Mesoporous Aluminosilicate Material with Hierarchical Porosity for

Research Article pubs.acs.org/journal/ascecg

Mesoporous Aluminosilicate Material with Hierarchical Porosity for Ultralow Density Wood Fiber Composite (ULD_WFC) Tingjie Chen,†,‡ Yongqun Xie,*,† Lili Cai,† Biaorong Zhuang,† Xiaodong Alice Wang,‡ Zhenzeng Wu,† Min Niu,† and Ming Lin† †

College of Material Engineering, Fujian Agriculture and Forestry University, 15 Shangxiadian Road, Fuzhou, Fujian, 350002, P. R. China ‡ Division of Wood Technology and Engineering, Luleå University of Technology, Forskargatan 1, Skellefteå, 93187, Sweden ABSTRACT: This study investigates the application of mesoporous aluminosilicate material with hierarchical porosity to ultralow density wood fiber composite (ULD_WFC) for improving their mechanical properties. A 300 nm thickness Si− Al inorganic film was applied to the surface of the fibers. The mesoporous aluminosilicate material with many mesopores ranging from 2 to 20 nm was obtained. Their total pore volume and Brunauer−Emmett−Teller surface area were 0.193 cm3/g and 355.2 m2/g, respectively. Thermogravimetric analysis indicated that the thermostability of ULD_WFCs was affected by Si−Al compounds. But the residual weight of ULD_WFC with Si−Al compounds was 23.87% greater than composite without Si−Al compounds. The X-ray diffraction analysis indicated partial conversion of SiO2 to α-SiC. These conditions attributed to improving the mechanical properties of ULD_WFC. The modulus of elasticity, modulus of rupture, and internal bond strength of composite with Si−Al compounds increased by 547.4%, 240.0%, and 400.0%, respectively, as compared with uncoated ULD_WFC. KEYWORDS: Crystallinity, Characterization, Mechanical properties, Mesoporous, Wood fiber

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fibers due to their charge neutralization, adsorption bridging and sweep coagulation properties.13−15 These findings suggested that both the fire resistance and mechanical properties of ULD_WFCs could be significantly improved by Si−Al compounds. The goal of this paper was mainly to clarify the mechanical properties of ULD_WFCs as affected by Si−Al compounds. Recently, researchers have been intensified efforts to construct the mesoporous SiC ceramics materials using biological materials as template.16−21 Silicate species have been found to penetrate into the cell wall structures of wood and condensed around the cellular tissues. When the wood tissues were removed by calcination, the samples roughly preserved their initial shape and the SiC ceramics are obtained.16 Due to the hierarchical porosity of SiC ceramics, they exhibited unique structure-mechanical properties.20 Actually, the fossilization process of wood very nearly replicates the process being discussed. When surrounded by mud and sand (i.e., siliceous material), the minerals percolate into the wood fibers, yielding the crystalline structure of petrified wood.17 However, to the best of our knowledge, mesoporous aluminosilicate material has

INTRODUCTION Ultralow density wood fiber composite (ULD_WFC) is an environmentally friendly material which is produced with a liquid frothing process.1 Due to its renewable nature, low thermal conductivities, and good sound absorption, etc., ULD_WFCs have a promising market. They can serve in some applications as substitutes for petroleum-based polymers, such as building insulation material and packaging buffer material.2−6 However, their applications are restricted because of poor mechanical properties and inflammability, due to its ultralow density and nature of its raw material.5,6 To overcome these deficiencies, WFCs have been subjected of numerous investigations involving chemical modification (i.e., water glass, silicium sol, boron compounds, aluminum compounds, and chlorinated paraffin).5−7 It has been found that all these modifications can improve fire resistance, but the silicium− aluminum (Si−Al) compounds have been shown to significantly improve both fire resistance and the mechanical properties of composites. For example, water glass has been shown to protect wood against fire through retarding the formation of laevoglucose.8−11 Aluminum compounds demonstrated improved the heat resistance of wood fiber materials by absorbing a lot of heat from the dehydration reaction when heated.12 Additionally, the polysilicic acid has been shown to combine with the hydrolysis products of Al to form hydroxylaluminosilicate, which is believed to absorb on the surface of © XXXX American Chemical Society

Received: April 5, 2016 Revised: May 15, 2016

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DOI: 10.1021/acssuschemeng.6b00691 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering

Beam (FIB, Helios 600i, FEI, Netherlands) with 200 nm thickness. Nuclear magnetic resonance (NMR) analysis. The 29Si and 27 A1 NMR spectra of Si−Al compounds and ULD_WFC specimens were recorded on a Bruker ADVANCE III 500 spectrometer, using 7 mm zirconia oxide rotor with a spinning speed of 4.5 kHz. All spectra were recorded at room temperature, using dry air as driving gas. The 29Si NMR spectra were recorded at a frequency of 79.45 MHz with a pulse length of 6 μs. The 27A1 NMR spectra were recorded at a frequency of 104.26 MHz with a pulse length of 1 μs. Thermogravimetric analysis (TGA). The thermal curves of TGA were obtained using a thermogravimetric analyzer (NETZSCH STA 449F3, Germany). The temperature range was from 20 to 500 °C with a heating rate of 10 °C min−1 under nitrogen atmosphere. X-ray diffraction (XRD). The crystallization of fibers and Si− Al compound were determined by X-ray diffraction (XRD, X’Pert PRO MPD, Philips-FEI, Netherlands), and a typical diffraction pattern and intensity profile showing peaks were recorded using Co Kα radiation (at a wavelength λ = 1.78901 nm) with a 5 mm variable divergence slit between 4.9° and 65.0° (2θ) at a step size of 0.0129° and a speed of 0.133°/s. The empirical Equation 1 of calculating the crystallinity index (CrI) was mentioned in Segal et al.23

not been previously utilized for simultaneously improving the mechanical properties and fire resistance of ULD_WFCs. The objective of present research was mainly focusing on the properties of ULD_WFCs and the interface between mesoporous aluminosilicate and the fibers. We also paid attention to the atomic-scale structural and crystallinity characterization of mesoporous aluminosilicate. To clarify these issues, the microstructures of the composite were measured by scanning electron microscopy with an energydispersive spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). The crystalline structure of ULD_WFCs was revealed by X-ray diffraction (XRD). The thermal properties of composites were evaluated by thermogravimetric analysis (TGA).

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EXPERIMENTAL SECTION Materials. Kraft pulp (KP, spruce-pine-f ir; Tembec Inc., Quebec, Canada) was utilized as a raw material to manufacture ultralow density wood fiber composite (ULD_WFC). Aluminum sulfate and sodium silicate, purchased from Tianjin Fuchen Chemical Reagents Factory (China) were used to generate the Si−Al compound. Sodium dodecylbenzenesulfonate surfactant, purchased from Jiangsu Qingting Washing Products Co., Ltd. (China), was utilized as a foaming agent. Methods. Preparation of Ultralow Density Wood Fiber Composites. Ultralow density wood fiber composites (200 mm × 200 mm × 50 mm) were made of 55 g dry pulp fiber, with a target bulk density of 20−90 kg·m−3. They were manufactured separately using various parameters in a demonstration line as described by Chen et al.2 The preparation process of the specimens is described in Figure 1. The 500 mL Si−Al

CrI = [(I 002 − Iam)/I 002] × 100%

(1)

Where I002 is the maximum in intensity of the peak at 2θ about 26° and Iam is the minimum intensity above baseline at 2θ about 22°, accounting for the crystalline part and the amorphous part, respectively. X-ray photoelectron spectroscopy (XPS). The XPS experiments were carried out at ambient temperature in an ultrahigh vacuum (UHV) system with a surface analysis system (ESCALAB 250, America). XPS is able to produce chemical state information from any surface (topmost 1 to 12 nm). Al Kα radiation from a monochromatized X-ray source was used. The spectra of survey scan were recorded with the pass energy of 100 eV; the energy step size was 1.00 eV and the spot size was 500 μm. High resolution spectra were recorded with the pass energy of 30 eV, and the energy step size was 0.05 eV. Specific surface area and pore size distribution analysis. The N2 adsorption−desorption experiments were performed on JW-BK132F specific surface area and porosity analyzer. Specific surface area was calculated according to the Brunauer− Emmett−Teller (BET) equation. Pore size distribution was calculated according to the BJH formula. Mechanical properties. The density (ρ) (measured at 12% moisture content), modulus of elasticity (MOE), modulus of rupture (MOR), and internal bond strength (IB strength) were tested in accordance with GB/T 17657−1999.24 The size of the specimens for testing of density was 100 × 100 × 30 mm (L × W × H). The size for MOE and MOR was 120 × 50 × 10 mm (L × W × H). The size for IB strength was 50 × 50 × 40 mm (L × W × H). Each specimen was sliced and trimmed by a MQ-433 bandsaw. Results reported are the average of five replications.

Figure 1. Preparation process of ULD_WFCs.

compound was produced by sol−gel process in a reaction between sodium silicate and aluminum sulfate. The detailed parameters of the Si−Al compound were given in the work of Chen et al.22 Here, 80 mL of sodium dodecylbenzenesulfonate surfactant (10% of concentration, foaming agent) was added to the mixture. Microanalysis (SEM-EDS and TEM). The micromorphology, elemental distribution and cross sections of fibers were characterized by a scanning electron microscopy (SEM, Phenom ProX, Netherlands) with an energy-dispersive spectroscopy (EDS, INCA Energy EDS for X-ray analysis, Phenom ProX, Netherlands). The mapping was performed on an area displaying the additive and the fibers using an acceleration voltage of 15 kV. The microstructure and size of the Si−Al inorganic film was characterized with a transmission electron microscope (TEM, Tecnai TF20, FEI, Netherlands) operated at an accelerated voltage of 100 kV. The sample was processed by Focused Ion

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RESULTS AND DISCUSSION Micromorphology of single fiber and mesoporous aluminosilicate material. As shown in Figure 2a and b, the surface and cross-section of fibers without Si−Al compounds B


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Figure 2. (a) and (b) SEM images of fiber without Si−Al compounds and its cross-section, (c) and (d) SEM images of fiber with Si−Al compounds and its cross-section, and the corresponding element mappings for the cross-section are presented (containing all elements mapping (d1), oxygen (d2), silicium (d3), and aluminum element mapping (d4)), (e) Magnification image of microscale mesoporous aluminosilicate material from the frame in (c), and (f) Mesoporous aluminosilicate from the frame in (e) at higher magnification.

Figure 3. (a) TEM image of the cross-section for fiber with Si−Al compounds. (b) Magnification images of microscale mesoporous aluminosilicate material. The two atomic-resolution images indicated by the frames in (b) were presented in (b1 and b2). (c) Simulated structural models for cross sections images fiber with Si−Al compounds. (d) The structural models of SiO2 and Si−Al compounds were overlaid on the images to show the oneto-one correspondence of image contrast. (e) Triaxial structural model of Si−Al compounds (Modified from Grim 1962). (f) Mesoporous aluminosilicate material with hierarchical porosity on the surface of ULD_WFCs.

(Si−Al), readily agglomerate.2 SEM images of the Si−Al treated fiber cross-section showed an inorganic film with a thickness of 300 to 400 nm existed around the fibers (Figure 3a). The corresponding element mappings revealed silicium uniformly distributed (Figure 2-d3), while aluminum and oxygen were found to be nonuniformly distributed and associated together, indicating their. It was also important to note that silicium and aluminum elements were also mapped in the cell cavities. This was ascribed to the porous property of fibers. Therefore, Si−Al

exhibited a typically smooth surface, with the grains of the fibers visible on the surface. Differently, the SEM image for the fibers treated by Si−Al compounds presented a multifarious surface. Some surfaces demonstrate helical and concave strips corresponding to morphological features of the fibers (Figure 2c), while others are much rougher with agglomerations consisting of many nanoparticles around 15 nm in size (upper right corner in Figure 2c). This is because that unreacted Si compounds and Al compounds, as well as reacted compounds C


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Figure 4. 27Al and 29Si NMR spectra of Si−Al compounds and ultralow density wood fiber composites.

compounds could not only deposit on the fibers’ surface as a small scale inorganic film, but it also entered the cell cavity through the fiber pits and becomes deposited. The images of mesoporous aluminosilicate material with hierarchical porous structures from the surface of fibers were presented in Figure 2e. At higher magnification (Figure 2f), the fine structures consisting of silica−alumina source were observed. The microtopography of mesoporous aluminosilicate material indicates that alumina hexahedron structures were incorporated in the silica network. The hierarchical porous structures with both mesoscale should have potential for the stabilization of additives which are helpful for improving the mechanical properties of ULD_WFC.18,25 Actually, atomic-scale structural characterization had been adopted as a general approach to explore the chemistry of this materials.26 As indicated by the two boxes in Figure 3b, two atomic-resolution images of aluminosilicate material were recorded. Similar to the structural models of SiO2 and Si−Al compounds modeled in Figure 3d, the SiO2 and Si−Al compounds show up in Figure 3b as white images contrasted against the darker images of two Si elements, or two white images contrasted against four darker elements of Si. Therein, the Si and Al contrasts in Si−Al compounds formed as a rhomboid structure (Figure 3-b1 and b2). This suggested that a new phase is formed in the Si and Al source.26−28 The triaxial structural model of this new phase, which is modified from Grim,29 is presented in Figure 3e. From the structural model, there are hydroxyls which contribute to the condensation between fibers and aluminosilicate material. This model indicates that the deposited aluminosilicate materials are of hierarchical and poriferous material. Their microstructure is presented in Figure 3f, which is similar to the structure of clay mineral.29,30

Chemically, wood fibers consist mainly made of cellulose containing a large numbers of polar groups (hydroxyl) which promote silicate and aluminum source condensation. The result of X-ray photoelectron spectroscopy analysis reveals that the covalent bonds of Si−O−C and Al−O−C were formed between Si−Al compounds and fibers.31 Additionally, further evidence of the eduction of silica and alumina framework, the 27 Al NMR and 29Si NMR spectra of Si−Al compounds and ULD_WFCs are presented in Figure 4. The 27A1 NMR spectrum of Si−Al compounds exhibits one small peak at around 71.96 ppm and the other sharp peak at 0.95 ppm, which are ascribed to the tetrahedral A1 in the framework and octahedral aluminum, respectively.32,33 It clearly indicated that nearly all the A1 atoms in Si−Al compounds are present in octahedral environment. On the contrary, the 27A1 NMR spectrum of ULD_WFC exhibits mainly a single peak at 55.80 ppm and a small peak at around 0 ppm. It indicated that most of Al is in tetrahedral coordination, suggesting that major part of Al entered into poriferous structure of silica compounds when it was added in the preparation process of ULD_WFC.32 The 29Si NMR spectra of Si−Al compounds and ULD_WFC consists of two well-resolved peaks at around −110 and −90 ppm which can be assigned to Q3(1Al), Q2(2Al), and Q4(0Al) structural units, respectively. The presence of Q4 units indicates a well-developed three-dimensional framework of Si−O−Si bonds, whereas Q3 and Q2 peaks mainly indicate the connectivity of Si to hydroxyl groups or Al atoms. The 29Si NMR spectrum of Si−Al compounds indicates that Si−Al compounds are mainly consisting of Q4 species. By contrast, the increase in the relative intensity of the peak at −98.81 ppm in ULD_WFC indicates that substantial amount of Al had incorporated into the structure.32−34 Therefore, the schematic of the reaction between Si−Al compounds and fibers could be D


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Figure 5. Schematic of the reaction between fiber and Si−Al compounds.

Figure 6. (a) TG and (b) DTG curves of Si−Al compounds (A), composite without Si−Al compounds (B), and composite with Si−Al compounds (C).

occurs at 291.9 °C, followed by a drastic reduction in weight at 291 °C-354 °C. In contrast, the initial decomposition of composite with Si−Al compounds is 256.4 °C and the significant weight loss occurs from 256 to 318 °C. Moreover, the DTG curves in Figure 6b show that the maximum weight loss appear at 335.2 °C for composite without Si−Al compounds and 288.1 °C for the composite with Si−Al compounds. Results indicate that the thermal stability of the composite is affected by Si−Al compounds. This is mainly caused by the desorption of interlayer water for the Si−Al compounds in the range of 200−350 °C. However, a total weight loss of 90.28% is observed in composite without Si−Al compounds (Figure 6a), while composite with Si−Al compounds is only 66.28%. Results indicate that the fire resistance of composite with Si−Al compounds is improved due to Si−Al compounds can effectively enhanced protection properties of the residues.38 For the composite without Si−Al compounds, the second and third stages of weight loss are 58.52% and 24.17%, respectively. In contrast, the weight loss of composite with Si−Al compounds in second stage is only 51.75%, which is associated with the combustion and decomposition of silanol groups to form siloxane bonds.33,39 Especially at temperatures higher than

described as Figure 5. And the structural model of cross sections images for fiber with Si−Al compounds may be simulated as illustrated in Figure 3c. Thermogravimetric analysis of pure Si−Al compounds and composites. The TG and differential thermogravimetric (DTG) curves of composites with and without Si−Al compounds and the pure Si−Al compounds are shown in Figures 6a and b, respectively. There are three distinct stages of weight loss observed in pure Si−Al compounds (a total weight loss of 28.56%), due to the loss of physical-sorbed water, interlayer water, and thermal dehydroxylation process which accounted for 3.14% (10−110 °C), 20.35% (110−300 °C), and 5.10% (300−500 °C), respectively. Additionally, a small shoulder at around 320 °C is observed in Figure 6b, implying some interaction between Si and Al in the framework.35,36 The composite without Si−Al compounds shows an initial slight weight loss between 20 and 110 °C associated with the evaporation of imbibed water in the specimens, which is not obvious for the composite with Si−Al compounds (only 3.09%). This indicates that the Si−Al/fiber composites are more hydrophobic than native fiber composite.37 For the composite without Si−Al compounds, the initial decomposition E


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ACS Sustainable Chemistry & Engineering 350 °C (third stage), only 11.44% weight loss occurs. These indicate that the residues are not only consisting of the residual aluminosilicate material, but they also contain the formation of SiC ceramics. It is seen in Figure 7, that aluminosilicate material

As can be seen in Figure 9a, the fiber remained completely intact and near its original shape after all the organic contents were thermally removed. This was because the silicate and aluminum elements were first deposited on the fiber’s surfaces and cellular walls when they were added in the preparation of ULD_WFC. Afterward, some unbound Si−Al compounds were lost when liquid was filtered out, while other Si−Al compounds were subjected to secondary growth in the oven at 100 °C.16 Then, a thin, uniform, and continuous inorganic film around the surface of fibers was generated. The aluminosilicate structure was preserved after the organic contents were removed by calcination in air. Due to the presence of the surfactant in the aluminosilicate network, a number of macroand mesoporous channels were produced during calcination (Figure 9b). These channels could provide pathways for the decomposed organic contents, thus facilitating the maintenance of the aluminosilicate structural integrity.18 Additionally, a typical nitrogen adsorption−desorption isotherm of the aluminosilicate material is presented in Figure 10. The adsorption capacity gradually increased with an increase of relative pressure, especially when the relative pressure of N2 is more than 0.8. The hysteresis loop indicates the presence of a mesoporous structure in aluminosilicate material.16,44 The mesopore distribution of the aluminosilicate material is shown in the inset of Figure 10. The pore diameter and the total pore volume of aluminosilicate material are 2−20 nm and 0.193 cm3/g, respectively. For aluminosilicate structure, the total BET surface area and micropore surface area are 355.2 and 254.1 m2/g, respectively. Results show that the integrated mesoporous aluminosilicate material with hierarchical porosity exhibit unique structure-mechanical properties which provide improved mechanical properties over that of untreated ULD_WFC.20 Mechanical Properties and Crystallinity of Composites. The presence of aluminosilicate material in the composites was further confirmed by XRD analysis. X-ray diffraction patterns of Si−Al compounds and composites with or without Si−Al compounds are showed in Figure 11. The corresponding crystallinity values of fiber without and with Si− Al compounds are presented in Table 1. The diffraction peaks of Si−Al compounds at a range from 25 to 60° were similar to the crystalline zeolite. The peaks at 2θ value of around 18.34°, 21.29°, and 22.67° correspond to the αAl(OH)3, β′-Al(OH)3, and β-AlO(OH) phase, respectively.45 A clear peak around 24.58° corresponds to a spectrum of crystalline Si−Al compounds or α-Al2O3 phase.46 This is

Figure 7. XRD patterns of composite without Si−Al compounds (A) and composite with Si−Al compounds (B) burned off at 800 °C in air.

obtained by this method is a multiphase material which contains α-SiC and β-SiC as the main crystal phase.17,19,40 Due to partial conversion of SiO2 to α-SiC, an improvement in the fire resistance of the fibers is realized in the presence of Si−Al compounds. To further confirm the formation of SiC ceramics, the typical XPS of C 1s and Si 2p curves of A (ULD_WFCs without burning) and B (ULD_WFCs burned off at 800 °C in air) is presented in Figure 8. It can be seen from Figure 8, C 1s peaks of A at binding energies of 284.6, 286.0, 286.5, and 289.2 eV are corresponding to the following groups: C−C or C−H, C−O, CO, and OC−O.31,41 By contrast, the C 1s peaks of B at binding energies of 286.0, 286.5, and 289.2 eV are disappearing, indicating the degradation of fibers. The additional binding energies of 288.6 and 293.0 eV may be attributed to the bonds of Si−C and Al−C. Additionally, the binding energy at 101.57 eV is ascribed to the Si 2p peak of B, which is lower 0.91 eV than the Si 2p peak of A with the binding energy of 102.48 eV. This is because the electronegativity of O, C, and Si was 3.5, 2.5, and 1.8, respectively, indicating that the Si−O is easier to absorb the electrons than Si−C. When ULD_WFCs are burned off at 800 °C in air, the formation of SiC ceramics leads the Si density of the electron cloud of B is lower than A.42,43

Figure 8. Typical XPS of C 1s and Si 2p core levels in A (ULD_WFCs without burning) and B (ULD_WFCs burned off at 800 °C in air). F


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Figure 9. (a) SEM image of mesoporous aluminosilicate material prepared from ULD_WFC after calcination in air. (b) Surface of mesoporous aluminosilicate material at higher magnification.

On the other hand, the fibers displayed the typical XRD patterns of cellulose I with the diffraction peaks at 2θ value of around 18.32°, 26.46°, and 40.64°, corresponding to the 101, 002, and 040 planes, respectively.48 For composite with Si−Al compounds, distinct differences were observed. The diffraction peaks of composite were obviously weaker. According to eq 1, the crystallinity indexes of composite without and with Si−Al compounds were calculated to be 38.83% and 14.14%, respectively (Table 1). This was associated with the reaction between Si−Al compounds and fibers and leading to a decrease in the amount of hydroxyl groups. As the Si always forms an amorphous phase of either compound or simple substance, the crystallinity of specimens was also influenced by amorphous SiO2 networks.49 Interestingly, the appearance of two new reflection at 2θ = 21.68° and 24.02° was observed in composites with Si−Al compounds. Compared to the patterns of Si−Al compounds, the disappearance of the β-AlO(OH) phase at 2θ = 22.67° might be attributed to the following reaction (eq 2):

Figure 10. Nitrogen adsorption−desorption isotherm and mesopore distribution of the aluminosilicate material.

Al(OH)3 + Al(OH)4 − − → 2Al(OH)3 + OH−

The XRD spectra of β′-Al(OH)3 and crystalline Si−Al compounds or α-Al2O3 phase gradually shifted from 21.29° to 21.68° and from 24.58° to 24.02°. These finding suggested that the order along the crystallographic c-axis of Si−Al compounds was disturbed by the reaction between the fibers and the Si−Al compounds.30,50 The α-Al2O3 phase on the surface of fiber can be seen in Figure 12a. Additionally, the spectrum of composite with Si−Al compounds was similar to crystalline aluminum silicate, indicating a new phase of aluminum silicate was formed. According to the studies of Tokoro et al.,46 gibbsite usually grows as platelets parallel to the layers of its layer lattice (basal planes). A hypothetical structure of gibbsite crystal and the hexagonal structures which were obtain from composite with Si−Al compounds can be found in Figure 12b and c. Apparently, the formation of thin platelets was similar to the Tokoro’s research. The rest of the crystal structure was not affected by the composite synthesis process, indicating that the crystallography of fibers was not affected. As shown in Table 2, the densities of the composites with Si−Al compounds was increased from 47.11 to 58.56 kg/m3 while Si−Al compounds were added. The MOE, MOR, and IB strength of composite with Si−Al compounds were increased by 547.4%, 240.0%, and 400.0%, respectively, relative to composite without Si−Al compounds. This was attributed to the covalent bonds of Si−O−C and Al−O−C bonds between fiber and silicate-aluminum sources and the mesoporous aluminosilicate material with hierarchical porosity around the surfaces of fibers. Overall, mesoporous aluminosilicate material

Figure 11. XRD patterns of Si−Al compounds and composite with/ without Si−Al compounds.

Table 1. Crystallinity Index of the Fiber without and with Si−Al Compounds specimens composite without Si−Al compound composite with Si−Al compound

2θ(am) (deg)

2θ(002) (deg)

crystallinity index (%)

18.32

26.46

38.83

18.70

26.30

14.14

(2)

because that the aluminum ion can react with hydroxyl ions to form Al(OH)2+, Al(OH)2+, Al(OH)3, and Al(OH)4−. When sufficient hydroxyl ions were added, aluminate ions cluster and form crystalline Al(OH)3. Also, growth and stacking of Al(OH)4− layers form gibbsite (Al(OH)3).47 G


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Figure 12. (a) α-Al2O3 phase on the surface of fiber. (b) Hypothetical structure of gibbsite crystal. (c) Hexagonal structure obtain from composite with Si−Al compounds.

Table 2. Density, MOE, MOR, and IB Strength of Composites without and with Si−Al Compounds specimens

density (kg/m3)

MOE (MPa)

MOE (MPa)

IB strength (MPa)

composite without Si−Al compounds composite with Si−Al compounds

47.11 (±2.51) 58.56 (±0.97)

3.21 (±0.20) 20.78 (±0.90)

0.05 (±0.004) 0.17 (±0.010)

0.005 (±0.0005) 0.025 (±0.0030)

(2008BADA9B01) and the National Natural Science Foundation of China (NSFC) (30781982).

with hierarchical porosity played a critical role in improving the mechanical properties of ULD_WFCs.

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CONCLUSIONS 1. We have demonstrated an innovative and feasible route to improve the mechanical properties of ULD_WFCs by mesoporous aluminosilicate material with hierarchical porosity. The various morphologies of composites revealed that there was a 300 nm thickness Si−Al inorganic film around the fibers. And the alumina hexahedron structures were incorporated in the silica network to form mesoporous aluminosilicate material. 2. The results showed that the phases of Al(OH)3 and Al2O3 exist in ULD_WFC. Although the crystallinity of composites was decreased in this process, the mechanical properties of composites were improved. The MOE, MOR, and IB strength of composite with Si−Al compounds increased by 547.4%, 240.0%, and 400.0%, respectively, over composite without Si−Al compounds. 3. The investigation by TGA demonstrated the fact that the residual weight of ULD_WFC with Si−Al compounds was 23.87% greater than composite without Si−Al compounds. The fiber remained completely intact and close to its original shape after the organic contents was thermally removed. Additionally, the integrated mesoporous aluminosilicate material with hierarchical porosity demonstrated improved mechanical properties over untreated ULD_WFC.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +86 591 83789307. Fax: +86 591 83789135. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This paper is supported by the Scientific Research Foundation of Graduate School of Fujian Agriculture and Forestry University (1122YB020) and the Studying Abroad Scholarships of China. The authors are also grateful for the financial support of the National Science and Technology Support Program H


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Mesoporous Aluminosilicate Material with Hierarchical Porosity for

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