Modification of degradable polyurethane materials using L-tyrosine and its application

Soilless culture is gradually becoming a new direction in the development of agricultural cultivation. However, the synthetic substrates currently used suffer from the problems of being nutrient-less and non-degradable, which will ultimately lead to the misuse of chemical fertilizers and serious environmental pollution. In this study, L-Tyrosine(L-Tyr) was used as a nitrogen nutrient modifier, and L-Tyr-PCL-PCDL-PUF/KHA (L-Tyrosine-Polycaprolactone-Polycarbonate-Polyurethane Foam/Kalium Humate, LTPPPK) soilless substrate was prepared by using biodegradable polycaprolactone and potassium humate, a natural plant-stimulating hormone, as raw materials. The experimental results demonstrated that the incorporation of L-Tyr significantly enhanced the LTPPPK material's vesicular pore structure and morphology, characterized by an apparent density of 65.69 kg/m³, a porosity of 85.58%, a pore diameter of 0.96 ± 0.17 mm, a compressive strength of 0.015 MPa, and optimal thermal stability when the L-Tyr content was 3%. Additionally, L-Tyr enhanced the water absorption and retention capabilities, as well as the degradation performance of the material, achieving a maximum water absorption factor of 12.524 g/g. The degradation rate was found to be 10.95% after 6 months of degradation by N435 lipase, indicating that the material is environmentally friendly upon disposal. As a lettuce growing substrate, the LTPPPK material showed a 7.90% and 9.34% growth in root whisker and leaf width compared with the unmodified one after 42 days of lettuce growth, and the content of chlorophyll and soluble protein increased by 4.46% and 16.42%. It was shown that LTPPPK material can provide a certain amount of nitrogen and potassium for plant growth when used as lettuce cultivation substrate.