Page 1/15

Preparation of Natural Silk Protein-Based FlameRetardantZhihao Sun 

Jiangsu UniversityZheng Li 

Jiangsu UniversityZhongfei Ma  ( mzf@ujs.edu.cn )

Jiangsu UniversityMinxue Zheng 

Jiangsu UniversityWang Zhan 

Jiangsu University

Research Article

Keywords: �ammability, microstructure, decomposition, surface

Posted Date: September 2nd, 2021

DOI: https://doi.org/10.21203/rs.3.rs-780049/v1

License: This work is licensed under a Creative Commons Attribution 4.0 International License.  Read Full License

Page 2/15

AbstractTo counter paper �ammability, SF-JR400/MP-SiO2 sourced from natural silk protein may be applied to thepaper surface using layer-by-layer assembly (LbL). The microstructure and composition of the coatingmay be assessed using SEM, FTIR and XPS. Presence of the coating increases the paper combustionlimiting oxygen index (LOI) from 20.4% to 38%. Compared to untreated DBP, TGA analysis shows that theinitial decomposition temperature of DBP rises from 115˚C to 148˚C. Residual char yield increases from11.3% to 38.8%. The formation of a surface char layer protects paper internal �bers from heat feedbackand consequent thermal decomposition. Analysis using CONE indicates that a 25-layer assembly canreduce the peak and total heat dissipation by 88.4% and 54.7%, respectively analysis suggests that silkmay function as an agent to accelerate the coating, formation of a protective. 

IntroductionSilk �broin (SF) extracted from silk has long been a raw material the generation many arti�cialbiomaterials. This natural polymer is rugged, �exible, durable and biodegradable. These arecharacteristics not found in several chemical synthetic materials [1–7]. Protein can introduce anintumescent effect in �ame retardants by providing both a carbon source and a gas source. At the sametime, it does not contain halogen and is more eco-friendly than many traditional �ame retardants. Soyprotein has been used as a main component of a biodegradable intumesceant, �ame retardant forpolybutene. The presence of soy protein promotes carbon formation, signi�cantly increases LOI, andlower PHRR and THR for combustion. It represents an environmentally-friendly �ame retardant forbiodegradable polymers [8]. Comparable to soy protein, SF can also ameliorate surface properties ofpaper by chemical modi�cation of amino and other side chains of certain organics. Thus it is suitable foruse in the development of �ame retardant materials [9].

LbL has been widely used in surface coating due to its low cost, mild assembly requirement, coatingthickness control, and small negative in�uence on substrate attributes [10]. In recent years, LbL has beenshown to provide a functional coating for materials. This makes it attractive for practical applications.New applications can be developed through combinction of LbL with biological systems[11–15]. A �ameretardant fabric has been prepared using this technique. Char formation in the condensed phase and theradical activity in the gas phase brought about an improvement in �ame retardancy[16]. Melamine-phosphate sheets prepared using LbL, improved the thermal stability and �ame retardant properties of acoated material [17]. Polyphenolic acid has been used to generate a �ame retardant surface coating forramie fabric. The presence additional expandable coating led to enhanced residual char formation andenhanced thermal stability and reduced �ammablity[18]. In addition, �ame retardant wood preparedusing the LbL technology broadens the scope of application and improves the safety of wood products[19–21].

Silk �broin may serve as both a carbon source and a gas source for construction of an expandable �ameretardant system. A surface coating containing SF may from a protective char layer on a substrate during

Page 3/15

the combustion process. The layer-by-layer assembly of SF-JR400 and MP-SiO2 has been used to preparea green renewable �ame retardant coating for paper. The physical properies and �ammability of paperbearing this coating have been assessed.

Experimental

2.1 MaterialsSilk �broin (98%, Ø=2 µm) was purchased from Xi'an Zhanxun Biotechnology Co., Ltd. Polyquaternium-10(JR-400, viscosity 300–500) and EDTA (99%) are from Shandong Yousuo Chemical Technology Co., Ltd.Silicon dioxide (99%, Ø=20nm) was purchased from Nanjing Paukert New Material Co., Ltd. LiBr comesfrom Dezhou Kexi Chemical Products Co., Ltd. Melamine (MP,99.5%) phosphate was purchased fromShanghai Liming Chemical Co., Ltd. Paper mulberry made handmade Lijiang Dongba paper (DBP).Sodium bicarbonate, sodium hydroxide, hydrochloric acid AR, sulfuric acid AR, SDBS, anhydrous CuSO4,potassium persulfate, DMSO are all from Sino pharm Chemical Reagent Co., Ltd. The dialysis bag (35KDa) was purchased from Beijing Yami Biotechnology Co., Ltd.;The dialysis device is self-made.

2.2 Measurements and characterizationUse Nano ZS to measure Zeta potential three times. Use Nicolet IS5 to measure FTIR in the scanningrange of 400–4000 cm− 1.FEI Quanta 250 FEG measured SEM under vacuum sprayed gold conditions.InThermo Scienti�c K-Alpha + X photoelectron spectrometer, ordinary scanning and high-resolutionscanning are used for carbon layer element analysis.Set the temperature of the XFH-30CA electric heatingpressure steam sterilizer to 120˚C.Using water as a reference, UV2600 ultraviolet-visible photometer wasused to measure the absorbance at wavelengths of 220nm and 275nm

Use CZF-1 vertical combustion meter, JF-3 oxygen index tester, iConemini cone calorimeter (35 KW/m2,625˚C) to test the �ame retardant performance. The M-T TGA2 analyzer is used to test the thermalproperties of the sample in a nitrogen atmosphere at a temperature of 10˚C/min within 30˚C 800˚C.

2.3 Preparation of layer-by-layer assembled paperTake 2g of SF powder and dissolve it in 9.3M LiBr solution, heat it in a 60˚C water bath to dissolve, thentake it out and cool it down to room temperature. Pour the mixed solution into a clean dialysis bag,dialysis under running water for two days, and deionized water for one day to obtain an SF solution. Thentake 1g of JR-400 powder and dissolve it in 25ml of deionized water, stir for 0.5 h in a 60˚C water bathuntil it becomes viscous, and obtain a 4% JR-400 solution. Pour the prepared SF solution slowly into theJR-400 solution, add 1% anhydrous CuSO4 powder. Stir in a 90˚C water bath for 1.5 hours, take it out toroom temperature, add 75% hydrochloric acid dropwise to adjust the PH, centrifuge for 5 minutes, repeatseveral times, take out the precipitate, add deionized water to make a 6% SF-JR400 solution. The Zetapotential measured by sampling is positive.

Page 4/15

Weigh MP powder, SiO2 powder, and SDBS in a ratio of 2:1:1, respectively, and dissolve them in 60mlDMSO, magnetically stir for 1h until the silica is evenly dispersed to obtain an MP-SiO2 solution. The Zetapotential was negative.

The DBP was ultrasonically cleaned for 30 minutes, dried and weighed. After drying, immerse in SF-JR400 solution for 5 minutes, let it stand for 1 minute and then dry. Then immerse in the MP-SiO2

solution for 5 minutes, stand still to clean the sample and then dry. Use this method to assemble 5, 10, 15,20, 25 layers of DBP (note 5, 10, 15, 20, 25 BL).

Results And Discussion

3.1 Characterization of silk �broin and assembled DBPTo explore the functional group composition of modi�ed silk �broin and DBP coating, the FTIR spectrumis shown in Fig. 1. The stretching vibration peak of the hydroxyl group appeared at 3279 cm− 1 during thegrafting process and gradually became weaker with the increase of LbL components, which may becaused by the decrease of transmittance due to the number of assembled layers. The stretching vibrationpeak of the alkane group appeared at 2920 − 2848 cm− 1. The stretching vibration peak at 1621 cm− 1

indicates that there is an intramolecular hydrogen bond interaction during the assembly process.Vibration absorption peaks of -NH2 bonds appeared at 1621 − 1520 cm− 1 and 1060 cm− 1, and the

absorption peaks of -NH2 bonds at 1060 cm− 1 increased signi�cantly with the increase of the number of

assembled layers. At the same time, the absorption peak of C-Cl bond appeared at 792 cm− 1. During theassembly process, there was no C = C bond absorption peak at 2242 cm− 1,and there was no carboxylabsorption peak at 1760 − 1685 cm− 1.

C2-NH2 in the alanine structure of SF has a strong reactive nucleophilicity, which changes the length ofthe protein chain. JR-400 has good water solubility. Under the condition of acidic aqueous solution, thehydroxyl group 0-H in JR-400 breaks, the interaction of hydrogen bond occurs, and the SF main chainopens at the same time. The amino group and free -Cl− in the quaternary ammonium salt group undergoa ring-opening graft reaction with the epoxy group and C2-NH2 in the alanine of the SF backbone to forma silk �broin quaternary ammonium salt.

The alkaline potassium persulfate solution converts the nitrogen in the nitrogen-containing compounds inthe sample into nitrate. The grafted product SF-JR400 is diluted with water by 50–125 times. After thecomplete reaction, the solution is diluted by 125–200 times. Finally, the absorbance at 220nm and275nm wavelengths were measured. A total of 6 measurements, according to formula (1), the averagegrafting rate is 3.8448% (con�dence interval [3.388,4.240], where 1-α = 0.95)

  (1)

Page 5/15

Where: M1——SF-JR400 grafted product (mg);M2——Unreacted product (mg); G——Grafting rate (nitrogencontent) %.

After the silk �broin is modi�ed, it is attached to the surface of the substrate in the form of a �lm. Figure 2shows the microscopic image of silk �broin before and after modi�cation. In Fig. 2(a), the untreated 2 µmSF powder is presented in a rod-like lamella structure, arranged in an irregular order. Figure 2(b) The SFrod-like structure after graft modi�cation swells and disappears, and then it is clearly presented as across-linked porous �lm-like structure.

As shown in Fig.3, SEM was used to observe the surface and internal microstructure of �ame-retardantcoating DBP with different assembled layer. As the number of assembled layers increases, the loadingcapacity of the �ame-retardant coating on the DBP surface increases and becomes more and moresmooth. It can be seen from Fig.3 that the untreated DBP �ber tube bundle (approximatively d=10µm) isclearly visible. During the assembly process, irregular granular materials are wrapped on the surface andthe paper surface becomes rough. At 15 assembled layers, it is clear that the coating tends to be �at andsmooth. The outer surface of the assembled 25 layers becomes smooth, and the �ber bundles on thesurface of the paper are completely covered. According to the internal structure, it can be seen that theinternal �ber arrangement of untreated DBP is disordered. After assembling 5 layers, the �ber bundle iswrapped. Delamination began to appear after 15 layers of coating, and gradually appeared as theassembly process proceeded. When assembling the 25th layer, there is visible delamination inside. Itproves that the SF-JR400/MP-SiO2 coating was successfully assembled and deposited on the surface ofthe DBP.

3.2 Combustion properties analysis of DBPThe �ammability of DBP is evaluated by LOI and UL-94 tests, and the results are summarized in Table 1.The results are illustrated in Fig. 4, the �ame continues to burn for 12s after the untreated DBP is ignited,and burns out after 22s, and the paper is completely carbonized. The �ve-layer assembly has a highdegree of carbonization, but as the number of assembled layers increases, the DBP becomes more andmore non-�ammable, and the oxygen concentration required for combustion is increasing. 12s afterignition, the DBP assembled with more than 10 layers no longer produces open �ames and sparks, andthe average carbonization length gradually decreases. From the limit oxygen index data in the table,compared with the untreated �ammable material DBP (oxygen index < 22%), the composite material afterassembling 5 layers has reached the level of materials which are di�cult to combust (oxygen index > 27%). It begins to char at the contact of �re and self-extinguish once moved away from the �ame. After25 BL DBP are assembled, the limiting oxygen index reaches 38%, making it on par with non-combustiblematerials, and the �ame retardant performance is improving. In an economical point of view, 10 BL �ame-retardant DBP can meet the production and application standards.

Page 6/15

Table 1UL-94 and LOI of samples (Ignition time 12s)

Sample Flameduration(s)

Afterburningtime(s)

Carbonizedlength(mm)

Limit oxygenindex(%)

0 BL 4.2 6.06 / 20.4

5 BL 2.34 1.14 195 27

10 BL 0 0 115 29.8

15 BL 0 0 205 31.4

20 BL 0 0 113 33.7

25 BL 0 0 89 38

In order to further study the combustion performance of DBP, cone test was carried out, and the relevantdata are shown in Table 2. The heat release rate (HRR) and total heat release (THR) curves are shown inFig. 5. It can be seen that the HRR curve becomes more and more stable with the increase of assembledcoatings. The heat release rate of untreated DBP is 38.9 KW/m2 to the heat release rate of assembled 25-layer DBP is 4.5 KW/ m2. The value is signi�cantly reduced, and the �ame retardant coating has asigni�cant effect. PHRR appears in the 5-15s period. The THR decreases and the �ame-retardant coatingabsorbs heat and decomposes violently, generating water vapor to absorb heat, and the high-temperature-resistant dense carbon layer blocks external oxygen, reduces the generation of combustibles, anddecreases the total heat released by the paper. From the perspective of ignition time (TTI), the ignitiontime of untreated paper is very short. When more than 15 layers are assembled, the ignition time is greatlyextended, and the stability of the �ame-retardant coating becomes better. In addition, after 27s, the totalheat release of 15-layer DBP is 85.5 MJ/m2, which is 15.3% and 23.2% lower than that of 20 and 25layers, respectively. It is concluded that as the test time increases, the 15-layer DBP has the best �ameretardant effect.

Table 2Cone calorimeter date of DBP

Lable TTI(s) PHRR(KW/m2) THR(MJ/m2)

0 BL 7 38.9 254.2

5 BL 9 25.6 179.6

10 BL 13 23.7 215.8

15 BL 19 10 85.5

20 BL 30 6.1 98.6

25 BL 40 4.5 105.4

3.3 Thermal behaviors of DBP

Page 7/15

For evaluating DBP on the thermal stability, the TGA tests were conducted under nitrogen atmosphere.The TGA and DTG curves of EP composites are presented in Fig. 6, and the corresponding data are listedin Table 3. The untreated DBP gradually decomposes at 250˚C 400˚C. After the coating is adsorbed, thedecomposition temperature advances to the region of 250˚C 300˚C, and the corresponding Tmaxtemperature is lower than that of the 0 layer DBP. The advancement of the temperature in this stage ofthermal degradation promotes the carbonization of the DBP surface layer �bers, the paper surface formsa protective layer faster, and the acid source provided by MP accelerates the paper surface carbonization.The char formation rate is increased at 800˚C, and the nano-SiO2 particles adsorbed on the surface arecharred when heated, which increases by 27.5% from 0 BL (11.3%) to 25 BL (38.8%), which effectivelyprotects DBP and enhances thermal stability. With the addition of the �ame-retardant layer, a strongdehydrating agent may be produced, the water will gradually evaporate, and the initial decompositiontemperature will gradually increase, making it harder to be thermally decomposed.

Table 3TGA and DTG data of DBP under N2 atmosphere

Sample T5%(˚C) Tmax(˚C) Residues at 800˚C (wt%)

0 BL 115 362 11.3

5 BL 108 301 25.7

10 BL 123 307 27.6

15 BL 163 308 31.3

20 BL 152 303 33.5

25 BL 148 314 38.8

In order to study the possible �ame-retardant mechanism of DBP in the condensed phase, the residualcarbon of different assembled layers obtained by cone calorimeter test was analyzed. The micromorphology of the carbon layer is shown in Fig. 7. The exposed �bers of the unassembled sample weredirectly burned, and the carbonized �ber bundles were clear. The sample treated by LbL shrinks slightlydue to combustion [22], the coating expands when the 10 BL DBP is burned, and the carbon layer coversthe sample �ber. The carbon layers became uniform, dense and porous when 15 layers were assembled,effectively blocking the oxygen. The increase in particulate matter on the �ber surface is due to the nano-SiO2 �lling the carbon layer and isolating heat transfer.

In order to further study the element structure of the residue, XPS was used to characterize the carbon ofeach assembled layer. The results of C1s, N1s, O1s and the total spectrum are shown in Fig. 8. Combinedwith the data in Table 4, the carbon layer C and N content is signi�cantly higher than the untreated DBP,and the O content gradually decreases. As the coating thickens, the C and N increases from 44.86–48.78% and 1.89–7.81%. The O have declined from 31.97–18.17%. This shows that the coating expandsduring combustion and the carbon increases, making the carbon slag more regular and denser. The

Page 8/15

ConclusionIn this work, the phosphorus-silicon-nitrogen synergistic �ame-retardant system is introduced by SFgrafting, and the surface of DBP is attached by electrostatic adsorption to achieve the best �ame-retardant effect. When it reaches 25 layers, DBP surface structure is loose with granular shedding.According to the comparison of various characteristics, the 15 BL DBP has the best �ame-retardant and

increase of nitrogen is more conducive to the formation of a protective layer on the surface of the �bermaterial, which inhibits the material and energy transfer at the burning area. The oxygen graduallydecreases, and the anti-oxidation ability of the carbon layer increases. The denser the internal structure,the less likely it is to absorb oxygen in the air, thereby blocking oxygen and enhancing stability. Inaddition, while the �ame retardancy increases, the presence of C, N, and O after burning the assembled15-layer DBP is better than that of the assembled 20-layer DBP. When comparing to the untreatedmaterial, the growth rate of C, N content is 14.7% and 52%, respectively. The reduction rate of O contentreached 56.1%. After assembling 25 layers, the content of C, N, and O in the carbon slag increased andthe reduction rate declined, and the �ame retardant effect was not as good as that of assembled 20layers. Assembling 15 layers of DBP to form a carbon layer has better effect and stronger stability.

Table 4Untreated and assembled 15, 20, 25 BL of DBP carbon residue C, N, O content

Element 0 BL 15 BL 20 BL 25 BL

Atomic percentage(%)

Atomic percentage(%)

Atomic percentage(%)

Atomic percentage(%)

C1s 44.86 51.46 48.78 31.75

01s 31.97 14.04 18.17 25.1

N1s 1.89 11.76 7.81 2.87

3.4 Flame retardant mechanism of DBP SampleIn this �ame-retardant system, SF is regarded as a gas source and carbon source, MP is used as an acidsource, SiO2 is regarded as a protective layer, and the adsorption speci�c surface area is increased duringthe assembly process [23]. During the combustion process, SF is heated in a molten state, expands andfoams, and rapidly carbonizes, releasing foam gas. The surface MP decomposes to releasepolyphosphoric acid and melamine, and the melamine continues to decompose to accelerate thedehydration process of the �ber surface to form an insulating coke layer. The addition of nano-SiO2

promotes the formation of a dense and uniform porous carbon layer, thereby absorbing a large amountof heat, reducing the heat transfer of high-energy free radicals to the lower �bers, protecting the substratefrom further decomposition, and interrupting the combustion chain reaction. To achieve the purpose ofheat insulation, oxygen isolation, smoke suppression, and reduction of heat release [24]. On the surfaceof paper �bers, the phosphorus-nitrogen-silicon synergistic �ame-retardant system shows goodperformance.

Page 9/15

thermal properties. The micro morphology and XPS content of the carbon layer show that the DBP carbonlayer with fewer assembled layers is looser and have more pores, while the DBP carbon layer with moreassembled layers has a dense and regular structure, which effectively isolates oxygen. An absence of�ame was observed during the combustion of the 10 layers sample, the LOI of 25 layers samples reaches38%, and the �ame retardant performance is greatly improved. TGA and CONE show that the 25 BLsample retains more than 3 times the residual carbon at 800˚C compared to the untreated sample. ThePHRR signi�cantly decreases with the number of assembled layers and the TTI increases. SF promotesthe carbon-forming effect of paper �bers, makes the carbon layer have good thermal stability, and givesthe paper good �ame-retardant properties.

DeclarationsCompliance with Ethical Standards: 

Funding: This study was funded by Jiangsu University.

To the best of our knowledge, the named authors have no con�ict of interest, �nancial or otherwise. Westrictly abide by the Cellulose submission instructions. 

Zhongfei Ma

References[1] Kim, H. L., et al. (2011). "Preparation and Characterization of Silk Fibroin/Gelatin Hybrid Scaffolds."Polymer-Korea 35(5): 378-384.

[2] Jin, H., et al. (2012). Effect of gamma irradiation on the biocompatibility and biodegradation of silk�broin in vivo. Advanced Engineering Materials Ii, Pts 1-3. C. X. Cui, Y. L. Li and Z. H. Yuan. 535-537: 2361-2364.

[3] Zhao, Z., et al. (2017). "Preparation and characterization of solution spinning of protein/cellulose �ber:A new �ame-retardant grade." Journal of Industrial Textiles 47(2): 233-251.

[4] Mogas Soldevila L.,Matzeu G.,Presti M. Lo,Omenetto F.G.. Additively manufactured leather-like silkprotein materials[J]. Materials & Design,2021,203(prepublish).

[5] Shao Yun Fei,Qing Xiangcheng,Peng Yizhong,Wang Hui,Shao Zengwu,Zhang Ke Qin. Enhancement ofmechanical and biological performance on hydroxyapatite/silk �broin scaffolds facilitated bymicrowave-assisted mineralization strategy[J]. Colloids and Surfaces B: Biointerfaces,2021,197.

[6] Wang Fang,Li Yingying,Gough Christopher R.,Liu Qichun,Hu Xiao. Dual-Crystallizable SilkFibroin/Poly(L-lactic Acid) Biocomposite Films: Effect of Polymer Phases on Protein Structures in Protein-Polymer Blends[J]. International Journal of Molecular Sciences,2021,22(4).

Page 10/15

[7] Zhu, Lu,Xu, Weilin,Ma, Mingbo,Zhou, Hao. Effect of Plasma Treatment of Silk Fibroin Powder on theProperties of Silk Fibroin Powder/Polyurethane Blend Film[J]. Polymer Engineering andScience,2010,50(9). 

[8] Wang, Y. H., et al. (2020). "Soy protein and halloysite nanotubes-assisted preparation ofenvironmentally friendly intumescent �ame retardant for poly (butylene succinate)." Polymer Testing 81:12.

[9] Cai Kaiyong,Yao Kangde,Cui Yuanlu,Yang Zhiming,Li Xiuqiong,Xie Huiqi,Qing Tingwu,Gao Laibao.In�uence of different surface modi�cation treatments on poly(D,L-lactic acid) with silk �broin and theireffects on the culture of osteoblast in vitro.[J]. Biomaterials,2002,23(7).

[10] G. Laufer, C. Kirkland, A. B. Morgan, and J. C. Grunlan, Biomacromolecules, 13, 2843 (2012). 

[11] Chen Zhiquan,Jiang Juncheng,Yu Yuan,Chen Gang,Chen Tingting,Zhang Qingwu. Layer‐by‐layerassembled bagasse to enhance the �re safety of epoxy resin: A renewable environmental friendly �ameretardant[J]. Journal of Applied Polymer Science,2020,138(11).

[12] Keeney, M., et al. (2015). "Nanocoating for biomolecule delivery using layer-by-layer self-assembly."Journal of Materials Chemistry B 3(45): 8757-8770.

[13] Yang Zhong,Bingyun Li,Donald T. Haynie. Fine Tuning of Physical Properties of Designed PolypeptideMultilayer Films by Control of pH[J]. Biotechnology Progress,2006,22(1).

[14] Li, Bingyun,Haynie, Donald T.,Palath, Naveen,Janisch, Danielle. Nanoscale Biomimetics: Fabricationand Optimization of Stability of Peptide-Based Thin Films[J]. Journal of Nanoscience andNanotechnology,2005,5(12).

[15] H. F. Pan, W. Wang, Y. Pan, L. Song, Y. Hu, and K. M. Liew, Carbohydr. Polym., 115, 516 (2015). 

[16] Liu, X. D., et al. (2020). "Improving the �ame retardant properties of polyester-cotton blend fabrics byintroducing an intumescent coating via layer by layer assembly." Journal of Applied Polymer Science137(41): 10.

[17] Shang, S., et al. (2019). "Facile preparation of layered melamine-phytate �ame retardant viasupramolecular self-assembly technology." Journal of Colloid and Interface Science 553: 364-371.

[18] Yan, H. Q., et al. (2017). "Application of poly(diphenolic acid-phenyl phosphate)-based layer by layernanocoating in �ame retardant ramie fabrics." Journal of Applied Polymer Science 134(20): 13.

[19] Zhou, L. and Y. C. Fu (2020). "Flame-Retardant Wood Composites Based on Immobilizing withChitosan/Sodium Phytate/Nano-TiO2-ZnO Coatings via Layer-by-Layer Self-Assembly." Coatings 10(3):12.

Page 11/15

[20] Zhao, F. Y., et al. (2020). "Preparation and Synergistic Effect of Chitosan/Sodium Phytate/MgONanoparticle Fire-Retardant Coatings on Wood Substrate through Layer-By-Layer Self-Assembly."Coatings 10(9): 9.

[21] Wan, Y., et al. (2021). "Surface Properties of Spray-Assisted Layer-By-Layer ElectroStatic Self-Assembly Treated Wooden Take-Off Board." Applied Sciences-Basel 11(2).

[22] Federico Carosio,Alessandro Di Blasio,Jenny Alongi,Giulio Malucelli. Green DNA-based �ameretardant coatings assembled through Layer by Layer[J]. Polymer,2013,54(19).

[23] Li, S. S., et al. (2019). "Layer-by-Layer Self-assembly of Organic-inorganic Hybrid Intumescent FlameRetardant on Cotton Fabrics." Fibers and Polymers 20(3): 538-544.

[24] Federico Carosio,Galina Laufer,Jenny Alongi,Giovanni Camino,Jaime C. Grunlan. Layer-by-layerassembly of silica-based �ame retardant thin �lm on PET fabric[J]. Polymer Degradation andStability,2011,96(5).

Figures

Figure 1

Page 12/15

DBP FTIR spectra of different assembled layers

Figure 2

Micro morphology of SF before and after modi�cation

Figure 3

Surface and internal microstructure of DBP

Page 13/15

Figure 4

Digital photo of EP composites after UL-94 test.

Figure 5

HRR, THR of DBP

Page 14/15

Figure 6

TGA and DTG curves of DBP under N2 atmosphere.

Figure 7

SEM image of carbon residue in different assembled layers

Page 15/15

Figure 8

DBP residual carbon C1S, N1S, O1S and total high-resolution XPS spectra.