Polycaprolactone polyol/castor oil composite polyol polyurethane coated urea: field validation of rubber tree yield increase and nitrogen release

Research background and material design: Controlled release fertilizers are an important way to improve nitrogen fertilizer utilization efficiency and reduce agricultural non-point source pollution. The choice of coating material directly determines the nutrient release curve and degradation behavior. A study published in the September 2026 issue of Industrial Crops and Products (Volume 251), by Hailin Liu、Fei Lei、Hongzhu Yang、Chunhua Ji、Peisong Zhang、Zhengzao Cha、Lina Huang、Qinghuo Lin A polyurethane coated urea was prepared using a composite polyol system consisting of polycaprolactone polyol and castor oil. A systematic evaluation was conducted on the nitrogen release characteristics, coating degradation behavior, and field yield performance of rubber trees. The material science significance of this work lies in the composite of biodegradable polycaprolactone segments with naturally sourced castor oil polyols to construct a polyurethane coating network. This design approach not only utilizes the controllable degradation of polycaprolactone in soil environment, but also utilizes the natural skeleton of castor oil polyols to regulate crosslinking density and hydrophobicity, thereby achieving the regulation of coating structure and release behavior without relying on pure petroleum based raw materials.

Nitrogen Release and Coating Degradation Behavior

The nitrogen release characteristics of coated urea were investigated.

. As a barrier for nutrient release, the thickness, cross-linking degree, and degradation rate of the coating jointly determine the release rhythm of nitrogen in the soil. The polyurethane coating formed by the polycaprolactone polyol/castor oil composite polyol system will undergo hydrolysis and gradual degradation under microbial action in soil, and there is a coupling relationship between the destruction of the coating structure and nitrogen release. The study also focused on the degradation behavior of the capsule, which provides a basis for understanding the “release degradation” matching: if the capsule degrades too quickly, the controlled release cycle is insufficient; If the degradation is too slow, it may cause residual problems. The design goal of this composite polyol system is to seek a balance between the two.

Field performance of rubber trees

In the field experiment, the effect of coated urea on the yield of rubber trees was evaluated.

. Rubber trees are a typical tropical economic crop, and their rubber cutting yield is closely related to nitrogen nutrition supply. However, the hot and rainy climate conditions in tropical regions require higher requirements for fertilizer release and maintenance. This study applied coated urea to rubber trees and examined their field performance, providing direct data for the application of controlled-release fertilizers in perennial economic forests. Although the specific increase in yield and release cycle values were not disclosed at the abstract level, the study included “nitrogen release characteristics – coating degradation – field yield” in the same evaluation framework, reflecting the complete verification logic from material design to agronomic effects.

Significance for polymer additives and agricultural materials industry

From the perspective of the polymer materials industry, the value of this research is first reflected in the route selection of biobased and biodegradable agricultural polymers.. Castor oil, as a renewable source of polyols, when combined with polycaprolactone polyols, provides the possibility of reducing fossil material dependence for polyurethane coating. For enterprises engaged in the development of controlled release and coating materials, the composite polyol system means greater regulation space at the formulation end: by adjusting the ratio of polycaprolactone to castor oil, the flexibility, cross-linking density, and degradation rate of the coating can be changed, thereby matching the fertilizer requirements of different crops. Secondly, research on the degradation behavior of coatings suggests that weather resistant masterbatch and stabilizer systems are equally crucial in agricultural polymers. The UV irradiation, temperature and humidity cycling, and microbial activity in tropical field environments accelerate the aging and degradation of coatings. Balancing controllable degradation with sufficient service life is the core proposition of coating material formulation design. This study takes degradation behavior as an independent evaluation dimension, which has reference significance for the selection of additives and stabilizers. Finally, the rubber tree field experiment directly correlated material properties with crop yield, indicating that the evaluation of agricultural materials cannot be limited to laboratory release curves. For agricultural polymer products such as agricultural film, greenhouse film, and controlled-release coating, the complex degradation environment is composed of field climate, soil microorganisms, and crop root activity. Only formulas that have been validated in the field have promotional value. This study uses polyurethane coated urea as a carrier, linking three clues of bio based polyols, coating degradation, and crop yield increase, providing a reference research paradigm for biodegradable controlled release systems in the field of agricultural materials.

Information source:Polycaprolactone polyol/castor oil composite polyol-based polyurethane-coated urea: Nitrogen release characteristics, coating degradation behavior, and field performance on rubber tree yield， Organized by Herun Chemical.