Hydrophobically modified sustainable bio-based polyurethane for controllable release of coated urea

Poly(vinyl alcohol)/sodium alginate polymer membranes as eco-friendly and biodegradable coatings for slow release fertilizers

BACKGROUND

The use of slow release fertilizers (SRFs) is an effective approach for reducing agriculture cost, environmental and ecological issues simultaneously. The present study provides a series of poly(vinyl alcohol) (PVA)/sodium alginate (SA) polymer membranes as eco-friendly and biodegradable coatings for SRFs. Moreover, polymer-coated urea (PCU) granules were fabricated through coating the urea granules with the resulting membranes. Our first interest was to fabricate three membranes (PS1, PS2, PS3) of different PVA/SA weight ratios (9:1, 8:2, 7:3) using glutaraldehyde as a crosslinking agent, and crosslink the PS3 membrane with a CaCl₂ solution further to obtain the PC3 membrane. The chemical properties and morphologies of the membranes were characterized. Second, the nitrogen release behavior of the PCU granules was measured and calculated, respectively.

RESULTS

Crosslinking with glutaraldehyde made the PS1, PS2, PS3 membranes uniform and compact, whereas crosslinking with a CaCl₂ solution formed an 'egg box' structure inside the PC3 membrane. PS3 membrane with the minimum PVA/SA weight ratio had the highest hydrophily (water uptake: 106.25%, water contact angle: 55.1^o ), whereas PC3 membrane had the lowest hydrophily (water uptake: 21.57%, water contact angle: 67.3^o ). The biodegradation ratios of the membranes were in the range 44-60% in 90 days, indicating that they had excellent biodegradability. The measured fractional release on the day 30 of the PCU granules ranged from 89.33% to 97.07%. The calculated nitrogen release behavior agreed well with the measured values.

CONCLUSION

The resulting eco-friendly and biodegradable PVA/SA membranes are alternative coatings for SRFs. © 2022 Society of Chemical Industry.

Nutrient controlled release performance of bio-based coated fertilizer enhanced by synergistic effects of liquefied starch and siloxane

The porous structure and hydrophilicity of coating shells affect the nutrient controlled-release performance of castor oil-based (CO) coated fertilizers. In order to solve these problems, in this study, the castor oil-based polyurethane (PCU) coating material was modified with liquefied starch polyol (LS) and siloxane, and a new coating material with cross-linked network structure and hydrophobic surface was synthesized, and used it to prepare the coated controlled-release urea (SSPCU). The results demonstrated that the cross-linked network formed by LS and CO improved the density and reduced the pores on the surface of the coating shells. The siloxane was grafted on the surface of coating shells to improve its hydrophobicity and thus delayed water entry. The nitrogen release experiment indicated that the synergistic effects of LS and siloxane improved the nitrogen controlled-release performance of bio-based coated fertilizers. Nutrient released longevity of SSPCU with 7 % coating percentage reached >63 days. Moreover, the nutrient release mechanism of coated fertilizer was further revealed by the analysis of the release kinetics analysis. Therefore, the results of this study provide a new idea and technical support for development of efficient and environment-friendly bio-based coated controlled-release fertilizers.

Bio-based Polyurethane Based on a Dynamic Covalent Network with Damage Tolerance for Controlled Release of Fertilizers

Bio-based polyurethanes are promising for the controlled release of nutrients and fertilizers, but their toughness and plasticity need to be improved. We developed a smooth, dense, elastic, and indestructible bio-based polyurethane (BPU) coating with a nutrient controlled release ∼150% superior, a tensile strength ∼300% higher, and a toughness ∼1200% higher than those for the original BPU coating. Through a one-step reaction of soybean oil polyols (accounting for more than 60%), isocyanate, and benzil dioxime, the dynamic covalent network based on oxime-carbamate replaces part of irreversible covalent cross-linking. The dynamic fracture-bonding reaction in the modified coating BPU can effectively promote the hydrogen bond recombination and oxime-carbamate chain migration in the coating process, which avoids the structural defects caused by coating tear and fertilizer collision. This work provides a simple and versatile strategy for building controlled-release fertilizer coatings.

Waste Cabbage-Integrated Nutritional Superabsorbent Polymers for Water Retention and Absorption Applications

To alleviate soil impoverishment and water shortage in desert areas, as well as to reduce the impact of waste cabbage on the environment and human health, we used waste cabbage as a substrate, 2-acrylamide-2-methyl-1-propane sulfonic acid (AMPS) and acrylic acid (AA) as polymerization units, and NH₄Cl and KNO₃ as nutriment to obtain two waste cabbage-superabsorbent polymers (CB-SAP_NH4Cl and CB-SAP_KNO3) by the one-pot method. The chemical structure, thermal stability, and morphology of the polymers were investigated by Fourier-transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and scanning electron microscope (SEM). Meanwhile, the water retention, water absorption, and salt resistance were compared with the purchased polymers. The results showed that the nutriment was successfully encapsulated inside the polymer, and CB-SAP_NH4Cl and CB-SAP_KNO3 at 1% nutrient concentration showed excellent water retention properties, salt resistance, and water absorption performance of 1546 and 1131 g/g (distilled water), 306 and 277 g/g (tap water), and 116 and 91 g/g (0.9% NaCl solution). Therefore, they are highly promising materials for the application.

Hydrophobic Epoxy Caged Silsesquioxane Film (EP-POSS): Synthesis and Performance Characterization

Hydrophobic films are widely used in aerospace, military weapons, high-rise building exterior glass, and non-destructive pipeline transportation due to their antifouling and self-cleaning properties. This paper details the successful preparation of hydrophobic epoxy caged sesquioxane (EP-POSS) via two steps of simple organic synthesis, along with studies on the effects of viscosity and reaction time on the reaction. Interestingly, the EP-POSS presented a large contact angle of 125°, indicating its excellent hydrophobicity. The surface micromorphology was observed via FE-SEM (field emission scanning electron microscopy), transmission electron microscopy (TEM), and atomic force microscopy (AFM), and the structural composition and elemental contents were analyzed via X-ray photoelectron spectroscopy (XPS) and energy-dispersive spectrometry (EDS). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) tests showed that EP-POSS had excellent thermal properties, and the first degradation reaction occurred at 354 °C. The mechanical performance and abrasion resistance results demonstrated that EP-POSS could be used in solar panels.