ABSTRACT In this work, the role of the degree of acetalization of polyvinylbutyral (PVB) on the dynamic mechanical properties of PVB nanocomposites was evaluated. Nanocomposites reinforced with carbon nanoparticles (pristine or oxidized multiwalled carbon nanotubes, graphene oxide and graphene nanoplatelets) were prepared by in situ addition during the synthesis of PVB from polyvinyl alcohol. It was found that the presence of nanoreinforcements during the synthesis considerably alters the degree of acetalization (AD) of PVB (ca. 65 mol% for the neat polymer), which values ranged from 50 to 77 mol%. Dynamic mechanical analyses were used to calculate the storage modulus and other parameters such as: factor C, degree of entanglement and adhesion factor, which were correlated with scanning electron microscopy images. There was a tendency to decrease AD with the increase in the degree of oxidation of the nanoreinforcements, however this contributed to a better dispersion and adhesion of these to the polymer matrix and, consequently, altered positively the nanocomposite properties.

RESUMO A utilização de materiais nanoestruturados sintetizados a partir de sais metálicos tem atraído cada vez mais a atenção de pesquisadores e indústrias no sentido de desenvolver aplicações inovadoras em áreas como a de energia, saúde e alimentos. A prata, o cobre e o óxido de zinco, por apresentarem propriedades antibacterianas, possuem um grande potencial para aplicação como substituintes aos tradicionais agentes antibacterianos organoclorados e derivados de arsênio. O óxido de zinco, por apresentar baixíssima toxicidade às células humanas, não sendo classificado como metal pesado e por ser um material biocompatível, aparece como alternativa em aplicações como na área médica e no tratamento de água para o consumo. O presente trabalho teve como principal objetivo sintetizar nanopartículas de óxido de zinco pelo método do poliol, e avaliar a atividade antibacteriana destas nanoestruturas contra a bactéria Gram negativa Escherichia coli. As sínteses foram conduzidas na presença e ausência da poli(vinil pirrolidona) para investigar a influência deste agente estabilizante nas propriedades morfológicas das nanopartículas obtidas. Todas as amostras foram caracterizadas por espectrofotometria na região do UV-Vis, difratometria de raios-X, microscopia eletrônica de varredura com efeito de campo e microscopia eletrônica de transmissão. Testes para avaliação da atividade antibacteriana com diferentes quantidades de nanopartículas de óxido de zinco sintetizadas sem a poli(vinil pirrolidona) foram conduzidos conforme a norma ASTM E-2149. Os resultados obtidos demonstraram que o método do poliol foi capaz de produzir nanopartículas de óxido de zinco com elevado grau de pureza e diâmetro médio em torno de 20 nm, na ausência ou presença da poli(vinil pirrolidona). Os ensaios microbiológicos comprovaram que as nanopartículas de óxido de zinco produzidas apresentaram excelente atividade antibacteriana contra a bactéria Escherichia coli quando aplicadas em concentrações superiores a 50 mg.L-1.

ABSTRACT The use of nanostructured materials synthesized from metal salts has increasingly attracted the attention of researchers and industries to develop innovative applications in areas such as energy, health and food. Due to the antibacterial properties of silver, copper and zinc oxide, they are potential substituents to the traditional antibacterial agents, such as organochlorines and arsenic derivatives. Once zinc oxide is not classified as heavy meta, has low toxicity, and is biocompatible, it appears as an alternative material for applications in the medical area and water treatment. The main objective of this work was to synthesize zinc oxide nanoparticles by the polyol method and evaluate the antibacterial activity of these nanostructures against the Gram negative bacteria Escherichia coli. The syntheses were carried out in the presence and absence of poly(vinyl pyrrolidone) to investigate the influence of this stabilizing agent on the morphological properties of the nanoparticles. All of the samples were characterized by UV-Vis spectrophotometry, X-ray diffractometry, field emission scanning electron microscopy and transmission electron microscopy. Tests to evaluate the antibacterial activity of different amounts of the zinc oxide nanoparticles were performed according to the ASTM E-2149. The results obtained demonstrated that the polyol method was able to produce zinc oxide nanoparticles with high purity and average diameter around 20 nm, regardless the presence of poly(vinyl pyrrolidone). Microbiological assays showed that zinc oxide nanoparticles produced excellent antibacterial activity against the bacteria Escherichia coli when applied at concentrations higher than 50 mg.L-1.