Contribuição ao estudo da influência de variáveis de síntese no desempenho de terpolímeros utilizados como melhoradores do índice de viscosidade

• Ano de defesa: 2016
• Autor(a) principal: Alessandra Chagas Daniel
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: automotivos; Polímeros; Lubrificantes; Melhoradores do índice de viscosidade; Viscosidade Índices; Engenharia quimica; Automóveis
• Link de acesso: http://hdl.handle.net/1843/BUOS-AA4F3R

Viscosity index improvers are essential for good performance of automotive lubricant oil, because of their ability to reduce the variation of viscosity with temperature. In this work terpolymers were synthesized as viscosity index improvers using mineral oil SN-150 from Petrobras, as solvent, from dodecylmethacrylate, octadecylmethacrylate and maleicanhydride, and from monofunctional initiator Luperox® TBEC, at temperatures of 100°C (group A) and 120°C (group B), with dodecantiol as chain transfer agent. Twenty-four systems were obtained at different relative concentrations of monomers. The materials were characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG). The rheological behavior of additivated samples was studied from the determination of the kinematic viscosities, viscosity indexes (VIs), shear stability and from steady state flow test. The TG results for the initial degradation temperature showed that oils containing additives are stable (Tinitial 238ºC), being suitable for use in automotive engines, especially the group of samples A. The FTIR spectra confirmed the formation of additives by observing vibrations bands and by the absence of vibrations bands of the unsaturation between carbons, which are typical of dodecylmethacrylate and octadecylmethacrylate and besides the displacement of the deformation band regarding to double bond between carbon and oxygen, characteristic of maleic anhydride. The values of kinematic viscosities for all additivated systems, at 40 and 100°C, were increased compared to the base oil, specially the group A. All additivated oils showed an increased in viscosity indexes (VIs) in comparison with pure oil, as expected for a viscosity index improver polymer. Samples from group A showed higher VIs values than those from group B. Samples from group A showed higher VIs values even after the sheartests. Samples from group B exhibited lower VI values, but with lower shear losses. From rheometric tests, it was observed for all samples at 25°C, a gradual decrease in the viscosity curve with increasing shear stress. At lower shear rates, the viscosities remained constant. Samples from group B showed lower values as a result of their smaller molecular weight. From shear stress versus shear rate curves it was possible to predict the behavior of fluids through the power model, being classified as pseudoplastic fluids.