1.Introduction

Highly absorbent resin (Super Absorbent Polymer, SAP) is a functional polymer material with extremely strong water absorption and retention capabilities. It can absorb hundreds or even thousands of times its own weight of water and is not prone to releasing the absorbed water under pressure. Since its emergence in the 1960s, SAP has been widely used in hygiene products, agriculture, medicine, and industry, and has become one of the important research directions in modern materials science.

2. Structure and Absorption Mechanism of SAP

2.1 Chemical Composition

The main component of SAP is cross-linked polyacrylate sodium (NaPAA), which is formed by the polymerization of acrylic acid (AA) or sodium acrylate (NaAA), and is cross-linked chemically or physically to form a three-dimensional network structure. In addition, there are other types such as polyacrylamide (PAM) and starch-grafted acrylate.

2.2 Absorption Principle

The water absorption capacity of SAP depends on its molecular structure, which contains hydrophilic groups (-COONa) and a cross-linked network:

Osmotic water absorption: Water molecules enter the polymer network and combine with ionic groups, forming a hydration layer.

Network expansion: The cross-linked structure prevents the polymer from dissolving, allowing it to form a gel after absorbing water.

Water retention capacity: Even when pressure is applied, water is difficult to seep out, ensuring long-lasting water retention.

3. Main application areas of SAP

3.1 Hygiene products (the largest application market)

Infant diapers / adult incontinence products: SAP serves as the core absorbent layer, replacing traditional felt pulp, increasing liquid absorption capacity and reducing volume.

Women's sanitary napkins: Enhance water absorption and anti-leakage capabilities, and improve comfort.

3.2 Agriculture (Water Conservation and Soil Moisture Retention)

Soil water-retaining agents: SAP can reduce the frequency of irrigation and increase the survival rate of crops in arid areas.

Seed coating: Facilitates seed germination and enhances the drought resistance of seedlings.

3.3 Medicine and Biotechnology

Medical dressings: Used for the management of high-permeability wounds, they absorb interstitial fluid and maintain a moist environment.

Drug sustained-release: As a carrier, it controls the rate of drug release.

3.4 Industry and Environmental Protection

Wastewater treatment: Adsorbing heavy metal ions or organic pollutants.

Cable waterproofing: Materials used for water resistance of optical cables and cables.

4. The current market situation and development trends of SAP

4.1 Global market overview

Major producers: Nippon Shokubai from Japan, BASF from Germany, Evonik from the United States, etc. hold a dominant position.

Demand growth: Driven by the expansion of the baby diaper and adult care product markets, the global SAP market size is expected to exceed 10 billion US dollars by 2028 (with a CAGR of approximately 5.5%).

4.2 Technological Development Trends

Biobased SAP: Utilizing renewable resources such as starch and cellulose as raw materials to reduce reliance on petroleum.

Biodegradable SAP: Developing eco-friendly products to address the problem of plastic pollution.

High functionality: Enhances salt resistance (suitable for hard water environments), antibacterial properties (for medical applications), and other performance aspects.

5. Challenges and Opportunities

Challenges:

The price fluctuations of raw materials (acrylic acid) affect the cost.

The restrictions imposed by environmental regulations on traditional SAPs (such as the issue of microplastics).

Opportunity:

The demand for hygiene products in emerging markets (such as China and India) is increasing.

The promotion of agricultural water-saving technologies has driven the demand for SAP.

6. Conclusion

SAP, as a high-performance functional material, plays an irreplaceable role in fields such as healthcare, agriculture, and medicine. In the future, with the advancement of green chemistry and materials science, biodegradable and high-performance SAP will become the focus of research and development, further expanding its application boundaries and contributing to sustainable development.