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Natural fibrous nanoclay reinforced soy polyol-based polyurethane
Materials Letters 78 (2012) 85–87
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Natural fibrous nanoclay reinforced soy polyol-based polyurethane Chengshuang Wang a, Yuting Wang a, Weijing Liu a, Haiyan Yin a, Zuanru Yuan b, Qingjun Wang c, Hongfeng Xie a,⁎, Rongshi Cheng a, d a
Key Laboratory for Mesoscopic Chemistry of the Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China Modern Analysis Center, Nanjing University, Nanjing 210093, China Polymer Science and Engineering Department, School of Chemistry and Chemical Engineering, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China d College of Material Science and Engineering, South China University of Technology, Guangzhou 510641, China b c
a r t i c l e
i n f o
Article history: Received 10 February 2012 Accepted 15 March 2012 Available online 23 March 2012 Keywords: Attapulgite Polymers Soy polyol Nanocomposites Reinforcement
a b s t r a c t In this study, novel soy polyol-based polyurethane (PU) nanocomposites were synthesized with the aim of determining the effect of the natural fibrous nanoclay (attapulgite, ATT) loading on the properties of PU nanocomposites. Scanning electron microscopy demonstrated the relatively homogeneous dispersion of ATT in the PU matrix. After the addition of ATT, a significant ATT reinforcement effect on PU was found. In the case of 12 wt.% ATT addition, 16.8 °C improvement in the glass transition temperature, 443% increment in tensile strength, and 8-fold increase in Young's modulus were obtained. Furthermore, the elongation at break of PU nanocomposites decreased with increased ATT content. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction Recently, vegetable-oil-based polymers have attracted increasing attention because of their attractive properties related to the specific structures of the oils, as well as concerns about the environment and sustainability [1,2]. Among various vegetable-oil-based polymers, polyurethanes (PUs), one of the most versatile polymers, have been successfully employed in diverse applications such as adhesives, coatings, foams and composites [3,4]. For advanced PUs materials, PUs can be further improved via incorporation of various fillers, including clay [5–8], carbon nanotubes [9,10], glass [11], carbon nanofiber [12] and graphene [13]. The pioneering work of the Toyota group [14] has evoked great academic and commercial research interests in polymer/clay nanocomposites due to their low-price, high availability and chemical accessibility [15–17]. As a hydrated magnesium aluminum silicate, the natural fibrous attapulgite (ATT) is one of ideal and available clay sources. With a length of several micrometers and approximately 20 nm in diameter, the fibrous single crystal contains ribbons of a 2:1 phyllosilicate structure different from other layered silicates in that it lacks continuous octahedral sheets. Each ribbon is linked to the next by the inversion of SiO4 tetrahedra along a set of Si\O\Si bonds and extends parallel to the x-axis to form rectangular channels [18]. For diverse commercial applications, ATT has been used as catalyst supports, adsorbents, rheological agents,
⁎ Corresponding author. Tel./fax: + 86 25 83592568. E-mail address: [email protected] (H. Xie).
fillers and so on [19]. Because of its fibrous morphology with large surface areas and reactive \OH groups on the surface, one can expect its great potential as reinforcing filler for nanocomposites. However, the research work on the PU/ATT nanocomposites is still rather limited [20–22]. In this letter, we explored the properties of soy polyol-based PU nanocomposites reinforced with ATT for developing environmentfriendly, biodegradable materials for specific applications. ATT was dispersed in solvent by sonication and mixed with soy polyol by mechanical stirring. Then solvent-free polymerization was carried out to synthesize PU/ATT nanocomposites (Fig. 1). The morphology and mechanical properties of the resulting PU nanocomposites were then measured using various characterization techniques. 2. Results and discussion The morphology and dispersion of ATT and their physical interactions with the PU matrix were examined with SEM. As shown in Fig. 2a, the ATT shows uniform fibrous shape and has a length of several micrometers and the smallest diameter of approximately 30 nm (single ATT crystal). Fig. 2b–e shows the low magnification SEM images of the fractured surface morphology of neat PU and PU nanocomposites. ATTs tend to form irreversible agglomerates due to their high specific surface areas, hydrogen bonding and the intrinsic van der Waals interaction. Despite of some aggregations, the ATT dispersion was relatively homogeneous throughout the PU matrix. As shown in Fig. 2b–d, the PU-embedded ATTs appeared as bright points (the ends of broken ATTs) in the micrographs. These broken ATTs
0167-577X/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.03.067
86
C. Wang et al. / Materials Letters 78 (2012) 85–87
Fig. 1. Schematic route to synthesize PU/ATT nanocomposites.
indicated the strong chemical covalent attachment between the reactive \OH groups on the ATT surface and isocyanate, reducing the mobility of polymer segments near the solid surface [23]. Therefore, the introduction of more \OH groups through acid modification could dramatically increase the load transfer efficiency, and further improve the mechanical performance of PU, as described below. The glass transition temperature (Tg) also provides an indication of the interfacial adhesion between ATT and PU matrix [24]. The storage moduli (E′) and loss tangent (tan δ) as a function of temperature for neat PU and PU nanocomposites are shown in Fig. 3. The behaviors of the E′ versus the temperature were very similar in nature for neat PU and PU nanocomposites. It can be seen that the E′ increased with the addition of ATT (Fig. 3a). Obviously, the neat PU had a logarithmic E′ value of 0.70 MPa, which increased to 2.36 MPa for PU nanocomposites with 12 wt.% ATT at 25 °C (increased 237%). In the cases of 4 and 8 wt.% ATT loading, the logarithmic E′ of the PU nanocomposites at 25 °C increased 133% and 204%, respectively. These results were consistent with the recently reported results, which indicated that the restricted segmental motion not only elevate the Tg of polymer nanocomposites but also change the temperature dependence of segmental relaxation around the Tg [16,23,24]. The Tgs of PU and PU nanocomposites are presented in Fig. 3b. Tg was defined as the temperature at which tan δ is maximum. The Tgs of PU nanocomposites were greater than that of
Fig. 3. Dynamic mechanical spectra in terms of (a) log E′ and (b) tan δ for neat PU and PU nanocomposites. Insets show effect of ATT loading on the logarithmic E′ at 25 °C and Tg.
Fig. 2. SEM images of ATT and PU nanocomposites: (a) ATT, (b) 4 wt.%, (c) 8 wt.% and (d) 12 wt.% loadings. The inset (e) shows the SEM image of neat PU.
C. Wang et al. / Materials Letters 78 (2012) 85–87
neat PU and increased with the increasing of ATT content. Especially, at 12 wt.% ATT loading, the Tg of PU nanocomposite was improved by 16.8 °C, which indicated effective interfacial adhesion between ATT and PU matrix [24]. On the molecular scale, Tg represents the mobility level of polymer chains/networks in the material. An increased Tg corresponds to a decreased segmental mobility of the polymer chains and effective interfacial adhesion between nanofillers and polymer matrix [25]. In the PU matrix, the polymer chain has stronger interaction with the ATTs through hydrogen bonding with siloxane oxygen and direct chemical bonding with \OH groups on the surface. In our previous work, the properties of PU can be tailored ranging from rigid plastic to flexible elastomer by changing the type and functionality of soy polyol [26]. Similarly, incorporating fillers such as ATT would also be an efficient method. The stress–strain curves of neat PU and PU nanocomposites are shown in Fig. 4a. The initial slope of the curves increased with increased ATT content. The addition of ATT to PU matrix significantly enhanced their tensile strength and Young's modulus. These findings were consistent with the results of DMA. The tensile strength and Young's modulus of neat PU and PU nanocomposites are presented in Fig. 4b. It can be seen that the addition of ATT obviously enhanced the strength and modulus of PU. Compared with neat PU, the PU nanocomposites with increased ATT content had a 113%, 217% and 443% increase in the tensile strength, and had a 118%, 191% and 800% increase in the Young's modulus. Tensile strength enhancement implied that adding ATTs reinforced the PU matrix significantly. As shown in the SEM images (Fig. 2), despite the existence of some aggregations, the ATT dispersion was relatively homogeneous. The strong
87
interaction between the ATT and the PU matrix could greatly enhance the mechanical strength of the nanocomposites. This trend is consistent with the results reported in the literature, where it was demonstrated that the interfacial adhesion between nanoparticles and polymer matrixes was critical for efficient load transfer and enhanced mechanical performance [27]. Apparently, the ATT reinforcement is desirable for the PU matrix due to its low-price and high availability. Besides, the elongation at break decreased drastically with increased ATT content (Fig. 4a), which was due to the restricted mobility imposed by unidirectionally aligned, dimensionally stable ATT. 3. Conclusions We have successfully developed ATT to reinforce a soy polyolbased PU matrix. The measurements of the resulted PU nanocomposites demonstrated that the mechanical properties could be greatly enhanced via the loading of ATT, which was mainly due to the strong interfacial adhesion between ATT and PU matrix. Especially, at 12 wt.% ATT loading, 16.8 °C improvement in the glass transition temperature, 443% increment in tensile strength, and 8-fold increase in Young's modulus were obtained. This strategy might open a new perspective for the fabrication of environment-friendly advanced PU-based materials. Acknowledgments Financial support for this study was provided by the Fundamental Research Funds for the Central Universities (1106020514). Appendix A. Supplementary data Supplementary data to this article can be found online at doi:10. 1016/j.matlet.2012.03.067. References [1] Raquez JM, Deleglise M, Lacrampe MF, Krawczak P. Prog Polym Sci 2010;35(4): 487–509. [2] Wang HJ, Rong MZ, Zhang MQ, Hu J, Chen HW, Czigany T. Biomacromolecules 2008;9:615–23. [3] Petrovic ZS. Polym Rev 2008;48(1):109–55. [4] Lu Y, Larock RC. Prog Org Coat 2010;69(1):31–7. [5] Ray SS, Okamoto M. Prog Polym Sci 2003;28(11):1539–641. [6] An L, Pan Y, Shen X, Lu H, Yang Y. J Mater Chem 2008;18(41):4928–41. [7] Chen B, Evans JRG, Greenwell HC, Boulet P, Coveney PV, Bowden AA, et al. Chem Soc Rev 2008;37(3):568–94. [8] Jia QM, Zheng MS, Chen HX, Shen RJ. Mater Lett 2006;60:1306–9. [9] Xie HF, Liu BH, Yuan ZR, Shen JY, Cheng RS. J Polym Sci, Part B: Polym Phys 2004;42:3701–12. [10] Wang CS, Chen XY, Xie HF, Cheng RS. Compos Part A 2011;42(11):1620–6. [11] Husic S, Javni I, Petrovic ZS. Compos Sci Technol 2005;65(1):19–25. [12] Barick AK, Tripathy DK. Compos Part A 2010;41(10):1471–82. [13] Cai D, Yusoh K, Song M. Nanotechnology 2009;20(8):085712. [14] Okada A, Kawasumi M, Kurauchi T, Kamigaito O. Abstr Pap Am Chem Soc 1987;194:10. [15] Chen TK, Tien YI, Wei KH. Polymer 2000;41(4):1345–53. [16] Maji PK, Guchhait PK, Bhowmick AK. ACS Appl Mater Interfaces 2009;1(2):289–300. [17] Manias E, Touny A, Wu L, Strawhecker K, Lu B, Chung TC. Chem Mater 2001;13(10):3516–23. [18] Bradley WF. Am Mineral 1940;25(6):405–10. [19] Liu P. Appl Clay Sci 2007;38:64–76. [20] Wang C-H, Auad ML, Marcovich NE, Nutt S. J Appl Polym Sci 2008;109(4):2562–70. [21] Shi J, Yang X, Han Q, Wang X, Lu L. Appl Clay Sci 2009;46(3):333–5. [22] Peng L, Zhou L, Li Y, Pan F, Zhang S. Compos Sci Technol 2011;71(10):1280–5. [23] Lu HB, Nutt S. Macromolecules 2003;36(11):4010–6. [24] Lu HB, Shen HB, Song ZL, Shing KS, Tao W, Nutt S. Macromol Rapid Commun 2005;26(18):1445–50. [25] Xie HF, Liu BH, Yang H, Wang ZL, Shen JY, Cheng RS. J Appl Polym Sci 2006;100(1): 295–8. [26] Wang CS, Yang LT, Ni BL, Shi G. J Appl Polym Sci 2009;114(1):125–31. [27] Ajayan PM, Schadler LS, Giannaris C, Rubio A. Adv Mater 2000;12(10):750–3.
Fig. 4. (a) Stress–strain curves and (b) effect of ATT loading on the tensile strength and Young's modulus of neat PU and PU nanocomposites.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Natural fibrous nanoclay reinforced soy polyol-based polyurethane Chengshuang Wang a, Yuting Wang a, Weijing Liu a, Haiyan Yin a, Zuanru Yuan b, Qingjun Wang c, Hongfeng Xie a,⁎, Rongshi Cheng a, d a
Key Laboratory for Mesoscopic Chemistry of the Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China Modern Analysis Center, Nanjing University, Nanjing 210093, China Polymer Science and Engineering Department, School of Chemistry and Chemical Engineering, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China d College of Material Science and Engineering, South China University of Technology, Guangzhou 510641, China b c
a r t i c l e
i n f o
Article history: Received 10 February 2012 Accepted 15 March 2012 Available online 23 March 2012 Keywords: Attapulgite Polymers Soy polyol Nanocomposites Reinforcement
a b s t r a c t In this study, novel soy polyol-based polyurethane (PU) nanocomposites were synthesized with the aim of determining the effect of the natural fibrous nanoclay (attapulgite, ATT) loading on the properties of PU nanocomposites. Scanning electron microscopy demonstrated the relatively homogeneous dispersion of ATT in the PU matrix. After the addition of ATT, a significant ATT reinforcement effect on PU was found. In the case of 12 wt.% ATT addition, 16.8 °C improvement in the glass transition temperature, 443% increment in tensile strength, and 8-fold increase in Young's modulus were obtained. Furthermore, the elongation at break of PU nanocomposites decreased with increased ATT content. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction Recently, vegetable-oil-based polymers have attracted increasing attention because of their attractive properties related to the specific structures of the oils, as well as concerns about the environment and sustainability [1,2]. Among various vegetable-oil-based polymers, polyurethanes (PUs), one of the most versatile polymers, have been successfully employed in diverse applications such as adhesives, coatings, foams and composites [3,4]. For advanced PUs materials, PUs can be further improved via incorporation of various fillers, including clay [5–8], carbon nanotubes [9,10], glass [11], carbon nanofiber [12] and graphene [13]. The pioneering work of the Toyota group [14] has evoked great academic and commercial research interests in polymer/clay nanocomposites due to their low-price, high availability and chemical accessibility [15–17]. As a hydrated magnesium aluminum silicate, the natural fibrous attapulgite (ATT) is one of ideal and available clay sources. With a length of several micrometers and approximately 20 nm in diameter, the fibrous single crystal contains ribbons of a 2:1 phyllosilicate structure different from other layered silicates in that it lacks continuous octahedral sheets. Each ribbon is linked to the next by the inversion of SiO4 tetrahedra along a set of Si\O\Si bonds and extends parallel to the x-axis to form rectangular channels [18]. For diverse commercial applications, ATT has been used as catalyst supports, adsorbents, rheological agents,
⁎ Corresponding author. Tel./fax: + 86 25 83592568. E-mail address: [email protected] (H. Xie).
fillers and so on [19]. Because of its fibrous morphology with large surface areas and reactive \OH groups on the surface, one can expect its great potential as reinforcing filler for nanocomposites. However, the research work on the PU/ATT nanocomposites is still rather limited [20–22]. In this letter, we explored the properties of soy polyol-based PU nanocomposites reinforced with ATT for developing environmentfriendly, biodegradable materials for specific applications. ATT was dispersed in solvent by sonication and mixed with soy polyol by mechanical stirring. Then solvent-free polymerization was carried out to synthesize PU/ATT nanocomposites (Fig. 1). The morphology and mechanical properties of the resulting PU nanocomposites were then measured using various characterization techniques. 2. Results and discussion The morphology and dispersion of ATT and their physical interactions with the PU matrix were examined with SEM. As shown in Fig. 2a, the ATT shows uniform fibrous shape and has a length of several micrometers and the smallest diameter of approximately 30 nm (single ATT crystal). Fig. 2b–e shows the low magnification SEM images of the fractured surface morphology of neat PU and PU nanocomposites. ATTs tend to form irreversible agglomerates due to their high specific surface areas, hydrogen bonding and the intrinsic van der Waals interaction. Despite of some aggregations, the ATT dispersion was relatively homogeneous throughout the PU matrix. As shown in Fig. 2b–d, the PU-embedded ATTs appeared as bright points (the ends of broken ATTs) in the micrographs. These broken ATTs
0167-577X/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.03.067
86
C. Wang et al. / Materials Letters 78 (2012) 85–87
Fig. 1. Schematic route to synthesize PU/ATT nanocomposites.
indicated the strong chemical covalent attachment between the reactive \OH groups on the ATT surface and isocyanate, reducing the mobility of polymer segments near the solid surface [23]. Therefore, the introduction of more \OH groups through acid modification could dramatically increase the load transfer efficiency, and further improve the mechanical performance of PU, as described below. The glass transition temperature (Tg) also provides an indication of the interfacial adhesion between ATT and PU matrix [24]. The storage moduli (E′) and loss tangent (tan δ) as a function of temperature for neat PU and PU nanocomposites are shown in Fig. 3. The behaviors of the E′ versus the temperature were very similar in nature for neat PU and PU nanocomposites. It can be seen that the E′ increased with the addition of ATT (Fig. 3a). Obviously, the neat PU had a logarithmic E′ value of 0.70 MPa, which increased to 2.36 MPa for PU nanocomposites with 12 wt.% ATT at 25 °C (increased 237%). In the cases of 4 and 8 wt.% ATT loading, the logarithmic E′ of the PU nanocomposites at 25 °C increased 133% and 204%, respectively. These results were consistent with the recently reported results, which indicated that the restricted segmental motion not only elevate the Tg of polymer nanocomposites but also change the temperature dependence of segmental relaxation around the Tg [16,23,24]. The Tgs of PU and PU nanocomposites are presented in Fig. 3b. Tg was defined as the temperature at which tan δ is maximum. The Tgs of PU nanocomposites were greater than that of
Fig. 3. Dynamic mechanical spectra in terms of (a) log E′ and (b) tan δ for neat PU and PU nanocomposites. Insets show effect of ATT loading on the logarithmic E′ at 25 °C and Tg.
Fig. 2. SEM images of ATT and PU nanocomposites: (a) ATT, (b) 4 wt.%, (c) 8 wt.% and (d) 12 wt.% loadings. The inset (e) shows the SEM image of neat PU.
C. Wang et al. / Materials Letters 78 (2012) 85–87
neat PU and increased with the increasing of ATT content. Especially, at 12 wt.% ATT loading, the Tg of PU nanocomposite was improved by 16.8 °C, which indicated effective interfacial adhesion between ATT and PU matrix [24]. On the molecular scale, Tg represents the mobility level of polymer chains/networks in the material. An increased Tg corresponds to a decreased segmental mobility of the polymer chains and effective interfacial adhesion between nanofillers and polymer matrix [25]. In the PU matrix, the polymer chain has stronger interaction with the ATTs through hydrogen bonding with siloxane oxygen and direct chemical bonding with \OH groups on the surface. In our previous work, the properties of PU can be tailored ranging from rigid plastic to flexible elastomer by changing the type and functionality of soy polyol [26]. Similarly, incorporating fillers such as ATT would also be an efficient method. The stress–strain curves of neat PU and PU nanocomposites are shown in Fig. 4a. The initial slope of the curves increased with increased ATT content. The addition of ATT to PU matrix significantly enhanced their tensile strength and Young's modulus. These findings were consistent with the results of DMA. The tensile strength and Young's modulus of neat PU and PU nanocomposites are presented in Fig. 4b. It can be seen that the addition of ATT obviously enhanced the strength and modulus of PU. Compared with neat PU, the PU nanocomposites with increased ATT content had a 113%, 217% and 443% increase in the tensile strength, and had a 118%, 191% and 800% increase in the Young's modulus. Tensile strength enhancement implied that adding ATTs reinforced the PU matrix significantly. As shown in the SEM images (Fig. 2), despite the existence of some aggregations, the ATT dispersion was relatively homogeneous. The strong
87
interaction between the ATT and the PU matrix could greatly enhance the mechanical strength of the nanocomposites. This trend is consistent with the results reported in the literature, where it was demonstrated that the interfacial adhesion between nanoparticles and polymer matrixes was critical for efficient load transfer and enhanced mechanical performance [27]. Apparently, the ATT reinforcement is desirable for the PU matrix due to its low-price and high availability. Besides, the elongation at break decreased drastically with increased ATT content (Fig. 4a), which was due to the restricted mobility imposed by unidirectionally aligned, dimensionally stable ATT. 3. Conclusions We have successfully developed ATT to reinforce a soy polyolbased PU matrix. The measurements of the resulted PU nanocomposites demonstrated that the mechanical properties could be greatly enhanced via the loading of ATT, which was mainly due to the strong interfacial adhesion between ATT and PU matrix. Especially, at 12 wt.% ATT loading, 16.8 °C improvement in the glass transition temperature, 443% increment in tensile strength, and 8-fold increase in Young's modulus were obtained. This strategy might open a new perspective for the fabrication of environment-friendly advanced PU-based materials. Acknowledgments Financial support for this study was provided by the Fundamental Research Funds for the Central Universities (1106020514). Appendix A. Supplementary data Supplementary data to this article can be found online at doi:10. 1016/j.matlet.2012.03.067. References [1] Raquez JM, Deleglise M, Lacrampe MF, Krawczak P. Prog Polym Sci 2010;35(4): 487–509. [2] Wang HJ, Rong MZ, Zhang MQ, Hu J, Chen HW, Czigany T. Biomacromolecules 2008;9:615–23. [3] Petrovic ZS. Polym Rev 2008;48(1):109–55. [4] Lu Y, Larock RC. Prog Org Coat 2010;69(1):31–7. [5] Ray SS, Okamoto M. Prog Polym Sci 2003;28(11):1539–641. [6] An L, Pan Y, Shen X, Lu H, Yang Y. J Mater Chem 2008;18(41):4928–41. [7] Chen B, Evans JRG, Greenwell HC, Boulet P, Coveney PV, Bowden AA, et al. Chem Soc Rev 2008;37(3):568–94. [8] Jia QM, Zheng MS, Chen HX, Shen RJ. Mater Lett 2006;60:1306–9. [9] Xie HF, Liu BH, Yuan ZR, Shen JY, Cheng RS. J Polym Sci, Part B: Polym Phys 2004;42:3701–12. [10] Wang CS, Chen XY, Xie HF, Cheng RS. Compos Part A 2011;42(11):1620–6. [11] Husic S, Javni I, Petrovic ZS. Compos Sci Technol 2005;65(1):19–25. [12] Barick AK, Tripathy DK. Compos Part A 2010;41(10):1471–82. [13] Cai D, Yusoh K, Song M. Nanotechnology 2009;20(8):085712. [14] Okada A, Kawasumi M, Kurauchi T, Kamigaito O. Abstr Pap Am Chem Soc 1987;194:10. [15] Chen TK, Tien YI, Wei KH. Polymer 2000;41(4):1345–53. [16] Maji PK, Guchhait PK, Bhowmick AK. ACS Appl Mater Interfaces 2009;1(2):289–300. [17] Manias E, Touny A, Wu L, Strawhecker K, Lu B, Chung TC. Chem Mater 2001;13(10):3516–23. [18] Bradley WF. Am Mineral 1940;25(6):405–10. [19] Liu P. Appl Clay Sci 2007;38:64–76. [20] Wang C-H, Auad ML, Marcovich NE, Nutt S. J Appl Polym Sci 2008;109(4):2562–70. [21] Shi J, Yang X, Han Q, Wang X, Lu L. Appl Clay Sci 2009;46(3):333–5. [22] Peng L, Zhou L, Li Y, Pan F, Zhang S. Compos Sci Technol 2011;71(10):1280–5. [23] Lu HB, Nutt S. Macromolecules 2003;36(11):4010–6. [24] Lu HB, Shen HB, Song ZL, Shing KS, Tao W, Nutt S. Macromol Rapid Commun 2005;26(18):1445–50. [25] Xie HF, Liu BH, Yang H, Wang ZL, Shen JY, Cheng RS. J Appl Polym Sci 2006;100(1): 295–8. [26] Wang CS, Yang LT, Ni BL, Shi G. J Appl Polym Sci 2009;114(1):125–31. [27] Ajayan PM, Schadler LS, Giannaris C, Rubio A. Adv Mater 2000;12(10):750–3.
Fig. 4. (a) Stress–strain curves and (b) effect of ATT loading on the tensile strength and Young's modulus of neat PU and PU nanocomposites.