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Synthesis of PAMAM-GO as new nanofiller to enhance the crystallization properties of polylactic acid
Materials Letters 235 (2019) 27–30
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Synthesis of PAMAM-GO as new nanofiller to enhance the crystallization properties of polylactic acid Xiaodong Liu, Yujing Sheng, Dongliang Wu, Ruliang Zhang ⇑, Honzhi Cui ⇑ School of Materials Science and Engineering, Shandong University of Science and Technology, 266590 Qingdao, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 12 March 2018 Received in revised form 27 September 2018 Accepted 28 September 2018 Available online 29 September 2018 Keywords: Carbon materials Polymers XPS Poly(lactic acid) Functionalized graphene oxide
a b s t r a c t The aim of this work is to study the effect of PAMAM-GO (fGO) on the crystallization properties of poly (lactic acid) (PLA). The results demonstrate that the isothermal crystallization rates are prominently enhanced with the addition of fGO. The spherulitic size of PLA in the composites are remarkably reduced in comparison with PLA, while crystallization half-time of PLA/fGO is almost decreased by 18.3%. Based on the results of this work, the use of fGO can serve as efficient heterogeneous nucleating agent for adjustable crystallization of PLA. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Ever-increasing environmental pollution caused by continual worsening of global ‘‘white pollution” is one of the challenging tasks for the scientific community [1–4]. Recently, Poly (lactic acid) (PLA) nanocomposites has been widely studied due to intrinsic properties of PLA as a potential replacement for petroleum-based polymers and the interesting results achieved [5]. The nanofillers were incorporated into the PLA matrix as reinforcing or fillers agent by melt compounding or solution blending for simultaneously providing a remarkable improvement in the crystallization rate and in the physical properties of its resulting composites [6,7]. However, the final properties of using nanofiller not only requires a good adhesion between the nanofiller and the organic polymer matrix but also demands adequate dispersion in the polymeric phase [7]. Graphene oxide (GO), consisting of organic functional groups, is much more compatible with polymers. Nanocomposites consisting of PLA and GO has gained increasing attention [8]. In particular, introduction of polyamidamine (PAMAM) dendrimer into PLA matrix was exhibit faster crystallization rate and wider range of crystallinity [9]. In addition, design and creation of new nanocomposites with controllable structures and functional
⇑ Corresponding Authors. E-mail addresses: [email protected], [email protected] (R. Zhang), hzhcui@163. com (H. Cui). https://doi.org/10.1016/j.matlet.2018.09.154 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
groups have permitted by the recent technical innovations [7,10,11]. In the present work, a novel nanocomposite consisting of PLA and PAMAM functionalized GO (fGO) have been prepared for the first time. As a highly branched macromolecule consisting of plenty of functional groups, in-situ growth PAMAM on the surface of GO could simultaneously provide plenty of adjustable groups as well as remain its solubility. And the effect of fGO on the crystallization properties of PLA matrix were investigated in detail with differential scanning calorimetry (DSC) and polarizing optical microscope (POM).
2. Experimental All chemicals were obtained from Sigma-Aldrich and used as purchased. PLA was purchased from Nature Works (U.S.A). GO and functionalized GO containing amino groups (GO-G0.0PAMAM) was prepared and described in the literatures [12]. GOG0.0-PAMAM was added to 200 mL of absolute ethyl alcohol, followed by slow addition of 50 mL of methyl acrylate (MA) under stirring. The reaction was stirred at 30 °C for 30 h. The reactants were separated by suction filtration and rinsed with ethyl alcohol for 4–5 times. The products were dried in a vacuum oven for 24 h and the resultant was named as GO-G0.5-PAMAM. Next, GOG0.5-PAMAM was reacted with 150 mL methanol and ethylenediamine (EDA) at 30 °C for 36 h. And the reactants were washed with methanol and dried at 60 °C for 24 h to obtain GO-G1.0-PAMAM
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X. Liu et al. / Materials Letters 235 (2019) 27–30
(fGO). Finally, the PLA nanocomposites with 0.5 wt% weight of fGO (PLA/fGO) were obtained through solution blending. 3. Results and discussion 3.1. Characterization of fGO The surface morphology of samples was investigated by transmission electron microscope (TEM), as shown in Fig. 1. Marked differences of surface microstructures could be observed between the GO and fGO. Spherical-like particles were observed in the cases of fGO (Fig. 1b), which resulted from the graft of PAMAM. The X-ray photoelectron spectroscopy (XPS) of fGO (Fig. 2a) shows a new peak at around 400 eV, typical of N1s corresponding to nitrogen in the PAMAM [13]. The atomic ratios of carbon to oxygen (C/O) in GO and fGO are (70.04/28.87) 2.43 and (83.02/10.85) 7.65, respectively. And the atomic ratios of carbon to nitrogen (N/ C) in fGO are (83.02/6.13) 13.54. Furthermore, to support this chemical reaction, the C1s spectra were compared by deconvoluting each spectrum into following component peaks. In the GO, there are three main types of peaks that correspond to CAC (284.6 eV), C-O (286.2 eV), C@O (287.3 eV), OAC@O (288.5 eV) (Fig. 2b). Compared to GO, there are new peaks corresponding to the existence of CANH2 (285.4 eV) and CAN bonds (286.1 eV) (Fig. 2c). Furthermore, the successful introduction of NH2 (399.1 eV), C-N (399.9 eV) and NAC@O (401.1 eV) can also be proved by XPS N1s curve fit spectra (Fig. 2d) [13]. These results confirm that PAMAM were successfully grafted onto GO via in situ reaction. Fig. 1. The TEM images of: (a) GO, (b) fGO.
Fig. 2. XPS spectra of GO and fGO (a), high-resolution XPS C1s spectra of GO (b) and fGO (c), high-resolution XPS N1s spectra of fGO (d).
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X. Liu et al. / Materials Letters 235 (2019) 27–30
Fig. 3. Relative degree of crystallization versus crystallization time traces of PLA and PLA/ fGO at 125 °C (a), Plots of log[ ln(1
Table 1 The isothermal crystallization kinetics parameters of PLA and PLA/fGO at 125 °C based on Avrami equation. Sample
K
n
t0.5
1 3
7.77 * 10 4 1.503 * 10 3
2.76 2.72
11.68 9.54
Xt)] versus logt for PLA and PLA/fGO (b).
t0.5 of PLA/fGO almost decreased by 18.3%. The crystallization rate can thus be easily improved with corporation of fGO. Beyond the crystallization kinetics aforementioned, the crystalline morphology was investigated by POM (Fig. 4). It is observed that typically spherulitic morphology and Maltese-cross patterns was exhibited despite the samples. The diameter is remarkably diminished with additional fGO. It can be concluded that in our work, the presence of fGO was acted as heterogeneous nucleating agent in the PLA matrix.
3.2. The crystallization of PLA and PLA composites 4. Conclusions Fig. 3(a) shows relative degree of crystallization versus crystallization time curves of PLA and PLA/0.5fGO in the temperature 125 °C. Apparently, Xt increases with the increasing crystallization time, and PLA/fGO crystallized faster than PLA. The well-known Avrami equation 1 Xt = exp( ktn) was further used to analyze the isothermal crystallization process. Plots of log[ ln(1 Xt)] versus logt for PLA and PLA/fGO was also shown in Fig. 3(b), and the crystallization half-time (t0.5), the values of the Avrami exponent (n), the isothermal crystallization rate constant (K) are listed in Table 1. The t0.5 of PLA, PLA/fGO are around 11.68 min and 9.54 min, respectively. In comparison with PLA,
In order to improve the crystallization properties of PLA matrix, GO modified with PAMAM via in-situ polymerization was introduced into PLA matrix by solution blending. TEM and XPS results revealed that GO was successfully modified by PAMAM. The experimental results indicate that fGO could accelerate the crystallization rate of PLA. A distinct increase of the nucleation density and obvious reduction of the spherulite size was obtained in the POM micrograph of PLA/fGO nanocomposites. Specifically, fGO could improve the crystallization performance of PLA.
Fig. 4. Polarized optical micrographs of: (a) PLA, (b) PLA/fGO after isothermal crystallization at 125 °C for 24 h.
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X. Liu et al. / Materials Letters 235 (2019) 27–30
Acknowledgement This work was supported by the funding from Project funded by National Natural Science Fund Program of China (Grant No. 51403119). References [1] W. Gao, R. Razavi, A. Fakhri, Int. J. Boil. Macromol. 114 (2018) 357–362. [2] A. Fakhri, M. Azad, L. Fatolahi, S. Tahami, J. Photoch. Photobio. B. 178 (2018) 108–114. [3] A. Fakhri, M. Azad, S. Tahami, J. Mater. Sci.: Mater. Electron. 28 (2017) 16397– 16402. [4] A. Fakhri, M. Naji, L. Fatolahi, J. Mater. Sci.: Mater. Electron. 28 (2017) 16484– 16492.
[5] R. Mangin, H. Vahabi, R. Sonnier, C. Chivas-Joly, J.-M. Lopez-Cuesta, M. Cochez, Polym. Degrad. Stabil. 155 (2018) 52–66. [6] M. Brzezin´ski, T. Biela, Mater. Lett. 121 (2014) 244–250. [7] J.M. Raquez, Y. Habibi, M. Murariu, P. Dubois, Prog. Polym. Sci. 38 (2013) 1504– 1542. [8] H.S. Wang, Z.B. Qiu, Thermochim. Acta 527 (2012) 40–46. [9] Y.L. Zhao, Q. Cai, J. Jiang, X.T. Shuai, J.Z. Bei, C.F. Chen, F. Xi, Polymer 43 (2002) 5819–5825. [10] V.K. Gupta, A. Fakhri, S. Agarwal, M. Naji, J. Mol. Liq. 249 (2018) 61–65. [11] V.K. Gupta, A. Fakhri, S. Agarwal, E. Ahmadi, P.A. Nejad, J. Photoch. Photobio. B. 174 (2017) 235–242. [12] R.L. Zhang, B. Gao, W.T. Du, J. Zhang, H.Z. Cui, L. Liu, Q.H. Ma, C.G. Wang, F.H. Li, Compos. Part A: Appl. Sci. Manufac. 84 (2016) 455–463. [13] R.L. Zhang, B. Gao, J. Zhang, H.Z. Cui, D.W. Li, Appl. Surf. Sci. 359 (2015) 812– 818.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Synthesis of PAMAM-GO as new nanofiller to enhance the crystallization properties of polylactic acid Xiaodong Liu, Yujing Sheng, Dongliang Wu, Ruliang Zhang ⇑, Honzhi Cui ⇑ School of Materials Science and Engineering, Shandong University of Science and Technology, 266590 Qingdao, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 12 March 2018 Received in revised form 27 September 2018 Accepted 28 September 2018 Available online 29 September 2018 Keywords: Carbon materials Polymers XPS Poly(lactic acid) Functionalized graphene oxide
a b s t r a c t The aim of this work is to study the effect of PAMAM-GO (fGO) on the crystallization properties of poly (lactic acid) (PLA). The results demonstrate that the isothermal crystallization rates are prominently enhanced with the addition of fGO. The spherulitic size of PLA in the composites are remarkably reduced in comparison with PLA, while crystallization half-time of PLA/fGO is almost decreased by 18.3%. Based on the results of this work, the use of fGO can serve as efficient heterogeneous nucleating agent for adjustable crystallization of PLA. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Ever-increasing environmental pollution caused by continual worsening of global ‘‘white pollution” is one of the challenging tasks for the scientific community [1–4]. Recently, Poly (lactic acid) (PLA) nanocomposites has been widely studied due to intrinsic properties of PLA as a potential replacement for petroleum-based polymers and the interesting results achieved [5]. The nanofillers were incorporated into the PLA matrix as reinforcing or fillers agent by melt compounding or solution blending for simultaneously providing a remarkable improvement in the crystallization rate and in the physical properties of its resulting composites [6,7]. However, the final properties of using nanofiller not only requires a good adhesion between the nanofiller and the organic polymer matrix but also demands adequate dispersion in the polymeric phase [7]. Graphene oxide (GO), consisting of organic functional groups, is much more compatible with polymers. Nanocomposites consisting of PLA and GO has gained increasing attention [8]. In particular, introduction of polyamidamine (PAMAM) dendrimer into PLA matrix was exhibit faster crystallization rate and wider range of crystallinity [9]. In addition, design and creation of new nanocomposites with controllable structures and functional
⇑ Corresponding Authors. E-mail addresses: [email protected], [email protected] (R. Zhang), hzhcui@163. com (H. Cui). https://doi.org/10.1016/j.matlet.2018.09.154 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
groups have permitted by the recent technical innovations [7,10,11]. In the present work, a novel nanocomposite consisting of PLA and PAMAM functionalized GO (fGO) have been prepared for the first time. As a highly branched macromolecule consisting of plenty of functional groups, in-situ growth PAMAM on the surface of GO could simultaneously provide plenty of adjustable groups as well as remain its solubility. And the effect of fGO on the crystallization properties of PLA matrix were investigated in detail with differential scanning calorimetry (DSC) and polarizing optical microscope (POM).
2. Experimental All chemicals were obtained from Sigma-Aldrich and used as purchased. PLA was purchased from Nature Works (U.S.A). GO and functionalized GO containing amino groups (GO-G0.0PAMAM) was prepared and described in the literatures [12]. GOG0.0-PAMAM was added to 200 mL of absolute ethyl alcohol, followed by slow addition of 50 mL of methyl acrylate (MA) under stirring. The reaction was stirred at 30 °C for 30 h. The reactants were separated by suction filtration and rinsed with ethyl alcohol for 4–5 times. The products were dried in a vacuum oven for 24 h and the resultant was named as GO-G0.5-PAMAM. Next, GOG0.5-PAMAM was reacted with 150 mL methanol and ethylenediamine (EDA) at 30 °C for 36 h. And the reactants were washed with methanol and dried at 60 °C for 24 h to obtain GO-G1.0-PAMAM
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X. Liu et al. / Materials Letters 235 (2019) 27–30
(fGO). Finally, the PLA nanocomposites with 0.5 wt% weight of fGO (PLA/fGO) were obtained through solution blending. 3. Results and discussion 3.1. Characterization of fGO The surface morphology of samples was investigated by transmission electron microscope (TEM), as shown in Fig. 1. Marked differences of surface microstructures could be observed between the GO and fGO. Spherical-like particles were observed in the cases of fGO (Fig. 1b), which resulted from the graft of PAMAM. The X-ray photoelectron spectroscopy (XPS) of fGO (Fig. 2a) shows a new peak at around 400 eV, typical of N1s corresponding to nitrogen in the PAMAM [13]. The atomic ratios of carbon to oxygen (C/O) in GO and fGO are (70.04/28.87) 2.43 and (83.02/10.85) 7.65, respectively. And the atomic ratios of carbon to nitrogen (N/ C) in fGO are (83.02/6.13) 13.54. Furthermore, to support this chemical reaction, the C1s spectra were compared by deconvoluting each spectrum into following component peaks. In the GO, there are three main types of peaks that correspond to CAC (284.6 eV), C-O (286.2 eV), C@O (287.3 eV), OAC@O (288.5 eV) (Fig. 2b). Compared to GO, there are new peaks corresponding to the existence of CANH2 (285.4 eV) and CAN bonds (286.1 eV) (Fig. 2c). Furthermore, the successful introduction of NH2 (399.1 eV), C-N (399.9 eV) and NAC@O (401.1 eV) can also be proved by XPS N1s curve fit spectra (Fig. 2d) [13]. These results confirm that PAMAM were successfully grafted onto GO via in situ reaction. Fig. 1. The TEM images of: (a) GO, (b) fGO.
Fig. 2. XPS spectra of GO and fGO (a), high-resolution XPS C1s spectra of GO (b) and fGO (c), high-resolution XPS N1s spectra of fGO (d).
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Fig. 3. Relative degree of crystallization versus crystallization time traces of PLA and PLA/ fGO at 125 °C (a), Plots of log[ ln(1
Table 1 The isothermal crystallization kinetics parameters of PLA and PLA/fGO at 125 °C based on Avrami equation. Sample
K
n
t0.5
1 3
7.77 * 10 4 1.503 * 10 3
2.76 2.72
11.68 9.54
Xt)] versus logt for PLA and PLA/fGO (b).
t0.5 of PLA/fGO almost decreased by 18.3%. The crystallization rate can thus be easily improved with corporation of fGO. Beyond the crystallization kinetics aforementioned, the crystalline morphology was investigated by POM (Fig. 4). It is observed that typically spherulitic morphology and Maltese-cross patterns was exhibited despite the samples. The diameter is remarkably diminished with additional fGO. It can be concluded that in our work, the presence of fGO was acted as heterogeneous nucleating agent in the PLA matrix.
3.2. The crystallization of PLA and PLA composites 4. Conclusions Fig. 3(a) shows relative degree of crystallization versus crystallization time curves of PLA and PLA/0.5fGO in the temperature 125 °C. Apparently, Xt increases with the increasing crystallization time, and PLA/fGO crystallized faster than PLA. The well-known Avrami equation 1 Xt = exp( ktn) was further used to analyze the isothermal crystallization process. Plots of log[ ln(1 Xt)] versus logt for PLA and PLA/fGO was also shown in Fig. 3(b), and the crystallization half-time (t0.5), the values of the Avrami exponent (n), the isothermal crystallization rate constant (K) are listed in Table 1. The t0.5 of PLA, PLA/fGO are around 11.68 min and 9.54 min, respectively. In comparison with PLA,
In order to improve the crystallization properties of PLA matrix, GO modified with PAMAM via in-situ polymerization was introduced into PLA matrix by solution blending. TEM and XPS results revealed that GO was successfully modified by PAMAM. The experimental results indicate that fGO could accelerate the crystallization rate of PLA. A distinct increase of the nucleation density and obvious reduction of the spherulite size was obtained in the POM micrograph of PLA/fGO nanocomposites. Specifically, fGO could improve the crystallization performance of PLA.
Fig. 4. Polarized optical micrographs of: (a) PLA, (b) PLA/fGO after isothermal crystallization at 125 °C for 24 h.
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X. Liu et al. / Materials Letters 235 (2019) 27–30
Acknowledgement This work was supported by the funding from Project funded by National Natural Science Fund Program of China (Grant No. 51403119). References [1] W. Gao, R. Razavi, A. Fakhri, Int. J. Boil. Macromol. 114 (2018) 357–362. [2] A. Fakhri, M. Azad, L. Fatolahi, S. Tahami, J. Photoch. Photobio. B. 178 (2018) 108–114. [3] A. Fakhri, M. Azad, S. Tahami, J. Mater. Sci.: Mater. Electron. 28 (2017) 16397– 16402. [4] A. Fakhri, M. Naji, L. Fatolahi, J. Mater. Sci.: Mater. Electron. 28 (2017) 16484– 16492.
[5] R. Mangin, H. Vahabi, R. Sonnier, C. Chivas-Joly, J.-M. Lopez-Cuesta, M. Cochez, Polym. Degrad. Stabil. 155 (2018) 52–66. [6] M. Brzezin´ski, T. Biela, Mater. Lett. 121 (2014) 244–250. [7] J.M. Raquez, Y. Habibi, M. Murariu, P. Dubois, Prog. Polym. Sci. 38 (2013) 1504– 1542. [8] H.S. Wang, Z.B. Qiu, Thermochim. Acta 527 (2012) 40–46. [9] Y.L. Zhao, Q. Cai, J. Jiang, X.T. Shuai, J.Z. Bei, C.F. Chen, F. Xi, Polymer 43 (2002) 5819–5825. [10] V.K. Gupta, A. Fakhri, S. Agarwal, M. Naji, J. Mol. Liq. 249 (2018) 61–65. [11] V.K. Gupta, A. Fakhri, S. Agarwal, E. Ahmadi, P.A. Nejad, J. Photoch. Photobio. B. 174 (2017) 235–242. [12] R.L. Zhang, B. Gao, W.T. Du, J. Zhang, H.Z. Cui, L. Liu, Q.H. Ma, C.G. Wang, F.H. Li, Compos. Part A: Appl. Sci. Manufac. 84 (2016) 455–463. [13] R.L. Zhang, B. Gao, J. Zhang, H.Z. Cui, D.W. Li, Appl. Surf. Sci. 359 (2015) 812– 818.