Waste Lock - Superabsorbent Polymer Network Waste Lock - Superabsorbent Polymer Network

Waste Lock® is a superabsorbent polymer product available from M2Polymer.com.

Production of Superabsorbent Polymers

Superabsorbent chemistry

Superabsorbent polymers are now commonly made from the polymerization of acrylic acid blended with sodium hydroxide in the presence of an initiator to form a poly-acrylic acid sodium salt (Sodium Polyacrylate). This polymer is the most common type of SAP made in the world today.

Other materials are also used to make a superabsorbent polymer, such as polyacrylamide copolymer, ethlyene maleic anhydride copolymer, cross-linked carboxymethylcellulose, polyvinyl alcohol copolymers, cross-linked polyethylene oxide, and starch grafted copolymer of polyacrylonitrile (PAN) to name a few. The starch-grated PAN is one of the oldest SAP forms created.  For the first few decades of commercial SAP production, most products were starch-grafted products.  This type of SAP was gradually discontinued in the late 1990's and virtually all commercial SAPs are made without starch.

Today superabsorbent polymers are made using one of three primary methods:  (1) suspension polymerization, (2) solution polymerization or (3) gel polymerization. Each process has certain advantages over the others and there are trade-offs between them.   All yield a consistent quality of product.

(1) Suspension Polymerization

Suspension polymerization is practiced by only a few companies because it requires a higher degree of production control and product engineering during the polymerization step. This process suspends the water-based reactant in a hydrocarbon-based solvent such as cyclo-hexane -- although volatile silicones have been used.  The net result is that the suspension polymerization creates the primary polymer particle in the reactor rather than mechanically in post-reaction stages. Performance enhancements (Addition of cross-linking agents) can also be made during, or just after, the reaction stage.  These particle are marking by a true spherical shape and most have a large intercalated void volume that affords rapidly fluid uptake and/or the ability to handle more viscous liquids.

(2)  Solution polymerization

Solution polymers offer the absorbency of a granular polymer supplied in solution form. Solutions and can be diluted with water prior to application. Can coat most substrates or used to saturated. After drying at a specific temperature for a specific time, the result is a coated substrate with superabsorbent functionality. For example, this chemistry can be applied directly onto wires & cables, though it is especially optimized for use on components such as rolled goods or sheeted substrates.

Solution based polymerization is commonly used today for SAP manufacture of co-polymers -- particularly those with the toxic acrylamide monomer. This process is efficient and generally has a lower capital cost base. The solution process uses a water based monomer solution to produce a mass of reactant polymerized gel. The polymerization's own reaction energy (exothermic) is used to drive much of the process, helping reduce manufacturing cost. The reactant polymer gel is then chopped, dried and ground to its final granule size. Any treatments to enhance performance characteristics of the SAP are usually accomplished after the final granule size is created.

(3) Gel Polymerization

A mixture of glacial acrylic acid (GAA), water, cross-linking agents and UV initiator chemicals are blended and placed either on a moving belt or in large tubs. The liquid mixture then goes into a "reactor" which is a long chamber with a series of strong UV lights. The UV radiation drives the polymerization and cross-linking reactions. The resulting "logs" are sticky gels containing 60-70% water. The logs are shredded or ground and placed in various sorts of driers. Additional cross-linking agent may be sprayed on the particles' surface; this "surface cross-linking" increases the product's ability to swell under pressure -- a property measured as Absorbency Under Load (AUL) or Absorbency Against Pressure (AAP). The dried polymer particles are then screened for proper particle size distribution and packaging. The Gel Polymerization (GP) method is currently the most popular method for making the sodium polyacrylate superabsorbent polymers now used in baby diapers and other disposable hygienic articles.