Oil and the Straight of Malacca oil
Oil absorbentsOil spillages from industrial accidentsand leaking of oil tankers are the big problems, and greatly affected the qualityof human life. 10 Examplesof other recent spilling of oil in recent years include the purposeful dumpingof 2.5–4 million barrels into the Gulf of Suez during the Persian Gulf war, therelease of 260,000 barrels into the gulf of Alaska by Exxon Valdez, the loss of24,000 barrels into the Monongahela River due to a ruptured storage tank andthe Japan Sea and the Straight of Malacca oil tanker accident 11. Commercial polyurethane (PU) foams, and other porous materials, havebeen used as filters for oil/water separation.
PU sponges allow oil and organicsolvents to penetrate through them, while keeping the water out of thematerials due to their low density, high porosity, and high absorption ability.However, PU sponges are naturally hydrophilic making them inefficient to bedirectly used for the selective removal of oils from water. Adebajoet al. 11 reviewed in detail synthesis and the absorbing properties of the poroussorbent materials such as silica aerogels, zeolites, organoclays and natural sorbentsincluding PU foams.
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Urethane-isocyanate-alcohol polymer has highest oil uptake(oil weight times absorbing material weight) of 34.4 g/g exception of exfoliatedgraphite of 88 g/g and CF3-functionalised silica aerogel up to 237g/g oiluptake (but not indicate which oil). Shimizu et al.12 studied the effect of cell structure on oil absorption for polyurethanefoam for on-site foaming. The result showed that the airflow ofthis foam increased by crushing, and the oil absorption of this foam increasedsharply in a narrow airflow range (from 0.1 to 0.8 scfm).
The author consideredthis increase was due to the decrease of closed cell structures by crushingtreatment.Liet al.13 studied improvement in oleophilic and hydrophobic properties ofpolyurethane foams for oil spill cleanup.
PU foam was modified by grafting witholeophilic monomer lauryl methacrylate (LMA) in solvent (PU-g-LMA) and/orcoating with LMA microspheres (PU-LMA microspheres) through heating and curing.The result showed that the water sorption capacity was 14.13 g/g for neat PUfoam and 7.
03 g/g for polyurethane-grafted LMA (PU-g-LMA), and 10.69 g/g for PU-LMAmicrospheres. Similarly, modified PU cubes showed superior performance in absorbingdiesel and kerosene in the water–oil system (Figure 1). The sorption capacity of modified PU-g-LMA wasincreased by 44% for diesel and 100% for kerosene, diesel and kerosene sorptioncapacities of PU-LMA microspheres were increased by 20% and 7% relative to neatpolyurethane (Fig.1). Wanget al 14 modified polyurethane (PU) sponge using polyhedral oligmeric silsesquioxane(POSS), where the resulting material exhibited super-hydrophobic property withvery high oil absorption capability.
The POSS modified PU sponges exhibitedtwo times higher oil absorption capacity than that of unmodified ones and good recyclabilityby manual squeezing.Zhouet al 15 used a facile approach to fabricate superhydrophobic andsuperoleophilic sponges coated with polypyrrole (PPy). Water contact angles ofPPy?PTES sponge can be up to 154oC after 60 min of vapor-phase deposition. Theabsorption capacities of the PPy?PTES sponges were 24 g/g for motor oil, 23.5g/g for lubricating oil, 21.8 g/g for pump oil, 31 g/g for silicone oil, and27.4 g/g for soybean oil.
Shiet al. 16 prepared PU composite foam which induced carbonaceous nanoparticles(CNP) onto flexible PU foam (CNP-PU foam) by ultrasonication. The resultsshowed this CNP-PU foam have excellent elasticity and high mechanicaldurability even when it was subjected to 500 cyclic compression and hadexcellent absorption of organic solvents up to 121 times the weight of theinitial PU foam. (Fig.
2) PUsponges consisting of 3-mercaptopropyl)trimethoxysilane (MPS) functionalizedgraphene/PU sponge (FGN/PU sponge) showedexcellent super-hydrophobic properties due to their increased surface roughnessand decreased surface tension values leading to improved oil-water separationefficiency 10. The water contact angle in FGN/PUsponges was 160o while in PU sponges it was 50o.Regarding the mechanical properties, the compressive strength of FGN/PU spongeswas almost doubled (15 kPa after 400 times of repetition) compared to PU ones(6.8 kPa after 400 times of repetition). Finally, the absorption capacities of a FGN/PU sponge were 25-44 times ofits original mass, higher than that of a neat PU sponge (21-36 times) for n-hexane, diesel oil, lubricating oiland crude oil, respectively. (Fig.2)