Banca de QUALIFICAÇÃO: JOSÉ AURÉLIO PINHEIRO

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : JOSÉ AURÉLIO PINHEIRO
DATE: 06/12/2019
TIME: 14:00
LOCAL: LAPET
TITLE:

Salt and temperature responsive cellulose nanocrystals: Evaluation of applicability in the stabilization of water in oil emulsions

KEY WORDS:

Poly(N-isopropylacrylamide), nanocellulose, thermosensitive, grafting

PAGES: 100
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Orgânica
SPECIALTY: Polímeros e Colóides
SUMMARY:

In this study, cellulose nanocrystals (CNC) were obtained from acid hydrolysis of a commercial cotton cellulose sample. Then, the CNCs were chemically modified by grafting chains of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM). Grafting was performed using the monomer N-isopropylacrylamide (NIPAM) with the redox pair potassium persulfate/N,N,N',N'-tetramethylethylenediamine as initiators at room temperature (~ 25°C), or by thermal activation (60°C) of potassium persulfate. The materials were characterized by Elemental Analysis, Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance Spectroscopy (NMR), X-ray Diffraction (XRD) and Thermogravimetric Analysis (TGA). The properties of cotton CNC and their respective modified CNC in aqueous medium were evaluated by Dynamic Light Scattering (DLS) and confocal microscopy. In addition, the visual stability of modified materials in solvents of different polarities was evaluated. Elemental analysis revealed the presence of nitrogen in the modified nanocrystals, which raised when the amount of NIPAM in the reaction medium was increased. Infrared spectra showed bands referring to both the CNC and PNIPAM functional groups. ¹³C NMR spectra also showed peaks concerning the PNIPAM and CNC chains and absence of the monomer double bond, indicating that the grafting reaction was effective. As expected, the increase in the amount of NIPAM in the reaction medium led to a decrease on the CNC crystallinity. The TGA revealed that the grafted CNC showed higher initial degradation temperature than the precursor CNC. The hydrodynamic radius of the modified CNC varied as a function of the measurement temperature, the reaction temperature and the amount of NIPAM added in the reaction medium. Confocal microscopy revealed a change in CNC needle shape to a more oval structure of grafted CNC. Modified nanocrystals with higher amounts of NIPAM in the reaction medium showed higher stability in the different solvents. Because PNIPAM's hydrophobic character is increased as a function of temperature and salinity, the synthesized materials have the potential to act as stabilizers for inverse emulsions of brine in oil.

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Externa ao Programa - 2203888 - MARCIA RODRIGUES PEREIRA
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