Silicon Rubber that Soaks up Oil

Team 7l: Absorption of Oil Spills Presentation Video
https://mediaspace.carleton.ca/media/Team%207-presentation%20of%20findings/1_24jvjnc5

Overview

Figure 1: Oil Spill in Ogogiland River, Nigeria [1]

Commercially available melamine sponges coated with a small amount of silicone rubber and solvent hexane is a low cost, environmentally sound solution for the removal of oils and other pollutants from water. The coating material forms a thin layer which is superhydrophobic and superoleophilic allowing oil to be absorbed into the pores of the sponges and repelling water from the surface. The target contaminant is any pollutant that is immiscible with water such as hydrocarbons, coolants and certain pesticides which all have a low surface tension causing it to be absorbed by the sponge. The sponge has an absorption capacity of 45 – 75 times its own weight and can be reused many times. Other technologies which incorporate the same properties using exotic materials are expensive, difficult to scale up which is why the development of melamine sponges with high selectivity in absorbing oil is of great ecological importance in removing pollutants from contaminated water sources. 

Polymer Sponge Material: Arkash Sundralingam

Figure 2: Melamine sponge used for absorbing oil [2]

Porosity is the ratio that is expressed as a percentage of the spaces or pores in comparison to the total area of the object [1]. Porosity is important in explaining 1) why the polymer sponge material absorbs oil and 2) how this oil is stored within the sponge. In the application of silicon rubber that soaks up oil, the basic principle of how this technology will work is to allow water through and as the oil enters the pores but cannot escape due to the rubber’s ability to “absorb” the oil [2]. A quality of the polymer sponge that makes it ideal for absorbing oil is to be made of porous natural polymer similar to luffas that are called melamine, white sponge in figure above. The more porous a material is, the more spaces for the oil to enter and be absorbed.

References

[1]  Pu, X., 2020. Porosity - An Overview | Sciencedirect Topics. [online] Sciencedirect.com. Available at: <https://www.sciencedirect.com/topics/earth-and-planetary-sciences/porosity> [Accessed 7 October 2020]

[2] V. Pham and J. Dickerson, “[PDF] Superhydrophobic silanized melamine sponges as high efficiency oil absorbent materials.: Semantic Scholar,” undefined, 01-Jan-1970. [Online]. Available: https://www.semanticscholar.org/paper/Superhydrophobic-silanized-melamine-sponges-as-high-Pham-Dickerson/83050af51958f37c9fea4ec0867334e67fec7f7a. [Accessed: 04-Nov-2020].

Optimization of Sponge Material: Mitchell Cornwall

Figure 3: The rough surface of the sponge interacting with a water molecule [3]

To optimize the oil and toxic compounds absorption of a melamine sponge, the sponge must undergo a modification to the surface. The sponge will be treated with a rough texture upon the exterior surface. This rough coating allows the sponge to repel liquid water to create a water repellent surface. The water is repelled from the surface because when the water meets the solid sponge it overtakes the contact angle threshold of 150 degrees. This enables the water to run right off the surface[1]. Having a surface that is water repellent will maximize the absorbance of other chemicals, which is the main purpose of the sponge [2]. When the sponge repels the water in leaves behind air pockets that exists in the outer pores of the sponge.  As the melamine sponge is used to float on the top of the water and collect toxins, it will absorb chemicals that are less dense than water in the sponge’s pores.

Figure 4: Absorbent melamine sponge pads seeping up oil from a body of water [4]

References

[1] R. Alla, “Comparison of melamine and conventional sponges for washing dishes and cleaning a house,” Comparison Melamine Conventional Sponges Washing Dishes Stock Photo (Edit Now) 1496021810, 12-Apr-2003. [Online]. Available: https://www.shutterstock.com/image-photo/comparison-melamine-conventional-sponges-washing-dishes-1496021810. [Accessed: 04-Nov-2020].

[2] Shirtcliffe, N. Atherton, S, “The Effect of Roughness Geometry on Superhydrophobicity and Related Phenomena”, Comprehensive Nanoscience and Nanotechnology (Second Edition) 2019. [online]. Available:https://www.sciencedirect.com/topics/engineering/lotus-effect.[Accessed: 22-Sep-2020].

Sponge Coating Material: Andy Hinch

Figure 5: Mechanical adhesion and the coating material interlocked with pores [Andrew Hinchliffe]


The coating material of the sponge is what gives it the oil absorbing and water rejecting properties. The coating is made up by two materials being the silicon Polydimethylsiloxane (PDMS) and the solvent hexane. To absorb oil, the sponge is required to be squeezed and stretched resulting in the coating material having to do the same. This is achieved by mechanical adhesion which is when the coating material interlocks with the pores of the underlying sponge [1]. By creating anchor points to hold the coating in place all around the sponge, a flexible and strong coating is created. The chemical properties in which allows the sponge to reject water are due to both materials being insolvent with water. The PDMS aspect of the coating will only absorb organic compounds such as oil, and with water being inorganic, it will not be rejected [2]. Hexane is a nonpolar molecule meaning it is unable to form hydrogen bonds with water resulting in the material pushing water away from the sponge [3].

References

[1] M. K. Chuadhury, The Mechanics of Adhesion, vol. 1 & 2. Amsterdam, Netherlands: Elsevier Science & Technology, 2002.

[2] Scheirs, J. (2000). Modern fluoropolymers (Vol. 48). Chichester: Wiley, 1997.

[3] ‘POLAR AND NONPOLAR COMPOUNDS,” Polar vs. Nonpolar. [Online]. Available: http://users.stlcc.edu/gkrishnan/polar.html. [Accessed: 04-Nov-2020]. 

Density: Olaitan Edu

Figure 6: Oil floating above water in a sample tube [5]

Oil is made up of hydrocarbons and is processed into different fuels such as diesel, kerosene, and gasoline to power boats and ships. These fuels are categorized by the physical property of density which is the mass of a substance per unit volume. The densities of gasoline, diesel and saltwater are 820, 720 and 1023 kg/m3 respectively. The lower densities of gasoline and diesel results in these fuels floating above water and forming two distinct layers [1][2].

References

[1] Engineering Toolbox, 2001 [online]. Available at: https://www.engineeringtoolbox.com [Accessed Oct 21st 2020] 

Image citations

[1] U. N. News, “cleaning-nigerian-oil-pollution,” UN News, 14-Jun-2011. [Online]. Available: https://news.un.org/en/story/2011/08/383512-cleaning-nigerian-oil-pollution-could-take-30-years-cost-billions-un, . [Accessed: 24-Nov-2020].

[2] R. Alla, “Comparison of melamine and conventional sponges for washing dishes and cleaning a house,” Comparison Melamine Conventional Sponges Washing Dishes Stock Photo (Edit Now) 1496021810, 12-Apr-2003. [Online]. Available: https://www.shutterstock.com/image-photo/comparison-melamine-conventional-sponges-washing-dishes-1496021810. [Accessed: 04-Nov-2020].

[3] S. X. staff, “Lotus leaf inspires scientists to create world's first self-cleaning metals,” Phys.org, 28-Jun-2016. [Online]. Available: https://phys.org/news/2016-06-lotus-leaf-scientists-world-self-cleaning.html. [Accessed: 24-Nov-2020].

[4]  C. E. P. Complete Environmental Products, “Booms,” Complete Environmental Products, 28-Jan-2020. [Online]. Available: https://www.cepsorbents.com/products/sorbent-technologies/oil-only/booms/. [Accessed: 25-Nov-2020]

[5] M. Bailey and J. Martin, “FUNDAMENTALS OF ENGINEERING THERMODYNAMICS Eighth Edition,” Academia.edu, 12-Jan-2018. [Online]. Available: https://www.academia.edu/21431299/FUNDAMENTALS_OF_ENGINEERING_THERMODYNAMICS_Eighth_Edition. [Accessed: 25-Nov-2020].