Polyester Polyol for Slow-release Fertilizers

Polyester polyols are used in some slow-release fertilizers to form polyurethane coatings that control nutrient release, with their biodegradability, cost, and release period being adjustable by incorporating bio-based polyols or fillers like lignite. These coatings prevent rapid dissolution of nutrients by gradually releasing them as water penetrates the polymer membrane, improving nutrient use efficiency and reducing environmental impact.

How Polyester Polyols Work in Slow-Release Fertilizers: 

1. Polyurethane Formation:

Polyester polyols react with isocyanates to form a polyurethane membrane on the fertilizer granules.

2. Controlled Nutrient Release:

The polyurethane coating acts as a barrier, allowing water to slowly diffuse through it, which then gradually releases the fertilizer nutrients into the soil over time.

3. Adjustable Properties:

The characteristics of the polyester polyol influence the fertilizer's performance. For instance:

Degradability: Modifying the polyol with bio-based alternatives like soybean oil polyols can improve the coating's degradability.

Release Period: The type of polyester, its molecular weight, and structure affect the release rate.

Cost: Some polyester polyols offer a lower cost of material compared to others, like polyether polyols, and can achieve longer release periods.

4. Bio-based Alternatives and Fillers:

Soybean oil polyols (SOPs): Substituting petrochemical-based polyester polyols with SOPs can improve biodegradability and allow for control of nutrient release without changing coating thickness, according to MDPI.

Natural fillers: Incorporating natural materials such as lignite can further enhance the slow-release effect of polyester-based coatings.

Benefits of Polyester Polyol Coatings

• Improved Nutrient Use Efficiency: Ensures that plants receive nutrients over a sustained period, matching their growth needs.

• Environmental Protection: Reduces nutrient runoff into water bodies, minimizing environmental pollution.

• Reduced Cost: Some polyester polyols offer a more economical option for developing slow-release fertilizers compared to other materials.

• Customized Performance: The ability to adjust the polyol type, composition, and the overall coating thickness allows for the creation of customized fertilizer products.