Valéria D. Ramos

Efeito do óleo de mamona em composiçõesde borracha natural contendo sílica

The possible use of castor oil fatty acid as an activator for the vulcanization reaction in silica-filled natural rubber (NR) compounds was investigated. The design and analysis of the experiments were carried out by keeping constant the concentration of silica and the other ingredients while the amounts of stearic acid, castor oil and poly(ethylene glycol) were varied. Cure was carried out on a TI-100 oscillating disk rheometer, and the tensile strength was chosen as the control variable. The results show that the addition of castor oil does not significantly change the mechanical performance of silica-filled natural rubber compounds.

Epoxidation of 4-methyloct-4-ene: identification of reaction products and kinetic study

Abstract The performic acid epoxidation of 4-methyloct-4-ene, a model compound for 1,4-polyisoprene, is the subject of this study. The purpose was the optimization of the conditions for the epoxidation reaction by this oxidation agent. The first part of this work is concerned with the identification and characterization of the reaction products through NMR and FTIR spectroscopies. Four main products were characterized. Among them, an epoxide results from the epoxidation of 4-methyloct-4-ene by performic acid and three others, namely a ketone, a diol and a glycol ester, are the result of epoxide rearrangements. The second part is devoted to kinetic studies of the epoxidation reaction through high performance liquid chromatography (HPLC) technique. This investigation allowed an insight into the influence of the reaction parameters (temperature and concentration of hydrogen peroxide) on the conversion rate. The determining step of the epoxidation reaction was the formation of performic acid. The enthalpy of activation was found to be ΔH∗ = 91 kJ/mol and the entropy of activation ΔS ∗ =−34.6 J/mol K.

Addition of 2-hydroxyethyl methacrylate upon 4,5- epoxy-4-methyloctane catalyzed by ceric ammonium nitrate 1: identification of the reaction products

The alkoxylation of 4,5-epoxy-4-methyloctane, a model compound for epoxidized 1 ,4-polyisoprene, by 2-hydroxyethyl methacrylate (HEMA) in the presence of ceric ammonium nitrate (CAN) as catalyst was studied. The purpose was the identification and characterization of the reaction products formed during the addition of a photosensitive alcohol onto epoxidized 1,4-polyisoprene type structures, when the reaction is carried out in mild conditions. The products were characterized through NMR and FTIR spectroscopy, after fractionation by semi-preparative HPLC. Five main products were identified and characterized. Three of them result from the addition of the alcohol onto the epoxide (one saturated 1:1 adduct and two allylic 1:1 adducts). The other two are the result of epoxide rearrangements (a ketone and an allylic alcohol). The methacrylate photosensitive groups were recovered unchanged after the reaction.

Efeito de um resíduo do processo de galvanoplastia sobre a vulcanização da borracha natural (NR)

Um residuo gerado no processo de galvanoplastia (RG), rico em metais, foi incorporado em composicoes de borracha natural (NR) em substituicao parcial ou total ao ativador comum do processo de vulcanizacao, o oxido de zinco (ZnO). As diferentes misturas foram preparadas em um misturador de calandras e, apos a reometria, foram vulcanizadas a 150 °C. As propriedades mecânicas de resistencia a tracao e rasgo foram determinadas, alem do teor de gel. Alem disso, o efeito do residuo RG sobre a cinetica de vulcanizacao foi analisado atraves do modelo de Coran, usando-se as temperaturas de 150, 160 e 170 °C. Os resultados mostraram que RG desenvolve algum efeito catalitico sobre a vulcanizacao de NR, embora exista uma consideravel perda na resistencia a tracao quando o teor de RG excede o do ZnO nas composicoes. Quanto ao rasgo, a propriedade e mantida em um patamar satisfatorio enquanto teores menores de RG sao utilizados.

Effect of the Electroplating Process Waste upon Vulcanization and Mechanical Properties of Natural Rubber (NR) Compositions

The potential of EWPS (electroplating waste of the polishing step) as activator for vulcanization process has been evaluated. EWPS was incorporated into natural rubber (NR) formulation in replacement partial or total to ZnO. The different mixtures were obtained in a laboratory-size two-roll mill and conventional vulcanization system (CV) was chosen for vulcanization. Rheometer parameters (ts1, t90, and Mh), mechanical properties (tensile and tear strength) and cure studies at 150, 160 and 170°C for a kinetic model were carried out. EWPS shows some catalytic effect upon NR vulcanization with reduction of scorch and optimum cure time. However, the compounds where EWPS is present in major quantity, in relation to ZnO, or alone as activator present a depleted performance with a continuous reduction of properties, such as, tensile strength.