Efficient Flame-Retardant and Smoke-Suppression Properties of Mg

Subscriber access provided by TUFTS UNIV

Article

Efficient Flame-Retardant and Smoke-Suppression Properties of Mg– Al Layered Double Hydroxide Nanostructures on Wood Substrate Bingtuo Guo, Yongzhuang Liu, Qi Zhang, Fengqiang Wang, Qingwen Wang, Yixing Liu, Jian Li, and Haipeng Yu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b06803 • Publication Date (Web): 21 Jun 2017 Downloaded from http://pubs.acs.org on June 22, 2017

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 free 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 accessible to all readers and 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.

ACS Applied Materials & Interfaces 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 32

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 Materials & Interfaces

Efficient Flame-Retardant and Smoke-Suppression Properties of Mg–Al Layered Double Hydroxide Nanostructures on Wood Substrate Bingtuo Guo†, Yongzhuang Liu†, Qi Zhang†, Fengqiang Wang†, Qingwen Wang†, Yixing Liu†, Jian Li†, Haipeng Yu*,† †

Key laboratory of Bio-based Material Science and Technology of Ministry of Education, Northeast Forestry University, Harbin, 150040, P. R. China

*

Corresponding: Haipeng Yu, E-mail: [email protected].

ABSTRACT: Improving the flame retardancy of wood is an imperative, yet highly challenging step in the application of wood in densely populated spaces. In this study, Mg–Al layered double hydroxide (LDH) coating was successfully fabricated on a wood substrate to confer flame-retardant and smoke-suppression properties. The chemical compositions and bonding states characterized by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirmed the coating constituents of Mg–Al LDH. The coating evenly covered the sample wood surfaces and provided both mechanical enhancement and flame-retardancy effects. The limiting oxygen index of the Mg–Al LDH-coated wood increased to 39.1% from 18.9% in the untreated wood. CONE calorimetry testing revealed a 58% reduction in total smoke production and a 41% reduction in maximum smoke production ratio in the Mg–Al LDH-coated wood compared to the untreated wood; the peak heat release rate and total heat release were also reduced by 49% and 40%, respectively. The Mg–Al LDH coating is essentially hydrophilic, but simple surface modification by fluoroalkyl silane could make it superhydrophobic, with a

ACS Paragon Plus Environment


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

Page 2 of 32

water contact angle of 152° and a sliding angle of 8.6°. The results of this study altogether suggest that Mg–Al LDH coating is a feasible and highly effective approach to nanoconstructing wood materials with favorable flame-retardant and smoke-suppression properties. KEYWORDS: layered double

hydroxides,

coatings,

wood, flame

retardancy,

superhydrophobicity

1. INTRODUCTION Wood is widely popular as a furniture and interior decoration material due to its unique aesthetic characteristics and excellent mechanical properties.1 The flammability of wood represents a major restriction on its use in indoor environments, however – especially in densely populated areas. There is urgent demand for innovative flame-retarding technologies and flame-retardant wood materials.2 Traditional flame-retardant processing techniques involve soaking with flame retardants and applying organic fire-proof coatings or inorganic coatings to the wood surface.3−5 Inorganic coatings such as TiO2, SiO2, ZnO, FeOOH, and Al(OH)3, are non-toxic and not as easily run out as traditional organic retardants. They not only provide stiffness, hydrophobicity, UV resistance, and antimicrobial properties to wood,6−8 but also reduce its flammability and smoke production.9−12 Saka et al., for example, reported that Al(OH)3- or SiO2-based polynary inorganic oxides are very successful in endowing wood materials with flame-retardancy.13 A recent study by Carosio et al. reported that the


Page 3 of 32

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


maximum average rate of heat emission (MARHE) of wood can be reduced by 46% after applying nanocellulose/clay thin film as a fire-protective coating via hot pressing.14 Layered double hydroxide (LDH) is a class of hydrotalcite-like compounds with two kinds of metallic cations and exchangeable hydrated anions located in the interlayer region.15 LDH has flexible, tunable chemical composition and high anion exchange capacity which make it useful in an array of applications; it has been successfully used in catalysts,16 supercapacitance materials,17 photofunctional materials,18 textile coatings for oil/water separation,21 and adsorbents for As(V) polluted water cleanup.22 Mg–Al LDH has been reported to have a particularly strong resistance to flame as a result of the synergistic effect of Mg(OH)2 and Al(OH)3 in the layered structure.20−24 Majoni et al. investigated the effect of a palmitate containing 5 wt.% Mg–Al–C16 LDH on the flammability of polystyrene, and found that it results in a 47% reduction in the peak heat release rate (HRR) of the polymer.23 Li et al. introduced 4.5 wt.% Mg–Al LDH in sisal-fiber-reinforced silicone-modified phenolic composites to find that the total heat release (THR) was reduced by 60% compared to samples without LDH.24 Wood has inherently moisture absorption-caused dimension deformation problem and dangerous flammable characteristic, which are expected to be mitigated by applying a LDH coating. To the best of our knowledge, however, there has been no report to date on the fabrication of Mg–Al LDH coating on wood with both flame-retardancy and superhydrophobicity. This paper reports a two-step method for inducing the formation of Mg–Al LDH nanostructures on wood substrates to improve flame-retardancy and smoke-suppression performance. The method involves the formation of a boehmite (γ-AlOOH) gel layer on



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

Page 4 of 32

the wood surface via sol-gel processing followed by the in situ hydrothermal synthesis of Mg–Al LDH coating via solution intercalation. The morphology and chemical composition of the γ-AlOOH layer and Mg–Al LDH coating were analyzed with transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The combustion properties of the Mg–Al LDH-coated wood were investigated using thermogravimetric (TG) analysis, dynamic mechanical analysis (DMA), limiting oxygen index (LOI) test, and CONE calorimetry. Superhydrophobic Mg–Al LDH-coated wood

was

also

obtained

by

conducting

a

surface

modification

with

trimethoxy(1H,1H,2H,2H-heptadecafluorodecyl)silane (TDFS); the superhydrophobicity was confirmed by contact angle measurements.

2. MATERIALS AND METHODS 2.1. Materials Heartwood section of birch (Betula costata) grown in the Mao’er Mountain region was cut tangentially into timber specimens of four different sizes: 60 of them were 50 × 50 × 3 mm3 (L × T × R) for technological tests and characterization, 30 were 50 × 10 × 3 mm3 (L × T × R) for DMA tests; 35 specimens were 150 × 6.5 × 3 mm3 (L × T × R) for LOI tests, and 9 were 100 × 100 ×10 mm3 (L × T × R) for CONE calorimetry tests. All specimens were washed with acetone and water and oven-dried at 60 °C for 12 h, then stored in sealed containers prior to the coating reaction and combustion tests.


Page 5 of 32

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


Isopropyl alcohol [(CH3)2CHOH], aluminum isopropoxide [Al(OPr)3], magnesium chloride (MgCl2·6H2O), polyvinyl pyrrolidone, urea [CO(NH2)2], and TDFS were all analytically pure and produced by Kermel Chemical Reagent Co., Ltd. (Tianjin, China). 2.2. Fabrication of Mg–Al LDH Coating on Wood Samples Step 1: Formation of γ-AlOOH gel layer on wood First, 0.01 mol Al(OPr)3 was dissolved in 1,000 mL (CH3)2CHOH to obtain a transparent colloidal solution (solution A). The wood specimens were soaked in solution A and vacuum impregnated for 12 h, then the Al(OPr)3 on the wood surface was hydrolyzed to γ-AlOOH in an oven at 65 °C for 12 h.25 Step 2: Formation of Mg–Al LDH nanosheets on wood First, 0.025 mol MgCl2 and 0.3 g polyvinyl pyrrolidone were dissolved in 250 ml water (solution B), and 0.075 mol CO(NH2)2 was dissolved in 250 mL water (solution C). Solution C was slowly added to solution B to obtain a colloidal solution. The γ-AlOOH-coated wood specimens and colloidal solution were then placed in a Teflon-lined stainless steel autoclave and processed at 100 °C for various reaction times (8 h, 10 h, and 12 h). After the treatment, the specimens were cleaned and rinsed with alcohol and water. The final Mg–Al LDH-coated wood specimens were dried at 60 °C in a vacuum oven. 2.3. Surface Modification with TDFS The Mg–Al LDH-coated wood was immersed in 80 ml ethanol solution containing 5% TDFS (v/v) at room temperature, stirred continuously for 20 h, and dried at 60 °C in a vacuum oven to complete the modification process.



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

2.4. Characterization The surface element composition and chemical bonding states of the samples were analyzed by XPS (Thermo Fisher Scientific, East Grinstead, West Sussex, UK) under the following conditions: Excitation by monochromatic Al Kα; X-ray beam 6 mA; energy resolution 0.5 eV; sensitivity 350 kcps. A charge correction was made to reflect the fact that the C1s signal of contaminating carbon was centered at 284.8 eV. The elemental composition of the Mg–Al LDH-coated wood was examined by EDX (X-MaxN, Oxford Instruments, Oxford, UK). TEM observation of the Mg–Al LDH was performed using a JEM-2100 microscope (JEOL, Tokyo, Japan) at an acceleration voltage of 200 kV. The surface morphology of the Mg–Al LDH-coated wood was observed using a field-emission SEM device (JSM-7500, JEOL, Tokyo, Japan) at an operating voltage of 15 kV. A TG 209 analyzer (Netzsch, Selb, Germany) was used for thermal weight loss analysis with a range from ambient temperature to 760°C at a heating rate of 10°C min−1 under N2 protection. DMA tests were performed with a DMA242 analytical instrument (Netzsch, Selb, Germany) in three-point bending mode with 10 Hz frequency and 10°C min−1 heating rate from ambient temperature to 260°C. Three analyses were performed for each reaction condition. LOI tests were performed on a JF-3 oxygen index instrument (Jiangning Analysis Instrument Co., Nanjing, China) according to ISO 4589. This included O2 and N2 at 0.1 MPa with a 10 ml min-1 flow rate; the N2 flow rate changed with the adjustment of O2.


Page 6 of 32

Page 7 of 32

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


The combustion test was carried out on a dual CONE calorimeter (Fire Testing Technology Ltd., East Grinstead, UK) according to ISO 5660-1 standard at an irradiance of 50 kW m−2 (~715 °C). The nominal duct flow rate was 24 s−1 and the sampling interval was 5 s. The samples were arranged horizontally and protected with a stainless steel grid to prevent them from bending or expanding during combustion. Water contact angles of the untreated wood, Mg–Al LDH-coated wood, and TDFS-modified Mg–Al LDH-coated wood were obtained by OCA20 contact angle measuring system (Dataphysics, Stuttgart, Germany) at ambient temperature. An SNS-D 051/025 needle was used for this test. The volume of the individual water droplet in the static contact angle test was 5 µL. To measure the advancing and receding angles, a 4 µL droplet was placed on the surface and enlarged to 10 µL, to obtain the advancing angle. The droplet was then shrunk back down to 4 µL to obtain the receding contact angle. Sliding angles of the water were measured by increasing and decreasing the droplet volume while taking screenshots and calculating the difference between advancing and receding contact angles.26,27

3. RESULTS AND DISCUSSION 3.1. Elemental Composition and Chemical Bonding State Analysis The elemental composition and distribution of the Mg–Al LDH-coated wood were revealed by EDX analysis as illustrated in Figure 1. In addition to C and O elements corresponding to the wood components, high percentages of Mg and Al elements were clearly detected in the samples. As shown in the EDX mapping images, the Mg, Al, and O



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

elements were distributed uniformly on the wood surfaces. In short: the XPS and EDX analyses confirm that the Mg–Al compound was formed successfully and uniformly covered the wood surfaces. The XPS survey spectra of the untreated wood, γ-AlOOH-coated wood, and Mg–Al LDH-coated wood are shown in Figure 2. An Al2p peak with a binding energy of 74.3 eV was observed in the γ-AlOOH-coated wood sample (Figure 2a); this energy is in accordance with that in γ-AlOOH.27 Peaks at 1302.9 and 74.2 eV in the Mg–Al LDH-coated wood are attributable to the Mg1s and Al2p binding energies in Mg–Al LDH, respectively (Figure 2b,c).28 The binding energies of both Mg1s and Al2p were lower than those in the γ-AlOOH-coated wood, suggesting that Al3+ was substituted for Mg2+ during the formation of Mg–Al LDH, which destroyed the Al–O–Al and formed Al–O–Mg bonds.29 These observations further confirm that Mg–Al LDH was successfully synthesized on the wood surface. TEM measurements (Figure 2d) showed that the Mg–Al LDH had a laminated structure with roughly 20 nm thickness. 3.2. Morphological Observation Digital photographs and SEM images of the untreated wood, γ-AlOOH-coated wood, and Mg–Al LDH-coated wood are shown in Figure 3a-i. Aside from the color, the appearance of the wood did not dramatically change during the synthesis of the Mg–Al LDH coating. The wood became slightly lighter in color after the formation of the smooth γ-AlOOH layer (Figure 3b), which uniformly masked the wood substrate after colloidal solution-phase growth. High-magnification observations of the γ-AlOOH coating indicated a mostly homogeneous, uniformly distributed microstructure (Figure 3d). The


Page 8 of 32

Page 9 of 32

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


γ-AlOOH coat clearly contained uniformly-distributed mesopores. By contrast, after the in situ hydrothermal synthesis of Mg–Al LDH from the γ-AlOOH layer via solution intercalation technology, the wood darkened slightly in color (Figure 3e). This may have been due to the heat-induced discoloration and degradation of lignin during the 10-h hydrothermal process at 100 °C. The microstructure of the Mg–Al LDH coating contained flower-like hexagonal platelets (Figure 3f) with an average thickness of ~20 nm (inset, Figure 3g), which is markedly different from that of the γ-AlOOH layer structure. The average thickness of the Mg–Al LDH coating is about 1 µm, which cannot mask the color and texture of wood (Figure 3h,i). Although wood is a structurally anisotropic and morphologically heterogeneous material, the Mg–Al LDH coating is found to be sufficiently continuous and homogeneous on the substrate of wood at a more macroscopic scale. 3.3. Growth Process Analysis The synthesis of the Mg–Al LDH coating on the wood substrate was also investigated in detail. A schematic diagram of the process is shown in Figure 4. When a one-step co-precipitation method (Figure 4a) was used for the fabrication of the Mg–Al LDH coating, uneven aggregates of Mg–Al LDHs were generated on the wood substrate (Figure 4e) because nucleation, growth, and intercalation occurred simultaneously and randomly, both in the solution and on the wood substrate. The aggregation process was effectively resolved when the fabrication process was separated into two steps, however (Figure 4b). After pre-preparation of the γ-AlOOH layer on the wood substrate, the Mg–Al LDH coating based on the γ-AlOOH crystallite structure was successfully hydrothermally



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

synthesized by in-situ incorporating Mg2+ in the γ-AlOOH structure (Figure 4f). During this process, the charge was imbalanced by replacing Al3+ with the less-charged Mg2+, destroying the hydrogen bonds between the γ-AlOOH structures. The carbonate ions in the solution were intercalated into the interlayer to balance the charge, then the main layers formed a three-dimensional network with the positive charge being balanced by the ions. This formed a laminated intercalation structure of Mg–Al LDH on wood surfaces.30–32 When the growth time was prolonged from 8 h to 10 h, a more complex and interlaced microstructure formed as shown in Figure 4g. Longer reaction times allowed more Mg2+ to be incorporated into the γ-AlOOH layer, but the Mg–Al LDH content was limited by the γ-AlOOH precursors; after longer reaction times, the morphology of the Mg–Al LDH nanostructure remained fairly stable (Figure 4h). Our results suggest that a 10-h reaction time is optimal for obtaining high quality Mg–Al LDH coating with low energy consumption. 3.4. TG Analysis The TG curves for the untreated wood and the Mg−Al LDH-coated wood are shown in Figure 5. The wood components were degraded in three stages. Stage one (180°C–280°C) showed a low pyrolysis rate and mass loss mostly due to the partial degradation of hemicelluloses and lignin. Stage two (280°C–380°C) was mainly caused by the continued degradation of lignin and cellulose decomposition, with a maximal pyrolysis rate at 380°C and mass loss of 64%. In the third stage, starting from 380°C, the residual wood components continued to aromatize and carbonize until about 18 wt.% of remained. The thermal decomposition of the Mg−Al LDH coated-wood can similarly be divided


Page 10 of 32

Page 11 of 32

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 three stages: 1) Loss between 160 and 280 °C (with peak at 247.4 °C) was due to the decomposition of hemicelluloses and mainly the interlayer H2O of Mg–Al LDHs.33 2) Approximate 40% mass loss between 280 and 380 °C was due to the decomposition of lignin and cellulose, as well as the thermotropic phase transition of Mg−Al LDHs to diaspore and brucite structures. 3) Loss above 380°C was mainly caused by the decomposition of wood residues. 3.5. DMA Analysis Storage modulus (E′) is a pivotal index for measuring the energy storage capability of material after elastic deformation. Figure 6a shows the E′ of the untreated wood and Mg–Al LDH coated-wood samples. The E′ of untreated wood decreased as temperature increased due to the increased chain mobility of wood components at high temperatures. The E′ of the Mg–Al LDH coated-wood increased by 32% compared to that of untreated wood, which was attributed to that the γ-AlOOH soaked inside the wood and the Mg–Al LDH coating on wood substrate had modified the bulk properties of wood and therefore the mechanical properties. The stiffness enhancement by them effectively compensated for the E′ loss caused by the degradation of wood components during the hydrothermal treatment. Figure 6b shows the loss tangent of the untreated and Mg–Al LDH coated-wood samples. The loss tangent of both samples increased too, suggesting the viscoelastic properties had also been changed by the γ-AlOOH inside the wood. The compounds bonds with the wood substrate hindered the movement of internal molecular chains in the wood, which consumed more energy to overcome the obstacles. 3.6. Combustion Test



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

The combustion properties of the Mg–Al LDH coated-wood were determined by LOI and CONE calorimetry testing. In comparison with the untreated wood, the LOI value increased from 18.9±1.3% to 39.1±2.7% after treatment, indicating a significant improvement in thermal stability and flame resistance. The effect of the Mg–Al LDH coating on the flame-retardant properties of wood was further explored using CONE calorimetry. The large amount of smoke produced in the early stages of a fire is very harmful, because smoke comprised of carbon particles can diminish visibility and release very harmful gases. The total smoke production (TSP) and smoke production ratio (SPR) of the Mg–Al LDH-coated wood decreased by 58% and 41%, respectively, compared to those of untreated wood (Figure 7a,b); further, the first peak of the specific extinction area was nearly eliminated (Figure 7d). The heat release rate (HRR) is the most important parameter in evaluating the intensity of flame, and the effective heat of combustion (EHC) can be calculated from the ratio of total heat evolved and mass loss within a given time period. The HRR and THR peaks of the Mg–Al LDH-coated wood decreased by 49% and 40%, respectively, compared to the untreated wood (Figure 7c,f). The maximum average rate of heat emission (MARHE), which is a good measure of the propensity for fire development under real-world conditions, was also calculated (Figure S1, Supporting Information (SI)).34 This MAHRE of Mg–Al LDH-coated wood decreased from 198.2 kW m–2 to 114.5 kW m–2 compared to the untreated sample, suggesting that the presence of Mg–Al LDH coating can indeed diminish the propensity for fire development. The combustion performance between Mg–Al LDH-coated wood


Page 12 of 32

Page 13 of 32

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


and intumescent flame retardants and inorganic flame retardants in the literature (Table 1) further indicates that Mg–Al LDH coating performs as well or better than other protective coatings on the market today.35–42 The flame-retardant properties of LDH can be attributed to heat absorption and char formation. We found that during thermal decomposition, Mg–Al LDH loses the interlayer H2O while intercalated anions are decomposed under dehydroxylation into mixed metal oxides. The metal oxides are conducive the formation of a char layer (Figure S2, S3, S4). The metal oxide network then reacts with acid gases in the smoke.43,44 During thermal decomposition, the metal hydroxide network adsorbs large amounts of heat to reduce heat release and minimize the amount fuel available for propagating the reaction. This process dilutes the concentration of O2 and promotes the formation of expanded char, which protects the wood from exposure to air.45,46 These factors combined characterize the superior flame-retardant properties and smoke-inhibition performance of the Mg–Al LDH coating. 3.7. Superhydrophobic Modification with TDFS Wood products should, ideally, have water repellent and self-cleaning properties. We tested the wettability of the untreated and Mg–Al LDH-coated wood samples using the dynamic contact angle measurement with distilled water. The static contact angle of the untreated wood is in the range of 70° to 90°, and that of the treated wood is 50° or lower over time (Figure 8a,e). The initial contact angle of the Mg–Al LDH-coated wood is about 90°, but decreases quickly to 20° (Figure 8b,e). These results suggest that the Mg–Al LDH



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

coating is not water-blocking, and thus further hydrophobic modification is necessary to attach the water-repellent and self-cleaning properties. The formation of a fluoroalkyl silane layer on the Mg–Al LDH coating can create a surface coating with both flame-retardant and superhydrophobic performance.47–49 In our study, the TDFS-modified Mg–Al LDH-coated wood sample exhibited an initial contact angle larger than 150° which was maintained over time (Figure 8c,e). The sliding angle of approximately 8.6±0.6° was calculated with the advancing angle and receding angles (Figure 8d, Movie S1). The TDFS modification of the Mg–Al LDH-coated wood shows little effect on its combustion performance (Figure S5), altogether suggesting that superhydrophobic Mg–Al LDH-coated wood with flame-retardant properties can be obtained after facile modification with TDFS.

4. CONCLUSIONS In this study, a flame-retardant Mg–Al LDH coating was fabricated on a wood surface with a two-step synthetic method. The as-synthesized Mg–Al LDH coating considerably enhanced the mechanical properties and flame-retardancy of birch wood specimens. The storage modulus of the Mg–Al LDH-coated wood was improved by up to 32% compared to that of untreated wood, while the limiting oxygen index increased from 18.9% to 39.1%. The heat release index from CONE calorimetry was reduced by 40% and the smoke emission was reduced by 58%. Through facile modification with TDFS, a superhydrophobic surface with a contact angle of 152±2° and a sliding angle of 8.6±0.6° was achieved on the Mg–Al LDH-coated wood. In other words, the proposed strategy


Page 14 of 32

Page 15 of 32

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


represents

an

innovative,

efficient inorganic

coating for the protection

and

functionalization of wood.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acsami.7b068034. Figures and photographs for CONE calorimetry test and SEM, EDX characterizations (PDF).

AUTHOR INFORMATION Corresponding Author *H. Yu, E-mail: [email protected]. ORCID Haipeng Yu: 0000-0003-0634-7913 Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (Grant No. 31622016; 31170523).



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

REFERENCES (1) Hill, C. A. S. Wood Modification: Chemical, Thermal and Other Processes. John Wiley & Sons, 2006. (2) Lowden, L. A.; Hull, T. R. Flammability Behaviour of Wood and a Review of the Methods for its Reduction. Fire Sci. Rev. 2013, 2, 1–19. (3) Zhao, G.; Yu, Z. Recent Research and Development Advances of Wood Science and Technology in China: Impacts of Funding Support from National Natural Science Foundation of China. Wood Sci. Technol. 2016, 50, 193–215. (4) Gu, J.; Zhang, G.; Dong, S.; Zhang, Q.; Kong, J. Study on Preparation and Fire-Retardant Mechanism Analysis of Intumescent Flame-Retardant Coatings. Surf. Coat. Tech. 2007, 201, 7835–7841. (5) Liu, Y.; Fu, Y.; Yu, H.; Liu, Y. Process of In Situ Forming Well-Aligned Zno Nanorod Arrays on Wood Substrate using a Two-Step Bottom-Up Method. J. Colloid Interf. Sci. 2013, 407:116–121. (6) Devi, R. R.; Gogoi, K.; Konwar, B. K.; Maji, T. K. Synergistic Effect of NanoTiO2 and Nanoclay on Mechanical, Flame Retardancy, UV Stability, and Antibacterial Properties of Wood Polymer Composites. Polym. Bull. 2013, 70, 1397–1413. (7) Tshabalala, M. A.; Libert, R.; Schaller, C. M. Photostability and Moisture Uptake Properties of Wood Veneers Coated with a Combination of Thin Sol-Gel Films and Light Stabilizers. Holzforschung 2010, 65, 215–220.


Page 16 of 32

Page 17 of 32

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


(8) Rao, X.; Liu, Y.; Fu, Y.; Liu, Y.; Yu, H. Formation and Properties of Polyelectrolytes/TiO2 composite Coating on Wood Surfaces Through Layer-By-Layer Assembly Method. Holzforschung 2016, 70, 361–367. (9) Sun, Q.; Yu, H.; Liu, Y.; Li, J.; Cui, Y.; Lu, Y. Prolonging the Combustion Duration of Wood by TiO2 Coating Synthesized using Cosolvent-Controlled Hydrothermal Method. J. Mater. Sci. 2010, 45, 6661–6667. (10) Mahr, M. S.; Hübert, T.; Schartel, B. Fire Retardancy Effects in Single and Double Layered Sol–Gel Derived TiO2 and SiO2-Wood Composites. J. Sol-Gel Sci. Technol. 2012, 64, 452–464. (11) Jiang, J.; Li, J.; Hu, J.; Fan, D. Effect of Nitrogen Phosphorus Flame Retardants on Thermal Degradation of Wood. Constr. Build. Mater. 2010, 24, 2633–2637. (12) Wang, N.; Fu, Y.; Liu, Y.; Yu, H.; Liu, Y. Synthesis of Aluminum Hydroxide Thin Coating and its Influence on the Thermomechanical and Fire-Resistant Properties of Wood. Holzforschung 2014, 68, 781–789. (13) Miyafuji, H.; Saka, S.; Yamamoto, A. SiO2-P2O5-B2O3 Wood-Inorganic Composites Prepared by Metal Alkoxide Oligomers and their Fire-Resisting Properties. Holzforschung 1998, 52, 410–416. (14) Carosio, F.; Cuttica, F.; Medina, L.; Berglund, L. A. Clay Nanopaper as Multifunctional Brick and Mortar Fire Protection Coating–Wood Case Study. Mater. Design 2016, 93, 357–363. (15) Wang, Q.; O’Hare, D. Recent Advances in the Synthesis and Application of Layered Double Hydroxide (LDH) Nanosheets. Chem. Rev. 2012, 112, 4124–4155.



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

Page 18 of 32

(16) Du, X.; Zhang, D.; Gao, R.; Huang, L.; Shi, L.; Zhang, J. Design of Modular Catalysts Derived from NiMgAl-LDH@m-SiO2 with Dual Confinement Effects for Dry Reforming of Methane. Chem. Commun. 2013, 49, 6770–6772. (17) Ning, F.; Shao, M.; Zhang, C.; Xu, S.; Wei, M.; Duan, X. Co3O4@Layered Double Hydroxide Core/Shell Hierarchical Nanowire Arrays for Enhanced Supercapacitance Performance. Nano Energy 2014, 7, 134–142. (18) Tian, R.; Zhang, S.; Li, M.; Zhou, Y; Lu, B.; Yan, D.; Wei, M.; Evans, D. G.; Duan, X. Localization of Au Nanoclusters on Layered Double Hydroxides Nanosheets: Confinement-Induced

Emission

Enhancement

and

Temperature-Responsive

Luminescence. Adv. Funct. Mater. 2015, 25, 5006–5015. (19) Liu, X.; Ge, L.; Li, W.; Wang, X.; Li, F. Layered Double Hydroxide Functionalized Textile for Effective Oil/Water Separation and Selective Oil Adsorption. ACS Appl. Mater. Interfaces 2015, 7, 791–800. (20) Wen, T.; Wu, X.; Tan, X.; Wang, X.; Xu, A. One-Pot Synthesis of Water-Swellable Mg–Al Layered Double Hydroxides and Graphene Oxide Nanocomposites for Efficient Removal of As(V) from Aqueous Solutions. ACS Appl. Mater. Interfaces 2013, 5, 3304–3311. (21) Kalali, E. N.; Wang, X.; Wang, D. Functionalized Layered Double Hydroxide-Based Epoxy Nanocomposites with Improved Flame Retardancy and Mechanical Properties. J. Mater. Chem. A 2015, 3, 6819–6826. (22) Camino, G.; Maffezzoli, A.; Braglia, M.; Lazzaro, M. D.; Zammarano, M. Effect of Hydroxides and Hydroxycarbonate Structure on Fire Retardant Effectiveness and


Page 19 of 32

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


Mechanical Properties in Ethylene-Vinyl Acetate Copolymer. Polym. Degrad. Stabi. 2001, 74, 457–464. (23) Majoni, S. Thermal and Flammability Study of Polystyrene Composites Containing Magnesium–Aluminum Layered Double Hydroxide (MgAl–C16 LDH), and an Organophosphate. J. Therm. Anal. Calorim. 2015, 120, 1435–1443. (24) Li, C.; Wan, J.; Pan, Y.; Zhao, P.; Fan, H.; Wang, D. Sustainable, Biobased Silicone with Layered Double Hydroxide Hybrid and their Application in Natural-Fiber Reinforced Phenolic Composites with Enhanced Performance. ACS Sustain. Chem. Eng. 2016, 4, 3113–3121. (25) Zakharchenya, R. I.; Vasilevskaya, T. N. Influence of Hydrolysis Temperature on the Hydrolysis Products of Aluminium Alkoxides. J. Mater. Sci. 1994, 29, 2806–2812. (26) Wu, Y.; Jia, S.; Qing, Y.; Luo, S.; Liu, M. A Versatile and Efficient Method to Fabricate Durable Superhydrophobic Surfaces on Wood, Lignocellulosic Fiber, Glass, and Metal Substrates. J. Mater. Chem. A 2016, 4, 14111–14121. (27) Zimmermann, J.; Seeger, S.; Reifler, F. A. Water Shedding Angle: A New Technique to Evaluate the Water-Repellent Properties of Superhydrophobic Surfaces. Text. Res. J. 2009, 79, 1565–1570. (28) Kloprogge, J. T.; Duong, L. V.; Wood, B. J.; Frost, R. L. XPS Study of the Major Minerals in Bauxite: Gibbsite, Bayerite and (Pseudo-) Boehmite. J. Colloid Interf. Sci. 2006, 296, 572–576.



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

(29) Yang, Y.; Zhao, X.; Zhu, Y.; Zhang, F. Transformation Mechanism of Magnesium and Aluminum Precursor Solution into Crystallites of Layered Double Hydroxide. Chem. Mater. 2011, 24, 81–87. (30) Gu, Z.; Atherton, J. J.; Xu, Z. Hierarchical Layered Double Hydroxide Nanocomposites: Structure, Synthesis and Applications. Chem. Commun. 2015, 51, 3024–3036. (31) Zhang, T.; Zhou, Y.; Bu, X.; Xue, J.; Hu, J.; Wang, Y.; Zhang, M. Bio-Inspired Fabrication of Hierarchically Porous Mg–Al Composites for Enhanced BSA Adsorption Properties. Micropor. Mesopor. Mater. 2014, 188, 37–45. (32) Zhao, Y.; He, S.; Wei, M.; Evans, D. G.; Duan, X. Hierarchical Films of Layered Double Hydroxides by using a Sol–Gel Process and their High Adaptability in Water Treatment. Chem. Commun. 2010, 46, 3031–3033. (33) Lin, Y.; Li, D.; Evans, D. G.; Duan, X. Modulating Effect of Mg–Al–CO3 Layered Double Hydroxides on the Thermal Stability of PVC Resin. Polym. Degrad. Stabil. 2005, 88, 286–293. (34) Duggan, G.; Kumar, S. New Fire Classifications and Fire Test Methods for the European Railway Industry: Flame Retardants. Intersci. Commun. 2004, 11, 233–240. (35) Zhang, X.; Mu, J.; Chu, D.; Zhao, Y. Synthesis of Fire Retardants Based on N and P and Poly(Sodium Silicate-Aluminum Dihydrogen Phosphate)(PSADP) and Testing the Flame-Retardant Properties of PSADP Impregnated Poplar Wood. Holzforschung 2016, 70, 341–350.


Page 20 of 32

Page 21 of 32

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


(36) Kang, H.; Ma, L.; Zhang, S.; Li, J. Synthesis and Characterization of Nitrogen-Phosphorus-Based Fire Retardants Modified by Boride/Propanetriol Flyeidyl Ether Complex. IOP Conf. Ser. 2015, 87, 012028. (37) Chuang, C. S.; Tsai, K. C.; Wang, M. K.; Ou, C. C.; Ko, C. H.; Shiau, L. Effects of Intumescent Formulation for Acrylic-Based Coating on Flame-Retardancy of Painted Red Lauan (Parashorea spp.) Thin Plywood. Wood Sci. Technol. 2008, 42, 593–607. (38) Merk, V.; Chanana, M.; Gaan, S.; Burgert, I. Mineralization of Wood by Calcium Carbonate Insertion for Improved Flame Retardancy. Holzforschung 2016, 70, 867–876. (39) Zhang, H.; Zhang, W.; Jin, C.; Li, S. Inorganic Antiflaming Wood Caused by a-Decorated ZnO Nanorod Arrays Coating Prepared by a Facile Hydrothermal Method. J. Nanomater. 2016, 2016, 2358276. (40) He, X.; Li, X.; Zhong, Z.; Mou, Q.; Yan, Y.; Chen, H.; Liu, L. Effectiveness of Impregnation of Ammonium Polyphosphate Fire Retardant in Poplar Wood using Microwave Heating. Fire Mater. 2015, 40, 818–825. (41) Mahr, M. S.; Hübert, T.; Schartel, B.; Bahr, H.; Sabel, M.; Militz, H. Fire Retardancy Effects in Single and Double Layered Sol–Gel Derived TiO2 and SiO2-Wood Composites. J. Sol-Gel Sci. Technol. 2012, 64, 452–464. (42) Terzi, E.; Kartal, S. N.; White, R. H.; Shinoda, K.; Imamura, Y. Fire Performance and Decay Resistance of Solid Wood and Plywood Treated with Quaternary Ammonia Compounds and Common Fire Retardants. Eur. J. Wood Wood Prod. 2011, 69, 41–51.



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

(43) Zammarano, M.; Franceschi, M.; Bellayer, S.; Gilman, J. W.; Meriani, S. Preparation and Flame Resistance Properties of Revolutionary Self-Extinguishing Epoxy Nanocomposites Based on Layered Double Hydroxides. Polymer 2005, 46, 9314–9328. (44) Gao, Y.; Wu, J.; Wang, Q.; Wilkie, C. A.; O'Hare, D. Flame Retardant Polymer/Layered Double Hydroxide Nanocomposites. J. Mater. Chem. A 2014, 2, 10996–11016. (45) Gao, Y.; Wang, Q.; Wang, J.; Huang, L.; Yan, X.; Zhang, X.; He, Q.; Xing, Z.; Guo, Z. Synthesis of Highly Efficient Flame Retardant High-Density Polyethylene Nanocomposites with Inorgano-Layered Double Hydroxides as Nanofiller using Solvent Mixing Method. ACS Appl. Mater. Interfaces 2014, 6, 5094–5104. (46) Elbasuney, S. Surface Engineering of Layered Double Hydroxide (LDH) Nanoparticles for Polymer Flame Retardancy. Powder Technol. 2015, 277, 63–73. (47) Li, Y.; Li, S.; Zhang, Y.; Yu, M.; Liu, J. Fabrication of Superhydrophobic Layered Double Hydroxides Films with Different Metal Cations on Anodized Aluminum 2198 Alloy. Mater. Lett. 2015, 142, 137–140. (48) Zhang, F.; Zhang, C.; Zeng, R.; Song, L.; Guo, L.; Huang, X. Corrosion Resistance of the Superhydrophobic Mg(OH)2/Mg–Al Layered Double Hydroxide Coatings on Magnesium Alloys. Metals 2016, 6, 040085. (49) Zhang, W.; Xiang, T.; Liu, F.; Zhang, M.; Gan, W.; Zhai, X.; Di, X.; Wang, Y.; Liu, G.; Wang, C. Facile Design and Fabrication of Superwetting Surfaces with Excellent Wear-Resistance. ACS Appl. Mater. Interfaces 2017, 9, 15776–15784.


Page 22 of 32

Page 23 of 32

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


Figure 1 EDX elemental mapping analysis of C, O, Al, and Mg of the Mg–Al LDH-coated wood



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

Figure 2 (a) XPS survey of untreated wood, the γ-AlOOH-coated wood, and the Mg–Al LDH-coated wood. XPS high-resolution spectra of (b) Al2p and (c) Mg1s. (d) TEM image of the Mg–Al LDH.


Page 24 of 32

Page 25 of 32

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


Figure 3 Digital photographs and SEM images of (a, b) untreated wood, (c, d) the γ-AlOOH-coated wood, and (e, f) the Mg–Al LDH-coated wood. (g) High-magnification image shows the microstructure of Mg–Al LDH. (h, i) Cross-section SEM images of the Mg–Al LDH coating.



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

Figure 4 Schematic diagram and SEM images show the formation of the Mg–Al LDH coating via one-step co-precipitation (a, e) and two-step process with (b, f) 8 h, (c, g) 10 h, and (d, h) 12 h hydrothermal treatment, respectively.


Page 26 of 32

Page 27 of 32

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


Figure 5 TG and derivative TG (DTG) curves of untreated wood and the Mg–Al LDH-coated wood.



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

Figure 6 DMA results of untreated wood and the Mg–Al LDH-coated wood: (a) E′, storage modulus; (b) tan δ, loss tangent.


Page 28 of 32

Page 29 of 32

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


Figure 7 CONE combustion parameters of untreated wood and the Mg–Al LDH-coated wood: (a) Total smoke production, (b) smoke production ratio, (c) heat release rate, (d) specific extinction area, (e) effective heat of combustion, and (f) total heat release.



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

Figure 8 SEM image and initial contact angle of (a) untreated wood, (b) the Mg–Al LDH-coated wood, and (c) the TDFS-modified Mg–Al LDH-coated wood. (d) Advancing angle and receding angle of the TDFS-modified Mg–Al LDH-coated wood. (e) Variation of the water contact angle with time.


Page 30 of 32

Page 31 of 32

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


Table 1. Comparison of flame-retardancy between proposed coating and others. Retardant or Materials

TSP / % THR / % PHRR / % EHC / %

Ref.

coating Birch

Mg–Al LDH

58

40

49

-

This work

Poplar

NP/PSADP

50.0

41.6

55.1

34.9

33

Poplar

NPB/PTGE

89.2

56.5

45.8

-

34

Red lauan

APMA

-

40.3

43.1

-

35

Spruce/beech

CaCO3

-

34.8

62.1

-

36

Poplar

TiO2/ZnO

42.0

35.0

34.0

-

37

Poplar

APP

68.6

35.6

48.3

-

38

TiO2/SiO2

-

-

36.3

-

39

Scots pine

MAP

-

-

37.4

29.0

40

Scots pine

AS

-

-

33.3

17.5

40

Pine

Annotation: NP/PSADP: nitrogen-phosphorus and poly(sodium silicate-aluminum dihydrogen phosphate); NPB/PTGE: nitrogen-phosphorus-based fire retardants modified by

boride/propanetriol

flyeidyl

ether

resin/pentaerythritol/melamine/ammonium

complex;

APMA:

polyphosphate;

acrylic APP:

polyphosphate; MAP: monoammonium phosphate; AS: ammonium sulfate.


emulsion ammonium


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

Table of Contents (TOC) Graphic


Page 32 of 32

Efficient Flame-Retardant and Smoke-Suppression Properties of Mg

Recommend Documents