Synthesis and Characterization of a High Oil-Absorbing Poly (Methyl Methacrylate-Butyl Acrylate)/ATP–Fe3O4 Magnetic Composite Material
Fathelrahman Mohammed Soliman1, 2, Wu Yang1, Hao Guo1, Mahgoub Ibrahim Shinger3,
Ahmed Mahmoud Idris3, Emtenan Suliman Hassan4
1Analytical Chemistry (Functional Materials), College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, China
2Key Lab of Eco-environment Related Polymer Materials of MOE, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, China
3Analytical Chemistry (Photocatalysis), College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, china
4Analytical Chemistry (Functional Materials), College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, China
To cite this article:
Fathelrahman Mohammed Soliman, Wu Yang, Hao Guo, Mahgoub Ibrahim Shinger, Ahmed Mahmoud Idris, Emtenan Suliman Hassan. Synthesis and Characterization of a High Oil-Absorbing Poly (Methyl Methacrylate-Butyl Acrylate)/ATP–Fe3O4 Magnetic Composite Material. American Journal of Polymer Science and Technology. Vol. 2, No. 1, 2016, pp. 1-10. doi: 10.11648/j.ajpst.20160201.11
Received: July 10, 2016; Accepted: August 19, 2016; Published: August 30, 2016
Abstract: A highly oil-absorptive Poly (methyl methacrylate-butyl acrylate)/ ATP–Fe3O4 magnetic composite resin was prepared by a conventional suspension polymerization using methyl methacrylate, and butylacrylate were used as monomers, and N, N-methylenebis acrylamide (MBA) as crosslinking agent and ammonium persulfate (APS) as initiator on the modified ATP–Fe3O4substrate. The optimum reaction condition was examined in detail. The results indicated that the prepared composite resin combined characteristics of stronger magnetism and higher oil absorbency. The resultant resin had high oil absorbency and the highest absorbencies respectively reaches 23.8, 25, 30.0, 32.6g.g for xylene, toluene, carbon tetrachloride and chloroform, which were higher than some oil absorptive materials previously reported. At the same time, it could easily be recovered and reused too. Kinetic investigation proved that the oil absorption obeyed the pseudo-first-order kinetic model and intraparticle diffusion model.
Keywords: High Oil-Absorption, Magnetic Composite Resin, Modified ATP–Fe3O4
Oil pollution of marine environments is becoming a serious issue with the growth of the off-shore petroleum industry and the necessity of marine oil transportation. Various Materials, including natural absorbents and synthesized polymeric materials, for example, brick clay, activated carbon, silicon dioxide, polyurethane foam, paper pulp, polypropylene fiber, and oil absorbing resin, have been employed to deal with oil pollution hazards and recover the spilled oils on water. Among them, the capability of oil-absorbing resin is seen to be superior to other ordinary materials [1-4]. High oil-absorption resin, different from ordinary oil-absorption material, is a new kind of self-swelling oil-absorbing material with many virtues of large absorbing quantity and variety of oils, as well as good oil-retention, and has a promising future. Synthesis and application of high oil-absorption resins have very important practical significance in environment protection and medicine, and so on. It is this broad range of possible applications that has led to recent interest in this system [5,6]. In previous work, the magnetite-covered clay particles were prepared with Na-montmorillonite flakes as supports . Clays offer an option for the removal of organic and inorganic contaminants . The adsorption of several organic contaminants in water such as pesticides, phenols, and chlorophenols has been widely reported recently [9–15]. The adsorption capacity of clays results from a relatively high surface area and a net negative charge on their structure. Attapulgite (ATP), one of these clays with the same functions but different structure, possessing of an ideal molecular formula of [Si8Mg5O20(OH)2(H2O)4·4H2O, is a kind of natural fibrous mineral, has also been widely used in polymer nanocomposite due to its large specific surface area, adjustable surface chemistry, non-toxicity, low cost and abundance in nature [16-19].
In this work, Poly (methyl methacrylate-butyl acrylate)/ATP–Fe3O4, magnetic composite resin with high oil-absorbency were synthesized by a suspension copolymerization on the modified ATP–Fe3O4 substrate. ATP-Fe3O4 magnetic particles, possessing special structure, stable properties and low-cost, were coated with a thin layer of poly (MMA-BA). Poly (MMA-BA) was obtained using methyl methacrylate and butylacrylate as monomers, and N, N-methylenebisacrylamide as crosslinking agent, ammonium persulfate (APS) as initiator, and gelatin as the dispersants. The influencing factors on the oil absorbency of the high-oil-absorption resin were studied in detail including the monomers mass ratio, amounts of the cross linking agent, initiator, and ATP–Fe3O4. The oil absorbency for several organic compounds (representative oil contaminations) was examined.
Methyl methacrylate (MMA), butyl acrylate (BA) were washed with 5% sodium hydroxide three times before use, and then washed with deionized water until neutralization. After being dried over anhydrous magnesium sulfate, they were distilled twice under reduced pressure. N, N-methylenebisacrylamide (MBA) was used as received. Ammonium persulfate (APS) was recrystallized from water. Benzoyl peroxide (BPO) (Kang-Wei Chemical Reagent Factory, Shanghai, China). Attapulgite nano-fibrillar clay provided by Gansu ATP Co. Ltd., Gansu, China, was milled and passed through a 320-mesh screen before use. Ferric chloride hexahydrate (FeCl3.6H2O), ferrous chloride tetrahydrate (FeCl2.4H2O) and ammonium hydroxide (NH4OH, 25% of ammonia), gelatin glue (Chemical Reagent Factory, Shanghai, China), toluene, xylene, carbon tetrachloride, and chloroform were of analytical reagent grade.
2.2. 2.2. Synthesis of the ATP–Fe3O4 Magnetic Particles
The synthetic process of ATP–Fe3O4 magnetic particles was carried out by a modified co-precipitation method . The ATP was dispersed into water and then pretreated with the FeCl3 salt in flask under magnetic stirring as following: 4.0 g of FeCl3.6H2O was added into water (total volume: 200 ml), then 1.50 g of attapulgite was dispersed into the above mixture in ultrasonic bath for 30 min to obtain a stable suspension. And last, the mixture was stirred for 12 h under magnetic stirring and the suspension was used for further experiments directly.
A given concentration of FeCl2 solution was added to the suspension of ATP with FeCl3 in N2 atmosphere. After the solution was heated to 90°C, different amount of NH4OH (25%, w/w) (6.0 ml, 3.0 ml, 2.0 ml, or 2.0 ml) was added rapidly under stirring and black precipitate appeared immediately. The mixture was kept under stirring for another 1 h. The products were precipitated and washed with water after the reaction mixtures were cooled to room temperature. Finally, the black product ATP–Fe3O4 magnetic particles were dried in the vacuum.
2.3. Preparation of the Composite Resin
A given amount of gelatin glue was dissolved in a known volume of distilled water in a 250-ml round bottomed flask equipped with stirrer and a reflux condenser at 30°C for 30 min. The mixture of butylacrylate, methyl methacrylate and MBA was then added to the above flask, as well as APS and modified ATP–Fe3O4. After suspension reaction for 6h at the stirring speed of 200 rpm under nitrogen atmosphere at 90°C, the prepared composite resin was collected by filtration when the solution was cooled, then washed with hot water of 60°C, and dried in a vacuum at 60°C until a constant weight was reached.
Synthesis and oil absorption of the magnetic high oil absorption resin field were shown in Fig. 1.
2.4.1.Fourier Transforms Infrared (ATR FT-IR)
The attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectra were collected by using a Nicolet NEXUS 670 FT-IR single-beam spectrometer (USA) with a 4 cm-1 resolution maintaining constant contact pressure between the Ge crystal and the specimens.
Thermal stability measurements were performed on a Metter Toledo TG apparatus (Switzerland) from 30 to 800°C, with a heating rate of 10°C/min under a nitrogen flow rate of 50 mL/min.
2.4.3.Transmission Electron Microscopy (TEM)
The morphology and structure of the composite particles was determined by transmission electron microscopy (TEM) on a JEM 100 CX instrument (JEOL Co., Japan).
2.4.4. Scanning Electron Microscopy (SEM)
Scanning electron microscopy (SEM) images were taken with a JSM-5600LV scanning electron microscope (Japan) at an applied voltage of 20 kV.
2.4.5. X-ray Diffraction (XRD)
A crystallographic study was performed on the ATP-Fe3O4 modified by D/max 2400 X-ray diffractometer (XRD; Rigaku, Japan) by using Fe K and radiation. Magnetic properties were detected by vibrating sample magnetometer (VSM) (Lakeshore 7304).
2.4.6. Removal of Oil
The sample was immersed in various oils for given time periods at room temperature and then taken out from the oil. The excess oil on the resin surfaces was removed by tissue paper. The oil absorbing sample was then weighed. The equation q (g.g-1) = (mS - mD)/mD was applied to evaluate the oil absorbency, where mD (g) was the weight of the dry sample and mS (g) was the weight of the swollen sample.
3. Results and Discussion
Characterization of the magnetic composite
3.1. Attenuated Total Reflectance Fourier Transforms Infrared (ATR FT-IR)
Fig. 2 showed infrared spectra of the samples. In Fig. 2 (a), IR spectra of ATP, 3609cm-1 and 3459cm-1 peaks were assigned to (Al) O–H stretching vibration and the (Si) O–H stretching vibration of ATP respectively, and 1650cm-1 absorption peak was ascribed to –OH bending vibration . These three characteristic peaks of ATP disappeared in the spectra of magnetic composite resin as shown in Fig. 2 (c). In the spectra of ATP–Fe3O4 as shown in Fig. 2 (b), the absorbance bands at 3404 cm-1 ascribed to the characteristic peak of –OH groups was very weak, suggesting that the crystallization was basically complete. In addition, the absorbance bands at 598 cm-1 and 461 cm-1 ascribed to the vibrations of Fe+2─O2− and Fe3+─O2−, were typical characteristics of spinel Fe3O4 . It revealed that the materials contained crystallized spinel Fe3O4 and the nanoparticles absorbed onto ATP were Fe3O4. The absorption bands at 607 cm-1 and 487 cm-1 assigned to the Fe–O bond for spinel Fe3O4 particles in ATP-Fe3O4  disappeared in the spectra of magnetic composite resin (figure 2 c). The characteristic band of Si–O–Si for ATP-Fe3O4 was observed around 1060 cm-1. In Fig. 2 (c), the absorptions at 1223 and 1257 cm-1 were characteristic absorption peaks of MMA and absorptions at 923 and 966 cm-1 were butyl ester characteristic absorption peaks. Appearance of the peaks at 2937 cm-1 and 2865 cm-1 indicated the presence of saturated C–H stretching bands of both –CH3 and –CH2 groups. No peaks from 3000 to 3200cm-1 observed suggested all monomers had been polymerized. All of the results confirmed that the co-polymerization of MMA and BA on the surface ATP-Fe3O4 in the presence of APS has been initiated.
3.2. Thermogravimetric Analysis
Thermogravimetric analysis of the composite resin was used to evaluate the thermal stability of the Poly (MMA-BA)/ATP–Fe3O4 composites. Fig. 3 showed the first weight loss stage could be ascribed to the evaporation of water molecules, which were 5.38% and 4.36% for ATP-Fe3O4 and magnetic composite resin respectively . Structure destroy of the composite resin started at 300oC, indicating that the composite resin had a higher thermostability. Compared with Poly (MMA-BA)/ATP–Fe3O4, ATP-Fe3O4 could not be almost decomposed at high temperatures, which showed little weight loss (8.10% below 600◦C). So, the remaining mass for magnetic composite resin was attributed to the thermal resistance of ATP-Fe3O4 particles.
3.3. Scanning Electron Microscopy (SEM)
The morphologies of ATP, ATP-Fe3O4 and corresponding magnetic composite were observed by SEM. As shown in 4 A and 4 B, corresponding SEM images, also supported above conclusions. Due to the negative surface charges, iron cations could be bonded onto the surface of ATP via electrostatic forces easily  so that Fe3O4 particles obtained by co-precipitation process could disperse in situ onto the ATP surface. Fig. 4C displayed MMA-BA copolymer possessed a porous structure with a few of small pores. However, magnetic composite Poly (MMA-BA)/ATP-Fe3O4 containing modified ATP–Fe3O4 particles showed larger size pores and obviously different structure from MMA-BA copolymer (Fig. 4 D), which suggested that the incorporation of proper amount of ATP-Fe3O4 was benefit to improve the surface structure of the magnetic composite. Furthermore, the images also gave a direct observation that ATP-Fe3O4 was uniformly dispersed in the polymer matrix with good interface compatibility.
3.4. Transmission Electron Microscopy (TEM)
The morphologies of ATP, ATP-Fe3O4 and corresponding magnetic composite were observed by TEM. As shown in Fig. 5 (1), TEM image of ATP showed that ATP had a fibrillar single crystal structure, whose smallest structure unit possessed a length of 500–2000 nm and a diameter of 10–25 nm . Fig. 5 (2) displayed that Fe3O4 nanoparticles uniformly dispersed on the surface of ATP fiber and the average thickness of raw ATP particles was 42 ± 8.0 nm, and the average size of Fe3O4 particles (black particles) was 10 nm.
3.5. X-ray Diffraction (XRD)
Fig. 6 showed the X-ray diffraction (XRD) patterns of ATP-Fe3O4 (a) and magnetic composite resin (b). In the 2θ range of 20 – 70°, six characteristic peaks corresponding to Fe3O4 (2θ = 30.3°, 35.7°, 43.3°, 53.50°, 57.5°, and 63.0°) were observed in the ATP-Fe3O4 and magnetic composite resin, and the peaks could be indexed to (220), (311), (400), (422), (511) and (440) diffractions (JCPDS card (19-0629) for Fe3O4). In 27.01° appeared ATP (131) diffraction peak. The results suggested that the addition of raw ATP particles or polymers into Fe3O4 did not change its crystalline form. Moreover, it also could be seen that the XRD patterns of magnetic composite resin was similar to that of ATP-Fe3O4, indicating they had the same cylinder wall structure and interplanar spacing.
3.6. Magnetic Properties of the Modified ATP–Fe3O4 and Poly (MMA-BA)/ATP-Fe3O4 Magnetic Composite Resin
Fig. 7 showed the magnetic properties of the modified ATP–Fe3O4 and poly (MMA-BA)/ATP-Fe3O4 magnetic composite resin at room temperature. The saturation magnetization (Ms) value of the modified ATP–Fe3O4 was 0.481 emu.g-1, while that of the magnetic composite resin was 0.132 emu.g-1. It indicated that robust coating of MMA-BA on their surface and the introduction of the inorganic clay mineral of ATP quenched the magnetic moment of nanosized Fe3O4 particles by electron exchange between coating and surface atoms . However, the magnetic composite resin still maintained an obvious magnetism, which was advantageous to separate the resin using a magnet.
3.7. Digital Photograph Images of Oil Absorbency from Water Surface
As expected, the magnetism of the composite resin was related to its ability applied to environmental water treatment. The highly hydrophobic and superoleophilic nanoparticles exhibited a property called selective absorbance. Fig. 8 (A, B, C) was the digital photographs of oil absorbency from water surface by poly (MMA-BA)/ATP–Fe3O4 magnetic composite resin under magnetic field. Fig. 8 A - 8 B showed when it contacted with a layer of oil on a water surface, poly (MMA-BA)/ATP–Fe3O4 magnetic composite resin quickly absorbed the oil while repelling the water, then the oil-absorbed magnetic composite resin could be readily removed with a magnet bar over the water surface.
3.8. Optimization of Polymerization Conditions
3.8.1. Effect of Amount of Crosslinking
Effect of the amount of crosslinking on the oil absorbency was shown in Fig. 9 (a). Oil absorbency increased at first with increasing MBA concentration from 0.18 to 0.40 wt % and then decreased with further increase in MBA concentration. The oil absorbency reached the highest when the amount of crosslinking was 0.40%. If the amount of crosslinking was too small, resin density reduced and the ratio of soluble resin increased, so that the oil absorbency decreased. When the crosslinking content was below 0.25 wt %, the composite was semi-soluble and the oil absorbency could hardly be measured. As a result, the oil absorbency was very low, which was consistent with the Flory theory .
3.8.2. Effect of Amount of Initiator
Fig. 9 (b) showed the relation between the amount of initiator and the oil absorbency. The oil absorbency was the highest when the amount of initiator was 1.0%. It is known that the amount of initiator has important influence on molecular weight of polymer and effective network dimension of synthetic resin [24-28]. Where the oil absorbing resin was free of modified ATP–Fe3O4, the optimum amount of initiator was about 1.25%.
3.8.3. Effect of Monomer Ratio
The effect of monomer ratio on the crosslinking polymerization was investigated. Fig. 10 (a) an exhibited the relation between the monomer ratio and the oil absorption. It could be seen that the oil absorption curve showed a peak profile. With MMA content increasing, the oil absorption increased. Addition of MMA changed the stability of the network structure of the resins. However, if the amount of MMA was too great, the oil absorption reduced, because the lipophilicity was much worse than that of BA. Oil absorption reached its highest value of 22.07 g/g at the ration of MMA/BA of 1:1.
3.8.4. Effect of Amount of the Modified ATP–Fe3O4
The effect of the amount of the modified ATP- Fe3O4 on oil absorbency was shown in Fig. 10 (b). Oil absorption of the composite resin increased with the amount of the modified ATP- Fe3O4 increasing from 0.5 to 2.0 wt % and then decreased with further increase in the modified ATP- Fe3O4. The modified ATP–Fe3O4 occupied part of the interior space of the resin and was distributed in the resin dispersedly. When the amount of a modified ATP- Fe3O4 reached 2.0%; the oil absorption reached the highest of 25.0 g/g for toluene.
3.9. Absorption Rate and Absorption Kinetics
To test the absorption rate, the sample was immersed in excess solvent at room temperature. And then it was taken out and weighed every 1 h. The absorption reached saturation after 7h the highest oil absorbency was respectively 18.3, 19.2, 23 and 25 g/g for xylene, toluene, carbon tetrachloride and chloroform. It could be seen from Fig. 11, oil absorbency increased rapidly at the beginning due to the solvation of the network chains. The main driving force of this process was the change in the free energies of mixing and elastic deformation. However, the swelling was limited, that is, with the time increasing the absorption rate became slower and finally reached saturation.
Absorption of oil onto the superabsorbent was studied in terms of the kinetics of the absorption mechanism by using three models. Assuming that the absorption kinetic process obeyed the first-order model, the kinetics equation was
Where qt (g/g) was the amount of an absorption time t (h), k1 was the rate constant of the equation (h-1) and qe was the amount of absorption equilibrium (g/g). The absorption rate constant k1 could be determined experimentally by plotting of ln (qe-qt) versus t.
Similarly, if the absorption obeyed the second-order kinetics model, kinetics equation became following form:
Where k2 (g/g.h) was the rate constant of the second order equation. The rate constant k2 could be obtained by plotting 1/ (qe-qt) versus t.
Where Kid (g/g/h1/2) was the rate constant of intraparticle diffusion, which could be measured by plotting qt verses t1/2.
k1, k2 and kid for the four kinds of oils, chloroform, carbon tetrachloride, toluene and xylene were respectively calculated from the slopes and listed in Table 1.1. Obviously the correlation coefficients for the first-order model were better than the second-order model, indicating that the first order model was more suitable to describe the absorption process. The correlation coefficients for the intraparticle diffusion model were over 0.9900 indicating that the absorption of these four oils onto the resin was mainly intraparticle diffusion controlled.
Corresponding linear fitting curves of the three models were showed in Fig. 12 (a, b, c).
|Oils||qmax (g/g)||The first-order model||The second-order model||Intraparticle diffusion model|
|k1 (h-1)||R||k2 (g/g.h)||R||Kid (g/g/h1/2)||C (g/g)||R|
3.10. Comparison of the Prepared High Oil-Absorbing Magnetic Composition Resin with Reported Oil Absorbents
A comparison of oil absorbency of the prepared high oil-absorbing magnetic composition resin with reported absorbents was given Table 1.2. The magnetic composition resin had a relatively high absorbency as comparable with that of the other adsorbents. Therefore, considering the low cost and conventional use of this resin, it could be used as an alternative material to remove oils from water.
|Oil absorbents||Oil absorbency (g/g)||References|
|Cetane methacrylate highly oil absorptive resin||36.6 for CCl4|||
|Oil absorption resin (B-PEHA)||30.88 for chloroform, 19.75 for toluene, 18.78 for xylene|||
|CEMA/IOA copolymers||13.94 for toluene|||
|Magnetic composite oil absorption resin||20 for chloroform, 10.5 for toluene|||
|PC-CPMA||4.08 for toluene|||
|Poly (Butyl Methacrylate-Styrene) highly oil absorptive resin||14.12 for toluene|||
|poly (methyl methacrylate-butyl acrylate)/ATP–Fe3O4 magnetic composite||32.6 for chloroform, 30.0 for carbon tetrachloride, 25.0 for toluene, 23.8 for xylene||This work|
A high oil-absorbing magnetic composite resin was synthesized by using a simple and conventional suspension polymerization method. It combined high oil-absorption with magnetic separation technology, because of its magnetic character; it can be easily collected by magnetic means in a short time. The prepared high oil absorption magnetic composite resin had higher oil absorbency than some previously reported oil absorptive materials, which indicated the prepared high oil absorption magnetic resin had a good application prospect. Kinetic investigation proved that the oil absorption obeyed the pseudo-first-order kinetic model and intraparticle diffusion model.