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A novel slurry blending method for a uniform dispersion of carbon nanotubes in natural rubber composites
Journal Pre-proofs A novel slurry blending method for a uniform dispersion of carbon nanotubes in natural rubber composites Jiang-Shan Gao, Zhiming Liu, Zhengqi Yan, Yan He PII: DOI: Reference:
S2211-3797(19)32703-2 https://doi.org/10.1016/j.rinp.2019.102720 RINP 102720
To appear in:
Results in Physics
Received Date: Revised Date: Accepted Date:
8 September 2019 2 October 2019 2 October 2019
Please cite this article as: Gao, J-S., Liu, Z., Yan, Z., He, Y., A novel slurry blending method for a uniform dispersion of carbon nanotubes in natural rubber composites, Results in Physics (2019), doi: https://doi.org/10.1016/j.rinp. 2019.102720
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
A novel slurry blending method for a uniform dispersion of carbon nanotubes in natural rubber composites Jiang-Shan Gao, Zhiming Liu, Zhengqi Yan, Yan He* College of Electromechanical Engineering, Shandong Engineering Laboratory for Preparation and Application of High-performance Carbon Materials, Qingdao University of Science and Technology, Qingdao 266061, China Corresponding Author：Yan He Phone：+86 0532-88959067 Fax: +86 053288959488 Email：[email protected] Abstract Carbon nanotubes (CNTs)/natural rubber (NR) composites were prepared by the slurry blending method to get a better dispersion of CNTs in NR composites. The slurry blending method was a new method to improve and optimize the commonly used traditional method (the latex blending method). The treatment of slurry blending for CNTs/NR composites could reduce the agglomeration and settlement of CNTs than that of latex blending process. In order to show the superiority of this method, the morphology, mechanical properties, Payne effect, thermal conductivity, permittivity and dynamic mechanical properties of the composites prepared by the two methods were measured and compared. Compared with latex blending method, the slurry blending method contributed a better dispersion of CNTs in the NR, and the tensile strength of the sample was increased by 15.2%. Meanwhile, the CNTs/NR composites prepared by the slurry method had more stable thermal conductivity, weaker Payne effect and higher permittivity due to the uniform dispersion of CNTs. More importantly, this work further extended the dispersion method of CNTs in the matrix and may shed some light on the design of advanced technology on rubber industry. Keywords：carbon nanotubes, the slurry blending method, dispersion, thermal conductivity, natural rubber. 1. Introduction CNTs have attracted numerous attentions due to their excellent performances such as high mechanical properties, high thermal conductivity and high electric conductivity [1-3]. Therefore, CNTs have been widely used in catalytic [4-5], electronic devices [6-8], various composite materials [9-12] since the advent of CNTs. In the rubber industry, CNTs were added into the rubber materials in order to further improve the mechanical property, electric conductivity, thermal conductivity and other properties of rubbers [13-18]. Good dispersion of CNTs was the key point to give full play of excellent properties and achieve a desirable reinforcing effect for rubbers, so the blending process of CNTs and rubber was quite important. However, the blending process of CNTs and rubber existing now had critical shortcomings. A large aspect ratio of CNTs and a large Vander Waals force between two tubes made CNTs easily be entangled with each other [19,20], and it was difficult to be homogenously dispersed in the matrix, which led to a series of defects in the blending process of CNTs and rubber.
In the previous work, there were five main blending methods intending to obtain a better dispersion of CNTs in the rubber matrix. (1) Mechanical blending method. For example, Nakaramontri and co-authors [21] prepared CNTs/ENR composites by mechanical blending method, and in detail, the CNTs/ENR composites were prepared by mixing in an internal mixer and thereafter in a two-roll mill. (2) Latex blending technology. Peng and co-authors [22] prepared CNTs/NR composites by latex blending method. Acid treated MWCNTs and SDS were dispersed in water and then the above product was dropped into negatively charged latex. Finally, the mixture was dried in the fume chamber and the dried mixture was taken out and ready to be mixed with other rubber additives on a two-roll mill. (3) The solution blending method. Ismail [23] prepared CNTs/NR composites using organic solution blending method. Natural rubber and CNTs were dissolved in two bottles of toluene, respectively. The above two solutions were mixing and the mixture was dried before it was mixed with other rubber additives on a two-roll mill. Wang [24] prepared CNTs/silicone rubber by solution blending method, CNTs were dispersed into liquid silicone rubber matrix to fabricate the composite. (4) Spray drying method. For example, Zhou and co-authors [25] prepared CNTs/SBR composites using spray drying method. A suspension of CNTs in SBR latex was prepared to disperse CNTs in the liquid medium. Then CNTs/SBR composites were prepared by a spray drying process. (5) Melt method. For example, Verge and co-authors [26] prepared CNTs/NBR composites utilizing melt method. NBR, CNTs, and vulcanization agents were mixed simultaneously in a Brabender internal mixer. Then, all the compounds were prepared by stiring at 50 ℃ for 10 min at 60 rpm and were vulcanized at 190 ℃ under 50 bars for 15 min. In these previous studies, CNTs could be partially dispersed in the rubber matrix, however, these traditional methods still had some inevitable drawbacks. The mechanical shear forces could not allow CNTs to be well dispersed in the rubber matrix with the mechanical blending method. For the latex blending method, a large amount of deionized water which was used to disperse CNTs [22] could dilute the latex as well, therefore CNTs tended to settle in the diluted latex and it led to a secondary agglomeration. A large amount of organic solvent was consumed with the solution mixing method and it caused an irreversible environmental pollution. Spray drying process [25] was very complex and hardly implemented. Melt blending was only suitable for certain specific rubber varieties. Thus, an effective and easy method needed to be discovered to get a uniform dispersion of CNTs in rubbers. In the present work, a facile slurry blending method was applied to prepare well dispersed CNTs in NR composites. The method was divided into two steps: First, the preparation of natural rubber slurry allowed CNTs to be uniformly dispersed into the rubber matrix by adding sodium dodecyl sulfate (SDS). Second, the dried rubber was blended with CB and sulfur in the open two-roll mill and then vulcanized. For comparison, CNTs/NR composites were also prepared by latex blending method. Comparing the morphology, mechanical properties, thermal conductivity and other properties of the composites, CNTs in NR prepared by the slurry method were remarkably more uniform than that by latex blending method. 2. Experimental 2.1. Materials Multi wall carbon nanotubes (MWCNTs, GT300, purity>95%, diameter: 5-15 nm, length:0.5-5 μm). Carbon black (CB) N220, natural rubber latex (solid content 62%), antioxidant 4020, stearic acid (SA), zinc oxide (ZnO), sulfur, accelerator NS, sodium dodecyl sulfate (SDS) are commercially available. The formula of the CNTs/NR composite is in Tab.1.
Tab.1 The composition of composites.
a Per b 100
Ingredients
phra
NR Sulfur Zinc oxide Accelerator NS Stearic acid Antioxidant 4020 SDS Carbon black MWCNTs GT-300
100b 3 5 1 2 1 4 40 3
hundred of natural rubber in quality. phr natural rubber means 161.3g natural rubber latex.
2.2. Preparation of CNTs/NR slurry
Fig. 1. Preparation of CNTs/NR slurry. The concrete implementation process of slurry blending method was as shown in Fig. 1. Four kinds of granular rubber ingredients (antioxidant 4020, SDS, accelerator NS, ZnO) were polished into powder by mortar for 5 min in Fig. 1a. And SDS was added into natural rubber latex in the ultrasound instrument and kept being stirred for 15 min (Fig. 1b) Then, the griding ingredients in Fig. 1a and the latex in Fig. 1b were blended with each other to increase the viscosity of latex, as shown in Fig. 1c. Afterwards, 3 g CNTs was divided into twenty copies equally and the one of them was mixed into natural rubber latex and being kept stirred for 2~4 min in Fig. 1d. This procedure was repeated until all the CNTs were mixed into the natural rubber latex in Fig. 1e and the obtained slurry-like composite was as Fig. 1f. At last, the CNTs/NR slurry was dried in the air blowing thermostatic oven at 60 ℃ for 12 h to volatilize water. 2.3. Preparation of CNTs / NR rubber composites
The dried rubber with the CNTs was blended with CB and sulfur in the open two-roll mill and then vulcanized at 150 ℃ for 12 min. For comparison, CNTs/NR composites was also prepared by latex blending method according to Peng [22] with the same composition. 2.4. Measurements In order to observe the dispersion of CNTs in NR composites, TEM was performed on the samples with 50 nm thickness prepared by cryo-ultramicrotomy (Leica, Germany). TEM was performed by using a JEM-2100 electron microscope (JEOL, Japan) with an accelerating voltage of 200 kV. RPA was performed by using an RPA2000 (Alpha Technologies, USA). The test condition was as following: the test configuration was strain-sweep mode in the range of 0.7~70%, the operating temperature was 85 ℃, the operating frequency was 0.1 Hz. The mechanical properties were performed by using an AI-70000M universal testing machine (Gotech, China). And the operating temperature was 25 ℃, the operating speed was 500 mm/min. The thermal conductivity was obtained by using a LFA447 laser flash thermal conductivity analyzer(Netzsch, Germany)with the operating temperature 25 ℃. The diameter and thickness of the round sample were 12.7 mm and 2 mm, respectively. The permittivity was obtained by a Concept 10 permittivity and impedance Analyzers (Novocontrol GmbH, Germany). The operating frequency range and AC Volt were 1×106 Hz~3×109 Hz and 0.1 Vrms, respectively. DMA was performed by a DMAD-29693 (Gaboqualimeter, Germany) and the operating temperature range was -80 ℃ ~80 ℃. 3. Results and discussion 3.1. Morphology
Fig. 2 TEM images of CNTs/NR composites prepared by slurry blending method and latex blending method, (a) slurry blending method, (b) latex blending method. (c) The SEM image of CNTs/NR composites prepared by slurry blending method. The morphologies of the CNTs/NR composites prepared by the slurry method and latex blending method were shown in Fig. 2. As shown in Fig. 2a, CNTs were uniformly dispersed into the rubber matrix in the entire figure and many single CNTs (as indicated by the red arrows) run through the carbon black particles in the composite prepared by the slurry method. The CNTs (indicated by the red arrows) have a uniform distribution in the rubber as shown in Fig. 2c, being consistent with above image (Fig. 2a). In Fig. 2b, some aggregated CNTs were found in the red dotted circle, indicating that the CNTs cannot be dispersed well in the NR matrix by latex blending method. The reasons were as follows: Firstly, SDS improved the attraction between NR
and CNTs by decreasing the interfacial tension of NR. The alkyl of SDS could adsorb CNTs through the hydrophobic effect [27]. Meanwhile, the sulfate radical of SDS increased the amount of negative charge of CNTs [28], and it led to an enhanced electrostatic repulsive-force among CNTs which had a better dispersion of CNTs in the rubber latex. Furthermore, the additives (except CB, CNTs and sulfate) provided a suitable viscosity of NR latex and the NR latex turned to be a density paste with a low interfacial tension. At this point, a proper amount of CNTs were added into NR and kept being stirred and the fluidity was weakened with the increase of the viscosity of the mixing latex. Hence, the position of CNTs was fixed after they were blended into the mixing latex and the secondary agglomeration was also avoided. 3.2. The Payne effect
Fig. 3 Payne effect of CNTs/NR composites prepared by latex blending method and slurry method. The Payne effect of CNTs/NR composites prepared by latex blending method and slurry method was shown in Fig. 3. "Payne effect" referred to the phenomenon that the storage modulus (G') of rubber composites decreased with the increase of strain in a certain range, and it could represent the degree of agglomeration of the filler [29]. This non-linear behavior of filled rubber appeared at small strain range (below 100%), so it was accepted by most researchers that the breakdown of network formed by filler agglomerates was the main reason for "Payne effect" [30]. In practical application, "Payne effect" could be quantified by the specific value ∆G' (the difference between initial G' and final G'). The smaller value of ∆G', the weaker interaction between filler and filler, and the better dispersion of the fillers [31]. Fig. 3 showed that slurry blending method and latex blending method had different ∆G', the ∆G' value of slurry method and latex blending method are 255.53 and 287.18, respectively. Thus, the RPA results showed that a lower aggregation level of nanofillers for the composites produced by
slurry method than those by latex blending method, suggesting that the slurry method enabled the CNTs to be well dispersed into the rubber matrix compared to latex blending method. 3.3. Mechanical properties
Fig. 4 The mechanical properties of CNTs/NR composites. (a) tensile strength; (b) tear strength. Five dumbbell samples and three right angle samples were obtained for the mechanical properties testing. The mechanical properties of CNTs/NR composites were shown in Fig.4. The tensile strengths of the samples generated by latex blending method possessed a relatively large fluctuation, and the average tensile strength and tear strength of the CNTs/NR composites were 20.603 MPa and 68.283 KN·m-1 respectively. The fluctuation for tensile strengths of the samples prepared by slurry method were relatively small, the average tensile strength and tear strength of the CNTs/NR composites were 23.740 MPa and 71.865 KN·m-1, respectively. In comparison with the CNTs/NR composites generated by two methods, tensile strengths and tear strengths of the samples prepared by slurry method were increased by 15.2% and 5.2%, respectively. As shown in Fig. 4(a), the tensile strengths of CNTs/NR composites samples prepared by latex blending method revealed a relatively large fluctuation, and the tensile strength of the slurry method sample was almost stable. It was due to a better CNTs dispersion from slurry mixing. Slurry blending method enabled the CNTs to be uniformly dispersed in the rubber matrix so that CNTs could play a superior reinforcement performance. However, CNTs were agglomerated during the mixing process with natural rubber latex with latex blending method. Actually, the aggregates with poor dispersion in the rubber led to a poor compatibility of CNTs and rubber matrix [32,33]. Meanwhile, the agglomerations became the defects of the materials, which limit the mechanical properties of the CNTs/NR composites [34].
3.4. Thermal conductivity
Fig. 5 The thermal conductivity of CNTs/NR composites (a) and the mechanism of thermal conductivity (b,c). The thermal conductivity of the CNTs/NR composites prepared by slurry blending method and latex blending method was tested to show the uniformity of CNTs in NR by evaluating numerical stability. The results were plotted and shown in Fig. 5(a). The thermal conductivity of samples prepared by slurry method was relatively stable. As we know, composites exhibit stable properties due to its uniform dispersion as shown in Fig. 5(b). CNTs were uniformly dispersed into the rubber matrix and single CNTs run through the carbon black particles to be “the bridges” of CB particles [15] in the composite prepared by the slurry method. In contrast, the thermal conductivity of the samples prepared by latex blending method possessed a larger fluctuation. This was due to CNTs aggregations in the composite as shown in Fig. 5(c). And a sample with many CNTs could get a high thermal conductivity because of the ultrahigh thermal conductivity of CNTs. Hence, CNTs aggregations in NR resulted in a high thermal conductivity and a low thermal conductivity resulted from CNTs without aggregations. Therefore, the samples prepared by latex blending method had an inhomogeneous distribution of thermal conductivity [35-37]. Thus, in comparison with the thermal conductivity of the samples prepared by slurry method and latex blending method, it is indirectly proved that CNTs were homogeneously dispersed in the rubber matrix by the slurry method.
3.5. Permittivity
Fig. 6 The permittivity of CNTs/NR composites under different frequency. (a) 1.0022×107 Hz; (b) 2.0030×107 Hz. Fig. 6 showed the effect of different blending methods on the permittivity of CNTs/NR composites. Fig. 6a and 6b showed that the average (AVG) of permittivity of CNTs/NR composites prepared by slurry method is higher than that prepared by latex blending method under different frequency. When the frequency were 1.0022×107 Hz and 2.0030×107 Hz, the average of the permittivity of samples processed by slurry method were increased by 39.4% and 44.2% than that of samples processed by slurry method, respectively. It was resulting from the better CNTs dispersion by slurry mixing. The reunion of the filler had a significant effect on the electrical properties of the composite, so the dispersion of the filler was an essential factor to improving the dielectric properties. Meanwhile, the good dispersion of the filler was beneficial to increasing the permittivity of the composites [38]. Hence, CNTs/NR composites prepared by slurry method had a higher permittivity because of the good dispersion of CNTs in NR. 3.6. Dynamic mechanical properties
(a)
(b)
Fig. 7 Dynamic mechanical properties of CNTs/NR composites (a) tan δ, (b) storage modulus (E'). The dynamic mechanical properties of CNTs/NR composites prepared by two methods were shown in Fig.7. Compared with latex blending method, the CNTs/NR composites prepared by slurry method showed higher tanδmax in Fig.7a. CNTs and rubber macromolecules formed a good
combination due to the CNTs with better dispersion in the rubber matrix, which allowed CNTs to inhibit the movement of the rubber molecular chains [39], leading to the increment of tanδmax. In addition, the storage modulus (E') of the CNTs/NR composites prepared by slurry method was slightly lower than that prepared by latex blending method in Fig.7b. It was also due to the movement of rubber molecular chains was inhibited, which temporarily reduced the crosslinking density and storage capacity of rubber [40]. In conclusion, in comparison with the dynamic mechanical properties of CNTs/NR composites prepared by two methods, CNTs had a better dispersion and a stronger binding force with NR by the slurry method. 4. Conclusions CNTs/NR composites were prepared by slurry method and latex blending method and slurry method enable CNTs to disperse more uniformly in the NR according to a series of measurements. The mechanism of uniform dispersion of CNTs is as follows. Firstly, SDS improved the attraction between NR and CNTs by decreasing the interfacial tension of NR and it led to an enhanced electrostatic repulsive-force among CNTs which had a better dispersion of CNTs in the rubber latex. Secondly, the mashed additives increased the viscosity of NR latex that turned to be a paste with a low interfacial tension. Hence, the position of CNTs was fixed after blended into the NR and the secondary agglomeration was also avoided. Therefore, uniform dispersion of CNTs resulted in excellent performances of CNTs/NR composites by the slurry blending method. Acknowledgments This work was supported by National Natural Science Foundation of China (No. 51676103) and Taishan Scholar Foundation of Shandong Province. References [1] Du M R, Jing H W, Duan W H,et al. Methylcellulose stabilized multi-walled carbon nanotubes dispersion for sustainable cement composites .Construction and Building Materials,2017,146:76-85. [2] Mei H, Xia J, Zhang D, et al. Highly conductive and high-strength carbon nanotube film reinforced silicon carbide composites . Ceramics International, 2017, 43(12):8873-8878. [3] Seong M,Jeong C,Yi H,et al. Adhesion of bioinspired nanocomposite microstructure at high temperatures .Applied Surface Science, 2017,413:275-283. [4] Xiao J, Pan X, Zhang F, et al. Size-dependence of carbon nanotube confinement in catalysis. Chemical Science, 2017, 8:278-283. [5] Tavares I S, Figueiredo C F B R, Magalhaes A L. The inner cavity of a carbon nanotube as a chemical Reactor: The effect of geometry on the catalysis of a menshutkin SN2 reaction, 2017, 121:2165-2172. [6] Zhang Y, Li K, Ji P, et al. Silicon-multi-walled carbon nanotubes-carbon microspherical composite as high-performance anode for lithium-ion batteries. Journal of Materials Science, 2017, 52:3630-3641. [7] Tang H, Huang K, Bao Y, et al. Rationally designed layer-by-layer structure of Fe3O4, Nanospheres@MWCNTs/Graphene as electrode for lithium ion batteries with enhanced electrochemical performance . Journal of Alloys & Compounds, 2017, 699:812-817 [8] Zeng Q,Tian H,Jiang J, et al. High-purity helical carbon nanotubes with enhanced electrochemical properties for supercapacitors. Rsc Advances, 2017, 12(7):7375-7381 [9] Han J J, Su D, Zhao Z H, et al. Fabrication and toughening behavior of carbon nanotube (CNT) scaffold reinforced SiBCN ceramic composites with high CNT loading. Ceramics International, 2017, 43(12):9024-9031.
[10] Song X, Wang L, Mao L, et al. Nanocomposite membrane with different carbon nanotubes location for nanofiltration and forward osmosis applications. Acs Sustainable Chemistry & Engineering, 2016, 4(6):2990-2997. [11] Kaseem M, Hamad K, Ko Y G. Fabrication and materials properties of polystyrene/carbon nanotube (PS/CNT) composites: A review. European Polymer Journal, 2016, 79:36-62. [12] Wang B, Zhou G, Wang L, et al. Preparation and properties of hierarchical composites based on carbon nanotubes-coated glass babric preform . Polymer Composites, 2016, 37(4):979-986. [13] Kumar V, Lee D. Studies of nanocomposites based on carbon nanomaterials and RTV silicone rubber. Journal of Applied Polymer Science, 2017, 134(4):44407. [14] Lu Y, Liu J, Hou G, et al. From nano to giant? Designing carbon nanotubes for rubber reinforcement and their applications for high performance tires. Composites Science & Technology, 2016, 137:94-101. [15] Gao J, He Y, Gong X . Effect of electric field induced alignment and dispersion of functionalized carbon nanotubes on properties of natural rubber. Results in Physics, 2018, 9:493-499. [16] Mat Desa M S Z, Hassan A, Arsad A, et al. Influence of rubber content on mechanical, thermal, and morphological behavior of natural rubber toughened poly(lactic acid)-multiwalled carbon nanotube nanocomposites . Journal of Applied Polymer Science, 2016, 133(48):44344. [17] Nakaramontri Y, Kummerlöwe C, Nakason C, et al. The effect of surface functionalization of carbon nanotubes on properties of natural rubber/carbon nanotube composites. Polymer Composites, 2015, 36(11):2113-2122. [18] Gao J, He Y, Gong X, et al. The role of carbon nanotubes in promoting the properties of carbon black-filled natural rubber/butadiene rubber composites. Results in physics, 2017, 7: 4352-4358. [19] Chen S, Chen J, Xu K, et al. Effect of coal gangue/carbon black/multiwall carbon nanotubes hybrid fillers on the properties of natural rubber composites . Polymer Composites, 2016, 37(10):3083-3092. [20] Basirjafari S, Khadem S E, Malekfar R. Radial breathing mode frequencies of carbon nanotubes for determination of their diameters . Current Applied Physics, 2013, 13(3):599-609. [21] Nakaramontri Y, Nakason C, Kummerlöwe C, et al. Enhancement of electrical conductivity and other related properties of epoxidized natural rubber/carbon nanotube composites by optimizing concentration of 3-aminopropyltyiethoxy silane . Polymer Engineering and Science, 2017, 57(4):381-391. [22] Peng Z, Feng C, Luo Y, et al. Self-assembled natural rubber/multi-walled carbon nanotube composites using latex compounding techniques. Carbon, 2010, 48(15):4497-4503. [23] Hanafi Ismail, Faizal Ramly, Nadras othman. multiwall carbon nanotube-filled natural rubber: the effects of filler loading and mixing Method . Polymer-Plastics Technology and Engineering, 2010, 49(3):260-266. [24] Wang L, Wang X, Li Y. Relation between repeated uniaxial compressive pressure and electrical resistance of carbon nanotube filled silicone rubber composite. Composites Part A Applied Science & Manufacturing, 2012, 43(2):268-274. [25] Zhou X, Zhu Y, Liang J, et al. New fabrication of Styrene-Butadiene Rubber /Carbon nanotubes nanocomposite and corresponding mechanical properties. Journal of Materials Sciences & technology, 2010, 26(12):1127-1132 [26] Verge P, Peeterbroeck S, Bonnaud L, et al. Investigation on the dispersion of carbon nanotubes in nitrile butadiene rubber: Role of polymer-to-filler grafting reaction. Composites Science & Technology, 2010, 70(10):1453-1459.
[27] Zueva O S, Makshakova O N, Idiyatullin B Z, et al. Structure and properties of aqueous dispersions of sodium dodecyl sulfate with carbon nanotubes. Russian Chemical Bulletin, 2016, 65(5):1208-1215. [28] Sinani V A, Gheith M K, Yaroslavov A A, et al. Aqueous dispersions of single-wall and multiwall carbon nanotubes with designed amphiphilic polycations. Journal of the American Chemical Society, 2005, 127(10): 3463-3472. [29] Payne A R, Whittaker R E. Low Strain Dynamic Properties of Filled Rubbers. Rubber Chemistry & Technology, 1971, 44(2):440-478. [30] Wang M J. Effect of Polymer-Filler and Filler-Filler Interactions on Dynamic Properties of Filled Vulcanizates . Rubber Chemistry & Technology, 1998, 71(3):520-589. [31] Lu Y L, Ma J, Xu T-Y, et al. Preparation and properties of natural rubber reinforced with polydopamine-coating modified carbon nanotubes. Express Polymer Letters, 2017, 11(1):21-34. [32] Das A, Stöckelhuber K W, Jurk R, et al. Coupling activity of ionic liquids between diene elastomers and multi-walled carbon nanotubes. Carbon, 2009, 47(14):3313-3321. [33] Lu Z. X. and Ruan X. L. Non-Equilibrium Thermal Transport: A Review of Applications and Simulation Approaches, ES Energy Environment, 2019, 4, 5-14 [34] Datta J, Woch M. Preparation, morphology and properties of natural rubber composites filled with untreated short jute fibres. Polymer Bulletin, 2017, 74(3):763-782 [35] Liu C, Chen M, Yu W, et al. Recent advance on graphene in heat transfer enhancement of composites. ES Energy Environment, 2018, 2: 31-42. [36] Qiu L, Guo P, Zou H, et al. Extremely low thermal conductivity of graphene nanoplatelets using nanoparticle decoration. ES Energy Environment, 2018, 2: 66-72. [37] Zhu D, Huang G, Zhang L, et al. Silver Nanowires Contained Nanofluids with Enhanced Optical Absorption and Thermal Transportation Properties. Energy & Environmental Materials, 2019, 2(1): 22-29. [38] Kim P, Jones S, Hotchkiss P, et al. Phosphonic Acid‐Modified Barium Titanate Polymer Nanocomposites with High Permittivity and Dielectric Strength. Advanced Materials, 2007, 19(7):1001-1005. [39] Gao W, Guo J. A novel processing method namely fast evaporation mixing to prepare fluoroelastomer/montmorillonite composites. Composites Science & Technology, 2017, 139:26-35. [40] Wei J, Qiu J. Allyl-Functionalization enhanced thermally stable graphene/fluoroelastomer nanocomposites. Polymer, 2014, 55(16):3818-3824.
Highlights 1 A novel method (named as slurry blending method) was reported. 2 An uniform dispersion of carbon nanotubes was obtained in natural rubber . 3
The slurry blending method was a new method to improve and
optimize the latex blending method.
Fig.1 The thermal conductivity of CNTs/NR composites (a) and the mechanism of thermal conductivity (b,c).
Conflict of Interest The authors declare no conflict of interest.
Author statement All persons have made substantial contributions to this work in the manuscript. Yan He provided the overall mentality and experiment design. Jiangshan Gao carried on the experiment design, data analysis and article writing. Zhiming Liu carried on the modification of article and data analysis. Zhengqi Yan carried on the instrument operation and data analysis.
S2211-3797(19)32703-2 https://doi.org/10.1016/j.rinp.2019.102720 RINP 102720
To appear in:
Results in Physics
Received Date: Revised Date: Accepted Date:
8 September 2019 2 October 2019 2 October 2019
Please cite this article as: Gao, J-S., Liu, Z., Yan, Z., He, Y., A novel slurry blending method for a uniform dispersion of carbon nanotubes in natural rubber composites, Results in Physics (2019), doi: https://doi.org/10.1016/j.rinp. 2019.102720
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
A novel slurry blending method for a uniform dispersion of carbon nanotubes in natural rubber composites Jiang-Shan Gao, Zhiming Liu, Zhengqi Yan, Yan He* College of Electromechanical Engineering, Shandong Engineering Laboratory for Preparation and Application of High-performance Carbon Materials, Qingdao University of Science and Technology, Qingdao 266061, China Corresponding Author：Yan He Phone：+86 0532-88959067 Fax: +86 053288959488 Email：[email protected] Abstract Carbon nanotubes (CNTs)/natural rubber (NR) composites were prepared by the slurry blending method to get a better dispersion of CNTs in NR composites. The slurry blending method was a new method to improve and optimize the commonly used traditional method (the latex blending method). The treatment of slurry blending for CNTs/NR composites could reduce the agglomeration and settlement of CNTs than that of latex blending process. In order to show the superiority of this method, the morphology, mechanical properties, Payne effect, thermal conductivity, permittivity and dynamic mechanical properties of the composites prepared by the two methods were measured and compared. Compared with latex blending method, the slurry blending method contributed a better dispersion of CNTs in the NR, and the tensile strength of the sample was increased by 15.2%. Meanwhile, the CNTs/NR composites prepared by the slurry method had more stable thermal conductivity, weaker Payne effect and higher permittivity due to the uniform dispersion of CNTs. More importantly, this work further extended the dispersion method of CNTs in the matrix and may shed some light on the design of advanced technology on rubber industry. Keywords：carbon nanotubes, the slurry blending method, dispersion, thermal conductivity, natural rubber. 1. Introduction CNTs have attracted numerous attentions due to their excellent performances such as high mechanical properties, high thermal conductivity and high electric conductivity [1-3]. Therefore, CNTs have been widely used in catalytic [4-5], electronic devices [6-8], various composite materials [9-12] since the advent of CNTs. In the rubber industry, CNTs were added into the rubber materials in order to further improve the mechanical property, electric conductivity, thermal conductivity and other properties of rubbers [13-18]. Good dispersion of CNTs was the key point to give full play of excellent properties and achieve a desirable reinforcing effect for rubbers, so the blending process of CNTs and rubber was quite important. However, the blending process of CNTs and rubber existing now had critical shortcomings. A large aspect ratio of CNTs and a large Vander Waals force between two tubes made CNTs easily be entangled with each other [19,20], and it was difficult to be homogenously dispersed in the matrix, which led to a series of defects in the blending process of CNTs and rubber.
In the previous work, there were five main blending methods intending to obtain a better dispersion of CNTs in the rubber matrix. (1) Mechanical blending method. For example, Nakaramontri and co-authors [21] prepared CNTs/ENR composites by mechanical blending method, and in detail, the CNTs/ENR composites were prepared by mixing in an internal mixer and thereafter in a two-roll mill. (2) Latex blending technology. Peng and co-authors [22] prepared CNTs/NR composites by latex blending method. Acid treated MWCNTs and SDS were dispersed in water and then the above product was dropped into negatively charged latex. Finally, the mixture was dried in the fume chamber and the dried mixture was taken out and ready to be mixed with other rubber additives on a two-roll mill. (3) The solution blending method. Ismail [23] prepared CNTs/NR composites using organic solution blending method. Natural rubber and CNTs were dissolved in two bottles of toluene, respectively. The above two solutions were mixing and the mixture was dried before it was mixed with other rubber additives on a two-roll mill. Wang [24] prepared CNTs/silicone rubber by solution blending method, CNTs were dispersed into liquid silicone rubber matrix to fabricate the composite. (4) Spray drying method. For example, Zhou and co-authors [25] prepared CNTs/SBR composites using spray drying method. A suspension of CNTs in SBR latex was prepared to disperse CNTs in the liquid medium. Then CNTs/SBR composites were prepared by a spray drying process. (5) Melt method. For example, Verge and co-authors [26] prepared CNTs/NBR composites utilizing melt method. NBR, CNTs, and vulcanization agents were mixed simultaneously in a Brabender internal mixer. Then, all the compounds were prepared by stiring at 50 ℃ for 10 min at 60 rpm and were vulcanized at 190 ℃ under 50 bars for 15 min. In these previous studies, CNTs could be partially dispersed in the rubber matrix, however, these traditional methods still had some inevitable drawbacks. The mechanical shear forces could not allow CNTs to be well dispersed in the rubber matrix with the mechanical blending method. For the latex blending method, a large amount of deionized water which was used to disperse CNTs [22] could dilute the latex as well, therefore CNTs tended to settle in the diluted latex and it led to a secondary agglomeration. A large amount of organic solvent was consumed with the solution mixing method and it caused an irreversible environmental pollution. Spray drying process [25] was very complex and hardly implemented. Melt blending was only suitable for certain specific rubber varieties. Thus, an effective and easy method needed to be discovered to get a uniform dispersion of CNTs in rubbers. In the present work, a facile slurry blending method was applied to prepare well dispersed CNTs in NR composites. The method was divided into two steps: First, the preparation of natural rubber slurry allowed CNTs to be uniformly dispersed into the rubber matrix by adding sodium dodecyl sulfate (SDS). Second, the dried rubber was blended with CB and sulfur in the open two-roll mill and then vulcanized. For comparison, CNTs/NR composites were also prepared by latex blending method. Comparing the morphology, mechanical properties, thermal conductivity and other properties of the composites, CNTs in NR prepared by the slurry method were remarkably more uniform than that by latex blending method. 2. Experimental 2.1. Materials Multi wall carbon nanotubes (MWCNTs, GT300, purity>95%, diameter: 5-15 nm, length:0.5-5 μm). Carbon black (CB) N220, natural rubber latex (solid content 62%), antioxidant 4020, stearic acid (SA), zinc oxide (ZnO), sulfur, accelerator NS, sodium dodecyl sulfate (SDS) are commercially available. The formula of the CNTs/NR composite is in Tab.1.
Tab.1 The composition of composites.
a Per b 100
Ingredients
phra
NR Sulfur Zinc oxide Accelerator NS Stearic acid Antioxidant 4020 SDS Carbon black MWCNTs GT-300
100b 3 5 1 2 1 4 40 3
hundred of natural rubber in quality. phr natural rubber means 161.3g natural rubber latex.
2.2. Preparation of CNTs/NR slurry
Fig. 1. Preparation of CNTs/NR slurry. The concrete implementation process of slurry blending method was as shown in Fig. 1. Four kinds of granular rubber ingredients (antioxidant 4020, SDS, accelerator NS, ZnO) were polished into powder by mortar for 5 min in Fig. 1a. And SDS was added into natural rubber latex in the ultrasound instrument and kept being stirred for 15 min (Fig. 1b) Then, the griding ingredients in Fig. 1a and the latex in Fig. 1b were blended with each other to increase the viscosity of latex, as shown in Fig. 1c. Afterwards, 3 g CNTs was divided into twenty copies equally and the one of them was mixed into natural rubber latex and being kept stirred for 2~4 min in Fig. 1d. This procedure was repeated until all the CNTs were mixed into the natural rubber latex in Fig. 1e and the obtained slurry-like composite was as Fig. 1f. At last, the CNTs/NR slurry was dried in the air blowing thermostatic oven at 60 ℃ for 12 h to volatilize water. 2.3. Preparation of CNTs / NR rubber composites
The dried rubber with the CNTs was blended with CB and sulfur in the open two-roll mill and then vulcanized at 150 ℃ for 12 min. For comparison, CNTs/NR composites was also prepared by latex blending method according to Peng [22] with the same composition. 2.4. Measurements In order to observe the dispersion of CNTs in NR composites, TEM was performed on the samples with 50 nm thickness prepared by cryo-ultramicrotomy (Leica, Germany). TEM was performed by using a JEM-2100 electron microscope (JEOL, Japan) with an accelerating voltage of 200 kV. RPA was performed by using an RPA2000 (Alpha Technologies, USA). The test condition was as following: the test configuration was strain-sweep mode in the range of 0.7~70%, the operating temperature was 85 ℃, the operating frequency was 0.1 Hz. The mechanical properties were performed by using an AI-70000M universal testing machine (Gotech, China). And the operating temperature was 25 ℃, the operating speed was 500 mm/min. The thermal conductivity was obtained by using a LFA447 laser flash thermal conductivity analyzer(Netzsch, Germany)with the operating temperature 25 ℃. The diameter and thickness of the round sample were 12.7 mm and 2 mm, respectively. The permittivity was obtained by a Concept 10 permittivity and impedance Analyzers (Novocontrol GmbH, Germany). The operating frequency range and AC Volt were 1×106 Hz~3×109 Hz and 0.1 Vrms, respectively. DMA was performed by a DMAD-29693 (Gaboqualimeter, Germany) and the operating temperature range was -80 ℃ ~80 ℃. 3. Results and discussion 3.1. Morphology
Fig. 2 TEM images of CNTs/NR composites prepared by slurry blending method and latex blending method, (a) slurry blending method, (b) latex blending method. (c) The SEM image of CNTs/NR composites prepared by slurry blending method. The morphologies of the CNTs/NR composites prepared by the slurry method and latex blending method were shown in Fig. 2. As shown in Fig. 2a, CNTs were uniformly dispersed into the rubber matrix in the entire figure and many single CNTs (as indicated by the red arrows) run through the carbon black particles in the composite prepared by the slurry method. The CNTs (indicated by the red arrows) have a uniform distribution in the rubber as shown in Fig. 2c, being consistent with above image (Fig. 2a). In Fig. 2b, some aggregated CNTs were found in the red dotted circle, indicating that the CNTs cannot be dispersed well in the NR matrix by latex blending method. The reasons were as follows: Firstly, SDS improved the attraction between NR
and CNTs by decreasing the interfacial tension of NR. The alkyl of SDS could adsorb CNTs through the hydrophobic effect [27]. Meanwhile, the sulfate radical of SDS increased the amount of negative charge of CNTs [28], and it led to an enhanced electrostatic repulsive-force among CNTs which had a better dispersion of CNTs in the rubber latex. Furthermore, the additives (except CB, CNTs and sulfate) provided a suitable viscosity of NR latex and the NR latex turned to be a density paste with a low interfacial tension. At this point, a proper amount of CNTs were added into NR and kept being stirred and the fluidity was weakened with the increase of the viscosity of the mixing latex. Hence, the position of CNTs was fixed after they were blended into the mixing latex and the secondary agglomeration was also avoided. 3.2. The Payne effect
Fig. 3 Payne effect of CNTs/NR composites prepared by latex blending method and slurry method. The Payne effect of CNTs/NR composites prepared by latex blending method and slurry method was shown in Fig. 3. "Payne effect" referred to the phenomenon that the storage modulus (G') of rubber composites decreased with the increase of strain in a certain range, and it could represent the degree of agglomeration of the filler [29]. This non-linear behavior of filled rubber appeared at small strain range (below 100%), so it was accepted by most researchers that the breakdown of network formed by filler agglomerates was the main reason for "Payne effect" [30]. In practical application, "Payne effect" could be quantified by the specific value ∆G' (the difference between initial G' and final G'). The smaller value of ∆G', the weaker interaction between filler and filler, and the better dispersion of the fillers [31]. Fig. 3 showed that slurry blending method and latex blending method had different ∆G', the ∆G' value of slurry method and latex blending method are 255.53 and 287.18, respectively. Thus, the RPA results showed that a lower aggregation level of nanofillers for the composites produced by
slurry method than those by latex blending method, suggesting that the slurry method enabled the CNTs to be well dispersed into the rubber matrix compared to latex blending method. 3.3. Mechanical properties
Fig. 4 The mechanical properties of CNTs/NR composites. (a) tensile strength; (b) tear strength. Five dumbbell samples and three right angle samples were obtained for the mechanical properties testing. The mechanical properties of CNTs/NR composites were shown in Fig.4. The tensile strengths of the samples generated by latex blending method possessed a relatively large fluctuation, and the average tensile strength and tear strength of the CNTs/NR composites were 20.603 MPa and 68.283 KN·m-1 respectively. The fluctuation for tensile strengths of the samples prepared by slurry method were relatively small, the average tensile strength and tear strength of the CNTs/NR composites were 23.740 MPa and 71.865 KN·m-1, respectively. In comparison with the CNTs/NR composites generated by two methods, tensile strengths and tear strengths of the samples prepared by slurry method were increased by 15.2% and 5.2%, respectively. As shown in Fig. 4(a), the tensile strengths of CNTs/NR composites samples prepared by latex blending method revealed a relatively large fluctuation, and the tensile strength of the slurry method sample was almost stable. It was due to a better CNTs dispersion from slurry mixing. Slurry blending method enabled the CNTs to be uniformly dispersed in the rubber matrix so that CNTs could play a superior reinforcement performance. However, CNTs were agglomerated during the mixing process with natural rubber latex with latex blending method. Actually, the aggregates with poor dispersion in the rubber led to a poor compatibility of CNTs and rubber matrix [32,33]. Meanwhile, the agglomerations became the defects of the materials, which limit the mechanical properties of the CNTs/NR composites [34].
3.4. Thermal conductivity
Fig. 5 The thermal conductivity of CNTs/NR composites (a) and the mechanism of thermal conductivity (b,c). The thermal conductivity of the CNTs/NR composites prepared by slurry blending method and latex blending method was tested to show the uniformity of CNTs in NR by evaluating numerical stability. The results were plotted and shown in Fig. 5(a). The thermal conductivity of samples prepared by slurry method was relatively stable. As we know, composites exhibit stable properties due to its uniform dispersion as shown in Fig. 5(b). CNTs were uniformly dispersed into the rubber matrix and single CNTs run through the carbon black particles to be “the bridges” of CB particles [15] in the composite prepared by the slurry method. In contrast, the thermal conductivity of the samples prepared by latex blending method possessed a larger fluctuation. This was due to CNTs aggregations in the composite as shown in Fig. 5(c). And a sample with many CNTs could get a high thermal conductivity because of the ultrahigh thermal conductivity of CNTs. Hence, CNTs aggregations in NR resulted in a high thermal conductivity and a low thermal conductivity resulted from CNTs without aggregations. Therefore, the samples prepared by latex blending method had an inhomogeneous distribution of thermal conductivity [35-37]. Thus, in comparison with the thermal conductivity of the samples prepared by slurry method and latex blending method, it is indirectly proved that CNTs were homogeneously dispersed in the rubber matrix by the slurry method.
3.5. Permittivity
Fig. 6 The permittivity of CNTs/NR composites under different frequency. (a) 1.0022×107 Hz; (b) 2.0030×107 Hz. Fig. 6 showed the effect of different blending methods on the permittivity of CNTs/NR composites. Fig. 6a and 6b showed that the average (AVG) of permittivity of CNTs/NR composites prepared by slurry method is higher than that prepared by latex blending method under different frequency. When the frequency were 1.0022×107 Hz and 2.0030×107 Hz, the average of the permittivity of samples processed by slurry method were increased by 39.4% and 44.2% than that of samples processed by slurry method, respectively. It was resulting from the better CNTs dispersion by slurry mixing. The reunion of the filler had a significant effect on the electrical properties of the composite, so the dispersion of the filler was an essential factor to improving the dielectric properties. Meanwhile, the good dispersion of the filler was beneficial to increasing the permittivity of the composites [38]. Hence, CNTs/NR composites prepared by slurry method had a higher permittivity because of the good dispersion of CNTs in NR. 3.6. Dynamic mechanical properties
(a)
(b)
Fig. 7 Dynamic mechanical properties of CNTs/NR composites (a) tan δ, (b) storage modulus (E'). The dynamic mechanical properties of CNTs/NR composites prepared by two methods were shown in Fig.7. Compared with latex blending method, the CNTs/NR composites prepared by slurry method showed higher tanδmax in Fig.7a. CNTs and rubber macromolecules formed a good
combination due to the CNTs with better dispersion in the rubber matrix, which allowed CNTs to inhibit the movement of the rubber molecular chains [39], leading to the increment of tanδmax. In addition, the storage modulus (E') of the CNTs/NR composites prepared by slurry method was slightly lower than that prepared by latex blending method in Fig.7b. It was also due to the movement of rubber molecular chains was inhibited, which temporarily reduced the crosslinking density and storage capacity of rubber [40]. In conclusion, in comparison with the dynamic mechanical properties of CNTs/NR composites prepared by two methods, CNTs had a better dispersion and a stronger binding force with NR by the slurry method. 4. Conclusions CNTs/NR composites were prepared by slurry method and latex blending method and slurry method enable CNTs to disperse more uniformly in the NR according to a series of measurements. The mechanism of uniform dispersion of CNTs is as follows. Firstly, SDS improved the attraction between NR and CNTs by decreasing the interfacial tension of NR and it led to an enhanced electrostatic repulsive-force among CNTs which had a better dispersion of CNTs in the rubber latex. Secondly, the mashed additives increased the viscosity of NR latex that turned to be a paste with a low interfacial tension. Hence, the position of CNTs was fixed after blended into the NR and the secondary agglomeration was also avoided. Therefore, uniform dispersion of CNTs resulted in excellent performances of CNTs/NR composites by the slurry blending method. Acknowledgments This work was supported by National Natural Science Foundation of China (No. 51676103) and Taishan Scholar Foundation of Shandong Province. References [1] Du M R, Jing H W, Duan W H,et al. Methylcellulose stabilized multi-walled carbon nanotubes dispersion for sustainable cement composites .Construction and Building Materials,2017,146:76-85. [2] Mei H, Xia J, Zhang D, et al. Highly conductive and high-strength carbon nanotube film reinforced silicon carbide composites . Ceramics International, 2017, 43(12):8873-8878. [3] Seong M,Jeong C,Yi H,et al. Adhesion of bioinspired nanocomposite microstructure at high temperatures .Applied Surface Science, 2017,413:275-283. [4] Xiao J, Pan X, Zhang F, et al. Size-dependence of carbon nanotube confinement in catalysis. Chemical Science, 2017, 8:278-283. [5] Tavares I S, Figueiredo C F B R, Magalhaes A L. The inner cavity of a carbon nanotube as a chemical Reactor: The effect of geometry on the catalysis of a menshutkin SN2 reaction, 2017, 121:2165-2172. [6] Zhang Y, Li K, Ji P, et al. Silicon-multi-walled carbon nanotubes-carbon microspherical composite as high-performance anode for lithium-ion batteries. Journal of Materials Science, 2017, 52:3630-3641. [7] Tang H, Huang K, Bao Y, et al. Rationally designed layer-by-layer structure of Fe3O4, Nanospheres@MWCNTs/Graphene as electrode for lithium ion batteries with enhanced electrochemical performance . Journal of Alloys & Compounds, 2017, 699:812-817 [8] Zeng Q,Tian H,Jiang J, et al. High-purity helical carbon nanotubes with enhanced electrochemical properties for supercapacitors. Rsc Advances, 2017, 12(7):7375-7381 [9] Han J J, Su D, Zhao Z H, et al. Fabrication and toughening behavior of carbon nanotube (CNT) scaffold reinforced SiBCN ceramic composites with high CNT loading. Ceramics International, 2017, 43(12):9024-9031.
[10] Song X, Wang L, Mao L, et al. Nanocomposite membrane with different carbon nanotubes location for nanofiltration and forward osmosis applications. Acs Sustainable Chemistry & Engineering, 2016, 4(6):2990-2997. [11] Kaseem M, Hamad K, Ko Y G. Fabrication and materials properties of polystyrene/carbon nanotube (PS/CNT) composites: A review. European Polymer Journal, 2016, 79:36-62. [12] Wang B, Zhou G, Wang L, et al. Preparation and properties of hierarchical composites based on carbon nanotubes-coated glass babric preform . Polymer Composites, 2016, 37(4):979-986. [13] Kumar V, Lee D. Studies of nanocomposites based on carbon nanomaterials and RTV silicone rubber. Journal of Applied Polymer Science, 2017, 134(4):44407. [14] Lu Y, Liu J, Hou G, et al. From nano to giant? Designing carbon nanotubes for rubber reinforcement and their applications for high performance tires. Composites Science & Technology, 2016, 137:94-101. [15] Gao J, He Y, Gong X . Effect of electric field induced alignment and dispersion of functionalized carbon nanotubes on properties of natural rubber. Results in Physics, 2018, 9:493-499. [16] Mat Desa M S Z, Hassan A, Arsad A, et al. Influence of rubber content on mechanical, thermal, and morphological behavior of natural rubber toughened poly(lactic acid)-multiwalled carbon nanotube nanocomposites . Journal of Applied Polymer Science, 2016, 133(48):44344. [17] Nakaramontri Y, Kummerlöwe C, Nakason C, et al. The effect of surface functionalization of carbon nanotubes on properties of natural rubber/carbon nanotube composites. Polymer Composites, 2015, 36(11):2113-2122. [18] Gao J, He Y, Gong X, et al. The role of carbon nanotubes in promoting the properties of carbon black-filled natural rubber/butadiene rubber composites. Results in physics, 2017, 7: 4352-4358. [19] Chen S, Chen J, Xu K, et al. Effect of coal gangue/carbon black/multiwall carbon nanotubes hybrid fillers on the properties of natural rubber composites . Polymer Composites, 2016, 37(10):3083-3092. [20] Basirjafari S, Khadem S E, Malekfar R. Radial breathing mode frequencies of carbon nanotubes for determination of their diameters . Current Applied Physics, 2013, 13(3):599-609. [21] Nakaramontri Y, Nakason C, Kummerlöwe C, et al. Enhancement of electrical conductivity and other related properties of epoxidized natural rubber/carbon nanotube composites by optimizing concentration of 3-aminopropyltyiethoxy silane . Polymer Engineering and Science, 2017, 57(4):381-391. [22] Peng Z, Feng C, Luo Y, et al. Self-assembled natural rubber/multi-walled carbon nanotube composites using latex compounding techniques. Carbon, 2010, 48(15):4497-4503. [23] Hanafi Ismail, Faizal Ramly, Nadras othman. multiwall carbon nanotube-filled natural rubber: the effects of filler loading and mixing Method . Polymer-Plastics Technology and Engineering, 2010, 49(3):260-266. [24] Wang L, Wang X, Li Y. Relation between repeated uniaxial compressive pressure and electrical resistance of carbon nanotube filled silicone rubber composite. Composites Part A Applied Science & Manufacturing, 2012, 43(2):268-274. [25] Zhou X, Zhu Y, Liang J, et al. New fabrication of Styrene-Butadiene Rubber /Carbon nanotubes nanocomposite and corresponding mechanical properties. Journal of Materials Sciences & technology, 2010, 26(12):1127-1132 [26] Verge P, Peeterbroeck S, Bonnaud L, et al. Investigation on the dispersion of carbon nanotubes in nitrile butadiene rubber: Role of polymer-to-filler grafting reaction. Composites Science & Technology, 2010, 70(10):1453-1459.
[27] Zueva O S, Makshakova O N, Idiyatullin B Z, et al. Structure and properties of aqueous dispersions of sodium dodecyl sulfate with carbon nanotubes. Russian Chemical Bulletin, 2016, 65(5):1208-1215. [28] Sinani V A, Gheith M K, Yaroslavov A A, et al. Aqueous dispersions of single-wall and multiwall carbon nanotubes with designed amphiphilic polycations. Journal of the American Chemical Society, 2005, 127(10): 3463-3472. [29] Payne A R, Whittaker R E. Low Strain Dynamic Properties of Filled Rubbers. Rubber Chemistry & Technology, 1971, 44(2):440-478. [30] Wang M J. Effect of Polymer-Filler and Filler-Filler Interactions on Dynamic Properties of Filled Vulcanizates . Rubber Chemistry & Technology, 1998, 71(3):520-589. [31] Lu Y L, Ma J, Xu T-Y, et al. Preparation and properties of natural rubber reinforced with polydopamine-coating modified carbon nanotubes. Express Polymer Letters, 2017, 11(1):21-34. [32] Das A, Stöckelhuber K W, Jurk R, et al. Coupling activity of ionic liquids between diene elastomers and multi-walled carbon nanotubes. Carbon, 2009, 47(14):3313-3321. [33] Lu Z. X. and Ruan X. L. Non-Equilibrium Thermal Transport: A Review of Applications and Simulation Approaches, ES Energy Environment, 2019, 4, 5-14 [34] Datta J, Woch M. Preparation, morphology and properties of natural rubber composites filled with untreated short jute fibres. Polymer Bulletin, 2017, 74(3):763-782 [35] Liu C, Chen M, Yu W, et al. Recent advance on graphene in heat transfer enhancement of composites. ES Energy Environment, 2018, 2: 31-42. [36] Qiu L, Guo P, Zou H, et al. Extremely low thermal conductivity of graphene nanoplatelets using nanoparticle decoration. ES Energy Environment, 2018, 2: 66-72. [37] Zhu D, Huang G, Zhang L, et al. Silver Nanowires Contained Nanofluids with Enhanced Optical Absorption and Thermal Transportation Properties. Energy & Environmental Materials, 2019, 2(1): 22-29. [38] Kim P, Jones S, Hotchkiss P, et al. Phosphonic Acid‐Modified Barium Titanate Polymer Nanocomposites with High Permittivity and Dielectric Strength. Advanced Materials, 2007, 19(7):1001-1005. [39] Gao W, Guo J. A novel processing method namely fast evaporation mixing to prepare fluoroelastomer/montmorillonite composites. Composites Science & Technology, 2017, 139:26-35. [40] Wei J, Qiu J. Allyl-Functionalization enhanced thermally stable graphene/fluoroelastomer nanocomposites. Polymer, 2014, 55(16):3818-3824.
Highlights 1 A novel method (named as slurry blending method) was reported. 2 An uniform dispersion of carbon nanotubes was obtained in natural rubber . 3
The slurry blending method was a new method to improve and
optimize the latex blending method.
Fig.1 The thermal conductivity of CNTs/NR composites (a) and the mechanism of thermal conductivity (b,c).
Conflict of Interest The authors declare no conflict of interest.
Author statement All persons have made substantial contributions to this work in the manuscript. Yan He provided the overall mentality and experiment design. Jiangshan Gao carried on the experiment design, data analysis and article writing. Zhiming Liu carried on the modification of article and data analysis. Zhengqi Yan carried on the instrument operation and data analysis.