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Improved piezoelectric properties of electrospun poly(vinylidene fluoride) fibers blended with cellulose nanocrystals
Materials Letters 187 (2017) 86–88
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
crossmark
Improved piezoelectric properties of electrospun poly(vinylidene fluoride) fibers blended with cellulose nanocrystals ⁎
⁎
Runfang Fu, Sheng Chen , Yi Lin, Sihang Zhang, Jie Jiang, Qingbi Li, Yingchun Gu Department of Textile Engineering and Functional Polymer Materials Laboratory, Sichuan University, Chengdu 610065, China
A R T I C L E I N F O
A BS T RAC T
Keywords: Electrospinning PVDF Cellulose nanocrystals Composites Piezoelectricity Power generators
Poly(vinylidene fluoride) (PVDF) and cellulose nanocrystals (CNCs) fibrous composites were prepared by electrospinning. Compared with neat PVDF fibers, PVDF/CNCs composites contain higher content of β phase with help of rod-liked CNCs. The highest content of β phase among these fibrous membranes is as high as 89.96%. Furthermore, the piezo-voltage generated by the power generator which is made of PVDF/CNCs fibrous composite indicates that addition of CNCs to PVDF fiber matrix contributes to improving piezoelectric performance of PVDF fiber.
1. Introduction
cellulose material, which was reported as a type of electroactive polymer [11], can be made into films or other materials being potentially used in components requiring a piezoelectric response [12]. CNC is usually used as reinforcing agent (especially in electrospun fibers) for different polymers including PVDF [13–16] and it is piezoelectric by itself [12]. But CNCs being used as nanofillers in another piezoelectric material has not been reported at present. In the present study, CNCs prepared by method of sulfuric acid hydrolysis from viscose fibers were added into PVDF solutions for preparing electrospun PVDF/CNCs composite fibers. The relationship between the overall crystallinity and the amount of β phase present in the fibers obtained with different content of CNCs was investigated. The piezoelectric signals of different PVDF/CNCs fibrous membranes were detected to analyze the influence of CNCs on the piezoelectricities of PVDF fibrous membranes.
Poly(vinylidene fluoride) (PVDF) with good toughness, flexibility, and biocompatibility was the most widely investigated piezoelectric polymer material [1,2]. It is well-known that PVDF has five crystalline phases with different conformations, all-trans (TTTT) in the β phase, an alternation of trans and gauche (TG+TG-) in the α and δ phases, and TTTG+TTTG- in the γ and ε phases [3–5]. Among these five crystalline phases, the polar β phase is the most important one due to its piezoelectric and pyroelectric properties [2]. Therefore, researchers pay great attention to developing methods of enhancing the content of β phase or conversion of nonpolar α phase to polar β phase. Recently, adding nanofillers, such as: ceramic particles, nanoclay, conductive particles, into PVDF matrix is becoming attractive because of its simplicity and effectiveness [6–9]. Jia found that both the polydopamine (Pdop) coated BaTiO3 nanoparticles and BaTiO3 nanoparticles could contribute to significant increase of β-phase content in the PVDF resulting in the enhanced piezoresponse behavior and d33-meter values [6]. Liu added organically modified montmorillonite (OMMT) into PVDF matrix obtaining PVDF/OMMT composite nanofibers and found that nonpolar α phase completely disappears in the composite nanofibers [8]. Ahn reported that the addition of multiwalled carbon nanotubes (MWCNTs) promoted the conversion of PVDF molecules' α phase into β phase and the polymer chain orientation in the electrospinning PVDF fibers [7]. Cellulose nanocrystals (CNCs) are crystalline rod like particles which could be derived from a variety of renewable sources including wood, cotton, ramie, bacteria, and tunicates [10]. CNCs as a kind of
⁎
2. Experimental 2.1. Electrospinning of PVDF and PVDF/CNCs Fibers CNCs dispersed in deionized water were prepared by method of sulfuric acid hydrolysis which was reported by Lu et al. [17]. Then, CNCs dispersed in deionized water were solvent-exchanged into dimethyl formamide (DMF) (Chengdu Kelong Chemical Plant, China) dispersion by vacuum-assisted rotary evaporator (B-260, Shanghai Yarong Biochemical Instrument Plant, China). PVDF solutions were prepared by dissolving PVDF powders (Mw=1200,000, Chenguang R.I.C.I, China) in the mixed solvent of DMF and acetone (1:1 wt%)
Corresponding authors. E-mail addresses: [email protected] (S. Chen), [email protected] (Y. Gu).
http://dx.doi.org/10.1016/j.matlet.2016.10.068 Received 17 June 2016; Received in revised form 19 September 2016; Accepted 16 October 2016 Available online 17 October 2016 0167-577X/ © 2016 Elsevier B.V. All rights reserved.
Materials Letters 187 (2017) 86–88
R. Fu et al.
Fig. 1. (a) TEM image of CNCs, (b) SEM images of electrospun neat PVDF, (c) PVDF/CNCs-2 wt%, (d) PVDF/CNCs-4 wt%.
Fig. 2. (a) ATR-FTIR spectra and (b) XRD patterns of PVDF/CNCs fibrous membranes.
3. Results and discussion
Table 1 The crystallinity and relative fraction of β phases (Fβ) of PVDF/CNCs fibrous membranes.
ΔXc(%) Fβ(%)
Neat PVDF
1 wt% CNCs
2 wt% CNCs
3 wt% CNCs
4 wt% CNCs
48.43 85.08
54.07 88.20
68.09 89.96
56.92 87.35
32.45 86.76
It was obvious in Fig. 1(a) that the CNCs showed a rod-liked morphology. The lengths and diameters of CNCs as well as diameters of electrospun fibers were measured by Nano Measurer soft. The average length of CNCs was about 183 nm and the average diameter was about 15 nm. Fig. 1(b) and (c) show the SEM images of the electrospun PVDF fibers with different content of CNCs. In this study, a rotating drum collector at a take-up speed of 2000 rpm was invited to collect electrospun fibers. According to Fig. 1(b) and (c), most of the electrospun fibers were arranged regularly along the direction of rotation. In the ATR-FTIR spectra (Shown in Fig. 2(a)), the absorption peaks at 763 cm−1, 795 cm−1 and 976 cm−1, which were related to the α phase crystalline structure [7,18], disappeared from the spectra from all electrospun fibrous membranes, while peaks at 840 cm−1, 1276 cm−1 and 1431 cm−1, which were associated with the β phase [7,18], were obvious to be observed. To quantitatively characterize the content of β phase in the PVDF and PVDF/CNCs fibrous membranes, the relative fraction for the β phase (Fβ) could be calculated by the following equation
(Chengdu Kelong Chemical Plant, China). The requisite amount of CNCs in the DMF dispersion was added to the PVDF solutions. The mixed solution which contains 5 wt% PVDF was placed into a 20 mL injection syringe with a metal syringe needle of inner diameter of 0.8 mm and the feed rate was 2 mL h−1. The electrospun PVDF and PVDF/CNCs fibers were prepared at a high voltage of 10 kV and were deposited on a rotating drum at rotation speed of 2000 rpm which was connected to a negative voltage of 1 kV. The distance between the needle tip and the collector was 20 cm.
2.2. Characterization of electrospun PVDF and PVDF/CNCs fibrous membranes
Fβ = Aβ/[(K β/K α)A α + Aβ]
The CNCs were examined by transmission electron microscopy (TEM) on a Tecnai G2 F20 S-TWIN (FEI, USA) scanning transmission electron microscope. The morphology of the electrospun neat PVDF and PVDF/CNCs fibrous membranes was examined using scanning electron microscopy (Quanta 250, FEI, USA). The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectra were recorded with a FTIR spectrophotometer (Tracer100, Shimadzu Corporation, Japan). X-ray diffraction (XRD) patterns were recorded using an Ultima diffractometer (Rigaku Corporation, Japan). The voltage outputs of the fibrous membrane power generators were recorded using an oscilloscope when they were bent by a periodic external force with a certain frequency (GA1102CAL, Nanjing Glarun Atten Technology Co. Ltd. China).
where Aα and Aβ are the absorbencies of the α and β phases at the 763 cm−1 and 840 cm−1 characteristic peaks, Kα and Kβ are the absorption coefficients at each wavenumber and are 6.1×104 and 7.7×104 cm2 mol−1, respectively [6,18]. The calculated results were listed in Table 1. It is shown that all of the PVDF/CNCs composite fibers contain higher Fβ than neat PVDF fibers. What's more, the highest Fβ was achieved by adding 2 wt% CNCs to the PVDF fiber matrix. Fig. 2(b) shows the XRD patterns of the PVDF fibers with different content of CNCs. As seen from the figures, the PVDF fibers with 2 wt% and 3 wt% CNCs exhibited prominent peaks of the β phase at 2θ= 20.8°, 36.1° corresponding to the (110), (020) reflections of the phase [7,9]. In addition, the peak intensities of PVDF fibrous composites at 87
(1)
Materials Letters 187 (2017) 86–88
R. Fu et al.
Fig. 3. The output voltages of PVDF or PVDF/CNCs-based power generators.
2θ= 36.1° increased compared with the neat PVDF fibers. The degree of crystallinities (Shown in Table 1) of neat PVDF fibrous membranes and PVDF/CNCs composites were calculated on the basis of the XRD data. The crystallinities of fibrous composites increase along with the increase of CNCs from 1 wt% to 2 wt% but decrease with further increase of CNCs. It is obvious that the crystallinity was higher than any other PVDF/CNCs fibers when the CNCs concentration was 2 wt%. In order to find out the influence of CNCs on the piezoelectricity of PVDF fibrous membrane, the membranes were all made into testable devices (power generators). Fig. 3 shows output voltages of these PVDF or PVDF/CNCs-based power generators. It is obvious that PVDF/ CNCs-2 wt% fibrous membrane showed the highest output voltage than any other fibrous membranes due to its high crystallinity and relative high Fβ shown in Table 1. Both low crystallinity and low Fβ are unpleasant to good piezoelectricity of PVDF fibers. In a word, the moderate addition of CNCs contributes to promote the piezoelectricity of PVDF fibers and piezo-response of power generators.
[2] [3] [4] [5] [6]
[7]
[8] [9]
[10]
4. Conclusions [11]
CNCs prepared by method of sulfuric acid hydrolysis from viscose fibers were added into PVDF solutions and PVDF/CNCs composite fibers were prepared by electrospinning. The relative fractions of β phase as well as crystallinities of PVDF/CNCs composite fibers were higher than that of neat PVDF fibers. The electrospun fiberous membrane based generator produced maximum piezo-voltage of 60 V by adding 2 wt% CNCs to PVDF fiber matrix. In a word, both high content of β phase and high crystallinity resulting from being blended with CNCs are important for good piezoelectricity of PVDF fibers.
[12] [13]
[14]
[15]
[16]
Acknowledgement
[17]
This work was supported by the Science and Technology Foundation of Sichuan Province (2014JY0146) and the Open Project Program of Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University (No. KLET1510).
[18]
References [1] B.S. Lee, B. Park, H.S. Yang, J.W. Han, C. Choong, J. Bae, et al., Effects of substrate
88
on piezoelectricity of electrospun poly(vinylidene fluoride)-nanofiber-based energy generators, ACS Appl. Mat. Interfaces 6 (2014) 3520–3527. J. Zheng, A. He, J. Li, C.C. Han, Polymorphism control of poly(vinylidene fluoride) through electrospinning, Macromol. Rapid Commun. 28 (2007) 2159–2162. M. Bachmann, W.L. Gordon, S. Weinhold, J.B. Lando, The crystal structure of phase IV of poly(vinylidene fluoride), J. Appl. Phys. 51 (1980) 5095. A.J. Lovinger, Unit cell of the gamma phase of poly(vinylidene fluoride), Macromolecules 14 (1981) 322–325. R. Hasegawa, Y. Takahashi, Y. Chatani, H. Tadokoro, Crystal structures of three crystalline forms of poly(vinylidene flouride), Polym. J. 3 (1972) 600–610. N. Jia, Q. Xing, G. Xia, J. Sun, R. Song, W. Huang, Enhanced β-crystalline phase in poly(vinylidene fluoride) films by polydopamine-coated BaTiO3 nanoparticles, Mater. Lett. 139 (2015) 212–215. Y. Ahn, J.Y. Lim, S.M. Hong, J. Lee, J. Ha, H.J. Choi, et al., Enhanced piezoelectric properties of electrospun poly (vinylidene fluoride)/multiwalled carbon nanotube composites due to high β-phase formation in poly (vinylidene fluoride), J. Phys. Chem. C 117 (2013) 11791–11799. Y. Xin, X. Qi, H. Tian, C. Guo, X. Li, J. Lin, et al., Full-fiber piezoelectric sensor by straight PVDF/nanoclay nanofibers, Mater. Lett. 164 (2016) 136–139. H. Yu, T. Huang, M. Lu, M. Mao, Q. Zhang, H. Wang, Enhanced power output of an electrospun PVDF/MWCNTs-based nanogenerator by tuning its conductivity, Nanotechnology 24 (2013) 405401. H. Dong, K.E. Strawhecker, J.F. Snyder, J.A. Orlicki, R.S. Reiner, A.W. Rudie, Cellulose nanocrystals as a reinforcing material for electrospun poly(methyl methacrylate) fibers: formation, properties and nanomechanical characterization, Carbohydr. Polym. 87 (2012) 2488–2495. J. Kim, S. Yun, Discovery of cellulose as a smart material, Macromolecules 39 (2006) 4202–4206. L. Csoka, I.C. Hoeger, O.J. Rojas, I. Peszlen, J.J. Pawlak, P.N. Peralta, Piezoelectric effect of cellulose nanocrystals thin films, ACS Macro Lett. 1 (2012) 867–870. A.A. Issa, M. Al-Maadeed, A.S. Luyt, M. Mrlik, M.K. Hassan, Investigation of the physico-mechanical properties of electrospun PVDF/cellulose (nano)fibers, J. Appl. Polym. Sci. 133 (2016). http://dx.doi.org/10.1002/app.43594. M.S. Mohammadi, C. Hammerquist, J. Simonsen, J.A. Nairn, The fracture toughness of polymer cellulose nanocomposites using the essential work of fracture method, J. Mater. Sci. 51 (2016) 8916–8927. J. Kelley, J. Simonsen, D. Jie, Poly(vinylidene fluoride-co-hexafluoropropylene) nanocomposites incorporating cellulose nanocrystals with potential applications in lithium ion batteries, J. Appl. Polym. Sci. 127 (2013) 487–493. K. O-Rak, E. Phakdeepataraphan, N. Bunnak, S. Ummartyotin, M. Sain, H. Manuspiya, Development of bacterial cellulose and poly(vinylidene fluoride) binary blend system: structure and properties, Chem. Eng. J. 237 (2014) 396–402. P. Lu, Y.-L. Hsieh, Preparation and characterization of cellulose nanocrystals from rice straw, Carbohydr. Polym. 87 (2012) 564–573. P. Martins, A.C. Lopes, S. Lanceros-Mendez, Electroactive phases of poly(vinylidene fluoride): determination, processing and applications, Prog. Polym. Sci. 39 (2014) 683–706.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
crossmark
Improved piezoelectric properties of electrospun poly(vinylidene fluoride) fibers blended with cellulose nanocrystals ⁎
⁎
Runfang Fu, Sheng Chen , Yi Lin, Sihang Zhang, Jie Jiang, Qingbi Li, Yingchun Gu Department of Textile Engineering and Functional Polymer Materials Laboratory, Sichuan University, Chengdu 610065, China
A R T I C L E I N F O
A BS T RAC T
Keywords: Electrospinning PVDF Cellulose nanocrystals Composites Piezoelectricity Power generators
Poly(vinylidene fluoride) (PVDF) and cellulose nanocrystals (CNCs) fibrous composites were prepared by electrospinning. Compared with neat PVDF fibers, PVDF/CNCs composites contain higher content of β phase with help of rod-liked CNCs. The highest content of β phase among these fibrous membranes is as high as 89.96%. Furthermore, the piezo-voltage generated by the power generator which is made of PVDF/CNCs fibrous composite indicates that addition of CNCs to PVDF fiber matrix contributes to improving piezoelectric performance of PVDF fiber.
1. Introduction
cellulose material, which was reported as a type of electroactive polymer [11], can be made into films or other materials being potentially used in components requiring a piezoelectric response [12]. CNC is usually used as reinforcing agent (especially in electrospun fibers) for different polymers including PVDF [13–16] and it is piezoelectric by itself [12]. But CNCs being used as nanofillers in another piezoelectric material has not been reported at present. In the present study, CNCs prepared by method of sulfuric acid hydrolysis from viscose fibers were added into PVDF solutions for preparing electrospun PVDF/CNCs composite fibers. The relationship between the overall crystallinity and the amount of β phase present in the fibers obtained with different content of CNCs was investigated. The piezoelectric signals of different PVDF/CNCs fibrous membranes were detected to analyze the influence of CNCs on the piezoelectricities of PVDF fibrous membranes.
Poly(vinylidene fluoride) (PVDF) with good toughness, flexibility, and biocompatibility was the most widely investigated piezoelectric polymer material [1,2]. It is well-known that PVDF has five crystalline phases with different conformations, all-trans (TTTT) in the β phase, an alternation of trans and gauche (TG+TG-) in the α and δ phases, and TTTG+TTTG- in the γ and ε phases [3–5]. Among these five crystalline phases, the polar β phase is the most important one due to its piezoelectric and pyroelectric properties [2]. Therefore, researchers pay great attention to developing methods of enhancing the content of β phase or conversion of nonpolar α phase to polar β phase. Recently, adding nanofillers, such as: ceramic particles, nanoclay, conductive particles, into PVDF matrix is becoming attractive because of its simplicity and effectiveness [6–9]. Jia found that both the polydopamine (Pdop) coated BaTiO3 nanoparticles and BaTiO3 nanoparticles could contribute to significant increase of β-phase content in the PVDF resulting in the enhanced piezoresponse behavior and d33-meter values [6]. Liu added organically modified montmorillonite (OMMT) into PVDF matrix obtaining PVDF/OMMT composite nanofibers and found that nonpolar α phase completely disappears in the composite nanofibers [8]. Ahn reported that the addition of multiwalled carbon nanotubes (MWCNTs) promoted the conversion of PVDF molecules' α phase into β phase and the polymer chain orientation in the electrospinning PVDF fibers [7]. Cellulose nanocrystals (CNCs) are crystalline rod like particles which could be derived from a variety of renewable sources including wood, cotton, ramie, bacteria, and tunicates [10]. CNCs as a kind of
⁎
2. Experimental 2.1. Electrospinning of PVDF and PVDF/CNCs Fibers CNCs dispersed in deionized water were prepared by method of sulfuric acid hydrolysis which was reported by Lu et al. [17]. Then, CNCs dispersed in deionized water were solvent-exchanged into dimethyl formamide (DMF) (Chengdu Kelong Chemical Plant, China) dispersion by vacuum-assisted rotary evaporator (B-260, Shanghai Yarong Biochemical Instrument Plant, China). PVDF solutions were prepared by dissolving PVDF powders (Mw=1200,000, Chenguang R.I.C.I, China) in the mixed solvent of DMF and acetone (1:1 wt%)
Corresponding authors. E-mail addresses: [email protected] (S. Chen), [email protected] (Y. Gu).
http://dx.doi.org/10.1016/j.matlet.2016.10.068 Received 17 June 2016; Received in revised form 19 September 2016; Accepted 16 October 2016 Available online 17 October 2016 0167-577X/ © 2016 Elsevier B.V. All rights reserved.
Materials Letters 187 (2017) 86–88
R. Fu et al.
Fig. 1. (a) TEM image of CNCs, (b) SEM images of electrospun neat PVDF, (c) PVDF/CNCs-2 wt%, (d) PVDF/CNCs-4 wt%.
Fig. 2. (a) ATR-FTIR spectra and (b) XRD patterns of PVDF/CNCs fibrous membranes.
3. Results and discussion
Table 1 The crystallinity and relative fraction of β phases (Fβ) of PVDF/CNCs fibrous membranes.
ΔXc(%) Fβ(%)
Neat PVDF
1 wt% CNCs
2 wt% CNCs
3 wt% CNCs
4 wt% CNCs
48.43 85.08
54.07 88.20
68.09 89.96
56.92 87.35
32.45 86.76
It was obvious in Fig. 1(a) that the CNCs showed a rod-liked morphology. The lengths and diameters of CNCs as well as diameters of electrospun fibers were measured by Nano Measurer soft. The average length of CNCs was about 183 nm and the average diameter was about 15 nm. Fig. 1(b) and (c) show the SEM images of the electrospun PVDF fibers with different content of CNCs. In this study, a rotating drum collector at a take-up speed of 2000 rpm was invited to collect electrospun fibers. According to Fig. 1(b) and (c), most of the electrospun fibers were arranged regularly along the direction of rotation. In the ATR-FTIR spectra (Shown in Fig. 2(a)), the absorption peaks at 763 cm−1, 795 cm−1 and 976 cm−1, which were related to the α phase crystalline structure [7,18], disappeared from the spectra from all electrospun fibrous membranes, while peaks at 840 cm−1, 1276 cm−1 and 1431 cm−1, which were associated with the β phase [7,18], were obvious to be observed. To quantitatively characterize the content of β phase in the PVDF and PVDF/CNCs fibrous membranes, the relative fraction for the β phase (Fβ) could be calculated by the following equation
(Chengdu Kelong Chemical Plant, China). The requisite amount of CNCs in the DMF dispersion was added to the PVDF solutions. The mixed solution which contains 5 wt% PVDF was placed into a 20 mL injection syringe with a metal syringe needle of inner diameter of 0.8 mm and the feed rate was 2 mL h−1. The electrospun PVDF and PVDF/CNCs fibers were prepared at a high voltage of 10 kV and were deposited on a rotating drum at rotation speed of 2000 rpm which was connected to a negative voltage of 1 kV. The distance between the needle tip and the collector was 20 cm.
2.2. Characterization of electrospun PVDF and PVDF/CNCs fibrous membranes
Fβ = Aβ/[(K β/K α)A α + Aβ]
The CNCs were examined by transmission electron microscopy (TEM) on a Tecnai G2 F20 S-TWIN (FEI, USA) scanning transmission electron microscope. The morphology of the electrospun neat PVDF and PVDF/CNCs fibrous membranes was examined using scanning electron microscopy (Quanta 250, FEI, USA). The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectra were recorded with a FTIR spectrophotometer (Tracer100, Shimadzu Corporation, Japan). X-ray diffraction (XRD) patterns were recorded using an Ultima diffractometer (Rigaku Corporation, Japan). The voltage outputs of the fibrous membrane power generators were recorded using an oscilloscope when they were bent by a periodic external force with a certain frequency (GA1102CAL, Nanjing Glarun Atten Technology Co. Ltd. China).
where Aα and Aβ are the absorbencies of the α and β phases at the 763 cm−1 and 840 cm−1 characteristic peaks, Kα and Kβ are the absorption coefficients at each wavenumber and are 6.1×104 and 7.7×104 cm2 mol−1, respectively [6,18]. The calculated results were listed in Table 1. It is shown that all of the PVDF/CNCs composite fibers contain higher Fβ than neat PVDF fibers. What's more, the highest Fβ was achieved by adding 2 wt% CNCs to the PVDF fiber matrix. Fig. 2(b) shows the XRD patterns of the PVDF fibers with different content of CNCs. As seen from the figures, the PVDF fibers with 2 wt% and 3 wt% CNCs exhibited prominent peaks of the β phase at 2θ= 20.8°, 36.1° corresponding to the (110), (020) reflections of the phase [7,9]. In addition, the peak intensities of PVDF fibrous composites at 87
(1)
Materials Letters 187 (2017) 86–88
R. Fu et al.
Fig. 3. The output voltages of PVDF or PVDF/CNCs-based power generators.
2θ= 36.1° increased compared with the neat PVDF fibers. The degree of crystallinities (Shown in Table 1) of neat PVDF fibrous membranes and PVDF/CNCs composites were calculated on the basis of the XRD data. The crystallinities of fibrous composites increase along with the increase of CNCs from 1 wt% to 2 wt% but decrease with further increase of CNCs. It is obvious that the crystallinity was higher than any other PVDF/CNCs fibers when the CNCs concentration was 2 wt%. In order to find out the influence of CNCs on the piezoelectricity of PVDF fibrous membrane, the membranes were all made into testable devices (power generators). Fig. 3 shows output voltages of these PVDF or PVDF/CNCs-based power generators. It is obvious that PVDF/ CNCs-2 wt% fibrous membrane showed the highest output voltage than any other fibrous membranes due to its high crystallinity and relative high Fβ shown in Table 1. Both low crystallinity and low Fβ are unpleasant to good piezoelectricity of PVDF fibers. In a word, the moderate addition of CNCs contributes to promote the piezoelectricity of PVDF fibers and piezo-response of power generators.
[2] [3] [4] [5] [6]
[7]
[8] [9]
[10]
4. Conclusions [11]
CNCs prepared by method of sulfuric acid hydrolysis from viscose fibers were added into PVDF solutions and PVDF/CNCs composite fibers were prepared by electrospinning. The relative fractions of β phase as well as crystallinities of PVDF/CNCs composite fibers were higher than that of neat PVDF fibers. The electrospun fiberous membrane based generator produced maximum piezo-voltage of 60 V by adding 2 wt% CNCs to PVDF fiber matrix. In a word, both high content of β phase and high crystallinity resulting from being blended with CNCs are important for good piezoelectricity of PVDF fibers.
[12] [13]
[14]
[15]
[16]
Acknowledgement
[17]
This work was supported by the Science and Technology Foundation of Sichuan Province (2014JY0146) and the Open Project Program of Key Laboratory of Eco-textiles, Ministry of Education, Jiangnan University (No. KLET1510).
[18]
References [1] B.S. Lee, B. Park, H.S. Yang, J.W. Han, C. Choong, J. Bae, et al., Effects of substrate
88
on piezoelectricity of electrospun poly(vinylidene fluoride)-nanofiber-based energy generators, ACS Appl. Mat. Interfaces 6 (2014) 3520–3527. J. Zheng, A. He, J. Li, C.C. Han, Polymorphism control of poly(vinylidene fluoride) through electrospinning, Macromol. Rapid Commun. 28 (2007) 2159–2162. M. Bachmann, W.L. Gordon, S. Weinhold, J.B. Lando, The crystal structure of phase IV of poly(vinylidene fluoride), J. Appl. Phys. 51 (1980) 5095. A.J. Lovinger, Unit cell of the gamma phase of poly(vinylidene fluoride), Macromolecules 14 (1981) 322–325. R. Hasegawa, Y. Takahashi, Y. Chatani, H. Tadokoro, Crystal structures of three crystalline forms of poly(vinylidene flouride), Polym. J. 3 (1972) 600–610. N. Jia, Q. Xing, G. Xia, J. Sun, R. Song, W. Huang, Enhanced β-crystalline phase in poly(vinylidene fluoride) films by polydopamine-coated BaTiO3 nanoparticles, Mater. Lett. 139 (2015) 212–215. Y. Ahn, J.Y. Lim, S.M. Hong, J. Lee, J. Ha, H.J. Choi, et al., Enhanced piezoelectric properties of electrospun poly (vinylidene fluoride)/multiwalled carbon nanotube composites due to high β-phase formation in poly (vinylidene fluoride), J. Phys. Chem. C 117 (2013) 11791–11799. Y. Xin, X. Qi, H. Tian, C. Guo, X. Li, J. Lin, et al., Full-fiber piezoelectric sensor by straight PVDF/nanoclay nanofibers, Mater. Lett. 164 (2016) 136–139. H. Yu, T. Huang, M. Lu, M. Mao, Q. Zhang, H. Wang, Enhanced power output of an electrospun PVDF/MWCNTs-based nanogenerator by tuning its conductivity, Nanotechnology 24 (2013) 405401. H. Dong, K.E. Strawhecker, J.F. Snyder, J.A. Orlicki, R.S. Reiner, A.W. Rudie, Cellulose nanocrystals as a reinforcing material for electrospun poly(methyl methacrylate) fibers: formation, properties and nanomechanical characterization, Carbohydr. Polym. 87 (2012) 2488–2495. J. Kim, S. Yun, Discovery of cellulose as a smart material, Macromolecules 39 (2006) 4202–4206. L. Csoka, I.C. Hoeger, O.J. Rojas, I. Peszlen, J.J. Pawlak, P.N. Peralta, Piezoelectric effect of cellulose nanocrystals thin films, ACS Macro Lett. 1 (2012) 867–870. A.A. Issa, M. Al-Maadeed, A.S. Luyt, M. Mrlik, M.K. Hassan, Investigation of the physico-mechanical properties of electrospun PVDF/cellulose (nano)fibers, J. Appl. Polym. Sci. 133 (2016). http://dx.doi.org/10.1002/app.43594. M.S. Mohammadi, C. Hammerquist, J. Simonsen, J.A. Nairn, The fracture toughness of polymer cellulose nanocomposites using the essential work of fracture method, J. Mater. Sci. 51 (2016) 8916–8927. J. Kelley, J. Simonsen, D. Jie, Poly(vinylidene fluoride-co-hexafluoropropylene) nanocomposites incorporating cellulose nanocrystals with potential applications in lithium ion batteries, J. Appl. Polym. Sci. 127 (2013) 487–493. K. O-Rak, E. Phakdeepataraphan, N. Bunnak, S. Ummartyotin, M. Sain, H. Manuspiya, Development of bacterial cellulose and poly(vinylidene fluoride) binary blend system: structure and properties, Chem. Eng. J. 237 (2014) 396–402. P. Lu, Y.-L. Hsieh, Preparation and characterization of cellulose nanocrystals from rice straw, Carbohydr. Polym. 87 (2012) 564–573. P. Martins, A.C. Lopes, S. Lanceros-Mendez, Electroactive phases of poly(vinylidene fluoride): determination, processing and applications, Prog. Polym. Sci. 39 (2014) 683–706.