- Email: [email protected]
PET nanocomposites evaluated by novel rheological analysis approach
Applied Clay Science 166 (2018) 181–184
Contents lists available at ScienceDirect
Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Note
Recycled clay/PET nanocomposites evaluated by novel rheological analysis approach
T
Milan Kracalik Institute of Polymer Science, Johannes Kepler University Linz, Altenberger Str. 69, 4040 Linz, Austria
A R T I C LE I N FO
A B S T R A C T
Keywords: Rheology Recycled PET Shear flow Oscillatory shear Polymer Clay Nanocomposites
Clay-polymer nanocomposites exhibit complex rheological behavior due to physical and also possibly chemical interactions between individual phases. Up to now, rheology of clay-polymer nanocomposites has been usually described by evaluation of complex viscosity curve (shear thinning phenomenon), storage modulus curve (G´ secondary plateau) or plotting parameters characterizing damping behavior (e.g. Van Gurp-Palmen-plot, ColeCole plot). On the contrary to evaluation of damping behavior, new approach – based on evaluation of rigidity behavior – was tested, where the values of cot δ were calculated and called as „storage factor“, analogically to broadly used loss factor. Afterwards, values of storage factor were integrated over measured frequency range and called as “cumulative storage factor”. In this contribution, clay-PET nanocomposites with different organoclays have been prepared and characterized by both conventional as well as novel analysis approach. Rheological results have been supported by AFM micrographs.
1. Introduction Nanotechnology was already introduced as a new method of improvement of polymer properties in 1995. The technology involves not only incorporation of nanosized particles into the polymer but, more importantly, investigation of interactions between the polymer matrix and the enormously large nanofiller surface. Especially for clay/ polymer nanocomposites (CPNs), the surface effects are responsible for improvement of barrier, mechanical and rheological properties, dimensional stability, heat, flame and oxidative resistance. In comparison with traditional fillers (20–40 wt% loading), 2–5 wt% filling of clay minerals is sufficient to achieve analogous material improvement. Generally, the primary particle shape of different nanofillers can be sphere, needle or a plate. High aspect ratio (particle length/thickness) of filler facilitates high reinforcement of polymer. Therefore, layered and needle-formed fillers have been widely used for enhancement of polymer property profile. Montmorillonite belongs to the group of phyllosilicates and theoretically it is possible to reach aspect ratio of 1000 by proper dispersion of this mineral in polymer matrix. Montmorillonite is a three-sheet-silicate where the primary layer consists of one octahedral sheet surrounded by two tetrahedral sheets. Na+ or Ca2+ ions in the interlayer space have been usually replaced by long alkylammonium ions in order to increase interlayer space and, consequently, to facilitate dispersion in polymer melt during melt-compounding process. Nanocomposites using different polymer matrices
and clay minerals have been intensively investigated because of the improvements in their processing and use properties. Consequently, it is possible to prepare new, tailored, materials or to use nanofillers in polymer recycling (Ghanbari et al., 2013; Cassagnau, 2008; Laske et al., 2012; Paul and Robeson, 2008; Ray et al., 2002; Százdi et al., 2006). Especially using nanoparticles for enhancement of recycled PET (Banda-Cruz et al., 2017; Gao, 2012; Liang et al., 2015; MajdzadehArdakani et al., 2017; Mallakpour and Javadpour, 2016; Rosnan and Arsad, 2013; Kracalik et al., 2005) is of great interest due to broad potential applications. The enhancement of material properties because of nanoparticles addition has usually been analyzed using a combination of morphological (X-ray diffraction (XRD), transmission electron microscopy (TEM)), mechanical (tensile testing) and rheological (rotational rheometry) measurements. In the case of highly dispersed systems, a three dimensional physical network is achieved, formed due to interactions between clay mineral layers and the polymer chains. This phenomenon can be investigated by analysis of the melt elasticity using rotational rheometry. Such studies are mainly based on evaluation of viscosity curve shape (shear thinning phenomenon), storage modulus curve at low frequencies (formation of secondary plateau), phase homogeneity (Cole-Cole plot) or plotting information about damping behavior (e.g. Van Gurp-Palmen-plot, comparison of loss factor tan δ). In order to enable simple comparison of nanocomposites reinforcement in the shear flow, new way to analyze data of the shear flow has been tested
E-mail address: [email protected]. https://doi.org/10.1016/j.clay.2018.09.007 Received 15 May 2018; Received in revised form 10 August 2018; Accepted 5 September 2018 0169-1317/ © 2018 Elsevier B.V. All rights reserved.
Applied Clay Science 166 (2018) 181–184
M. Kracalik
Fig. 1. Complex viscosity of nanocomposites.
Fig. 4. AFM micrograph of PET/Cloisite 30B.
(Kracalik, 2015; Kracalik et al., 2011). The storage modulus G´ reflects the elastic part while the loss modulus gives information about the viscous part of the dynamic shear flow. The relation of G´´/G´ is defined as tan δ and describes damping behavior of the polymer system. On the contrary, the G´/G´´ ratio (cot δ) has not been used for rheological evaluation of nanocomposites up to now. Compared to tan δ (loss factor), cot δ (named as storage factor, SF) reflects melt rigidity, which can be associated with reinforcement effect of nanostructured filler (combination of chain elasticity with clay layers rigidity in the polymer melt). In order to reduce the values of storage factor to one representative magnitude for one nanocomposite sample, G´ as well as G´´ curves have been integrated over the measured frequency range as following: 628rad / s
CSF =
Fig. 2. Storage modulus of nanocomposites.
∫ 0.1rad / s
628rad / s
G ´/
∫ 0.1rad / s
G ´´ (1)
In this way, cumulative storage factor (CSF) and some further cumulative rheological parameters (e.g. cumulative complex viscosity CCV, cumulative complex modulus CCM, cumulative storage modulus
Fig. 3. Cumulative storage factor. 182
Applied Clay Science 166 (2018) 181–184
M. Kracalik
modulus in dependency on angular frequency are plotted. As can be seen from Fig. 1, the CPN systems prepared with 6A and 10A revealed pronounced shear-thinning behavior, as result of disruption of network structures and, consequently, by orientation of filler particles in flow. On the other hand, PET_R matrix as well as nanocomposite with Na+ showed typical liquid viscoelastic behavior. CPN with 30B showed shear-thinning behavior only in a very short range of low frequencies. Concerning the range of high frequencies, the complex viscosity of CPN systems using 30B and 10A was lower than that of pure PET_R matrix, which reflects strong degradation reactions occurring during the processing, described more in detail in previous work (Kracalik et al., 2005). For CPN systems with high dispersion grade, the dependence of G´(ω) becomes almost invariable at low frequencies. Such “secondary” plateau indicates the formation of a network structure (“rubber-like” behavior) reflecting the exfoliation of clay layers in CPN (Cassagnau, 2008; Kracalik et al., 2011; Krishnamoorti et al., 2010; Pötschke et al., 2002; Ray et al., 2002; Százdi et al., 2006; Thomas et al., 2016; Vermant et al., 2007; Wagener and Reisinger, 2003; Wang et al., 2014; Wood-Adams et al., 2000). As can be seen in Fig. 2, CPN systems prepared with 6A, 10A and 30B showed “rubber-like” behavior i.e. high dispersion grade, while pure PET_R matrix as well as CPN nanocomposite with Na+ exhibited typical viscoelastic behavior. Using previously introduced analysis based on “rigidity” behavior (Kracalik, 2015; Kracalik et al., 2011), there is possibility to analyze reinforcement level as result of 3D physical network between polymer chains and filler particles and, consequently, to obtain some information hidden in analysis based on damping behavior. The CSF plotted over CCV in Fig. 3 shows clearly differencies in material reinforcement between various CPNs. It can be seen that CSF values can be divided into three groups: CSF of the neat polymer matrix, CPNs with lower CSF values (10A, 30B) and CPNs with higher CSF values (6A, Na+). It means that effective material reinforcement was reached only in CPN systems using 6A and Na+. This is result of complex physical and chemical reactions, which occur during the processing. On one side, physical interactions based on electrostatic forces between polymer and clay mineral result into formation of differently organized structures (combination of agglomerated, delaminated and exfoliated structure) depending on achieved 3D network. On the other side, processing of PET CPNs is concomitant with different chemical reactions (e.g. chain scission, Hofmann elimination (Kracalik et al., 2005)) that lower CPN mechanical performance. Using cumulative storage factor, it can be clearly said which organoclays leads to effective material reinforcement (effect of 3D physical network is higher than effect of chemical degradation) and vice versa. In order to get morphological information, atomic force microscopy has been employed and micrographs of CPNs with highest (30B) and lowest (Na+) dispersion grade have been compared. As expected, organoclay with highest polar surface modification (30B) led to highest dispersion level (only a few small agglomerates visible in Fig. 4) comparing to very low dispersion level using clay without surface modification (Na+) in Fig. 5.
Fig. 5. AFM micrograph of PET/Cloisite Na+.
CSM) were introduced (Kracalik, 2015). It was proven that values of CSF can be correlated with values of melt strength, i.e. the reinforcement in polymer nanocomposites can be assessed and compared in both, shear as well in elongational flow (Kracalik et al., 2011). In this paper, recycled clay-PET nanocomposites with different dispersion grades (physical networks) are reported. The obtained data is analyzed in this paper using typical rheological approaches as well as cumulative rheological parameters like CSF or CCV. 2. Experimental 2.1. Materials The used clay minerals Cloisite Na+ (Na+), Cloisite 6A (6A), Cloisite 10A (10A) and Cloisite 30B (30B) were supplied by BYKChemie Ltd., Wesel, Germany / POLYchem Ltd., Markt Allhau, Austria, respectively. Colour-sorted recycled poly(ethylene)terephthalate (PET_R), with the intrinsic viscosity 0.73 dl/g (dilution in phenol/tetrachloroethane 1:3), supplied by Polymer Institute Brno, Ltd. was used as matrix. 2.2. Methods Mixtures & samples have been prepared using laboratory compounder MiniLab II Haake Rheomex CTW5 in combination with Haake MiniJet Pro (Thermo Fisher Scientific, Germany). Performance of five different compositions (pure PET_R matrix, 5 wt% of different clay minerals in PET_R) have been compared. Rheological properties in the shear flow were studied using a Physica MCR 502 rheometer (Anton Paar Ltd., Graz, Austria) with the cone-plate geometry of 25 mm diameter and measuring gap of 43 μm. Morphology of nanocomposites has been checked using atomic force microscope MFP-3D AFM (Oxford Instruments Asylum Research, Inc., Santa Barbara, CA).
4. Conclusions PET CPNs with natural and organically modified clays were prepared and analyzed by conventional as well by new rheological approach. Using novel approach based on melt rigidity analysis the effective material reinforcement (caused by 3D physical network between polymer chains and nanofiller particles) could be analyzed taking in account material deterioration (caused by chemical reactions during the processing). In this way, new insight into performance characterization of CPNs has been introduced and will be tested on CPNs based on different polymers and polymer blends in future work.
3. Results and discussion The nanocomposites dispersion grade and effect of matrix molar mass on final morphology can be evaluated using analysis of viscosity curve (shear-thinning effect) in combination with information obtained from the storage modulus curve (G´ secondary plateau; (Kracalik et al., 2005). In Fig. 1–2, magnitudes of complex viscosity as well as storage 183
Applied Clay Science 166 (2018) 181–184
M. Kracalik
Acknowledgement
com/science/book/9780323313063. Majdzadeh-Ardakani, Kazem, Zekriardehani, Shahab, Coleman, Maria R., Jabarin, Saleh A., 2017. A novel approach to improve the barrier properties of PET/clay nanocomposites. Int. J. Polymer Sci. 2017, S. 1–10. https://doi.org/10.1155/2017/ 7625906. Mallakpour, Shadpour, Javadpour, Mashal, 2016. The potential use of recycled PET bottle in nanocomposites manufacturing with modified ZnO nanoparticles capped with citric acid. Preparation, thermal, and morphological characterization. RSC Adv. 6 (18), S. 15039–15047. https://doi.org/10.1039/C5RA27631D. Paul, D.R., Robeson, L.M., 2008. Polymer nanotechnology. Nanocomposites. Polymer 49 (15), S. 3187–3204. https://doi.org/10.1016/j.polymer.2008.04.017. Pötschke, Petra, Fornes, T.D., Paul, D.R., 2002. Rheological behavior of multiwalled carbon nanotube/polycarbonate composites. Polymer 43 (11), S. 3247–3255. https://doi.org/10.1016/S0032-3861(02)00151-9. Ray, Suprakas Sinha, Okamoto, Kazuaki, Maiti, Pralay, Okamotoa, Masami, 2002. New poly(butylene succinate)/layered silicate nanocomposites. preparation and mechanical properties. J. Nanosci. Nanotechnol. 2 (2), S. 171–176. https://doi.org/10.1166/ jnn.2002.086. Rosnan, Rizuan Mohd, Arsad, Agus, 2013. Effect of MMT concentrations as reinforcement on the properties of recycled PET/HDPE nanocomposites. J. Polym. Eng. 33 (7). https://doi.org/10.1515/polyeng-2013-0107. Százdi, László, Ábrányi, Ágnes, Pukánszky, Béla, Vancso, Julius G., 2006. Morphology characterization of PP/clay nanocomposites across the length scales of the structural architecture. Macromol. Mater. Eng. 291 (7), S. 858–868. https://doi.org/10.1002/ mame.200600026. Thomas, Sabu, Muller, Rene, Abraham, Jiji, 2016. Rheology and processing of polymer nanocomposites. John Wiley & Sons, Inc., Hoboken, NJ, USA. Vermant, J., Ceccia, S., Dolgovskij, M.K., Maffettone, P.L., Macosko, C.W., 2007. Quantifying dispersion of layered nanocomposites via melt rheology. J. Rheol. 51 (3), S. 429–450. https://doi.org/10.1122/1.2516399. Wagener, Reinhard, Reisinger, Thomas J.G., 2003. A rheological method to compare the degree of exfoliation of nanocomposites. Polymer 44, S. 7513–7518. Wang, M., Fan, X., Thitsartarn, W., He, C., 2014. Rheological and mechanical properties of epoxy/clay nanocomposites with enhanced tensile and fracture toughnesses. Polymer 58, S. 43–52. Wood-Adams, Paula M., Dealy, John M., deGroot, A. Willem, Redwine, O. David, 2000. Effect of molecular structure on the linear viscoelastic behavior of polyethylene. Macromolecules 33 (20), S. 7489–7499. https://doi.org/10.1021/ma991533z.
Lisa Maria Uiberlacker from VTA Austria GmbH, Rottenbach, Austria for AFM measurements is gratefully acknowledged. References Banda-Cruz, Ernestina Elizabeth, Flores-Gallardo, Sergio Gabriel, Rivera-Armenta, José Luis, 2017. Study of the dispersion of Cloisite 10A in recycled polyethylene terephtalate by extrusion. DYNA 84 (200), S. 107–111. https://doi.org/10.15446/dyna. v84n200.52720. Cassagnau, Ph., 2008. Melt rheology of organoclay and fumed silica nanocomposites. Polymer 49 (9), S. 2183–2196. https://doi.org/10.1016/j.polymer.2007.12.035. Gao, Fengge, (Hg.), 2012. Advances in Polymer Nanocomposites. Woodhead Pub (Woodhead Publishing in materials), Cambridge, UK Online verfügbar unter. http:// proquest.tech.safaribooksonline.de/9781845699406. Ghanbari, Abbas, Heuzey, Marie-Claude, Carreau, Pierre J., Ton-That, Minh-Tan, 2013. Morphological and rheological properties of PET/clay nanocomposites. Rheol Acta 52, S. 59–74. Kracalik, Milan, 2015. Rheology of multiphase polymer systems using novel “melt rigidity” evaluation approach. In: Novel Trends in Rheology VI. AIP Publishing LLC (AIP Conference Proceedings), Zlín, Czech Republic, pp. S. 40002 28–29 July 2015. Kracalik, Milan, Mikesowa, Jana, Puffr, Rudolf, Friedrich, Christian, 2005. Effect of 3D PET/organoclay nanocomposites. Polymer Bull. 58, S. 313–319. Kracalik, Milan, Laske, Stephan, Witschnigg, Andreas, Holzer, Clemens, 2011. Elongational and shear flow in polymer-clay nanocomposites measured by on-line extensional and off-line shear rheometry. Rheologica Acta 50, S. 937–944. Krishnamoorti, Ramanan, Banik, Indranil, Xu, Liang, 2010. Rheology and processing of polymer nanocomposites. Rev. Chem. Eng. 26 (1–2), S. 354. https://doi.org/10. 1515/REVCE.2010.003. Laske, Stephan, Witschnigg, Andreas, Mattausch, Hannelore, Kracalik, Milan, Pinter, Gerald, Feuchter, Michael, et al., 2012. Determining the ageing of polpropylene nanocomposites using rheological measurements. Appl. Rheol. 22. Liang, Mong, Visakh, P.M., (Hg.), 2015. Poly(Ethylene Terephthalate) Based Blends, Composites and Nanocomposites. William Andrew (Plastics Design Library. PDL Handbook series), Waltham, MA Online verfügbar unter. http://www.sciencedirect.
184
Contents lists available at ScienceDirect
Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Note
Recycled clay/PET nanocomposites evaluated by novel rheological analysis approach
T
Milan Kracalik Institute of Polymer Science, Johannes Kepler University Linz, Altenberger Str. 69, 4040 Linz, Austria
A R T I C LE I N FO
A B S T R A C T
Keywords: Rheology Recycled PET Shear flow Oscillatory shear Polymer Clay Nanocomposites
Clay-polymer nanocomposites exhibit complex rheological behavior due to physical and also possibly chemical interactions between individual phases. Up to now, rheology of clay-polymer nanocomposites has been usually described by evaluation of complex viscosity curve (shear thinning phenomenon), storage modulus curve (G´ secondary plateau) or plotting parameters characterizing damping behavior (e.g. Van Gurp-Palmen-plot, ColeCole plot). On the contrary to evaluation of damping behavior, new approach – based on evaluation of rigidity behavior – was tested, where the values of cot δ were calculated and called as „storage factor“, analogically to broadly used loss factor. Afterwards, values of storage factor were integrated over measured frequency range and called as “cumulative storage factor”. In this contribution, clay-PET nanocomposites with different organoclays have been prepared and characterized by both conventional as well as novel analysis approach. Rheological results have been supported by AFM micrographs.
1. Introduction Nanotechnology was already introduced as a new method of improvement of polymer properties in 1995. The technology involves not only incorporation of nanosized particles into the polymer but, more importantly, investigation of interactions between the polymer matrix and the enormously large nanofiller surface. Especially for clay/ polymer nanocomposites (CPNs), the surface effects are responsible for improvement of barrier, mechanical and rheological properties, dimensional stability, heat, flame and oxidative resistance. In comparison with traditional fillers (20–40 wt% loading), 2–5 wt% filling of clay minerals is sufficient to achieve analogous material improvement. Generally, the primary particle shape of different nanofillers can be sphere, needle or a plate. High aspect ratio (particle length/thickness) of filler facilitates high reinforcement of polymer. Therefore, layered and needle-formed fillers have been widely used for enhancement of polymer property profile. Montmorillonite belongs to the group of phyllosilicates and theoretically it is possible to reach aspect ratio of 1000 by proper dispersion of this mineral in polymer matrix. Montmorillonite is a three-sheet-silicate where the primary layer consists of one octahedral sheet surrounded by two tetrahedral sheets. Na+ or Ca2+ ions in the interlayer space have been usually replaced by long alkylammonium ions in order to increase interlayer space and, consequently, to facilitate dispersion in polymer melt during melt-compounding process. Nanocomposites using different polymer matrices
and clay minerals have been intensively investigated because of the improvements in their processing and use properties. Consequently, it is possible to prepare new, tailored, materials or to use nanofillers in polymer recycling (Ghanbari et al., 2013; Cassagnau, 2008; Laske et al., 2012; Paul and Robeson, 2008; Ray et al., 2002; Százdi et al., 2006). Especially using nanoparticles for enhancement of recycled PET (Banda-Cruz et al., 2017; Gao, 2012; Liang et al., 2015; MajdzadehArdakani et al., 2017; Mallakpour and Javadpour, 2016; Rosnan and Arsad, 2013; Kracalik et al., 2005) is of great interest due to broad potential applications. The enhancement of material properties because of nanoparticles addition has usually been analyzed using a combination of morphological (X-ray diffraction (XRD), transmission electron microscopy (TEM)), mechanical (tensile testing) and rheological (rotational rheometry) measurements. In the case of highly dispersed systems, a three dimensional physical network is achieved, formed due to interactions between clay mineral layers and the polymer chains. This phenomenon can be investigated by analysis of the melt elasticity using rotational rheometry. Such studies are mainly based on evaluation of viscosity curve shape (shear thinning phenomenon), storage modulus curve at low frequencies (formation of secondary plateau), phase homogeneity (Cole-Cole plot) or plotting information about damping behavior (e.g. Van Gurp-Palmen-plot, comparison of loss factor tan δ). In order to enable simple comparison of nanocomposites reinforcement in the shear flow, new way to analyze data of the shear flow has been tested
E-mail address: [email protected]. https://doi.org/10.1016/j.clay.2018.09.007 Received 15 May 2018; Received in revised form 10 August 2018; Accepted 5 September 2018 0169-1317/ © 2018 Elsevier B.V. All rights reserved.
Applied Clay Science 166 (2018) 181–184
M. Kracalik
Fig. 1. Complex viscosity of nanocomposites.
Fig. 4. AFM micrograph of PET/Cloisite 30B.
(Kracalik, 2015; Kracalik et al., 2011). The storage modulus G´ reflects the elastic part while the loss modulus gives information about the viscous part of the dynamic shear flow. The relation of G´´/G´ is defined as tan δ and describes damping behavior of the polymer system. On the contrary, the G´/G´´ ratio (cot δ) has not been used for rheological evaluation of nanocomposites up to now. Compared to tan δ (loss factor), cot δ (named as storage factor, SF) reflects melt rigidity, which can be associated with reinforcement effect of nanostructured filler (combination of chain elasticity with clay layers rigidity in the polymer melt). In order to reduce the values of storage factor to one representative magnitude for one nanocomposite sample, G´ as well as G´´ curves have been integrated over the measured frequency range as following: 628rad / s
CSF =
Fig. 2. Storage modulus of nanocomposites.
∫ 0.1rad / s
628rad / s
G ´/
∫ 0.1rad / s
G ´´ (1)
In this way, cumulative storage factor (CSF) and some further cumulative rheological parameters (e.g. cumulative complex viscosity CCV, cumulative complex modulus CCM, cumulative storage modulus
Fig. 3. Cumulative storage factor. 182
Applied Clay Science 166 (2018) 181–184
M. Kracalik
modulus in dependency on angular frequency are plotted. As can be seen from Fig. 1, the CPN systems prepared with 6A and 10A revealed pronounced shear-thinning behavior, as result of disruption of network structures and, consequently, by orientation of filler particles in flow. On the other hand, PET_R matrix as well as nanocomposite with Na+ showed typical liquid viscoelastic behavior. CPN with 30B showed shear-thinning behavior only in a very short range of low frequencies. Concerning the range of high frequencies, the complex viscosity of CPN systems using 30B and 10A was lower than that of pure PET_R matrix, which reflects strong degradation reactions occurring during the processing, described more in detail in previous work (Kracalik et al., 2005). For CPN systems with high dispersion grade, the dependence of G´(ω) becomes almost invariable at low frequencies. Such “secondary” plateau indicates the formation of a network structure (“rubber-like” behavior) reflecting the exfoliation of clay layers in CPN (Cassagnau, 2008; Kracalik et al., 2011; Krishnamoorti et al., 2010; Pötschke et al., 2002; Ray et al., 2002; Százdi et al., 2006; Thomas et al., 2016; Vermant et al., 2007; Wagener and Reisinger, 2003; Wang et al., 2014; Wood-Adams et al., 2000). As can be seen in Fig. 2, CPN systems prepared with 6A, 10A and 30B showed “rubber-like” behavior i.e. high dispersion grade, while pure PET_R matrix as well as CPN nanocomposite with Na+ exhibited typical viscoelastic behavior. Using previously introduced analysis based on “rigidity” behavior (Kracalik, 2015; Kracalik et al., 2011), there is possibility to analyze reinforcement level as result of 3D physical network between polymer chains and filler particles and, consequently, to obtain some information hidden in analysis based on damping behavior. The CSF plotted over CCV in Fig. 3 shows clearly differencies in material reinforcement between various CPNs. It can be seen that CSF values can be divided into three groups: CSF of the neat polymer matrix, CPNs with lower CSF values (10A, 30B) and CPNs with higher CSF values (6A, Na+). It means that effective material reinforcement was reached only in CPN systems using 6A and Na+. This is result of complex physical and chemical reactions, which occur during the processing. On one side, physical interactions based on electrostatic forces between polymer and clay mineral result into formation of differently organized structures (combination of agglomerated, delaminated and exfoliated structure) depending on achieved 3D network. On the other side, processing of PET CPNs is concomitant with different chemical reactions (e.g. chain scission, Hofmann elimination (Kracalik et al., 2005)) that lower CPN mechanical performance. Using cumulative storage factor, it can be clearly said which organoclays leads to effective material reinforcement (effect of 3D physical network is higher than effect of chemical degradation) and vice versa. In order to get morphological information, atomic force microscopy has been employed and micrographs of CPNs with highest (30B) and lowest (Na+) dispersion grade have been compared. As expected, organoclay with highest polar surface modification (30B) led to highest dispersion level (only a few small agglomerates visible in Fig. 4) comparing to very low dispersion level using clay without surface modification (Na+) in Fig. 5.
Fig. 5. AFM micrograph of PET/Cloisite Na+.
CSM) were introduced (Kracalik, 2015). It was proven that values of CSF can be correlated with values of melt strength, i.e. the reinforcement in polymer nanocomposites can be assessed and compared in both, shear as well in elongational flow (Kracalik et al., 2011). In this paper, recycled clay-PET nanocomposites with different dispersion grades (physical networks) are reported. The obtained data is analyzed in this paper using typical rheological approaches as well as cumulative rheological parameters like CSF or CCV. 2. Experimental 2.1. Materials The used clay minerals Cloisite Na+ (Na+), Cloisite 6A (6A), Cloisite 10A (10A) and Cloisite 30B (30B) were supplied by BYKChemie Ltd., Wesel, Germany / POLYchem Ltd., Markt Allhau, Austria, respectively. Colour-sorted recycled poly(ethylene)terephthalate (PET_R), with the intrinsic viscosity 0.73 dl/g (dilution in phenol/tetrachloroethane 1:3), supplied by Polymer Institute Brno, Ltd. was used as matrix. 2.2. Methods Mixtures & samples have been prepared using laboratory compounder MiniLab II Haake Rheomex CTW5 in combination with Haake MiniJet Pro (Thermo Fisher Scientific, Germany). Performance of five different compositions (pure PET_R matrix, 5 wt% of different clay minerals in PET_R) have been compared. Rheological properties in the shear flow were studied using a Physica MCR 502 rheometer (Anton Paar Ltd., Graz, Austria) with the cone-plate geometry of 25 mm diameter and measuring gap of 43 μm. Morphology of nanocomposites has been checked using atomic force microscope MFP-3D AFM (Oxford Instruments Asylum Research, Inc., Santa Barbara, CA).
4. Conclusions PET CPNs with natural and organically modified clays were prepared and analyzed by conventional as well by new rheological approach. Using novel approach based on melt rigidity analysis the effective material reinforcement (caused by 3D physical network between polymer chains and nanofiller particles) could be analyzed taking in account material deterioration (caused by chemical reactions during the processing). In this way, new insight into performance characterization of CPNs has been introduced and will be tested on CPNs based on different polymers and polymer blends in future work.
3. Results and discussion The nanocomposites dispersion grade and effect of matrix molar mass on final morphology can be evaluated using analysis of viscosity curve (shear-thinning effect) in combination with information obtained from the storage modulus curve (G´ secondary plateau; (Kracalik et al., 2005). In Fig. 1–2, magnitudes of complex viscosity as well as storage 183
Applied Clay Science 166 (2018) 181–184
M. Kracalik
Acknowledgement
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