- Email: [email protected]
butadiene-acrylonitrile rubber (NBR) blends: Filling-polymer network and supernanosphere
Polymer xxx (xxxx) xxx
Contents lists available at ScienceDirect
Polymer journal homepage: http://www.elsevier.com/locate/polymer
Novel reinforcement behavior in nanofilled natural rubber (NR) / butadiene-acrylonitrile rubber (NBR) blends: Filling-polymer network and supernanosphere Tinghui Han a, b, 1, Selvaraj Nagarajan b, 1, Hongying Zhao c, Chong Sun a, b, *, Shipeng Wen a, Suhe Zhao a, Shugao Zhao b, Liqun Zhang a a
Beijing Engineering Research Center of Advanced Elastomers, Beijing University of Chemical Technology, Beijing, 100029, People’s Republic of China Key Laboratory of Rubber-Plastics, Ministry of Education/Shandong Provincial Key Laboratory of Rubber-plastics, Qingdao University of Science & Technology, Qingdao, 266042, People’s Republic of China c Institute of Polymer Materials and Plastics Engineering, Clausthal University of Technology, Clausthal-Zellerfeld, 38678, Germany b
A R T I C L E I N F O
A B S T R A C T
Keywords: Reinforcement Rubber blend Filling-polymer network Supernanosphere Carbon black
It is worthy to understand the reinforcement of nanoparticle in rubber blends in application prospect because of its dispersion and distribution. The dielectric and mechanical methods were used to study the reinforcement impact of the carbon black (CB) in NR/NBR blends, based on the percolation and reinforcement theories. Results indicated that the CB aggregates had dispersed in NBR phase and the reinforcement effect was dependent on both CB concentration and the rubber blend ratio. It has been observed that the CB particles diffused and filling in the NBR reinforcement network at 50:50 ratio of NR/NBR blend, CB particles assembled as supernanosphere at 70:30 ratio and CB particles wrapped/covered supernanosphere at 90:10 ratio. The highest elongation at break was observed in 90:10 ratio of NR/NBR. The new observations are conducive to providing guidelines for producing high mechanical performance and low conductivity percolation threshold elastomers via a maturely industrial method for a wide range of application.
1. Introduction It is widely accepted that the nanoparticles are incorporated into rubber matrixes to improve the mechanical properties of rubber prod ucts [1–5]. It is common to use rubber blends in the industry for the sake of meeting multifunctional requirements of rubber products. The filler dispersion, distribution, filler network and some other factors are very crucial to dominate the mechanical properties of filled rubber blends. The investigation of reinforcement mechanism lasts for a long time [6]. However, most of them focus on the single rubber filled with different kinds of fillers. It is rare to investigate the filled rubber blends system. The hydrodynamic reinforcement was proposed by Einstein [7,8]. However, it is incomplete to make an explanation to reinforcement only with it [9]. At least, the occluded rubber, located inside of filler aggre gates and inducing hydrodynamic reinforcement, leads to much more
improved reinforcement effect [10,11]. The filler-polymer interaction is considered to be one of the important factors, which is in favor of €ritz et al., enhancing the reinforcement effect [12–21]. Maier and Go proposed the variable network density model to elucidate the rein forcement, based on the assumptions that the adsorption/desorption process reaches a balance and that desorption rate is proportional to strain amplitude. The contribution of strong and weak interaction be tween filler and polymer to storage modulus is distinguished in terms of this model [22,23]. The filler network dominates the reinforcement when the filler content exceeds the percolation threshold [24]. Several models have been proposed to discuss the structure of filler network. Kraus et al. proposed the strain-dependent breaking and reforming of interparticle connections in the filler network [25,26]. The Kraus model has developed by Klüppel via proposing the conception of the filler cluster [18]. The glass-bridge model is very popular in filler network
* Corresponding author. Beijing Engineering Research Center of Advanced Elastomers, Beijing University of Chemical Technology, Beijing, 100029, People’s Republic of China E-mail address: [email protected] (C. Sun). 1 These authors contributed equally. https://doi.org/10.1016/j.polymer.2019.122005 Received 20 September 2019; Received in revised form 29 October 2019; Accepted 14 November 2019 Available online 14 November 2019 0032-3861/© 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Tinghui Han, Polymer, https://doi.org/10.1016/j.polymer.2019.122005
T. Han et al.
Polymer xxx (xxxx) xxx
its dependency. The NMR [40,41], DMA (loss factor peak value [42–44], loss modulus peak value [45,46]), FTIR [47], DSC [48,49]and some other methods [50–54]have been used to evaluate the filler distribution behavior in rubber blends. Plenty of factors are considered to influence filler distribution behavior in rubber blends, such as filler-polymer interaction [46], mixing technology [55], the polar of filler and rub ber [42], viscosity [44,56], filler concentration [57] and so on. In this work, The NR and NBR with the similar Mooney viscosity (NR Mooney viscosity is 57, and NBR Mooney viscosity is 54), but remarkably different polarities (The polarity of NBR is stronger than that of NR) were used. The common mixing technology conditions in rubber in dustry have been used to prepare the NR/NBR blends vulcanizates with variation of CB contents at different NR/NBR blend ratios. The inter esting findings are that the carbon black aggregates tend to enter into the NBR phase spontaneously, and the reinforcement behavior depends on both the carbon black content and rubber blend ratio simultaneously.
Table 1 Rubber compounding weight fractions in phr. No.
NR
NBR
ZnO
SA
NS
S
RD
CB(variation)
1 2 3 4 5 6 7
100 90 70 50 30 10 0
0 10 30 50 70 90 100
3 3 3 3 3 3 3
1 1 1 1 1 1 1
1 1 1 1 1 1 1
2 2 2 2 2 2 2
1 1 1 1 1 1 1
0–60 0–60 0–60 0–60 0–60 0–60 0–60
construction. It considered that the neighboring filler aggregates are connected by a glassy polymer layer in this model [27–33]. However, Mujtaba A et al. [34] considered that it is not necessary to form the complete glassy polymer shell on the surface of filler aggregates. In addition, Klüppel M [35] proposed dynamic flocculation model, and the layer-fiber model has also been proposed recently [36–39]. In over all view, there are many reports related to rubber reinforcement. However, some issues remain to be understood and this topic is practically valu able. Therefore, it is still one of the hot issues in scientific research. In the past decades, the discussion of reinforcement behavior for filled rubber blends did not bring to the attention, especially for the polar rubber and nonpolar rubber blends, because of the poor compat ibility. Therefore, the potential advantages of application with this rubber blend have not been clearly revealed. The researches mainly focus on the characterization methods of filler distribution behavior and
2. Experimental section 2.1. Materials All materials were used as received. Natural rubber (NR-SVRCV60), Acrylonitrile - Butadiene rubber (NBR-3305, with acrylonitrile content 33%) and zinc oxide (ZnO), stearic acid (SA), N-tert-butylbenzothiazole2-sulphenamide (NS), sulfur (S) and poly (1,2-dihydro-2,2,4-trimethylquinoline) (RD) were of commercial grade and were supplied by Taicang
Fig. 1. a: TEM images of NR/NBR ¼ 30/70 (CB 20phr), b: NR/NBR ¼ 50/50 (CB 20phr), c: NR/NBR ¼ 70/30 (CB 20phr), d: NR/NBR ¼ 50/50 (CB 40phr). The dark part stands for NBR phase and the bright part stands for NR phase, according to the variation of ratios between NR and NBR in the blends. 2
T. Han et al.
Polymer xxx (xxxx) xxx
Guanlian polymeric Material Co., Ltd., (China). The CB (HAF N330) was provided by Cabot Corporation (America). It has a nitrogen-specific surface area of 77 m2 g-1 [58]. 2.2. Methods The NR and NBR rubbers were mixed in a Banbury-type internal mixer (HAAKE Rheomix OS, Thermo Fisher Scientific, Germany) for 2 min at 60 � C with a rotor speed of 60 rpm. Then ZnO, SA, and RD were added into the mixing chamber, after 1.5 min fixed amount of CB was added slowly into the mixer. In the second step, the rotor speed was decreased to 20 rpm. Then curing package (NS and S) was introduced into the blender and mixed for 2 min. Later the mixtures were dis charged from the internal mixing chamber. The discharged compound was mixed in two-roll open mill at room temperature. The friction ratio of the rolling mill was 1:1.4 during the mixing tenure. After the mixing process, the stocks were cured under pressure at 160 � C to the optimum cure in respect to the tc90 vulcanization time determined with a moving die rheometer (RHEOMETER MDR 2000, ALPHA Technologies, Amer ica) [55]. The rubber compounding ratios are summarized in Table 1, where ‘phr’ stands for (weight) parts per hundred concerning with rubber.
Fig. 2. Relationship between critical strain from Kraus equation and NR con tent in NR/NBR blend. The code CB 10 to CB 60 indicating the composition of CB varied from 10 to 60 phr.
2.3. Instruments
NR/NBR blend at 30/70, the morphology shows the CB aggregates dispersed in the NBR domains and it forms a “Filling-Polymer Network” structure (Fig. 1 a). The decreasing concentration of the NBR in blend leads to CB particles aggregate in the limited NBR domain. So the CB aggregates densely packed in the NBR domain in Fig. 1(b and c) and it forms a “Nanosphere” structure made up of NBR and CB aggregates, which is in the nano-scale (dozens of hundreds of nanometers) at least one dimension, as circled in Fig. 1(c). At the same time, increasing concentration of the CB in Fig. 1(d) results in denser aggregates CB particle in the NBR phase, and the size of NBR phase in rubber blend filled 40phr CB is smaller than that of NBR phase in rubber blend filled with 20phr CB (Fig. 1 b). It arises from the larger shearing force during mixing for 40phr CB filled rubber blends. Therefore, the NBR phase containing much more CB is destroyed seriously. Meanwhile, the CB aggregates distribution of filled NBR phase increases concerning CB content.
The ultrathin sections of the Rubber compound were cut by ultra microtome (LEICA EM FC7, Germany) at 100 � C and the Transmission Electron Microscopy (TEM) images were taken by JEM 2100 (JEOL, Japan) with an acceleration voltage of 200 kV. TEM energy dispersive Xray spectroscopy (EDS) analysis was performed using an atomic reso lution microscope (JEM-AEM200F; JEOL Ltd, Japan.) equipped with an EDS system operation at 200 kV. Dynamic mechanical analysis (DMA) was carried out on an Eplexor 500N dynamic measurement system (GABO Qualimeter, Germany) in tension mode. The temperature sweeps were in the range from 90 to 120 � C with a heating rate of 2K/min under liquid nitrogen flow, using a constant frequency of 10 Hz. For the complex modulus E* measurement, a static load of 2% pre-strain was applied, then the samples oscillated to a dynamic load of 0.2% strain. The strain sweeps were conducted with Eplexor 500N dynamic mea surement system in tension mode. A pre-strain of magnitude 30% was selected to keep the sample straightly, and the dynamic amplitudes increased from 0.1% to 20% at 1 Hz frequency and room temperature. The dielectric measurements were performed with a broadband dielec tric spectrometer, BDS 40 system, manufactured by Novocontrol GmbH Germany, providing a bandwidth from 0.1 Hz to 10 MHz. Thin platinum layers were sputtered onto the flat surfaces of the samples to ensure electrical contact to the electrode plates. The measurement geometry was a disk-shaped plate capacitor of 20 mm in diameter. The specimen, whose thickness was about 2 mm, was set between two gold-plated brace electrodes. The real and imaginary parts of the conductivity were obtained in this measurement. Uniaxial tensile-tests were carried out by using dumbbell samples (about 2 mm in thickness), with a ma terial testing machine (Zwick/Roell Z005, Germany) at a crosshead speed of 200 mm/min (ISO 527) and room temperature.
3.2. Filler network percolation behavior It is well known that the Payne effect is one of the most important behaviors in the filled elastomers. It attributed to the filler dispersion and aggregation state, filler content, specific surface area and temper ature [18]. However, there are some controversial arguments in the research sociality [22,23,25–28,34,36]. Kraus explained the Payne ef fect to some degree by means of proposing a strain-dependent breaking and reforming of inter-particle connection model in the filler network [26,62]. � �.� 1 þ ðγ=γc Þ2m (1) G’ ðγÞ ¼ G’∞ þ G’0 G’∞ where G’∞ -the storage modulus at high strain amplitude, G’0 -the storage modulus at low strain amplitude. G’ ðγÞ-the storage modulus at random strain, γ-strain, and all the parameters are from strain sweep. The “γc” denotes the critical strain for filler network damage and “m”is the dimension coefficient of filler network. Both “γc” and “m” are from the fitting of equation (1). The γc decreases obviously when CB content is 40phr in pure NBR. The critical strain from Kraus equation and NR content in NR/NBR blend with the different composition of the CB were plotted in Fig. 2. Based on the CB and NR concentration, the critical strain changes randomly at CB10, CB20 and CB30. At this low concen tration of the CB, it is difficult to form filler network and filler dispersion
3. Results and discussion 3.1. Carbon black distribution The TEM images of CB dispersion in different NR/NBR blends were given in Fig. 1. The bright surface area of TEM image is from NR and the dark surface is coming from NBR. It is very clear that the CB is mostly distributed in the NBR phase in all NR/NBR composition (30/70, 50/50 – N group in the acrylonitrile unit have and 70/30). The polarity of the C– – better interaction with the CB so the carbon black aggregates are attracted towards NBR domains in NR/NBR blends [59–61]. When the 3
T. Han et al.
Polymer xxx (xxxx) xxx
21
CB10 CB20 CB30 CB40 CB50 CB60
18
Reinforcement
15 12
A
B
9 6 3 0
0
20
40 60 NR content/phr
80
100
Fig. 3. Relationship between percolation threshold from percolation theory and NR content in NR/NBR blend.
Fig. 4. Relationship between Reinforcement factor and NR content in rub ber blends.
is in discontinues phase on the NBR rubber, when the NBR content is not much enough, so the random γc pattern was observed in Fig. 2. Increasing CB (CB40, CB50 and CB60) possibly dispersed in the continuous NBR phase due to this continues phase, and increasing NR concentration decreases the critical strain up to NBR50 in A-region. This is due to that the filler content in the NBR phase is higher than that in the NR phase, and the CB aggregates packed density in NBR phase increases with decrease of NBR content in rubber blends, so increasing CB content and NR content enhance the filler network in the form of so-called “Filling-Polymer Network”. It reduces the critical strain value in the rubber blend. When the NBR is less than 50phr, the CB dispersed in confined phase, and within this, the CB distribution is denser. The CB is easy to disperse into the NBR phase spontaneously. Increasing NR con tent results highly packed CB in the NBR region. The lower densely packed CB and NBR concentration, the much more difficult to break, comparing to high densely packed region and NBR concentration, so the critical strain is increased in C-region. In this case, both the NBR and CB aggregates, inside in NBR phases, form “Super nanoparticles”, whose sizes are around hundreds of nanometers, even up to micro-scale when CB content is 20phr and the NR/NBR ¼ 70/30 in Fig. 1 (c). Nevertheless, the filled-phase size will decrease with increase of CB content, according to the morphology evolution from Fig. 1 (b) to Fig. 1 (d). On the other hand, it is reasonable to consider that the nano-scale and micro-scale filling-polymer structure will co-exist in the overall system. This kind of super-nanoparticles is much more difficult to be disintegrated. As a result, the γc increases again in the Fig. 1 (c) zone. The B zone in Fig. 2 is the transition area for NBR from continuous phase to dispersion phase. It is controlled by both rubber blend ratio and filler content. The relationship between conductivity, arising from dielectric relaxation spectrum, and filler volume content has been successfully used to evaluate the filler network behavior, combined with the perco lation theory in equation (2) [22,63]. In which, σdc -direct current con ductivity, σ ∞ -infinite conductivity, μ-critical exponent,φ -volume content of carbon black, φc - critical volume content of carbon black forming conductivity filler network. The value of σdc is from dielectric measurement and the values of σ∞ , φc and μ are from the fitting of equation (2) (percolation theory). � �μ ðφ φc Þ σdc ¼ σ∞ � (2) ð1 φc Þ
G’unfilled
G’filled
¼ 1 þ 2:5 � φ þ a � φ2
(3)
the increase of CB relative content in NBR phase. The NBR phase turns to be narrow and finally broken into dispersed phase with increase of NR content. Even if the NBR phase is broken and leads to small distance between neighboring CB clusters, the percolation threshold value further decreases, as long as the electron can jump from one CB aggre gate to another [64]. Due to the coating effect of NBR on CB, as the NBR phase becomes dispersed phase from continuous phase in Fig. 3 zone B, the percolation threshold value increases. When the NR/NBR blend ratio is in the range of 50/50 to 90/10, the NBR phase becomes dispersed phase from continuous phase in Fig. 3. Nevertheless, the range can narrow to 50/50 to 70/30 compared with the case in Fig. 1. In addition, it is clear that the percolation threshold value of filler network in filled NBR is higher than that in filled NR. It is agreed with the result, arising from the Kraus equation prediction above. The minimum of percolation threshold value is ca. 7% at the NR/NBR ¼ 70/30. 3.3. Reinforcement and loss mechanism analysis It is known that the reinforcement factor is one of the most important parameters in evaluating the reinforcement behavior [65]. In this work, equation (3) is adopted, in which, G0 filled-storage modulus at 0.1% strain for filled sample, G0 -unfilled-storage modulus at 0.1% strain for unfilled sample, φ-vol.% of the fillers and “a” is 14.1 in Guth-Gold equation [66]. However, it is verified that it has been underestimated [35]. It is out of the range of this work and will not influence the subsequent discussion. Therefore, “a” is used instead of the controversial value. The rein forcement effect increases at any rubber blend ratios with increase of CB content. The reinforcement factor increases with decrease of NBR con tent in rubber blends in Fig. 4 (zone A). The relative CB content increases in NBR phase with decrease of its content in rubber blends. It leads to an enhanced reinforcement effect. The reinforcement effect is the best at the NR/NBR ¼ 50/50 at any CB contents. In this case, there are dual-continuous “rubber phase networks” and the “filling-polymer network”, which improves the reinforcement effect. As descripted in Fig. 2, both the NBR and CB aggregates, which are inside in NBR phases, form “super nanoparticles” in Fig. 4 (B zone), because of the evolution of NBR phase from continuous phase to dispersed phase. The reinforcement effect is higher to the CB aggregates and smaller region appeared in filled-polymer network. In addition, the
The percolation threshold as a function of NR content in rubber blend is presented in Fig. 3. The percolation threshold value decreases with increase of NR content in rubber blends in Fig. 3 zone A. It is because of 4
T. Han et al. 1000
(a)
Polymer xxx (xxxx) xxx B
A
800
-EA
600
CB10 CB20 CB30 CB40 CB50 CB60
C' C B
400
B' A
200 0
0
20
40 60 80 NR content (phr)
Fig. 7. Schematic sketch of the reinforcement mechanism model for CB filled rubber blends: (a) Filling-polymer network reinforcement; (b) Filled super nanoparticles reinforcement; (c) Filler Wrapped/Covered super nanoparticles reinforcement.
100
Fig. 5. Relationship between activation energy and NR content in rubber blends with different CB contents (a), as well as the tanδ relative peak value (the ratio between the tanδ peak value for the filled and unfilled samples) related to NBR phase and CB contents at different NR/NBR blend ratios (b). All data derive from temperature-dependent relationship.
is continuous phase when its content is not more than 50phr. The rela tive rubber content decreases in NBR phase with increase of CB contents. It induces the decrease of relative loss factor (tanδ) peak value in Fig. 5 (b) (curve A) [42]. The NBR turns to be dispersed phase when the NR content is up to 70phr in rubber blend (Fig. 1(c)). As for the curve B in Fig. 5(b), it is possible that the CB aggregates located at the interphase between NBR and NR phases induce the isolation effect at the low CB concentration [57]. In this case, the relative loss factor increases with increase of CB content. It is clear that the NBR phase size is larger than that of CB aggregates at NR/NBR ¼ 70/30 (Fig. 1(c)). Hence, more and more CB aggregates enter into the NBR phases with increase of CB content. It decreases the relative rubber content in NBR phase, which dominates the relative loss factor of the system and makes it decreases again (Fig. 5 zone B-B’). When the NR/NBR ¼ 90/10, It is possible that the size of NBR is too small to contain CB aggregates. In this case, the NBR phase will be wrapped or covered by CB aggregates, and it will lead to phase sepa ration. The more CB aggregates, the more severe phase separation. Therefore, the relationship between tan δ relative peak value and CB content is shown as Fig. 5 (b) (zone C to C’). It shows that the effect of CB aggregates on tan δ relative peak value changes, when the CB content is between 30phr and 40phr. It is clear that the NBR phase size is reduced to “hundred” to “ten” nm, when the NR phase content is 90phr in NR/NBR blend. In Fig. 6(a) and (b), it shows better clarity about the morphology change from Fig. 1 (b)–(d). The NBR phase size scale is comparable with (or even smaller than) that of CB aggregates. Therefore, it is easy to be wrapped (or covered) by CB aggregates, and leads to phase separation. It confirms the discussion about Fig. 5 (b) (zone C to C’). The more CB content, the more severe phase separation. The amplification of phase separation degree decreases with increase of CB content when the CB concentration rea ches to 40phr. Based on the results of Figs. 1 and 6 the schematic sketch
filling-polymer network forms as the NR/NBR blend ratio is between 50/ 50 and 70/30, compared the Fig. 3 with Fig. 4. The activation energy is an efficient parameter to indirectly show the CB aggregates average distance. It can be calculated by means of Arrhenius equation [22]. The activation energy increases with increase of CB content at the constant NR/NBR blend ratio in Fig. 5 (a). The NBR content is much more than NR content in Fig. 5 (a) (A zone). It domi nates the EA of the system. The relative CB content in NBR phase in creases with decrease of NBR content in rubber blends. It induces that the decrease of the average distance among the neighboring CB aggre gates results in the increase of EA. As the description for Fig. 4 (B zone), the super-nanoparticle is formed by NBR phase and CB aggregates in Fig. 5 a (B zone). The supernanoparticle average distance decreases with decrease of NBR content in rubber blends. Therefore, the EA decreases with decreases of NBR content in this zone. In addition, it is clear that the CB dispersion in filled single NBR is better than that in filled single NR, according to the comparison of the EA for these two filled single rubber systems. It is accordance with the result in Fig. 3. It is well known that the tanδ peak value is obviously influ enced by incorporating fillers because of the decrease of rubber content with increase of fillers [42]. Meanwhile, the absolute value of tanδ is also affected by the structure of rubber matrix. Therefore, the relative peak value of tanδ is adopted to investigate the contribution of filler to the loss property. Furthermore, the NBR phase is in glassy state when the NR phase undergoes the glass transition process. The NBR phase is filler-like at low temperature. It is unquestionable that the result will be misunderstood if the tanδ peak value of NR is used. Hence, we adopt the relative peak value of NBR phase as the object in rubber blends. The NBR
Big
Small
(a)
Smaller
(b)
(c)
Fig. 6. STEM mapping images for NR/NBR ¼ 90/10 filled with 20phr CB. (a): STEM image, the bright parts are CBs and the dark parts are NR/NBR; (b) and (c) are carbon element and nitrogen element distribution images, respectively, the bright parts stand for relatively high carbon element and nitrogen contents, and the dark parts stand for relatively low carbon element and nitrogen contents. It is considered that the nitrogen element dispersion stands for NBR phase dispersion. 5
T. Han et al. 35
Polymer xxx (xxxx) xxx 30
a)
30
10 5 0
30
400
%
600
(MPa)
NR0 NR10 NR30 NR50 NR70 NR90 NR100
15 10 5 0
5 0
0
200
d)
20phr 40phr 60phr
12
CB 60phr
20
0
10
15
c)
NR0 NR10 NR30 NR50 NR70 NR90 NR100
15
200
%
400
600
400 20phr 40phr 60phr
600 400
6
200
3 0
20
40 60 NR content (phr)
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
800
9
0
Declaration of competing interest
600
80
100
elongation at break/%
25
200
NR0 NR10 NR30 NR50 NR70 NR90 NR100 800
(MPa)
15
0
CB 40phr
20
20
100% modulus
(MPa)
25 CB 20phr
tuned by means of changing NR/NBR blend ratios and CB concentration. These novel findings offer a unified explanation for reinforcement mechanism in filled elastomers, and may contribute to developing a maturely industrial method to produce high mechanical performance and low conductivity percolation threshold elastomers.
b)
25
Acknowledgement The authors gratefully acknowledge GUAN LIAN Corporation, China, for providing the NR and rubber chemicals for the research work. The work is supported by the National Natural Science Foundation of China (51503114) (51573007),German Academic Exchange Service(DAAD) (57317599) and China Scholarship Council (CSC) (2017 (6052)). We thank Prof. Yonglai Lu for many fruitful discussions.
0
Fig. 8. Relationship between stress-strain behavior and NR content in rubber blends with different CB contents.
of the reinforcement mechanism model was shown in Fig. 7. In Fig. 7, the reinforcement mechanisms depend on rubber blend ratios and CB contents. In NR/NBR blend at 30/70, the “Filling-Polymer Network” structure forms owing to the dual-continuous “rubber phase networks” and the dispersion of CB in NBR phase (Fig. 7 a). As NBR content decreases to the dispersed phase, CB aggregates densely packed in the NBR domain and supernanoparticles form, consisting of NBR and CB aggregates (Fig. 7 b). The low composition of NBR illustrated in Fig. 7 (c) (NR/NBR ¼ 90/10). The NBR phase size scale is comparable with (or even smaller than) that of CB aggregates. It is easy to be wrapped (or covered) by CB aggregates, leading to phase separation.
References [1] S.K. Kumar, N. Jouault, B. Benicewicz, et al., Nanocomposites with polymer grafted nanoparticles, Macromolecules 46 (9) (2013) 3199–3214. [2] M.E. Mackay, A. Tuteja, P.M. Duxbury, et al., General strategies for nanoparticle dispersion, Science 311 (5768) (2006) 1740–1743. [3] D. Zhao, S. Ge, E. Senses, et al., Role of filler shape and connectivity on the viscoelastic behavior in polymer nanocomposites, Macromolecules 48 (15) (2015) 5433–5438. [4] Z. Rigbi, Reinforcement of rubber by carbon black, Rubber Chem. Technol. J. 55 (4) (1982) 1180–1220. [5] S. Merabia, P. Sotta, D.R. Long, A microscopic model for the reinforcement and the nonlinear behavior of filled elastomers and thermoplastic elastomers (Payne and mullins effects), Macromolecules 41 (21) (2008) 8252–8266. [6] S. Dupres, D.R. Long, P.A. Albouy, et al., Local deformation in carbon black-filled polyisoprene rubbers studied by NMR and X-ray diffraction, Macromolecules 42 (7) (2009) 2634–2644. [7] A. Einstein, A new determination of molecular dimensions, Ann. Phys. 19 (1906) 289–306. [8] H.M. Smallwood, Limiting law of the reinforcement of rubber, J. Appl. Phys. 15 (11) (1944) 758–766. [9] A. Mujtaba, M. Keller, S. Ilisch, et al., Mechanical properties and cross-link density of styrene–butadiene model composites containing fillers with bimodal particle size distribution, Macromolecules 45 (45) (2012) 6504–6515. [10] C.G. Robertson, R. Bogoslovov, C.M. Roland, Structural arrest and thermodynamic scaling in filler-reinforced polymers, Rubber Chem. Technol. J. 82 (2) (2009) 202–213. [11] A.I. Medalia, Effective degree of immobilization of rubber occluded within carbon black aggregates, Rubber Chem. Technol. J. 45 (5) (1972) 1171–1194. [12] M. Michelle, M. Tania, B. Guido, et al., A fourier transform infrared (FTIR) study of the reaction of triethoxysilane (TES) and bis[3-triethoxysilylpropyl]tetrasulfane (TESPT) with the surface of amorphous silica, J. Phys. Chem. B 108 (11) (2004) 3563–3572. [13] L. Bokobza, The reinforcement of elastomeric networks by fillers, Macromol. Mater. Eng. 289 (2004) 607–621. [14] M. Castellano, L. Conzatti, A. Turturro, et al., Influence of the silane modifiers on the surface thermodynamic characteristics and dispersion of the silica into elastomer compounds, J. Phys. Chem. B 111 (17) (2007) 4495–4502. [15] J.N. Paquien, J. Galy, J.F. G�erard, et al., Rheological studies of fumed silica–polydimethylsiloxane suspensions, Colloid. Surf. Physicochem. Eng. Asp. 260 (1) (2005) 165–172. [16] F. Cl�ement, L. Bokobza, L. Monnerie, Investigation of the Payne effect and its temperature dependence on silica-filled polydimethylsiloxane networks. Part I: experimental results, Rubber Chem. Technol. J. 78 (2) (2005) 211–231. [17] J. Ramier, C. Gauthier, L. Chazeau, et al., Payne effect in silica-filled styrene–butadiene rubber: influence of surface treatment, J. Polym. Sci. B Polym. Phys. 45 (3) (2006) 286–298. [18] A.P. Meera, S. Said, Y. Grohens, et al., Nonlinear viscoelastic behavior of silicafilled natural rubber nanocomposites, J. Phys. Chem. C 113 (42) (2009) 17997–18002. [19] N. Jouault, F. Dalmas, F. Bou� e, et al., Multiscale characterization of filler dispersion and origins of mechanical reinforcement in model nanocomposites, Polymer 53 (3) (2012) 761–775. [20] B. Zhong, Z. Jia, D. Hu, et al., Enhancing interfacial interaction and mechanical properties of styrene-butadiene rubber composites via silica-supported vulcanization accelerator, Composites Part A Applied Science & Manufacturing 96 (2017) 129–136.
3.4. Stress-strain behavior The elongation at break decreases with increases of CB in Fig. 8(a–c). It is limited to some degree due to CB entering into NBR phase and forming a filling-polymer network. The elongation at break is higher at low NBR concentration in rubber blends, because the so-called “Supernanoparticle”, which is formed by NBR and CB aggregates, possesses the deformable ability. It’s worth noting that the elongation at break is the highest for the NR/NBR ¼ 90/10 system at any CB concentration in Fig. 8(d). It is the result of phase separation between NR and NBR arising from the isolation effect of CB aggregates at their interfaces. The peak value of 100% modulus appears in NR/NBR ¼ 50/50 blend, and it in creases with the increase of CB content (Fig. 8(d)). It indicates the reinforcement effect is very obvious for the filling-polymer network. 4. Conclusions In summary, the CB aggregates tend to entry into NBR phase spon taneously in NR/NBR blends. Increasing composition of NR leads to suppress the NBR from continuous phase to discontinuous phase. In discontinuous phase, increasing CB aggregates are within the confine ment NBR phase. The size of NBR phase decreases with increase of CB content. The conductivity filler network percolation threshold decreases in NR/NBR blends, compared with single rubber composition. The elongation at break in 60phr CB filled NR/NBR ¼ 90/10 is 25% more than that in filled NR with the same CB content. The reinforcement is evidently enhanced in NR/NBR blend. The reinforcement effect of CB aggregates increases in the form of “filled polymer network” when the NBR is continuous phase in rubber blends. The results show that the “filled super-nanoparticles” and “filler wrapped/covered super-nano particles” contribute for the reinforcement, when the NR/NBR blend ratios are 70/30 and 90/10,respectively. All these properties can be 6
T. Han et al.
Polymer xxx (xxxx) xxx [42] C. Sirisinha, N. Prayoonchatphan, Study of carbon black distribution in BR/NBR blends based on damping properties: influences of carbon black particle size, filler, and rubber polarity, J. Appl. Polym. Sci. 81 (13) (2001) 3198–3203. [43] S. Maiti, S.K. De, A.K. Bhowmick, Quantitative estimation of filler distribution in immiscible rubber blends by mechanical damping studies, Rubber Chem. Technol. J. 65 (2) (1992) 293–302. [44] C. Sirisinha, J. Thunyarittikorn, S. Yartpakdee, Study of carbon black distribution in butadiene rubber-nitrile/butadiene rubber blends based on damping properties: effect of some grades of carbon black, Plastics 27 (8) (1998) 373–375. [45] M. Wunde, M. Klüppel, Influence of phase morphology and filler distribution in NR/BR and NR/SBR blends on fracture mechanical properties, Rubber Chem. Technol. J. 89 (4) (2016) 588–607. [46] R.H. Schuster, J. Meier, M. Klüppel, Role of interphase in filler partition in rubber blends, Kautsch. Gummi Kunstst. 53 (11) (2000) 663–674. [47] H.H. Le, K. Oßwald, S. Ilisch, et al., Silica transfer in ternary rubber blends: calculation and experimental determination, Macromol. Mater. Eng. 297 (5) (2012) 464–473. [48] A.K. Sircar, T.G. Lamond, Carbon black transfer in blends of Cis-poly(butadiene) with other elastomers, Rubber Chem. Technol. J. 46 (1) (1973) 178–191. [49] J.M. Massie, R.C. Hirst, A.F. Halasa, Carbon black distribution in NR/ polybutadiene blends, Rubber Chem. Technol. J. 66 (2) (1993) 276–285. [50] V. Herrmann, K. Unseld, H.B. Fuchs, Atomic-force-microscopy for the investigation of inhomogenous polymer-systems, Kautsch. Gummi Kunstst. 54 (9) (2001) 453–457. [51] A.H. Tsou, W.H. Waddell, Morphology of elastomer blends by dynamic AFM, Kautsch. Gummi Kunstst. 55 (7) (2002) 382–387. [52] I.H. Jeon, H. Kim, S.S.G. Kim, Characterization of rubber micro-morphology by atomic force microscopy(AFM), Rubber Chem. Technol. J. 76 (1) (2003) 1–11. [53] C.C. Wang, J.B. Donnet, T.K. Wang, et al., AFM study of rubber compounds, Rubber Chem. Technol. J. 78 (1) (2005) 17–27. [54] G.R. Cotten, L.J. Murphy, Mixing of carbon black with rubber. VI. Analysis of NR/ SBR blends, Rubber Chem. Technol. J. 61 (4) (1988) 609–618. [55] A. Das, K.W. St€ ockelhuber, R. Jurk, et al., Modified and unmodified multiwalled carbon nanotubes in high performance solution-styrene–butadiene and butadiene rubber blends, Polymer 49 (24) (2008) 5276–5283. [56] W.M. Hess, C.E. Scott, J.E. Callan, Carbon black distribution in elastomer blends, Rubber Chem. Technol. J. 40 (2) (1967) 371–384. [57] P. Phewphong, P. Saeoui, C. Sirisinha, The use of dynamic mechanical thermal analysis technique for determining an uneven distribution of precipitated silica in CPE/NR blends, Polym. Test. 27 (7) (2008) 873–880. [58] M. Huang, L.B. Tunnicliffe, J. Zhuang, et al., Strain-dependent dielectric behavior of carbon black reinforced natural rubber, Macromolecules 49 (6) (2016) 2339–2347. [59] W.M. Hess, V.E. Chirico, Elastomer blend properties—influence of carbon black type and location, Rubber Chem. Technol. J. 50 (2) (1977) 301–326. [60] M.H. Walters, D.N. Keyte, Heterogeneous structure in blends of rubber polymers, Rubber Chem. Technol. J. 38 (1) (1965) 62–75. [61] M. Kawazoe, H. Ishida, A new concept for nanoparticle distribution in SBR/NBR blend solution and films via molecular confinement, Macromolecules 41 (8) (2008) 2931–2937. [62] C.S. Boland, U. Khan, G. Ryan, et al., Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites, Science 354 (6317) (2016) 1257. [63] P. Ghosh, A. Chakrabarti, Conducting carbon black filled EPDM vulcanizates: assessment of dependence of physical and mechanical properties and conducting character on variation of filler loading, Eur. Polym. J. 36 (5) (2000) 1043–1054. [64] J. Fritzsche, M. Klüppel, Structural dynamics and interfacial properties of fillerreinforced elastomers, J. Phys. Condens. Matter 23 (3) (2011), 035104. [65] E. Guth, Theory of filler reinforcement, J. Appl. Phys. 16 (1) (1945) 20–25. [66] E. Guth, On the hydrodynamical theory of the viscosity of suspensions, Phys. Rev. 53 (1) (1938) 322.
[21] I. Morabarrantes, A. Rodríguez, L. Ibarra, et al., Overcoming the disadvantages of fumed silica as filler in elastomer composites, J. Mater. Chem. 21 (20) (2011) 7381–7392. [22] C. Sun, P. Zhang, C. Wrana, et al., Combined dielectric and mechanical investigation of filler network percolation behavior, filler-filler contact, and fillerpolymer interaction on carbon black-filled hydrogenated acrylonitrile-butadiene rubber, Rubber Chem. Technol. J. 87 (4) (2014) 647–663. [23] P.G. Maier, D. G€ oritz, Molecular interpretation of the Payne effect, Kautsch. Gummi Kunstst. 49 (1996) 18–21. [24] G.P. Baeza, A.C. Genix, C. Degrandcourt, et al., Multiscale filler structure in simplified industrial nanocomposite silica/SBR systems studied by SAXS and TEM, Macromolecules 46 (1) (2013) 317–329. [25] G. Heinrich, M. Klüppel, Recent advances in the theory of filler networking in elastomers, Adv. Polym. Sci. 160 (2002) 1–44. [26] G. Kraus, Mechanical losses in carbon-black-filled rubbers, Appl. Polym. Symp. 39 (1984) 75–92. [27] M. Tauban, J.Y. Delannoy, P. Sotta, et al., Effect of filler morphology and distribution state on the linear and nonlinear mechanical behavior of nanofilled elastomers, Macromolecules 50 (17) (2017) 6369–6384. [28] D. Long, S. Merabia, P. Sotta, Unique plastic and recovery behaviour of nano-filled elastomers and thermoplastic elastomers, J. Polym. Sci. B Polym. Phys. 48 (13) (2010) 1495–1508. [29] A. Papon, S. Merabia, L. Guy, et al., Unique nonlinear behavior of nano-filled elastomers: from the onset of strain softening to large amplitude shear deformations, Macromolecules 45 (6) (2012) 2891–2904. [30] A.A. Gusev, Micromechanical mechanism of reinforcement and losses in filled rubbers, Macromolecules 39 (18) (2006) 5960–5962. [31] D. Fragiadakis, P. Pissis, L. Bokobza, Modified chain dynamics in poly (dimethylsiloxane)/silica nanocomposites, J. Non-Cryst. Solids 352 (42–49) (2006) 4969–4972. [32] J. Berriot, H. Montes, F. Lequeux, et al., Evidence for the shift of the glass transition near the particles in silica-filled elastomers, Macromolecules 35 (26) (2002) 9756–9762. [33] S. Wu, L. Zhang, P. Weng, et al., Correlating synergistic reinforcement with chain motion in elastomer/nanocarbon hybrids composites, Soft Matter 12 (33) (2016) 6893–6901. [34] A. Mujtaba, M. Keller, S. Ilisch, et al., Detection of surface-immobilized components and their role in viscoelastic reinforcement of rubber–silica nanocomposites[J], ACS Macro Lett. 3 (5) (2014) 481–485. [35] M. Klüppel, The role of disorder in filler reinforcement of elastomers on various length scales, Adv. Polym. Sci. 164 (2003) 1–86, 2003. [36] K.W. St€ ockelhuber, A.S. Svistkov, A.G. Pelevin, et al., Impact of filler surface modification on large scale mechanics of styrene butadiene/silica rubber composites[J], Macromolecules 44 (11) (2011) 4366–4381. [37] P. Sotta, P.A. Albouy, T.M. Abou, et al., Nonentropic reinforcement in elastomer nanocomposites, Macromolecules 50 (16) (2017) 6314–6322. [38] A.A. Gavrilov, A.V. Chertovich, P.G. Khalatur, et al., Study of the mechanisms of filler reinforcement in elastomer nanocomposites, Macromolecules 47 (15) (2014) 5400–5408. [39] Z. Wang, J. Liu, S. Wu, et al., Novel percolation phenomena and mechanism of strengthening elastomers by nanofillers, Phys. Chem. Chem. Phys. PCCP 12 (12) (2010) 3014–3030. [40] K. Marina, D. Hidehiko, K. Hideaki, et al., Characterization of carbon filler distribution ratio in polyisoprene/polybutadiene rubber blends by high-resolution solid-state 13C NMR, Macromolecules 40 (26) (2007) 9451–9454. [41] W. Hu, M.D. Ellul, A.H. Tsou, et al., Filler distribution and domain size of elastomer compounds by solid-state NMR and AFM, Rubber Chem. Technol. J. 80 (1) (2007) 1–13.
7
Contents lists available at ScienceDirect
Polymer journal homepage: http://www.elsevier.com/locate/polymer
Novel reinforcement behavior in nanofilled natural rubber (NR) / butadiene-acrylonitrile rubber (NBR) blends: Filling-polymer network and supernanosphere Tinghui Han a, b, 1, Selvaraj Nagarajan b, 1, Hongying Zhao c, Chong Sun a, b, *, Shipeng Wen a, Suhe Zhao a, Shugao Zhao b, Liqun Zhang a a
Beijing Engineering Research Center of Advanced Elastomers, Beijing University of Chemical Technology, Beijing, 100029, People’s Republic of China Key Laboratory of Rubber-Plastics, Ministry of Education/Shandong Provincial Key Laboratory of Rubber-plastics, Qingdao University of Science & Technology, Qingdao, 266042, People’s Republic of China c Institute of Polymer Materials and Plastics Engineering, Clausthal University of Technology, Clausthal-Zellerfeld, 38678, Germany b
A R T I C L E I N F O
A B S T R A C T
Keywords: Reinforcement Rubber blend Filling-polymer network Supernanosphere Carbon black
It is worthy to understand the reinforcement of nanoparticle in rubber blends in application prospect because of its dispersion and distribution. The dielectric and mechanical methods were used to study the reinforcement impact of the carbon black (CB) in NR/NBR blends, based on the percolation and reinforcement theories. Results indicated that the CB aggregates had dispersed in NBR phase and the reinforcement effect was dependent on both CB concentration and the rubber blend ratio. It has been observed that the CB particles diffused and filling in the NBR reinforcement network at 50:50 ratio of NR/NBR blend, CB particles assembled as supernanosphere at 70:30 ratio and CB particles wrapped/covered supernanosphere at 90:10 ratio. The highest elongation at break was observed in 90:10 ratio of NR/NBR. The new observations are conducive to providing guidelines for producing high mechanical performance and low conductivity percolation threshold elastomers via a maturely industrial method for a wide range of application.
1. Introduction It is widely accepted that the nanoparticles are incorporated into rubber matrixes to improve the mechanical properties of rubber prod ucts [1–5]. It is common to use rubber blends in the industry for the sake of meeting multifunctional requirements of rubber products. The filler dispersion, distribution, filler network and some other factors are very crucial to dominate the mechanical properties of filled rubber blends. The investigation of reinforcement mechanism lasts for a long time [6]. However, most of them focus on the single rubber filled with different kinds of fillers. It is rare to investigate the filled rubber blends system. The hydrodynamic reinforcement was proposed by Einstein [7,8]. However, it is incomplete to make an explanation to reinforcement only with it [9]. At least, the occluded rubber, located inside of filler aggre gates and inducing hydrodynamic reinforcement, leads to much more
improved reinforcement effect [10,11]. The filler-polymer interaction is considered to be one of the important factors, which is in favor of €ritz et al., enhancing the reinforcement effect [12–21]. Maier and Go proposed the variable network density model to elucidate the rein forcement, based on the assumptions that the adsorption/desorption process reaches a balance and that desorption rate is proportional to strain amplitude. The contribution of strong and weak interaction be tween filler and polymer to storage modulus is distinguished in terms of this model [22,23]. The filler network dominates the reinforcement when the filler content exceeds the percolation threshold [24]. Several models have been proposed to discuss the structure of filler network. Kraus et al. proposed the strain-dependent breaking and reforming of interparticle connections in the filler network [25,26]. The Kraus model has developed by Klüppel via proposing the conception of the filler cluster [18]. The glass-bridge model is very popular in filler network
* Corresponding author. Beijing Engineering Research Center of Advanced Elastomers, Beijing University of Chemical Technology, Beijing, 100029, People’s Republic of China E-mail address: [email protected] (C. Sun). 1 These authors contributed equally. https://doi.org/10.1016/j.polymer.2019.122005 Received 20 September 2019; Received in revised form 29 October 2019; Accepted 14 November 2019 Available online 14 November 2019 0032-3861/© 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Tinghui Han, Polymer, https://doi.org/10.1016/j.polymer.2019.122005
T. Han et al.
Polymer xxx (xxxx) xxx
its dependency. The NMR [40,41], DMA (loss factor peak value [42–44], loss modulus peak value [45,46]), FTIR [47], DSC [48,49]and some other methods [50–54]have been used to evaluate the filler distribution behavior in rubber blends. Plenty of factors are considered to influence filler distribution behavior in rubber blends, such as filler-polymer interaction [46], mixing technology [55], the polar of filler and rub ber [42], viscosity [44,56], filler concentration [57] and so on. In this work, The NR and NBR with the similar Mooney viscosity (NR Mooney viscosity is 57, and NBR Mooney viscosity is 54), but remarkably different polarities (The polarity of NBR is stronger than that of NR) were used. The common mixing technology conditions in rubber in dustry have been used to prepare the NR/NBR blends vulcanizates with variation of CB contents at different NR/NBR blend ratios. The inter esting findings are that the carbon black aggregates tend to enter into the NBR phase spontaneously, and the reinforcement behavior depends on both the carbon black content and rubber blend ratio simultaneously.
Table 1 Rubber compounding weight fractions in phr. No.
NR
NBR
ZnO
SA
NS
S
RD
CB(variation)
1 2 3 4 5 6 7
100 90 70 50 30 10 0
0 10 30 50 70 90 100
3 3 3 3 3 3 3
1 1 1 1 1 1 1
1 1 1 1 1 1 1
2 2 2 2 2 2 2
1 1 1 1 1 1 1
0–60 0–60 0–60 0–60 0–60 0–60 0–60
construction. It considered that the neighboring filler aggregates are connected by a glassy polymer layer in this model [27–33]. However, Mujtaba A et al. [34] considered that it is not necessary to form the complete glassy polymer shell on the surface of filler aggregates. In addition, Klüppel M [35] proposed dynamic flocculation model, and the layer-fiber model has also been proposed recently [36–39]. In over all view, there are many reports related to rubber reinforcement. However, some issues remain to be understood and this topic is practically valu able. Therefore, it is still one of the hot issues in scientific research. In the past decades, the discussion of reinforcement behavior for filled rubber blends did not bring to the attention, especially for the polar rubber and nonpolar rubber blends, because of the poor compat ibility. Therefore, the potential advantages of application with this rubber blend have not been clearly revealed. The researches mainly focus on the characterization methods of filler distribution behavior and
2. Experimental section 2.1. Materials All materials were used as received. Natural rubber (NR-SVRCV60), Acrylonitrile - Butadiene rubber (NBR-3305, with acrylonitrile content 33%) and zinc oxide (ZnO), stearic acid (SA), N-tert-butylbenzothiazole2-sulphenamide (NS), sulfur (S) and poly (1,2-dihydro-2,2,4-trimethylquinoline) (RD) were of commercial grade and were supplied by Taicang
Fig. 1. a: TEM images of NR/NBR ¼ 30/70 (CB 20phr), b: NR/NBR ¼ 50/50 (CB 20phr), c: NR/NBR ¼ 70/30 (CB 20phr), d: NR/NBR ¼ 50/50 (CB 40phr). The dark part stands for NBR phase and the bright part stands for NR phase, according to the variation of ratios between NR and NBR in the blends. 2
T. Han et al.
Polymer xxx (xxxx) xxx
Guanlian polymeric Material Co., Ltd., (China). The CB (HAF N330) was provided by Cabot Corporation (America). It has a nitrogen-specific surface area of 77 m2 g-1 [58]. 2.2. Methods The NR and NBR rubbers were mixed in a Banbury-type internal mixer (HAAKE Rheomix OS, Thermo Fisher Scientific, Germany) for 2 min at 60 � C with a rotor speed of 60 rpm. Then ZnO, SA, and RD were added into the mixing chamber, after 1.5 min fixed amount of CB was added slowly into the mixer. In the second step, the rotor speed was decreased to 20 rpm. Then curing package (NS and S) was introduced into the blender and mixed for 2 min. Later the mixtures were dis charged from the internal mixing chamber. The discharged compound was mixed in two-roll open mill at room temperature. The friction ratio of the rolling mill was 1:1.4 during the mixing tenure. After the mixing process, the stocks were cured under pressure at 160 � C to the optimum cure in respect to the tc90 vulcanization time determined with a moving die rheometer (RHEOMETER MDR 2000, ALPHA Technologies, Amer ica) [55]. The rubber compounding ratios are summarized in Table 1, where ‘phr’ stands for (weight) parts per hundred concerning with rubber.
Fig. 2. Relationship between critical strain from Kraus equation and NR con tent in NR/NBR blend. The code CB 10 to CB 60 indicating the composition of CB varied from 10 to 60 phr.
2.3. Instruments
NR/NBR blend at 30/70, the morphology shows the CB aggregates dispersed in the NBR domains and it forms a “Filling-Polymer Network” structure (Fig. 1 a). The decreasing concentration of the NBR in blend leads to CB particles aggregate in the limited NBR domain. So the CB aggregates densely packed in the NBR domain in Fig. 1(b and c) and it forms a “Nanosphere” structure made up of NBR and CB aggregates, which is in the nano-scale (dozens of hundreds of nanometers) at least one dimension, as circled in Fig. 1(c). At the same time, increasing concentration of the CB in Fig. 1(d) results in denser aggregates CB particle in the NBR phase, and the size of NBR phase in rubber blend filled 40phr CB is smaller than that of NBR phase in rubber blend filled with 20phr CB (Fig. 1 b). It arises from the larger shearing force during mixing for 40phr CB filled rubber blends. Therefore, the NBR phase containing much more CB is destroyed seriously. Meanwhile, the CB aggregates distribution of filled NBR phase increases concerning CB content.
The ultrathin sections of the Rubber compound were cut by ultra microtome (LEICA EM FC7, Germany) at 100 � C and the Transmission Electron Microscopy (TEM) images were taken by JEM 2100 (JEOL, Japan) with an acceleration voltage of 200 kV. TEM energy dispersive Xray spectroscopy (EDS) analysis was performed using an atomic reso lution microscope (JEM-AEM200F; JEOL Ltd, Japan.) equipped with an EDS system operation at 200 kV. Dynamic mechanical analysis (DMA) was carried out on an Eplexor 500N dynamic measurement system (GABO Qualimeter, Germany) in tension mode. The temperature sweeps were in the range from 90 to 120 � C with a heating rate of 2K/min under liquid nitrogen flow, using a constant frequency of 10 Hz. For the complex modulus E* measurement, a static load of 2% pre-strain was applied, then the samples oscillated to a dynamic load of 0.2% strain. The strain sweeps were conducted with Eplexor 500N dynamic mea surement system in tension mode. A pre-strain of magnitude 30% was selected to keep the sample straightly, and the dynamic amplitudes increased from 0.1% to 20% at 1 Hz frequency and room temperature. The dielectric measurements were performed with a broadband dielec tric spectrometer, BDS 40 system, manufactured by Novocontrol GmbH Germany, providing a bandwidth from 0.1 Hz to 10 MHz. Thin platinum layers were sputtered onto the flat surfaces of the samples to ensure electrical contact to the electrode plates. The measurement geometry was a disk-shaped plate capacitor of 20 mm in diameter. The specimen, whose thickness was about 2 mm, was set between two gold-plated brace electrodes. The real and imaginary parts of the conductivity were obtained in this measurement. Uniaxial tensile-tests were carried out by using dumbbell samples (about 2 mm in thickness), with a ma terial testing machine (Zwick/Roell Z005, Germany) at a crosshead speed of 200 mm/min (ISO 527) and room temperature.
3.2. Filler network percolation behavior It is well known that the Payne effect is one of the most important behaviors in the filled elastomers. It attributed to the filler dispersion and aggregation state, filler content, specific surface area and temper ature [18]. However, there are some controversial arguments in the research sociality [22,23,25–28,34,36]. Kraus explained the Payne ef fect to some degree by means of proposing a strain-dependent breaking and reforming of inter-particle connection model in the filler network [26,62]. � �.� 1 þ ðγ=γc Þ2m (1) G’ ðγÞ ¼ G’∞ þ G’0 G’∞ where G’∞ -the storage modulus at high strain amplitude, G’0 -the storage modulus at low strain amplitude. G’ ðγÞ-the storage modulus at random strain, γ-strain, and all the parameters are from strain sweep. The “γc” denotes the critical strain for filler network damage and “m”is the dimension coefficient of filler network. Both “γc” and “m” are from the fitting of equation (1). The γc decreases obviously when CB content is 40phr in pure NBR. The critical strain from Kraus equation and NR content in NR/NBR blend with the different composition of the CB were plotted in Fig. 2. Based on the CB and NR concentration, the critical strain changes randomly at CB10, CB20 and CB30. At this low concen tration of the CB, it is difficult to form filler network and filler dispersion
3. Results and discussion 3.1. Carbon black distribution The TEM images of CB dispersion in different NR/NBR blends were given in Fig. 1. The bright surface area of TEM image is from NR and the dark surface is coming from NBR. It is very clear that the CB is mostly distributed in the NBR phase in all NR/NBR composition (30/70, 50/50 – N group in the acrylonitrile unit have and 70/30). The polarity of the C– – better interaction with the CB so the carbon black aggregates are attracted towards NBR domains in NR/NBR blends [59–61]. When the 3
T. Han et al.
Polymer xxx (xxxx) xxx
21
CB10 CB20 CB30 CB40 CB50 CB60
18
Reinforcement
15 12
A
B
9 6 3 0
0
20
40 60 NR content/phr
80
100
Fig. 3. Relationship between percolation threshold from percolation theory and NR content in NR/NBR blend.
Fig. 4. Relationship between Reinforcement factor and NR content in rub ber blends.
is in discontinues phase on the NBR rubber, when the NBR content is not much enough, so the random γc pattern was observed in Fig. 2. Increasing CB (CB40, CB50 and CB60) possibly dispersed in the continuous NBR phase due to this continues phase, and increasing NR concentration decreases the critical strain up to NBR50 in A-region. This is due to that the filler content in the NBR phase is higher than that in the NR phase, and the CB aggregates packed density in NBR phase increases with decrease of NBR content in rubber blends, so increasing CB content and NR content enhance the filler network in the form of so-called “Filling-Polymer Network”. It reduces the critical strain value in the rubber blend. When the NBR is less than 50phr, the CB dispersed in confined phase, and within this, the CB distribution is denser. The CB is easy to disperse into the NBR phase spontaneously. Increasing NR con tent results highly packed CB in the NBR region. The lower densely packed CB and NBR concentration, the much more difficult to break, comparing to high densely packed region and NBR concentration, so the critical strain is increased in C-region. In this case, both the NBR and CB aggregates, inside in NBR phases, form “Super nanoparticles”, whose sizes are around hundreds of nanometers, even up to micro-scale when CB content is 20phr and the NR/NBR ¼ 70/30 in Fig. 1 (c). Nevertheless, the filled-phase size will decrease with increase of CB content, according to the morphology evolution from Fig. 1 (b) to Fig. 1 (d). On the other hand, it is reasonable to consider that the nano-scale and micro-scale filling-polymer structure will co-exist in the overall system. This kind of super-nanoparticles is much more difficult to be disintegrated. As a result, the γc increases again in the Fig. 1 (c) zone. The B zone in Fig. 2 is the transition area for NBR from continuous phase to dispersion phase. It is controlled by both rubber blend ratio and filler content. The relationship between conductivity, arising from dielectric relaxation spectrum, and filler volume content has been successfully used to evaluate the filler network behavior, combined with the perco lation theory in equation (2) [22,63]. In which, σdc -direct current con ductivity, σ ∞ -infinite conductivity, μ-critical exponent,φ -volume content of carbon black, φc - critical volume content of carbon black forming conductivity filler network. The value of σdc is from dielectric measurement and the values of σ∞ , φc and μ are from the fitting of equation (2) (percolation theory). � �μ ðφ φc Þ σdc ¼ σ∞ � (2) ð1 φc Þ
G’unfilled
G’filled
¼ 1 þ 2:5 � φ þ a � φ2
(3)
the increase of CB relative content in NBR phase. The NBR phase turns to be narrow and finally broken into dispersed phase with increase of NR content. Even if the NBR phase is broken and leads to small distance between neighboring CB clusters, the percolation threshold value further decreases, as long as the electron can jump from one CB aggre gate to another [64]. Due to the coating effect of NBR on CB, as the NBR phase becomes dispersed phase from continuous phase in Fig. 3 zone B, the percolation threshold value increases. When the NR/NBR blend ratio is in the range of 50/50 to 90/10, the NBR phase becomes dispersed phase from continuous phase in Fig. 3. Nevertheless, the range can narrow to 50/50 to 70/30 compared with the case in Fig. 1. In addition, it is clear that the percolation threshold value of filler network in filled NBR is higher than that in filled NR. It is agreed with the result, arising from the Kraus equation prediction above. The minimum of percolation threshold value is ca. 7% at the NR/NBR ¼ 70/30. 3.3. Reinforcement and loss mechanism analysis It is known that the reinforcement factor is one of the most important parameters in evaluating the reinforcement behavior [65]. In this work, equation (3) is adopted, in which, G0 filled-storage modulus at 0.1% strain for filled sample, G0 -unfilled-storage modulus at 0.1% strain for unfilled sample, φ-vol.% of the fillers and “a” is 14.1 in Guth-Gold equation [66]. However, it is verified that it has been underestimated [35]. It is out of the range of this work and will not influence the subsequent discussion. Therefore, “a” is used instead of the controversial value. The rein forcement effect increases at any rubber blend ratios with increase of CB content. The reinforcement factor increases with decrease of NBR con tent in rubber blends in Fig. 4 (zone A). The relative CB content increases in NBR phase with decrease of its content in rubber blends. It leads to an enhanced reinforcement effect. The reinforcement effect is the best at the NR/NBR ¼ 50/50 at any CB contents. In this case, there are dual-continuous “rubber phase networks” and the “filling-polymer network”, which improves the reinforcement effect. As descripted in Fig. 2, both the NBR and CB aggregates, which are inside in NBR phases, form “super nanoparticles” in Fig. 4 (B zone), because of the evolution of NBR phase from continuous phase to dispersed phase. The reinforcement effect is higher to the CB aggregates and smaller region appeared in filled-polymer network. In addition, the
The percolation threshold as a function of NR content in rubber blend is presented in Fig. 3. The percolation threshold value decreases with increase of NR content in rubber blends in Fig. 3 zone A. It is because of 4
T. Han et al. 1000
(a)
Polymer xxx (xxxx) xxx B
A
800
-EA
600
CB10 CB20 CB30 CB40 CB50 CB60
C' C B
400
B' A
200 0
0
20
40 60 80 NR content (phr)
Fig. 7. Schematic sketch of the reinforcement mechanism model for CB filled rubber blends: (a) Filling-polymer network reinforcement; (b) Filled super nanoparticles reinforcement; (c) Filler Wrapped/Covered super nanoparticles reinforcement.
100
Fig. 5. Relationship between activation energy and NR content in rubber blends with different CB contents (a), as well as the tanδ relative peak value (the ratio between the tanδ peak value for the filled and unfilled samples) related to NBR phase and CB contents at different NR/NBR blend ratios (b). All data derive from temperature-dependent relationship.
is continuous phase when its content is not more than 50phr. The rela tive rubber content decreases in NBR phase with increase of CB contents. It induces the decrease of relative loss factor (tanδ) peak value in Fig. 5 (b) (curve A) [42]. The NBR turns to be dispersed phase when the NR content is up to 70phr in rubber blend (Fig. 1(c)). As for the curve B in Fig. 5(b), it is possible that the CB aggregates located at the interphase between NBR and NR phases induce the isolation effect at the low CB concentration [57]. In this case, the relative loss factor increases with increase of CB content. It is clear that the NBR phase size is larger than that of CB aggregates at NR/NBR ¼ 70/30 (Fig. 1(c)). Hence, more and more CB aggregates enter into the NBR phases with increase of CB content. It decreases the relative rubber content in NBR phase, which dominates the relative loss factor of the system and makes it decreases again (Fig. 5 zone B-B’). When the NR/NBR ¼ 90/10, It is possible that the size of NBR is too small to contain CB aggregates. In this case, the NBR phase will be wrapped or covered by CB aggregates, and it will lead to phase sepa ration. The more CB aggregates, the more severe phase separation. Therefore, the relationship between tan δ relative peak value and CB content is shown as Fig. 5 (b) (zone C to C’). It shows that the effect of CB aggregates on tan δ relative peak value changes, when the CB content is between 30phr and 40phr. It is clear that the NBR phase size is reduced to “hundred” to “ten” nm, when the NR phase content is 90phr in NR/NBR blend. In Fig. 6(a) and (b), it shows better clarity about the morphology change from Fig. 1 (b)–(d). The NBR phase size scale is comparable with (or even smaller than) that of CB aggregates. Therefore, it is easy to be wrapped (or covered) by CB aggregates, and leads to phase separation. It confirms the discussion about Fig. 5 (b) (zone C to C’). The more CB content, the more severe phase separation. The amplification of phase separation degree decreases with increase of CB content when the CB concentration rea ches to 40phr. Based on the results of Figs. 1 and 6 the schematic sketch
filling-polymer network forms as the NR/NBR blend ratio is between 50/ 50 and 70/30, compared the Fig. 3 with Fig. 4. The activation energy is an efficient parameter to indirectly show the CB aggregates average distance. It can be calculated by means of Arrhenius equation [22]. The activation energy increases with increase of CB content at the constant NR/NBR blend ratio in Fig. 5 (a). The NBR content is much more than NR content in Fig. 5 (a) (A zone). It domi nates the EA of the system. The relative CB content in NBR phase in creases with decrease of NBR content in rubber blends. It induces that the decrease of the average distance among the neighboring CB aggre gates results in the increase of EA. As the description for Fig. 4 (B zone), the super-nanoparticle is formed by NBR phase and CB aggregates in Fig. 5 a (B zone). The supernanoparticle average distance decreases with decrease of NBR content in rubber blends. Therefore, the EA decreases with decreases of NBR content in this zone. In addition, it is clear that the CB dispersion in filled single NBR is better than that in filled single NR, according to the comparison of the EA for these two filled single rubber systems. It is accordance with the result in Fig. 3. It is well known that the tanδ peak value is obviously influ enced by incorporating fillers because of the decrease of rubber content with increase of fillers [42]. Meanwhile, the absolute value of tanδ is also affected by the structure of rubber matrix. Therefore, the relative peak value of tanδ is adopted to investigate the contribution of filler to the loss property. Furthermore, the NBR phase is in glassy state when the NR phase undergoes the glass transition process. The NBR phase is filler-like at low temperature. It is unquestionable that the result will be misunderstood if the tanδ peak value of NR is used. Hence, we adopt the relative peak value of NBR phase as the object in rubber blends. The NBR
Big
Small
(a)
Smaller
(b)
(c)
Fig. 6. STEM mapping images for NR/NBR ¼ 90/10 filled with 20phr CB. (a): STEM image, the bright parts are CBs and the dark parts are NR/NBR; (b) and (c) are carbon element and nitrogen element distribution images, respectively, the bright parts stand for relatively high carbon element and nitrogen contents, and the dark parts stand for relatively low carbon element and nitrogen contents. It is considered that the nitrogen element dispersion stands for NBR phase dispersion. 5
T. Han et al. 35
Polymer xxx (xxxx) xxx 30
a)
30
10 5 0
30
400
%
600
(MPa)
NR0 NR10 NR30 NR50 NR70 NR90 NR100
15 10 5 0
5 0
0
200
d)
20phr 40phr 60phr
12
CB 60phr
20
0
10
15
c)
NR0 NR10 NR30 NR50 NR70 NR90 NR100
15
200
%
400
600
400 20phr 40phr 60phr
600 400
6
200
3 0
20
40 60 NR content (phr)
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
800
9
0
Declaration of competing interest
600
80
100
elongation at break/%
25
200
NR0 NR10 NR30 NR50 NR70 NR90 NR100 800
(MPa)
15
0
CB 40phr
20
20
100% modulus
(MPa)
25 CB 20phr
tuned by means of changing NR/NBR blend ratios and CB concentration. These novel findings offer a unified explanation for reinforcement mechanism in filled elastomers, and may contribute to developing a maturely industrial method to produce high mechanical performance and low conductivity percolation threshold elastomers.
b)
25
Acknowledgement The authors gratefully acknowledge GUAN LIAN Corporation, China, for providing the NR and rubber chemicals for the research work. The work is supported by the National Natural Science Foundation of China (51503114) (51573007),German Academic Exchange Service(DAAD) (57317599) and China Scholarship Council (CSC) (2017 (6052)). We thank Prof. Yonglai Lu for many fruitful discussions.
0
Fig. 8. Relationship between stress-strain behavior and NR content in rubber blends with different CB contents.
of the reinforcement mechanism model was shown in Fig. 7. In Fig. 7, the reinforcement mechanisms depend on rubber blend ratios and CB contents. In NR/NBR blend at 30/70, the “Filling-Polymer Network” structure forms owing to the dual-continuous “rubber phase networks” and the dispersion of CB in NBR phase (Fig. 7 a). As NBR content decreases to the dispersed phase, CB aggregates densely packed in the NBR domain and supernanoparticles form, consisting of NBR and CB aggregates (Fig. 7 b). The low composition of NBR illustrated in Fig. 7 (c) (NR/NBR ¼ 90/10). The NBR phase size scale is comparable with (or even smaller than) that of CB aggregates. It is easy to be wrapped (or covered) by CB aggregates, leading to phase separation.
References [1] S.K. Kumar, N. Jouault, B. Benicewicz, et al., Nanocomposites with polymer grafted nanoparticles, Macromolecules 46 (9) (2013) 3199–3214. [2] M.E. Mackay, A. Tuteja, P.M. Duxbury, et al., General strategies for nanoparticle dispersion, Science 311 (5768) (2006) 1740–1743. [3] D. Zhao, S. Ge, E. Senses, et al., Role of filler shape and connectivity on the viscoelastic behavior in polymer nanocomposites, Macromolecules 48 (15) (2015) 5433–5438. [4] Z. Rigbi, Reinforcement of rubber by carbon black, Rubber Chem. Technol. J. 55 (4) (1982) 1180–1220. [5] S. Merabia, P. Sotta, D.R. Long, A microscopic model for the reinforcement and the nonlinear behavior of filled elastomers and thermoplastic elastomers (Payne and mullins effects), Macromolecules 41 (21) (2008) 8252–8266. [6] S. Dupres, D.R. Long, P.A. Albouy, et al., Local deformation in carbon black-filled polyisoprene rubbers studied by NMR and X-ray diffraction, Macromolecules 42 (7) (2009) 2634–2644. [7] A. Einstein, A new determination of molecular dimensions, Ann. Phys. 19 (1906) 289–306. [8] H.M. Smallwood, Limiting law of the reinforcement of rubber, J. Appl. Phys. 15 (11) (1944) 758–766. [9] A. Mujtaba, M. Keller, S. Ilisch, et al., Mechanical properties and cross-link density of styrene–butadiene model composites containing fillers with bimodal particle size distribution, Macromolecules 45 (45) (2012) 6504–6515. [10] C.G. Robertson, R. Bogoslovov, C.M. Roland, Structural arrest and thermodynamic scaling in filler-reinforced polymers, Rubber Chem. Technol. J. 82 (2) (2009) 202–213. [11] A.I. Medalia, Effective degree of immobilization of rubber occluded within carbon black aggregates, Rubber Chem. Technol. J. 45 (5) (1972) 1171–1194. [12] M. Michelle, M. Tania, B. Guido, et al., A fourier transform infrared (FTIR) study of the reaction of triethoxysilane (TES) and bis[3-triethoxysilylpropyl]tetrasulfane (TESPT) with the surface of amorphous silica, J. Phys. Chem. B 108 (11) (2004) 3563–3572. [13] L. Bokobza, The reinforcement of elastomeric networks by fillers, Macromol. Mater. Eng. 289 (2004) 607–621. [14] M. Castellano, L. Conzatti, A. Turturro, et al., Influence of the silane modifiers on the surface thermodynamic characteristics and dispersion of the silica into elastomer compounds, J. Phys. Chem. B 111 (17) (2007) 4495–4502. [15] J.N. Paquien, J. Galy, J.F. G�erard, et al., Rheological studies of fumed silica–polydimethylsiloxane suspensions, Colloid. Surf. Physicochem. Eng. Asp. 260 (1) (2005) 165–172. [16] F. Cl�ement, L. Bokobza, L. Monnerie, Investigation of the Payne effect and its temperature dependence on silica-filled polydimethylsiloxane networks. Part I: experimental results, Rubber Chem. Technol. J. 78 (2) (2005) 211–231. [17] J. Ramier, C. Gauthier, L. Chazeau, et al., Payne effect in silica-filled styrene–butadiene rubber: influence of surface treatment, J. Polym. Sci. B Polym. Phys. 45 (3) (2006) 286–298. [18] A.P. Meera, S. Said, Y. Grohens, et al., Nonlinear viscoelastic behavior of silicafilled natural rubber nanocomposites, J. Phys. Chem. C 113 (42) (2009) 17997–18002. [19] N. Jouault, F. Dalmas, F. Bou� e, et al., Multiscale characterization of filler dispersion and origins of mechanical reinforcement in model nanocomposites, Polymer 53 (3) (2012) 761–775. [20] B. Zhong, Z. Jia, D. Hu, et al., Enhancing interfacial interaction and mechanical properties of styrene-butadiene rubber composites via silica-supported vulcanization accelerator, Composites Part A Applied Science & Manufacturing 96 (2017) 129–136.
3.4. Stress-strain behavior The elongation at break decreases with increases of CB in Fig. 8(a–c). It is limited to some degree due to CB entering into NBR phase and forming a filling-polymer network. The elongation at break is higher at low NBR concentration in rubber blends, because the so-called “Supernanoparticle”, which is formed by NBR and CB aggregates, possesses the deformable ability. It’s worth noting that the elongation at break is the highest for the NR/NBR ¼ 90/10 system at any CB concentration in Fig. 8(d). It is the result of phase separation between NR and NBR arising from the isolation effect of CB aggregates at their interfaces. The peak value of 100% modulus appears in NR/NBR ¼ 50/50 blend, and it in creases with the increase of CB content (Fig. 8(d)). It indicates the reinforcement effect is very obvious for the filling-polymer network. 4. Conclusions In summary, the CB aggregates tend to entry into NBR phase spon taneously in NR/NBR blends. Increasing composition of NR leads to suppress the NBR from continuous phase to discontinuous phase. In discontinuous phase, increasing CB aggregates are within the confine ment NBR phase. The size of NBR phase decreases with increase of CB content. The conductivity filler network percolation threshold decreases in NR/NBR blends, compared with single rubber composition. The elongation at break in 60phr CB filled NR/NBR ¼ 90/10 is 25% more than that in filled NR with the same CB content. The reinforcement is evidently enhanced in NR/NBR blend. The reinforcement effect of CB aggregates increases in the form of “filled polymer network” when the NBR is continuous phase in rubber blends. The results show that the “filled super-nanoparticles” and “filler wrapped/covered super-nano particles” contribute for the reinforcement, when the NR/NBR blend ratios are 70/30 and 90/10,respectively. All these properties can be 6
T. Han et al.
Polymer xxx (xxxx) xxx [42] C. Sirisinha, N. Prayoonchatphan, Study of carbon black distribution in BR/NBR blends based on damping properties: influences of carbon black particle size, filler, and rubber polarity, J. Appl. Polym. Sci. 81 (13) (2001) 3198–3203. [43] S. Maiti, S.K. De, A.K. Bhowmick, Quantitative estimation of filler distribution in immiscible rubber blends by mechanical damping studies, Rubber Chem. Technol. J. 65 (2) (1992) 293–302. [44] C. Sirisinha, J. Thunyarittikorn, S. Yartpakdee, Study of carbon black distribution in butadiene rubber-nitrile/butadiene rubber blends based on damping properties: effect of some grades of carbon black, Plastics 27 (8) (1998) 373–375. [45] M. Wunde, M. Klüppel, Influence of phase morphology and filler distribution in NR/BR and NR/SBR blends on fracture mechanical properties, Rubber Chem. Technol. J. 89 (4) (2016) 588–607. [46] R.H. Schuster, J. Meier, M. Klüppel, Role of interphase in filler partition in rubber blends, Kautsch. Gummi Kunstst. 53 (11) (2000) 663–674. [47] H.H. Le, K. Oßwald, S. Ilisch, et al., Silica transfer in ternary rubber blends: calculation and experimental determination, Macromol. Mater. Eng. 297 (5) (2012) 464–473. [48] A.K. Sircar, T.G. Lamond, Carbon black transfer in blends of Cis-poly(butadiene) with other elastomers, Rubber Chem. Technol. J. 46 (1) (1973) 178–191. [49] J.M. Massie, R.C. Hirst, A.F. Halasa, Carbon black distribution in NR/ polybutadiene blends, Rubber Chem. Technol. J. 66 (2) (1993) 276–285. [50] V. Herrmann, K. Unseld, H.B. Fuchs, Atomic-force-microscopy for the investigation of inhomogenous polymer-systems, Kautsch. Gummi Kunstst. 54 (9) (2001) 453–457. [51] A.H. Tsou, W.H. Waddell, Morphology of elastomer blends by dynamic AFM, Kautsch. Gummi Kunstst. 55 (7) (2002) 382–387. [52] I.H. Jeon, H. Kim, S.S.G. Kim, Characterization of rubber micro-morphology by atomic force microscopy(AFM), Rubber Chem. Technol. J. 76 (1) (2003) 1–11. [53] C.C. Wang, J.B. Donnet, T.K. Wang, et al., AFM study of rubber compounds, Rubber Chem. Technol. J. 78 (1) (2005) 17–27. [54] G.R. Cotten, L.J. Murphy, Mixing of carbon black with rubber. VI. Analysis of NR/ SBR blends, Rubber Chem. Technol. J. 61 (4) (1988) 609–618. [55] A. Das, K.W. St€ ockelhuber, R. Jurk, et al., Modified and unmodified multiwalled carbon nanotubes in high performance solution-styrene–butadiene and butadiene rubber blends, Polymer 49 (24) (2008) 5276–5283. [56] W.M. Hess, C.E. Scott, J.E. Callan, Carbon black distribution in elastomer blends, Rubber Chem. Technol. J. 40 (2) (1967) 371–384. [57] P. Phewphong, P. Saeoui, C. Sirisinha, The use of dynamic mechanical thermal analysis technique for determining an uneven distribution of precipitated silica in CPE/NR blends, Polym. Test. 27 (7) (2008) 873–880. [58] M. Huang, L.B. Tunnicliffe, J. Zhuang, et al., Strain-dependent dielectric behavior of carbon black reinforced natural rubber, Macromolecules 49 (6) (2016) 2339–2347. [59] W.M. Hess, V.E. Chirico, Elastomer blend properties—influence of carbon black type and location, Rubber Chem. Technol. J. 50 (2) (1977) 301–326. [60] M.H. Walters, D.N. Keyte, Heterogeneous structure in blends of rubber polymers, Rubber Chem. Technol. J. 38 (1) (1965) 62–75. [61] M. Kawazoe, H. Ishida, A new concept for nanoparticle distribution in SBR/NBR blend solution and films via molecular confinement, Macromolecules 41 (8) (2008) 2931–2937. [62] C.S. Boland, U. Khan, G. Ryan, et al., Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites, Science 354 (6317) (2016) 1257. [63] P. Ghosh, A. Chakrabarti, Conducting carbon black filled EPDM vulcanizates: assessment of dependence of physical and mechanical properties and conducting character on variation of filler loading, Eur. Polym. J. 36 (5) (2000) 1043–1054. [64] J. Fritzsche, M. Klüppel, Structural dynamics and interfacial properties of fillerreinforced elastomers, J. Phys. Condens. Matter 23 (3) (2011), 035104. [65] E. Guth, Theory of filler reinforcement, J. Appl. Phys. 16 (1) (1945) 20–25. [66] E. Guth, On the hydrodynamical theory of the viscosity of suspensions, Phys. Rev. 53 (1) (1938) 322.
[21] I. Morabarrantes, A. Rodríguez, L. Ibarra, et al., Overcoming the disadvantages of fumed silica as filler in elastomer composites, J. Mater. Chem. 21 (20) (2011) 7381–7392. [22] C. Sun, P. Zhang, C. Wrana, et al., Combined dielectric and mechanical investigation of filler network percolation behavior, filler-filler contact, and fillerpolymer interaction on carbon black-filled hydrogenated acrylonitrile-butadiene rubber, Rubber Chem. Technol. J. 87 (4) (2014) 647–663. [23] P.G. Maier, D. G€ oritz, Molecular interpretation of the Payne effect, Kautsch. Gummi Kunstst. 49 (1996) 18–21. [24] G.P. Baeza, A.C. Genix, C. Degrandcourt, et al., Multiscale filler structure in simplified industrial nanocomposite silica/SBR systems studied by SAXS and TEM, Macromolecules 46 (1) (2013) 317–329. [25] G. Heinrich, M. Klüppel, Recent advances in the theory of filler networking in elastomers, Adv. Polym. Sci. 160 (2002) 1–44. [26] G. Kraus, Mechanical losses in carbon-black-filled rubbers, Appl. Polym. Symp. 39 (1984) 75–92. [27] M. Tauban, J.Y. Delannoy, P. Sotta, et al., Effect of filler morphology and distribution state on the linear and nonlinear mechanical behavior of nanofilled elastomers, Macromolecules 50 (17) (2017) 6369–6384. [28] D. Long, S. Merabia, P. Sotta, Unique plastic and recovery behaviour of nano-filled elastomers and thermoplastic elastomers, J. Polym. Sci. B Polym. Phys. 48 (13) (2010) 1495–1508. [29] A. Papon, S. Merabia, L. Guy, et al., Unique nonlinear behavior of nano-filled elastomers: from the onset of strain softening to large amplitude shear deformations, Macromolecules 45 (6) (2012) 2891–2904. [30] A.A. Gusev, Micromechanical mechanism of reinforcement and losses in filled rubbers, Macromolecules 39 (18) (2006) 5960–5962. [31] D. Fragiadakis, P. Pissis, L. Bokobza, Modified chain dynamics in poly (dimethylsiloxane)/silica nanocomposites, J. Non-Cryst. Solids 352 (42–49) (2006) 4969–4972. [32] J. Berriot, H. Montes, F. Lequeux, et al., Evidence for the shift of the glass transition near the particles in silica-filled elastomers, Macromolecules 35 (26) (2002) 9756–9762. [33] S. Wu, L. Zhang, P. Weng, et al., Correlating synergistic reinforcement with chain motion in elastomer/nanocarbon hybrids composites, Soft Matter 12 (33) (2016) 6893–6901. [34] A. Mujtaba, M. Keller, S. Ilisch, et al., Detection of surface-immobilized components and their role in viscoelastic reinforcement of rubber–silica nanocomposites[J], ACS Macro Lett. 3 (5) (2014) 481–485. [35] M. Klüppel, The role of disorder in filler reinforcement of elastomers on various length scales, Adv. Polym. Sci. 164 (2003) 1–86, 2003. [36] K.W. St€ ockelhuber, A.S. Svistkov, A.G. Pelevin, et al., Impact of filler surface modification on large scale mechanics of styrene butadiene/silica rubber composites[J], Macromolecules 44 (11) (2011) 4366–4381. [37] P. Sotta, P.A. Albouy, T.M. Abou, et al., Nonentropic reinforcement in elastomer nanocomposites, Macromolecules 50 (16) (2017) 6314–6322. [38] A.A. Gavrilov, A.V. Chertovich, P.G. Khalatur, et al., Study of the mechanisms of filler reinforcement in elastomer nanocomposites, Macromolecules 47 (15) (2014) 5400–5408. [39] Z. Wang, J. Liu, S. Wu, et al., Novel percolation phenomena and mechanism of strengthening elastomers by nanofillers, Phys. Chem. Chem. Phys. PCCP 12 (12) (2010) 3014–3030. [40] K. Marina, D. Hidehiko, K. Hideaki, et al., Characterization of carbon filler distribution ratio in polyisoprene/polybutadiene rubber blends by high-resolution solid-state 13C NMR, Macromolecules 40 (26) (2007) 9451–9454. [41] W. Hu, M.D. Ellul, A.H. Tsou, et al., Filler distribution and domain size of elastomer compounds by solid-state NMR and AFM, Rubber Chem. Technol. J. 80 (1) (2007) 1–13.
7