Damping Analysis of Some Inorganic Particles on Poly(butyl-methacrylate)

Viscoelastic polymers can be used as damping materials to control unexpected vibration and noise through energy dissipation. To investigate the effect of an inorganic filler on damping property, a series of inorganic particles, Ferriferous oxide(Fe3O4), Graphene/Fe3O4(GF), and Fe3O4 of demagnetization(α-Fe2O3) were incorporated into poly(butyl-methacrylate) (PBMA). The effects of the dispersion of particles, as well as the interaction between particles and the PBMA matrix on the damping property of composites, were systematically studied. Results revealed that the addition of three types of particles can effectively improve the damping properties and broaden the effective damping temperature range. Dispersion of α-Fe2O3 in the PBMA matrix is better than that of Fe3O4. As a result, the damping peak can be increased more. The interaction between GF and the PBMA matrix is stronger than that between Fe3O4 and the PBMA. The damping peak of the composites can be suppressed by GF, which is opposite to Fe3O4 and α-Fe2O3. In addition, glass transition temperature (Tg) of all composites in the study shifted to low temperatures.


Introduction
With the development of modern technology, all kinds of mechanical equipment are developing high speed, high efficiency, and automation, but vibration and noise, which are produced during work, seriously damage the reliability and stability of the machine itself [1,2]. Passive or active damping are extremely effective ways for, mostly, vibration control [3,4]. Passive vibration control involves the modification of the stiffness and damping of a vibrating system. A straightforward and effective solution for vibration and noise control is the application of a viscoelastic material, such as polymers [5]. Because of its high damping characteristics around the glass temperature, viscoelastic polymer is usually used as a damping material to control noise and vibration, which has attracted considerable attention [6]. The loss tangent (tan δ), which is the ratio of E" to E (tan δ = E"/E ), is used as an assessment of the ability to dissipate energy by elastomers. E and E" represent the storage modulus and loss modulus, respectively [7]. High-performance viscoelastic damping materials should meet the requirement of tan δ > 0.3 over a broad damping temperature range of at least 60-80 • C [8].
Matrix polymers must be considered according to the application and environment in which the material is to be applied [9]. Polyacrylate materials are well known for their excellent damping properties for plenty of polar ester groups [10,11] and PBMA has an excellent adhesion property, with its macromolecular chain having many branched chains, which can effectively increase internal friction and improve damping properties. A great efforts have been devoted to broaden the effective damping temperature range of acrylic polymers, including co-polymers, interpenetrating polymer networks (IPN), and blends [12][13][14]. One of the most important ways is blends consisting of adding filler with modifications. Fe 3 O 4 (ferriferrous oxide), in our previous study, was found to have a strong interaction with ethylene vinyl acetate (EVA), which has polar vinyl acetate (VA) segments [15,16]. Fe 3 O 4 , theoretically, should also have strong interactions with PBMA because of its polar carbanyl groups. So, after hybridization with Fe 3 O 4 , the particles will have interactions with PBMA, which can make a great contribution to mechanical loss [17]. However, it is easy for Fe 3 O 4 particles to aggregate due to magnetism between particles [18,19]. Thus, the dispersion state of particles in the matrix and the interactions between particles and the matrix are very important for damping properties of composites. To improve the dispersion of Fe 3 O 4 in the PBMA matrix, Fe 3 O 4 particles of demagnetization were prepared in high temperatures [20,21]. Moreover, to study the effect of fillers-matrixes interactions on the damping properties of PBMA, Fe 3 O 4 and graphene/Fe 3 O 4 hybrid particles were incorporated into PBMA. These two particles have a distinguishable interaction with PBMA, since they have different interfaces. Graphene, with a two-dimensional layer, prevents Fe 3 O 4, with three-dimensional sphere shape, from aggregating. Meanwhile, due to the magnetism of graphene [22], it is easier for Fe 3 O 4 to load graphene as the core.
In this article, to study the effects of the dispersion of particles, as well as the interactions between particles and the PBMA matrix on damping property of composites, Fe 3 O 4 , Graphene/Fe 3 O 4 (GF), and α-Fe 2 O 3 are incorporated into PBMA. The elemental analysis, morphology, and specific surface area of graphene hybrid particles are analyzed by energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), and specific surface area and pore size tester, respectively. The structures, particle size, and magnetization of Fe 3 O 4 of demagnetization(α-Fe 2 O 3 ) are characterized by X-ray diffraction (XRD), laser particle size analyzer, and vibrating sample magnetometer analysis (VSM). The dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) are used to characterize the damping materials. It is expected to find far-ranging applications as damping materials in vibration control.

Synthesis of Graphene/Fe 3 O 4 Hybrid Particles
First, 0.2 g of pristine graphene was added into a NaOH (sodium hydroxide) aqueous solution (0.1 mol/L) and heated to 80 • C with vigorous stirring. Then FeCl 3 ·6H 2 O and FeSO 4 ·7H 2 O were dissolved in a PVA aqueous solution to prepare the mixed solution of iron ions with 2:1 molar ratio of Fe 3+ to Fe 2+ , then 200 mL mixed solution of iron ions was dropped slowly into the NaOH aqueous solution with graphene through a constant pressure drop funnel at 80 • C in a water bath. The reaction continued for 40 min and the black precipitates were washed with alcohol and deionized water for at least five times, followed by freeze drying at 50 • C for 96 h.

Preparation of Samples of Poly(butyl-methacrylate)-Based Hybrid Material
Blends of PBMA with different particle contents were prepared via solution mixing at room temperature for 15 min. The basic formulation of the composites is listed in Table 1; the blends were compression molded to form sheets (20 mm long, 12 mm wide, and 3 mm thick) under a pressure of 10 MPa for 20 min at 160 • C.

Characterization
X-ray diffraction (XRD, X Pert PRO MPD, Almelo, the Netherlands) was used to test the crystal structure of Fe 3 O 4 . The scanning range was from 5 • to 70 • and the scanning speed was 3.6 • /min. Particle sizes were characterized by Laser Particle Size Analyzer (Master sizer 2000, Malvern Instruments Ltd., Malvern, UK), ethanol was used as a dispersant, and the shade was 3.5%.
The specific surface areas were tested by a specific surface area and pore size tester (ST-MP-9, Quantachrome Instruments, Beijing, China). The test results were analyzed by the multipoint Brunauer-Emmet-Teller (BET) method. Before the test, samples were kept at 423 K in a vacuum environment for about 2 h. VSM (BKT-4500Z, Quantum Design Ltd., San Diego, CA, USA) was carried out to measure the saturated magnetic strengths of particles, in open circuit mode at normal temperature.
The morphology of the poly(butyl-methacrylate)-based composite material was studied by scanning electron microscopy (SEM; ZEISS EV0 MA15, Carl Zeiss microscopy Co., Ltd., Jena, Germany). To prepare samples for SEM analysis, the composites were quenched in liquid nitrogen and cryogenically fractured.
Elemental analysis was carried out at Energy Dispersive Spectrometer (EDS; Elementar, Langenselbold, Germany) for determination of the Fe, O and C content.
Dynamic mechanical analysis (DMA) was carried out on Q800 (TA Instruments, New Castle, DE, USA) by using a dual cantilever clamp and a testing method of temperature ramp-frequency sweep with a frequency of 1 Hz. The samples were trimmed to dimensions of 20 mm long, 12 mm wide and 3 mm thick. The oscillation strain amplitude was set to be 15 mm.

Morphologies and EDS of Graphene/Fe 3 O 4 Hybrid Particles
The morphology of the GF composite particle is shown in Figure 1a. As we can see, GF presents a near-spherical shape. Fe 3 O 4 particles, as the core and most of the particle surface, are surrounded by graphene sheets. To further testify the structure of GF, the GF particle was analyzed by energy dispersive spectrometer. Figure 1b-d are the mapping images of iron, oxygen, and carbon elements, respectively. The above discussion indicates that Graphene and Fe 3 O 4 particle was compounded when available.

Demagnetization of Fe 3 O 4
As reported in the literature, a high temperature is commonly used for demagnetization [21].  Moreover, the values of particle size are listed in Table 2. The particle size of α-Fe 2 O 3 quite close to that of Fe 3 O 4 , which further indicates that the interaction between the two particles and matrix is similar.

Morphology
The dispersion of the fillers was researched by SEM measurements on the brittle and snapped sample surface. As shown in Figure 4

Damping Property of PBMA/Fe 3 O 4 and PBMA/α-Fe 2 O 3
Dynamic mechanical analysis (DMA) is widely used to determine material damping properties as functions of temperature, frequency, and stress [23] and to investigate the effect of an increasing content of inorganic particles on the damping properties of PBMA/Fe 3 O 4 and PBMA/α-Fe 2 O 3 . Results of the DMA tests are presented in the form of loss factor, tan δ, as functions of temperature.
Curves of the variations of tan δ with the temperature of Fe 3 O 4 and α-Fe 2 O 3 composites are shown in Figures 5 and 6, respectively. The loss tangent (tan δ) is commonly called damping and is the evaluation measure of energy dissipation. The values of the maximum heights versus the loads of particles are shown by Figure 6. As is seen, Fe 3 O 4 and α-Fe 2 O 3 show similar influences on the maximum heights of tan δ.   Table 3 shows that all PBMA/Fe 3 O 4 blends have efficient damping (tan δ > 0.3) over a wide temperature range of more than 64 • C. Moreover, the peak area under the tan δ temperature curves is abbreviated as TA, which is a measure of the energy dissipation of a transition process [24]. The TA values of PBMA/Fe 3 O 4 composites are also summarized in Table 3. Compared with blank PBMA, PBMA/Fe 3 O 4 composites exhibit relatively high TA values. The glass transition temperature (T g ) of the composites, taken at the maximum value of the tan δ, is determined by the DMA [25,26]. As observed from Figure 5a, increasing the mass fraction of Fe 3 O 4 shifted the curve peak to low temperatures, with the incorporation of 1% Fe 3 O 4 into the PBMA matrix leading to the greatest decrease in T g , referring to neat PBMA. This phenomenon can be interpreted as follows: With the inclusion of Fe 3 O 4 into PBMA, the Fe 3 O 4 particles interact with and shield carbanyl groups and, as a result, a lowered T g was observed.
For α-Fe 2 O 3 , to improve the dispersion of Fe 3 O 4 in the PBMA matrix in the present study, demagnetization of Fe 3 O 4 (α-Fe 2 O 3 ) was incorporated into the PBMA. The maximum tan δ of PBMA/α-Fe 2 O 3 increased and the temperature range with tan δ > 0.3 became wider, as shown in Figure 5b and Table 3. The damping properties of the composites improved. Moreover, when the weight content of α-Fe 2 O 3 was 1%, the tan δ reached 1.63, and the corresponding temperature range, with tan δ > 0.3, was about 103 • C. The results show the demagnetization of Fe 3 O 4 (α-Fe 2 O 3 ) could increase the internal friction due to homogeneous dispersion of α-Fe 2 O 3 in the PBMA matrix (Figure 4e). Moreover, T g of the α-Fe 2 O 3 composites shifts to low temperature as seen from Figure 5b and it is more obvious to shift to low temperature comparing to Fe 3 O 4 composites.

Damping Property of PBMA/GF
As shown in Figure 7, the loss tangent, tan δ, of PBMA/GF composites increased compared with neat PBMA. However, Figure 7 and Table 4 demonstrated that the damping factor of PBMA/GF composites is lower than that of PBMA/Fe 3 O 4 composites, although, Fe 3 O 4 particles with a modified surface can better disperse in the PBMA matrix. These results are because the interfacial interaction in PBMA/GF hybrids is stronger than that in the PBMA/Fe 3 O 4 hybrids, as shown in Table 3. The adhering of Fe 3 O 4 to graphene, as shown in Figure 1, changes the interaction surfaces between particles and molecular chains that interact between Fe 3 O 4 and PBMA and become the interaction between graphene and PBMA. GF particles have a larger specific surface area, as shown in Figure 8, which enhances interaction between GF and PBMA, thus, resulting in lower internal friction.
It is interesting that the glass transition temperature of PBMA/GF composites also shifts to low temperatures. The results are attributed to Fe 3 O 4 adhering to graphene, which changes the interaction surfaces between particles and molecular chains as mentioned above. Moreover, graphene is a typical two-dimensional layered material. The layered structure is held together by van der Walls interactions, shown in Figure 1. An intercalation state or, even, exfoliation state of fillers is possibly formed due to the weak van der Walls interactions between adjacent layers. Furthermore, the layer of two-dimensional layered fillers could slip to some extent [27]. For example, Jiang et al. [28] prepared chlorinated butyl rubber/graphene oxide composites (CIIR/GO) and proposed a slippage of the lamellae to interpret the results that the T g of CIIR/GO composites shifts towards low temperatures. The mechanism is also used to interpret our case in that the slippage of the lamellae could increase the mobility of PBMA chains so that the glass transition temperatures of PBMA/GF hybrids shift towards low temperatures.

Surface Properties of Inorganic Particles
To study the effects of the interaction between particles and PBMA on the damping property of composites, the results of a specific surface area and pore size tester were analyzed by the BET method; then, the surface areas of particles measured by BET (S BET ) can be calculated by: where: • V m → single layer adsorption volume • V → all adsorption volume • P → partial pressure of adsorption thing • P 0 → saturated vapor pressure of adsorption thing • C → BET constant • A → Avogodro constant (6.023 × 10 23 /mol) • σ m → the sectional area of an adsorption thing (for the adsorption of N 2 , σ m = 16.2 × 10 −20 m 2 ).
Thus, the (P/P 0 )/V × (1 − P/P 0 ) vs. (P/P 0 ) should be linearity. The linear fitting was used and the results (BET spectra) are plotted in Figure 8. According to the slope and intercept of these fitting lines, we can obtain the value of V m . In Figure 8, all dots can be linearly fitted in some degree (R 2 > 0.9). The values of the surface areas measured by BET (S BET ) are listed in Table 5. According to Table 5, the S BET of GF is larger than that of Fe 3 O 4 , which may be caused by graphene, which has a larger specific surface. Moreover, to better understand the surface distribution of the materials, the spectra of nitrogen absorption and desorption for BET is shown in Figure 9.

Conclusions
In this study, hybrid composites based on poly(butyl-methacrylate), Ferriferous oxide(Fe 3 O 4 ), Graphene/Fe 3 O 4 (GF), and demagnetization of Fe 3 O 4 (α-Fe 2 O 3 ) were successfully prepared. The SEM and EDS results show that Graphene/Fe 3 O 4 (GF) was synthesized and that α-Fe 2 O 3 can be finely dispersed in the PBMA matrix. VSM results revealed that α-Fe 2 O 3 showed the lowest magnetization after heating at 500 • C. The SEM results show that dispersion of α-Fe 2 O 3 in the PBMA matrix is better than that of Fe 3 O 4 and the BET results, exhibiting interfacial interactions between PBMA and GF, is stronger than that between PBMA and Fe 3 O 4 . The DMA results indicate that the damping properties of PBMA can be improved by filling Fe 3 O 4 , GF and α-Fe 2 O 3 . When the weight content of α-Fe 2 O 3 was 1%, the PBMA/α-Fe 2 O 3 had the best damping performance, with the tan δ reaching 1.63 and the corresponding temperature range, with tan δ > 0.3, being about 103 • C. Moreover, it is also worth mentioning that the T g of the composites shifted to low temperatures. This result needs to be further studied.