Fabrication of Nitrogen-Doped Graphene ... - ACS Publications

Subscriber access provided by Kaohsiung Medical University

Article

Fabrication of nitrogen-doped graphene decorated with organophosphor and lanthanum towards high-performance ABS nanocomposites Guobo Huang, Deman Han, Yanxian Jin, Pingan Song, Qidong Yan, and Chao Gao ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00411 • Publication Date (Web): 05 Jun 2018 Downloaded from http://pubs.acs.org on June 5, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Nano Materials

Fabrication

of

nitrogen-doped

graphene

decorated

with

organophosphor and lanthanum towards high-performance ABS nanocomposites Guobo Huang,a,b,* Deman Han,b Yanxian Jin,b Pingan Song,c Qidong Yan,d Chao Gaoa, a

MOE Key Laboratory of Macromolecular Synthesis and Functionalization,

Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China b

School of Pharmaceutical and Chemical Engineering, Taizhou University, Taizhou

318001, China c

Department of Materials, College of Engineering, Zhejiang A & F University,

Hangzhou, 311300, China d

Department of Medicine and Pharmaceutical Engineering, Taizhou Vocational &

Technical College, Taizhou 318000, China ABSTRACT: Despite substantial advances, it remains imperative but challenging to develop high-performance polymer/graphene nanocomposites combining with excellent mechanical, thermal and fire retardant properties. In this work, a novel kind of graphene-based multifunctional nanofiller (La@PN-RGO) was fabricated via the nitrogen doping and the decoration with organophosphorus and lanthanum based on graphene oxide, which is then incorporated into acrylonitrile butadiene styrene (ABS) resin via melt-blending to obtain resultant ABS nanocomposites. As expected, the La@PN-RGO nanosheets were well dispersed in ABS composites. Attractively, with only 1.0 wt% of La@PN-RGO incorporated into ABS matrix, the peak heat release

ACS Paragon Plus Environment

ACS Applied Nano Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

rate (PHRR) and total smoke production (TSP) were significantly reduced by 38 % and 36 %, which is much superior to its counterparts at the same nanofillers loading level. The notably enhanced fire safety was primarily attributed to the rare earth catalysis accompanied with the lamellae blocking effect and intumescent flame retardancy of La@PN-RGO. Additionally, ABS/La@PN-RGO composite exhibited a 16 % enhancement in tensile strength without at the expense of extensibility. This effective and promising method may open a new pathway to obtain high-performance polymer/graphene nanocomposites. KEYWORDS: Nanocomposites; graphene oxide; nitrogen-doping; rare earth; flame retardancy; smoke-suppression; mechanical


Page 2 of 34

Page 3 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Recent development of carbon nanomaterials has drawn much attention in a wide range of fields owing to their intrinsic structure, mechanical,1-3 electrical,4,5 gas barrier properties,6,7 and flame retardation.8-11 Interest in the flame-retardant field has shifted from carbon nanotubes and carbon fullerenes toward another novel carbon nanomaterials such as graphene. A few of articles have been reported about the flame retardancy of graphene on polymer in recent years. During combustion, graphene plays a central role in forming compact protective layers shielding the polymer matrix from heat feedback and external radiation from flame.12-15 As a result, a very low loading graphene often improve significantly the flame retardant properties of polymeric nanocomposites.8,9,13 Unfortunately, the great majority of graphene based polymer composites frequently do not pass the UL-94 test, and therefore the flame-retardant

efficiency

of

graphene

should

be

further

improved

for

high-performance polymer nanocomposites. As is known to all, carbon nanomaterials functionalized with intumescent flame retardants (IFRs) have been pondered as a hopeful candidate for their high efficiency and environment-friendly advantages recently.16-22 Functionalization not only can promote their dispersion in polymeric matrix when preparing composites and conferring outstanding reinforcing performances on polymer composites, but also can provide the intumescent flame retardancy with the barrier effect from carbon nanomaterials during combustion, thereby improving the flammability of polymeric nanocomposites. For example, Fang and Song, et al have fabricated carbon nanotubes



and fullerene decorated with oligomeric IFRs, and found that the functionalized carbon nanotubes and fullerene could achieve better dispersion in polymeric matrix, and postpone significantly the thermal oxidation process of polymeric matrix and confer excellent flame retardancy on polymer composites.16,17 Besides, much work has been done in our group about investigating graphene functionalized with IFRs on the flame retarded effect of nanocomposites. Some oligomeric and dendritic IFRs were designed and used as graphene modification reagents in order to enhance the fire retardant properties of nanocomposites.19,20 Most of these works has demonstrated that functionalization can increase the dispersion of graphene within polymeric matrix, and enhance the synergism between graphene and IFRs, which improves the performance of nanocomposites. Recently, polymer nanocomposites modified with IFRs-functionalized graphene have achieved encouraging progress in both fundamental research and industrial application. However, it is still challenging to obtaining the high flame-retardant efficiency graphene. For this purpose, much graphene functionalization had been designed to enhance the flame retardancy of polymeric nanocomposites. Meanwhile, nitrogen doping should be a feasible method for optimizing graphene properties by modifying composition, structure and surface chemical state of graphene.23-27 Nitrogen-doped graphene (N-doped graphene), as a starting material for further chemical modifications, could be used for reversible nitrogen storage or as a new blowing agent for IFRs system from the view of polymer flame retardancy. Previous work has also proven that it is feasible that the N-doped graphene with high nitrogen


Page 4 of 34

Page 5 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


content could be synthesized via hydrothermal method, providing a new method for the development of improving the grafting degree of IFRs-functionalized graphene. It is well-known that IFRs have been usually utilized in the flame retardacy modification of polymers for their environment friendly. However, in order to reach combustible grade, the high content IFRs are usually added into the polymeric matrix. A small amount of rare earth compounds, such as lanthanum,28,29 cerium,30 neodymium31 and so forth, often bring significant improvements in fire retardant properties, which implies that they can promote the improvement of IFRs effectiveness. Inspired by the reported flame retardancy of rare earth and IFRs oxide, a novel kind of graphene-based nanofillers should be fabricated via the nitrogen doping and decoration with organophosphor and lanthanum, and used to improve the flame retardance of acrylonitrile-butadiene-styrene copolymer (ABS) composites. These functional graphene is expected to not only improve the efficiency of intumescent systems with rare earth catalysis, but also enhance the mechanical properties of resultant ABS composites owing to good dispersion. Therefore, this work will provide a new strategy to obtain high-performance flame retardant ABS composites, and address the existing bottleneck of current graphene-based flame retardants with low efficiency.

EXPERIMENTAL SECTION Materials. Natural graphite was bought from Qingdao BCSM Co. Ltd (Qingdao, China) and it had an average size of around 4 µm. Graphene oxide (GO) was synthesized according to the modified Hummer’s method and then dried with P2O5



under vacuum condition for at least 7 days.32,33 Diphenyl phosphoryl chloride (DPC) was purchased by Linhai Duqiao Fine Chemical Factory (Taizhou, China). Phosphoryltrichloride was provided by Shanghai Chemical Reagent Co. (Shanghai, China). Lanthanum nitrate six hydration (La(NO3)3·6H2O) was purchased by Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). ABS (0215A) was supplied as pellets by CNPC Jilin Chemical (Jilin, China). Fabrication of La@PN-RGO. The typical synthesis route to nitrogen-doped graphene decorated with organophosphor and lanthanum (La@PN-RGO) was shown in Scheme 1 including three steps. As for the first step, i.e. the N-doped reaction of GO, 100 mg GO was dispersed into 10 mL of deionized water to form a brown-black suspension after 2 h sonication at ambient temperature. 10 mL of ammonia solution with ~28 % concentration was put into the dispersion with ultrasonic treatment for 0.5 h. This above mixture, sealed in a teflon-lined autoclave, was placed in 110 °C oven for 8 h. At the end of the reaction, the filtered mixture was washed with deionized water for several times , then was dried by vacuum filtration. The product was designated as N-RGO. The next step is the graft reaction of organophosphor DPC. The amine groups of N-RGO react with phosphonyl chloride of DPC or phosphoryltrichloride with the by-products of HCl. Briefly, 0.2 g of DPC and a small amount phosphoryltrichloride were put into a 100 mL of trichloromethane filled with 0.8 g N-RGO and 0.2 g triethylamine. Afterwards, the solution was allowed to ultrasonic react for 10 h at ambient temperature. The slurry product was filtered upon the completion of the


Page 6 of 34

Page 7 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reaction and the target product designated as PN-RGO was obtained. The last step is the ionic reaction of lanthanum nitrate compound with PN-RGO, i.e., the phosphonyl chloride groups grafted on the surface of PN-RGO react with H2O and turn into phosphoric acid, which reacts with La ion subsequently by complexation. Typically, 1.0 g of PN-RGO were put into 100 mL of deionized water with ultrasonic treatment for 2 h, then 0.02 g of La(NO3)3·6H2O was added into the above mixture, which continues to be stirred for 8 h at 25 oC. The product was filtered and washed with distilled water several times to withdraw redundant reactant. The final product designated as La@PN-RGO. Fabrication of ABS nanocomposites. The ABS/La@PN-RGO composites containing 0.2 and 1.0 wt% of La@PN-RGO were prepared via melt blending (the processing temperature of Thermo Haake Rheometer: 190 oC, screw speed: 80 rpm, and the mixing time: 15 min). The mixed samples were shaped in put into a square mold at 210 oC, and cooled to room temperature for further measurement. ABS composites filled with 0.2 and 1.0 wt% of La@PN-RGO were designated as ABS/[email protected] and ABS/La@PN-RGO1. ABS composites filled with 0.2 and 1.0 wt% of PN-RGO were designated as ABS/PN-RGO0.2 and ABS/PN-RGO1 respectively. Reduced graphene oxide (RGO) was obtained according to previous literatures.13 The ABS parallel samples filled with 0.2 and 1.0 wt% RGO were designated as ABS/RGO0.2 and ABS/RGO1 respectively. Characterization and testing. Fourier transform infrared spectroscopy (FT-IR) was obtained on a Nicolet-5700 FT-IR spectrometer using KBr pellet technique over



the wavenumber ranging from 4000 to 400 cm-1. X-ray photoelectron spectroscopy (XPS) measurements was carried out by a Kratos AXIS Ultra DLD electron spectrometer. Transmission electron microscopy (TEM) measurements, high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images and the EDX mapping were photographed using a Tecnai G2 F30 S-TWIN microscope embedded with energy-dispersive X-ray spectroscopy. Transmission electron microscopy (TEM) observation was conducted by a JEM-1230 transmission electron microscope. The ABS composite specimens were stained with OsO4 in order to observe clearly the styrene-acrylonitrile (SAN) and polybutadiene (PB) phase of ABS. Dynamic mechanical thermal analysis (DMA) was carried out by a DMA 8000 dynamic mechanical analyzer at a constant frequency of 1 Hz with a heating rate of 1 °C/min. Tensile stress strain test was measured using a AG-IS mechanical strength tester following ASTM D-638 procedure. Thermogravimetric analysis (TGA) was done in a Q600SDT thermal analyzer in nitrogen (N2) flow at a heating rate of 10 °C/min. Combustion behavior of ABS composites was evaluated according to the procedures in ISO 5660-1 under the external heat flux value of 35 kW/m2. The limiting oxygen index (LOI) and UL-94 rating was measured according to ASTM-D-2863 and ASTM-D-3801. Morphological study of residual chars was performed using scanning electron microscopy (SEM).

RESULTS AND DISCUSSION Characterization of La@PN-RGO. Figure 1a shows the FT-IR spectra of GO, D-GO, PN-RGO and La@PN-RGO. The FT-IR spectrum of GO presents some


Page 8 of 34

Page 9 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


absorption peaks at 3147, 1726, 1636, 1386 and 1091 cm-1 can be assigned to stretching vibrations of hydroxyl, carbonyl, carbon-carbon double bond, C-OH and C-O groups, respectively. Compared with GO, several new absorption peaks located at 3444, 1569 and 1128 cm-1 appear in the spectrum of N-RGO sample.23,24 These peaks can belong to the bending or stretching vibrations of N-H and C=N bonds from N-RGO. After aminoacryl reaction, the new peaks at 1258, 1070 and 1001 cm-1, assigned to P-O and P=O bonds of DPC, appear in the PN-RGO spectrum, indicating that N-RGO has been grafted by DPC. As for the La@PN-RGO sample, its FT-IR spectrum is similar to that of PN-RGO. The XPS survey scans are presented in Figure 1b. Relative to the GO sample with two binding energy (BE) peak of C1s at 284.8 eV and BE peak of O1s 533.1 eV, N-RGO presents BE peak of N1s at ~399.4 eV indicating the presence of N in N-RGO. Besides C1s, N1s and O1s BE peaks, peaks at 191.4, 199.2 eV (P2s) and 132.8 eV (P2d) are also probed from the PN-RGO sample, further supporting the grafting of phosphorus oxychloride onto N-RGO. Compared with PN-RGO, La@PN-RGO shows an extra peak at 834.9 eV correspond to La3d peak, which indicate the presence of La in this sample. In addition, the element composition of the above sample is presented in Table S1. N-RGO shows the nitrogen content of 7.38 wt%, while the oxygen content of N-RGO is evidently reduced by nitrogen doping and reduction process. For PN-RGO sample, besides of a nitrogen content of 6.37 wt%, the content of phosphorus reaches 2.72 wt%. Compared with PN-RGO, La@PN-RGO exhibits a similar content of nitrogen and phosphorus, and a lanthanum



content of 0.72 wt% owing to complexation of lanthanum ions. Figure 2 shows C1s, N1s, P2p and La3d spectra of the functionalized graphene La@PN-RGO. The dominant peaks in the GO spectrum, assigned to groups with carbon oxygen bond and carbonyl, are located at 286.8 and 288.6 eV. The N-RGO sample possesses sharply fewer of the above oxygen functionality. The N 1s peaks located at 398.6 eV show that the nitrogen of N-RGO may come from amine or pyridine groups, while the width of N 1s peaks indicates contributions from quaternary nitrogen and pyridone groups (see Figure S1). Similarly, the C1s spectrum of La@PN-RGO displays two BE peaks, ascribed to the C-C/H and CO-N groups, are located at 285.4 and 286.8 eV, respectively. From N1s spectrum of La@PN-RGO, BE peaks for pyridine, pyridone and quaternary nitrogen groups, located at 398.7, 400.1 and 401.1 eV respectively, are found. This further supports that the amide-like intermediates are formed after ammonia reacts with oxidized functional groups of GO.27 P2p and La3d spectra for La@PN-RGO are respectively shown in Figure 2c and Figure 2d. Figure 2c shows the peak at 131.26 ascribed to the P-O bond from phosphorus oxychloride, which furtherly confirm that phosphorus oxychloride DCP has been reacted with N-RGO. Additionally, the distinct La3d peak around 834.9 eV is clearly observed in Figure 2d. This is typical value for trivalent La, indicating that the loaded La is ionic compound. XRD patterns of GO, N-RGO, PN-RGO and La@PN-RGO are shown in Figure S2. For the GO sample, the characteristic diffraction peak disappears completely, and a new diffraction peak appears at about 10 o in the pattern, which may be attributed to


Page 10 of 34

Page 11 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(001) crystal plane of GO. After nitrogen doping of GO, the peak at about 25 ° reappears with weaker intensity and broader width relative to graphite while the peak at about 10 ° disappears, which indicates reduction of GO. For the PN-RGO and La@PN-RGO samples, the dominant 002 reflections shift to higher angles, indicating lower spacing values of graphene sheet (~0.37 nm). These chemical shifts show a decrease in the oxygen content owing to the reaction with ammonia. These similar results are reported in previous literatures.26 TEM images provide another evidence of the morphologic variations. As shown in Figure 3a, b, GO sheet displays a typically transparent and slightly crumpled sheet-like structure, however, La@PN-RGO nanosheet is relatively rough with “darkening features” discernible on the surfaces owing to the flame retardant loading on GO, which is further proved by the uniform distribution of carbon, oxygen, nitrogen, phosphorus and lanthanum elements on La@PN-RGO (Figure 3g-j). The functionalized graphene was further confirmed by Raman spectra. As shown in Figure S3, the G-band of N-RGO red-shifts to 1583 cm-1, which is close to the pristine graphite value (1579 cm-1), indicating the thermal reduction of GO via hydrothermal process in ammonia solution. The functionalized graphene sheets show apparently higher intensity ratio of D to G (I (D/G)) (1.41 for N-RGO, 1.45 for PN-RGO, and 1.47 for La@PN-RGO) than GO (1.24), which suggests that the functionalized graphene nanosheets are more disordered as compared to GO, which is aligned with the corrugation structure observed by TEM and XRD. Morphology. The dispersion of nanofiller and interfacial interaction of constituents,



as the controlling factors for polymer nanocomposites, influence the properties of the composite materials. In order to obtain the dispersion and morphology of functional graphene within polymeric matrix, XRD and TEM observations were conducted. ABS matrix shows a broad diffraction peak with 2θ=21.4° (see Figure S4). After RGO, PN-RGO and La@PN-RGO dispersed into the ABS matrix, the diffraction peak for GO disappears in the ABS/RGO, ABS/PN-RGO and ABS/La@PN-RGO composites under 1 wt% loading (see Figure S4), which indicates that graphene losses its structure regularity. Figure 4 shows the TEM images of ABS/RGO and ABS/La@PN-RGO composites contained 1 wt% nanofillers. As shown in Figure 4a, most of graphene sheets agglomerate each other in ABS/RGO composites. However, at higher magnification (Figure 4c), intercalation structure of graphene sheets can be also observed. Compared with the ABS/RGO sample, the TEM image of ABS/La@PN-RGO composites (Figure 4b) shows better dispersion for the grafting of organophosphor from La@PN-RGO. Furthermore, at higher magnification (Figure 4d), many exfoliated graphene are dispersed in the shape of dark-grey lines in polymeric matrix. The organophosphor compound, grafted onto the surface of graphene sheets, contains a number of functional groups (phenoxy, phosphoramide, amide, etc.) producing the stronger interactions between polymeric chains and graphene nanosheets, which improve the graphene dispersion in ABS resin matrix. In additional, both nitrogen doping and organophosphor modification weaken the interactions of polar groups on the surface of graphene sheets and prompt exfoliation to take place during melt blending. Some graphene-base nanocomposites had been


Page 12 of 34

Page 13 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


produced via melt blending with hydrophobic polymers such as polypropylene, polyurethane

20,36

7,34,35

and ABS 37 in previous literature.

Mechanical properties. Generally, a major shortcoming associated with the traditional flame retardants such as ATH, bromine-based flame retardants, IFRs, and so forth regardless of incorporating into ABS resin by melt blending or covalently grafting strategies, is the deterioration in mechanical properties. Here the storage modulus (E') and loss factor (tan δ) from ABS composites are presented in Figure 5. Qualitatively, the E' values of ABS/La@PN-RGO composites increase dramatically with the stepwise loading of La@PN-RGO, indicating the efficient reinforcement effects of La@PN-RGO. Under the same loading, the E' values of ABS/La@PN-RGO composites are higher than that of ABS/RGO composites, indicating that the reinforcement of La@PN-RGO for ABS matrix excels that of RGO. The glass transition temperature (Tg) of ABS composites, determined by the transition peak of tan δ values, shows the similar trend, namely obviously shifting toward higher temperature with increasing La@PN-RGO content. For example, the Tg increases from 117.3 °C for ABS to 125.4 °C for the ABS/La@PN-RGO1 sample. By comparison, the enhancement for Tg is not observed in ABS/RGO composites. Such enhancements are mainly ascribed to the better dispersion and improved interfacial interaction between La@PN-RGO and ABS matrix owing to the existence of organophosphor on the surface of graphene sheets. Figure 5c, d, show the stress-strain profiles of ABS composites and their mechanical parameters, respectively. It is clear that the tensile strength (σ) of ABS



Page 14 of 34

composites is obviously enhanced by adding RGO and La@PN-RGO, while the reduction in the elongation (ε). Relative to ABS resin, ABS/RGO1 shows a nearly 6 % increase in σ (~55.1 MPa), and the strength of ABS/La@PN-RGO1 reaches ~60.4 MPa and displays ~16 % increase in σ, which indicate the excellent reinforcement effect of La@PN-RGO for ABS resin. Moreover, the ε of ABS/La@PN-RGO is more than that of ABS/RGO. The remarkable improvements in mechanical performances are primarily owing to the uniform dispersion of La@PN-RGO within the polymer matrix and the mechanical reinforcement effect of modified graphene, well agreeing with both XRD and TEM results. In comparison, adding other conventional halogen-,38

phosphorus-,39

phosphorus-nitrogen-containing

12,13,40

compounds,

normally results in a noticeable reduction in the tensile strength and toughness of the polymer matrix because of weak interfacial compatibilization between polymer host with flame retardants. Thermal stability. Thermal degradation behaviour for ABS nanocomposites is investigated by thermogravimetry analysis (TGA). TGA curves and data of ABS composites are shown in Figure 6 and Table S2. The initial degradation temperature (Ti) of ABS is 362 °C, and the temperature of maximum weight loss (Tmax) reaches 420 °C. Relative to ABS resin, the Ti and Tmax of ABS/RGO composites filled with 1 wt% loading display a slight increase, which are increased by only 3°C and 4°C respectively, which indicates that graphene can prevent the thermal degradation of ABS resin for the sheet barrier effect. The similar reports were found from another polymer/graphene nanocomposites.41,42 However, adding PN-RGO or La@PN-RGO


Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


into ABS resin increases the Ti and Tmax to different extent. For ABS composites filled with PN-RGO, Ti and Tmax is higher than that of ABS resin. This phenomenon can be ascribed to the char-forming of organophosphor on the surface of graphene sheet, which delays effectively the degradation of ABS matrix. However, Ti and Tmax of La@PN-RGO contained samples are higher than that of RGO or PN-RGO contained samples, moreover, the residual weights are improved extremely by the addition of La@PN-RGO. For example, relative to pure ABS resin, the Ti and Tmax of the ABS/La@PN-RGO1 sample increases 12oC and 16 oC, respectively, and the residual weights of ABS/La@PN-RGO1 increase about six times. The results indicate that catalytic action of rare earth (La) loaded on the surface of graphene sheet greatly enhances char-forming effect on the ABS matrix. Flammability and smoke suppression. As presented in Figure 7a and Table 1, the ABS resin is of an flammable polymeric material and the peak heat release rate (PHRR) reaches a value 736 kW/m2. As for the RGO contained ABS samples, the values of PHRR are obviously reduced, while TTI, total heat release (THR) and average mass loss rate (AMLR) exhibit little change compared with ABS resin. For ABS/PN-RGO samples, PHRR, THR and AMLR are reduced by adding PN-RGO. The PHRR of ABS/PN-RGO1 is reduced by about 19 % compared with neat ABS resin. The THR reduction indicates that some polymer chains are carbonized, which attributes to the intumescent flame retardancy of N-doped graphene modified with organophosphor. Compared with neat ABS resin, the PHRR of ABS/La@PN-RGO1 is reduced by about 38 %. For the ABS/La@PN-RGO1 sample, TTI is 15 seconds



longer than that of ABS resin. Meanwhile, the values of PHRR, THR, ASEA and AMLR of ABS/La@PN-RGO1 are lower than those of ABS/RGO1 and ABS/PN-RGO1. These indicate that the rare earth catalysis based on nitrogen-doped graphene decorated with organophosphorus improve effectively the flammability properties of ABS. Figure 7b and Table 1 show that the addition of RGO decreases the peak smoke production rate (PSPR) of ABS resin, but the total smoke production (TSP) remain slight change. In the case of ABS/La@PN-RGO composites, the PSPR and TSP greatly decrease in comparison with neat ABS resin. Moreover, the PSPR and TSP of ABS/La@PN-RGO samples are lower than that of ABS/RGO and ABS/PN-RGO. The PSPR and TSP of ABS resin is 0.272 m2/s and 42.7 m2/s, while the only 1.0 wt% addition of La@PN-RGO makes the PSPR and TSP decrease by 44 % and 36 %, respectively. At the same loading, PN-RGO makes the PSPR and TSP of ABS resin to decline by only 27 % and 17 %, respectively. This provides further evidence that the rare earth catalysis of IFRs-functionalized graphene enhances greatly the smoke suppression properties of ABS composites. The combination between IFRs and rare earth had been already reported for polymer composites.

27-31

Flame retardant polymeric composites with enhanced fire

resistance were prepared by using rare earth metal compound as synergist. In this paper, the lamellae blocking effect of graphene, intumescent flame retardancy and rare earth catalysis are clarified clearly as compared with the flammability of ABS composites above. Compared with the PHRR values of ABS and ABS/RGO1, the


Page 16 of 34

Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


lamellae blocking effect of graphene shows a 11 % reduction in the PHRR of ABS. Similarly, the flame retardancy of IFRs system comprised of N-doped graphene and organophosphor and rare earth catalysis shows a 8 % and 19 % reduction in the PHRR of ABS, respectively. As for smoke suppression, the flame retardancy of graphene, IFRs system and rare earth catalysis makes TSP to decline by 8 %, 9 % and 19 %, respectively, according to the calculation methods above. Such outstanding flame retardancy and smoke suppression for La@PN-RGO are mainly due to the rare earth catalysis only at very low concentrations (

Fabrication of Nitrogen-Doped Graphene ... - ACS Publications

Recommend Documents