Polyacrylamide or poly(1-carbamoylethylene), abbreviated
as PAM) is a polymer formed from acrylamide subunits. It can be
synthesized as a simple linear-chain structure or cross-linked, typically
using N,N‍ '​-methylenebisacrylamide. In the cross-linked form, the possibility
of the monomer being present is reduced even further. It is highly
water-absorbent, forming a soft gel when hydrated, used in such applications as
polyacrylamide gel electrophoresis and in manufacturing soft contact lenses. In
the straight-chain form, it is also used as a thickener and suspending agent.
More recently, it has been used as a subdermal filler for aesthetic facial
surgery. Uses of polyacrylamide
One of the largest uses for polyacrylamide is to flocculate solids
in a liquid. This process applies to water treatment, and processes like
paper making, Screen Printing. Polyacrylamide can be supplied in a
powder or liquid form, with the liquid form being subcategorized as solution
and emulsion polymer. Even though these products are often called
'polyacrylamide', many are actually copolymers of acrylamide and one or more
other chemical species, such as an acrylic acid or a salt thereof. The main
consequence of this is to give the 'modified' polymer a particular ionic
character. Another common use of polyacrylamide and
its derivatives is in subsurface applications such as Enhanced Oil
Recovery. High viscosity aqueous solutions can be generated with low
concentrations of polyacrylamide polymers, and these can be injected to
improve the economics of conventional waterflooding.
It has also been advertised as a soil conditioner called Krilium by Monsanto
Company in the 1950s and today "MP", which is stated to be a "unique
formulation of PAM". It is often used for horticultural and agricultural use
under trade names such as Broadleaf P4, Swell-Gel and so on. The anionic form of
cross-linked polyacrylamide is frequently used as a soil conditioner on
farm land and construction sites for erosion control, in order to protect the
water quality of nearby rivers and streams.
The polymer is also used to make Gro-Beast toys, which expand when placed
in water, such as the Test Tube Aliens. Similarly, the absorbent properties of
one of its copolymers can be utilized as an additive in body-powder.
The ionic form of polyacrylamide has found an important role in the potable
water treatment industry. Trivalent metal salts like ferric chloride and
aluminium chloride are bridged by the long polymer chains of polyacrylamide.
This results in significant enhancement of the flocculation rate. This allows
water treatment plants to greatly improve the removal of total organic
content from raw water. Polyacrylamide is often used in
molecular biology applications as a medium for electrophoresis of proteins
and nucleic acids in a technique known as PAGE.
It was also used in the synthesis of the first Boger fluid.
= Soil Conditioner = The primary functions of Polyacrylamide
Soil Conditioners are to increase soil tilth, aeration, and porosity and reduce
compaction, dustiness and water run-off. Secondary functions are to increase
plant vigor, color, appearance, rooting depth and emergence of seeds while
decreasing water requirements, diseases, erosion and maintenance expenses. FC
2712 is used for this purpose. Stability
In dilute aqueous solution, such as is commonly used for Enhanced Oil Recovery
applications, polyacrylamide polymers are susceptible to chemical, thermal,
and mechanical degradation. Chemical degradation occurs when the labile amine
moiety hydrolyzes at elevated temperature or pH, resulting in the
evolution of ammonia and a remaining carboxyl group. Thus, the degree of
anionicity of the molecule increases. Thermal degradation of the vinyl
backbone can occur through several possible radical mechanisms, including
the autooxidation of small amounts of iron and reactions between oxygen and
residual impurities from polymerization at elevated temperature. Mechanical
degradation can also be an issue at the high shear rates experienced in the
near-wellbore region. However, cross-linked variants of polyacrylamide
have shown greater resistance to all of these methods of degradation, and have
proved much more stable. Environmental effects
Concerns have been raised that polyacrylamide used in agriculture may
contaminate food with acrylamide, a known neurotoxin. While polyacrylamide
itself is relatively non-toxic, it is known that commercially available
polyacrylamide contains minute residual amounts of acrylamide remaining from its
production, usually less than 0.05% w/w. Additionally, there are concerns that
polyacrylamide may de-polymerise to form acrylamide. In a study conducted in 2003
at the Central Science Laboratory in Sand Hutton, England, polyacrylamide was
treated similarly as food during cooking. It was shown that these
conditions do not cause polyacrylamide to de-polymerise significantly.
In a study conducted in 1997 at Kansas State University, the effect of
environmental conditions on polyacrylamide were tested, and it was
shown that degradation of polyacrylamide under certain conditions can cause the
release of acrylamide. The experimental design of this study as well as its
results and their interpretation have been questioned, and a 1999 study by the
Nalco Chemical Company did not replicate the results.
See also Aquamid
Chitosan Rhoca-Gil
Sodium polyacrylate, a similar material References