Polyurea Microcapsules Research Articles

Preparation and performance of a BTDA-modified polyurea microcapsule for encapsulating avermectin

A pesticide microcapsule was prepared by encapsulating avermectin (AVM) in a polyurea microcapsule via interfacial polymerization in acetic ether/water emulsion. The polyurea microcapsule was consisted of chitosan oligomer (CO) as the membrane material and diphenyl methane-4,4′-diisocyanate (MDI) as the crosslinker. A chemical modification was carried out by grafting a UV-absorbent, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), to CO before interfacial polymerization to enhance the UV-resistance of the microcapsule. The BTDA grafted CO (CO-BTDA) and the AVM microcapsules were characterized by a variety of instrumental techniques, including NMR, FTIR, UV–vis, GPC-LS, DLS, SEM and TEM. The in vitro release test showed that the polyurea microcapsule maintained the sustained release of AVM for a longer period (up to 120 h) in comparison with the commercial AVM formulations (within 24 h). The photodegradation test revealed that the polyurea microcapsule significantly reduced the AVM degradation and extended the half-life of AVM from 4.16 h to 9.43 h. The AVM degradation was further reduced by using the BTDA-modified polyurea microcapsule. The corresponding half-life was extended up to 17.33 h and can be mediated by changing the mass ratio of BTDA: CO during the synthesis of CO-BTDA. The use of polyurea microcapsule did not raise a concern about pesticide residue as no AVM was detected after the photodegradation test. In addition, the polyurea microcapsule itself was subject to degradation under sunlight exposure, which reduced its residue in the environment.

Toxicity of engineered micro- and nanomaterials with antifouling properties to the brine shrimp Artemia salina and embryonic stages of the sea urchin Paracentrotus lividus

Antifouling booster biocides are chemicals used in protective paints to tackle the adhesion of fouling organisms to maritime artificial structures. However, they are also known to exert toxic effects on non-target organisms. Recent research developments have highlighted the potential use of engineered micro/nanomaterials (EMNMs) as carriers of antifouling booster biocides in order to control their release and to reduce the harmful effects on living biota. In the present study, we sought to assess the toxicity of two commercially-available booster biocides: (zinc pyrithione (ZnPT) and copper pyrithione (CuPT)); three unloaded engineered micro/nanomaterials (EMNMs); layered double hydroxides (LDH), silica nanocapsules (SiNC), polyurea microcapsules (PU); , and six novel EMNMs (loaded with each of the two biocides). The exposure tests were conducted on the larval stage (nauplii) of the brine shrimp Artemia salina and on two embryonic developmental stages of the European purple sea urchin Paracentrotus lividus. The findings indicate that the unloaded LDH and PU (i.e. both biocide-free EMNMs) have non/low toxic effects on both species. The unloaded SiNC, in contrast, exerted a mild toxic effect on the A. salina nauplii and P. lividus embryos. The free biocides presented different toxicity values, with ZnPT being more toxic than CuPT in the P. lividus assays. LDH-based pyrithiones demonstrated lower toxicity compared to the free forms of the state-of-the-art compounds, and constitute good candidates in terms of their antifouling efficacy.

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

ABSTRACTIn 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.

Experimental Studies on n-Octane and Cyclohexane as Organic Solvent for Synthesis of Polyurea Microcapsules by Interfacial Polycondensation

Interfacial polycondensation (IP) is one of the most important step polymerization technique used for synthesis of polyurea microcapsules. IP reaction between diamine and diisocyanate monomers which are soluble in aqueous phase and organic phase respectively is very fast therefore the overall process of polyurea synthesis via interfacial polycondensation, by and large, mass transfer controlled reaction. Selection of proper organic solvent is one of the important parameter for IP reactions. The objective of this experimental work was to study the effect of n-Octane and Cyclohexane as an organic solvent on kinetics of polyurea microcapsules synthesized by interfacial polycondensation reaction. In this reaction system IP reaction occurs on organic side of the interface so reaction rate increased with increase in relative polarity of organic solvent. Characterization of polyurea was carried out by XRD and DSC which demonstrated that semi crystalline polyurea microcapsules with good thermal stability were synthesized.

Preparation and application of pyraclostrobin microcapsule formulations

In this paper, pyraclostrobin-loaded polyurea microcapsules were prepared through interfacial polymerization reaction between isocyanates and amines. The microcapsules had size distribution ranging from 0.815 μm to 8.674 μm, nearly spherical shapes, and excellent encapsulation efficiency (EE > 90%). The release of pyraclostrobin from microcapsules was controlled by diffusion and erosion. The results of acute toxicity to zebrafish, spreadability on rice blades, and control effect on rice blast showed that the microcapsule formulations had significantly decreased toxicity to zebrafish (lower by 8–9-fold than that of emulsifiable concentrate), high spreadability on rice leaves, and satisfactory control efficacy against rice panicle blast (85.03%). This novel microencapsulation technology helps promote the environmental safety and control efficacy of pyraclostrobin.

Controlled Release of Insecticides through Polyurea Microcapsules Synthesized by Interfacial Polycondensation

Controlled Release of Insecticides through Polyurea Microcapsules Synthesized by Interfacial Polycondensation

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.

Preparation of polyurea microcapsules containing phase change materials in a rotating packed bed

Polyurea microcapsules containing a phase change material with a much shorter preparation time, good morphology, high actual core content and encapsulation efficiency were firstly synthesized through interfacial polymerization in a rotating packed bed.

Preparation and characterization of microcapsules containing industrially important reactive water-soluble polyamine

Polyurea microcapsules containing water-soluble reactive polyamine, namely, polyaziridine (A33), were prepared by interfacial polymerization technique in non-aqueous medium, wherein (i) A33 was encapsulated for the first time as a neat amine without forming its salt or adduct and (ii) microcapsules formed were without any deleterious effect on A33. A systematic study was conducted by preparing microcapsules with different polyurea wall architectures. Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopic analysis of extracted A33 from microcapsules do not show any structural changes during microencapsulation. A titration method was developed to analyze the amount of encapsulated A33 quantitatively. Polyurea microcapsules obtained from reaction of ethylene diamine (E) and isophorone diisocyanate (I) monomers have shown better properties such as encapsulation efficiency and extent of agglomeration. Significant reduction in the size was observed when microcapsules of EI wall material were prepared by homogenizing the initial emulsion of A33 in paraffin oil. The process described in this paper for the preparation of microcapsules is cost-effective and industrially viable, which can find applications in agrochemicals, coatings, self-healing composites, etc.

Pickering emulsion-based fabrication of epoxy and amine microcapsules for dual core self-healing coating

Facile and efficient encapsulation of epoxy and tetraethylenepentamine (TEPA) in polyurea (PU) microcapsules are accomplished with Pickering emulsion templates by one-step, interfacial polymerization. The formation of microcapsule is deftly achieved by lightly shaking Pickering emulsions. The whole process is time andenergy saving hardly with any waste and residual. Epoxy microcapsules keep the spherical shape with core content of more than 90 wt%. Amine microcapsules shrink a little for evaporation of water and the conserved TEPA after air-dried is 82.1 wt%. The shell walls of two microcapsules are about 1 μm. With the protection of PU shells, both microcapsules exhibit excellent thermal resistance. Furthermore, self-healing function of epoxy and amine microcapsules is measured by incorporating microcapsules into epoxy coating, and tested by brine-submersion corrosion-accelerating experiment. The dual core self-healing coatings demonstrate excellent self-repairing performance with the crack of embedded microcapsules and reaction between epoxy and amine. The core materials can outflow from microcapsules and form isolations for metal substrate from corrosion hazard, therefore, make for good self-repairing and preserving function of the self-healing coating.

Designing of polyamidoamine-based polyurea microcapsules containing tung oil for anticorrosive coating applications

A novel method for the fabrication of robust polyurea microcapsules containing tung oil as a core material was developed for self-healing anticorrosive coating application. Well-distinct microcapsules with polyurea as a shell were prepared by reacting hexamethylene diisocyanate trimer with 0.0 G polyamidoamine (PAMAM) via interfacial polymerization technique. Fourier transform infrared spectroscopic analysis was performed to elucidate the chemical structure of microcapsules as well as to confirm successful encapsulation of core by the polyurea shell. Surface morphology, particle size, distribution of particle size, thermal, and mechanical properties of the prepared PAMAM-based polyurea microcapsules were compared with microcapsules that were prepared using diethylenetriamine (DETA) and triethylenetetramine (TETA). The prepared microcapsules were embedded with acrylic polyol-based polyurethane (PU) coatings to ensure anticorrosive performance. The immersion study of self-healing PU coatings loaded with 5% PAMAM-based polyurea microcapsules possesses satisfactory anticorrosive property under an accelerated corrosion process in 5% NaCl salt solution.

Synthesis, characterization, and controlled release study of polyurea microcapsules containing metribuzin herbicide

Controlled release herbicide formulation was prepared by microencapsulation using interfacial polymerization technique. Methylene bisdiphenyl diisocynate (MDI) based polyuria as shell wall material containing mertribuzin herbicide as a core moiety has been prepared by an interfacial polycondensation reaction in emulsion globules between diisocyanate and ethylene diamine.

Encapsulation of ionic liquid BMIm[PF6] within polyurea microspheres

The encapsulation of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIm[PF6]) in polyurea microspheres is demonstrated. This method is based on the encapsulation of ionic liquid within a polyurea shell by emulsification and interfacial polymerization of amine and isocyanate monomers. Emulsification of BMIm[PF6] was performed in water or oil, enabling formation of two different BMIm[PF6] polyurea microcapsules with different chemical features. While the BMIm[PF6]-in-water emulsion enables the formation of BMIm[PF6] polyurea microcapsules with regular aliphatic diamines, the BMIm[PF6]-in-oil emulsion requires the utilization of a specific diamine functionalized with ionic liquid groups. The microcapsules were characterized by scanning electron microscopy, thermal gravimetric analysis, infrared and solid NMR.

Using Chain Extenders to Modify Release Rates of Orange Oil from Poly(Urea-Urethane) Microcapsules

Poly(urea-urethane) and polyurea microcapsules were prepared by an interfacial polymerisation using orange oil as a core material and a mixture of polymeric 4,4'-methylene diphenyl diisocyanate and toluene diisocyanate in a molar ratio of 1:0.2 as oil-soluble monomers. The membrane composition, thickness, and other properties were varied by changing the type and amount of oil-soluble monomers and water-soluble chain extenders, such as ethylenediamine and diethylenetriamine based on amine groups and 1,4-butanediol and polyethylene glycol 400 based on hydroxyl groups. Studies of the morphology and release behaviour show high dependency on the reaction conditions and reactants' properties. The release rate of the orange oil from microcapsules is highest when using a polymeric linear chain extender, polyethylene glycol with a molecular mass of 400. Microcapsules with improved mechanical stability and a slower release rate were obtained by a thicker membrane and by using the branched multi-functional chain extender diethylenetriamine.

Synergy between Galvanic Protection and Self-Healing Paints.

Painting is a cost-effective technique to delay the onset of corrosion in metals. However, the protection is only temporary, as corrosion begins once the coating becomes scratched. Thus, an increasingly common practice is to add microencapsulated chemical agents to paint in order to confer self-healing capabilities. The additive's ability to protect the exposed surface from corrosion depends upon (i) how long the chemical agent takes to spread across the exposed metal; (ii) how long the agent takes to form an effective barrier layer; and (iii) what happens to the metal surface before the first two steps are complete. To understand this process, we first synthesized 23 ± 10 μm polyurea microcapsules filled with octadecyltrimethoxysilane (OTS), a liquid self-healing agent, and added them to a primer rich in zinc, a cathodic protection agent. In response to coating damage, the microcapsules release OTS into the scratch and initiate the self-healing process. By combining electrochemical impedance spectroscopy, chronoamperometry, and linear polarization techniques, we monitored the progress of self-healing. The results demonstrate how on-demand chemical passivation works synergistically with the cathodic protection: zinc preserves the surface long enough for self-healing by OTS to reach completion, and OTS prolongs the lifetime of cathodic protection.

Neem acetylated polyester polyol—Renewable source based smart PU coatings containing quinoline (corrosion inhibitor) encapsulated polyurea microcapsules for enhance anticorrosive property

In this article, we represent preparation of renewable source based smart polyurethane coatings reacting polyols prepared by acetylation of neem oil with different diisocyanates in presence of encapsulated corrosion inhibitor. The structures of polyols were confirmed by Fourier transfer infra-red and nuclear magnetic resonance spectroscopic techniques. The prepared polyols were used to form polyurethane coatings by treating with diisocyanates such as methylene phenyl, dicyclohexylmethane, and isophorone diisocyanates. Further, conversion of polyurethane to smart coatings was carried by incorporation of encapsulated form of quinoline as a corrosion inhibitor. Coatings were characterized for their thermal stability and physico-chemical properties by suitable sophisticated techniques. Anticorrosive properties of the smart coatings were studied by exposing them to corrosive medias like 0.5M HCl and 3.5% NaCl solutions. Incorporation of encapsulated corrosion inhibitor into the neem oil based smart PU coatings shown enhanced anticorrosive property. Finding of this study also shown encapsulated form of commercial corrosion inhibitor can be extended for other PU coatings.

Corrosion protection of AA2024 by sol–gel coatings modified with MBT-loaded polyurea microcapsules

In this work we report the synthesis of polyurea microcapsules loaded with corrosion inhibitor 2-mercaptobenzothiazole (MBT) for corrosion protection of 2024 aluminum alloy. The microcapsules were prepared by interfacial polycondensation. The resulting capsules exhibit spherical shape, with diameter ranging between 100nm and 2μm. The loading content of MBT was found to be 5wt% and release studies showed that MBT is preferentially released under acidic and alkaline conditions and follows a Fickian diffusion model. This pH dependency seems suitable for protection of metallic alloys where corrosion processes are accompanied by local pH changes. Furthermore, the microcapsules were added to a hybrid sol–gel coating and its performance assessed by electrochemical and accelerated standard tests. The results obtained indicate that capsules loaded with MBT do not affect negatively the barrier properties of sol–gel coatings, and contribute for the enhancement of adhesion of coatings to the metallic substrate. More relevant, these additives impart active corrosion protection suppressing corrosion activity at defect sites, which opens prospects for application of polyurea microcapsules as additives for high-performance coatings.

Effects of shell crosslinking on polyurea microcapsules containing a free‐radical initiator

ABSTRACTMicroencapsulation of a material is often used when a controlled release of a substance is desired. This study examines the effects of crosslinking in polyurea microcapsule shells on stability of microcapsules containing the free‐radical initiator cumene hydroperoxide (CHP). Crosslinking of polyurea shells was varied by using amine monomers containing different amine functionalities, and/or changing the isocyanate/primary amine ratio. Thermogravimetric analysis was performed to determine thermal properties of these microcapsules, and the pot lives of monomer systems containing these microcapsules were measured. Thermal stability is greater with a moderate degree of crosslinking from a trifunctional amine, and decreases when crosslinking is increased through use of higher amine functionality. Stability in monomer media generally increases with increased crosslinking through higher amine functionality, but is less predictable due to crosslinks formed between capsules. Generally, increasing crosslinking through altering the isocyanate to primary amine ratio decreases capsule stability in both dry and monomer storage. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42408.

Microencapsulation of quinoline as a corrosion inhibitor in polyurea microcapsules for application in anticorrosive PU coatings

Abstract The use of reservoirs containing corrosion inhibitors as active substances for corrosion protection is an issue of great interest in the scientific literature. The aim of the present study is to encapsulate quinoline, a corrosion inhibitor, into a micro-reservoir to overcome disadvantages caused by its direct addition into a coating layer. Quinoline incorporated microcapsules with different core solvents were synthesized at room temperature by an interfacial polymerization method. The morphologies, wall structures, particle size and thermal properties of the synthesized microcapsules were investigated. The release study of core material was carried out by loss on drying and UV spectrophotometric methods. The prepared quinoline based microcapsules were incorporated in polyurethane (PU) coatings to study their effect on corrosion of substrate. The anticorrosive performance of coatings loaded with different weight % of microcapsules containing quinoline was tested by immersion of the PU coated mild steel specimens in 5 wt% HCl solution by visual observation and weight loss measurements.

Polyurea microcapsules in microfluidics: surfactant control of soft membranes.

Interfacial polymerization techniques offer a versatile route for microcapsule synthesis. We designed a microfluidic process to synthesize monodisperse polyurea microcapsules (PUMCs); the microcapsules are formed by an interfacial polymerization of isocyanate dissolved in the oil and an amine dissolved in water. We measure the mechanical properties of the capsule as well as transport properties through the membrane using two microfluidic methods. We show that the elasticity and the permeability of the shell are controlled by surfactant additives, added during the synthesis. The control of the nanostructure of the shell by surfactants provides new means to design encapsulation systems with tailored mechanical and physicochemical properties.