Absorbent polymers can be used, for instance, to absorb hydrocarbons from an aqueous medium such as the absorption of oil from water. In some configurations, conventional absorbent polymers are contained within a permeable material; for example, conventional spill “socks” and booms can hold an absorbent polymer within a fabric to enable the absorbent polymer to be applied directly to the site of interest. Moreover, conventional absorbent booms can float on a water surface to help contain a spill from spreading beyond the boom. This application, however, requires the absorbent polymer to be contained within a permeable membrane or fabric.
Conventional absorbent polymers also may be applied as a powder to a water surface. The absorbent may absorb the hydrocarbon and even gel together; however, this process requires the removal of the resulting gel formed from the swelled absorbent polymer. The resulting gel can lack adequate shear and tensile mechanical strength, and may be difficult to remove. Consequently, a need exists for an absorbent polymer that has an enhanced shear and tensile mechanical strength to facilitate recovery of the polymer after absorbing the desired liquid.
To address this need, a reinforced absorbent polymer was developed to improve mechanical properties without degrading their absorption performance. The reinforced polymer includes an absorbent polymer, and at least one fiber for reinforcement disposed in the polymer.
Improving the polymer’s mechanical properties can be achieved by incorporating fibers of a material with a high mechanical strength relative to that of the absorbent polymer. There are numerous possible configurations for reinforcing fiber, but the performance can be optimized by meeting four main criteria:
The frictional interface between the fibers and the polymer should have low surface tension to permit the polymer to slide past the fiber during volume expansion caused by absorption, and the fibers should be of sufficient length to accommodate the expansion of the reinforced polymer.
If the polymer cannot slide past the fibers during expansion, the fibers can be localized along a line or plane contained within the material and close to one face or edge of the material.
The length of the fibers should be adequate to provide the desired mechanical strength, but short enough to enable the fibers to be pulled through the material if desired.
The fibers should be largely co-directional to enable for lateral expansion between the fibers, and easier slippage at the fiber-polymer interface. The fibers can extend orthogonally to one another provided that criteria 1 and 3 are met and the fibers are not connected at the cross points, or if the fibers satisfy criterion 2.
The fibers are embedded into the polymer by their disposition in the pre-polymer mixture (monomers, solvent, constituent polymers, etc.), and subsequently performing the polymerization. To ensure slippage at the interface between the fibers and the polymer, the fiber surface should be as smooth as possible, insoluble in the pre-polymer mixture, and chemically inert under the polymerization conditions.
The fibers can be of arbitrary length provided they are largely co-directional, enable the desired level of expansion, and permit slippage at the fiber-to-polymer interface within the desired time frame. Typical fiber lengths range from millimeters to meters. The fiber diameter can also be adjusted to attain the desired mechanical properties, with a typical range of 10 nm to 1 mm. The reinforced polymer can be of arbitrary size and form factor. In addition, the reinforcement can be implemented in either a batch or continuous process.
The reinforcing fiber and absorbent polymer form an interface with appropriate surface tension, sliding past each other during volume expansion of the absorbent polymer caused by absorption of the liquid. For liquids, surface tension (force-per-unit-length) corresponds to surface energy density (effectively energy-per-unit-area or flux). Water, for example, has a value of .072 newtons-per-meter or joules-per-square-meter. Interfaces with low energy density possess more complete wetting (spreading of the liquid along a surface) and shallower contact angles than interfaces with high energy density. The surface tension should be sufficiently low to enable the fiber to slip past the polymer while avoiding being pulled through, effectively being ejected and thereby unable to provide structural reinforcement to the polymer.