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

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Preparation of Polyurea Microcapsules by Interfacial Polymerization of Isocyanate and Chitosan Oligosaccharide materials Article Preparation of Polyurea Microcapsules by Interfacial Polymerization of Isocyanate and Chitosan Oligosaccharide Fuqiang Yu 1,2, Ying Wang 2, Yan Zhao 3,*, Jingyu Chou 2 and Xiaowu Li 1,* 1 Department of Materials Physics and Chemistry, School of Materials Science and Engineering, and Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China; [email protected] 2 State Key Laboratory for the Discovery and Development of Novel Pesticides, Shenyang Sinochem Agrochemicals R&D Co., Ltd., Shenyang 110021, China; [email protected] (Y.W.); [email protected] (J.C.) 3 Jihua Laboratory, Nanhai, Foshan 528200, China * Correspondence: [email protected] (Y.Z.); [email protected] (X.L.) Abstract: (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 oligosac- charide (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, agita- tion 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 Citation: Yu, F.; Wang, Y.; Zhao, Y.; were characterized by infrared spectroscopy, thermogravimetric analysis, and scanning electron Chou, J.; Li, X. Preparation of microscopy, etc., and the encapsulation efficiency and release behaviors were investigated. The Polyurea Microcapsules by Interfacial results show that the microcapsules have a smooth surface and 93.3% of encapsulation efficiency. Polymerization of Isocyanate and Chitosan Oligosaccharide. Materials The microcapsules showed slow-release behavior following a first-order kinetic equation, and the 2021, 14, 3753. https://doi.org/ accumulative release rates of the microcapsules with core/shell mass ratios of 8.0/4.0, 8.0/5.0, and 10.3390/ma14133753 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 Academic Editors: Simona Strnad applications in controlled release of pesticides, growth regulators, and fertilizer. and Lidija Fras Zemljiˇc Keywords: polyurea; microcapsule; chitosan oligosaccharide; pesticides; slow release Received: 13 May 2021 Accepted: 30 June 2021 Published: 5 July 2021 1. Introduction Publisher’s Note: MDPI stays neutral As one of the major diseases, rice sheath blight is caused by Rhizoctonia solani Kühn with regard to jurisdictional claims in and occurs every year in the word, resulting in a large reduction of rice yield [1]. As it published maps and institutional affil- can occur in the whole growth stage of rice, it is necessary to use carriers to release the iations. fungicide slowly in order to cope with the lasting effect of rice sheath blight. One of the most important forms of slow-release carriers is microcapsules, which have core—shell structure cores where active ingredients are coated with natural or synthetic polymers, i.e., shell materials, by physical, chemical, or physicochemical methods [2] and have a Copyright: © 2021 by the authors. range of desirable properties [3–6]. (i) The core active ingredient can be released at a Licensee MDPI, Basel, Switzerland. designed rate, which enables improved deinsectization, weed killing, and fungi inhibition. This article is an open access article (ii) Decomposition of pesticides caused by environmental factors such as light, air, and distributed under the terms and microorganisms is reduced. (iii) The pesticide efficacy is prolonged, which saves labor and conditions of the Creative Commons Attribution (CC BY) license (https:// reduces administration times. (iv) Direct contact between the pesticide and the human body creativecommons.org/licenses/by/ is decreased, unpleasant odors are masked or decreased, and drifting and poisoning of 4.0/). non-target organisms are decreased. The encapsulation of pesticides such as cypermethrin, Materials 2021, 14, 3753. https://doi.org/10.3390/ma14133753 https://www.mdpi.com/journal/materials Materials 2021, 14, x FOR PEER REVIEW 2 of 19 Materials 2021, 14, 3753 2 of 16 non-target organisms are decreased. The encapsulation of pesticides such as cyperme- thrin, phoxim, chlorpyrifos, abamectin, pyraclostrobin, and clomazone have been studied phoxim, chlorpyrifos, abamectin, pyraclostrobin, and clomazone have been studied for use for use in commercial pesticide microcapsule release agents [7–9]. in commercial pesticide microcapsule release agents [7–9]. Many materials have been studied for use as shell materials in pesticide microcap- Many materials have been studied for use as shell materials in pesticide microcapsules. sules. Polyurea is generally used because of properties such as high stability and mechan- Polyurea is generally used because of properties such as high stability and mechanical ical strength, low cost, and good release characteristics [8,10,11]. Polyurea, which contains strength, low cost, and good release characteristics [8,10,11]. Polyurea, which contains strongly polar urea groups (–NHCONH–), can be synthesized from polyisocyanates and strongly polar urea groups (–NHCONH–), can be synthesized from polyisocyanates and polyamines.polyamines. TheThe most most widely widely used used polyisocyanates polyisocyanates are are polyaryl polyaryl polymethylene polymethylene isocyanate, isocya- isophoronenate, isophorone diisocyanate diisocyanate (IPDI), (IPDI), hexamethylene hexamethylene diisocyanate, diisocyanate, methylene methylene diphenyl diphenyl diiso- cyanatediisocyanate (MDI), (MDI), dicyclohexylmethane-4,4 dicyclohexylmethane-4,40-diisocyanate,′-diisocyanate, and toluene and toluene diisocyanate diisocyanate (TDI). Commonly(TDI). Commonly used polyamines used polyamines are ethylenediamine, are ethylenediamine, hexanediamine, hexanediamine, triethylenetetramine, triethylenetet- andramine, diethylenetriamine and diethylenetriamine [12–19]. [12–19]. For example, For example, Jiang et Jiang al. [13 et] preparedal. [13] prepared polyurea polyurea micro- capsulesmicrocapsules containing containingn-octadecane n-octadecane by using by IPDIusing and IPDI diethylenetriamine and diethylenetriamine as the as monomers. the mon- Zhangomers. etZhang al. [16 et] fabricatedal. [16] fabricated chlorpyrifos chlorpyrifos microcapsules microcapsules with a polyurea with a polyurea shell synthesized shell syn- fromthesized TDI from and ethylenediamine.TDI and ethylenediamine. PolyaminesPolyamines have several disadvantages, disadvantages, ho however,wever, as as the the water-soluble water-soluble reactants reactants in inmicrocapsule microcapsule preparation, preparation, e.g., e.g., toxicity, toxicity, vola volatility,tility, and and flammability, flammability, can can damage damage the theen- environment.vironment. Greenness, Greenness, environmental environmental protec protection,tion, and and sustainable sustainable development are nownow ofof greatgreat importance,importance, andand thethe developmentdevelopment ofof new,new, environmentallyenvironmentally friendlyfriendly reagentsreagents isis urgentlyurgently needed.needed. ChitosanChitosan is is a a partial partial deacetylation deacetylation product product of of chitin chitin and and consists consists of randomly of randomly distributed distrib- βuted-(1 ! β-(14)-linked → 4)-linked D-glucosamine D-glucosamine units units (deacetylated (deacetylated unit) unit) and Nand-acetyl- N-acetyl- D-glucosamine D-glucosa- (acetylatedmine (acetylated unit). unit). Chitin Chitin is widely is widely found found in the in exoskeletons the exoskeletons of arthropods of arthropods and insects,and in- andsects, in and the cellin the walls cellof walls fungi. of Chitosanfungi. Chitosan oligosaccharide oligosaccharide (COS) is(COS) the product is the product of enzymatic of en- orzymatic chemical or chemical depolymerization depolymerization of chitosan; of chitosan; its structure its structure is shown is inshown Figure in1 Figure. Some 1. of Some the propertiesof the properties of COS of differCOS differ from from those those of chitosan, of chitosan, e.g., e.g., it has it has good good aqueous aqueous solubility. solubility. It hasIt has anti-inflammatory, anti-inflammatory, anticancer, anticancer, antioxidant, antioxidant, and and antifungal antifungal properties properties and and has has beenbeen widelywidely used in medical medical applications, applications, animal animal feed, feed, fertilizers, fertilizers, and and pesticides pesticides [20–31]. [20–31 In]. the In thefield field of crop of crop protection, protection, COS COShas been has beenshown shown to change to change the soil the flora, soil promote flora, promote the growth the growthof beneficial of beneficial microorganisms, microorganisms, and induce and disease induce diseaseresistance resistance of plants; of it plants; can be it used can bein usedbiological in biological pesticides, pesticides, growth growthregulators, regulators, and fertilizers and fertilizers
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