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New Salt Resistant Water Retaining Agent Synthesis

Water scarcity and saline‑alkali soil are major global challenges for agriculture and ecological restoration. Superabsorbent polymers (SAP)—also called water retaining agents—are key functional materials that can absorb and retain hundreds of times their weight in water. However, many traditional SAPs show poor performance in salt solutions.

This study introduces a new salt‑resistant water retaining agent synthesised from acrylic acid, methyl allyl polyoxyethylene ether (HPEG), and isopentenyl polyoxyethylene ether (TPEG). It delivers ultrahigh water absorption in both pure water and saline water, making it ideal for water‑saving agriculture, dryland farming, and saline‑alkali soil improvement.

What Makes This New Salt-Resistant Water Retainer Special?

Uses eco‑friendly polyether monomers (HPEG + TPEG)
Strong hydrophilic groups + 3D porous network structure
Excellent salt tolerance (stable in 0.9% NaCl solution)
Fast water absorption rate
High water retention capacity
Safe, biodegradable, pollution‑free

Raw Materials & Synthesis Method

Core Materials

Acrylic acid (AA): main hydrophilic monomer
Methyl allyl polyoxyethylene ether (HPEG‑2400): improves flexibility and salt resistance
Isopentenyl polyoxyethylene ether (TPEG‑2600A): enhances water absorption and network structure
Potassium persulfate (KPS): initiator
N,N‑methylene bisacrylamide (MBA): crosslinking agent
NaOH: for neutralisation

Synthesis Process

Neutralise acrylic acid with NaOH to 80% neutralization under an ice bath.
Dissolve HPEG and TPEG in water to form a homogeneous solution.
Mix two solutions, purge with nitrogen to avoid oxidation.
Add initiator and crosslinking agent, react at 60°C until gel forms.
Keep warming for 2 hours to complete polymerisation.
Wash with ethanol and water, dry at 80°C, then grind to a powder.

Structural Characterization

FT‑IR Analysis

The infrared spectrum confirms successful polymerisation:

Strong –OH peak at 3448 cm⁻¹
C–H stretching at 2945 cm⁻¹
Amide and carboxylate peaks at 1598 cm⁻¹, 1456 cm⁻¹
Typical C–O–C ether bond peaks at 1110 cm⁻¹ and 1149 cm⁻¹

SEM Morphology

The product shows:

Rich micro‑pores around 1 μm
Connected 3D network structure
Large specific surface area
Ideal channels for fast water absorption

This porous structure directly supports its super‑high water absorbency.

Key Performance Data of New Salt Resistant Water Retaining Agent Synthesis

The new salt‑resistant water-retaining agent was tested in distilled water and in a 0.9% NaCl solution (simulating body fluid/saline soil).

Water Absorption After 16 Hours

In distilled water: 443.27 g/g
In 0.9% NaCl saline water: 161.54 g/g

Water Absorption Speed

Rapid absorption within the first 15 minutes
Continuous absorption until full saturation
Stable and durable swelling

Why Saline Absorption Is Lower

Salt ions (Na⁺, Cl⁻) compete with the polymer for water molecules, reducing the osmotic pressure difference and lowering the absorption capacity. Even so, this new SAP outperforms most conventional water retainers in salt solutions.

Water Absorption Mechanism

Surface wetting: hydrophilic groups attract water molecules quickly.
Pore diffusion: water rapidly enters the porous network.
Network expansion: polymer chains stretch to hold as much water as possible.
Elastic equilibrium: swelling stabilises at maximum capacity.

Advantages Over Traditional Products

Much higher salt resistance
Faster water uptake
More stable in saline‑alkali environments
Better water retention under drought stress
Environmentally friendly raw materials
Suitable for farmland, desert control, horticulture, and ecological restoration

Ideal Applications

Water‑saving agriculture & dryland farming
Saline‑alkali soil improvement
Desertification and stony desertification control
Garden greening, lawns, landscaping
Seedling raising and transplanting
Soil water retention and fertiliser preservation

Conclusion

This new ternary copolymer salt‑resistant water retaining agent, based on acrylic acid, HPEG, and TPEG, offers:

Ultrahigh water absorption: 443 g/g in pure water
Strong salt tolerance: 161 g/g in 0.9% NaCl
Fast absorption, stable performance, and eco‑friendly

It provides a practical, high‑efficiency solution for global water shortages and supports the development of water‑saving, high‑yield, and sustainable agriculture.