http://www.youtube.com/watch?v=RMO6srwL2pQ

Hello.  This is Martin Matushek from M² Polymer Technologies.   We are experts in super absorbent polymer chemistry.  We sell
most of our products for industrial and environmental waste applications.

The first patent for SAP was issued in 1962 to the US Dept of Agriculture for use as
water conservation in soil.  The product used starch as the basis for the polymer and then grafted acrylamide and
acrylonitrile monomers along the chain with crosslinking agents.  Starch is made of repeating units of the
sugar, glucose, and there are a lot of places to add things and to crosslink these polymer chains so they become and absorbent.  SAP technology has changed a lot from that time.

The basic idea behind any of these is to first crosslink polymer chains and then to partially neutralize some of the acid functions to create a diffusion gradient.  It is this diffusion gradient that actually draws water molecules into the network of polymer chains and then
hydrogen bonding holds the water tightly in place.

Current superabsorbent technology no longer uses starch to form the main polymer chains.  SAPs today typically use acrylic
acid or acrylamide as the base monomers to form the polymer chains then they add crosslinking agents to bridge these chains and then they partially neutralize the acid groups to create the diffusion gradient.

First…. What is a polymer?  A polymer is a large molecule made up of repeating, smaller molecules called “monomers.”  Most common plastics are polymers but there are also many natural substances that are polymers – starch, collagen and insulin (a protein made of amino acid monomers) are all examples of “polymers.”

To understand super absorbents, it helps to start by understanding the acrylic acid monomer

(Show structure)  CH2=CH-COOH

Super absorbents are a ”petrochemical” which means that the basic starting material for these comes from a barrel of crude oil or from natural gas.  The original starting material to make the acrylic acid monomer is propylene:

CH2=CHCH3

It takes take 1 mole of propylene and 1.5 moles of Oxygen to form acrylic acid:

CH2=CHCH3   +  1.5 O2   –>     CH2=CHCOOH (Acrylic Acid)  +   H₂O

The acrylic acid molecule has two interesting reactive areas that we will talk about later.  They are (1) an unsaturated alkene group C=C
and (2) the carboxylic acid group (-COOH).

CH2=CH-COOH
is polymerized by removing two hydrogen protons to create a free radical:

~CH2-CH~ (-COOH)

The free radical monomer reacts with others to create a repeating chain of polyacrylate polymer that look like
this:

~ CH2 – CH – CH2 – CH – CH2 – CH ~

|                      |                      |

COOH           COOH            COOH

One of the first big commercial uses of polyacrylates was in laundry detergents.  These –COOH groups bind with
metal ions like Calcium and Magnesium.   For that reason, polyacrylates were used in laundry detergents to
replace phosphates that were causing algae pollution in lakes & streams.  Phosphates and Polyacrylates both
bind the Calcium and Magnesium metals in water and this allows detergent surfactants to work better and to get clothes cleaner.

Using this acid group (-COOH) we can neutralize this part of the chain to form Sodium Polyacrylate  (-COO-Na)…
and the basis of the diffusion gradient that a superabsorbent polymer needs.

Polyacrylates are also used as thickening agents or rheology modifiers.  The reason is for their hydrogen bonding interaction with water molecules.

In a dry state, a polyacrylate is curled up like a pig’s tail.

However, once surrounded by water molecules, the interaction between H
and O on the chains and from the water molecules causes these chains straighten
out like strands of spaghetti.

Once straightened out, these polymer strands exert greater resistance in fluid flow thereby thickening the fluid.

A special crosslinked acrylate called a “Carbomer” is widely used as a thickener in cosmetics and personal care products.  As little at 1/4^th of 1% forms a perfectly clear gel like this hair gel.
(DEMO).

The basic idea in designing a superabsorbent polymer is to build small crosslinking bonds between the polymer strands so that they are kept linked as they straighten out.

Adding more and more chains and then partially neutralizing the –COOH acid groups, you get something that looks like this:

This then forms a kind of a “cage” where water molecules are drawn insid and then held in place there through Hydrogen bonding.  It only takes a very small amount of crosslinking agent – typically only ¼ – ½% by weight to accomplish this!

(DEMO)  This is a 4mm sphere of SAP.  In it’s dry state it is 99% polymer and about 1% water moisture.  After soaking, this
same sphere swells about 30X its original size and its mass balance is now 99% water and 1% polymer!  No chemical changes ….  Just a lot of water pulled into the matrix of polymer chains!

(DEMO)  This little toy is called a Hoberman sphere and it expands many times its size – like these SAP Spheres do when soaked in
water.  These SAP Spheres (as we call them) take water into the matrix of polymer chains because of a diffusion gradient that is caused by the neutralization of many of the carboxylic acid  (-COOH) groups along the backbone.  These chains want to uncurl – but can’t fully – because they are constrained by the small crosslinking molecules.

A final demonstration shows what the choice of crosslinking agent can do to a superabsorbent polymer.  The amount of crosslinking agent used it typically very small – only ¼ to ½% by weight.

A crosslinking agent is a small molecule or monomer that has dual binding functionality on at least two sites.
A common example of a crosslinking agent would be something like Methylene-bis-acryamide  (MBA):

O                        O

||                        ||

CH2=CH-C-NH-CH-NH-C-CH=CH2

Note the symmetry in the molecule and the two highly reactive alkene groups on each end!

(DEMO) By varying the choice of crosslinking agent we can change the properties of the superabsorbent.  This sample of Waste Lock® 770 will solidify the 100 mls of water in 30-45 seconds whereas a second sample – MediSAP 715 – solidifies the water in under 10 seconds!  A third sample actually expands in volume as it absorbs and looks like snow (We sell this as “Snow SAP.”)

All three chemicals are polyacrylate superabsorbent polymers but offer different and unique properties based on the crosslinking agent.

For more information, please visit us on-line at    www.m2polymer.com

Cool Tie SAP:

These large grain SAP particles hold about 400-times their weight in water and can be sewn into cool ties, headband and cooling vests.  The AgSAP™ Water Crystals are available in three sizes (S=Small, M=Medium and L=Large).

• Type S = 200 to 800 microns
• Type M = 800 to 2000 microns (or 2 mm)
• Type L = 2 to 4 millimeters

BEAT THE HEAT & CHILL OUT with an attractive Cool Tie Scarf!

These scarves are an easy, fast project made from readily available materials. They make great gifts, school projects and give-aways. Let your imagination and creativity run wild with fabric patterns and colors!

The AgSAP™ Water Crystals are nontoxic polyacrylamide granules of super absorbent polymer available from M² Polymer Technologies (www.m2polymer.com). These same water crystals are used to conserve water and nurture plants in arid conditions. They are concealed in the casing of a cotton neck scarf. When the scarf is soaked in water, the crystals absorb the water, expand, and turn into a crystalline gel. The cotton fabric absorbs water from the gel, and then the water slowly evaporates for a cooling effect. Scarves stay cool and moist for hours due to the polymer’s water-retaining properties and the slower evaporation rate than plain water alone.

For more information, visit:

http://www.m2polymer.com/html/cool_ties_water_crystals.html

Thanks for visiting our Blog!

chemistry, sorbents, super absorbent polymer, superabsorbent

Until the 1980’s, water absorbing materials were cellulosic or fiber-based products. Choices were tissue paper, cotton, sponge, and fluff pulp. The water retention capacity of these types of materials is only 20 times their weight – at most.

In the early 1960s, the United States Department of Agriculture (USDA) was conducting work on materials to improve water conservation in soils. They developed a resin based on the grafting of acrylonitrile polymer onto the backbone of starch molecules (i.e. starch-grafting). The hydrolyzed product of the hydrolysis of this starch-acrylonitrile co-polymer gave water absorption greater than 400 times its weight. Also, the gel did not release liquid water the way that fiber-based absorbents do.

The polymer came to be known as “Super Slurper”. The USDA gave the technical know how several USA companies for further development of the basic technology. A wide range of grating combinations were attempted including work with acrylic acid, acrylamide and polyvinyl alcohol (PVA).

Since Japanese companies were excluded by the USDA, they started independent research using starch, carboxy methyl cellulose (CMC), acrylic acid, polyvinyl alcohol (PVA) and isobutylene maleic anhydride (IMA).

Early global participants in the development of super absorbent chemistry included Dow Chemical, Hercules, General Mills Chemical, DuPont, National Starch & Chemical, Enka (Akzo), Sanyo Chemical, Sumitomo Chemical, Kao, Nihon Starch and Japan Exlan.

In the early 1970s, super absorbent polymer was used commercially for the first time – not for soil amendment applications as originally intended – but for disposable hygienic products. The first product markets were feminine sanitary napkins and adult incontinence products.

In 1978, Park Davis (d.b.a. Professional Medical Products) used super absorbent polymers in sanitary napkins.

Super absorbent polymer was first used in Europe in a baby diaper in 1982 when Schickendanz and Beghin-Say added the material to the absorbent core. Shortly thereafter, UniCharm introduced super absorbent baby diapers in Japan while Proctor & Gamble and Kimberly-Clark in the USA began to use the material.

The development of super absorbent technology and performance has been largely led by demands in the disposable hygiene segment. Strides in absorption performance have allowed the development of the ultra-thin baby diaper which uses a fraction of the materials – particularly fluff pulp – which earlier disposable diapers consumed.

Over the years, technology has progressed so that there is little if any starch-grafted super absorbent polymer used in disposable hygienic products. These super absorbents typically are cross-linked acrylic homo-polymers (usually Sodium neutralized).

Super absorbents used in soil amendments applications tend to be cross-linked acrylic-acrylamide co-polymers (usually Potassium neutralized).

Besides granular super absorbent polymers, ARCO Chemical developed a super absorbent fiber technology in the early 1990s. This technology was eventually sold to Camelot Absorbents. There are super absorbent fibers commercially available today. While significantly more expensive than the granular polymers, the super absorbent fibers offer technical advantages in certain niche markets including cable wrap, medical devices and food packaging.

M² Polymer Technologies was formed in January of 2000 with an emphasis on environmnetal and industrial markets for SAPs.  Our WASTE LOCK® brand of superabsorbent polymers is widely used at most US Department of Energy remediation sites to absorb and stabilize liquid low level radioactive waste.    The polymers are also widely used in processing metal plating waste, unused latex paint and sludge from oil & gas exploration and production.

More information can be found at: http://www.m2polymer.com/html/history_of_superabsorbents.html

Thanks for visiting our Blog!