Layer-by-layer deposition of clay and a polycation to control diffusive release from polyurea microcapsules

Lignin microcapsules prepared on the basis of flexible skeleton with high foliar retention and UV shielding properties

Lignin-based microcapsules are extremely attractive for their biodegradability and photolysis resistance. However, the water-soluble all-lignin shells were unsatisfactory in terms of rainfall and foliar retention, and lacked the test of agricultural production practices. Herein, a novel microcapsule based on a flexible skeleton formed by interfacial polymerization and absorbed with lignin particles (LPMCs) was prepared in this study. Further analysis demonstrated that the shell was formed by cross-linking the two materials in layers and showed excellent flexibility and photolysis resistance. The pesticide loaded LPMCs showed about 98.68 % and 73.00 % improvement in scour resistance and photolysis resistance, respectively, as compared to the bare active ingredient. The foliar retention performance of LPMCs was tested in peanut plantations during the rainy season. LPMCs loaded with pyraclostrobin (Pyr) and tebuconazole (Teb) exhibited the best foliar disease control and optimum plant architecture, resulting in an increase in yield of about 5.36 %. LPMCs have a promising application prospect in the efficient pesticide utilization, by controlling its deformation, adhesion and release, an effective strategy for controlling diseases and managing plant growth was developed.

Nano-clay modified membranes: A promising green strategy for microalgal antifouling filtration

Membrane fouling is a major challenge which limits the sustainable application of membrane filtration-based microalgal harvesting at industrial level. Membrane fouling leads to increased operational and maintenance costs and represents a major obstacle to microalgal downstream processing. Nano-clays are promising naturally occurring nanoparticles in membrane fabrication due to their low-cost, facile preparation, and their superior properties in terms of surface hydrophilicity, mechanical stability, and resistance against chemicals. The membrane surface modification using nano-clays is a sustainable promising approach to improve membranes mechanical properties and their fouling resistance. However, the positive effects of nano-clay particles on membrane fouling are often limited by aggregation and poor adhesion to the base polymeric matrix. This review surveys the recent efforts to achieve anti-fouling behavior using membrane surface modification with nano-clay fillers. Further, strategies to achieve a better incorporation of nano-clay in the polymer matrix of the membrane are summarised, and the factors that govern the membrane fouling, stability, adhesion, agglomeration and leaching are discussed in depth.

Amphiphilicity-Driven Small Alcohols Regulate the Flexibility of Pesticide-Loaded Microcapsules for Better Foliar Adhesion and Utilization

The foliar loss of pesticides causes serious utilization decline and environmental risk. On the basis of biomimetics, pesticide-loaded microcapsules (MCs) with spontaneous deformation on foliar micro/nanostructures, like the snail suction cup, are prepared by interfacial polymerization. By controlling the usage or types of small alcohols in the MC preparation system, the flexibility of MCs is tunable. Through the investigation of emulsions and MC structures, we discover that the migration and distribution of small alcohols driven by amphiphilicity affect the process of interfacial polymerization between polyethylene glycol and 4,4-methylenediphenyl diisocyanate. By hydrophobic modification of the polymer and competition for oil monomers of small alcohols, the thickness and compactness of shells are reduced, whereas the density of the core is increased. As a result of the regulation in structures, the flexibility of MCs is improved significantly. In particularly, the MCs-N-pentanol (0.1 mol kg^-1) with the best flexibility show strong scouring resistance on varied foliar structures, sustained release property on the air/solid interface, and persistent control effect against foliar diseases. The pesticide-loaded soft MCs provide an effective way to improve pesticide foliar utilization.

Glutathione-Responsive Pyraclostrobin-Loaded Polyurea Microcapsules for Their Intelligent Controlled Release

The utilization of intelligent controlled release technology to create stimuli-responsive pesticide formulations has been shown to effectively improve pesticide efficacy and reduce environmental pollution. Herein, a glutathione-responsive release polyurea (PU) microcapsules (MCs) loaded with pyraclostrobin were developed via the interface polymerization method. The pyraclostrobin-loaded PU-MCs showed a regular spherical shape with an average diameter of 480 nm. It also showed good thermal stability and rheological properties. Furthermore, the pyraclostrobin-loaded PU-MCs exhibited favorable wettability on wheat leaves, which was beneficial for enhancing the retention capacity of pesticide droplets and improving pesticide utilization. The pyraclostrobin can be released from MCs and directly proportional to glutathione (GSH) concentrations with Fickian diffusion. Importantly, the control efficacy of pyraclostrobin-loaded PU-MCs against Fusarium graminearum was positively correlated with GSH, indicating a promising candidate for a controlled release of pesticides in agriculture and laying the foundation for further field experiments.

Preparation of Polyurea Microcapsules by Interfacial Polymerization of Isocyanate and Chitosan Oligosaccharide

(2-((1-(4-chlorophenyl)-1H-pyrazol-3-yl)oxy)-N-(3,4-dichlorophenyl)-propanamide) is a new oil-soluble compound with good fungicidal activity against Rhizoctonia solani. Chitosan oligosaccharide (COS) is the depolymerization product of chitosan and can be developed into biological pesticides, growth regulators, and fertilizers due to its various bioactivities. COS is an oligomer of β- (1 → 4)-linked d -glucosamine and can be taken as a polyamine. In this study, microcapsules were prepared by interfacial polymerization of oil-soluble methylene diphenyl diisocyanate and water-soluble COS. The effects of several key preparation parameters, e.g., emulsifier dosage, agitation rate during emulsification, and core/shell ratio, on properties of the microcapsules such as the encapsulation efficiency, particle size, and size distribution were investigated. The microcapsules were characterized by infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy, etc., and the encapsulation efficiency and release behaviors were investigated. The results show that the microcapsules have a smooth surface and 93.3% of encapsulation efficiency. The microcapsules showed slow-release behavior following a first-order kinetic equation, and the accumulative release rates of the microcapsules with core/shell mass ratios of 8.0/4.0, 8.0/5.0, and 8.0/6.0, were 95.5%, 91.4%, and 90.1%, respectively, on day 30. Due to many high biological activities, biodegradability, and the pure nature of COS, microcapsules formed from COS are promising for applications in controlled release of pesticides, growth regulators, and fertilizer.

Effect on the characterization of metolachlor polyurea microcapsules with urea instead of polyamines

In this paper, a novel metolachlor microcapsules suspension (CS) was prepared by interfacial polymerization. Metolachlor polyurea microcapsules suspension was successfully prepared by urea instead of polyamines which could reduce the use of organic solvents and production costs. The synthesized microcapsules were characterized by Fourier Transform Infrared Spectrometer, Scanning Electron Microscope, Ultraviolet Spectrometry, Thermogravimetric analyses and particle size analyzer. In conclusion, the diameter of the urea microcapsules were the smallest (11.52 μm) and excellent encapsulation efficiency (81.45%). In addition, Urea microcapsules had compact microstructures and global shapes, which had a good thermal stability and metolachlor could be preserved better in the polyurea microcapsules. These results indicated that the prepared microcapsules by urea had better thermal storage properties and physicochemical property. The microcapsule suspension of metolachlor hasn’t been researched yet. Therefore, it is significant to prepare microcapsule suspension. More importantly, there is no use of organic solvents in the preparation of microcapsules suspension, which avoided the pollution of solvents to the ecological environment. It is hoped that this polyurea material will be applied in the field of pesticide synthesis and polymers.

Sustained Dye Release Using Poly(urea-urethane)/Cellulose Nanocrystal Composite Microcapsules

The aim of this study is to develop methods to reinforce polymeric microspheres with cellulose nanocrystals (CNCs) to make eco-friendly microcapsules for a variety of applications such as medicines, perfumes, nutrients, pesticides, and phase change materials. Surface hydrophobization treatments for CNCs were performed by grafting poly(lactic acid) oligomers and fatty acids (FAs) to enhance the dispersion of nanoparticles in the polymeric shell. Then, a straightforward process is demonstrated to design sustained release microcapsules by the incorporation of the modified CNCs (mCNCs) in the shell structure. The combination of the mCNC dispersion with subsequent interfacial polyurea (PU) to form composite capsules as well as their morphology, composition, mechanical properties, and release rates were examined in this study. The PU microcapsules embedded with the mCNC were characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The morphologies of the microcapsules were characterized by optical microscopy (OM) and scanning electron microscope (SEM). The rupture stress and failure behavior of the microcapsules were determined through single-capsule compression tests. Oil-soluble Sudan II dye solution in mineral oil was utilized as a model hydrophobic fill, representing other latent fills with low partition coefficients, and their encapsulation efficiency was measured spectroscopically. The release rates of the encapsulated dye from the microcapsules were examined spectroscopically by both ethanol and 2-ethyl-1-hexanol medium at room temperature. The concentration of released dye was determined by using UV-vis absorption spectrometry (UV-vis). The mCNC embedded poly(urea-urethane) capsules have strong and dense walls, which function as excellent barriers against leakage due to their extended diffusion path length and ensure enough mechanical strength from rupture for handling or postprocessing.

Phoxim Microcapsules Prepared with Polyurea and Urea-Formaldehyde Resins Differ in Photostability and Insecticidal Activity

The application of pesticide microcapsules (MCs) in agriculture is becoming more and more popular. In this study, the effects of different wall materials on the stomach toxicity, contact toxicity, length of efficacy, and photolysis characteristics of pesticide microcapsules were investigated. The results showed that microencapsulation reduced the stomach and contact toxicities of phoxim and prolonged the efficacy of this light-sensitive chemical in the greenhouse test. Neither of the degradation curves for microencapsulated phoxim under ultraviolet light fit a first-order model, although the emulsifiable concentrate (EC) degradation curve fit it well. The phoxim-loaded polyurea microcapsules (PUA-MCs) showed significantly increased UV-resistance ability, stomach toxicity, and contact toxicity compared with the phoxim-loaded urea-formaldehyde microcapsules (UF-MCs). These experiments indicated that it is crucial to select the appropriate wall materials for pesticide microcapsules on the basis of application sites and physicochemical properties of pesticide active ingredients.

Cross-linked nanofilms for tunable permeability control in a composite microdomain system

Use of cross-linked nanofilms to manipulate the permeability of analytes in LbL microcapsule enabled nanocomposite devices.

Pickering-Emulsion-Templated Encapsulation of a Hydrophilic Amine and Its Enhanced Stability Using Poly(allyl amine)

Efficient encapsulation of tetraethylenepentamine (TEPA), as an example aliphatic amine, was achieved by an emulsion-templated, in situ polymerization. Hydrophobically modified clay nanoplatelets were employed as emulsifiers to obtain water-in-oil (W/O) dispersions followed by interfacial polymerization between a portion of the TEPA cargo and polymethylene polyphenylene isocyanate (PMPPI). The resultant capsules exhibit spherical shape, desirable thermal stability, modest barrier properties, and shear-induced release in an epoxide monomer mixture. Most importantly, a significant gain in capsule barrier properties was realized by introducing poly(allyl amine) (pAAm) as an interface-selective reactive additive in the Pickering emulsions. In addition to the fundamental interest of pAAm localization and interface-selective reactivity, this microencapsulation system for aliphatic amines has technological potential in coating, self-healing, and drug-delivery applications.

Size dependence of shape and stiffness of single sessile oil nanodroplets as measured by atomic force microscopy

This article presents results and guidelines on the quantitative analysis of size, shape, and stiffness of single sessile oil droplets in air and in water. Atomic force microscopy (AFM) facilitates the analysis of micro- and nanoscale droplets which are of growing importance for agrochemicals, cosmetics, or foodstuffs containing emulsions with nanoscale compartments or droplets. Measurement of droplet shape and stiffness provides information on the contact angle with the support surface as well as the interfacial tension of the liquid-liquid interface. In this study, micro- and nanoscale droplets were imaged both in amplitude modulation (AM) and force mapping modes. The effects of the AM mode set point ratio on the measured droplet shape are discussed, and a modified spherical cap model is suggested to extract the droplet-substrate contact angle. This model was applied to a population of different sized oil droplets imaged in water and led to the finding that the contact angle with the solid support varies with the droplet size. Force mapping was undertaken to measure the droplet stiffness as a function of the droplet size. Smaller droplets were found to be stiffer, in reasonable agreement with the Attard-Miklavcic model [Langmuir 2001, 17, 8217-8223] which describes the deformation of a sessile droplet in the nonwetting regime, i.e., by partial wrapping of the droplet around the probe surface. The model limitations are discussed in terms of the diverging droplet stiffness predicted for droplet radii similar to the probe radius as well as the error propagation associated with the droplet shape function.

Clay-chitosan nanobrick walls: completely renewable gas barrier and flame-retardant nanocoatings

Thin films prepared via a layer-by-layer (LbL) assembly of renewable materials exhibit exceptional oxygen barrier and flame-retardant properties. Positively charged chitosan (CH), at two different pH levels (pH 3 and pH 6), was paired with anionic montmorillonite (MMT) clay nanoplatelets. Thin-film assemblies prepared with CH at high pH are thicker, because if the low polymer charge density. A 30-bilayer (CH pH 6-MMT) nanocoating (~100 nm thick) reduces the oxygen permeability of a 0.5-mm-thick polylactic acid film by four orders of magnitude. This same coating system completely stops the melting of a flexible polyurethane foam, when exposed to direct flame from a butane torch, with just 10 bilayers (~30 nm thick). Cone calorimetry confirms that this coated foam exhibited a reduced peak heat-release rate, by as much as 52%, relative to the uncoated control. These environmentally benign nanocoatings could prove beneficial for new types of food packaging or a replacement for environmentally persistent antiflammable compounds.