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High strength, thermostable and fast-drying hybrid transparent membranes with POSS nanoparticles aligned on aramid nanofibers
Composites Part A 110 (2018) 154–161
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Composites Part A journal homepage: www.elsevier.com/locate/compositesa
High strength, thermostable and fast-drying hybrid transparent membranes with POSS nanoparticles aligned on aramid nanofibers ⁎
Fang Wang1, Yadong Wu1, , Yudong Huang
T
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MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Aramid nanofiber POSSeCOOH NPs Fast-dying membrane Tensile strength Thermal performance
Hybrid organic/inorganic nanocomposites based on aramid nanofibers (ANFs) and different amounts of polyhedral oligomeric silsesquioxane (POSS) nanostructured chemicals were prepared via solution blending and vacuum-assisted flocculation, compared with traditional film fabrication methods, this process is time-saving by adopting ethanol as agglomerator. The mechanical properties of ANFPs membranes could be altered by changing the POSS content, in which the POSS served as a cross-linking agent between nanofibers, and ANFPs composite membrane presented the optimal tensile strength with 6 wt.% POSS NPs embedding in the nanocomposite. In addition to the satisfactory mechanical performance and vitreousness, the unique thermal assets of ANFs and POSS further enabled the membranes with high thermal stability. Based on these results, it could be concluded that the ANFPs membranes developed here might provide the alternative materials for the practical application of strong, transparent and heat-resistant membrane.
1. Introduction Polyparaphenylene terephthalamide (PPTA), a high performance para-aramid polymer better known by its trade-name Kevlar, has outstanding mechanical properties such as high modulus and high tenacity at a significant low density [1,2]. Kevlar is suitable membrane materials due to their superior mechanical and thermal properties. Encouragingly, aramid nanofibers (ANFs) is obtained in dimethyl sulfoxide (DMSO) and potassium hydroxide (KOH) [3–5] which have been developed with maintaining excellent mechanical properties similar to its original bulk fibers and considered as an essential nanoscale “building block” [2]. Inspired by remarkable potential to combine two dramatically different material classes at the molecular level [6–13], the synergistic combination of individual inorganic/organic components provides promising potential to tune the resulting structure and to design or tailor the resulting properties for extend applications in many areas [14–19], such as packaging, electronics, optical devices, aerospace, automotive engineering, and biomaterials. Nanoscale inorganic fillers which can impact desirable structural and functional properties in a polymeric material are widely studied because of their effective reinforcement at very low loadings [20–23]. ANFs has also been investigated and introduced into the fabrication and
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1
Corresponding authors. E-mail addresses: [email protected] (Y. Wu), [email protected] (Y. Huang). These authors contributed equally to this work.
https://doi.org/10.1016/j.compositesa.2018.04.031 Received 18 January 2018; Received in revised form 22 March 2018; Accepted 30 April 2018 Available online 02 May 2018 1359-835X/ © 2018 Elsevier Ltd. All rights reserved.
application of the high-performance advanced hybrid organic-inorganic nanohybrid membranes. For instance, ANFs hybrids with gold nanoparticles [24], carbon nanomaterials such as carbon nanotubes (CNTs) [25,26] and graphene sheet [27,28] have been successfully manufactured, and the results have proved that the mechanical properties of the obtained nanohybrid membranes enhanced obviously. While, the incorporation of nanoparticles into a polymeric matrix is often difficult. The general challenge is that very small particles tend to form agglomerates resulting in membranes with an inhomogeneous distribution. Hence the focus nowadays is to use particles with a small size and functional side groups for a homogenous incorporation into a polymeric matrix. POSS nanostructures, sizing approximately 1–3 nm, with general formula (RSiO1.5)n, where n refers to the number of Si atom in the cage and R is hydrogen or an organic group, such as alkyl, aryl, or any of their derivatives [29]. The inorganic silica core of POSS is thermally and chemically robust while the diversity of the R groups makes them compatible with various polymer systems. Therefore, regarded as the smallest possible particles of silica, well defined three-dimensional nanoscale architecture, and monodisperse particle size, incorporation of POSS macromers within polymeric architectures allows the organic and inorganic phases to interact at the molecular level and with assured compatibilization and it may be another hopeful candidate as the
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2.4. Characterization of POSSeCOOH
dispersed phase for the fabrication of molecular-level mixed matrix membranes. POSS molecules possess the very high flexibility to be functionalized, thus creating an excellent compatibility and dispersibility at the molecular level in diverse polymer matrices [30]. Furthermore, POSS compounds can act as cross-linkers between polymer chains. Via crosslinking a three dimensional network can be achieved which improves the membrane properties with regard to chemical stability and temperature resistance. In addition, the significance of mechanical reinforcement of optically functional materials has been witnessed by the rapid growth of electronic industries which, in turn, have created a great demand for transparent and strong materials [31]. Encouragingly, the availability of nanofibers with diameters significantly smaller than the wavelengths of visible light offer a potential way to avoid this limitation of opaqueness [32]. Since their unique properties and high potential as additive [33–39], over the past decade, POSS became an attractive candidate as additive for the preparation of nanomaterials in membrane technology to modify a wide range of polymer chain such as polyolefin, polystyrene, poly (methyl methacrylate), polycarbonate, poly (ethylene terephthalate), polyamide and a few thermoset systems [40–46]. However, since very few studies exist on the utility of on POSS as additives for ANFs membranes is available. Herein, a kind of co-effectively transparency, high strength and thermal stability ANFPs nanohybrid membrane based on ANFs with incorporation of well distributed POSS compounds acting as cross-linker was synthesized efficiently. The transparency and flexibility of ANFPs nanocomposite membranes could be maintained. Furthermore, the mechanical properties and thermal stability of the hybrid membranes improved, i.e. high tensile strength as expected. It might be the promising candidates for potential application as strong, transparent and heat-resistant nanocomposite in many fields.
A series of characterization tools were adopted to investigate the physicochemical property of POSSeCOOH NPs. FTIR spectroscopy were used to determine chemical structure of POSSeCOOH products. Transmission electron microscope (TEM) were used to observe the nanoscale morphology and dispersibility. To identify the stacking in POSSeCOOH, XRD measurement was carried out. Thermo-gravimetric analysis of samples was employed by TGA using a heating rate of 10 °C/ min from 30 to 800 °C in the atmosphere of nitrogen. 2.5. Synthesis of ANFPs nanocomposites membranes ANFs/DMSO and POSSeCOOH/DMSO solutions were mixed with a given ration followed by an equal volume of ethanol to substitute DMSO and precipitate the ANFPs. Specifically, 5 ml of as-obtained ANFs/DMSO dispersion was diluted to 30.0 ml by the additional DMSO (inset of Fig. 1a). Then POSSeCOOH/DMSO solutions of different volumes (0, 2.04, 4.17, 6.38, 8.70 and 11.11 ml) were added dropwise with the change in color from dark red to yellow under vigorously stirring (inset of Fig. 1b), creating membrane samples with designated names of ANFPs-2, ANFPs-4, ANFPs-6, ANFPs-8 and ANFPs-10 for membranes with POSS loadings 2 wt.%, 4 wt.%, 6 wt.%, 8 wt.% and 10 wt.%, respectively, subsequent with additional 1 h stirring. After that, 4.0 ml of ethanol was further added dropwise under vigorously stirring for all mixtures which resulted in a gel-like state, following another 2 h stirring to achieve a uniform dispersion. The obtained jelly was vacuum filtrated using nylon membranes and the product was soaked in ethanol 12 h followed with air drying within a few seconds. Finally, the dried nylon membrane integrated with ANFPs membrane was soaked in ethanol again about 10 min to make the composite membrane fall off automatically, subsequent with air drying to volatilize ethanol which takes a very short time. Finally, pristine ANFs and ANFPs composite membrane were obtained.
2. Experimental and methods
2.6. Characterization and performance study of ANFPs composites membranes
2.1. Materials Kevlar-29 (136 dtex) brand yarns (M.Wt. ∼25000, stiffness 109 Gpa and strength 3.6 Gpa) were purchased from DuPont Co., Ltd (USA). Polyhedral oligomeric silsesquioxane marked with CA0298 (OctaMaleamic Acid POSS, abbreviated as POSSeCOOH) was purchased from Hybrid Plastics Co., Ltd (USA) as crystalline powders and used as received. Potassium hydroxide (KOH), Dimethyl sulfoxide (DMSO) and ethanol were supplied by Aladdin Co., Ltd (China). All chemicals were used as received without further purification. Nylon filtration membranes with 0.1 µm pore diameter (Filtration Equipment Factory Co., Ltd., Haining, China.) were used in this study.
ATR-FTIR studies was measured on a Perkin Elmer Spectrum One spectrometer (Nicolet Nexus 670, USA) to investigate the functional groups of membrane surfaces and the presence of POSSeCOOH. The size and morphology of as-prepared ANFs and ANFPs were characterized by using a transmission electron microscope (TEM), and all the TEM images were obtained on a JEOL 2000 FX microscope. The surface morphology of hybrid membranes was analyzed using scanning electron microscopy (SEM) with a Hitachi S-4700 SEM. XRD measurement was carried out by a D/man-rBX X-ray generator operated at 30 mA and 40 kV to study the crystalline structure and distribution of the POSSeCOOH. Mechanical strength of the synthesized membranes were tested by Cmt8102 electric universal testing machine with tensile speed at 10 mm/min. The tensile strength measurements were repeated five times for each specimen and average tensile strength was reported. The thermal properties of the composite membrane were analyzed by a thermogravimetric analyzer (TA Q500) using a heating rate of 10 °C/ min from 30 to 800 °C under an atmosphere of nitrogen.
2.2. Preparation of ANFs/DMSO dispersion The aramid nanofiber (ANFs)/DMSO dispersion was prepared employing the method described previously by Kotov’s group [2]. In a nutshell, accurately weighing of 1.0 g Kevlar-29 yarns and 1.5 g KOH before adding them into 500 ml of DMSO. After constant magnetic stirring for 5–7 days at room temperature, a crimson and viscous ANFs/ DMSO dispersion was obtained successfully with the concentration of 2 mg/ml as displayed in Fig. 1a.
3. Results and discussion 3.1. Characterization of POSSeCOOH NPs
2.3. Preparation of POSSeCOOH/DMSO solution In order to investigate the physicochemical structure of POSSeCOOH samples, a series of characterization methods such as TEM, FTIR, XRD and TGA were used in this paper. The basic informations of POSS NPs were listed in Table 1. The homogeneous dispersion of POSS NPs in DMSO was evaluated by means of TEM as shown in Fig. 2a. POSS particles are visible clearly
The as-received POSSeCOOH could easily dissolved in DMSO. A 100 mg amount of POSSeCOOH was added into 1000 ml DMSO, forming a homogeneous and colorless transparent POSSeCOOH/DMSO aqueous solution with the concentration of 0.1 mg/ml assisted by the adopting of ultrasonic treatment for 0.5 h. 155
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Fig. 1. (a) optical image of the initial status of macro Kevlar fiber immerging into DMSO/KOH mixed solution (inset: a diluted dark red solution of ANFs); (b) TEM of ANFPs solution with content of POSS 6 wt.% (inset: photograph of ANFPs solution with change in color); (c and d) Low and high mag. SEM image of pure ANFs membrane (inset: graph of pristine ANFs membrane showing transparency); (e and f) Low and high mag. SEM image of ANFPs-6 hybrid membrane (inset: graph of ANFPs-6 membrane showing transparency). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
3.2. Structural morphology observation
Table 1 Chemical structures and properties of POSS nanoparticles. POSS type
OctaMaleamic Acid POSS (POSSbCOOH)
Chemical structure
Commercial Kevlar thread is an organic fiber in the aromatic polyamide family. It is a golden yarn consisting of amount of microfibers which have a unique combination of high strength, high modulus, toughness and thermal stability. Fig. 1a shows the initial status of macro Kevlar thread immerging into DMSO/KOH mixed solution. Using vacuum-assisted filtration, we can obtain pure ANFs membrane with eligible transparency (inset of Fig. 1c), and its surface is decorated by small ridges likely consisting of sheet-like aggregates of ANFs (Fig. 1c). TEM images of ANFs-POSS dispersion with the content of 6 wt.% POSS was obtained as Fig. 1b. It is worth noting that POSS NPs adsorbed along the ANFs throughout the ANFs matrix, and an interconnected network structure formed. The adsorption mechanism for POSSeCOOH NPs on the ANFs could be explained by hydrogen bonding. ANFPs-6 composite membrane demonstrates superior vitreousness owe to the introduction of POSS NPs exhibited as inset of Fig. 1d. SEM of ANFPs-6 composite membrane illustrated in Fig. 1d indicates that no bulky agglomeration among nanoparticles was observed and the nanofibers packed more closely which is corresponding to the enhancement of mechanical strength. In addition, interestingly, all of ANFPs hybrid membranes up to 30% of nanoparticle loading exhibit a macroscopically transparent feature. Naturally, when the POSS NPs is dissolved to give 1–2 nm entities, the medium remains transparent as the POSS is too small to scatter the visible light. Therefore, the macroscopic transparency of membranes may prove an excellent molecular-level dispersion of POSS in the polymeric medium to a certain extent.
Solvent solubility DMSO DMF
and distributed uniformly with a diameter about 2 nm. The FTIR spectra of neat POSS NPs (Fig. 2b) shows a broad band around 3300 cm−1 which can be attributed to OeH functional group stretching, a strong SieOeSi stretching absorption band at 1100 cm−1 which is the typical absorption of the silsesquioxane inorganic framework could be collected [47]. The double peaks at 2930 and 2873 cm−1 correspond to the CeH stretching of the eCH2 groups in the organic corner groups of the cage structure. The strong absorption at 1720 cm−1 can be assigned to the carbonyl group stretching vibration of a eCOOH in POSS. The sharp diffraction peaks of the reactant POSS (Fig. 2c) is characterized by well-defined peaks indicating the high crystallinity of the sample consistent with previous reports [48]. The POSSeCOOH NPs displays a two-steps degradation mechanism as shown in Fig. 2d, the mass loss below 200 °C is mainly due to the loss of solvents (DMSO) and decomposition of oxygen-containing groups such as carboxyl groups. POSS NPs show an outstanding thermal stability with initial thermal decomposition temperature, Td at around 440 °C.
3.3. Characterization and performance study of ANFPs hybrid membranes 3.3.1. FTIR and XPS study of composites membranes The adsorption mechanism for POSS on the ANFs could be explained by hydrogen bonding (schematic diagram shown in Fig. 3). The 156
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Fig. 2. TEM image (a), FTIR spectrum (b), XRD pattern (c) and TGA curve (d) of POSS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
very tightly to the ANFs. Furthermore, each POSS molecular owns eight carboxylic acid groups, it can act as cross-linkers between polymer chains. Via cross-linking a three dimensional network can be achieved which improves the membrane properties.
ANFs backbones have multitudinous amide groups, each containing a hydrogen atom acting as a hydrogen bound acceptor, while Octamaleamic acid POSS are capped by carboxylic acid groups on each corner silicon. Upon contact, hydrogen bonding occurs, which binds the POSS
Fig. 3. Schematic diagram of POSSeCOOH NPs adsorption on ANFs. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 157
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Fig. 6. XRD patterns of ANFPs membranes with different amounts of POSS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 4. FTIR spectra of ANFPs composite membranes with different amounts of POSS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
signal at 100.60 eV could be assigned to Si2p upon the addition of POSS, which agrees with the results of FTIR spectra and confirms the presence of POSS in the composite membranes.
FTIR is used to verify this interaction (Fig. 4). FTIR spectroscopy of neat ANFs membrane shows characteristic peaks of Kevlar at 3320 cm−1 (NeH stretching vibrations), 1649 cm−1 (C]O stretching vibrations), 1541 cm−1 (NeH deformation), and 1516 cm−1 (C]C stretching vibrations), respectively. After the POSS were decorated on ANFs, together with the peaks characteristics of the neat polymer matrix, band at 1100 cm−1 increased due to SieOeSi stretching vibration and proved the presence of POSS on the polymer surface. Besides, a broad peak around 3300 cm−1 (OeH stretching vibrations) and an increased peak at 1541 cm−1 were observed, indicative of the formation of hydrogen bonds (NeH ⋯ O). In addition, a FTIR peak at 1640 cm−1 arises from the hydrogen bonds formed by C]O groups with NeH groups, indicative of the hydrogen bonds between ANFs and POSS [7]. Furthermore, the successful introduction of POSS into ANFs matrix could be demonstrated from X-ray photoelectron spectroscopy (XPS) spectra as shown in Fig. 5. Specifically speaking, for neat ANFs membrane (Fig. 5a), C1s, N1s and O1s appear at 283.3 eV, 398.57 eV and 530.08 eV, respectively. By contrast, there is an obvious difference in XPS spectran of ANFPs hybrid membrane (take ANFP-6 for example) as shown in Fig. 5b, in addition to the peaks that attributed to C1s, N1s and O1s, the small
3.3.2. XRD analysis of ANFPs composites membranes Kevlar is a kind of highly-aligned backbone crystalline materials with 2θ values of 20.06° and 21.37° from 110 and 200 planes, respectively. The pure ANFs membranes represent similar prominent peaks which means the nanoscale fibers retain substantial crystallinity despite reduction in diameter. After the incorporation of POSS, all hybrid membranes show similarly crystalline profiles to the neat ANFs membrane regardless of the content of POSS (see Fig. 6). Neither did any new peak appear, nor did any of the existing peaks disappear, indicating no considerable change in crystallinity after modification. The disappearance of POSS dominant peaks suggests that the grafted POSS dispersed well in ANFs matrix. Beyond that, the stronger and sharper peak shape of ANFPs hybrid membranes states that the introduction of POSS benefit for the crystallization of ANFs, indicating that the interactions between polymer and POSS. This is helpful for the ANFPs hybrid membranes to maintain their basic mechanical properties based on the intermolecular hydrogen bonds. It’s worth noting that XRD patterns of ANFPs membranes with a low content of POSS (≤2 wt.%) represent similar Bragg prominent peaks at
Fig. 5. XPS spectra of neat ANFs membrane (a) and ANFPs-6 composite membrane (b). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 158
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3.3.3. Mechanical properties of ANFs and ANFPs hybrid membranes The mechanical properties of hybrid membranes are critical for design of devices. The tensile strength of hybrid membranes was tested in order to investigate the effect of POSS on the strength and ensure the optimal proportion of addition of POSSeCOOH. Fig. 7 illustrates the relation between the tensile strength and various ANFs/POSS ratio. The pure ANFs membrane shows a tensile strength of 212.2 MPa. The ANFPs-2 and ANFPs-4 improves the tensile strength to 229.09 MPa and 268.95 MPa, respectively. The increase of POSS loading to 6.0 wt.% (AFNPs-6) resulted in further improvement of the tensile strength of composite membrane to 376.25 MPa. The result is not inferior to any reported work such as ANFsMWCNTs composite films (383 Mpa [25], ANF-RGO nanocomposite paper (209.4 Mpa) [28], ANFs-Au films (196 Mpa) [24] and ANFs-Ag composite paper (139.8 MPa) [49]. This is exciting because the incorporation of nanomaterials above into ANFs for imparting increased properties or special characteristics sometimes deteriorates its intrinsic performance such as transparency, which may restrict its application to a certain extent. Therefore, the favourable vitreousness of ANFPs hybrid membrane embroads their application sphere as it may serve as a basis for further application in various fields. However, a further increase of the amounts of POSS will cause the decrease of the tensile strength. When POSS are grafted to the polymer chain or copolymerized with other monomers, nanoscale dispersion of POSS molecules in the matrix is facilitated by the strong covalent bonds between POSS and the polymer. Therefore, the nanoscale reinforcement on the polymer matrix is significant [50,51]. Here, POSS NPs are likely to affect the tensile strength via two opposing mechanisms. One is a reinforcing effect since they present octahedral structure, it could serve
Fig. 7. Tensile strength of ANFPs membranes with different amounts of POSS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
2θ values to original ANFs membranes. While 2θ values of ANFPs composite membrane with higher content POSS (≥4 wt.%) shift to 21.37° and 23.22° indicating a constringent d-spacing compared to that of ANFs which is coincide with SEM graph. It is speculated legitimately that the predictable improvement of mechanical strength of ANFPs composite membrane could be achieved. Combining with the FTIR, the insertion of POSS into the interlayers space between ANFs by hydrogen bonding has been certified.
Fig. 8. Thermal performance analysis of ANFPs membranes. (a and b) TG, DTG and DSC of pure ANFs membrane; (c and d) TG, DTG and DSC of ANFPs hybrid membrnae. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 159
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Acknowledgements
Table 2 Thermogravimetric parameters of the each sample. Sample
ANFs ANFPs-6
Temperature (°C)
This work was financially supported by China Postdoctoral Science Foundation (2013M541372). We would like to thank the financial support from Heilongjiang Postdoctoral Fund (LBH-Z13086). This work was also supported by “The Fundamental Research Funds for the Central Universities” (Grant No. HIT. NSRIF. 2015047).
Char(%)
Tonset
Tmax
Tg
Td-5%
Td-50%
485 530
512 557
379 386
148 178
517 563
22.48 35.97
References as a cross-linking agent in order to strengthen the interaction between the aramid nanofibers. The second is a weakening effect due to the NPinduced stress concentration. In this case, the reinforcing effect is predominant, thus the ANFPs films strength is higher than that of the pure ANF films. While the inappropriate higher content of POSS NPs result in the downtrend of tensile strength. This behavior is typical of polymer composites reinforced with fillers of nanoscale dimension [52]. Generally, the addition of higher amounts of filler content to polymers leads to poor processability and inferior mechanical performance [53].
[1] Lee JU, Park B, Kim BS, Bae DR, Lee W. Electrophoretic deposition of aramid nanofibers on carbon fibers for highly enhanced interfacial adhesion at low content. Compos Part A Appl S 2016;84:482–9. [2] Cao KQ, Siepermann CP, Yang M, Waas AM, Kotov NA, Thouless MD, et al. Reactive aramid nanostructures as high-performance polymeric building blocks for advanced composites. Adv Funct Mater 2013;23:2072–80. [3] Yang M, Cao KQ, Sui L, Qi Y, Zhu J, Waas A, et al. Dispersions of aramid nanofibers: a new nanoscale building block. ACS Nano 2011;5:6945–54. [4] Tung SO, Ho S, Yang M, Zhang RL, Kotov NA. A dendrite-suppressing composite ion conductor from aramid nanofibers. Nat Commun 2015;6:1–7. [5] Hu SY, Lin SD, Tu YY, Hu JW, Wu Y, Liu GJ, et al. Novel aramid nanofiber-coated polypropylene separators for lithium ion batteries. J Mate Chem A 2016;4:3513–26. [6] Camargo PHC, Satyanarayana KG, Wypych F. Nanocomposites: synthesis, structure, properties and new application opportunities. Mater Res 2009;12:1–39. [7] Sun K, Xie PT, Wang ZY, Su TM, Shao Q, Guo ZH, et al. Flexible polydimethylsiloxane/multi-walled carbon nanotubes membranous metacomposites with negative permittivity. Polymer 2017;125:50–7. [8] Huang JN, Cao YH, Shao Q, Peng XF, Guo ZH. Magnetic nanocarbon adsorbents with enhanced hexavalent chromium removal: morphology dependence of fibrillar vs particulate structures. Ind Eng Chem Res 2017;56(38):10689–701. [9] Zhang K, Li GH, Feng LM, Wang N, Guo J, Guo ZH, et al. Ultralow percolation threshold and enhanced electromagnetic interference shielding in poly(L-lactide)/ multi-walled carbon nanotube nanocomposites with electrically conductive segreated networks. J Mater Chem C 2017;5:9359–69. [10] Cheng XQ, Wang ZX, Jiang X, Li TX, Guo ZH, Shao L, et al. Towards sustainable ultrafast molecular-separation membranes: from conventional polymers to emerging materials. Prog Mater Sci 2018;92:258–83. [11] Wang C, He ZF, Xie XF, Mai XM, Li YC, Guo ZH, et al. Controllable cross-linking anion exchange membranes with excellent mechanical and thermal properties. Macromol Mater Eng 2018. http://dx.doi.org/10.1002/mame.201700462. [12] Hu C, Li ZY, Wang YL, Gao JC, Dai K, Guo ZH, et al. Comparative assessment of the strain-sensing behaviors of polylactic acid nanocomposites: reduced graphene oxide or carbon nanotubes. J Mater Chem C 2017;5:2318–28. [13] Wang C, Mo BM, He ZF, Xie XF, Zhao XX, Guo ZH, et al. Hydroxide ions transportation in polynorbornene anion exchange membrane. Polymer 2018;138:363–8. [14] Follain N, Alexandre B, Chappey C, Colasse L, Médéric P, Marais S. Barrier properties of polyamide 12/montmorillonite nanocomposites: effect of clay structure and mixing conditions. Compos Sci Technol 2016;136:18–28. [15] Dong RS, Raghu AV, Reddy KR, Han MJ. Compatibility of thermally reduced graphene with polyesters. J Macromol Sci Part B Phys 2016;55(11):1099–110. [16] Reddy KR, Byung CS, Kwang SR, Jaegeun N, Youngil L. In situ self-organization of carbon black-polyaniline comosites from nanospheres to nanorods: synthesis, morphology, structure and electrical conductivity. Synthetic Met 2009;159(19–20):1934–9. [17] Lee YR, Kim SC, Lee H, Jeong HM, Raghu AV, Reddy KR. Graphite oxides as effective retardants of epoxy resin. Macromol Res 2011;19(1):66–71. [18] Reddy KR, Jeong HM, Lee Y, Raghu AV. Synthesis of MWCNTs-core/thiophene polymer-sheath composite nanocables by a cationic surfactant-assisted chemical oxidative polymerization and their structural properties. J Polym Sci Pol Chem 2010;48(7):1477–84. [19] Reddy KR, Lee K, Gopalan AL. Self-assembly directed synthesis of poly(orthotoluidine)-metal(gold and palladium) composite nanospheres. J Nanosci Nanotechno 2007;7(9):3117–25. [20] Han SJ, Lee H, Jeong HM, Kim BK, Raghu AV, Reddy KR. Graphene modified lipophilically by stearic acid and its composite with low density polyethylene. J Macromol Sci Part B Phys 2014;53(7):1193–204. [21] Reddy KR, Park W, Sin BC, Noh J, Lee Y. Synthesis of electrically conductive and superparamagnetic monodispersed iron oxide-conjugated polymer composite nanoparticles by in situ chemical oxidative polymerization. J Colloid Interf Sci 2009;335(1):34–9. [22] Khan MU, Reddy KR, Snguanwongchai T, Haque E, Gomes VG. Polymer brush synthesis on surface modified carbon nanotubes via in situ emulsion polymerization. Colloid Polym Sci 2016;294(10):1599–610. [23] Choi SH, Kim DH, Raghu AV, Reddy KR, Lee H, Kim BK, et al. Properties of graphene/waterborne polyurethane nanocomposites cast from colloidal dispersion mixtures. J Macromol Sci Part B Phys 2012;51(1):197–207. [24] Lyu J, Wang XZ, Liu LH, Kim Y, Tanyi K, Chi H, et al. High strength conductive composite with plasmonic nanoparticles aligned on aramid nanofibers. Adv Funct Mater 2016;26:8435–45. [25] Zhu JQ, Cao WX, Yue ML, Hou Y, Han JC, Yang M. Strong and stiff aramid nanofiber/carbon nanotube nanocomposites. ACS Nano 2015;9:2489–501. [26] Fan JC, Wang JL, Shi ZX, Yu S, Yin J. Kevlar nanofiber-functionalized multiwalled carbon nanotubes for polymer reinforcement. Mater Chem Phys 2013;141:861–8.
3.3.4. Thermal properties of ANFs and ANFs/POSS hybrid membranes Based on the optimum mechanical strength of ANFPs-6 hybrid membrane, we further compare its thermal properties with that of pure ANFs membrane. TG-TGA-DSC curves of pure ANFs membrane and ANFPs-6 composite membrane are performed under nitrogen atmosphere as shown in Fig. 8, relevant thermogravimetric parameters of the each sample are list in Table 2. The TGA curves indicate that the pristine ANFs membrane show extraordinary thermal stability which is exciting because thermal stability is necessary to address the bottleneck preventing widespread application of flexible conductors composed of polymer substrates. The ANFPs-6 composite membrane displays very similar degradation behaviors to that of the neat ANFs membrane as shown in Fig. 8. This indicates that the degradation mechanism of the ANFs matrix has not been significantly altered by the presence of POSS fillers. The inorganic SieO framework of POSS, which has good thermal stability, could form a protective layer on the hybrid membranes preventing further degradation. This would contribute to the increased char yields (from 22.48% to 35.97%) observed in ANFPs hybrid membranes along with a significantly increased thermal stability. Obviously, the addition of 6 wt.% POSS into ANFs can increase Tonset and Tmax from 485 °C to 530 °C, 512 °C to 557 °C, respectively. All the experimental results indicate that the thermal performance of ANFPs hybrid membrane is improved. 4. Conclusions In the present study, pure ANFs membrane and fast-drying ANFPs nanohybrid membranes with different amounts of POSSeCOOH NPs are prepared via a vacuum-assisted flocculation method. The obtained ANFPs membranes could be pictured as cross-linked aramid nanofibers, linking by POSS through hydrogen bonds. Since the addition of POSS, the mechanical properties of the ANFPs membranes could be tuned, membranes with a relatively low POSS content exhibits an excellent tensile strength. It is also important to note that the achievement of such high mechanical performance at low loadings of POSS could be very desirable for retaining the good transparency of ANFPs membranes. We further demonstrate that ANFPs hybrid membranes present higher thermal stability. Therefore, the ANFPs hybrid membranes might be the promising candidates for potential application as strong, transparent and heat-resistant nanocomposite in many fields. Conflicts of interest There are no conflicts of interest to declare. 160
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[41] Ricco L, Russo S, Monticelli O, Bordo A, Bellucci F. ε-Caprolactam polymerization in presence of polyhedral oligomeric silsesquioxanes (POSS). Polymer 2005;46:6810–9. [42] Goffin AL, Duquesne E, Moins S, Alexandre M, Dubois P. New organic–inorganic nanohybrids via ring opening polymerization of (di)lactones initiated by functionalized polyhedral oligomeric silsesquioxane. Eur Polym J 2007;43:4103–13. [43] Choi J, Harcup J, Yee AF, Zhu Q, Laine RM. Organic/inorganic hybrid composites from cubic silsesquioxanes. J Am Chem Soc 2001;123:11420–30. [44] Liu H, Zheng S. Polyurethane networks nanoreinforced by polyhedral oligomeric silsesquioxane. Macromol Rapid Commun 2005;26:196–200. [45] Barral L, Diez FJ, Garcia-Garabal S, Lopez J, Montero B, Montes R, et al. Thermodegradation kinetics of a hybrid inorganic–organic epoxy system. Eur Polym J 2005;41:1662–6. [46] Zhang J, Xu R, Yu D. A novel poly-benzoxazinyl functionalized polyhedral oligomeric silsesquioxane and its nanocomposite with polybenzoxazine. Eur Polym J 2007;43:743–52. [47] Worthley CH, Constantopoulos KT, Ginnic-Markovic M, Markovic E, Clarke S. A study into the effect of POSS nanoparticles on cellulose acetate membranes. J Membrane Sci 2013;431:62–71. [48] Ma L, Geng HP, Song JX, Li JZ, Chen GX, Li QF. Hierarchical self-assembly of polyhedral oligomeric silsesquioxane end-capped stimuli-responsive polymer: from single micelle to complex micelle. J Phys Chem B 2011;115:10586–91. [49] Li JB, Fan JC, Liao KX, Xie JW, Chen YH, Liu P, et al. Facile fabrication of a multifunctional arami nanofiber-based composite paper. RSC Adv 2016;6:90263–72. [50] Ni Y, Zheng SX, Nie KM. Morphology and thermal properties of inorganic-organic hybrids involving epoxy resin and polyhedral oligomeric silsesquioxanes. Polymer 2004;45(16):5557–68. [51] Kim HU, Bang YH, Choi SM, Yoon KH. Morphology and mechanical properties of PET by incorporation of amine-polyhedral oligomeric silsesquioxane. Compos Sci Technol 2008;68(13):2739–47. [52] He LX, Tijon SC. Facile synthesis of silver-decorated reduced graphene oxide as a hybrid filler material for electrically conductive polymer composites. RSC Adv 2015;5:15070–6. [53] Liang GD, Bao SP, Tjong SC. Microstructure and properties of polypropylene composites filled with silver and carbon nanotube nanoparticles prepared by meltcompounding. Mat Sci Eng B 2007;142:55–61.
[27] Fan JC, Shi ZX, Zhang L, Wang JL, Yin J. Aramid nanofiber-functionalized graphene nanosheets for polymer reinforcement. Nanoscale 2012;4:7046–55. [28] Fan JC, Shi ZX, Tian M, Yin J. Graphene-aramid nanofiber nanocomposite paper with high mechanical and electrical performance. RSC Adv 2013;3:17664–7. [29] Eisenberg P, Erra-Balsells R, Ishikawa Y, Lucas JC, Nonami H, Williams RJJ. Silsesquioxanes derived from the bulk polycondensation of [3 (Methacryloxy) propyl]trimethoxysilane with concentrated formic acid: evolution of molar mass distributions and fraction of intramolecular cycles. Macromolecules 2002;35(4):1160–74. [30] Paul DR, Robeson LM. Polymer nanotechnology: nanocomposites. Polymer 2008;49:3187–204. [31] Zhu J, Shim BS, Prima MD, Kotov NA. Transparent conductors from carbon nanotubes LBL-assembled with polymer dopant with pi-pi electron transfer. J Am Chem Soc 2011;133:7450–60. [32] Yang M, Cao KQ, Yeom B, Thouless MD, Waas A, Arruda EM, et al. Aramid nanofiber-reinforced transparent nanocomposites. J Com Mat 2015;49:1873–9. [33] Zheng L, Farris RJ, Coughlin EB. Novel polyolefin nanocomposites: synthesis and characterizations of metallocene-catalyzed polyolefin polyhedral oligomeric silsesquioxane copolymers. Macromolecules 2001;34:8034–9. [34] Zheng L, Waddon AJ, Farris RJ, Coughlin EB. X-ray characterizations of polyethylene polyhedral oligomeric silsesquioxane copolymers. Macromolecules 2002;35:2375–9. [35] Waddon AJ, Zheng L, Farris RJ, Coughlin EB. Nanostructured polyethylene-POSS copolymers: control of crystallization and aggregation. Nano Lett 2002;2:1149–55. [36] Fina A, Tabuani D, Frache A, Camino G. Polypropylene-polyhedral oligomeric silsesquioxanes (POSS) nanocomposites. Polymer 2005;46:7855–66. [37] Haddad TS, Lichtenhan JD. Hybrid organic–inorganic thermoplastics: styryl-based polyhedral oligomeric silsesquioxane polymers. Macromolecules 1996;29:7302–4. [38] Lichtenhan JD, Otonari YA, Carr MJ. Linear hybridpolymer buildingblocks: methacrylate-functionalized polyhedral oligomeric silsesquioxane monomers and polymers. Macromolecules 1995;28:8435–7. [39] Zhao Y, Schiraldi DA. Thermal and mechanical properties of polyhedral oligomeric silsesquioxane (POSS)/polycarbonate composites. Polymer 2005;46:11640–7. [40] Ciolacu FCL, Choudhury NR, Dutta N, Kosior E. Molecular level stabilization of poly (ethylene terephthalate) with nanostructured open cage trisilanolisobutyl-POSS. Macromolecules 2007;40:265–72.
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Contents lists available at ScienceDirect
Composites Part A journal homepage: www.elsevier.com/locate/compositesa
High strength, thermostable and fast-drying hybrid transparent membranes with POSS nanoparticles aligned on aramid nanofibers ⁎
Fang Wang1, Yadong Wu1, , Yudong Huang
T
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MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Aramid nanofiber POSSeCOOH NPs Fast-dying membrane Tensile strength Thermal performance
Hybrid organic/inorganic nanocomposites based on aramid nanofibers (ANFs) and different amounts of polyhedral oligomeric silsesquioxane (POSS) nanostructured chemicals were prepared via solution blending and vacuum-assisted flocculation, compared with traditional film fabrication methods, this process is time-saving by adopting ethanol as agglomerator. The mechanical properties of ANFPs membranes could be altered by changing the POSS content, in which the POSS served as a cross-linking agent between nanofibers, and ANFPs composite membrane presented the optimal tensile strength with 6 wt.% POSS NPs embedding in the nanocomposite. In addition to the satisfactory mechanical performance and vitreousness, the unique thermal assets of ANFs and POSS further enabled the membranes with high thermal stability. Based on these results, it could be concluded that the ANFPs membranes developed here might provide the alternative materials for the practical application of strong, transparent and heat-resistant membrane.
1. Introduction Polyparaphenylene terephthalamide (PPTA), a high performance para-aramid polymer better known by its trade-name Kevlar, has outstanding mechanical properties such as high modulus and high tenacity at a significant low density [1,2]. Kevlar is suitable membrane materials due to their superior mechanical and thermal properties. Encouragingly, aramid nanofibers (ANFs) is obtained in dimethyl sulfoxide (DMSO) and potassium hydroxide (KOH) [3–5] which have been developed with maintaining excellent mechanical properties similar to its original bulk fibers and considered as an essential nanoscale “building block” [2]. Inspired by remarkable potential to combine two dramatically different material classes at the molecular level [6–13], the synergistic combination of individual inorganic/organic components provides promising potential to tune the resulting structure and to design or tailor the resulting properties for extend applications in many areas [14–19], such as packaging, electronics, optical devices, aerospace, automotive engineering, and biomaterials. Nanoscale inorganic fillers which can impact desirable structural and functional properties in a polymeric material are widely studied because of their effective reinforcement at very low loadings [20–23]. ANFs has also been investigated and introduced into the fabrication and
⁎
1
Corresponding authors. E-mail addresses: [email protected] (Y. Wu), [email protected] (Y. Huang). These authors contributed equally to this work.
https://doi.org/10.1016/j.compositesa.2018.04.031 Received 18 January 2018; Received in revised form 22 March 2018; Accepted 30 April 2018 Available online 02 May 2018 1359-835X/ © 2018 Elsevier Ltd. All rights reserved.
application of the high-performance advanced hybrid organic-inorganic nanohybrid membranes. For instance, ANFs hybrids with gold nanoparticles [24], carbon nanomaterials such as carbon nanotubes (CNTs) [25,26] and graphene sheet [27,28] have been successfully manufactured, and the results have proved that the mechanical properties of the obtained nanohybrid membranes enhanced obviously. While, the incorporation of nanoparticles into a polymeric matrix is often difficult. The general challenge is that very small particles tend to form agglomerates resulting in membranes with an inhomogeneous distribution. Hence the focus nowadays is to use particles with a small size and functional side groups for a homogenous incorporation into a polymeric matrix. POSS nanostructures, sizing approximately 1–3 nm, with general formula (RSiO1.5)n, where n refers to the number of Si atom in the cage and R is hydrogen or an organic group, such as alkyl, aryl, or any of their derivatives [29]. The inorganic silica core of POSS is thermally and chemically robust while the diversity of the R groups makes them compatible with various polymer systems. Therefore, regarded as the smallest possible particles of silica, well defined three-dimensional nanoscale architecture, and monodisperse particle size, incorporation of POSS macromers within polymeric architectures allows the organic and inorganic phases to interact at the molecular level and with assured compatibilization and it may be another hopeful candidate as the
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2.4. Characterization of POSSeCOOH
dispersed phase for the fabrication of molecular-level mixed matrix membranes. POSS molecules possess the very high flexibility to be functionalized, thus creating an excellent compatibility and dispersibility at the molecular level in diverse polymer matrices [30]. Furthermore, POSS compounds can act as cross-linkers between polymer chains. Via crosslinking a three dimensional network can be achieved which improves the membrane properties with regard to chemical stability and temperature resistance. In addition, the significance of mechanical reinforcement of optically functional materials has been witnessed by the rapid growth of electronic industries which, in turn, have created a great demand for transparent and strong materials [31]. Encouragingly, the availability of nanofibers with diameters significantly smaller than the wavelengths of visible light offer a potential way to avoid this limitation of opaqueness [32]. Since their unique properties and high potential as additive [33–39], over the past decade, POSS became an attractive candidate as additive for the preparation of nanomaterials in membrane technology to modify a wide range of polymer chain such as polyolefin, polystyrene, poly (methyl methacrylate), polycarbonate, poly (ethylene terephthalate), polyamide and a few thermoset systems [40–46]. However, since very few studies exist on the utility of on POSS as additives for ANFs membranes is available. Herein, a kind of co-effectively transparency, high strength and thermal stability ANFPs nanohybrid membrane based on ANFs with incorporation of well distributed POSS compounds acting as cross-linker was synthesized efficiently. The transparency and flexibility of ANFPs nanocomposite membranes could be maintained. Furthermore, the mechanical properties and thermal stability of the hybrid membranes improved, i.e. high tensile strength as expected. It might be the promising candidates for potential application as strong, transparent and heat-resistant nanocomposite in many fields.
A series of characterization tools were adopted to investigate the physicochemical property of POSSeCOOH NPs. FTIR spectroscopy were used to determine chemical structure of POSSeCOOH products. Transmission electron microscope (TEM) were used to observe the nanoscale morphology and dispersibility. To identify the stacking in POSSeCOOH, XRD measurement was carried out. Thermo-gravimetric analysis of samples was employed by TGA using a heating rate of 10 °C/ min from 30 to 800 °C in the atmosphere of nitrogen. 2.5. Synthesis of ANFPs nanocomposites membranes ANFs/DMSO and POSSeCOOH/DMSO solutions were mixed with a given ration followed by an equal volume of ethanol to substitute DMSO and precipitate the ANFPs. Specifically, 5 ml of as-obtained ANFs/DMSO dispersion was diluted to 30.0 ml by the additional DMSO (inset of Fig. 1a). Then POSSeCOOH/DMSO solutions of different volumes (0, 2.04, 4.17, 6.38, 8.70 and 11.11 ml) were added dropwise with the change in color from dark red to yellow under vigorously stirring (inset of Fig. 1b), creating membrane samples with designated names of ANFPs-2, ANFPs-4, ANFPs-6, ANFPs-8 and ANFPs-10 for membranes with POSS loadings 2 wt.%, 4 wt.%, 6 wt.%, 8 wt.% and 10 wt.%, respectively, subsequent with additional 1 h stirring. After that, 4.0 ml of ethanol was further added dropwise under vigorously stirring for all mixtures which resulted in a gel-like state, following another 2 h stirring to achieve a uniform dispersion. The obtained jelly was vacuum filtrated using nylon membranes and the product was soaked in ethanol 12 h followed with air drying within a few seconds. Finally, the dried nylon membrane integrated with ANFPs membrane was soaked in ethanol again about 10 min to make the composite membrane fall off automatically, subsequent with air drying to volatilize ethanol which takes a very short time. Finally, pristine ANFs and ANFPs composite membrane were obtained.
2. Experimental and methods
2.6. Characterization and performance study of ANFPs composites membranes
2.1. Materials Kevlar-29 (136 dtex) brand yarns (M.Wt. ∼25000, stiffness 109 Gpa and strength 3.6 Gpa) were purchased from DuPont Co., Ltd (USA). Polyhedral oligomeric silsesquioxane marked with CA0298 (OctaMaleamic Acid POSS, abbreviated as POSSeCOOH) was purchased from Hybrid Plastics Co., Ltd (USA) as crystalline powders and used as received. Potassium hydroxide (KOH), Dimethyl sulfoxide (DMSO) and ethanol were supplied by Aladdin Co., Ltd (China). All chemicals were used as received without further purification. Nylon filtration membranes with 0.1 µm pore diameter (Filtration Equipment Factory Co., Ltd., Haining, China.) were used in this study.
ATR-FTIR studies was measured on a Perkin Elmer Spectrum One spectrometer (Nicolet Nexus 670, USA) to investigate the functional groups of membrane surfaces and the presence of POSSeCOOH. The size and morphology of as-prepared ANFs and ANFPs were characterized by using a transmission electron microscope (TEM), and all the TEM images were obtained on a JEOL 2000 FX microscope. The surface morphology of hybrid membranes was analyzed using scanning electron microscopy (SEM) with a Hitachi S-4700 SEM. XRD measurement was carried out by a D/man-rBX X-ray generator operated at 30 mA and 40 kV to study the crystalline structure and distribution of the POSSeCOOH. Mechanical strength of the synthesized membranes were tested by Cmt8102 electric universal testing machine with tensile speed at 10 mm/min. The tensile strength measurements were repeated five times for each specimen and average tensile strength was reported. The thermal properties of the composite membrane were analyzed by a thermogravimetric analyzer (TA Q500) using a heating rate of 10 °C/ min from 30 to 800 °C under an atmosphere of nitrogen.
2.2. Preparation of ANFs/DMSO dispersion The aramid nanofiber (ANFs)/DMSO dispersion was prepared employing the method described previously by Kotov’s group [2]. In a nutshell, accurately weighing of 1.0 g Kevlar-29 yarns and 1.5 g KOH before adding them into 500 ml of DMSO. After constant magnetic stirring for 5–7 days at room temperature, a crimson and viscous ANFs/ DMSO dispersion was obtained successfully with the concentration of 2 mg/ml as displayed in Fig. 1a.
3. Results and discussion 3.1. Characterization of POSSeCOOH NPs
2.3. Preparation of POSSeCOOH/DMSO solution In order to investigate the physicochemical structure of POSSeCOOH samples, a series of characterization methods such as TEM, FTIR, XRD and TGA were used in this paper. The basic informations of POSS NPs were listed in Table 1. The homogeneous dispersion of POSS NPs in DMSO was evaluated by means of TEM as shown in Fig. 2a. POSS particles are visible clearly
The as-received POSSeCOOH could easily dissolved in DMSO. A 100 mg amount of POSSeCOOH was added into 1000 ml DMSO, forming a homogeneous and colorless transparent POSSeCOOH/DMSO aqueous solution with the concentration of 0.1 mg/ml assisted by the adopting of ultrasonic treatment for 0.5 h. 155
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Fig. 1. (a) optical image of the initial status of macro Kevlar fiber immerging into DMSO/KOH mixed solution (inset: a diluted dark red solution of ANFs); (b) TEM of ANFPs solution with content of POSS 6 wt.% (inset: photograph of ANFPs solution with change in color); (c and d) Low and high mag. SEM image of pure ANFs membrane (inset: graph of pristine ANFs membrane showing transparency); (e and f) Low and high mag. SEM image of ANFPs-6 hybrid membrane (inset: graph of ANFPs-6 membrane showing transparency). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
3.2. Structural morphology observation
Table 1 Chemical structures and properties of POSS nanoparticles. POSS type
OctaMaleamic Acid POSS (POSSbCOOH)
Chemical structure
Commercial Kevlar thread is an organic fiber in the aromatic polyamide family. It is a golden yarn consisting of amount of microfibers which have a unique combination of high strength, high modulus, toughness and thermal stability. Fig. 1a shows the initial status of macro Kevlar thread immerging into DMSO/KOH mixed solution. Using vacuum-assisted filtration, we can obtain pure ANFs membrane with eligible transparency (inset of Fig. 1c), and its surface is decorated by small ridges likely consisting of sheet-like aggregates of ANFs (Fig. 1c). TEM images of ANFs-POSS dispersion with the content of 6 wt.% POSS was obtained as Fig. 1b. It is worth noting that POSS NPs adsorbed along the ANFs throughout the ANFs matrix, and an interconnected network structure formed. The adsorption mechanism for POSSeCOOH NPs on the ANFs could be explained by hydrogen bonding. ANFPs-6 composite membrane demonstrates superior vitreousness owe to the introduction of POSS NPs exhibited as inset of Fig. 1d. SEM of ANFPs-6 composite membrane illustrated in Fig. 1d indicates that no bulky agglomeration among nanoparticles was observed and the nanofibers packed more closely which is corresponding to the enhancement of mechanical strength. In addition, interestingly, all of ANFPs hybrid membranes up to 30% of nanoparticle loading exhibit a macroscopically transparent feature. Naturally, when the POSS NPs is dissolved to give 1–2 nm entities, the medium remains transparent as the POSS is too small to scatter the visible light. Therefore, the macroscopic transparency of membranes may prove an excellent molecular-level dispersion of POSS in the polymeric medium to a certain extent.
Solvent solubility DMSO DMF
and distributed uniformly with a diameter about 2 nm. The FTIR spectra of neat POSS NPs (Fig. 2b) shows a broad band around 3300 cm−1 which can be attributed to OeH functional group stretching, a strong SieOeSi stretching absorption band at 1100 cm−1 which is the typical absorption of the silsesquioxane inorganic framework could be collected [47]. The double peaks at 2930 and 2873 cm−1 correspond to the CeH stretching of the eCH2 groups in the organic corner groups of the cage structure. The strong absorption at 1720 cm−1 can be assigned to the carbonyl group stretching vibration of a eCOOH in POSS. The sharp diffraction peaks of the reactant POSS (Fig. 2c) is characterized by well-defined peaks indicating the high crystallinity of the sample consistent with previous reports [48]. The POSSeCOOH NPs displays a two-steps degradation mechanism as shown in Fig. 2d, the mass loss below 200 °C is mainly due to the loss of solvents (DMSO) and decomposition of oxygen-containing groups such as carboxyl groups. POSS NPs show an outstanding thermal stability with initial thermal decomposition temperature, Td at around 440 °C.
3.3. Characterization and performance study of ANFPs hybrid membranes 3.3.1. FTIR and XPS study of composites membranes The adsorption mechanism for POSS on the ANFs could be explained by hydrogen bonding (schematic diagram shown in Fig. 3). The 156
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Fig. 2. TEM image (a), FTIR spectrum (b), XRD pattern (c) and TGA curve (d) of POSS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
very tightly to the ANFs. Furthermore, each POSS molecular owns eight carboxylic acid groups, it can act as cross-linkers between polymer chains. Via cross-linking a three dimensional network can be achieved which improves the membrane properties.
ANFs backbones have multitudinous amide groups, each containing a hydrogen atom acting as a hydrogen bound acceptor, while Octamaleamic acid POSS are capped by carboxylic acid groups on each corner silicon. Upon contact, hydrogen bonding occurs, which binds the POSS
Fig. 3. Schematic diagram of POSSeCOOH NPs adsorption on ANFs. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 157
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Fig. 6. XRD patterns of ANFPs membranes with different amounts of POSS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 4. FTIR spectra of ANFPs composite membranes with different amounts of POSS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
signal at 100.60 eV could be assigned to Si2p upon the addition of POSS, which agrees with the results of FTIR spectra and confirms the presence of POSS in the composite membranes.
FTIR is used to verify this interaction (Fig. 4). FTIR spectroscopy of neat ANFs membrane shows characteristic peaks of Kevlar at 3320 cm−1 (NeH stretching vibrations), 1649 cm−1 (C]O stretching vibrations), 1541 cm−1 (NeH deformation), and 1516 cm−1 (C]C stretching vibrations), respectively. After the POSS were decorated on ANFs, together with the peaks characteristics of the neat polymer matrix, band at 1100 cm−1 increased due to SieOeSi stretching vibration and proved the presence of POSS on the polymer surface. Besides, a broad peak around 3300 cm−1 (OeH stretching vibrations) and an increased peak at 1541 cm−1 were observed, indicative of the formation of hydrogen bonds (NeH ⋯ O). In addition, a FTIR peak at 1640 cm−1 arises from the hydrogen bonds formed by C]O groups with NeH groups, indicative of the hydrogen bonds between ANFs and POSS [7]. Furthermore, the successful introduction of POSS into ANFs matrix could be demonstrated from X-ray photoelectron spectroscopy (XPS) spectra as shown in Fig. 5. Specifically speaking, for neat ANFs membrane (Fig. 5a), C1s, N1s and O1s appear at 283.3 eV, 398.57 eV and 530.08 eV, respectively. By contrast, there is an obvious difference in XPS spectran of ANFPs hybrid membrane (take ANFP-6 for example) as shown in Fig. 5b, in addition to the peaks that attributed to C1s, N1s and O1s, the small
3.3.2. XRD analysis of ANFPs composites membranes Kevlar is a kind of highly-aligned backbone crystalline materials with 2θ values of 20.06° and 21.37° from 110 and 200 planes, respectively. The pure ANFs membranes represent similar prominent peaks which means the nanoscale fibers retain substantial crystallinity despite reduction in diameter. After the incorporation of POSS, all hybrid membranes show similarly crystalline profiles to the neat ANFs membrane regardless of the content of POSS (see Fig. 6). Neither did any new peak appear, nor did any of the existing peaks disappear, indicating no considerable change in crystallinity after modification. The disappearance of POSS dominant peaks suggests that the grafted POSS dispersed well in ANFs matrix. Beyond that, the stronger and sharper peak shape of ANFPs hybrid membranes states that the introduction of POSS benefit for the crystallization of ANFs, indicating that the interactions between polymer and POSS. This is helpful for the ANFPs hybrid membranes to maintain their basic mechanical properties based on the intermolecular hydrogen bonds. It’s worth noting that XRD patterns of ANFPs membranes with a low content of POSS (≤2 wt.%) represent similar Bragg prominent peaks at
Fig. 5. XPS spectra of neat ANFs membrane (a) and ANFPs-6 composite membrane (b). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 158
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3.3.3. Mechanical properties of ANFs and ANFPs hybrid membranes The mechanical properties of hybrid membranes are critical for design of devices. The tensile strength of hybrid membranes was tested in order to investigate the effect of POSS on the strength and ensure the optimal proportion of addition of POSSeCOOH. Fig. 7 illustrates the relation between the tensile strength and various ANFs/POSS ratio. The pure ANFs membrane shows a tensile strength of 212.2 MPa. The ANFPs-2 and ANFPs-4 improves the tensile strength to 229.09 MPa and 268.95 MPa, respectively. The increase of POSS loading to 6.0 wt.% (AFNPs-6) resulted in further improvement of the tensile strength of composite membrane to 376.25 MPa. The result is not inferior to any reported work such as ANFsMWCNTs composite films (383 Mpa [25], ANF-RGO nanocomposite paper (209.4 Mpa) [28], ANFs-Au films (196 Mpa) [24] and ANFs-Ag composite paper (139.8 MPa) [49]. This is exciting because the incorporation of nanomaterials above into ANFs for imparting increased properties or special characteristics sometimes deteriorates its intrinsic performance such as transparency, which may restrict its application to a certain extent. Therefore, the favourable vitreousness of ANFPs hybrid membrane embroads their application sphere as it may serve as a basis for further application in various fields. However, a further increase of the amounts of POSS will cause the decrease of the tensile strength. When POSS are grafted to the polymer chain or copolymerized with other monomers, nanoscale dispersion of POSS molecules in the matrix is facilitated by the strong covalent bonds between POSS and the polymer. Therefore, the nanoscale reinforcement on the polymer matrix is significant [50,51]. Here, POSS NPs are likely to affect the tensile strength via two opposing mechanisms. One is a reinforcing effect since they present octahedral structure, it could serve
Fig. 7. Tensile strength of ANFPs membranes with different amounts of POSS. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
2θ values to original ANFs membranes. While 2θ values of ANFPs composite membrane with higher content POSS (≥4 wt.%) shift to 21.37° and 23.22° indicating a constringent d-spacing compared to that of ANFs which is coincide with SEM graph. It is speculated legitimately that the predictable improvement of mechanical strength of ANFPs composite membrane could be achieved. Combining with the FTIR, the insertion of POSS into the interlayers space between ANFs by hydrogen bonding has been certified.
Fig. 8. Thermal performance analysis of ANFPs membranes. (a and b) TG, DTG and DSC of pure ANFs membrane; (c and d) TG, DTG and DSC of ANFPs hybrid membrnae. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 159
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Acknowledgements
Table 2 Thermogravimetric parameters of the each sample. Sample
ANFs ANFPs-6
Temperature (°C)
This work was financially supported by China Postdoctoral Science Foundation (2013M541372). We would like to thank the financial support from Heilongjiang Postdoctoral Fund (LBH-Z13086). This work was also supported by “The Fundamental Research Funds for the Central Universities” (Grant No. HIT. NSRIF. 2015047).
Char(%)
Tonset
Tmax
Tg
Td-5%
Td-50%
485 530
512 557
379 386
148 178
517 563
22.48 35.97
References as a cross-linking agent in order to strengthen the interaction between the aramid nanofibers. The second is a weakening effect due to the NPinduced stress concentration. In this case, the reinforcing effect is predominant, thus the ANFPs films strength is higher than that of the pure ANF films. While the inappropriate higher content of POSS NPs result in the downtrend of tensile strength. This behavior is typical of polymer composites reinforced with fillers of nanoscale dimension [52]. Generally, the addition of higher amounts of filler content to polymers leads to poor processability and inferior mechanical performance [53].
[1] Lee JU, Park B, Kim BS, Bae DR, Lee W. Electrophoretic deposition of aramid nanofibers on carbon fibers for highly enhanced interfacial adhesion at low content. Compos Part A Appl S 2016;84:482–9. [2] Cao KQ, Siepermann CP, Yang M, Waas AM, Kotov NA, Thouless MD, et al. Reactive aramid nanostructures as high-performance polymeric building blocks for advanced composites. Adv Funct Mater 2013;23:2072–80. [3] Yang M, Cao KQ, Sui L, Qi Y, Zhu J, Waas A, et al. Dispersions of aramid nanofibers: a new nanoscale building block. ACS Nano 2011;5:6945–54. [4] Tung SO, Ho S, Yang M, Zhang RL, Kotov NA. A dendrite-suppressing composite ion conductor from aramid nanofibers. Nat Commun 2015;6:1–7. [5] Hu SY, Lin SD, Tu YY, Hu JW, Wu Y, Liu GJ, et al. Novel aramid nanofiber-coated polypropylene separators for lithium ion batteries. J Mate Chem A 2016;4:3513–26. [6] Camargo PHC, Satyanarayana KG, Wypych F. Nanocomposites: synthesis, structure, properties and new application opportunities. Mater Res 2009;12:1–39. [7] Sun K, Xie PT, Wang ZY, Su TM, Shao Q, Guo ZH, et al. Flexible polydimethylsiloxane/multi-walled carbon nanotubes membranous metacomposites with negative permittivity. Polymer 2017;125:50–7. [8] Huang JN, Cao YH, Shao Q, Peng XF, Guo ZH. Magnetic nanocarbon adsorbents with enhanced hexavalent chromium removal: morphology dependence of fibrillar vs particulate structures. Ind Eng Chem Res 2017;56(38):10689–701. [9] Zhang K, Li GH, Feng LM, Wang N, Guo J, Guo ZH, et al. Ultralow percolation threshold and enhanced electromagnetic interference shielding in poly(L-lactide)/ multi-walled carbon nanotube nanocomposites with electrically conductive segreated networks. J Mater Chem C 2017;5:9359–69. [10] Cheng XQ, Wang ZX, Jiang X, Li TX, Guo ZH, Shao L, et al. Towards sustainable ultrafast molecular-separation membranes: from conventional polymers to emerging materials. Prog Mater Sci 2018;92:258–83. [11] Wang C, He ZF, Xie XF, Mai XM, Li YC, Guo ZH, et al. Controllable cross-linking anion exchange membranes with excellent mechanical and thermal properties. Macromol Mater Eng 2018. http://dx.doi.org/10.1002/mame.201700462. [12] Hu C, Li ZY, Wang YL, Gao JC, Dai K, Guo ZH, et al. Comparative assessment of the strain-sensing behaviors of polylactic acid nanocomposites: reduced graphene oxide or carbon nanotubes. J Mater Chem C 2017;5:2318–28. [13] Wang C, Mo BM, He ZF, Xie XF, Zhao XX, Guo ZH, et al. Hydroxide ions transportation in polynorbornene anion exchange membrane. Polymer 2018;138:363–8. [14] Follain N, Alexandre B, Chappey C, Colasse L, Médéric P, Marais S. Barrier properties of polyamide 12/montmorillonite nanocomposites: effect of clay structure and mixing conditions. Compos Sci Technol 2016;136:18–28. [15] Dong RS, Raghu AV, Reddy KR, Han MJ. Compatibility of thermally reduced graphene with polyesters. J Macromol Sci Part B Phys 2016;55(11):1099–110. [16] Reddy KR, Byung CS, Kwang SR, Jaegeun N, Youngil L. In situ self-organization of carbon black-polyaniline comosites from nanospheres to nanorods: synthesis, morphology, structure and electrical conductivity. Synthetic Met 2009;159(19–20):1934–9. [17] Lee YR, Kim SC, Lee H, Jeong HM, Raghu AV, Reddy KR. Graphite oxides as effective retardants of epoxy resin. Macromol Res 2011;19(1):66–71. [18] Reddy KR, Jeong HM, Lee Y, Raghu AV. Synthesis of MWCNTs-core/thiophene polymer-sheath composite nanocables by a cationic surfactant-assisted chemical oxidative polymerization and their structural properties. J Polym Sci Pol Chem 2010;48(7):1477–84. [19] Reddy KR, Lee K, Gopalan AL. Self-assembly directed synthesis of poly(orthotoluidine)-metal(gold and palladium) composite nanospheres. J Nanosci Nanotechno 2007;7(9):3117–25. [20] Han SJ, Lee H, Jeong HM, Kim BK, Raghu AV, Reddy KR. Graphene modified lipophilically by stearic acid and its composite with low density polyethylene. J Macromol Sci Part B Phys 2014;53(7):1193–204. [21] Reddy KR, Park W, Sin BC, Noh J, Lee Y. Synthesis of electrically conductive and superparamagnetic monodispersed iron oxide-conjugated polymer composite nanoparticles by in situ chemical oxidative polymerization. J Colloid Interf Sci 2009;335(1):34–9. [22] Khan MU, Reddy KR, Snguanwongchai T, Haque E, Gomes VG. Polymer brush synthesis on surface modified carbon nanotubes via in situ emulsion polymerization. Colloid Polym Sci 2016;294(10):1599–610. [23] Choi SH, Kim DH, Raghu AV, Reddy KR, Lee H, Kim BK, et al. Properties of graphene/waterborne polyurethane nanocomposites cast from colloidal dispersion mixtures. J Macromol Sci Part B Phys 2012;51(1):197–207. [24] Lyu J, Wang XZ, Liu LH, Kim Y, Tanyi K, Chi H, et al. High strength conductive composite with plasmonic nanoparticles aligned on aramid nanofibers. Adv Funct Mater 2016;26:8435–45. [25] Zhu JQ, Cao WX, Yue ML, Hou Y, Han JC, Yang M. Strong and stiff aramid nanofiber/carbon nanotube nanocomposites. ACS Nano 2015;9:2489–501. [26] Fan JC, Wang JL, Shi ZX, Yu S, Yin J. Kevlar nanofiber-functionalized multiwalled carbon nanotubes for polymer reinforcement. Mater Chem Phys 2013;141:861–8.
3.3.4. Thermal properties of ANFs and ANFs/POSS hybrid membranes Based on the optimum mechanical strength of ANFPs-6 hybrid membrane, we further compare its thermal properties with that of pure ANFs membrane. TG-TGA-DSC curves of pure ANFs membrane and ANFPs-6 composite membrane are performed under nitrogen atmosphere as shown in Fig. 8, relevant thermogravimetric parameters of the each sample are list in Table 2. The TGA curves indicate that the pristine ANFs membrane show extraordinary thermal stability which is exciting because thermal stability is necessary to address the bottleneck preventing widespread application of flexible conductors composed of polymer substrates. The ANFPs-6 composite membrane displays very similar degradation behaviors to that of the neat ANFs membrane as shown in Fig. 8. This indicates that the degradation mechanism of the ANFs matrix has not been significantly altered by the presence of POSS fillers. The inorganic SieO framework of POSS, which has good thermal stability, could form a protective layer on the hybrid membranes preventing further degradation. This would contribute to the increased char yields (from 22.48% to 35.97%) observed in ANFPs hybrid membranes along with a significantly increased thermal stability. Obviously, the addition of 6 wt.% POSS into ANFs can increase Tonset and Tmax from 485 °C to 530 °C, 512 °C to 557 °C, respectively. All the experimental results indicate that the thermal performance of ANFPs hybrid membrane is improved. 4. Conclusions In the present study, pure ANFs membrane and fast-drying ANFPs nanohybrid membranes with different amounts of POSSeCOOH NPs are prepared via a vacuum-assisted flocculation method. The obtained ANFPs membranes could be pictured as cross-linked aramid nanofibers, linking by POSS through hydrogen bonds. Since the addition of POSS, the mechanical properties of the ANFPs membranes could be tuned, membranes with a relatively low POSS content exhibits an excellent tensile strength. It is also important to note that the achievement of such high mechanical performance at low loadings of POSS could be very desirable for retaining the good transparency of ANFPs membranes. We further demonstrate that ANFPs hybrid membranes present higher thermal stability. Therefore, the ANFPs hybrid membranes might be the promising candidates for potential application as strong, transparent and heat-resistant nanocomposite in many fields. Conflicts of interest There are no conflicts of interest to declare. 160
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[41] Ricco L, Russo S, Monticelli O, Bordo A, Bellucci F. ε-Caprolactam polymerization in presence of polyhedral oligomeric silsesquioxanes (POSS). Polymer 2005;46:6810–9. [42] Goffin AL, Duquesne E, Moins S, Alexandre M, Dubois P. New organic–inorganic nanohybrids via ring opening polymerization of (di)lactones initiated by functionalized polyhedral oligomeric silsesquioxane. Eur Polym J 2007;43:4103–13. [43] Choi J, Harcup J, Yee AF, Zhu Q, Laine RM. Organic/inorganic hybrid composites from cubic silsesquioxanes. J Am Chem Soc 2001;123:11420–30. [44] Liu H, Zheng S. Polyurethane networks nanoreinforced by polyhedral oligomeric silsesquioxane. Macromol Rapid Commun 2005;26:196–200. [45] Barral L, Diez FJ, Garcia-Garabal S, Lopez J, Montero B, Montes R, et al. Thermodegradation kinetics of a hybrid inorganic–organic epoxy system. Eur Polym J 2005;41:1662–6. [46] Zhang J, Xu R, Yu D. A novel poly-benzoxazinyl functionalized polyhedral oligomeric silsesquioxane and its nanocomposite with polybenzoxazine. Eur Polym J 2007;43:743–52. [47] Worthley CH, Constantopoulos KT, Ginnic-Markovic M, Markovic E, Clarke S. A study into the effect of POSS nanoparticles on cellulose acetate membranes. J Membrane Sci 2013;431:62–71. [48] Ma L, Geng HP, Song JX, Li JZ, Chen GX, Li QF. Hierarchical self-assembly of polyhedral oligomeric silsesquioxane end-capped stimuli-responsive polymer: from single micelle to complex micelle. J Phys Chem B 2011;115:10586–91. [49] Li JB, Fan JC, Liao KX, Xie JW, Chen YH, Liu P, et al. Facile fabrication of a multifunctional arami nanofiber-based composite paper. RSC Adv 2016;6:90263–72. [50] Ni Y, Zheng SX, Nie KM. Morphology and thermal properties of inorganic-organic hybrids involving epoxy resin and polyhedral oligomeric silsesquioxanes. Polymer 2004;45(16):5557–68. [51] Kim HU, Bang YH, Choi SM, Yoon KH. Morphology and mechanical properties of PET by incorporation of amine-polyhedral oligomeric silsesquioxane. Compos Sci Technol 2008;68(13):2739–47. [52] He LX, Tijon SC. Facile synthesis of silver-decorated reduced graphene oxide as a hybrid filler material for electrically conductive polymer composites. RSC Adv 2015;5:15070–6. [53] Liang GD, Bao SP, Tjong SC. Microstructure and properties of polypropylene composites filled with silver and carbon nanotube nanoparticles prepared by meltcompounding. Mat Sci Eng B 2007;142:55–61.
[27] Fan JC, Shi ZX, Zhang L, Wang JL, Yin J. Aramid nanofiber-functionalized graphene nanosheets for polymer reinforcement. Nanoscale 2012;4:7046–55. [28] Fan JC, Shi ZX, Tian M, Yin J. Graphene-aramid nanofiber nanocomposite paper with high mechanical and electrical performance. RSC Adv 2013;3:17664–7. [29] Eisenberg P, Erra-Balsells R, Ishikawa Y, Lucas JC, Nonami H, Williams RJJ. Silsesquioxanes derived from the bulk polycondensation of [3 (Methacryloxy) propyl]trimethoxysilane with concentrated formic acid: evolution of molar mass distributions and fraction of intramolecular cycles. Macromolecules 2002;35(4):1160–74. [30] Paul DR, Robeson LM. Polymer nanotechnology: nanocomposites. Polymer 2008;49:3187–204. [31] Zhu J, Shim BS, Prima MD, Kotov NA. Transparent conductors from carbon nanotubes LBL-assembled with polymer dopant with pi-pi electron transfer. J Am Chem Soc 2011;133:7450–60. [32] Yang M, Cao KQ, Yeom B, Thouless MD, Waas A, Arruda EM, et al. Aramid nanofiber-reinforced transparent nanocomposites. J Com Mat 2015;49:1873–9. [33] Zheng L, Farris RJ, Coughlin EB. Novel polyolefin nanocomposites: synthesis and characterizations of metallocene-catalyzed polyolefin polyhedral oligomeric silsesquioxane copolymers. Macromolecules 2001;34:8034–9. [34] Zheng L, Waddon AJ, Farris RJ, Coughlin EB. X-ray characterizations of polyethylene polyhedral oligomeric silsesquioxane copolymers. Macromolecules 2002;35:2375–9. [35] Waddon AJ, Zheng L, Farris RJ, Coughlin EB. Nanostructured polyethylene-POSS copolymers: control of crystallization and aggregation. Nano Lett 2002;2:1149–55. [36] Fina A, Tabuani D, Frache A, Camino G. Polypropylene-polyhedral oligomeric silsesquioxanes (POSS) nanocomposites. Polymer 2005;46:7855–66. [37] Haddad TS, Lichtenhan JD. Hybrid organic–inorganic thermoplastics: styryl-based polyhedral oligomeric silsesquioxane polymers. Macromolecules 1996;29:7302–4. [38] Lichtenhan JD, Otonari YA, Carr MJ. Linear hybridpolymer buildingblocks: methacrylate-functionalized polyhedral oligomeric silsesquioxane monomers and polymers. Macromolecules 1995;28:8435–7. [39] Zhao Y, Schiraldi DA. Thermal and mechanical properties of polyhedral oligomeric silsesquioxane (POSS)/polycarbonate composites. Polymer 2005;46:11640–7. [40] Ciolacu FCL, Choudhury NR, Dutta N, Kosior E. Molecular level stabilization of poly (ethylene terephthalate) with nanostructured open cage trisilanolisobutyl-POSS. Macromolecules 2007;40:265–72.
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