Differences in Polymers
There are nearly 3 million metric tons of superabsorbent polymers made annually in the world. Most of this volume is used in the personal care markets – in finished goods such as disposable baby diapers, feminine care, and adult incontinence products. Only a small portion of this total volume is used in the technical niche markets that Emerging Technologies (ETi) serves. Our purpose is to identify the best SAPs for these markets and make them available on an ongoing basis in these specialty applications.
ETi does this by offering a broad array of granular superabsorbent polymers that encompass the most up-to-date superabsorbent technologies. These polymers may differ in manufacturing process, chemical make-up, particle size and shape, absorption speed, retention, gel strength and more. The information presented below gives a general overview about the two basic methods used for making superabsorbent polymers and how the processes will affect the different performance aspects of our products.
General Overview of Superabsorbent Polymer Manufacturing
A polymer is a substance made up of many (“poly”) repeating units (“mer”). The subunits of a polymer are called monomers. Superabsorbent polymers are made by connecting monomer units together to make a long polymer chain that carries an ionic charge (usually positive or negative… like the opposite ends of a magnet) along the chain itself. Acrylic acid and its neutralized form, sodium polyacrylate, are the monomers used. However, there are SAPs made with two monomers – acrylic acid and acrylamide. These products are called copolymers.
During the manufacturing process, the long polymer chains are linked together into a three-dimensional structure using specially designed crosslinking agents. This special polymer structure allows superabsorbents to chemically absorb and retain water-based fluids. This important feature is what sets superabsorbents apart from other absorbent products – water-based fluids cannot be “squeezed out,” nor will they “leak out” of the polymer, as the fluid is chemically bonded within the structure.
Superabsorbents can be made in two ways: through Inverse Suspension Polymerization or via Continuous Gel Polymerization. There are advantages to both systems. The physical characteristics and performance parameters of polymers are controlled through the manufacturing process, although, occasionally, post-treatment additives are used to alter or affect certain desirable properties.
Inverse Suspension Polymerization
In this process, SAPs are produced in batches in large reactors that produce particles that are perfect spheres. Under a microscope, these materials will look like bunches of grapes. Due to their very high surface-to-volume ratio, these SAPs have exceptional absorption speeds and capacities. They are also very low dust products. Our Premium Superabsorbents, LiquiBlock™ AT-03S and LiquiBlock™ 2G-110, fall into this category, as do LiquiBlock™ 2G-70 and LiquiBlock™ 2G-120.
Continuous Gel Polymerization
Using this method, SAPs are polymerized on long “poly-belts” that yield thick mats of polymer that are then chopped to the correct particle size and oven dried. These materials will look like shards of glass under a microscope. Due to their irregular shape, the absorption speeds and overall capacities of these polymers are lower than those that are perfect spheres; however, the overall gel strength (or performance against pressure) of these products is typically higher than their inverse suspension counterparts. Our All-Purpose Superabsorbents, WHS1, are made using this method. Additionally, products such as LiquiBlock™ HS Fines, and our copolymer products, LiquiBlock™ 40 Series Polymers, are made with Continuous Gel Polymerization.