A historical account into superabsorbent polymers, their current status and future ideas

1. Superabsorbents – a very personal perspective
Until around 1980, the commonly used absorbent materials were cellulose or fibre-based
products used in either woven items, opened fibre formats such as absorbent cotton (cotton
wool) and fluff pulp (bleached kraft or thermomechanical) or as seen in tissue. The water
absorbent capacity of these types of materials is only in the region of 11 times their weight,
but most of it is lost under low to moderate pressure. Many of these materials came from the
simple surgical dressings and related industries where expansions had been made into
feminine care and later very simple disposable products for infant care and for assisting in the
management of adult incontinence. This is where I fit in having entered this area through
surgical dressings and simple hygiene products in around 1974 with my then Family
Business, Vernon-Carus Ltd and their trapezoidal shaped disposable diaper called
“Supernap”. My work has since paralleled the discovery and growth of new absorbent media
for hygiene products.
As a quick aside, my late father in fact was one of the first inventors of a disposable diaper,
filing a patent in 1945 so it’s in the blood! (1) Following on from this, in the late 1940s, a few
other manufacturers of two-piece diapers appeared across Europe and the US. In 1947, for
example, Valerie Hunter Gordon developed a successful two-piece product consisting of a
disposable paper insert with cotton wool attached and a waterproof pant. She arranged in
1949 for Robinson & Sons, a maker of bandages and other medical products and a major
competitor to my own family business, to manufacture two-piece diapers under the brand
name Paddi Pad. But this history is a basis for a whole new article!

2. By searching the whole topic of absorbency and any “new thinking” on the topic in my then
new work, I became aware that 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 of water. Also, the gel did not release liquid water in the way that fibre-based
absorbents exhibited. This polymer came to be known as “Super Slurper”. The USDA gave
the technical know-how to several US companies for further development of the basic
technology. A wide range of grafting combinations were attempted including work with
acrylic acid, acrylamide and polyvinyl alcohol (PVA). (2)
It is worth noting that since Japanese companies were excluded by the USDA, I monitored
their activities in this area and noted that they started their own research using starch, carboxy
methyl cellulose (CMC), acrylic acid, polyvinyl alcohol (PVA) and isobutylene maleic
anhydride (IMA). I also noted that early global participants in the development of super
absorbent chemistry included Dow Chemical, Hercules, Buckeye Cellulose, General Mills
Chemical, DuPont, National Starch & Chemical, Enka (Akzo), Courtaulds, Sanyo Chemical,
Sumitomo Chemical, Kao, Nihon Starch and Japan Exlan.
I contacted the Grain Processing Corporation in Muscatine Iowa in 1975 and commenced
research into incorporating their USDA derived material, then known as Polymer 35-A-100
into simple fluff pulp pads then used by my company in an early disposable baby diaper. The
enhancements in absorbency performance were dramatic but two factors immediately came
to attention – the performance of this type of material was depressed when synthetic body
fluids were used (0.9% saline) to around 35 grams/gram under load and furthermore there

3. were great limitations due to the converting machinery used at that time, into the positioning
of the SAP in pads. This lead to non-idealized results as the problems of lack of fluid spread
coupled with gel blocking became very apparent. Also this original superabsorbent polymer
was somewhat “dusty” leading to processing risks. (Later work into “particulate formats”
addressed these dust concerns although even now; very small superabsorbent particles or
“fines” cause problems with SAP vendors.) It needs to be noted that much positive evolution
has occurred at Grain Processing Corporation since those very early days, their latest family
being a range of superabsorbents or SAPs being sold under the registered name of “Water
Lock”. (3)
Despite efforts into ascertaining the potential of the USDA derived SAP materials in infant
care products to provide a high absorbency performance and the benefits of low bulk,
conformity and all important “good fit” in diapers, and very aware of the converting
problems described, I also looked at cross-linked cellulose materials, as manifested in for
example Buckeye’s CLD and CLD 2 soft sheets available in roll format as an alternative
approach. Despite the environmental credentials of these cellulose derived materials and their
ease of incorporation onto the existing company diaper machinery, their absorbency
performance was not as dramatic as observed with the USDA derived SAPs. These results
were again skewed since these were early days where means to distribute fluid to the SAP
(acquisition and distribution materials) were hardly researched, SAP then, as now featuring
very little capability for the movement of entrapped liquids. It’s interesting to note that CLD
2 soft sheet contained some unmodified pulp in an attempt to improve fluid spreading in an
essentially “absorbent core” as we would describe today.
At this time, I also looked into alternative approaches into absorbency. In this context, I
researched in conjunction with the late Professor John T Scales OBE and his team at the

4. Royal National Orthopaedic Hospital, this involving the use of sphagnum moss, a material
used in absorbent wound dressings during World War 1 when cotton was hard to supply.
Promise was manifest in terms of sustainability, absorbency performance and in connection
with wound management. We determined the optimum strains of sphagnum moss in terms of
fluid management and wound synergy but importantly also devised methods to grow moss in
controlled hydroponic conditions to prevent natural contamination and from this ways to
extract and use the moss in a manageable manner. The very high surface area of sphagnum
moss yielded some absorbency characteristics (also seen in man-made analogues such as
cellulose acetate ultra high surface area “Fibrets”). Several patents were granted. A lack of
UK Government funding sadly put an end to this interesting work where promise still exists.
(4), (5), (6), (7)
The development of super absorbent technology and performance was largely led by
demands in the disposable hygiene segment. As described later in this article, advances in
research into fluid management and composite design thinking have ultimately allowed the
development of the ultra-thin baby diaper which uses a fraction of the materials – particularly
fluff pulp – which earlier disposable diapers consumed.
In the US, in 1978, Park Davis started to use SAP in sanitary napkins. SAP was first utilized
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.
From there the avalanche started!
Coincidently, at this stage in my work, my company abandoned its disposable diaper
products due to a refocus and I eventually, in a career shift, became a Research Fellow in
Absorbent Technology R&D at Kimberly-Clark in Neenah WI. In the 1980’s at the time of

5. my “work shift to K-C”, the ready availability of polyacrylate based SAPs became apparent
and lead to much research leading to their increasing incorporation in a range of hygiene
products. The new properties imparted by these SAPs lead to new composite designs whilst
the SAP content increased to over 30% in absorbent fluff-pulp cores by the end of the decade.
Fluid management to fully exploit the containment properties of these (and other SAP types)
led and is still leading to new “absorbent assemblies” whereby other components in these
assemblies take up and distribute fluid insults to the SAP itself using take up and acquisition
and distribution mechanisms whilst providing optimum skin condition to the users, be these
infants or adults. Current SAP quantities in the “core” of infant diapers and adult
incontinence products can now be up to 100% in “fluff-less” products thus allowing for
thinner products with excellent “fit” and low obtrusiveness. SAPs have now become integral
in the design of absorbent cores, these being attained by advances in fluff-pulp technology by
air laying technologies for example coupled in many cases by new thinking in adhesives. The
DryMax system was a key originator in this area. In the DryMax SAP core system, SAP is
deposited from reservoirs in a printing roll onto a substrate on a grid. Thermoplastic adhesive
is used to form a fibrous network applied to the SAP to immobilize this in both the dry and
wet states. The all important acquisition and distribution system involves chemical bonding
and curled cellulose fibres. (8)
Following the launch of “DryMax” by P&G in 2010, fluff-less diapers have had a mixed
reaction. In some areas such as Ireland, they are not being well accepted since people prefer
fluff pulp containing products. However, in Germany as well as in many western European
countries fluff-less products are having a much greater market acceptance.
Other fluff-less cores currently include the Drylock Core produced by Drylock Technologies,
the Hexacore fluff-less core by Fameccanica, Helixbond (Herrmann Ultrasonics), Pulpless

6. Core by DSG, a fluff-less core having zones – with some of these, called the insult target
region, have an increased absorbency. The Evonik Core uses a method for the continuous
production of a flexible liquid-absorbing material having two outer layers, between which are
inserted at least two stretchable-elastic intermediate layers that creates a matrix able to gather
the absorbent material. In the BASF/Bostik Core, bonding beads are used to bond two layers,
the first featuring an array of “absorbent receiving pockets” into which SAP is inserted. A
second layer is bonded to this using non water soluble bead between the pockets to impart
core integrity. The TWE Core is part of an absorbent structure comprising a nonwoven
substrate having a void volume suitable to be penetrated with SAP particles and adhesives.
SAP is dispersed according to a size distribution gradient along the depth direction of the
core.(8)
Low cellulose content pre-made cores are very suitable for incorporation on existing diaper
and related production equipment. Under this category, the I-CORE/E-CORE system by
Glatfelter which I particularly like features an intermediate storage layer (ICORE) taking care
of rapid urine intake, distribution and intermediate containment before the urine gets
absorbed by a high superabsorbent polymer containing absorbent layer (ECORE). More than
80 % SAP is possible. Described as “A sandwich web comprising a first and second outer
layer, preferably comprising cellulose fibers. Superabsorbent material (SAP) sandwiched
between the outer layers. Individualized fibres adapted to be interspaced between the SAP”
(9).
Work into acrylic acid SAPs continues. BASF in late 2014 announced plans for a major
investment in a pioneering superabsorbent technology platform of its hygiene business.
BASF researchers have worked intensively in the last decade to develop a new technology
and optimize the corresponding production processes. BASF will launch a new generation of

7. highly innovative superabsorbent polymers under the trademark SAVIVA™ in late 2016
based on its round-shaped particles with micro-pores, SAVIVA™ has an innovative liquid
distribution mechanism, making it a highly efficient superabsorbent polymer in a diaper core.
This SAP has been tested comprehensively in laboratories, in diaper prototypes and with end
consumers in home-use tests, confirming its outstanding properties and its performance in
diapers. Selected customers have already given positive feedback. (10) Although not
immediately indicative of any bio-based technology, BASF will certainly still have this area
high in their listing of future priorities in this and other developments I’m sure.
The vast majority of SAPs are presented in granular form (it’s interesting that the original
USDA approaches were also researched in flake and film formats). Starting with work by the
then Courtaulds company, a fibre SAP technology called SAF has been developed by
Technical Absorbents Ltd in Grimsby, UK. To quote: “The basic functionality of this product
is its claimed ability to absorb up to 200 times its own weight in water and 60 times its own
weight in saline at an extremely fast absorption rate. Being fibre-based, it can be precisely
tailored into a diverse range of nonwoven fabrics, tapes and spun yarn formats. Ease of
downstream handling and processing results in exceptionally substantive and uniform
distribution profiles within the final product constructions. As such, they offer truly
unparalleled levels of consistent absorption performance and media integrity.” (11) Cost
considerations need to be considered due to the complexities of this fibre formation – if these
are fully addressed then new exciting composite approaches can be considered in hygiene
assemblies and the risks of “SAP migration” in finished products considerably reduced.
Reverting back, it’s noteworthy that the first patent for superabsorbent polymer SAP, issued
in 1962 to the U.S. Department of Agriculture for use as water conservation in soil, was, in
fact, biobased. The product used starch as the basis for the polymer and then grafted

8. acrylamide and acrylonitrile monomers along the chain with crosslinking agents. Today,
however, the most common type of SAP is based on petroleum-based cross-linked
polyacrylic acid.
The increased and much needed consumer focus on sustainability has resulted in a rapidly
rising demand for alternatives to petroleum-derived SAPs. Various natural materials, such as
cellulose, starch, chitin, and natural gums, have been used as the basis to form the main
polymer chains, much research being published. . These studies have, for the most part, not
yet been able to match either the cost or performance of the oil-based SAPs, leading
numerous companies to explore possible routes to produce bio-acrylic acid.(12)
Currently, research in this area and the development of proprietary processes to produce
acrylic acid from natural sources for the production of high-performance SAPs is in hand by
major acrylic acid SAP producers.
In 2012, BASF, Cargill and Novozymes joined resources to develop technologies to produce
acrylic acid from renewable raw materials. They announced reaching a major stage in
successfully demonstrating the production of 3-hydroxypropionic acid (3-HP), a possible
chemical precursor to acrylic acid, on a pilot scale. However, later in 2014, BASF decided to
exit this R&D collaboration with Novozymes and Cargill. These two companies will continue
their work to commercialize naturally based derivatives. Meanwhile, they are seeking to find
a new commercialization partner.
Another collaborative partnership that is reporting success is between the Cargill acquired
OPXBio and Dow. Aiming to develop an industrial-scale process for the production of bio-
based acrylic acid based on a fermentable sugar feedstock, they used OPXBio's Efficiency
Directed Genome Engineering (EDGE) technology platform to 'design' microbes that were

9. able to produce 3-hydroxypropionic acid (3-HP) from fermented sugar. The 3-HP is then
recovered through a chemical process to yield acrylic acid.
Meanwhile, however, the production of SAPs from a starch basis has also continued to be
pursued in a low profile manner. Archer Daniels Midland Company has developed and
patented technology that uses modified starch to produce a high-quality, superabsorbent
polymer that, says ADM, is hypoallergenic, non-toxic, safe and made from renewable
resources, with physical properties similar to those of petroleum-based SAPs. (13) These are
apparently products that are viewed as having considerable potential for growth; ADM with
its partners CIC Holdings, and Chemanex, have formed a joint venture to build and operate a
biobased superabsorbent polymers production facility near Colombo, Sri Lanka.
The BioSAP produced at the plant will be derived from starches obtained from agricultural
feedstock and marketed by ADM. Little information has been provided on the capacity of the
facility and when it will start producing the BioSAP™. A question being posed by various
agencies is whether this BioSAP has to be mixed with regular polyacrylate SAP to work or
can a diaper product actually use 100% of the biobased and biodegradable BioSAP?
Despite the great advances being made in SAPs and their incorporation into hygiene
products, the whole area of the sustainability of SAPs I strongly consider still needs to be
further addressed.
Radical approaches to developing naturally sourced SAPs have been announced in 2014 by
the Israel-based nanotechnology company Cine’al Ltd using a technology to turn jellyfish
into a super-absorbent material for use in hygiene products and possibly even paper towels.
Researchers at Cine’al have converted jellyfish into “Hydromash” using a process that also
allows for the addition of antibacterial nano-particles. “Hydromash” is claimed to biodegrade

10. in less than 30 days and has been claimed to be cost-competitive with current superabsorbent
materials.(14) However searching has not found any updates on this work since 2014.
Further exotic SAP research has involved hagfish slime When the fish is attacked, it secretes
slime that gels within a split second, even in cold water. This slime essentially suffocates any
predator, thus allowing a captured hagfish to escape unharmed. This mechanism is under
investigation although such work will take many years to come to any fruition. (15) (16)
In the context of developing a truly realistic naturally sourced SAP, I am very aware that a
truly dramatic move towards fully sustainable product could come from some recent work in
the Netherlands at TU Delft in connection with aerobic granular sludge in sewage treatment
by the NEREDA process. This provides a probable commodity highly cost-effective source
of alginate-like exopolysaccharides (ALE) materials from sewage treatment, this hydrogel
type material being an economic commodity starting point for new totally sustainable SAPs.
ALE has been shown to bind strongly with water, can thicken or gel liquids and can be used
as a basis for coatings. These properties would be available at much lower price levels and
would feature “a waste product” to produce ALE and hence with research, a totally new
sustainable and environmentally responsible alginate derived SAP. (17) (18)
It is hoped that a technical “marriage” can take place to research this NEREDA sourced ALE
into new SAPs based on the work performed to date. Positive results would be a genuine
breakthrough!
Dr Edmund H Carus

11. Bibliography:
1. GB 591,070 “Improvements in Napkins” Edmund L Carus
2. USDA AgResearch Magazine May 1996 at
http://agresearchmag.ars.usda.gov/1996/may/starch and personal notes
3. Grain Processing Corporation “Water Lock” Superabsorbent Polymers
Pharmaceutical Online at http://www.pharmaceuticalonline.com/doc/water-lock-
superabsorbent-polymers-0001 and personal notes
4. GB2134792 “Bioactive composite dressing” Edmund H Carus and John T Scales
5. GB2134791 “Antibacterial dressing” Edmund H Carus and John T Scales
6. GB2134793 “Absorbent media comprising sphagnum moss” Edmund H Carus and
John T Scales
7. GB2135165 “Controlled growth of moss” Edmund H Carus and John T Scales
8. “The Vortex Effect : Liquid Holding Properties for Fluffless and Thinner Diapers” B
Bulleri, Texsus, Insight 2014 Conference at
http://www.inda.org/BIO/insight2014_790_PPT.pdf
9. “Glatfelter Launches Ultrathin Absorbent Core System” Breaking News from IDEA
13 and personal notes at http://shows.nonwovens-
industry.com/idea2013/news/35779
10. “BASF Plans Major Investment in Pioneering Superabsorbent Technology” BASF
Press Release. November 26th, 2014 at http://www.care-chemicals.basf.com/press-
center/news-detail?id=4eba9bfc-dae7-4caa-b2d1-88d9413c6b6d
11. SAF Literature, Technical Absorbents Ltd at http://techabsorbents.com/en/saf
12. J Biomed Mater Res. 2002;63(3):373-81.”Superabsorbentmaterials from shellfish
waste--a review” Dutkiewicz JK at http://www.ncbi.nlm.nih.gov/pubmed/12115771
13. ADM “Superabsorbents” literature at http://www.adm.com/en-
US/products/industrial/superabsorbents/Pages/default.aspx
14. “Israeli Team Turns Jellyfish into Super-Absorbent Diapers” Healthline News, April
14th, 2014 at https://www.healthline.com/health-news/israeli-team-turns-jellyfish-
into-diapers-041414
15. “Hagfish Slime may help Scientists create Super-absorbent Adhesives” Nature
World News, January 25th, 2016
16. US2009036853 “Gel forming polymer in an absorbent article” George G Allan
17. “Recovery and reuse of alginate from granular NEREDA sludge” Helle van der
Roest, Mark van Loosdrecht et al, Water 21, April 2015
18. “Water Innovation Award for research into recovery and reuse of alginate from
granular sludge” NEREDA news December 17th, 2013 at
https://www.royalhaskoningdhv.com/en-gb/nereda/news-events-and-
downloads/20131217a-water-innovation-award/572