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Fabrication of Cypermethrin/Beta-Cypermethrin Nanocapsules in Miniemulsion Polymerization System

Author: XiaChunMiao
Tutor: ZhouYiFeng
School: Anhui University
Course: Applied Chemistry
Keywords: Miniemulsion polymerization Nanocapsules Cypermethrin Beta-Cypermethrin
CLC: TB383
Type: Master's thesis
Year: 2012
Downloads: 79
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Abstract


The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell. Many different materials, ranging from organic and inorganic pigments, magnetite, or other solid nanoparticles, to hydrophobic and hydrophilic liquids, such as fragrances, drugs, or photoinitators, can be encapsulated. Functionalization of the nanoparticles can also be easily obtained. Compared to polymerization processes in organic solvents, miniemulsion polymerization to obtain polymeric nanoparticles can be performed in environmentally friendly solvents, usually water. Cypermethrin and beta-Cypermethrin are effective pesticides against many pests, particularly Lepidoptera. They have high insecticidal potency and relatively low side effects on birds and mammals, although it is acutely toxic to aquatic animals. Here we are interest in the special case of nanocapsules containing CP which can result in sufficient effects on pests yet reduce the side effects of the pesticide due to the small dosage used. Because of their small size, nanocapsules may be easy to deposit on the leaves of the plants, which helps to reduce waste of the pesticide. It is also a great advantage that pesticides encapsulated inside nanocapsules can be efficiently protected against enzymatic and hydrolytic degradation. Main contents and results are as follows:1. The present status of research as well as the development tendency of synthesis of nanocapsules in the miniemulsion system was summarized; The present status of research as well as the development tendency of Pyrethroid capsules was also summarized.2. The nanoencapsulation of pesticide was carried out by interfacial polymerization in miniemulsion system. The encapsulation was achieved by interfacial polymerization inducing phase separation within minidroplets dispersed in an aqueous phase. From a thermodynamic perspective, we focus on investigating different hydrophilic co-monomers with regard to defining the end morphology of the particles.3. The nanoencapsulation of Cypermethrin was carried out by miniemulsion polymerizationin in the system. The encapsulation was achieved by polymerization inducing phase separation within minidroplets dispersed in an aqueous phase. For nanocapsules prepared in this way, the type of surfactant and initiator, the level of the crosslinking agent or chain-transfer agent, and, the monomer/cypermethrin ratio, play a significant role in defining the end morphology of the latex particles. Specifically, for a styrene/cypermethrin system, there were optimum levels of ionic surfactant (1.0wt%sodium dodecyl sulfate), nonionic surfactant [0.5wt%poly(ethylene glycol) monooctylphenyl ether], oil-soluble initiator [1.0wt%azobis(isobutyronitrile)], crosslinking agent (1.0wt%divinylbenzene), and, a styrene/cypermethrin ratio of1:1for obtaining well-defined nanocapsules of cypermethrin.4. Beta-Cypermethrin nanocapsules made of a cross-linked polystyrene (PSt) shell were successfully synthesized by miniemulsion polymerization of styrene and divinylbenzene (DVB) adopting the xylene as hydrophobe. Transmission electron microscopy (TEM), dynamic light scattering (DLS), fourier-transform infrared (FT-IR) and differential scanning calorimetry (DSC) analyses were used to characterize the structure and properties of nanocapsules. The idea of the procedure is that the monomer and hydrophobe form a common miniemulsion, whereas the polymer is immiscible with the hydrophobe and demixes throughout polymerization to form a polymer shell surrounding the hydrophobe core. Great attention was paid to the characterization of nanocapsules and reaction effects on controlling the particle structure. The influence of factors such as the type of the initiator, the level of the crosslinking agent or chain transfer agent, and the monomer/hydrocarbon ratio were researched.

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