19

Application and Characteristics ofLipophilic Gels
Tomohiro Murakami＊, Syazwani Binti Mohd Najib＊＊and Shogo Umakoshi＊
Abstract
Equilibrium swelling curves of Octadecyl Acrylate (ODA) gels with various cross-linking densities inBenzene were measured as a function of temperature. The ODA gel with different five kinds of crosslink
densities was prepared. Sample ODA gels were prepared by a free radical copolymerization in Benzene. At
20℃, ODA gel molar ratio 90:1 is swelling in about 30 times compared with the original volume. WhenODA gels rises in temperature, the swelling ratio has grown, too. This change showed behavior opposite toPoly (N-isopropylacryamide) (PNIPA) gel of hydrogel. Moreover, the swelling degree of ODA gel has
increased with the decrease in the cross-linking density. It is found that the cross-linking density of thenetworked structure play a key role in the swelling and collapsing of neutral polymer gels. From theseresults, a basic finding concerning the application development of the oil-water separator gel sheet wasobtained.
Keywords : Octadecyl Acrylate (ODA) gels, cross-linking density, oil-water separator gel sheet, swelling ratio

1. Introduction
With the increasing awareness towards environmental
preservation, pollution by the outflow of oil has becomesa serious problem in recent years. We live in a world
encompassed by various environmental destructions,especially the pollution of rivers, lakes and marshes, theocean, and soil caused by the outflow of oil from tankers,
factories, homes and restaurants are becoming a serious
problem. Recently, an oil spill which occurred in South
Korea has ignited fear in us and thus, causing an increasetowards environmental preservation. There are numerous
lipophilic high polymer materials on the market for thepurpose of disposal and for the treatment of the outflowof oil. However, most of these materials are disposable
generating a lot of garbage, which results in a waste
problem.
One of the causes of oceanic water pollution is the out
flow of oil from the bilge of shipping vessels. As an effort
to overcome such problems, a new standard for theprocessing of bilge (a compound liquid of oil andseawater) in the engine room was adopted by the IMO(International Maritime Organization) in July of 2003 andit was enforced in January of 2005.Morover, on January
1, of 2007, the standard density of oil emitted from thebilge in the engine room or any other un diluted oil waschanged to 15ppm or less［1］. Most of the bilge in theengine room is treated by using a large-scale oil-water
separation machine. The rest of the bilge is usually wipedoff. The disposal of the cloth used for wiping the bilge
results in a lot of garbage, which leads to a waste
problem.
As a means to overcome said problem, there are many
lipophilic high polymer materials other than the gels usedfrom the disposal of cooking oil from homes andrestaurants to treatment of oil spills in the ocean.
However, due to the fact that most of these materials aredisposable, it becomes a large amount of trash, which
results in a waste problem. To overcome these problems,
this research uses a lipophilic gels instead of a lipophilic
high polymer material. At the present, lipophilic gels are
hardly utilized due to the fact that they have inferior
absorption and discharge rates when compared hydrogels.
Regardless to the demand of lypophilic gels, because thecharacteristic is hardly understood as it is, application ofsaid gel is not advanced. The reusability and physicalproperties of said lipophilic gel is researched. By
combining this lipophilic gel and the water absorbent gel
sheet, we hope to develop a reusable oil-water separator
gel sheet, as shown in Fig. 1.

＊Maritime Technology Department＊＊Department of Mechanical Engineering, University of Fukui

平成20年９月30日受理20弓削商船高等専門学校 紀要 第31号（平成21年）

Reusable absorbent gel sheet has up to now beenstudied in our laboratory［2-4］. From the results, it wasfound the absorption and the discharge properties of water
absorbent gel sheet were the same as the SAP sheet on themarket. And the sheet discharges the water rapidly in thetransition temperature. Therefore, it is the best for the gel
sheet repeatedly. It was thought that the oil-water
separator was possible if lipophilic gel was used together
with this hydrogel.

state of equilibrium, which takes more than 2 days (〜48hours).

Main ConstituentO

n-C18H37
O
Octadecyl Acrylate+CrosslinkerOOOFig. 1Structure of oil-water separator gel sheet

Ethylene Glycol Dimethacrylate

2. Experiment
2-1 Preparation of Sample Gels
Sample ODA gels were prepared by a free radical
copolymerization in Benzene. Five different kinds of gelswere made by changing the ratio of the main constituent,Octadecyl Acrylate (ODA) and the cross-linker, Ethylene
Glycol Dimethacrylate (EGDMA). The preparation
method of a ODA:EGDMA=95:1 gel is as follows［5］.
ODA monomer (9.863 g) was dissolved in 15.2 ml ofbenzene. After that cross-linker EGDMA (60.0 µl) wasadded. Followed by 0.099 g of Azobisisbutyronitrile(AIBN) as the initiator for polymerization. Gelation wascarried out in 24 hours in 5.5 mm in diameter glass tubes
at 60℃. ODA:EGDMA=90:1,85:1,80:1,75:1 gels wereprepared using the same method. The gels were removed
from the glass tubes and cut into segments ofapproximately 1 cm in length and placed in a glass vial
filled with benzene. The temperature of the bath could becontrolled within a±0.1℃ range. The temperature wasdecreased from 50 to 10℃ at 10℃ per interval.
Measurements of the gels diameters were taken. Themeasurements were taken after the gels had reached theAIBNBenzene*OOOOn-C18H37OOODA gelFig. 2

Structural chart of ODA gel

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Application and Characteristics ofLipophilic Gels（Murakami・Syazwani Binti Mohd Najib・Umakoshi）

The diameter of the gel, d, was measured by amicroscope with calibrated scale. The swelling ratio ofthe gel, V/V0, was calculated from the ratio of equilibrium
gel diameter to the original diameter, (d/d0), where d0 was5.5 mm. The temperature was controlled within 1℃ for
more than a day by circulating water during themeasurement.
The structural chart of ODA Gel is as shown in Fig. 2.
2-2 Swelling ratio of the gels
Fig. 3 shows the swelling ODA gel. The diameter (dwet)of the gel is 11.9 mm and mass (Wwet) is 1.0890 g. It isvery transparent, and looks like the PNIPA gel ofhydrogel well. However, it is more elastic than thePNIPA gel. On the other hand, a dry ODA gel is shown inFig. 4. The diameter (ddry) of the gel is 4.5 mm and mass(Wdry) is 0.0685 g. All benzenes in the gel has not been
exhausted, and some remains. The gel becomes cloudy
transparently and pure white. A dry gel is elasticity, and isvery hard. It easily returns to a transparent gel like Fig. 3
when this dry gel is soaked in benzene. Swelling degree
Q of the gel is defined by as the following equation:
Q = (Wwet -Wdry) / Wdry
Where Wdry and Wwet are the weight of the dried gel
and the wet gel, respectivity. The swelling degree of thegel was 15 times. The swelling degree of the gels inBenzene was about 20times. It is thought that thedifference of the swelling degree is done by the benzene
that remains in a dry gel as described in the above
sentence.
The swelling ratio, V/V 0 , was obtained from therelation, V/V0 = (d/d0)3, where V0 and d0 are the volumeand diameter of the when it was prepared, repectivity.

Fig. 4

Dry ODA gel

3. Conclusion and Discussion
3-1 Temperature Dependence of ODA Gels
Swelling curves measured on a series of gels in benzene
are shown in Fig. 5. The degree of swelling of ODA gelsof various cross-linking densities in Benzene is plotted asa function of temperature. When the ODA:EGDMA
molar fraction is at 95:1, as the temperature decreases thevolume ratio also decreases. Other molar fraction gelsalso show the same phenomenon. When the molar,
fraction is equal to 75:1, a greater decline in the gel s
volume ratio is seen between temperatures 20℃ and10℃. The decline of volume ratio for 95:1 and 85:1 gels
are smaller when compared to the decline of volume ratio
for the 80:1 and 75:1 gels. From these observations it isthought that ODA gels do have temperature dependence.
Both the compatibility of the polymer chain with theorganic solvents and the cross-linking density of thenetworked structure play a key role in the swelling andcollapsing of neutral polymer gels. As a result, thelipophilic gels swell using the same mechanism as that of
the ionic gels.
95:1
90:1
85:1
80:1
75:1

Swellig ratio(V/V0)50403020100010203040
temperature㧔͠㧕5060Fig. 5 The swelling degree of ODA gels with various
concentration in the network in Benzene is plotted as aFig. 3

Swollen ODA gel

function of temperature.

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弓削商船高等専門学校 紀要 第31号（平成21年）

3-2 Cross-linker concentration Dependence ofODA Gels
Ｆig. 6 shows the relationship between the swelling
ratio and the cross-linker concentration of ODA gels fromFig. 5. The swelling ratio of the gel with molar fraction
ODA:EGDMA = 90:1 is the largest of about 30 times.
Theoretically, as the concentration of the cross-linker
increases, the amount of oil absorbed should decrease,meaning that the swelling ratio should also decrease. Onthe other hand, reducing the amount of cross-linker
increases the swelling ability, but stable network cannot
from it density is too low. However, it was not seen as
such a tendency was remarkable. Therefore, it will benecessary to do a more detailed experiment.

Swelling ratio(V/V0)

50

50͠
40͠
30͠
20͠
10͠

4030
20
100
70

75
80
85
9095 100
Molar fraction(ODA:EGDMA)=x : 1

Fig. 6 Swelling ratio vs. concentration of cross-linker ofODA gels.

4. Summary
Equilibrium swelling curves of Octadecyl Acrylate(ODA) gel in Benzene were measured as a function oftemperature. From these observations, it is found that,when the temperature is decreased, ODA gel s volumeratio also decreases. This shows reverse temperaturedependency when compared to PNIPA gels. The gel does
not follow the theory that, when the cross-linker
concentration increases, the volume ratio decreases. Fromthese results, it is found that both the compatibility of thepolymer chain with the organic solvents and the crosslinking density of the networked structure play a key role.
And a basic finding concerning the application
development of the oil-water separator gel sheet wasobtained.
Finally, to be able to adopt this gel in the developmentof reusable oil-water separator sheets, more detailed
experiments are necessary. In addition to its scientificimportance, an understanding of the volume transition inlipophilic gels will hasten the application of gel
technology to reusable oil-water separator sheets.
Acknowledgment
This work was supported by KAKENHI (19760581).
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