Preparation and properties of novel flame-retardant PBS wood-plastic composites

2.1 Experimental materials

Decayed Pinus massoniana Lamb. was collected from the Liyang Forest region in south of China. The decayed Pinus massoniana Lamb. was dried in air and crushed into 40–80 mesh. The AHP, APP, CaHP and CaCO₃ were obtained from Chemical New Materials Co., Ltd. The PBS was obtained from Zhengzhou All Stroke Chemical Products Co., Ltd.

2.2 Experimental methods

3.1 Analysis of mechanical properties

The mechanical properties of materials are a main parameter for evaluating materials, and the tensile properties are the most important criteria in mechanical properties. The mechanical properties of the material generally provide a reliable basis for material selection, structural strength calculation and stiffness. The mechanical properties of the samples were significantly changed after mixing with different proportions of rotten wood flour, CaCO₃, AHP, APP and CaHP. The test results are shown in Table 2. Compared with the samples A2 and A14, with the addition of CaCO₃, the MOR and tensile strength of the composites were obviously improved. During the test, the parallel samples of A2 showed brittle fracture, and the composites showed the characteristics of brittle materials with high strength and low toughness. It can be clearly seen that the addition of CaCO₃ makes the material transition from plastic deformation to brittle deformation. This is due to CaCO₃ can improve the rigidity of the material, limiting the molecular motion, making it into a brittle deformation. In the PBS matrix, CaCO₃ particles play a rigid skeleton role. Compared with the samples A1, A2 and A3, it can be seen that the MOR, MOE and tensile strength of the composites have different trends. Comprehensive considerations, with the increase of wood flour, the composite materials have better comprehensive mechanical properties when the wood powder filling amount of 40 copies. Too much or too little wood will affect the mechanical properties of the composites. This is mainly due to the fact that wood powder is not easy to disperse, the wood fiber has strong polarity, and it has poor compatibility with PBS resin. The increase of wood powder increases the coagulation phenomenon, and the wood powder particle is concentrated into the stress concentration. In addition, the wood powder as organic filler, low density, the volume fraction of wood powder in the system increases, the relative content of PBS decreases, the load-bearing part decreases, the tensile strength of the composites increases first and then decreases. This is because, Wood powder acts as a dispersing phase and acts as a stress concentration in the matrix, which does not deform by force and does not stop cracks or produce crazing absorption shock energy, thereby increasing the brittleness of the filling system. Thus, the brittleness of the filling system is increased.

Compared with samples A2, A4, A5 and A6, it is observed that when a small amount of AHP is added to the composite, MOR, MOE and tensile strength increased to 36.50 MPa, 1907 MPa and 16.476 MPa. This phenomenon is mainly due to the role of AHP as a flame retardant with inorganic fillers and reinforcing agents. However, adding too much AHP can make the MOR and tensile strength decreased slightly, but with the increase of AHP, the MOE increased continuously. The above phenomenon is mainly caused by the inconsistency between the PBS molecules and the limited compatibility between the AHP particles with the polymer matrix.

Compared with samples A2, A7, A8 and A9, it is observed that when a small amount of APP is added to the composite, MOR, MOE and tensile strength increased to 39.24 MPa, 2252 MPa and 16.182 MPa. Why can appear this kind of phenomenon? The main reason is the APP in the composite cooling crystallization can act as the nucleus, resulting in the formation of the final crystal ball smaller, so that the toughness is improved, MOR, MOE and tensile strength of the composite material will increased. However, The interface between the small number of APP granules and the matrix PBS has a good compatibility, but the mechanical properties of the composites will be decreased with the increase of the amount of APP. This is due to the poor compatibility and non-uniform distribution, between the excessive APP and the polymer matrix, which makes it easy to form stress concentration and become the initiation point for stress destroy. That leads to a decline in mechanical properties.

Compared with samples A2, A10, A11 and A12, it is observed that when a small amount of CaHP is added to the composite, MOR, MOE and tensile strength increased to 39.48 MPa, 2261 MPa and 15.956 MPa. This phenomenon is mainly caused by the fact that CaHP, as a kind of inorganic flame retardants and reinforcing agents can improve the mechanical properties of materials, but the poor interfacial compatibility between the excessive CaHP and PBS, and easy to cause stress concentration, so when adding too much CaHP can lead to the decreased of the mechanical properties.

3.2 Analysis of cone calorimeter

The cone calorimeter is a test method which can effectively detect the combustion behavior of materials under real combustion conditions (Cheng et al., 2012). Figs. 3 and 4, are the heat release rate (HRR) curve and the total heat release (THR) curve of the sample under the condition of the different flame retardants were added, and the relevant data of the cone calorimeter were summarized in Table 3.

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Fig. 3

Heat release rate (HRR) plots for A4, A7, A10, A13 and A14, at a heat flux of 35 kW/m².

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Fig. 4

THR for A4, A7, A10, A13 and A14, at a heat flux of 35 kW/m².

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The A14 values of A4, A7, A10, A13 and TTI materials are 36 s, 39 s, 44 s, 44 s, and 44 s, respectively, as indicated in Table 3. The addition of AHP and APP makes the ignition time advance, which is very common in many composites with flame retardants. This is mainly due to the degradation of acidic such as phosphine or small molecule products, which is produced by AHP, and catalyze the degradation of PBS molecular chain. The polymer phosphoric acid produced by APP pyrolysis can catalyze the dehydration reaction of the xylan in the wood fiber and the combustion reaction is easier to be carried out. When adding CaHP, AHP, combination of APP and CaHP three kinds of flame retardants, the ignition time did not change, noted that adding CaHP has no effect on the ignition time of the material. The three kinds of flame retardants of AHP, APP and CaHP were inhibited during decomposition, which leads to the ignition time neither delay nor advance.

Heat release rate (HRR) is one of the important parameters of flame retardant properties. It is well known that the lower the heat release rate in the material combustion process, the better the flame retardant effect of the flame retardants. As shown in Fig. 3, and Table 3, the non-flame retardant composite A14 burns rapidly after 35 kw m⁻² radiation is ignited, the highest peak of heat release rate (pk-HRR) is 332.2 kW·m⁻², the total heat release of wood-plastic composites is 137.8 MJ m⁻². However, the pHRR of composite A4, A7, A10 and A13 decreased obviously after adding flame retardants. Among them, the A13 effect of three kinds of composite materials, such as AHP, APP and CaHP, is the most obvious, and the effect of adding AHP, APP and CaHP separately is weakened in turn. Fig. 3, curve shows that there are two peaks in the composite material, which is mainly caused by the rupture of the carbon layer, which leads to 2 peaks. With the addition of AHP, APP and CaHP, the time of peak heat release rate has been advanced in varying degrees, this is the result of flame retardants promoting PBS thermal degradation, and the heat release rate curve of combustion is further widened. For A4 and A10, there are two distinct peaks of heat release rate, and AHP, CaHP thermal decomposition absorbs the surface heat, reduces the heating temperature of composites, and releases large amounts of water to dilute oxygen on the surface, reducing the peak of the first heat release rate. The degradation of pH₃ produced by the AHP in the first stage, will rapidly react with oxygen in the air to produce H₃PO₄, and in this process, a large amount of H₃PO₄ exists in coagulation. H₃PO₄ at high temperature will be further condensed to produce poly-phosphoric acid with different degree of polymerization, and also water generated. The H₃PO₄ produced by large amounts of pH₃ oxidation and hypophosphorous acid produced by dehydration can promote PBS to catalyze carbon, to inhibit the complete combustion of PBS molecular chains. The degradation of aluminum hypophosphite produces relatively stable aluminum phosphate and aluminum pyrophosphate at the same. Principle of CaHP degradation of flame retardant is consistent with AHP, and it is obvious that the flame retardant efficiency of CaHP is slightly lower than AHP. For the A7 system, the APP can produced poly-phosphoric acid at high temperature and can catalyzed some of the PBS and wood fiber into carbon, the carbon layer formed on the surface can protect the following maldi, play the role of insulation, inhibiting material combustion, reducing the rate of heat release. For the A13 system, the pHRR and THR are the smallest of the three kinds of flame retardants, such as AHP, APP and CaHP, which shows that three kinds of flame retardants have synergistic effect on reducing the pHRR and THR.

In the actual fire, more than half of the number is not burned to death, but because of smoke inhalation of toxic smoke suffocated. Therefore, combustible materials in the combustion process, the less the release of smoke, the higher the safety, the greater the probability of escape. From Figs. 5 and 6, and Table 3, can be seen in the A4 system, AHP can effectively reduce the smoke release rate and total smoke generation. However, APP and CaHP cannot effectively reduce the release rate of smoke and the total amount of smoke in A7 and A10 system, but the increase of smoke release rate and total smoke production. In the A13 system, when AHP, APP and CaHP were used in combination with three kinds of flame retardants, the smoke release rate and total smoke production is slightly lower than the A14 system but higher than the A4 system. The main reason for this phenomenon is that AHP has a high smoke suppression effect. The release rate and total smoke generation of A13 system are lower than that of A14 system. However, when AHP, APP and CaHP are used in combination, Kinds of flame retardants in the suppression of smoke between the mutual inhibition, thereby reducing the AHP smoke suppression effect. Therefore, the A13 system smoke release rate and total smoke production and slightly higher than the A4 system. In addition, in the A7 system, the initial release rate of APP in the combustion of APP was slightly higher than that of the composite without adding flame retardant, and the release rate of smoke was slightly decreased. Indicating that APP to promote the decomposition of wood fiber dehydration process produced a large number of volatile gases, the formation of carbon and inhibit the composite of the smoke emissions. However, in the combustion process, due to the decomposition of APP to produce ammonia. Not only offset the carbon layer on the inhibition of smoke, but also the rapid increase in the rate of smoke release. The addition of APP improved the total smoke release of the composites.

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Fig. 5

SPR for A4, A7, A10, A13 and A14, at a heat flux of 35 kW/m².

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Fig. 6

TSP for A4, A7, A10, A13 and A14, at a heat flux of 35 kW/m².

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As can be seen from Fig. 7, and Table 3, the residual carbon content of the sample is as follows: A13, A7, A4, A10, A14. A13 > A7 > A4 > A10 > A14 indicates that the addition of flame retardants to the PBS composite material is better than the thermal stability of the formation of the carbon layer by the combustion of the PBS composite. A7 > A4 > A10 shows that APP has a significant effect on the thermal stability of the reinforced carbon layer, followed by AHP and CaHP. At the same time, AHP, APP and CaHP three kinds of flame retardant compound system used to form the maximum amount of carbon residue.

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Fig. 7

Mass for A4, A7, A10, A13 and A14, at a heat flux of 35 kW/m².

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3.3 Analysis of FT-IR

The broad and medium intensity peak at 955 cm⁻¹ is attributed to —C—OH bending of carboxylic groups in PBS. The stretching vibration of ester carbonyl (C⚌O) groups was observed at 1718 cm⁻¹ (Kim and Kim, 2008; Muthuraj et al., 2015). The band at 1041 cm⁻¹ corresponds to the —O—C—C— stretching vibration PBS (Phua et al., 2011). Most of the saturated hydrocarbons contain methyl groups. These methyl and methylene C—H stretching bands at 2954 cm⁻¹ and an asymmetric stretching band 2855 at cm⁻¹ (Cai et al., 2013). In PBS, methyl and methylene C—H stretching bands occur at 2945 and 2855 cm⁻¹, respectively (Liu et al., 2016; Zhang et al., 2015; Song et al., 2008;). The characteristic functional group of ester linkages is —C—O—C—. A strong —C—O—C— stretching peak (1164 cm⁻¹) was observed in PBS, which confirms that the PBS contains ester linkages (Song et al., 2008; Bourbigot et al., 1993).

FT-IR spectra were used to study the structural groups of wood flour and biocomposites. For comparison, the spectra of the fourteen samples listed above are shown in Fig. 8. Peaks at 955, 806 and 644 cm⁻¹ were attributed to C—O stretching, CH₂ in OC(CH₂)₂CO in-plane bending, and —COO bending bands of the PBS (Cai et al., 2013). These peaks are clear evidence to differentiate PBS from other polymers.

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Fig. 8

FT-IR spectra of composites.

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All spectra have similar spectral patterns in addition to different intensities of infrared absorption. The main components of wood flour, including cellulose, hemicellulose, lignin, whose infrared spectra is more complex, and the most obvious peak is the stretching vibration absorption peak of 3414 cm⁻¹. The most typical bands (1600, 1510, and 1460 cm⁻¹) are represented aromatic regions of lignin (Wen et al., 2014). The composite has the characteristic peaks of PBS, In the A4, A5, A6 and A13 systems, at 817 cm⁻¹, corresponding to the oscillatory vibration peak of pH₂ and 484 cm⁻¹ is the stretching vibration peak of Al—O bond. And the absorption peak of P—O—P appeared at 1100 cm⁻¹, indicating the formation of Al₄(P₂O₇)₃ (Yang et al., 2011). In the A10, A11, A12, and A13 systems, 817 cm⁻¹ corresponds to the rocking vibration peak of pH₂, and the characteristic peak in 467 cm⁻¹ is the stretching vibration of Ca—O bond. A significant P—O—P characteristic peak appears at 1080 cm⁻¹, indicating the formation of Ca₃(PO₄)₂ and Ca₂P₂O₇.

3.4 Analysis of TG

The thermal stability of polymer materials to a large extent determine its excellent flame retardant properties, therefore, the analysis of thermal stability is also an effective way to evaluate the flame retardancy of polymer materials. In order to further study the effect of AHP, APP, CaHP and CaCO₃ on the thermal stability of PBS, we conducted a TGA test. As shown in Figs. 9 and 10, the Fig. 9, is the TGA curve under air condition, and the Fig. 10, is the DTG curve under air condition. T_5wt%, T_50wt% and T_max, respectively, for weight loss of 5 wt%, 50 wt% and maximum weight loss rate. The specific test results are listed in Table 4. It can be seen from the chart, for A1, A2, A3 system, each group TGA curve is very similar, only one weight loss platform. The curves have a long period of gentle period, and then decreased suddenly between 300 °C and 460 °C, showing a typical one-step degradation reaction and a maximum heat loss temperature of 410 °C, 407 °C, and 405 °C, respectively. It is known that with the gradual increase in temperature, the decomposition of the composite material is sufficient, the final residual carbon quality is less. According to previous studies on the degradation mechanism of PBS (Chrissafis et al., 2005). PBS decomposition mainly through the following two successive stages: (1) when the decomposition temperature is low, PBS mainly through the elimination of the completion of some segments of the random fracture, during which the quality loss is not large; (2) when the decomposition temperature is high, the fracture of the specific chain segment causes PBS to decompose into smaller molecular units, resulting in a significant reduction in the quality of the system. As shown in Figs. 9 and 10, and Table 4, with the decrease of PBS ratio, T_5wt%, T_50wt% and T_max2 decreased, respectively. Indicating that the increase in the proportion of wood powder will reduce the decomposition temperature of composite materials. Compared with A2 and A14, it was found that the degradation temperature of the composites without adding CaCO₃ was 247 °C, T_max1 and T_max2 were 216 °C and 410 °C, respectively. This is mainly due to the fact that PBS is first in the process of heating the ester bond breaks to release small molecules, followed by complete cleavage of the PBS backbone. And because of the poor thermal conductivity of CaCO₃ and the addition of a large number of powders, suppressed the heated after PBS chain segment motion, thereby improving the thermal decomposition temperature of composite materials (Min et al., 2008). And appear T_max1, may be due to the composite material without CaCO₃ and other additives, resulting in rapid degradation of wood flour at 216 °C. The initial degradation temperature of the composite material A2 is 274 °C. With the increase of AHP content from 5% to 15%, the initial degradation temperatures of composite materials A4, A5 and A6 were 270 °C, 264 °C and 263 °C. It can be seen that the initial degradation temperature of the composite material is reduced after AHP addition, which is favorable for promoting the formation of wood powder. Because of the composite type containing AHP component of relatively poor stability; At the same time, AHP degradation products can capture free radicals released from wood flour, so that wood powder decomposition time ahead and speed up the wood powder into charcoal. In addition, AHP degradation products may cause degradation of the PBS component. Compared with A1, A2, A3 system, the composite material has only one maximum T_max at 407 °C. With the increase of AHP, the composites A4, A5 and A6 had a T_max at 400 °C and 366 °C, and there is a small degradation peak at 292 °C, 291 °C and 286 °C. This is mainly caused by AHP first degradation process. With the addition of AHP, the content of residual carbon increased from 5% to 14%, 20% and 27% respectively. The degradation of the AHP under air conditions may be carried out as follows:

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Fig. 9

TGA thermal curves of composites.

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Fig. 10

DTG thermal curves of composites.

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APP thermal degradation process is divided into two steps, its initial decomposition occurs near 248 °C, releasing H₂O and NH₃, and the degradation product is highly cross-linked polyphosphoric acid. The second step pyrolysis began in 540 °C, polyphosphoric acid dehydration is decomposed into phosphorus oxide (Fang et al., 2013). Compared with A2, thermal decomposition of A8 and A9 is advanced. This is due to the thermal decomposition products of APP for the cross-linked polyphosphoric acid. It can be used as acid catalyst to promote hemicellulose, cellulose and lignin dehydration. And T_5wt% and T_50wt% of A7, increased from 274 °C and 400 °C to 303 °C and 419 °C, respectively, while APP reduced the maximum weight loss rate. This suggests that a small amount of APP can promote the formation protection of carbon layer, the gas produced by the decomposition of APP can make the carbon layer foam expansion, which play the role of heat insulation, improve material thermal stability. The amount of residual carbon increased to about 17%, shows that by adding flame retardant can greatly improve the system of the residue amount, reduced the amount of flammable gas. Contrast A2, with the increase of CaHP, With the addition of CaHP, the T_5wt%, T_50wt% and T_max of the composites all decreased first and then increased. This is mainly caused by the dual role of CaHP, phosphine produced by CaHP decomposition, which can promote the degradation of the chain by PBS. CaHP degradation produces calcium phosphate and calcium pyrophosphate, which can cover the surface of the composite material, effectively prevent the combustion zone heat and material exchange, thus delaying the degradation of PBS. It can also lead to T_5wt%, T_50wt% and T_max decline; In the oxygen atmosphere, hypophosphorous acid produced by the rapid oxidation of phosphoric acid and phosphoric acid, which can effectively promote the decomposition of PBS into charcoal. This effect can lead to T_5wt% and T_50wt%, T_max values rise. CaHP content is low, the former factors dominate, CaHP content high, the latter dominated. With the increase of CaHP, the carbon residue of composites is greatly improved. In addition to the production of calcium phosphate and calcium pyrophosphate, the amount of carbon residue derived from PBS catalyzed charcoal has been significantly improved, indicating that the P from the gas phase to the solid phase and play a catalytic role in the formation of charcoal. Contrast and A4, A7, A10 and A13, there were no apparent different effects between using flame retardants and using one flame retardant. This is mainly due to the three kinds of flame retardants have mutual inhibition in improving the thermal stability of composite materials, which greatly reduces the use of three kinds of flame retardant effect.

3.5 Analysis of XRD

X-ray diffraction can distinguish the crystallization of polymer materials by interfering phenomena, but also distinguish between different crystal forms and the addition of components in the polymer material. The X-ray diffraction pattern of the PBS composite is shown in Fig. 11.

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Fig. 11

XRD test result spectrum.

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Each sample diffraction pattern shows all three strong diffraction peak, located in the 2θ = 19.5°, near 21.9° and 22.6°, respectively, for a crystal of PBS (0 2 0), (0 2 1) and (1 1 0) crystal plane (Dong et al., 2005). The main diffraction peaks of each group were consistent, indicating that the crystal structure of PBS did not change with the increase of AHP, APP and CaHP flame retardants and CaCO₃. It is worth noting that the intensities of (0 2 0), (0 2 1) and (1 1 0) diffraction peaks decreased with the addition of additives and their contents. This phenomenon can be attributed to AHP, APP, CaHP three kinds of flame retardants and CaCO₃ content of the increase, the crystallization of PBS matrix gradually reduced. This is mainly because with the increase of AHP, APP and CaHP flame retardants and CaCO₃ content, PBS matrix crystallization is also gradually reduced. And AHP, APP, CaHP and CaCO₃ have a certain nucleation effect, improving the nucleation density of PBS matrix. At the same time, AHP, APP, CaHP and CaCO₃ occupy a certain space, ultimately make the spherical crystal growth space is limited and prone to collision, resulting in reduced crystal perfection.

3.6 Analysis of TD-GC-MS

The total ion chromatograms of five kinds of extractives were shown in Figs. 12–16, which were analyzed by GC-MS. And the relative content of each component has been counted by area normalization. The MS data is analyzed by using the NIST standard MS map and publicly published books and papers, and then identify each component.

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Fig. 12

Total ion chromatogram of A2 composites.

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Fig. 13

Total ion chromatogram of A4 composites.

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Fig. 14

Total ion chromatogram of A7 composites.

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Fig. 15

Total ion chromatogram of A10 composites.

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Fig. 16

Total ion chromatogram of A14 composites.

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According to the results of TD-GC-MS analysis, 16 chemical constituents were identified in 37 peaks of A2 volatiles. The results show that the components are: Acetic acid (1.5%, 3.669 min), 1,2-Ethanediol (0.74%, 4.109 min), Furfural (0.74%, 4.109 min), Ethanol, 1-(2-butoxyethoxy)- (0.52%, 11.264 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (0.73%, 14.084 min), Ethanol, 2-(2-butoxyethoxy)-, acetate (6.65%, 14.259 min), Propanoic acid, 2-methyl-, 3-hydroxy-2,2,4-trimethylpentyl ester (1.79%, 14.427 min), Vanillin (2.14%, 14.886 min), 1H-3a,7-Methanoazulene, 2,3,4,7,8,8a-hexahydro-3,6,8,8-tetramethyl-, [3R-(3.alpha.,3a.beta.,7.beta.,8a.alpha.)]- (1.19%, 15.132 min), Dimethyl phthalate (1.3%, 15.74 min), 1,4-Benzenedicarboxylic acid, dimethyl ester (0.55%, 16.413 min), Benzene, 1,2,3-trimethoxy-5-(2-propenyl)- (1.35%, 17.228 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (2.9%, 17.862 min), 1,1′-Biphenyl, 2,2′,5,5′-tetramethyl- (1.21%, 19.071 min), 1,1′-Biphenyl, 3,4-diethyl- (1.21%, 19.162 min), Phthalic acid, hex-3-yl isobutyl ester (40.71%, 20.164 min).

According to the results of TD-GC-MS analysis, 32 chemical constituents were identified in 75 peaks of A4 volatiles. The results show that the components are: Acetic acid (8.72%, 3.469 min), Dihydroxyacetone (1.05%, 3.896 min), Formamide, N,N-dimethyl- (3.57%, 4.614 min), Furfural (7.95%, 4.685 min), 2(5H)-Furanone (0.53%, 6.373 min), 2-Furancarboxaldehyde, 5-methyl- (0.78%, 6.994 min), Phenol (1.82%, 7.376 min), 1H-Pyrrole-2-carboxaldehyde (2.72%, 8.029 min), Dihydro-3-methylene-5-methyl-2-furanone (0.86%, 9.161 min), Nonanal (0.52%, 9.608 min), Ethanol, 2-(2-butoxyethoxy)- (2.22%, 11.218 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (3.04%, 14.065 min), Ethanol, 2-(2-butoxyethoxy)-, acetate (15.9%, 14.233 min), Propanoic acid, 2-methyl-, 3-hydroxy-2,2,4-trimethylpentyl ester (5.4%, 14.414 min), Vanillin (6.66%, 14.847 min), Dimethyl phthalate (3.14%, 15.708 min),1,4-Benzenedicarboxylic acid, dimethyl ester (0.96%, 16.393 min), 2,4-Di-tert-butylphenol (1.44%, 16.536 min), Butylated Hydroxytoluene (0.58%, 16.594 min), Benzene, 1,2,3-trimethoxy-5-(2-propenyl)- (3.46%, 17.208 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (13.44%, 17.855 min), Cedrol (3.81%, 18.062 min), 1,1′-Biphenyl, 2,2′,5,5′-tetramethyl- (3.58%, 19.065 min), 1,1′-Biphenyl, 3,4-diethyl- (3.69%, 19.155 min), 1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester (100%, 21.614 min), Phthalic acid, butyl isohexyl ester (4.86%, 22.112 min), Hexadecanoic acid, methyl ester (12.66%, 22.183 min), 7,9-Di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione (12.76%, 22.228 min), Dibutyl phthalate (11.19%, 22.694 min), Phenol, 4-methyl-2-[5-(2-thienyl)pyrazol-3-yl]- (98.6%, 25.592 min), 9-Octadecenamide, (Z)- (11.14%, 27.112 min), 3,3′,4,4′-Tetramethoxystilbene (42.11%, 27.552 min).

According to the results of TD-GC-MS analysis, 30 chemical constituents were identified in 62 peaks of A7 volatiles. The results show that the components are: Acetic acid (8.39%, 3.708 min), Furfural (8.15%, 4.679 min), Formamide, N,N-dimethyl- (3.56%, 4.801 min), 2-Furancarboxaldehyde, 5-methyl- (0.65%, 6.988 min), 2,7-Dioxatricyclo[4.4.0.0(3,8)]dec-4-ene (0.89%, 7.486 min), 1H-Pyrrole-2-carboxaldehyde (1.52%, 8.016 min), Dihydro-3-methylene-5-methyl-2-furanone (1.66%, 9.161 min), Nonanal (0.7%, 9.608 min), Ethanol, 2-(2-butoxyethoxy)- (1.32%, 11.199 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (1.81%, 14.058 min), Ethanol, 2-(2-butoxyethoxy)-, acetate (7.39%, 14.207 min), Propanoic acid, 2-methyl-, 3-hydroxy-2,2,4-trimethylpentyl ester (2.84%, 14.401 min), Vanillin (6.25%, 14.828 min), Dimethyl phthalate (2.94%, 15.695 min), 2,4-Di-tert-butylphenol (1.08%, 16.529 min), Benzene, 1,2,3-trimethoxy-5-(2-propenyl)- (3.2%, 17.196 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (7.5%, 17.842 min), Cedrol (2.17%, 18.049 min), 1,1′-Biphenyl, 2,2′,5,5′-tetramethyl- (2.41%, 19.059 min), 1,1′-Biphenyl, 3,4-diethyl- (2.7%, 19.149 min), Tetradecane, 2,6,10-trimethyl- (0.57%, 19.291 min), 1,1′-Biphenyl, 2,2′,5,5′-tetramethyl- (1.75%, 19.466 min), 1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester (100%, 21.607 min), Phthalic acid, butyl hex-3-yl ester (5.47%, 22.105 min), Hexadecanoic acid, methyl ester (11.3%, 22.17 min), 7,9-Di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione (14.87%, 22.228 min), 7,9-Di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione (0.99%, 22.306 min), Dibutyl phthalate (9.57%, 22.688 min), 1,2-Benzenedicarboxylic acid, butyl octyl ester (1.3%, 22.759 min), 2-Methyl-E,E-3,13-octadecadien-1-ol (1.42%, 24.052 min).

According to the results of TD-GC-MS analysis, 32 chemical constituents were identified in 61 peaks of A10 volatiles. The results show that the components are: Acetic acid (3.98%, 3.275 min), Formamide, N,N-dimethyl- (1.9%, 4.51 min), Furfural (6.1%, 4.672 min), Dihydro-3-methylene-5-methyl-2-furanone (0.86%, 9.135 min), Nonanal (1.32%, 9.601 min), Ethanol, 2-(2-butoxyethoxy)- (1.52%, 11.199 min), 2-Hexene, 3,4,4-trimethyl- (0.76%, 11.943 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (2.92%, 14.058 min), Ethanol, 2-(2-butoxyethoxy)-, acetate (27.5%, 14.239 min), ropanoic acid, 2-methyl-, 3-hydroxy-2,2,4-trimethylpentyl ester (7.68%, 14.407 min), Vanillin (6.99%, 14.834 min), 1H-3a,7-Methanoazulene, 2,3,4,7,8,8a-hexahydro-3,6,8,8-tetramethyl-, [3R-(3.alpha.,3a.beta.,7.beta.,8a.alpha.)]- (2.41%, 15.125 min), Dimethyl phthalate (2.91%, 15.695 min), 1,4-Benzenedicarboxylic acid, dimethyl ester(0.6%, 16.387 min), 2,4-Di-tert-butylphenol (1.37%, 16.529 min), Benzene, 1,2,3-trimethoxy-5-(2-propenyl)- (3.62%, 17.202 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (10.77%, 17.849 min), Cedrol(2.38%, 18.049 min), 1,1′-Biphenyl, 2,2′,5,5′-tetramethyl- (1.8%, 19.058 min), 1,1′-Biphenyl, 3,4-diethyl-(1.96%, 19.149 min), Tetradecane, 2,6,10-trimethyl- (0.73%, 19.285 min), 1,1′-Biphenyl, 2, 2′,5,5′-tetramethyl- (1.57%, 19.466 min), Methyl tetradecanoate (1.29%, 19.556 min), 1-Heptatriacotanol (0.61%, 21.161 min), 1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester (100%, 21.614 min), Phthalic acid, butyl hex-3-yl ester (5.15%, 22.112 min), Hexadecanoic acid, methyl ester (17.62%, 22.183 min), 7,9-Di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione (12.62%, 22.228 min), 7,9-Di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione (0.76%, 22.312 min), Dibutyl phthalate (12.42%, 22.694 min), 2-Methyl-E,E-3,13-octadecadien-1-ol (1.94%, 24.052 min), 1H-2,8a-Methanocyclopenta[a]cyclopropa[e]cyclodecen-11-one, 1a,2,5,5a,6,9,10,10a-octahydro-5,5a,6-trihydroxy-1,4-bis(hydroxymethyl)-1,7,9-trimethyl-,[1S-(1.alpha.,1a.alpha.,2.alpha.,5.beta.,5a.beta.,6.beta.,8a.alpha.,9.alpha.,10a.alpha.)]- (0.64%, 24.117 min).

According to the results of TD-GC-MS analysis, 41 chemical constituents were identified in 67 peaks of A14 volatiles. The results show that the components are: Acetic acid (3.97%, 3.197 min), Furfural (23.32%, 4.691 min), 2,4-Hexadiene, 2,5-dimethyl- (0.69%, 5.248 min), 2-Furancarboxaldehyde, 5-methyl- (2.19%, 6.975 min), Phenol (2.46%, 7.318 min), Cyclotetrasiloxane, octamethyl- (0.56%, 7.576 min), 1H-Pyrrole-2-carboxaldehyde (1%, 7.952 min), 2-Cyclopenten-1-one, 2-hydroxy-3-methyl- (1.4%, 7.997 min), Dihydro-3-methylene-5-methyl-2-furanone (9.122%, 1.15 min), Nonanal (1.9%, 9.595 min), Ethanol, 2-(2-butoxyethoxy)- (2.78%, 11.192 min), 3,4-Dimethylcyclohexanol (9.3%, 11.904 min), Sulfurous acid, cyclohexylmethyl nonyl ester (5.01%, 11.949 min), Cyclopropanemethanol, 2,2,3,3-tetramethyl- (0.61%, 12.344 min), Benzeneacetaldehyde, .alpha.-ethyl- (0.52%, 12.693 min), Formamide, N,N-dibutyl- (0.82%, 13.204 min), Ethanol, 2-(2-butoxyethoxy)-, acetate (44.53%, 14.246 min), Propanoic acid, 2-methyl-, 3-hydroxy-2,2,4-trimethylpentyl ester (1.67%, 14.394 min), Vanillin (8.7%, 14.834 min), 1H-3a,7-Methanoazulene, 2,3,4,7,8,8a-hexahydro-3,6,8,8-tetramethyl-, [3R-(3.alpha.,3a.beta.,7.beta.,8a.alpha.)]- (7.44%, 15.125 min), Dimethyl phthalate (3.85%, 15.695 min), 2,4-Di-tert-butylphenol (2.43%, 16.536 min), Butylated Hydroxytoluene (0.57%, 16.594 min), Benzene, 1,2,3-trimethoxy-5-(2-propenyl)- (23.09%, 17.215 min), 4′-Hydroxy-3′-methoxyacetophenone, isopropyl ether (1.72%, 17.719 min), 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate (15.24%, 17.849 min), 1,3,5-Triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tri-2-propenyl- (0.63%, 18.838 min), 1,1′-Biphenyl, 3,4-diethyl- (0.56%, 19.143 min), Tetradecane, 2,6,10-trimethyl- (0.86%, 19.201 min), Tetradecane, 2,6,10-trimethyl- (1.26%, 19.285 min), Methyl tetradecanoate (2.38%, 19.557 min), Tetradecane, 2,6,10-trimethyl- (2.46%, 20.676 min), 1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester (100%, 21.594 min), Phthalic acid, butyl hex-3-yl ester 3.83%, 22.099 min), Hexadecanoic acid, methyl ester(21.42%, 22.176 min), Dibutyl phthalate (6.83%, 22.681 min), 1H-2,8a-Methanocyclopenta[a]cyclopropa[e]cyclodecen-11-one, 1a,2,5,5a,6,9,10,10a-octahydro-5,5a,6-trihydroxy-1,4-bis(hydroxymethyl)-1,7,9-trimethyl-, [1S-(1.alpha.,1a.alpha.,2.alpha.,5.beta.,5a.beta.,6.beta.,8a.alpha.,9.alpha.,10a.alpha.)]- (0.62%, 23.988 min), Oleanitrile (3.64%, 24.052 min), 2-Methyl-E,E-3,13-octadecadien-1-ol (1.34%, 24.098 min), Butyl citrate (8.24%, 25.294 min), Butyl citrate (1.96%, 25.391 min).

It is suggested that the 120 °C volatiles of PBS composite included acetic acid, phenol and its derivatives, and benzene and its derivatives, which could inhibit fungal growth. But phenol, benzene, and their derivatives are toxic. In addition, there was vanillin (2.14%) in the A2 sample, vanillin (6.66%) and cedrol (3.81%) in the A4 sample, vanillin (6.25%) and cedrol (2.17%) in the A7 sample, vanillin (6.99%) in the A10 sample, vanillin (8.7%) in the A14 sample. These contents resulted in the fragrant smell of the PBS composite. The results of TD-GC-MS show that there are many hydrocarbon compounds and lipid compounds in PBS composites, and the toxic components are few. Therefore, PBS composite material is a relatively new type of green composite materials.