Polybenzoxazine Resins with Polyphosphazene Microspheres: Synthesis, Flame Retardancy, Mechanisms, and Applications.

Polyphosphazene microspheres were fabricated by ultrasonic-assisted precipitation polymerization using 4,4'-(hexafluoroisopropylidene)diphenol, 4,4'-sulfonyldiphenol, 4,4-(9-fluorenylidene)diphenol, and phenolphthalein to obtain poly[4,4'-(hexafluoroisopropylidene)diphenol]phosphazene (PZAF), poly(4,4'- sulfonyldiphenol)phosphazene (PZS), poly[4,4'-(9-fluorenylidene)diphenol]phosphazene, and poly(phenolphthalein)phosphazene (PZPT) and were incorporated into polybenzoxazines (PBa) to obtain corresponding PZAF/PBa, PZS/PBa, fluorenyl polyphosphazene (PZFP)/PBa, and PZPT/PBa composites. Addition of 5 wt % of PZAF, PZS, PZFP, and PZPT microspheres improved the thermal stability and fire retardancy of PBa resin significantly. Notably, addition of PBa with 5% PZAF led to a 62.5% decrease in the peak heat release rate and 49.3% reduction in total heat release. The role of microspheres in the gas-phase flame-retardancy mechanism in the PBa matrix was studied. Dynamic mechanical analysis results demonstrated that the T g of PBa flame-retardant composites was still around 210 °C compared to 221 °C of pure PBa. Hence, the synthesized PBa composites had potential applications as high flame-retardancy materials.

Introduction

Polybenzoxazine resins are a new type of phenolic resins, which are obtained by ring-opening polymerization. They possess excellent mechanical properties, low water absorptivity, and near-zero shrinkage behavior after polymerization.[1−4] These performances increase the scope of applications of these polymers in military, aeronautics, and astronautics, automotive, and electronics fields.[5−8] However, bisphenol A-based benzoxazine (Ba) has a low limiting oxygen index (LOI) of about 22, which restricts its application in certain fields.[9] As a result, the fire resistance properties of polybenzoxazines (PBa) have to be improved.

In the past few decades, different types of flame retardants and fire-quenching mechanisms have been introduced to reduce the high combustibility of polymeric materials.[10] It is well known that traditional halogen flame retardants produce corrosive and toxic gases and hence are not environmentally safe and sustainable.[11−13] Halogen-free flame-retardant additives have recently attracted a lot of attention from both researchers and industrialists. Common halogen-free flame retardants, which contain phosphorus, nitrogen, and silicon, have been used in epoxy resins and have proven to cause no environmental problems.[14−17] Owing to their high efficiency, phosphorus–nitrogen flame retardants have been widely used in the above systems.[18]

Polyphosphazenes, a group of multipurpose organic–inorganic hybrid materials, possess many superior properties, such as superior mechanical property, high LOI, and thermal stability.[19,20] It is well known that polyphosphazenes have been used as biomaterials, optical materials, electrical materials, hybrid materials, and so forth.[19,21] The main chain of polyphosphazenes contains −P=N– units and exhibits self-extinguishing behavior in flame tests. They can be categorized into three types: linear phosphazene polymers and polyphosphazenes-containing cyclophosphazene units in main chain or side chains.[22−24] Cyclotriphosphazenes are similar to graphene, diamond, fullerenes, and carbon nanotubes and are characterized by layered, cubical, spherical, or tubular structures.[23−25] Moreover, micro- or nanoscale polymeric materials, such as polyphosphazene nanotubes, microspheres, nanofibers, nanochains, and so forth, have also been successfully synthesized from cyclotriphosphazenes by condensation polymerization.[24,26,27] For example, in order to improve the fire performance of epoxy resins, Liu et al. synthesized a novel azaphosphorine flame retardant (ADDPP-OH) containing P–C–N bond. The LOI value of the ADDPP-OH–EP composites reached 33.7% with a rating grade of UL-94V-0. At the same time, ADDPP-OH improved the thermal and mechanical properties of EP.[28] Three polyphosphazenes with different terminal groups were applied with ammonium polyphosphate to prepare flame-retardant polylactic acid (PLA). Introduction of cyclotriphosphazene endowed PLA with good flame retardancy. However, different terminal groups of flame-retardant additives show different flame-retardancy properties.[29]

Considering the characteristics of PBa, series of polyphosphazene microspheres were synthesized by ultrasound-assisted precipitation polymerization and were introduced into ploybenzoxazines to improve their thermal stabilities and flame-retardancy properties. The effects of polyphosphazene microsphere structures on the thermal stability, flame retardancy, and thermal performance of PBa were further investigated in detail.

Results and Discussion

Characterization of Polyphosphazene Microspheres

The Fourier transform infrared (FTIR) spectra of poly[4,4′-(hexafluoroisopropylidene)diphenol]phosphazene (PZAF), poly(4,4′- sulfonyldiphenol)phosphazene (PZS), fluorenyl polyphosphazene (PZFP), and poly(phenolphthalein)phosphazene (PZPT) microspheres are shown in Figure . The small absorption peak at 1013 cm–1 is attributed to the CF3 of 4,4′-(hexafluoroisopropylidene)diphenol (BPAF). Meanwhile, the strong peaks at 1186 and 883 cm–1 correspond to the P–N and P=N characteristic absorption of cyclotriphosphazene, respectively. The intensive absorption perk at 941 cm–1 is assigned to the P–O–Ar band, which is the obvious evidence to prove the occurrence of polycondensation between comonomers hexachlorocyclotriphosphazene (HCCP) and BPAF. From the Figure b, the main sharp absorption peaks at 1293 and 1153 cm–1 are associated with O=S=O of sulfonyldiphenol units, and the vibration of C=O from phenolphthalein (PT) of carbonyl group appeared at 1770 cm–1.Otherwise, the peak of C=C (1510 cm–1), P=N (1260 cm–1), and P–O–Ar (941 cm–1) also present in the spectrum of PZS, PZFP, and PZPT indirectly verified that PZAF, PZS, PZFP, and PZPT microspheres were successfully prepared.

Figure 1

FTIR spectra of PZAF (a), PZS, PZFP, and PZPT (b) microspheres.

The scanning electron microscopy (SEM) images of microspheres are shown in Figure . The PZAF microspheres in Figure a appeared uniformly spherical with an average diameter of about 1.5 μm. Figure b–d shows spherical morphologies of PZS, PZFP, and PZPT microspheres, which had particle size distributions of around 400 nm, 2 μm, and 1.2 μm, respectively. Although they were prepared using the same procedure, the microspheres had different sizes. The larger particle size of microspheres was due to the asymmetric nature of substituents, which destroyed the regularity of molecular chains and affected the stacking of molecular chains. Moreover, the presence of multiple benzene ring substituents caused changes in the three-dimensional structure of molecular chains. The close packing of the molecular chains increased the free volume of the polymer. Finally, it is concluded that the microspheres were synthesized successfully.

Figure 2

SEM images of (a) PZAF, (b) PZS, (c) PZFP, and (d) PZPT microspheres.

Thermal Performance of PBa Composites

The thermal stabilities of PZAF/PBa and other composites were analyzed by thermogravimetric analysis (TGA) in nitrogen atmosphere. The onset degradation temperature (Tonset) and the maximum degradation temperature (Tmax) are the temperatures corresponding to 5% mass loss and maximum mass loss rate of samples, respectively. The TGA results are shown in Figure and Table . In, Figure a,b pure PBa showed only one-stage of weight loss between 350 and 450 °C in N2 and 31.5 wt % residue at 700 °C. This was mainly due to the degradation of phenols and amines in PBa chains during combustion. Introduction of PZAF into PBa caused an increase in char residue at 700 °C, which was ascribed to the random dispersion of PZAF forming a cross-linked network structure. This structure prevented the release of degradation products. Moreover, the composites displayed a two-stage decomposition pattern: the first stage between 300 and 350 °C and second stage between 400 and 500 °C. The first step is the result of breaking of PBa chains. The second step resulted mainly from the further thermal degradation of phosphate groups. However, the Tonset and Tmax values were slightly reduced because of the formation of phosphoric acid and its phosphate derivatives, which further accelerated the decomposition of PZAF/PBa composites.

Figure 3

TGA (a,c) and DTG (b,d) curves of pure PBa and its composites in nitrogen.

Table 1

Results of Thermal Analysis of PBa and Its Composites in Nitrogen

sample	Tonset (°C)	Tmax1 (°C)	Tmax2 (°C)	Residue at 700 °C (%)	aCalculated residue at 700 °C (%)
PBa	334.1	397.3		31.5
PZAF/PBa-5%	323.6	339.0	430	36.5	32.2
PZAF/PBa-10%	322.6	337.0	429	37.1	33.0
PZAF/PBa-15%	323.0	336.3	453	37.4	33.7
PZAF/PBa-20%	322.6	335.0	448	37.4	34.4
PZS/PBa-5%	325.3	382		39.2	32.8
PZFP/PBa-5%	320	385.6	404	34.1	33.7
PZPT/PBa-5%	321	339.6	422.3	40.6	33.7

Calculated residue at 700 °C = residue at 700 °C of pure PBa × amount of PBain the composite + the residue at 700 °C of microsphere × amount of PBa in the composite.

The TGA and DTG curves of other microspheres and their composites are shown in Figure c,d. The residues at 700 °C in PZS/PBa-5%, PZFP/PBa-5%, and PZPT/PBa-5% composites were 39.2, 34.1, and 40.6%, respectively, which were slightly higher than that of pure PBa. It was evident that the addition of microspheres led to better thermal stability. Interestingly, the residue at 700 °C for PZPT/PBa-5% composite was highest among all composites. Probably, the high cross-link density of PZPT microspheres increased the rigidity of the polymer, which in turn increased the thermal stability of the material. From Table , the calculated residue at 700 °C was less, compared with the actual residue at 700 °C. The blending between the microspheres and resin was not simple, and the interaction between them helped to improve the high-temperature thermal stability of the polymer. After adding microspheres, the experimental determination of the residual amount was significantly higher than the theoretical calculation, indicating that the microspheres promote PBa cross-linking char formation.[30]

Flammability Performance of PBa and Its Composites

Flammability properties of the polymers, which are very important for assessment of flammability of various materials, were determined using a cone calorimeter (CONE). Figure shows the curves for the heat release rate (HRR) and total heat release (THR) of PZAF/PBa composites. The results, including time to ignition (TTI), peak of HRR (PHRR), THR, peak smoke production rate (PSPR), and the fire growth rate index (FIGRA) are summarized in Table S1 (see the Supporting Information).

Figure 4

HRR (a) and THR (b) curves of PBa and PZAF/PBa composites in CONE test.

From Figure a, the PHRR of pure PBa was found to be 653.3 kW/m2. The PHRR value of PBa apparently decreased on the addition of PZAF. Hence, the PHRR values of PZAF/PBa-5% and PZAF/PBa-10% were 245.2 and 237.4 kW/m2, with a reduction of 62.5 and 63.7%, respectively. The PHRR values of PZAF/PBa composites decreased gradually with the increase in loading of PZAF. Generally, a lower PHRR implies better fire performance. However, the decreasing trend of PHRR became less and less obvious. In short, the fire performance of PBa composites did not always increase by increasing the content of polyphosphazene microspheres. Moreover, in Figure b, the THR of PBa composites exhibited a decreasing trend similar to that of PHRR. For example, the THR of PZAF/PBa-5% showed 24.7% reduction. The introduction of PZAF could reduce the fire hazard because PZAF acted as physical barrier, preventing the exposure of the internal material to fire. Figure S1 (see the Supporting Information) also shows a trend similar to those of PHRR and THR of PZS/PBa composites. The reduction of PHRR and THR values, considered as the factors most responsible for reducing fire hazards, are significant. This is ascribed to similarities in the bisphenol structures of BPAF and 4,4′-sulfonyldiphenol (BPS).

Furthermore, the flammability properties of other composites were also evaluated and presented in Figure . The peaks in HRR curves of all PBa composites, with 5 wt % loading of polyphosphazene microspheres, were small. The PHRR and THR values of PZAF/PBa composites with the same additive content reached a minimum value, indicating the higher fire safety of PZAF/PBa composites. This explains that the above statement on PHRR and THR values is attributed to the difference in the chain structures of the polyphosphazene microspheres. The other reason is the compatibility between the polyphosphazene microspheres and substrates. From Figure , the CO production rate (COP) and smoke production rate (SPR) of flame-retarded PBa composites were lower than that of pure one. Specially, introduction of 20 wt % PZS to PBa significantly reduces the PSPR value, which is decreased from 0.34 to 0.17 m2/s with a reduction of 50%. The reduction of COP would create conditions for safe evacuation. During the combustion process, polyphosphazene microspheres formed a carbon layer with the matrix, which hindered the transfer of heat between the interior of composite and air, thereby reducing smog of the PBa composite material.

Figure 5

HRR (a) and THR (b) curves of flame-retardant composites in CONE test.

Figure 6

COP (a,c) and SPR (b,d) curves of flame-retardant composites in CONE test.

It was evident from Table S1 that the ignition time of pure PBa resin was longer than those of the PBa composites. This was due to the rapid softening of pure PBa resin. This resulted in an increase in the distance between the burned surface and heater during the burning process, causing reduction in heating efficiency. Meanwhile, it was expected that the loading of flame retardants would increase the viscosity and thermal conductivity of the neat polymers,[31] resulting in shortening of TTI. In addition, the increased melt viscosity would also significantly reduce the HRR, which was consistent with the changes of HRR.[32] It is well known that the main purpose of a flame retardant is not to prevent the ignition of the polymer but to minimize the rate of spreading of flame and prevent or avoid sustained burning. The FIGRA, which is calculated from the ratio of PHRR/the time to PHRR, is very useful to evaluate the contribution of a material to fire[33] The FIGRA values of PBa composites were lower than that of pure PBa, which showed that incorporation of flame retardants could decrease the susceptibility of PBa resins to a fire. Compared to that of pure PBa, the maximum FIGRA value of PZAF/PBa-5% decreased from 5.03 to 1.58 kW/m2/s, indicating an excellent fire safety performance.

Analysis of Flame Retardancy Mechanism

The microspheres used in this study have good flame retardancy. Considering their properties and structures, PZAF/PBa and PZS/PBa microspheres were selected for analyzing the mechanism of their flame retardancy and dynamic thermomechanical properties.

Condensed Phase Analysis

To study the flame-retardancy mechanism, the residual chars were characterized by SEM–energy dispersive X-ray spectroscopy (EDS). Figure a–c shows the digital photographs of residues of pure PBa, PZAF/PBa-5%, and PZS/PBa-5%. In Figure a, the residual char layer showed a cracked and incomplete surface. In contrast to this, PZAF/PBa-5% and PZS/PBa-5% in Figure b,c displayed continuous, compact, and denser char surfaces. Further, SEM images of the surfaces and inner residual chars of pure PBa, PZAF/PBa-5%, and PZS/PBa-5% are shown in Figure . From Figure (a1,a2), it is seen that although pure PBa could form an internal porous structure after combustion, its carbonized layer had poor flexibility, insufficient toughness on the outer surface, and cracks or faults. This fractured carbonized layer was fragile and vulnerable to destruction and hence was less protective to CO and CO2 gases and PBa pyrolysis fragments. However, Figure (b1,c1) shows dense surfaces that provided an effective barrier to prevent the transfer of oxygen, heat, and mass between the burning zone and inner unburnt area, thereby improving the flame-retardancy performance. In Figure , (b2) shows the obturator char residues and (c2) shows the perforated char residues, which can explain the better flame retardancy of PZAF than PZS.

Figure 7

Digital photobraphs of the residual chars from (a) pure PBa, (b) PZAF/PBa-5%, and (c) PZS/PBa-5%.

Figure 8

SEM images of the residual char surfaces (a1–c1) and interior regions (a2–c2) of (a) pure PBa, (b) PZAF/PBa-5%, and (c) PZS/PBa-5%.

To further explain the contribution of PZFP in flame retardancy of benzoxazine resin, EDS was conducted, and the results are presented in Figure . All of the elements were derived from residue of PZAF/PBa-5%. Compared to inner char, the P, O, and F contents of outer residue increased slightly. The P and F elements were derived from polyphosphazene microspheres. Lower contents of P and F are ascribed to the polyphosphazene microspheres accumulating on the surface of the benzoxazine substrate to form a protective carbon layer, which blocked the entry of oxygen during the combustion process. EDS of outer char residues and inner char residues of PZS/PBa-5% was provided in Figure S2 (see the Supporting Information). Because of the change in the N content and synergistic effect between the phosphorus and nitrogen elements, PZAF is superior to the flame-retardant efficiency of PZS.

Figure 9

EDS spectra of the residues of PZAF/PBa-5%: (a) outer residue; (b) inner residue.

Gas-Phase Analysis

In order to directly distinguish the changes in peak intensities of the main pyrolysis products at different temperatures, TGA/infrared spectrometry (TG/IR) spectroscopy was employed to analyze the gases produced by PBa, PZAF/PBa-5%, and PZS/PBa-5% during their thermal degradation. In Figures and 11, PZAF/PBa-5% and PZS/PBa-5% appeared similar to pure PBa. As the thermal decomposition progressed, water and amine-containing compounds (3500–3800 cm–1), hydrocarbons (2900–3000 cm–1), CO2 (2350 cm–1), and aromatic compounds (1500–1750 cm–1), the main pyrolysis products of pure PBa, appeared.[32,34] There was an early increase in the contents of water and amine-containing compounds, methyl or methylene compounds, CO2, and aromatic compounds compared to pure material, after the incorporation of microspheres. This suggested that the microspheres played an important role in catalyzing the thermal decomposition of PBa. For a more specific comparison of pure PBa and PZFP/PBa-5% gas-phase components, the FTIR spectra of gas-phase components at different temperatures were compared in detail as shown in Figure . In addition to the common thermal degradation products mentioned above, PZAF/PBa showed a small strengthened peak at around 1214 cm–1, which is due to the −P=O bond.[35] The appearance of this peak indicated the presence of phosphate and its derivatives, which could effectively capture or terminate the free radicals in the gas phase, consequently delaying the flame propagation. This demonstrated the flame-retardancy property of PZAF.

Figure 10

3D TG-FTIR images of pyrolysis products of (a) pure PBa, (b) PZAF/PBa-5%, and (c) PZS/PBa-5%.

Figure 11

FTIR spectra of (a) pure PBa, (b) PZAF/PBa-5%, and (c) PZS/PBa-5% at their maximum degradation temperatures.

Figure 12

FTIR spectra of (A) pure PBa, (B) PZAF/PBa-5% at different temperatures.

Mechanism of Flame Retardant

As shown in Scheme , the significant reduction in the fire hazard of microspheres can be ascribed to the gas-phase and condensed-phase action. On the one hand, the cooperative catalytic carbonization effect of the microspheres retards the escape of pyrolysis volatile. On the other hand, the well-dispersed microspheres networks act as physical barrier to hinder the heat and mass transfer and the release of degradation products, inhibit toxic gases, and enhance flame retardancy.

Scheme 1

Schematic Illustration of Mechanism for Flame Retardancy of Microspheres in Flaming PBa Composites

Dynamic Thermomechanical Properties

The above analyses confirmed that the incorporation of microspheres into the composites improved the fire properties of the composites. However, the mechanical properties of polymers were expected to deteriorate while catering to the requirements of flame retardancy.[36] Thus, the thermal behaviors of the composites, such as glass transition temperature (Tg), was determined by dynamic mechanical analysis (DMA). Figures and 14 present the storage modulus (E) and loss angle tangent (tan δ) versus temperature, respectively, of pure PBa, PZAF/PBa-5%, and PZS/PBa-5%. The images also showed changes in dynamic thermomechanical properties after the introduction of microspheres into Ba resin. From Figure , the storage moduli (E) of PZAF/PBa-5% and PZS/PBa-5% were slightly higher than that of pure PBa at room temperature, whereas the E values of pure PBa increased compared to others when the temperature increased to almost Tg. It is well known that the dynamic mechanical properties of cured resins are sensitive to their chemical structures and compositions.[37] The storage modulus increased as a result of restriction in the movement of the PBa segment due to rigidity.

Figure 13

Storage moduli of the pure PBa, PZAF/PBa-5%, and PZS/PBa-5%.

Figure 14

tan δ values of pure PBa, PZAF/PBa-5%, and PZS/PBa-5%.

Generally, Tg of thermosetting resins is a crucial parameter for determining their scope of practical applications. Figure shows single peaks for PBa, PZAF/PBa-5%, and PZS/PBa-5% in the DMA spectra, with peak values of 221, 208, and 210 °C, respectively. In short, the introduction of microspheres decreased the Tg of benzoxazine polymer. This was consistent with thermal analysis results, according to which the addition of microspheres reduced the Tonset. This is ascribed to the presence of inert microspheres in PBa composites that hindered the efficiency of ring-opening curing cross-linking of Ba monomers when microspheres were introduced into Ba monomer, resulting in decreased PBa cross-link density.[38,39] The mobility of the segments increased, which caused a decrease in Tg and storage modulus. The Tg values of PZAF/PBa-5% and PZS/PBa-5% were still above 200 °C, which were higher than those of the traditional thermosetting resins. Polyphosphazene microspheres had no significant effects on the application temperature and working environment of PBa.

Conclusions

In this work, various polyphosphazene microspheres were successfully fabricated by ultrasound-assisted condensation polymerization. All four types of polyphosphazene microspheres synthesized showed good flame-retardancy properties in the PBa matrix. The polyphosphazene microspheres enhanced the char yields of PBa at 500–800 °C. Moreover, the PZAF microspheres showed better flame retardancy, compared to the other polyphosphazene microspheres. The PHRR value of PZAF/PBa-5% decreased by 62.5%, compared with pure PBa, whereas PZS/PBa-5%, PZFP/PBa-5%, and PZPT/PBa-5% showed reduction of 49.3, 55.8, and 56.6%, respectively. The study of fire retardancy mechanism revealed a synergistic flame-retardancy effect of polyphosphazene microspheres. They catalyzed the thermal degradation of PBa into char in the condensed phase and promoted the decomposition in gas phase to produce more nonflammable gases. The DMA analysis showed that the Tg of PBa composites still was sufficiently high. Based on these results, it is clear that of the synthesized polyphosphazene microspheres can potentially increase the scope of application of PBa in fire protection and other fields.

Experimental Section

Materials

BPS, HCCP, PT, and BPAF were procured by Chengdu Best Reagents Co. Ltd. (China). Acetonitrile, trimethylamine (TEA), ethanol, and acetone were purchased from Chengdu Kelong Chemical Reagent Factory (China). 4,4′-(9-Fluorenylidene)diphenol was purchased from Chengdu Point Pure Technology Co. Ltd. (China). Ba was supplied by Sichuan Tiance Jucai Technology Co. Ltd. All reagents were of analytical grade and were used directly, unless otherwise specified.

Synthesis of Polyphosphazene Microspheres

A typical protocol for the preparation of polyphosphazene microspheres involves one-step precipitation copolymerization. The representative synthesis of PZAF microspheres is shown in Scheme . HCCP (0.4 g, 1.15 mmol) and BPAF (1.16 g, 3.45 mmol) were dissolved sequentially in 100 mL of acetonitrile in a 250 mL round-bottom flask. The system was stirred ultrasonically (250 W, 40 kHz) for 10 min. Then, TEA (4 mL) was added to the above system, and the flask was sealed immediately. The stirring was continued under ultrasonication for further 4 h. Meanwhile, the temperature was maintained precisely at 50 °C. Thereafter, the resultant product was obtained by centrifugation, followed by washing sequentially thrice with anhydrous ethanol, acetone, and deionized water. Finally, the solid product was dried in a vacuum oven at 60 °C for 12 h.

Scheme 2

Route for the Synthesis of Microspheres

A similar procedure was employed for the syntheses of PZS, PZFP, and PZPT. The structures of bisphenol monomers are displayed in Figure .

Figure 15

Chemical structures of bisphenol monomers.

Preparation of PBa and Its Flame-Retardant Composites

A typical process for the preparation of the PBa composite with 5 wt % of the flame-retardant material is as follows: PZAF (4 g) was dispersed in acetone by sonication for 30 min. Then, Ba (76 g) was introduced under continuous mechanical stirring. Subsequently, acetone was removed at 60–120 °C under low pressure. Thereafter, the mixture containing PZAF and Ba was cured at 180 °C for 2 h and then at 200 °C for 2 h. After curing, the sample was cooled down to room temperature naturally. The final composite was designated as PZAF/PBa-5%. PBa flame-retardant composites were all prepared by similar procedures. PBa without the addition of polyphosphazene microspheres was prepared as the contrast sample. The ratios of PBa, PZAF, PZS, PZFP, and PZPT are all presented in Table S2 (see the Supporting Information).

Characterization

SEMs and EDS were performed on ZEISS EV0 MA15 transmission electron microscope (Carl Zeiss Micro Image Co. Ltd). TGA was performed on SDTA85e thermo-analyzer instrument (Mettler Toledo, Switzerland) under a nitrogen atmosphere at a heating rate of 20 °C/min from 40 to 800 °C. TG/IR was conducted on a PerkinElmer STA6000 thermogravimetric analyzer, which was connected to a PerkinElmer FTIR spectrophotometer through a stainless steel transfer pipe. The fire performances of PBa and its composites were evaluated by CONE tests (Fire Testing Technology, UK), according to ASTM E1354/ISO 5660 standard. Each specimen was exposed horizontally under a heat flux of 35 kW/m2. The storage moduli and tangent loss angles of materials were investigated by dynamic thermomechanical analysis using a Q800 analyzer (TA instruments) in three-point bending mode with sample dimensions of 40 × 10 × 3 mm3 from 40 to 300 °C at a heating rate of 5 °C/step and frequency of 1 Hz.