Anionic polyacrylamides soil conditioners Jozef Kollr Polymeric soil

Anionic polyacrylamides – soil conditioners Jozef Kollár

Polymeric soil conditioners, were known since the 1950 s. These polymers were developed to improve the physical properties of soil in view of: Ø increasing their water holding capacity Ø increasing water use efficiency Ø enhancing soil permeability and infiltration rates Ø reducing irrigation frequency Ø stopping erosion and water runoff Ø reduce fertilizer and pesticides losses Wide commercial application failed even though the scientific basis for their use was quite well established. Reasons: Ø most of the studies with polymers were performed in the laboratory without consideration for the economics at the production level in large scale agriculture Ø complexity of application and poor distribution in the soil

The most commonly used water-soluble synthetic soil-conditioning polymers included: poly(ethylene glycol) poly(vinyl alcohol) poly(maleic anhydride-co-vinyl acetate) polyacrylates polyacrylamide poly(isobutylene maleic anhydride)

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 Ø Great water absorbing properties Ø Amount of crosslinker influenced a mechanical properties of hydrogels Ø Reduce water stress of plants Ø Hydrogels are also claimed to reduce fertilizer leaching

Polyacrylamide (PAM) is one of the most widely employed soil conditioner Advantages Ø Low toxicity Ø Safe Ø Inexpensive PAM Ø 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. poly(acrylamide-co-acrylic acid)

PAM as soil conditioner Ø Reduce surface sealing Ø Increase seedling emergence Ø Reduce runoff and erosion Ø 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 Ø Reduces soil loss Ø Prevent the loss of nutrients Ø Increase infiltration Ø Improvement of aggregate stability Ø 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.

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. 00 E+05 AM/TUL 80/20 1% AM/TUL 80/20 1. 5% AM/TUL 40/60 1. 5% 1. 00 E+04 1. 00 E+03 0. 1 1 10 100 angular frequency (rad/s) 1000