Fabrication of High Performance Magnetic Rubber from NBR and

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Fabrication of high performance magnetic rubber from NBR and Fe3O4 via in-situ compatibilization with zinc dimethacrylate Yukun Chen, Xunhui Huang, Zhou Gong, Chuanhui Xu, and Wen-Jie Mou Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b03833 • Publication Date (Web): 09 Dec 2016 Downloaded from http://pubs.acs.org on December 13, 2016

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Industrial & Engineering Chemistry Research

Fabrication of high performance magnetic rubber from NBR and Fe3O4 via in-situ compatibilization with zinc dimethacrylate Yukun Chen1,*, Xunhui Huang1, Zhou Gong1, Chuanhui Xu2,*, Wenjie Mou1 1 The Key Laboratory of Polymer Processing Engineering, Ministry of Education, China (South C hina University of Technology), Guangzhou, 510640, China 2 School of Chemistry and Chemical Engineering, Guangxi University, Nanning, 530004, China Corresponding Author: Chuanhui Xu ([email protected]) and Yukun Chen ([email protected]) Tel: 02087110804 Fax: 02085293483

ABSTRACT Fe3O4-based magnetic rubbers are desirable because they take advantage of high elasticity, large elongations and high magnetic saturation intensity of each component. However, directly compounding of rubbers and Fe3O4 usually resulted in low mechanical properties which made the magnetic rubbers unable to satisfy practical applications. In this paper, we prepared nitrile butadiene rubber (NBR)/Fe3O4-based magnetic rubbers with good mechanical properties by means of in-situ compatibilization using zinc dimethacrylate (ZDMA). Our strategy was based on the polymerization of ZDMA during a peroxide-induced vulcanization, in which the polymerized ZDMA (PZDMA) brought massive Zn2+ ion pairs into NBR. Zn2+ ion pairs not only increased the polarity of NBR but also strongly interacted with Fe3O4 nanoparticles. Because of the graft-PZDMA, the Zn2+ ion pairs finally strengthened interactions between Fe3O4 nanoparticles and NBR molecules. We hope this report laid an applied foundation for design of high-performance magnetic rubbers to satisfy the various potential applications. Keyword: Magnetic rubbers; Fe3O4 nanoparticles; in-situ compatibilization; mechanical properties; structures

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1. INTRODUCTION Magnetic polymeric material is a kind of charming functional materials which has potential applications in electromagnetic interference shielding, electronic devices, cell separation, drug targeting, etc1-7. In most practical applications, magnetic polymeric materials are required to achieve large elongation and high elasticity to satisfy various cases8-14. Therefore, magnetic rubber, an available rubber material with magnetic function, has attracted intensive attention due to its large strain, high saturation magnetic induction, low coercivity and high-frequency loss and so on14. Magnetic rubbers are usually prepared by adding magnetic powders such as ferrite15-21, Nd-Fe-B22 into rubber matrixes. In general, their magnetic properties are related to the types and contents of magnetic fillers. For instance, magnetite (Fe3O4) is a perfect paramagnetic material which has high initial permeability, biggish saturation magnetization and low coercivity23,24. It is reported that when the size of Fe3O4 nanoparticle is less than 30 nm, it presents a super paramagnetism that its coercivity equals to zero25. However, to achieve high magnetic performance, rubbers have to be filled with a large content of Fe3O4, consequently accompanying with an unwilling decreased mechanical property due to the weak interactions between Fe3O4 nanoparticles and rubber matrix, as well as the unsatisfactory dispersion of Fe3O4 nanoparticles26,27. Organic modification is a commonly applied method to improve the interfacial compatibility and the dispersion of fillers in rubbers. Unfortunately, in most cases, the organic treated Fe3O4 nanoparticles have a strong tendency to aggregate together at a dried status28-32, which hinders their dispersion in rubber compounding. Although the aggregation of organic treated Fe3O4 nanoparticles can be solved in a solution state, the available rubber latexes are quite limited and the subsequent drying, compounding and vulcanization of rubbers add cost. Furthermore, the organic treatment usually changes the crystalline structure of Fe3O427,28,33, may resulting in the formation of maghemite (γ-Fe2O3). From this point of view, it is still meaningful to find an effective method for improving the dispersion and interfacial compatibility of Fe3O4 nanoparticles in rubbers to improve the mechanical properties of magnetic rubbers. In recent years, zinc dimethacrylate (ZDMA), a kind of ionic compound, has attracted the significant interest of researchers due to its high chemical activity and ionization effect after polymerization. ZDMA was easily graft-polymerized onto rubber chains in the present of peroxides34,35. After polymerization, massive ion pairs in polymerized ZDMA (PZDMA) molecules had strong electrostatic interaction which strongly restricted the mobility of adjacent rubber chains36. Additionally, Zn2+ in rubber-graft-PZDMA provided additional adjoiners to the whole crosslink network of rubbers35,36. We noticed that the massive ion pairs generated from polymerization of ZDMA in rubbers might have strong affinity with Fe3O4 nanoparticles to enhance the interactions between Fe3O4 and rubber chains. At the same time, polymerization of ZDMA also increased the polarity of rubbers, which benefited to further improve rubber’s wettability on Fe3O4 nanoparticles. From this point of view, ZDMA is a potential effective in-situ compatibilizer for Fe3O4 nanoparticles to fabricate magnetic rubber though a common rubber process without any pre-modifications. Furthermore, ZDMA is also an effective reinforcer for rubbers36,37, which adds feasibilities for exploring it as a multifunctional additive for magnetic rubbers. Based on idea above, in this paper, we selected a polarity nitrile butadiene rubber (NBR) as the rubber matrix, and successfully prepared a NBR/Fe3O4-based magnetic rubber by using 2


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ZDMA as in-situ compatibilizer in the present of dicumyl peroxide (DCP). The preparation was fast, convenient, versatile and inexpensive. As expected, the dispersion of Fe3O4 was significantly improved. The resultant NBR/Fe3O4 composites exhibited excellent mechanical properties and magnetic property. We hope this study opens up an avenue to fabricate magnetic rubber with high mechanical properties to satisfy various engineering applications. 2. EXPERIMENTAL DETAILS 2.1. Materials. Nitrile butadience rubber (NBR-N41, 29% acrylonitrile content, ML(1+4 ,100°C)=77.5) was purchased from Lanzhou Petrochemical Company (China). ZDMA was purchased from Guangdong Qiangda New Materials Technology Company (China). Nano-Fe3O4 (average particle size=250 nm, density=5.7 g/cm3, specific surface area=13 m2/g) was purchased from Shanghai ST-NANO Science Technology Company (China). Dicumyl peroxide (DCP) was purchased from Sinopharm Chemical Reagent (China). Triallyl isocyanurate (TAIC), auxiliary crosslinking agent, was used as received. 2.2. Sample preparation. In our experiment, NBR/Fe3O4 compounds containing 100 weight parts of NBR, 1.5 phr (parts per 100 parts of rubber) DCP, 2.5 phr TAIC and 0-15 phr ZDMA were prepared in a two-roller mill. To ensure that the magnetic properties of the NBR/Fe3O4 composites were close to the properties of industrial magnetic NBR, the content of Fe3O4 nanoparticles was fixed at 70 phr. In the detailed rubber compounding, ZDMA was first added into NBR matrix for mixing 3 minutes. Then Fe3O4 nanoparticles were added and mixed for another 5 minutes. DCP and TAIC were added at last. NBR/Fe3O4 composites were cured at 170°C for their optimum cure time (T90) which was determined from a UR-2010 Rotorless Rheometer produced by U-CAN Dynatex (Taiwan). TAIC used here is an auxiliary crosslinking agent who helps to improve the crosslinking rate in our system. The addition of TAIC could thus shorten the vulcanization time and reduce the disadvantage of vulcanization against the magnetism property of Fe3O4. 2.3. Characterization Methods. The magnetic properties of NBR/Fe3O4composites were investigated at room temperature using a physical property measurement system (PPMS-9, Quantum Design, USA) equipped with a 9 T vibrating sample magnetometer (VSM). The ramping rate of magnetic field strength (dB/dt) is 15 mT/s. The range of magnetic field strength is from -1.5T to1.5T. The crystal structure of Fe3O4 was identified by X-ray Diffraction (XRD, D/MAX-III, Japan) using Cu Kα radiation. Step size was set at 0.02o with 0.02o/s scanning rate in between 10o and 80o diffraction angle (2θ). Nova Nano SEM 430 (FEI Company) was used to investigate the morphology of the NBR/Fe3O4 composites. The FTIR spectrum of composites was measured by a Tensor 27 sectrometer (Bruker, Germany) under the attenuated total reflectance (ATR) model (32 consecutive scans and resolution of 4 cm−1 wavenumber). Dynamic mechanical behavior was studied by a DMA242C (NETZSCH, Germany) under a tensile mode at 1 Hz and a heating rate of 3 °C/min in the range from −80 to 50 °C. Thermal stability was measured by a TG209F1 (NETZSCH, Germany) in nitrogen atmosphere from room temperature to 800 °C at a heating rate of 20 °C/min. Stress-strain behaviors were carried out on a UT-2080 (U-CAN, Taiwan) under a tensile mode with a crosshead speed of 500mm/min. Tear strength was also determined by UT-2080 under a tear mode. Shore A hardness was measured using a LX-A rubber durometer. 3. Results and discussion 3



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3.1. Design of the NBR/Fe3O4/ZDMA magnetic rubber composites NBR chains H3C

C

O C O

H2C

O

Zn2+

CH2 C

2+

C

O

Fe3O4

CH3

ZDMA H3C

H C

C

H2C

O O

Zn2+ Zn2+ 2+ Zn2+ H22+ O 2+Zn Zn ZnZn 2+ Zn2+ 2+ Zn 2+ 2+ O Zn Zn

C

H C

CH2

ZnZn2+ 2+ Zn 2+ 2+ Zn2+ Zn Zn Zn2+ 2+ 2+ Zn Zn 2+ 2+ Zn2+2+ Zn Zn Zn2+Zn 2+ 2+ Zn2+ZnZn Zn2+2+ 2+ Zn Zn 2+ Zn

CH3

NBR

PZDMA

Zn2+

DCP-Vulcanization H3C H2C

H C

C

Zn2+ Zn2+ 2+ Zn2+ H22+ O 2+Zn Zn OH ZnZn 2+ Zn2+ 2+ Zn 2+ Zn2+ O O Zn

C

H C

Zn2+ Zn2+ Zn2+ Zn2+ Zn2+ Zn2+ Zn2+ Zn2+ Zn2+ Zn2+ Zn2+ 2+ Zn2+ Zn 2+

Zn

Zn2+

CH2 CH3

vulcanizate graft-PZDMA

Figure 1. Schematics of chemical structures of ZDMA, PZDMA graft-PZDMA and the ideal in-situ compatibilization using ZDMA for Fe3O4 nanoparticles in NBR The main concept for preparing NBR/Fe3O4-based magnetic rubber with good mechanical properties is to increase the interactions between Fe3O4 nanoparticles and NBR molecules by means of in-situ compatibilization using ZDMA. Our strategy is based on the polymerization of ZDMA during a DCP-induced vulcanization, in which the PZDMA and graft-PZDMA brings massive Zn2+ ion pairs into NBR matrix. The Zn2+ ion pairs are expected not only to increase the polarity of NBR but also to strongly interact with Fe3O4 nanoparticles. Because of the NBR-graft-PZDMA36, the massive Zn2+ ion pairs finally strengthen the interactions between Fe3O4 nanoparticles and NBR molecules. The schematics of chemical structures of ZDMA, PZDMA, graft-PZDMA and the above ideal in-situ compatibilization using ZDMA for Fe3O4 nanoparticles in NBR are illustrated in Figure 1. The photos of the employed Fe3O4 nanoparticles, raw NBR and NBR/Fe3O4/ZDMA vulcanizate are also showed in Figure 1. Since the nature dark of Fe3O4, the final magnetic rubbers exhibited an inevitable black appearance. 3.2 Analysis of magnetic properties

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Figure 2. (a) Cure curves; (b) XRD results and (c) magnetic hysteresis loops of NBR/Fe3O4 composites in a weak magnetic field To satisfy the demand of practical applications, rubbers must be vulcanized at a high temperature to gain good mechanical properties. In general, the crystalline structures of Fe3O4 determine the cation distributions in structure, which has a direct influence on the magnetic properties of final material38. Unfortunately, the magnetism property of Fe3O4 drains seriously at high temperatures for a long period due to the change of its crystalline structure33,39. In this experiment, although a curing temperature of 170°C was accepted by Fe3O4, the curing time was better to be shorter as possible. As seen from the cure curves in Figure 2a, neat NBR showed an optimum cure time (T90) of 6.9min. After incorporation of Fe3O4 nanoparticles, its optimum cure time increased to 7.6min, which may be due to the adsorption and shielding effects of some DCP by a large amount of Fe3O4 nanoparticles18,26,40. With 5 phr and 15phr ZDMA, the optimum cure times of NBR/Fe3O4 composites were respectively reduced to 6.7min and 5.8min due to the effective aid-vulcanization of ZDMA in the present of DCP34-37. The promoted vulcanization rate decreased the curing time, hence contributing to reduce the possible loss of magnetism property to the minimum for Fe3O4. Additionally, the significant increased torques in Figure 2a revealed excellent reinforcing effect of ZDMA on the NBR/Fe3O4 composites. To further investigate the influence of curing period on the crystalline structures of Fe3O4, XRD was conducted. Figure 2b shows the XRD results of NBR/Fe3O4 composite and NBR/Fe3O4/ZDMA(10phr) composite. The strong diffraction peaks at about 30.0°, 35.5°, 43.1°, 53.8°, 57.1° and 62.8° were corresponded to (220), (311), (400), (422), (511) and (440) crystal planes of Fe3O4, respectively23-26, which confirmed that the crystalline structures of Fe3O4 was not changed during vulcanization at 170oC, and, the most important was that the polymerization of ZDMA also had no influence on the crystalline structure of Fe3O4 nanoparticles. Figure 2c shows the hysteresis loop of NBR/Fe3O4 composites with and without ZDMA in a weak magnetic field. A higher Br of the 5



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NBR/Fe3O4/ZDMA(10phr) composite suggested that it was easier magnetized than the NBR/Fe3O4 composite in the same condition. This implied a more uniform dispersion of Fe3O4 nanoparticles in the NBR/Fe3O4/ZDMA(10phr) composite. However, what must be pointed out is that the applied magnetic field was too weak to achieve the saturation magnetization of Fe3O4.

Figure 3. Hysteresis loop determined at room temperature in a strong magnetic field between ±10000 Oe: (a) NBR/Fe3O4 composite with various concentration of ZDMA; (b) fixed mass fractions of Fe3O4 in NBR/Fe3O4(70phr) composite and NBR/Fe3O4(77phr)/ZDMA(10phr) composite To investigate the saturation magnetization, the magnetic properties of NBR/Fe3O4 composite as function of ZDMA content measured in a strong magnetic field are shown in Figure 3a. In general, soft magnetic materials are better with an easy magnetization/demagnetizing process to minimize the energy dissipation with the alternating fields18,41. All of the test samples presented a similar narrow hysteresis loop, showing S-shaped over the applied magnetic field. This was a typical characteristic of paramagnetism for soft magnetic material18,26,41. With the magnetic intensity increasing, the magnetization strengths of the composites increased until to achieve their saturation magnetization strength. It was clearly seen that the saturation magnetization strengths of all the test samples were basically steady when applied magnetic intensity exceed 2500 Oe. However, the NBR/Fe3O4 composites showed a slight decrease in the saturation magnetization with increasing ZDMA content. It was seen that the saturation magnetization strengths of the NBR/Fe3O4 composites with 0, 5, 10 and 15phr ZDMA were 31.736, 30.646, 29.847 and 29.003 emu/g (corresponded to the weight of the composite), respectively. This result was mainly attributed to the dilution effect of ZDMA on the proportion of Fe3O4 nanoparticles in the composites. The ZDMA content increased from 0 to 15phr, while the mass fraction of Fe3O4 nanoparticles in the composite decreased from 40.23% to 37.04%. The saturation magnetization of the NBR/Fe3O4 composites depends on the mass fraction of Fe3O4 nanoparticles rather than the dispersion and interaction of Fe3O4 in rubber matrix38. Since the previous XRD result had confirmed that the polymerization of ZDMA did not change the crystalline structures of Fe3O4, the saturation magnetization strength of NBR/Fe3O4 composites was determined by the mass fraction of the Fe3O4 nanoparticles here. In order to further reveal whether ZDMA influence the saturation magnetization of NBR/Fe3O4 composites, we fixed the mass fraction of Fe3O4 in the NBR composite by changing the content of components. Figure 3b shows the hysteresis loops of NBR/Fe3O4(70phr) composite and NBR/Fe3O4(77phr)/ZDMA(10phr) composite in which the mass fractions of Fe3O4 were 40.23% and 40.31%, respectively. It was seen that their hysteresis loop curves almost overlapped, showing a saturation magnetization strength at about 31.7emu/g. 6


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This result strongly confirmed that the ZDMA did not affect the magnetic properties of NBR/Fe3O4 composites. 3.3 Interactions between Fe3O4 nanoparticle and Zn2+ ion pairs

Figure 4. (a) FTIR spectra of NBR/Fe3O4 composites with and without 10phr ZDMA; (b) partial enlarged detail of FTIR spectra at low wavenumber region The interactions between the surface of Fe3O4 nanoparticle and NBR molecular chains were verified by FTIR, using the NBR/Fe3O4 composite and NBR/Fe3O4/ZDMA(10phr) composite as observation objects. As shown in Figure 4a, the absorption peaks at 2236, 962 and 917 cm-1 were assigned to the –CN stretching vibration, the –CH deformation vibration of disubstituted olefin and the –CH deformation vibration of mono-substituted olefin respectively, which were the characteristic absorptions of NBR37,41. The characteristic stretching band of carbonyl groups was observed at 1731cm-1 in the curve of NBR/Fe3O4/ZDMA(10phr) composite. Besides, new peaks were observed at 1585 and 1419 cm-1, which were assigned to the antisymmetric and symmetric stretching vibrations of R–COO−, respectively25. According to the similar results in Hu42 and Wei’s25 reports, the bands near 1600 and 1400 cm−1 in their system suggested a possible coordination of –COO- with the surface of Fe3O4 nanoparticles, as shown in the inset in Figure 4a. Additionally, as shown in Figure 4b, the characteristic absorption of Fe3O4 shifted from 561 cm−1 to 570 cm-1 due to a change of the surrounded chemical environment of Fe3O418,25, which confirmed the interactions between the surface of Fe3O4 and Zn2+ ion pairs in PZDMA. As a result, because of the existence of NBR-graft PZDMA34-37, the PZDMA served as an interfacial compatibilizer for NBR molecular chains and Fe3O4 nanoparticles. This is in accordance with the SEM observation which will be discussed later. 3.4 Improved dispersion of Fe3O4 nanoparticles

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Figure 5. SEM images: (a) Fe3O4 nanoparticles; cryogenically fractured surface of (b) NBR/Fe3O4 composite without ZDMA; (c) NBR/Fe3O4/ZDMA(10phr) composite and (d) NBR/Fe3O4/ZDMA(15phr) composite To give an intuitive understanding of the anticipant in-situ compatibilization of ZDMA for Fe3O4 nanoparticles, SEM observation was conducted. Figure 5a shows the SEM image of the employed Fe3O4 nanoparticles. It is clearly seen that the Fe3O4 nanoparticles have a typical trans-spinel structure with an average size of ~250nm which is a favorite size for reinforcing rubbers in industry. Unfortunately, the observed smooth surface of Fe3O4 nanoparticles caused disappointed compatibility with NBR matrix. Without any compatibilizer, the Fe3O4 nanoparticles aggregated together, showing an uneven distribution in Figure 5b. As seen, the cryogenically fractured surface of NBR/Fe3O4 composite without ZDMA was pitted with bumps and hollows which originated from the dropped Fe3O4 aggregates. Additionally, the two-phase interface of NBR and Fe3O4 nanoparticles were sharp as marked with red arrows in the inset image with magnification, showing the bad affinity. As expected, the in-situ compatibilization of ZDMA changed the above unfavorable morphology structure. A uniform distribution of Fe3O4 nanoparticles in NBR matrix can be found in Figure 5c and 5d, which suggested that the formed massive Zn2+ ion pairs in PZDMA had a strong interaction with the Fe3O4 nanoparticles to reduce their aggregation. This directly resulted in a plat cryogenically fractured surface without any pull-out of Fe3O4 aggregates. It is clearly seen that interfaces of Fe3O4 nanoparticles and NBR are fuzzy, which are marked by green arrows in Figure 5c and 5d. This further indicated that an excellent interfacial compatibility of Fe3O4 nanoparticles in NBR was achieved after in-situ compatibilization of ZDMA. In essence, the agglomeration is mainly caused by the electrostatic force and van der Waals force of particles43. During vulcanization, the rubber molecules had a strenuous movement and rearrangement under heat and pressure before its complete crosslinking. The enhanced interactions between NBR molecules and Fe3O4 nanoparticles strengthened the tearing force on the Fe3O4 agglomeration, consequently turning out a more uniform dispersion morphology of the Fe3O4 nanoparticles. 8


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3.5 Mechanical properties

Figure 6. (a) typical stress-strain curves of NBR/Fe3O4 composites with various ZDMA concentrations; (b) Mooney-Rivlin curves and (c) Tan δ of NBR/Fe3O4 composites with different contents of ZDMA from -80- 50oC Figure 6a shows the typical stress-strain curves of NBR/Fe3O4 composites with various ZDMA concentrations. In theory, ~70wt% of nanofiller is a relative high loading which should bring a significant increased mechanical property to rubbers. However, the NBR/Fe3O4 composite without ZDMA only showed a slightly enhanced tensile behavior compared with neat NBR. Note that the smooth surface of Fe3O4 nanoparticles and the “pull-out” phenomenon which are observed in the previous SEM image, this turned out at least two reasons for the disappointed tensile property: the weak interaction between Fe3O4 and NBR and the serious agglomeration of Fe3O4. As expected, the NBR/Fe3O4 composites exhibited a remarkable improved tensile property after incorporation of ZDMA. With 5phr ZDMA, the tensile strength was increased to 6.8MPa, and it further increased to 12.4MPa with 15phr ZDMA, which was nearly 6 times that of the NBR/Fe3O4 composite without ZDMA. Clearly, ZDMA contributed immeasurably to the great improvement in the mechanical property of NBR/Fe3O4 composites. The reduced aggregation and uniform dispersion of Fe3O4 nanoparticles, combined a promoted wettability of NBR molecules, improved the mechanical properties of the NBR/Fe3O4/ZDMA composites44. Of course, the polymerization of ZDMA had an excellent reactive reinforcing effect on the NBR which also contributed to the enhanced tensile property36,37. The strain-to-failure reduced along with ZDMA contents due to the improved interfacial interactions between Fe3O4 nanoparticles and NBR and increased crosslink density of NBR, which restricted the motion of rubber chains45. Correspondingly, Mooney-Rivlin curves based on tensile curves were plotted according to the following equation46,47:

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δ* =

σ 2

λ − 1/ λ

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= 2C1 + 2C2λ−1 (1)

where σ is the applied stress, σ* is the reduced stress which represented σ/2(λ-1/λ2) in the equation, λ is extension ratio and 2C1 and 2C2 are constants. The mooney-rivlin curves can be used to analysis the interaction between filler and rubber molecules during stretching. In a filled rubber, the molecular chains between filler particles can be stretched but restricted by the interaction between fillers and rubber molecules. Additionally, the elongation of the rubber molecular chains will be strongly restricted when the crosslinking points are increased. As shown in Figure 6b, a sharp decrease in the σ* at initial extension was due to the Payne effect48(breakdown of filler network at small strains). Differ to the neat NBR and NBR/Fe3O4 composite without ZDMA, the composites with ZDMA showed an upturn in σ* at large extension region, which suggested that the finite extensibility of more NBR chains was achieved. This result indicated an increased crosslink density in NBR/Fe3O4/ZDMA composites since the Zn2+ salt-bondings generated from polymerization of ZDMA also brought more crosslinking points in NBR. Another reason was that the reduced aggregation and uniform dispersion of Fe3O4 nanoparticle enlarged its interface which was then strengthened by Zn2+ ion pairs. As a result, the polymerization of ZDMA provided two positive functions that serving as an in-situ compatibilizer for Fe3O4 nanoparticle and effective in-situ reinforcer for NBR. The displacement of Tan δ peak further confirmed the increased crosslink density of the NBR/Fe3O4/ZDMA composites. As shown in Figure 6c, the Tan δ peak of NBR/Fe3O4/ZDMA composite was shifted from -23.5°C to -16.6°C with 15phr ZDMA, suggesting an increased restriction on NBR molecular chains. This result was consistent with the former discussion. More experimental results of the improved mechanical properties of NBR/Fe3O4/ZDMA magnetic rubber composites can be found in Table 1. Table 1 Effect of ZDMA content on mechanical properties of NBR/Fe3O4 composites samples

Tensile strength (MPa)

Elongation at break (%)

Tear strength (kN/m)

Hardness

Neat NBR NBR/Fe3O4 NBR/Fe3O4/ZDMA(5phr) NBR/Fe3O4/ZDMA(10phr) NBR/Fe3O4/ZDMA(15phr)

2.3±0.6 2.5±0.8 6.8±1.4 8.8±0.8 13.1±2.2

151±35 170±40 179±28 141±17 145±27

4.9±1.1 8.8±1.5 14.2±1.5 16.3±1.2 21.1±2.1

58±2 62±4 71±3 75±5 80±6

3.6 Thermostability

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Figure 7. Mass of NBR/Fe3O4 composites with different contents of ZDMA from 30- 800oC At last, we showed the TGA results of the NBR/Fe3O4 composites with various ZDMA concentrations. According to Figure 7, the addition of ZDMA did not influence the thermostability of NBR/Fe3O4 composites basically. The mass of the composites with ZDMA reduced slightly before ~400°C was attributed to the increased organic ingredients of R–COO−. After 400°C, the thermostability of NBR/Fe3O4 composites with ZDMA showed a slight superiority, which might be attributed to the synergistic effect of Zn2+ and Fe3O4. The added Zn2+ ingredients also resulted in a slight increased residual yield. 4. CONCLUSION In this paper, ZDMA was used as an effective in-situ compatibilizer for Fe3O4 nanoparticles and NBR, as well as in-situ reinforcer for the resultant magnetic rubber composites. Polymerization of ZDMA brought massive Zn2+ ion pairs which increased the polarity of NBR and simultaneously interacted with Fe3O4 nanoparticles. The in-situ compatibilization using ZDMA finally reduced the Fe3O4 agglomeration and turned out a uniform dispersion of Fe3O4 nanoparticles in NBR matrix. At the same time, polymerization of ZDMA also brought Zn2+ salt-bondings and had a significant reinforcement for NBR, which had been reported in many documents. With a loading of 5phr ZDMA, the tensile strength of NBR/Fe3O4 composite increased to 6.8MPa, and it further increased to 12.4MPa with 15phr ZDMA, which was nearly 6 times that of the NBR/Fe3O4 composite without ZDMA. Polymerization of ZDMA did not change the crystalline structures of Fe3O4, preserving the excellent magnetic properties of NBR/Fe3O4 composites. At last, the addition of ZDMA had little change on the thermostability of NBR/Fe3O4 composites. However, what must be pointed out is that the introduction of ZDMA has a disadvantage on the chemical stability of NBR/Fe3O4 composites towards acid and base due to the formation of Zn2+ salt-bondings are sensitive to the acid and base. Nevertheless, we hope this paper contributes to design of high-performance magnetic rubber composites which can be used for potential electronic appliance, automotive parts and magnetostrictive actuators.

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Fabrication of High Performance Magnetic Rubber from NBR and

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