Fertilizing controlled-release fertilizer is apt to keep a reasonable concentration of nutrient in soil and increase the efficiency of fertilizer utilization. The production of film-coated ...controlled-release fertilizer using polymer latex is a green process. However, the release period is usually short because the film crosslinking density is low during the fast film formation of the dynamic granule coating. In this study, numerous epoxy groups were grafted onto the nanoparticle surface of single-particle-dispersed silica to prepare particulate crosslinker with abundant crosslinking sites. The epoxy groups on the surface of the particulate crosslinker reacted with the carboxyl groups on the surface of the styrene-acrylate latex particles during film formation, enhancing film crosslinking. With the addition of the particulate crosslinker, the polymer latex was used to coat urea granules in a fluidized bed via spray coating at a low coating content of 4 wt%. The release period of film-coated urea granules with an enhanced crosslinking film reached 40 d, which was five times longer than that in the absence of particulate crosslinker.
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•Particulate crosslinker was fabricated by grafting KH560 on silica sol particles.•Crosslinking of polymer latex film was enhanced by particulate crosslinker.•Release period of enhanced crosslinking film-coated urea granules was prolonged.•Provide a new route for producing controlled-release fertilizer.
The dispersibility of silica sol particles modified by γ-methacryloxy propyl trimethoxyl silane (γ-MPS) in an ethanol–water mixed solvent was investigated. In the modification process, the ...hydrolysate of γ-MPS condensed to form oligomers, which further formed hydrogen bonds with the hydroxyl groups on the surface of the silica sol particles to cause agglomeration. Increasing the ethanol concentration inhibited the hydrolysis of γ-MPS and the formation of oligomers, thus inhibiting the agglomeration of silica sol particles. When the ethanol concentration was above 74 wt%, the γ-MPS-modified silica sol slurry was transparent and with a TEM image in a single-particle dispersed state. The dispersibility of the silica sol particles was determined by a double electric layer repulsion mechanism before modification and a steric hindrance mechanism by organic molecules grafted on the surface of the particles after modification. The grafting density of γ-MPS on the surface of silica sol particles affected the hydrophobicity of the modified particles, which can be effectively controlled.
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•High ethanol concentration facilitates high dispersibility of particles.•High ethanol concentration inhibits γ-MPS hydrolysis and particle agglomeration.•Modified particles are single-particle dispersed by steric-hindrance.•Particle hydrophobicity has a positive correlation with γ-MPS grafting density.
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•A gradient hydrophobic film was prepared to improve control release of nutrient.•Nutrient diffusion was found to be directional via gradient hydrophobic film.•Interface tension ...gradient produces driving force for nutrient via film.•Inner hydrophilic and outer hydrophobic gradient film reduces release rate.•Inner hydrophobic and outer hydrophilic gradient film speeds up release rate.
A gradient hydrophobic film was prepared to improve the controlled release performance of film-coated fertilizers. A polyurethane (PU) was copolymerized with hydroxypropyl-terminated polydimethylsiloxane (HP-PDMS) at different ratios to produce a film with different levels of hydrophobicity. A film with a gradient hydrophobicity was prepared by successively coating a copolymer of PDMS/PU at different ratios. The urea diffusion rate via an inner hydrophilic and outer hydrophobic (InHL-OutHB) gradient hydrophobic film was reduced significantly, compared with that via a uniform hydrophilic or hydrophobic film. For the InHL-OutHB gradient hydrophobic film, the release period of the coated urea with a coating amount of 4 % was over 60 days, which was significantly longer than that of the uniform film.
Herein, efficient amino modification of silica (SiO2) nanoparticles using tris(hydroxymethyl)aminomethane (Tris) was performed via aqueous mixing, spray drying, and thermal treatment. The ...hydroxymethyl and amino groups of Tris reacted with the silanol groups on the SiO2 particle surface. Tris amination does not produce volatile organic compounds. Moreover, Tris does not condense itself and can be easily grafted in a single molecular layer on the particle surface. The grafting density of Tris reached 2.60 nm–2. Tris amination increases the reactivity of the particle surface and significantly enhances the grafting density of stearic acid on the SiO2 particles and the hydrophobicity of the particles.
An effective amination for SiO2 nanoparticles using aminobutanol to increase surface reactivity was realized via aqueous mixing, spray drying, and thermal treatment. The apparent grafting density of ...2-aminobutanol obtained reached to 2.20 nm−2, with a monomolecular layer. The amino group in aminobutanol acts as a self-catalyst in the amination reaction. The reactivity of SiO2 particles after amination is obviously increased, which enables the subsequent modification of carboxylic acids more readily, and increases the grafting density of carboxylic acids on the SiO2 particle surface significantly.
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•Surface amination of nanosilica using aminobutanol was effectively achieved.•Aminobutanol amination increases the surface reactivity of nanosilica particles.•The amino group in aminobutanol acts as a self-catalyst in the amination reaction.•The amination of aminobutanol in monomolecular layer was achieved.
The impact of particle hydrophobicity on the morphology and structure of hollow microspheres prepared by spray drying of silica sol was investigated through modification with ...γ-methylacryloxypropyltrimethoxysilane (γ-MPS). Hydrophobic attraction among the hydrophobic silica particles in the aqueous phase drives particles to gather inward the droplet at the early stages of dehydration, which delays the shell formation of the droplets. During the later stages of dehydration, hydrophobic particles form hydrophobic nanoconfined channels among themselves. Afterward, water undergoes rapid evaporation via the formation of molecular clusters, facilitating the formation of a thicker and stronger shell, which mitigates the formation of the tail vortex resulting from the adverse effects of airflow. After continued dehydration, regular hollow microspheres are formed. Cationic surfactant cetyltrimethylammonium bromide (CTAB) was absorbed onto the negatively charged particle surface of silica sol, thereby inducing hydrophobicity via electrostatic attraction. Subsequently, the CTAB-adsorbed silica sol is spray dried in a mixed solvent phase of ethanol and water, resulting in the preparation of regular, morphologically uniform hollow microspheres. The robust synthesis and the underlying mechanistic study provide a scalable and sustainable route to prepare hollow microspheres for potential application in cosmetics.
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•GCC particles were modified through aqueous mixing and thermal treatment.•The maximum contact angle of GCC particles after aqueous mixing was to 118.9°.•The contact angle of GCC ...particles after thermal treatment reached 139.6°.•The state of (RCOO)2Ca on GCC particles changed after thermal treatment.•The thermal stability of the modified layer increased after thermal treatment.
The surface modification of calcium carbonate (CaCO3) particles, which is used as a filler, significantly affects the properties of the composed materials. The effects of thermal treatment on ground calcium carbonate (GCC) particles subjected to hydrophobic modification using sodium stearate (RCOONa) were studied. The contact angle of the modified GCC particles increased from 24.7° to 118.9° when the amount of RCOONa added was increased from 0% to 5% and then decreased to 97.5° when the RCOONa content was further increased to 10%. When a large amount of RCOONa was added, RCOO− reacts with Ca2+ and generates (RCOO)2Ca nuclei, which are adsorbed on the surface of the GCC particles, forming a discontinuous (RCOO)2Ca modified layer. After thermal treatment under sealed conditions, the contact angle of the GCC particles modified using 1.5% RCOONa/GCC increased from 112.8° to 139.6°. The thermal stability of the (RCOO)2Ca modified layer was increased, with the temperature increase of the mass-loss peak from 358.0 to 463.0 °C. It is confirmed that the spreading of melted (RCOO)2Ca nuclei on the surface of the GCC particles during the thermal treatment increased the continuity of the modified layer, converting the physical adsorption of the (RCOO)2Ca nuclei into chemisorption. The grafting density of RCOO− on the GCC particle surface after thermal treatment approximates to 5.00/nm2, which is close to the single-molecular-layer grafting density of RCOO−, indicating that excellent modification was achieved.
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Yolk-shell TiO2@MgO@void@SiO2 pigment exhibited high hiding power and weather durability. Compared with the same coating amount of 20% in dense film, the consumption of coated TiO2 is ...reduced over 20%.
•TiO2@void@SiO2structurewaspreparedbysurface-protectedetching.•The void in the yolk-shell structure increased the refractive index difference.•TiO2@void@SiO2 has high hiding power and low weather durability.•TiO2@MgO@void@SiO2 was prepared to increase weather durability.•TiO2@MgO@void@SiO2 structure saves TiO2 consumption 21.2%.
High hiding power and weather durability are the key characteristic indices of the high-performance pigmentary titanium dioxide (TiO2). The film-coated TiO2 particles with a yolk-shell structure of silica were prepared by surface-protected etching with polyvinyl pyrrolidone. The hiding power of the TiO2 particles with the yolk-shell structure was 90.6, which is significantly higher than the hiding power of 87.7 for the dense film-coated TiO2 particles with the same amount of coating (20%). However, the TiO2 particles with the yolk-shell structure have low weather durability. The apparent degradation rate constant Kapp for rhodamine-B had a high value of 13.2. An improvement was made by coating a dense MgO film on the TiO2 particles first, and then coating a yolk-shell structure. The hiding power of the TiO2 particles with the improved yolk-shell structure reached 90.6, and the weather durability was significantly increased as the apparent degradation rate constant Kapp decreased to 2.2, reaching the excellent weather durability of the TiO2 particles with 5wt% dense film coating (Si3+Al2), which is a common product in industry (Kapp=1.8). For the same indices of hiding power and weather durability, the TiO2 particles with the improved yolk-shell structure obviously decreased the consumption of TiO2, compared with the dense SiO2-coated TiO2 particles (TiO2@SiO2). It is inferred that the void in the yolk-shell structure increased the light reflectivity of the TiO2 particles by increasing the difference of the refractive index between the core TiO2 and the surroundings, and the dense MgO film increased the weather durability of the TiO2 particles.
Influence of vacancies on the relaxation properties of graphene nanoribbons has been investigated by molecular dynamics simulation in several nanometre sizes. Moreover, three factors including ...vacancy size, number and distribution are taken into consideration. The results show graphene nanoribbons present different kinds of deformation at different sites with various vacancy distributions. The effects of vacancy distributions on the relaxation properties of graphene nanoribbons are discussed.
