumescent additives for fire retardant polyethylene formulations. Polym. Degrad. Stab. 1997, 56, 11−21. (13) Alongi, J.; Carletto, R. A.; Blasio, A.; Di Cuttica, F.; Carosio, F.; Bosco, F.; Malucelli, G. Intrinsic intumescent-like flame retardant properties of DNA-treated cotton fabrics. Carbohydr. Polym. 2013, 96 (1), 296−304. (14) Bosco, F.; Carletto, R. A.; Alongi, J.; Marmo, L.; Blasio, A. Di.; Malucelli, G. Thermal stability and flame resistance of cotton fabrics treated with whey proteins. Carbohydr. Polym. 2013, 94 (1), 372−377. 2788

DOI: 10.1021/jf505898d J. Agric. Food Chem. 2015, 63, 2782−2788