There are close to 2 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 very small portion of this total volume is used in the
specialized markets that Water Gel
Crystals (WGc)
serves. Our purpose is to identify the best SAPs for these markets and
make them available on an ongoing basis in these specialty applications.
WGc 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, 2G-70 (Texas Snow), and 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,10G-270
and 44-OC are made using this method. Additionally, products such as HS
Fines, and our copolymer products, 40F, 40K, 41K and 42K Polymers, are
made with Continuous Gel Polymerization.
Polymers
