Anionic polyacrylamides – soil conditioners
Jozef Kollár
Polymeric soil conditioners, were known since the 1950s.
These polymers were developed to improve the physical properties of soil in view of:
 increasing their water holding capacity
 increasing water use efficiency
 enhancing soil permeability and infiltration rates
 reducing irrigation frequency
 stopping erosion and water runoff
 reduce fertilizer and pesticides losses
Wide commercial application failed even though the scientific basis for
their use was quite well established.
Reasons:
 most of the studies with polymers were performed in the laboratory
without consideration for the economics at the production level in large
scale agriculture
 complexity of application and poor distribution in the soil
The most commonly used water-soluble synthetic soil-conditioning polymers
included:
O
n
*
n
*
*
*
OH
poly(ethylene glycol)
*
poly(vinyl alcohol)
m *
n
CO2CH3 O
O
n
*
*
n
*
*
CONH2
COOR
polyacrylates
polyacrylamide
*
*
n
O
poly(maleic anhydride-co-vinyl acetate)
O
O
O
poly(isobutylene maleic anhydride)
Gel forming polymers
Gel forming polymers or insoluble water absorbing polymers were first
introduced for agricultural use in the early 1980’s. These polymers do not
possess linear chain structures as described previously but the chains are rather
crosslinked to form a three dimensional network.
Advantages
 Great water absorbing properties
 Amount of crosslinker influenced a mechanical properties of hydrogels
 Reduce water stress of plants
 Hydrogels are also claimed to reduce fertilizer leaching
Polyacrylamide (PAM) is one of the most widely employed soil conditioner
Advantages
 Low toxicity
n
*
 Safe
H2N
 Inexpensive
*
O
PAM
 Relatively stable
More recently, polyelectrolytes such as acrylamide/acrylate copolymers have
attracted much attention as they have been shown to be most effective in
improving the properties of soils.
*
n
H2 N
O O
m
*
O
poly(acrylamide-co-acrylic acid)
PAM as soil conditioner
 Reduce surface sealing
 Increase seedling emergence
 Reduce runoff and erosion
 Reduce fertilizer and pesticides losses
The adsorption of PAM to soil particles depends
on both the polymer and the soil properties.
PAM differ with respect to molecular weight,
charge density and charge type.
Principle of adhering PAM
molecule to soil particles
Polyacrylamide Types
Granular
Emulsion
Solid
PAM can be used in furrow or sprinkler irrigation
furrow irrigation
sprinkler irrigation
PAM in furrow and sprinkler irrigation
 Reduces soil loss
 Prevent the loss of nutrients
 Increase infiltration
 Improvement of aggregate stability
 Increase quality of soil as well as water
PAM treated furrow
following irrigation
Untreated furrow
following irrigation
Synthesis of poly(acrylamide-co-tulipalin) hydrogels with crosslinker BIS
α-methylene-γ-butyrolactone also known as Tulipalin A, is present in
white tulips and is identified as a substance with fungitoxic activity.
OH
O
OH
O
+
O
O Na+
NH2
n
*
m
*
O
H2N
O O
O Na
+
Swelling capacity in water
dry hydrogel
swollen hydogel
Swelling capacity in water
400
Degree of swelling
350
300
AM/TUL 80/20 1%
250
AM/TUL 80/20 1.5%
AM/TUL 60/40 1%
200
AM/TUL 60/40 1.5%
AM/TUL 40/60 1%
150
AM/TUL 40/60 1.5%
100
50
0
0
20
40
60
Time [min]
80
100
120
Rheology of hydrogels
Rheology is study of deformation and flow of material
prediction of viscoelastic properties of polymers.
Elastic modulus (Pa)
1.00E+05
AM/TUL 80/20
1%
AM/TUL 80/20
1.5%
AM/TUL 40/60
1%
AM/TUL 40/60
1.5%
1.00E+04
1.00E+03
0.1
1
10
100
angular frequency (rad/s)
1000