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Preparation and characterization of porous PDMS beads for oil and organic solvent sorption.


The organic contamination, for example, petroleum product, from spills and leaks, is a great risk for human, animal and plant. It will affect wildlife in the water bodies and on the shores for a long time, moreover lead to substantial environmental and ecological problems. The methods of oil-spill processing are mainly classified as chemical method and physical method [1-4], The use of absorption materials for oil removal is attractive principally due to its ability to transform oil contaminant from the liquid phase into solid or semi solid phase [5], Many absorption materials, such as inorganic materials [6, 7], natural materials [8, 9], and synthetic materials [10-12], have been widely studied for the removal of spilled oils.

In the previous study, Genzer et al. have investigated the utilization of poly (dimethyl siloxane) (PDMS) as an absorbent for the removal of organics and crude oil from water 113]. PDMS materials are low-cost, highly hydrophobic, and commercially available (14, 15]. However, the densities of most of the commercial PDMS are close to or more than the density of water [16]. Therefore the particles of PDMS are inconvenient to be straightforwardly retrieved after oil absorption and even cannot absorb the oils floating on water due to these particles sinking in water. Based on these facts, it is necessary to decrease the density of PDMS for oil absorption.

In this study, we developed a simple and effective technology to prepare porous PDMS beads in order to decrease the density and improve the usability of PDMS, and investigated the characteristics of the beads. These beads were used as oil absorbents. The effects of several variables, such as immersion time and the amount of crosslinker, were investigated. The oil absorption capacities of different PDMS were examined through experimental investigations. The reused performances of PDMS were also studied.



SDM-801, a PDMS kit containing two components, a liquid silicon rubber base (component A: hydroxyl terminated PDMS prepolymer, a little of reinforcing agent and solvent) and a curing agent (component B: crosslinker, tetra ethyl orthosilicate, catalyst, dibutyltin dilaurate and solvent), was purchased from China Haohua Chemical Co. Gasoline and kerosene were collected from local gas station. Other reagents employed in these experiments were of analytical grade.

Preparation of Porous PDMS Beads

Porous PDMS beads were prepared as follows. Total of 0.5 g of component B was dissolved in 15 mL of diluent ["-octane or carbon tetrachloride (C[C1.sub.4])], then the solution was mixed with 20 g of component A, the mixtures were dropped into a beaker containing 500 mL gelatin solution (100 g/L) by a syringe. The dispersion system was stirred (80 r/min) with a mechanical stirrer at 70[degrees]C. After 1 h, the beads were solidified, then the wet beads were collected and extensively rinsed with hot distilled water to remove gelatin. Finally, the crosslinked porous beads were dried in a vacuum oven at 60[degrees]C until a constant weight (about 2 h).

Apparent Density and Porosity of the Beads

The apparent density ([[rho].sub.a], g/[cm.sup.3]) and the porosity are two important physical parameters for porous materials. The apparent density could be determined by the ratio of the mass to the total volume ([V.sub.T], [cm.sup.3], including the solid and void volumes) of the PDMS beads. Specifically, 3 g of dried beads were placed into a 10 mL volumetric flask of known weight at 20[degrees]C. The flask was then filled with water to the mark and weighted [17], The apparent density of the beads could be calculated from Eq. 1 [17]:

[[rho].sub.a] = [S.sub.0] / [V.sub.T] = [S.sub.0] / [10 - ([S.sub.w] - [S.sub.0])/[[rho].sub.w]] (1)

where [S.sub.w] (g) is the total weight of the PDMS beads and water, [S.sub.0] (g) is the weight of the dry PDMS beads, [[rho].sub.w] ([[rho].sub.w] = 0.998 g/[cm.sup.3]) is the density of water.

The porosity ([??]) of a porous medium describes the fraction of void space in the material. It is defined by the ratio [18]:

[theta] = [V.sub.p]/[V.sub.T] = 1 - [V.sub.0] / [V.sub.P] + [V.sub.0] (2)

where [V.sub.p] is the pore volume in the beads and [V.sub.0] is the solid (nonporous) volume of dry PDMS. Equation 2 could be expressed as Eqs. 3 or 4:

[theta] = 1 - [S.sub.0]/[[rho].sub.0] / [S.sub.0] / [[rho].sub.a] (3)

[theta] = 1 - [[rho].sub.a] / [[rho].sub.0] (4)

where [[rho].sub.0] ([[rho].sub.0]= 1-185 g/[cm.sup.3]) is the solid density of dry PDMS.

Scanning Electron Microscopy (SEM)

The morphologies of the macropores in the beads were observed by a scanning electron microscope (Philips, XL-30). For SEM observation, the porous beads were cut with a single edged razor blade, attached to the sample supports and coated with a gold layer.

Oil Absorbency Experiments

The oil absorbency experiments in the present work were carried out according to the methods reported previously [8, 19], Specifically, 0.2 g PDMS beads were put into a glass beaker (100 mL), then 20 mL of the solvent or oil (hereafter collectively called oil) was poured into the beaker, after a predetermined time, the beads were removed by a wire-mesh basket. Excess oil on the surface of the beads was allowed to drain for 30 [+ or -] 3 s. The saturated absorbent was then immediately transferred to a pre-weighed weighing bottle and weighed. The equilibrium absorption capacity was calculated according to the following equation:

Q = S - [S.sub.0] / [S.sub.0] (5)

where Q (g/g) is the equilibrium absorption capacity, S (g) is the weight of PDMS after absorption, and [S.sub.0] (g) is the weight of PDMS before absorption.

Each sample under the same conditions was measured three times in parallel, and the average value was calculated. All of the oil absorbency measurements were conducted at 20[degrees]C.


In order to investigate the reusability of the PDMS beads, a new parameter, desorption ratio, was defined in this article. Some pre-weighted dry PDMS beads ([S.sub.o], about 0.4 g) were immersed in n-heptane at room temperature for 5 h. Then the beads were removed by a wire-mesh basket. Excess oil on the surface of the beads was allowed to drain for 30 [+ or -] 3 s. The beads were immediately taken out and weighed. The weight was recorded as [S.sub.n] (g). Afterward, the beads were dried in a vacuum oven at 60[degrees]C to constant weight (about 2 h). The beads were taken out and weighed. The weight was recorded as [S.sub.d] (g). Six cycles of the absorption and desorption process were performed for each sample. The desorption ratio (R) was calculated by the following formula:

R = [S.sub.n] - [S.sub.d] / [S.sub.n] - [S.sub.0] x 100% (6)


Characterization of the PDMS Beads

In the preparation process of the PDMS beads, the simultaneously adding diluents had two main functions. (1) The addition of diluent could significantly decrease the viscosity of the pre-polymer system, so it was in favor of the dropping of PDMS with a syringe. Moreover, in suspension solution, it was well known that the size and shape of beads could be affected by many factors, such as the stirring speed, the viscosity of PDMS prepolymer system. (2) The diluent could act as a pore formation agent, and the porous beads could be formed due to the evaporation of the diluent in the polymerization system. The effects of different diluents addition on the PDMS beads were examined (Fig. 1). In the preparation of the beads, the beads of PDMS using n-octane as a diluent (O-PDMS) were spheres with smooth and almost nonporous surfaces (Fig. la), and all beads were sinkable in water (Fig. lb). The SEM images (Fig. 1c and d) clearly revealed that the interior profile of the beads were also almost nonporous. While the beads of PDMS using C[C1.sub.4] as a diluent (C-PDMS) were spongy spheres with porous surfaces (Fig. le), and all beads were floating on water (Fig. 1f). The SEM images (Fig. 1g and h) revealed that the interior profile of the CPDMS beads had a number of cavities with different sizes. The apparent density and porosity of the different PDMS beads were listed in Table 1.

Absorption Rate

In order to ascertain the minimum time to reach absorption equilibrium, a study on the effect of the immersion time will be necessary. Figure 2 illustrates the effect of the immersion time on the n-heptane absorption. It was shown that absorption rate was very fast at initial stages due to the rapid attachment of the absorbate to the surface of the beads. Nearly 40% of the equilibrium absorption value occurred in the first 10 min for O-PDMS and N-PDMS (no diluent was added in the preparation of PDMS); however, even 72% of the equilibrium absorption value occurred in the first 10 min for C-PDMS. At about 75 min, more than 90% of the equilibrium value reached for all beads. And thereafter the rate of absorption was found to be slow because the adsorbate molecules had to diffuse into the interior of the beads with the particles gradually swelling, until the equilibrium reached and remained constant at the immersion time of nearly 160 min. Similar results were obtained for other adsorbates, such as n-decane, n-nonane, ethyl acetate, chloroform, tetrahydrofuran. Differences could be found in the equilibrium absorption capacities for different beads (figures omitted). All the results confirmed the porosity of the beads was favorable to the oil absorption rate. The fast absorption rate was beneficial to the practical application of the beads as an absorbent. However, for subsequent experiments, the samples were immersed for 4 h to ensure the absorption equilibrium.

Effect of Component B Content on Oil Absorbency

To investigate the effect of the content of component B on the oil absorbency, a series of the PDMS beads with varied component B contents (A:B:C[C1.sub.4] = 100:2 to 5:60, g:g:mL; keeping all other conditions unchanged) were prepared. Figure 3 illustrates the relationship between the oil absorbency and the content of the component B. As shown in Fig. 3, for all the four oils used in the experiment, there was a maximum value in oil absorption when the mass ratio of A: B was 100: 2.6. A lower ratio of component B in the preparation of the PDMS beads could not form the cross-linked network. However, the PDMS beads with a higher ratio of component B would decrease the oil absorbency for all the four oils. An excess of cross-linking agent caused the formation of a too dense network of the polymer, which drastically reduced the chain length between cross-linking points, meanwhile resulted in an excessive decrease in the mobility of the polymeric chains. This was disadvantageous for the oils to flow inside of the network, the oil absorbency was low accordingly [20].

Effect of Diluents Content on Oil Absorbency

In the preparation, the diluents content affected the porosity and the apparent density of the beads, and therefore affected oil absorbency of the beads. A series of C-PDMS with varied diluents feed ratios (A:C[C1.sub.4] = 100:55, 100:65, 100:75, 100:85, g/mL; B: 2.6 g) were prepared with all other variables unchanged. The relevant oil absorbency investigations are depicted in Fig. 4. It could be seen that for all the four oils examined, there was a maximum value when the feed ratio was 100:75 (A:C[C1.sub.4], g/mL). A higher ratio of C[C1.sub.4] in the preparation would only form the smaller PDMS fractionlet.

Comparison of the Different PDMS Beads

Figure 5 depicts the absorption capacities for several oils by different PDMS beads. It could be seen that the equilibrium absorption capacities of N-PDMS and O-PDMS for C[C1.sub.4] were 2.48 and 3.93 g/g, respectively; however, the value was up to 5.72 g/g for C-PDMS. Comparing with N-PDMS, absorption capacity of C-PDMS was increased by 2.3 times. These PDMS beads had different oil absorption capacities for different oils. The order of equilibrium absorption capacities on these beads for all the six oils was C-PDMS > O-PDMS > N-PDMS. Based on the above comparison, it could be concluded that the increase of the porosity was an efficient way to improve the oil absorbency of the PDMS beads as expected.

Reusability of the C-PDMS Beads

The reusability is extremely important for an absorbent. On one hand, the reusability can allow the repeated use of the absorbent. On the other hand, the isolation of absorbate can allow its reuse or efficient disposal. The reusability of C-PDMS was investigated by measuring its oil absorbency and oil desorption properties. The relevant results are displayed in Fig. 6. The desorption ratio (R) of C-PDMS was almost up to 100% each time. There was not obvious change in the absorption capacity after treatment. Even after six times reusable tests performed, the reused C-PDMS exhibited almost the same absorption capacity as the new C-PDMS. The PDMS beads were of pretty high stability and recyclable values.


Porous poly (dimethyl siloxane) beads (C-PDMS) were prepared and characterized. The absorption experiments showed that C-PDMS exhibited more oils absorption capacity and faster oils absorption rate than the nonporous or oligoporous PDMS beads did. The porosity of PDMS was favorable to both absorption rate and equilibrium absorption capacity; accordingly, increasing the porosity was an efficient way to improve the oil absorbency of PDMS. The density of PDMS was greatly decreased after porous formation (about 0.6 g/[cm.sup.3]), so the porous PDMS beads could provide a possibility to absorb the oils floating on water. In order to verify whether the observed behavior was generally accepted, some additional work would be in progress in subsequent studies. The PDMS beads were of pretty high stability and recyclable values.


This study was supported by the Science & Technology Research Project of Chongqing Municipal Education Commission of China (KJ 110708), the 100 Academic & Discipline Talents Cultivation Plan of Chongqing, the Innovative Research Team Development Program in University of Chongqing (KJTD 201314), and the Training Programs of Innovation & Entrepreneurship for Undergraduates of Chongqing (201211799021).


(1.) C. Bravo-Linares, L. Ovando-Fuentealba, S.M. Mudge, and R. Loyola-Sepulveda, Fuel, 103, 876 (2013).

(2.) R.R. Lessard and G. Demarco, Spill. Sci. Technol. Bull., 6,59 (2000).

(3.) S.A. Shedid, J.H. Abou-Kassem, and A.Y. Zekri, Energ. Source, 27, 1257 (2005).

(4.) J. Wang, Y. Zheng, and A. Wang, Client. Eng. J., 213, 1 (2012).

(5.) O.K. Karakasi and A. Moutsatsou, Fuel, 89, 3966 (2010).

(6.) D. Bastani, A.A. Safekordi, A. Alihosseini, and V. Taghikhani, Sep. Purif. Technol., 52, 295 (2006).

(7.) O. Carmody, R. Frost, Y. Xi, and S. Kokot, J. Colloid Interface Sci., 305, 17 (2007).

(8.) M.A. Abdullah, A. Ur Rahmah, and Z. Man, J. Hazard. Mater., 177, 683 (2010).

(9.) M. Radetic, V. Ilic, D. Radojevic, R. Miladinovic, D. Jocic, and P. Jovancic, Chemosphere, 70, 525 (2008).

(10.) J. Lin, Y. Shang, B. Ding, J. Yang, J. Yu, and S.S. Mar, Pollut. Bull., 64, 347 (2012).

(11.) C. Song, L. Ding, F. Yao, J. Deng, and W. Yang, Carbohydr. Polym., 91, 217 (2013).

(12.) B. Wu and M.H. Zhou, Waste Manag., 29, 355 (2009).

(13.) I. Park, K. Efimenko, J. Sjoblom, and J. Genzer, J. Disper. Sci. Technol., 30, 318 (2009).

(14.) S. Pinto, P. Alves, C.M. Matos, A.C. Santos, L.R. Rodrigues, J.A. Teixeira, and M.H. Gil, Colloid Surface B, 81, 20 (2010).

(15.) N.S.M. Stevens and M.E. Rezac, Polymer, 40, 4289 (1999).

(16.) J.E. Mark, Polymer Data Handbook, Oxford University Press Inc, New York (1999).

(17.) Y.X. Bai and Y.F. Li, Carbohydr. Polym., 64, 402 (2006).

(18.) F. Zhao, B.Y. Yu, Z.R. Yue, T. Wang, X. Wen, Z.B. Liu, and C.S. Zhao, J. Hazard. Mater., 147. 67 (2007).

(19.) X.C. Gui, J.Q. Wei, K.L. Wang, A.Y. Cao, H.W. Zhu, Y. Jia, Q. K. Shu, and D.H. Wu, Adv. Mater., 22, 617 (2010).

(20.) A.M. Atta, R.A.M. El-Ghazawy, R.K. Farag, and A.A. Abdel-Azim, React. Fund. Polym., 66, 931 (2006).

Ning Li, (1,2,3) Tao Li, (1) Xiaomei Lei, (1) Bo Fu, (1) Weixi Liao, (1) Jian Qiu (4)

(1) Department of Chemistry & Chemical Engineering, College of Environmental & Biological Engineering, Chongqing Technology & Business University, Chongqing 400067, China

(2) Key Laboratory of Catalysis & Functional Organic Molecule of Chongqing, Chongqing 400067, China

(3) Key Laboratory of Catalysis Science & Technology of Chongqing Education Commission, Chongqing 400067, China

(4) Institute of Environmental Protection, Chongqing Technology & Business University, Chongqing 400067, China

Correspondence to: Ning Li; e-mail:

DOI 10.1002/pen.23860

Published online in Wiley Online Library (

TABLE 1. Apparent density and porosity of the different PDMS beads.

             Apparent density
Beads         (g/[cm.sup.3])    Porosity

N-PDMS (a)        1.185            0
O-PDMS            1.061          0.105
C-PDMS            0.599          0.494

(a) No diluent was added in the preparation.
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Title Annotation:poly dimethyl siloxane
Author:Li, Ning; Li, Tao; Lei, Xiaomei; Fu, Bo; Liao, Weixi; Qiu, Jian
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:9CHIN
Date:Dec 1, 2014
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