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Master's Dissertation
DOI
https://doi.org/10.11606/D.3.2020.tde-07022020-114648
Document
Author
Full name
Jéssica de Carvalho Arjona
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2019
Supervisor
Committee
Diaz, Francisco Rolando Valenzuela (President)
Peralta, Marvin Marco Chambi
Silva, Leonardo Gondim de Andrade e
Title in Portuguese
Desenvolvimento e caracterização de sistemas de nanocompósitos PHB/argila brasileira para encapsulação de ureia.
Keywords in Portuguese
Microcápsulas
Montmorilonita
Nanocompósitos
PHB
Ureia
Abstract in Portuguese
A ureia é o fertilizante a base de nitrogênio mais utilizado na agricultura; porém, é responsável por diversos problemas ambientais, que ocorrem devido às interações da ureia com o meio ambiente, nas quais essa substância pode ser degradada em moléculas menores que podem contaminar água, solo e ar, antes mesmo de poder ser absorvida pela planta. Para reduzir esses processos, uma das soluções seria empregar sistemas de liberação controlada, nos quais a ureia seria liberada em taxa contínua e controlada. Um desses sistemas são as microcápsulas, que são aplicadas em diversas áreas, como agrícolas, biomédicas e farmacêuticas, oferecendo vários benefícios, sendo um deles reduzir a perda dos princípios ativos encapsulados. Isso ocorre devido à encapsulação do mesmo, que o protegerá do contato direto com o meio externo. O objetivo deste trabalho foi investigar e caracterizar microcápsulas de poli(3-hidroxibutirato) (PHB) e de nanocompósito de PHB/argila com uma argila esmectita brasileira na forma natural (MMT) e também organofilizada (OMMT) para a liberação controlada de ureia para uso em fertilizantes. As microcápsulas de PHB, PHB/MMT e PHB/OMMT foram obtidas pelo método de emulsão óleo/água/óleo (o/a/o). A caracterização foi feita por Difração de Raios X (DRX), Espectroscopia Vibracional de Absorção no Infravermelho por Transformada de Fourier (FTIR), Microscopia Eletrônica de Varredura (MEV), Microscopia de Força Atômica (AFM), Análise Termogravimétrica (TG) e a biodegradação das microcápsulas foi determinada pela a norma ASTM D5988. Os dados de AFM forneceram a rugosidade da superfície das microcápsulas, mostrando que o aumento na concentração de agente emulsificante aumenta a rugosidade das microcápsulas. Além disso, a rugosidade está associada à cristalinidade das microcápsulas, como foi observado com as curvas de DRX. Pelas imagens de MEV observaram-se a morfologia e distribuição de diâmetro das microcápsulas, sendo que as microcápsulas encapsuladas com ureia tiveram seu aumento no diâmetro de cerca de 70%. A TG mostrou que os nanocompósitos apresentaram temperatura inicial de degradação levemente superior do que o PHB puro; e que a encapsulação de ureia reduziu a temperatura inicial de degradação para todas as microcápsulas, sendo as microcápsulas de PHB/MMT as que apresentaram maior temperatura de início de degradação entre elas. O ensaio de biodegradação indicou que as três microcápsulas apresentaram taxa de degradação semelhante e, assim sendo, foram degradas totalmente em um período de 5 meses e meio.
Title in English
Development and characterization of PHB/Brazilian clay nanocomposite systems for urea encapsulation.
Keywords in English
Microcapsules
Montmorillonite
Nanocomposite
PHB
Urea
Abstract in English
Urea is the most widely used nitrogen fertilizer in agriculture; however, it is responsible for several environmental problems, which occur due to the interactions of urea with the environment, in which this substance can be broken down into smaller molecules that can contaminate water, soil and air before it can even be absorbed by the plant. To reduce these processes, one solution would be to employ controlled release systems, in which urea would be released at a continuous and controlled rate. One such system is microcapsules, which are applied in many areas, such as agricultural, biomedical and pharmaceutical, offering several benefits, one of which is to reduce the loss of encapsulated active ingredients. This is due to its encapsulation, which will protect it from direct contact with the external environment. The aim of this work was to investigate and characterize poly (3-hydroxybutyrate) (PHB) and nanocomposite PHB/clay microcapsules with a Brazilian smectite clay (MMT) and also its organofilized clay (OMMT) for controlled release of urea for the use in fertilizers. PHB, PHB/MMT and PHB/OMMT microcapsules were obtained by the oil/water/oil (o/w/o) emulsion method. The characterization was performed by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Thermogravimetric Analysis (TG) and biodegradation of the microcapsules were determined by ASTM D5988. The AFM data provided the surface roughness of the microcapsules, showing that the increased of emulsifier agent increases the roughness of microcapsules. In addition, roughness is associated with microcapsule crystallinity, as observed with XRD curves. SEM images show the morphology and diameter distribution of the microcapsules. Urea-encapsulated nanocomposites microcapsules had a diameter increase of about 70%. The TG showed that nanocomposites had a slightly higher initial degradation temperature than pure PHB; and that urea encapsulation reduces the initial degradation temperature for all sorts of microcapsules, and PHB/MMT microcapsules showed the best thermal stability among them. The biodegradation assay indicated that the three microcapsules have a similar degradation rate and they were completely degraded over a period of 5 months approximately.
 
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Publishing Date
2020-02-07
 
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