Technical Parameters of Sodium Polyacrylate (SAP) in Ice Pack and Agricultural Applications

1. Storage and Delivery – Ice Pack Application

• Absorption and Gel Formation: Sodium polyacrylate can absorb 200–300 times its weight in distilled water and convert into a hydrogel. When saline or tap water is used, absorption is reduced (typically 30–60 times).

• Cooling Efficiency: Once hydrated and frozen, SAP hydrogel functions as an effective phase change medium.

• Ice State Retention:

  • At room temperature (20–25 °C): an SAP-based ice pack retains its “ice-like” cooled gel state for 4–8 hours depending on pack size, encapsulation, and insulation layer.

  • In insulated storage (e.g., cooler box): retention extends to 12–24 hours.

  • Average melting rate: approximately 0.1–0.2 °C/min under normal ambient exposure.

Implication: Compared to pure water ice packs, SAP ice packs melt more slowly due to better gel structure and water retention, making them suitable for medical cold chains, food preservation, and logistics.

2. Agricultural Use – Soil Amendment and Fertilizer Carrier

• Water Release Characteristics:

  • SAP hydrogels release 70–80% of absorbed water gradually over a period of 5–20 days, depending on soil type, temperature, and microbial activity.

  • Theoretical release rate: ~5–10% of stored water per day under average field conditions (25 °C, loamy soil).

• Nutrient & Microbe Release:

  • When fertilizers, micronutrients, or microbial inoculants are co-loaded into the hydrogel, release follows diffusion-controlled kinetics.

  • Fertilizer nutrients (e.g., urea, NPK):

    • ~50% released in first 3–5 days,

    • remainder slowly diffuses over 10–15 days.

  • Microbial viability: microbes survive better due to the moist microenvironment. Viability retention is reported for up to 2–4 weeks post-application.

• Soil and Crop Effectiveness:

  • Improves water-use efficiency by 30–50%,

  • Reduces irrigation frequency from daily watering to once every 5–7 days,

  • Enhances fertilizer utilization by 15–25%.

3. Reference and Past Studies

• Cooling applications: Phase-change and SAP-based gel packs studied in cold chain logistics (2000s–2020s).

• Agriculture applications: Numerous agronomy studies confirm SAP’s water-saving and fertilizer-efficiency benefits in arid/semi-arid regions since the 1990s.

• Theoretical models: Diffusion-based release curves and swelling kinetics are the main frameworks to quantify SAP performance.

✅ Summary:

• In ice packs, sodium polyacrylate keeps gel ice for 4–8 hours at room temp, 12–24 hours in insulated storage.

• In soil, SAP releases water and fertilizers gradually, with 70–80% of stored water released over 5–20 days and nutrient release spread across 2–3 weeks.

• These quantitative parameters make SAP an efficient carrier for cold storage and agricultural water/fertilizer management.