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Article

Facile Construction of Polypyrrole Microencapsulated Melamine-Coated Ammonium Polyphosphate to Simultaneously Reduce Flammability and Smoke Release of Epoxy Resin

by
Feiyue Wang
,
Jiahao Liao
,
Long Yan
* and
Mengtao Cai
Institute of Disaster Prevention Science and Safety Technology, School of Civil Engineering, Central South University, Changsha 410075, China
*
Author to whom correspondence should be addressed.
Polymers 2022, 14(12), 2375; https://doi.org/10.3390/polym14122375
Submission received: 12 May 2022 / Revised: 30 May 2022 / Accepted: 6 June 2022 / Published: 12 June 2022
(This article belongs to the Special Issue Advanced Epoxy-Based Materials III)
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Abstract

:
A unique mono-component intumescent flame retardant, named PPy-MAPP, of which melamine-coated ammonium polyphosphate (MAPP) was microencapsulated by polypyrrole (PPy), was synthesized and carefully characterized. The obtained PPy-MAPP was applied to epoxy resin (EP) for obtaining flame-retarded EP composites. The results show that PPy-MAPP imparts better flame retardancy and smoke suppression properties to EP compared to the same addition of MAPP. The EP composite with 15 wt% PPy-MAPP easily passes the UL94 V-0 rating and achieves an LOI value of 42.4%, accompanied by a 61.9% reduction in total heat release (THR) and a 73.9% reduction in total smoke production (TSP) when compared with pure EP. The char residue analysis shows that PPy-MAPP can promote a generation of more phosphorus-rich structures in the condensed phase that improve the integrity and intumescence of char against fire. The mechanical test indicates that PPy-MAPP has a less negative effect on the tensile strength and elastic modulus of epoxy resin due to the good compatibility between PPy-MAPP and the EP matrix, as supported by differential scanning calorimetry (DSC) analyses. In this paper, these attractive features of PPy-MAPP provide a new strategy to prepare satisfactory flame retardant and super flame retarding EP composites.

1. Introduction

Epoxy resin (EP) is a type of thermosetting polymer with a wide application in the fields of the national defense industry and automobile industry [1,2,3]. However, the high fire risk of EP limits its further application, especially in aerospace, electronics and other special fields. Generally, the limiting oxygen index (LOI) value of EP is only about 19.0%. Meanwhile, EP will release many toxic gases during combustion, which is an awful threat to human possessions, life and safety evacuation [4,5,6]. Therefore, many efforts have focused on the study and application of various flame retardants to reduce the fire risk of epoxy resin [7].
The performance of epoxy resin is greatly affected by additives. Different additives have different physicochemical properties, and their effects on the properties of epoxy resin are also different [8,9]. Mineral additives, such as sepiolite, zeolite, pumice, diorite and ocher [10,11,12], can significantly enhance the surface hardness, tensile strength and heat resistance of epoxy resin at high temperatures. In addition to enhancing the tensile strength of epoxy resin, natural fibers, such as sawdust, also play a positive role in enhancing flexural strength [13]. In addition, the particle size and dispersion of additives have a great influence on the physical properties of epoxy resin. Generally, the additive with a small particle size can cause higher physical and mechanical properties in EP [14,15]. Bao et al. [16] used silicon-containing flame retardant (PMDA) to modify carbon nanotubes (CNTs), and the obtained modified CNTs showed better dispersion performance in epoxy resin, showing good flame retardancy and thermal stability. Mostovoy et al. [17] reported the feasibility of using two kinds of phosphates (oligo (resorcinophenyl phosphate) and trichloropropyl phosphate) as epoxy resin plasticizers. The synthesized epoxy resin has excellent bending and impact properties and also has a positive effect on the improvement of flame-retardant properties. Zhou et al. [18] used phosphoric acid modified lignin as a flame-retardant modifier of epoxy resin. The results showed that although epoxy resin showed good flame-retardant properties and thermal stability, it sacrificed the tensile properties and elastic modulus of epoxy resin.
In recent years, ammonium polyphosphate (APP) has received extensive attention because of its high flame-retardant performance, and often acted as an acid source and a gas source in an intumescent system, which made it widely applied in the field of flame-retarded materials. However, APP has high hygroscopicity and poor compatibility with polymer substrate. The combination of APP and polymer organic matter will lead to a serious deterioration of mechanical properties, which limits its application in polymer materials [19,20]. Many efforts have tried to overcome the shortcomings of APP with modification methods. At present, modifications of APP mainly include surfactant modification [7,21], coupling modification [22,23], microencapsulation [24] and melamine modification [25]. Among them, microencapsulation has attracted extensive attention in the field of flame-retarded materials because of its controllable effect, strong variability and excellent compatibility.
Polypyrrole (PPy) is a type of polymer material with good stability and strong conductivity and is widely used in the fields of supercapacitors, lithium electronic batteries, energy storage and heavy metal adsorption [26,27,28]. PPy is mainly composed of a carbon atom and a nitrogen atom, which has potential application as a carbon source in intumescent systems. Pethsangave et al. [29] synthesized the functionalized polypyrrole-loaded graphene nanocomposites (G-fPPy) and then coated them on the surface of cotton fabrics and wood to obtain excellent flame-retardant materials. Wang et al. [30] wrapped copper phytate-doped PPy on the surface of boron nitride nanosheets and found that PPy modified boron nitride could improve both the flame retardancy and mechanical properties of polyurethane (PU) materials. These comprehensive studies indicate that PPy may be an ideal flame-retarded composition in a flame-retardant system.
In this work, PPy-MAPP was synthesized by microencapsulating MAPP with PPy, and the chemical composition, morphological characteristics and thermal stability of PPy-MAPP were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and a thermogravimetric analyzer (TG). Then, the obtained PPy-MAPP was added to the EP matrix to prepare flame-retarded EP composites. The flame retardancy, smoke suppression, thermal stability and mechanical properties of EP composites were evaluated by LOI, UL94, TG and cone calorimeter tests. Finally, the possible flame-retardant and smoke suppression mechanisms of PPy-MAPP in the EP matrix were proposed.

2. Materials and Methods

2.1. Materials

Ammonium polyphosphate (APP, form II) and melamine (MEL) were supplied by Hangzhou JLS Flame Retardants Chemical Co., Ltd. (Hangzhou, China). The phosphorus content of ammonium polyphosphate is 31~32%, the water solubility at 25 °C is less than 0.5, and the particle size is 18 μm. Pyrrole (PY) and ferric chloride were purchased from Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China). The epoxy resin (E-44) was obtained from Zhenjiang Danbao Resin Co., Ltd. (Zhenjiang, China). The epoxy value of the epoxy resin is 0.41~0.47 per 100 g, and the production standard is GB13657-1992. 4,4′-diaminodiphenylmethane (DDM) was purchased from Changzhou Runxiang Chemical Co., Ltd. (Changzhou, China). The molecular weight of DDM is 198.26 g/mol and its melting point is 89~91 °C. Ethanol was supplied by Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd. (Tianjin, China). All the reagents were used as received.

2.2. Synthesis of PPy-MAPP

PPy-MAPP was prepared through microencapsulation using polypyrrole after a melamine coating procession. Firstly, APP (60 g) was dissolved in a 400 mL mixed solution (volume (ethanol): volume (water) = 1:1), and then the above solution was dispersed by ultrasonics at 50 °C for 30 min. Then, MEL (6 g) was introduced into the solution with ultrasonic dispersion continued for 10 min. The above solution was injected into a three-necked flask with magnetic stirring for 1 h at 120 °C. After that, the mixture was adjusted to 90 °C for 2 h stirring. Finally, 100 mL of ferric chloride solution with a mass concentration of 0.9 g L−1 was slowly dropped into the above solution with stirring for 12 h. The obtained product was filtered, and then washed with water and ethanol 3 times, and then dried in an oven at 60 °C for 24 h to obtain PPy-MAPP.

2.3. Preparation of Pure EP and EP Composites

Firstly, EP was preheated at 60 °C in advance. Then, a certain amount of PPy-MAPP was added to the epoxy resin and stirred at 60 °C for 10 min at a stirring speed of 400 r min−1. Afterwards, a certain amount of DDM as a curing agent was introduced into the above epoxy resin mixture for stirring at a speed of 400 r min−1 for 5 min. The mixture was poured into a PTFE mold for 2 h at 120 °C and then heated at 150 °C for 1 h. Finally, EP composites were obtained after demolding. The synthesis process of PPy-MAPP and the resulting EP composites is shown in Figure 1. The composition and flammability of the EP composites are shown in Table 1.

2.4. Characterization and Measurements

Fourier transform infrared (FTIR) spectra were obtained on an I CAN 9 infrared spectrometer (Tianjin Energy Spectrum Technology Co., Ltd., Tianjin, China) in a wavenumber range of 4000–500 cm−1.
Scanning electronic microscopy (SEM) was utilized to obtain the microcosmic morphologies of the samples at an accelerating voltage of 20 kV on a TESCAN MIRA3 LMU (TESCAN CHINA, Ltd., Brno, Czech Republic). Energy dispersive spectroscopy (EDS) was equipped to study the element analysis on an X-Max20 X-ray probe (Oxford Instruments Co., Ltd., Abingdon Oxon, UK).
Thermogravimetric analysis (TGA) was obtained on a TGA/SD-TA851e thermal gravimetric analyzer (Mettler Toledo International Trading Co., Ltd., Shanghai, China). The sample (about 5 mg) was heated from 25 to 800 °C under air atmosphere of 50 mL min−1. The theoretical char residue (Wcal) was calculated according to Formula (1):
W cal ( T ) = ∑ i = 1 n χ i W i ( T )
where χi is the content of compound i, and Wi is the experimental weight of compound i after the TG test.
Differential scanning calorimetry (DSC) analysis was performed using the DSC823e (Mettler Toledo International Trading Co., Ltd., Shanghai, China). The sample was heated to 200 °C and maintained for 3 min, and then cooled down to room temperature with a cooling rate of 10 °C min−1 to eliminate the thermal history. Then, the sample was heated at a heating rate of 10 °C min−1 from 25 °C to 200 °C under a nitrogen 50 mL min−1 atmosphere.
The limiting oxygen index (LOI) values of pure EP and EP composites were obtained using an HC-2CZ oxygen index meter (Nanjing Shangyuan Analytical Instrument Co. Ltd., Nanjing, China) according to ASTM D2863-19, “Standard test method for measuring the minimum oxygen concentration to support candle-like combustion of plastics (oxygen index)” with a sample size of 130 × 6.5 × 3.2 mm3.
The UL94 test was conducted using a JL8333-3 horizontal combustion tester (Nanjing Jionglei Instrument Equipment Co., Ltd., Nanjing, China). The test is in accordance with the procedure of UL94-2016, “Standard for safety: Tests for flammability of plastic materials for parts in devices and appliances”, and the specimens for testing were 130 × 3 × 3.2 mm3.
A cone calorimeter was utilized using the FTT iCone classic instrument model FTT0001 (Fire Testing Technology Co., Ltd., East Grinstead, UK) to investigate the combustion behavior of the EP composites according to ISO 5660-1:2015, “Reaction-to-fire tests-Heat release, smoke production and mass loss rate-Part 1: Heat release rate (cone calorimeter method) and smoke production rate (dynamic measurement)”. All the samples for testing were horizontally irradiated at a heat flux of 50 kW m−2 with a size of 100 × 100 × 3.5 mm3.
The mechanical test was performed in a WDW-10D microcomputer controlled electronic universal testing machine (Jinan Hengsi Shengda Instrument Co., Ltd., Jinan, China) according to GB/T1040.2-2006, “Plastics-Determination of tensile properties-Part 2: Test conditions for molding and extrusion plastics”. The sample size was a type I standard sample and the test speed was 5 mm min−1. Each sample was tested three times, and the final experimental results were taken as the average of the three experiments.

3. Results and Discussion

3.1. Characterization of PPy-MAPP

FTIR spectra of MAPP and PPy-MAPP are shown in Figure 2. PPy-MAPP, MAPP and APP show similar characteristic peaks, which means that the original functional groups of APP have not changed after the modification process. Compared with MAPP, the peaks of 3400, 1625 and 1459 cm−1 are different in the spectrum of PPy-MAPP. The characteristic peak of 3400 cm−1 is assigned to the stretching vibration of the N–H group, while the peaks at 1625 and 1459 cm−1 are assigned to the vibration of the aromatic ring in the polypyrrole structure [31].
Figure 3 shows the morphologies of the APP, MAPP and PPy-MAPP flame retardants. It can be seen that the surface of APP is smooth without impurities, while MAPP is slightly rough, indicating that MEL successfully grafted onto the surface of APP. The surface of PPy-MAPP is rougher and flaky, which means that PPy is successfully wrapped on the surface of MAPP. From the results of EDS, the contents of carbon and nitrogen in PPy-MAPP are higher than that of APP and MAPP, further verifying that PPy-MAPP was synthesized successfully.
The thermal decomposition processes of APP and MAPP and PPy-MAPP were investigated by TG analysis. As shown in Figure 4, both MAPP and PPy-MAPP have two obvious decomposition processes at 250–350 °C and 350–500 °C, respectively. In addition to the obvious thermal decomposition of APP between 250 °C and 500 °C, a new thermal decomposition process appears at 500 °C and 700 °C, and the peak thermal decomposition is about 690 °C. By comparison, MAPP and PPy-MAPP have less thermal decompositions after 500 °C. Compared to MAPP, PPy-MAPP has a less mass loss at the temperature range of 500–800 °C, indicating an improvement in thermal stability at high temperatures. In addition, the residual weights of APP, MAPP and PPy-MAPP at 800 °C are 49.1%, 61.4% and 63.2%, respectively, further indicating a better char-forming ability of PPy-MAPP.

3.2. TG Analysis

TG analysis was utilized to evaluate the thermal stability of EP composites, and the TG and DTG curves are shown in Figure 5. From Figure 5, all the samples mainly decompose in the temperature range of 350–500 °C. Compared to pure EP, the mass loss of the EP composites containing either MAPP or PPy-MAPP is obviously decreased, which indicates that MAPP and PPy-MAPP can enhance both the charring ability and thermal stability of EP. Especially, the EP composite containing PPy-MAPP has an earlier decomposition and a lower PMLR value, indicating that PPy-MAPP changes the thermal decomposition process of epoxy resin.
The specific data for the thermal decomposition of EP composites are listed in Table 2. It can be seen that the T5% and Tmax values of pure EP are 396.1 °C and 421.4 °C, respectively. After adding PPy-MAPP, the T5% and Tmax values of EP composites are decreased obviously, among which EP/15PPy-MAPP has the lowest T5% and Tmax values, which is due to the low decomposition temperature of PPy-MAPP containing weak bonds of N-H and P-O-C [32]. The char residue of the EP composite containing 15 wt% PPy-MAPP increases to 33.8% from 19.9% of pure EP, exhibiting a super char-forming ability. In order to further assess the char-forming behavior of PPy-MAPP, ΔW can be utilized for quantitative analysis of the char-forming ability [33]. The value of ΔW is positively correlated with the content of PPy-MAPP, which indicates that the char-forming ability of EP composites increases with PPy-MAPP content. Especially, the ΔW value of EP/15PPy-MAPP is obviously improved by 17.7% compared with EP/15MAPP, meaning the PPy-MAPP could enhance the char-forming ability of EP composites. To sum up, the microencapsulation of MAPP by polypyrrole obviously enhances the char-forming ability of flame-retarded EPs.

3.3. DSC Analysis

The glass transition temperature (Tg) of EP composites is measured by DSC analysis, and the results are presented in Figure 6. As shown in Figure 6, the Tg value of pure EP is 170 °C. The Tg value of EP composites decreases gradually with the addition of flame retardant, which indicates that the presence of either MAPP or PPy-MAPP will directly affect the cross-linking network of the EP and reduce the cross-linking degree of the EP [34]. On the other hand, the addition of PPy-MAPP has a less negative effect on the glass transition temperature of epoxy resin compared with MAPP, indicating the better compatibility between PPy-MAPP and epoxy resin.

3.4. LOI and UL94 Tests

The flame retardancy of EP composites was evaluated using the LOI and UL94 tests, and the corresponding results are listed in Table 1 and Figure 7. As shown in Table 1, pure EP has high flammability with an LOI value of 26.3% and fails to pass the UL94 test. The increased degree of the LOI value and UL94 rating of EP composites vary with the content of flame retardants. Both MAPP and PPy-MAPP impart good flame-retardant performance to the EPs, among which EP/15PPy-MAPP has the best flame-retardant effect with an LOI value of 42.4% and passes the UL94 V-0 rating. It is noteworthy that the same content of PPy-MAPP imparts a higher LOI value to EP composite compared to MAPP, indicating that PPy-MAPP has a higher flame-retardant efficiency than that of MAPP.

3.5. Cone Calorimeter Test

In order to assess the fire risk of EP composites, the flammability of EP composites was tested by a cone calorimeter. Various cone calorimeter parameters, such as the time to ignition (TTI), total heat release (THR), peak heat release rate (PHRR), total smoke release (TSR), total smoke production (TSP) and peak smoke production rate (PSPR) are shown in Table 3 and Figure 8.
From Table 3, it is easily found that the TTI value of EP/15PPy-MAPP shows a slight increase compared with pure EP, while EP/15MAPP has no obvious change. From Figure 8a, pure EP burns violently after ignition and is concomitant with the release of a large amount of combustible gases, with its value of THR and PHRR being 107.9 MJ/m2 and 1138.2 KW/m2, respectively. Compared with pure EP, the PHRR value of EP/15PPy-MAPP and EP/15MAPP is 430.7 and 570.9 KW/m2, respectively, which is decreased by 62.2% and 49.8%, respectively. From Figure 8b, the THR value of EP/15PPy-MAPP is reduced by 58.0% while EP/15MAPP is only reduced by 36.7% compared to pure EP, further indicating that PPy-MAPP has a higher flame-retardant efficiency.
The major factor leading to death is smoke in most cases of real fire scenarios; therefore, it is necessary to assess the parameters of smoke release. The smoke production rate (SPR) and total smoke production (TSP) curves of the EP composites are shown in Figure 8c,d. The SPR and TSP values of EP decrease obviously after the addition of PPy-MAPP. Compared with pure EP, the PSPR and TSP values of EP/15PPy-MAPP decrease by 62.2% and 73.9%, respectively, while the corresponding data of EP/15MAPP is reduced by 51.6% and 55.2%, respectively. It indicates that PPy-MAPP has a more satisfactory smoke suppression efficiency in the EP matrix than MAPP.
Figure 9 shows the digital photos of the char residues of the pure EP and EP composites after the cone calorimeter test. In Figure 9a, pure EP has a char height of 17 mm, concomitant with a fragmented char after combustion. After the addition of PPy-MAPP and MAPP, the char residue of EP/15PPy-MAPP and EP/15MAPP has more integrity and expansion compared to pure EP, as seen in Figure 9b,c. The char height of EP/15PPy-MAPP is 78 mm, while EP/15MAPP is 56 mm, indicating a better char-forming ability of PPy-MAPP than MAPP. From Figure 9b*,c*, EP/15PPy-MAPP shows a more compact intumescent char with fewer voids and holes compared with EP/15MAPP, meaning the same addition of PPy-MAPP is beneficial to form a more integrated and intumescent char against fire. In order to further analyze our research results, we compare the performance of PPy-MAPP with other papers, and the details are shown in Table 4.

3.6. Char Residue Analysis

The SEM images and EDS maps of the char residues for the EP composites after the cone calorimeter test are shown in Figure 10. In Figure 10a, it can be observed that the surface of EP/15MAPP char has a lot of large pore structures, while the surface of EP/15PPy-MAPP char has a denser structure with smaller pores. It indicates that PPy-MAPP can effectively enhance the integrity and compactness of the char layer during combustion. From the EDS maps of char residues, the EP/15PPy-MAPP char has a higher phosphorus content compared to the EP/15MAPP char, which means more phosphorus-containing cross-linked structures are formed. The mass ratio of carbon and oxygen reflects the thermal stability and oxidation degree of the char residues, and a higher C/O ratio presents a better heat insulation property [36,37]. The C/O ratio of the EP/15PPy-MAPP char is higher than that of the EP/15MAPP char, indicating that EP/15PPy-MAPP generates a more intumescent and compact char with a better heat insulation effect.
To investigate the flame-retardant mechanism of PPy-MAPP, FTIR spectra of EP/15MAPP and EP/15PPy-MAPP treated at different temperatures are shown in Figure 11. It can be observed that both EP/15MAPP and EP/15PPy-MAPP show the obvious absorption peaks of the C=C group at 1600 cm−1, the C-C group in the aromatic ring at 1450 cm−1 and the P-O-C group at 1089 cm−1 [38,39]. When the temperature is below 450 °C, EP/15MAPP and EP/15PPy-MAPP have little difference in the types and intensities of chemical groups. When the temperature increases above 450 °C, the intensities of the peaks assigned to P-O-C and C=C groups in the spectrum of the EP/15PPy-MAPP sample are obviously stronger than those of EP/15MAPP, indicating that the addition of PPy-MAPP generates more aromatic and cross-linked structures in the condensed phase that effectively enhances the barrier effect and thermal stability of char residue. The possible flame-retardant mechanism of EP/PPy-MAPP composites is proposed in Figure 12.

3.7. Tensile Test

The results of the tensile tests of the pure EP and EP composites are shown in Table 5. From Table 5, the tensile strength of the samples shows a decreasing trend with the increasing content of flame retardant, which is due to the addition of fillers that easily causes concentrated stress. In addition, EP is a polymer compound formed by the interaction of covalent bonds and intermolecular forces, which has poor compatibility with inorganic ammonium polyphosphate bound by ionic bonds. The surface of PPy-MAPP has fewer ionic bonds due to the microencapsulation of PPy compared to MAPP [40], which indicates that PPy-MAPP has a less negative effect on the cross-linking process of EP. The elastic modulus of EP composites has been enhanced by adding PPy-MAPP, which may be due to the reaction between the N–H bond on the surface of polypyrrole and the cross-linking network of epoxy resin.

4. Conclusions

In this study, a mono-component intumescent flame retardant, named PPy-MAPP, was successfully prepared and then applied in epoxy resin to reduce its fire hazard. The flammability, thermal stability and mechanical properties of the EP composites were carefully characterized. The results show that PPy-MAPP exerts better flame-retardant and smoke suppression efficiencies in the EP matrix compared to the same addition of melamine-coated ammonium polyphosphate. In particular, EP/15PPy-MAPP can reach an LOI value of 42.4% and easily achieve a UL94 V-0 rating, accompanied by a reduction of 61.9% in the THR value and 65.6% in the PHRR value compared to pure EP. Moreover, the PSPR and TSP values of EP/15PPy-MAPP are 62.2% and 73.9%, respectively, lower than those of pure EP. The char residue analysis shows that PPy-MAPP can promote the generation of phosphorus-rich cross-linked and aromatic structures in the condensed phase that improves the integrity and intumescence of char residue against heat and mass transfer. The tensile test shows that Ppy-MAPP increases the elastic modulus of EP composites concomitant with a less negative effect on the tensile strength due to the good compatibility between the EP matrix and PPy-MAPP, as supported by the DSC analysis. Furthermore, the elastic modulus of EP/15PPy-MAPP is 38.5% higher than that of pure EP. Overall, these attractive features of PPy-MAPP provide a new insight to obtain EP composites with satisfactory flame retardancy, smoke suppression and mechanical properties.

Author Contributions

F.W.: conception, formal analysis, writing—review and editing; J.L.: methodology, validation, data curation, writing—original draft preparation; L.Y.: methodology, validation, data curation, writing—review and editing, supervision, project administration; M.C.: data curation, investigation. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the National Natural Science Foundation of China [No. 51906261]; the Key Research and Development Program of Hunan Province [No. 2021SK2054]; the Graduate Research and Innovation Project of Central South University [No. 2020zzts637].

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Huo, S.; Yang, S.; Wang, J.; Cheng, J.; Zhang, Q.; Hu, Y.; Ding, G.; Zhang, Q.; Song, P. A liquid phosphorus-containing imidazole derivative as flame-retardant curing agent for epoxy resin with enhanced thermal latency, mechanical, and flame-retardant performances. J. Hazard. Mater. 2020, 386, 121984. [Google Scholar] [CrossRef] [PubMed]
  2. Zhang, Q.; Yang, S.; Wang, J.; Cheng, J.; Zhang, Q.; Ding, G.; Hu, Y.; Huo, S. A DOPO based reactive flame retardant constructed by multiple heteroaromatic groups and its application on epoxy resin: Curing behavior, thermal degradation and flame retardancy. Polym. Degrad. Stab. 2019, 167, 10–20. [Google Scholar] [CrossRef]
  3. Wang, J.; Ma, C.; Wang, P.; Qiu, S.; Cai, W.; Hu, Y. Ultra-low phosphorus loading to achieve the superior flame retardancy of epoxy resin. Polym. Degrad. Stab. 2018, 149, 119–128. [Google Scholar] [CrossRef]
  4. Müller, P.; Schartel, B. Melamine poly(metal phosphates) as flame retardant in epoxy resin: Performance, modes of action, and synergy. J. Appl. Polym. Sci. 2016, 133, 43549. [Google Scholar] [CrossRef]
  5. Zhang, Q.; Wang, J.; Yang, S.; Cheng, J.; Ding, G.; Huo, S. Facile construction of one-component intrinsic flame-retardant epoxy resin system with fast curing ability using imidazole-blocked bismaleimide. Compos. Part B Eng. 2019, 177, 107380. [Google Scholar] [CrossRef]
  6. Shi, X.-H.; Xu, Y.-J.; Long, J.-W.; Zhao, Q.; Ding, X.-M.; Chen, L.; Wang, Y.-Z. Layer-by-layer assembled flame-retardant architecture toward high-performance carbon fiber composite. Chem. Eng. J. 2018, 353, 550–558. [Google Scholar] [CrossRef]
  7. Alongi, J.; Han, Z.; Bourbigot, S. Intumescence: Tradition versus novelty. A comprehensive review. Prog. Polym. Sci. 2015, 51, 28–73. [Google Scholar] [CrossRef]
  8. Mostovoy, A.S.; Nurtazina, A.S.; Burmistrov, I.N.; Kadykova, Y.A. Effect of Finely Dispersed Chromite on the Physicochemical and Mechanical Properties of Modified Epoxy Composites. Russ. J. Appl. Chem. 2018, 91, 1758–1766. [Google Scholar] [CrossRef]
  9. Moaseri, E.; Bazubandi, B.; Baniadam, M.; Maghrebi, M. Enhancement in mechanical properties of multiwalled carbon nanotube-reinforced epoxy composites: Crosslinking of the reinforcement with the matrix via diamines. Polym. Eng. Sci. 2019, 59, 1905–1910. [Google Scholar] [CrossRef]
  10. Ahmetli, G.; Kocak, N.; Dag, M.; Kurbanli, R. Mechanical and thermal studies on epoxy toluene oligomer-modified epoxy resin/marble waste composites. Polym. Compos. 2012, 33, 1455–1463. [Google Scholar] [CrossRef]
  11. Bekeshev, A.; Mostovoy, A.; Tastanova, L.; Kadykova, Y.; Kalganova, S.; Lopukhova, M. Reinforcement of epoxy composites with application of finely-ground ochre and electrophysical method of the composition modification. Polymers 2020, 12, 1437. [Google Scholar] [CrossRef] [PubMed]
  12. Bekeshev, A.; Mostovoy, A.; Kadykova, Y.; Akhmetova, M.; Tastanova, L.; Lopukhova, M. Development and Analysis of the Physicochemical and Mechanical Properties of Diorite-Reinforced Epoxy Composites. Polymers 2021, 13, 2421. [Google Scholar] [CrossRef] [PubMed]
  13. Kumar, R.; Kumar, K.; Sahoo, P.; Bhowmik, S. Study of Mechanical Properties of Wood Dust Reinforced Epoxy Composite. Procedia Mater. Sci. 2014, 6, 551–556. [Google Scholar] [CrossRef] [Green Version]
  14. Feng, L.; Zhao, H.; He, X.; Zhao, Y.; Gou, L.; Wang, Y. Synthesis and self-healing behavior of thermoreversible epoxy resins modified with nitrile butadiene rubber. Polym. Eng. Sci. 2019, 59, 1603–1610. [Google Scholar] [CrossRef]
  15. Kulkarni, S.M.; Kishore. Effect of filler–fiber interactions on compressive strength of fly ash and short-fiber epoxy composites. J. Appl. Polym. Sci. 2003, 87, 836–841. [Google Scholar] [CrossRef]
  16. Bao, X.; Wu, F.; Wang, J. Thermal Degradation Behavior of Epoxy Resin Containing Modified Carbon Nanotubes. Polymers 2021, 13, 3332. [Google Scholar] [CrossRef]
  17. Mostovoy, A.S.; Nurtazina, A.S.; Kadykova, Y.A.; Bekeshev, A.Z. Highly Efficient Plasticizers-Antipirenes for Epoxy Polymers. Inorg. Mater. Appl. Res. 2019, 10, 1135–1139. [Google Scholar] [CrossRef]
  18. Zhou, S.; Tao, R.; Dai, P.; Luo, Z.; He, M. Two-step fabrication of lignin-based flame retardant for enhancing the thermal and fire retardancy properties of epoxy resin composites. Polym. Compos. 2020, 41, 2025–2035. [Google Scholar] [CrossRef]
  19. Chen, X.L.; Wang, K.; Gu, Y.X.; Jiao, C.; Liang, H.; Li, S. Influence of nickel citrate in flame retardant thermoplastic polyurethane elastomer composites based on ammonium polyphosphate. Express Polym. Lett. 2021, 15, 445–458. [Google Scholar] [CrossRef]
  20. Shi, C.; Qian, X.; Jing, J.; Che, H. Influence of β-FeOOH nanorods and ammonium polyphosphate on reducing the fire hazard of epoxy resins composites. J. Ther. Anal. Calorim. 2021, 147, 3599–3607. [Google Scholar] [CrossRef]
  21. Kandola, B.K.; Magnoni, F.; Ebdon, J.R. Flame retardants for epoxy resins: Application-related challenges and solutions. J. Vinyl Addit. Technol. 2022, 28, 17. [Google Scholar] [CrossRef]
  22. Lin, H.; Yan, H.; Liu, B.; Wei, L.; Xu, B. The influence of KH-550 on properties of ammonium polyphosphate and polypropylene flame retardant composites. Polym. Degrad. Stab. 2011, 96, 1382–1388. [Google Scholar] [CrossRef]
  23. Zhou, L.; Guo, C.; Li, L. Influence of ammonium polyphosphate modified with 3-(methylacryloxyl) propyltrimethoxy silane on mechanical and thermal properties of wood flour–polypropylene composites. J. Appl. Polym. Sci. 2011, 122, 849–855. [Google Scholar] [CrossRef]
  24. Wang, N.; Mi, L.; Wu, Y.; Wang, X.; Fang, Q. Enhanced flame retardancy of natural rubber composite with addition of microencapsulated ammonium polyphosphate and MCM-41 fillers. Fire Saf. J. 2013, 62, 281–288. [Google Scholar] [CrossRef]
  25. Fukumura, C.; Iwata, M.; Narita, N.; Inoue, K.; Takahashi, R. Process for Producing a Melamine-Coated Ammonium Polyphosphate. U.S. Patent US5534291 A, 9 July 1996. [Google Scholar]
  26. Tian, F.; Liu, L.; Yang, Z.; Wang, X.; Chen, Q.; Wang, X. Electrochemical characterization of a LiV3O8–polypyrrole composite as a cathode material for lithium ion batteries. Mater. Chem. Phys. 2011, 127, 151–155. [Google Scholar] [CrossRef]
  27. Yue, B.; Wang, C.; Ding, X.; Wallace, G.G. Polypyrrole coated nylon lycra fabric as stretchable electrode for supercapacitor applications. Electrochim. Acta 2012, 68, 18–24. [Google Scholar] [CrossRef] [Green Version]
  28. Massafera, M.P.; Córdoba de Torresi, S.I. Evaluating the performance of polypyrrole nanowires on the electrochemical sensing of ammonia in solution. J. Electroanal. Chem. 2012, 669, 90–94. [Google Scholar] [CrossRef]
  29. Pethsangave, D.A.; Khose, R.V.; Wadekar, P.H.; Some, S. Novel Approach toward the Synthesis of a Phosphorus-Functionalized Polymer-Based Graphene Composite as an Efficient Flame Retardant. ACS Sustain. Chem. Eng. 2019, 7, 11745–11753. [Google Scholar] [CrossRef]
  30. Wang, J.; Zhang, D.; Zhang, Y.; Cai, W.; Yao, C.; Hu, Y.; Hu, W. Construction of multifunctional boron nitride nanosheet towards reducing toxic volatiles (CO and HCN) generation and fire hazard of thermoplastic polyurethane. J. Hazard. Mater. 2019, 362, 482–494. [Google Scholar] [CrossRef]
  31. Rashidzadeh, A.; Olad, A.; Ahmadi, S. Preparation and characterization of polypyrrole/clinoptilolite nanocomposite with enhanced electrical conductivity by surface polymerization method. Polym. Eng. Sci. 2013, 53, 970–975. [Google Scholar] [CrossRef]
  32. Wang, F.; Liao, J.; Yan, L.; Liu, H. Fabrication of Diaminodiphenylmethane Modified Ammonium Polyphosphate to Remarkably Reduce the Fire Hazard of Epoxy Resins. Polymers 2021, 13, 3221. [Google Scholar] [CrossRef] [PubMed]
  33. Si, M.; Feng, J.; Hao, J.; Xu, L.; Du, J. Synergistic flame retardant effects and mechanisms of nano-Sb 2 O 3 in combination with aluminum phosphinate in poly (ethylene terephthalate). Polym. Degrad. Stab. 2014, 100, 70–78. [Google Scholar] [CrossRef]
  34. Jian, R.; Wang, P.; Duan, W.; Wang, J.; Zheng, X.; Weng, J. Synthesis of a Novel P/N/S-Containing Flame Retardant and Its Application in Epoxy Resin: Thermal Property, Flame Retardance, and Pyrolysis Behavior. Ind. Eng. Chem. Res. 2016, 55, 11520–11527. [Google Scholar] [CrossRef]
  35. Qu, H.; Wu, W.; Hao, J.; Wang, C.; Xu, J. Inorganic-organic hybrid coating-encapsulated ammonium polyphosphate and its flame retardancy and water resistance in epoxy resin. Fire Mater. 2013, 38, 312–322. [Google Scholar] [CrossRef]
  36. Hu, X.; Wang, G.; Huang, Y. Study on the preparation and properties of novel transparent fire-resistive coatings. J. Coat. Technol. Res. 2013, 10, 717–726. [Google Scholar] [CrossRef]
  37. Yan, L.; Xu, Z.; Wang, X. Influence of nano-silica on the flame retardancy and smoke suppression properties of transparent intumescent fire-retardant coatings. Prog. Org. Coat. 2017, 112, 319–329. [Google Scholar] [CrossRef]
  38. Zheng, Z.; Liu, Y.; Zhang, L.; Wang, H. Synergistic effect of expandable graphite and intumescent flame retardants on the flame retardancy and thermal stability of polypropylene. J. Mater. Sci. 2016, 51, 5857–5871. [Google Scholar] [CrossRef]
  39. Xu, Z.; Chu, Z.; Yan, L. Enhancing the flame-retardant and smoke suppression properties of transparent intumescent fire-retardant coatings by introducing boric acid as synergistic agent. J. Anal. Calorim. 2018, 133, 1241–1252. [Google Scholar] [CrossRef]
  40. Meili, D.; Baolin, W.; Shidong, X.; Po, H. The effect of organic-phosphorus flame retardant on the performance of epoxy resin. Australian Joumal of Chemidtry. Fire Sci. Technol. 2017, 36, 1698–1702. [Google Scholar]
Polymers 14 02375 g001 550
Figure 1. Preparation process of PPy-MAPP and EP composites.
Figure 1. Preparation process of PPy-MAPP and EP composites.
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Polymers 14 02375 g002 550
Figure 2. FTIR spectra of APP, MAPP and PPy-MAPP.
Figure 2. FTIR spectra of APP, MAPP and PPy-MAPP.
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Polymers 14 02375 g003 550
Figure 3. Microstructure of APP (a), MAPP (b) and PPy-MAPP (c).
Figure 3. Microstructure of APP (a), MAPP (b) and PPy-MAPP (c).
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Polymers 14 02375 g004 550
Figure 4. TG and DTG curves of APP and MAPP and PPy-MAPP.
Figure 4. TG and DTG curves of APP and MAPP and PPy-MAPP.
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Polymers 14 02375 g005 550
Figure 5. TG (a) and DTG (b) curves of EP and flame-retarded EPs.
Figure 5. TG (a) and DTG (b) curves of EP and flame-retarded EPs.
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Figure 6. DSC curves of flame-retardant epoxy resin.
Figure 6. DSC curves of flame-retardant epoxy resin.
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Polymers 14 02375 g007 550
Figure 7. LOI value and UL94 rating of neat EP and EP composites.
Figure 7. LOI value and UL94 rating of neat EP and EP composites.
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Polymers 14 02375 g008a 550Polymers 14 02375 g008b 550
Figure 8. Cone calorimeter data of epoxy composites: heat release rate (a), total heat release (b), smoke production rate (c) and total smoke production (d).
Figure 8. Cone calorimeter data of epoxy composites: heat release rate (a), total heat release (b), smoke production rate (c) and total smoke production (d).
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Polymers 14 02375 g009 550
Figure 9. Char morphologies of EP (a), EP/15MAPP (b), EP/15PPy-MAPP (c), profile map of EP/15MAPP (b*) and EP/15PPy-MAPP (c*).
Figure 9. Char morphologies of EP (a), EP/15MAPP (b), EP/15PPy-MAPP (c), profile map of EP/15MAPP (b*) and EP/15PPy-MAPP (c*).
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Figure 10. SEM image of EP/15MAPP (a) and EP/15PPy-MAPP (b) after cone calorimetry test.
Figure 10. SEM image of EP/15MAPP (a) and EP/15PPy-MAPP (b) after cone calorimetry test.
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Polymers 14 02375 g011 550
Figure 11. FTIR spectra of EP/15MAPP (a) and EP/15PPy-MAPP (b) under different heating temperatures.
Figure 11. FTIR spectra of EP/15MAPP (a) and EP/15PPy-MAPP (b) under different heating temperatures.
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Polymers 14 02375 g012 550
Figure 12. Flame-retardant mechanism of EP/PPy-MAPP composites.
Figure 12. Flame-retardant mechanism of EP/PPy-MAPP composites.
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Table
Table 1. Formulations and flammability of pure EP and EP composites.
Table 1. Formulations and flammability of pure EP and EP composites.
SamplesAPP (wt%)MAPP (wt%)PPy-MAPP (wt%)EP (wt%)DDM (wt%)
EP0008020
EP/15APP15006817
EP/5MAPP0507619
EP/7.5MAPP07.507418.5
EP/10MAPP01007218
EP/12.5MAPP012.507017.5
EP/15MAPP01506817
EP/5PPy-MAPP0057619
EP/7.5PPy-MAPP007.57418.5
EP/10PPy-MAPP00107218
EP/12.5PPy-MAPP0012.57017.5
EP/15PPy-MAPP00156817
Table
Table 2. Typical thermal data of flame-retarded epoxy resins.
Table 2. Typical thermal data of flame-retarded epoxy resins.
SamplesT5% (°C)Tmax (°C)PMLR (% min−1)Wexp (%)WcalΔW
EP396.1421.41.5619.9––
EP/15MAPP362.4384.52.1928.726.152.55
EP/5PPY-MAPP376.5408.51.3326.421.954.45
EP/10 PPy-MAPP363.3384.52.4230.824.306.50
EP/15 PPy-MAPP359.5384.21.7633.826.457.35
Note: T5%—initial decomposition temperature, Tmax—the temperature of peak mass loss rate, PMLR—peak value of mass loss rate, ΔW = Wexp − Wcal.
Table
Table 3. Cone calorimeter data of pure EP and the flame-retarded EP composites.
Table 3. Cone calorimeter data of pure EP and the flame-retarded EP composites.
SamplesTTI (s)THR (MJ/m2)PHRR (KW/m2)TSR (m2/m2)TSP (m2)PSPR (m2/s)Residue (%)
EP58118.81252.01186.732.60.3046.8
EP/15MAPP5968.3570.9866.114.60.14724.7
EP/5PPy-MAPP59106.11040.0826.925.90.20516.9
EP/10PPy-MAPP6189.0896.7753.423.00.16117.1
EP/15PPy-MAPP6745.3430.7702.48.50.11530.3
Table
Table 4. Comparison of flame retardant property and smoke suppression performance between EP/15PPy-MAPP and other flame retardant additives in epoxy resin.
Table 4. Comparison of flame retardant property and smoke suppression performance between EP/15PPy-MAPP and other flame retardant additives in epoxy resin.
SamplesContent (wt%)LOI (%)UL94 RatingReduction of PHRR (%)Reduction of PSPR (%)Char Residue Weight (%)Refs.
EP/15PPy-MAPP1542.4V-065.662.230.3this work
EP/DDS/PBI-1.014.333.5V-049.5–21.2[2]
EP/APP/Fe-39.530.0V-075.8–23.5[20]
EP/15DDP1537.1V-040.847.834.0[32]
EP/12.5% DOPO-ABZ12.532.0V-043.0–20.1[34]
EPMAPP121232.5V-084.6––[35]
Annotation: Content is defined as the addition of flame retardant additives; the calculation of Reduction of PHRR and PSPR are based on pure epoxy resin; EP/DDS/PBI-1.0, DGEBA/dapsone/ is a flame retardant composed of phosphaphenanthrene, benzothiazole and imidazole groups (PBI); EP/APP/Fe-3, DEGBA/DDM/2.0 g β-FeOOH nanorods and 7.5 g APP; EP/15DDP, DEGBA/DDM/ DDM modified APP(DDP); EP/12.5% DOPO-ABZ, DEGBA/DDM/ is the combination of DOPO and 2-aminobenzothiazole (DOPO-ABZ); EPMAPP12, DEGBA/ethylenediamine/a is encapsulated APP using tetraethyl orthosilicate and octyltriethoxysilane (MAPP).
Table
Table 5. Mechanical property parameter of pure EP and EP composites.
Table 5. Mechanical property parameter of pure EP and EP composites.
SamplesElastic Modulus (MPa)Tensile Strength (MPa)
EP5710.3 ± 10.251.2 ± 2.4
EP/15MAPP7556.8 ± 23.133.2 ± 1.9
EP/5PPy-MAPP5792.7 ± 16.446.0 ± 2.3
EP/10PPy-MAPP5814.8 ± 8.939.2 ± 2.2
EP/15PPy-MAPP7907.0 ± 22.034.0 ± 1.6
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Wang, F.; Liao, J.; Yan, L.; Cai, M. Facile Construction of Polypyrrole Microencapsulated Melamine-Coated Ammonium Polyphosphate to Simultaneously Reduce Flammability and Smoke Release of Epoxy Resin. Polymers 2022, 14, 2375. https://doi.org/10.3390/polym14122375

AMA Style

Wang F, Liao J, Yan L, Cai M. Facile Construction of Polypyrrole Microencapsulated Melamine-Coated Ammonium Polyphosphate to Simultaneously Reduce Flammability and Smoke Release of Epoxy Resin. Polymers. 2022; 14(12):2375. https://doi.org/10.3390/polym14122375

Chicago/Turabian Style

Wang, Feiyue, Jiahao Liao, Long Yan, and Mengtao Cai. 2022. "Facile Construction of Polypyrrole Microencapsulated Melamine-Coated Ammonium Polyphosphate to Simultaneously Reduce Flammability and Smoke Release of Epoxy Resin" Polymers 14, no. 12: 2375. https://doi.org/10.3390/polym14122375

APA Style

Wang, F., Liao, J., Yan, L., & Cai, M. (2022). Facile Construction of Polypyrrole Microencapsulated Melamine-Coated Ammonium Polyphosphate to Simultaneously Reduce Flammability and Smoke Release of Epoxy Resin. Polymers, 14(12), 2375. https://doi.org/10.3390/polym14122375

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