Showing papers by "Leila L. Y. Visconte published in 2001"

Mechanical and flammability properties of ATH-Filled EPDM compositions

Abstract: Poly(ethylene-co-propylene-co-diene) (EPDM) compositions filled with mixtures of aluminium hydroxide (ATH) and carbon black (HAF) were evaluated for electrical applications. Mechanical and flammability tests were carried out in order to find out the relative amounts of the two fillers which would give the best balance of properties, mainly to meet the Brazilian Society for Technical Standards-ABNT. For good flame resistance, amounts as high as 160 phr ATH, at least, must be used.

Physical properties and swelling of natural rubber compounds containing rice husk ash

Abstract: Rice husk ash, used as received (RHA) or milled (MHA), was investigated in natural rubber (NR) for its potential as a new type of filler. The physical testing of the NR vulcanizates involved tensile, tear, and abrasion resistance, hardness and resilience. The interaction between rice husk ash and natural rubber was investigated by swelling in an organic solvent. The effect of the coupling agent, bis(3-triethoxy-silylpropyl)-tetrasulfane (Si-69), on the curing and physical properties of the vulcanizates was investigated. The presence of the silane coupling agent has not brought the expected increase in properties, yet MHA exhibits the best overall vulcanizates properties when compared to RHA, although still inferior to commercial fillers as precipitated silica (Zeosil-175) and carbon black (N762), especially with regard to tensile strength and abrasion resistance.

Propriedades Mecânicas e de Inflamabilidade de Composições de Borracha EPDM Carregadas com Negro de Fumo e Hidróxido de Alumínio

Abstract: Resumo: Composicoes de EPDM (terpolimero de etileno-propileno-dieno) contendo misturas de negro de fumo e hidroxido de aluminio (ATH) foram preparadas com o objetivo de se avaliar seu potencial de utilizacao em aplicacoes eletricas. O hidroxido de aluminio, conhecido por suas caracteristicas de retardante de chama, e uma carga semi-reforcante e, portanto, incapaz de fornecer o nivel de reforco necessario para diversas aplicacoes. Dessa forma, para aliar ao artefato propriedades de nao inflamabilidade e alto desempenho mecânico, foi tambem adicionado o negro de fumo (que e a carga reforcante mais larga- mente empregada). A escolha do EPDM se justifica pela facilidade de ser encontrado no mercado brasi- leiro, por sua caracteristica em aceitar grandes quantidades de carga e por ser um elastomero apolar, o que e um requisito basico para aplicacao em isolamento eletrico. Os materiais foram submetidos a testes mecânicos e de inflamabilidade, para se determinar aqueles que se ajustavam as normas estabelecidas pela Associacao Brasileira de Normas Tecnicas - ABNT. Verificou-se que pelo menos 160 phr de hidroxido de aluminio sao necessarios nessas composicoes para que a resistencia a chama seja alcancada. Palavras-chave: Elastomero EPDM, hidroxido de aluminio, propriedades mecânicas, resistencia a chama. Mechanical and flammability properties of EPDM (ethylene-propylene terpolymer) rubber compositions filled with carbon black and aluminum hydroxide Abstract: EPDM composition filled with mixtures of aluminum hydroxide (ATH) and carbon black were evaluated for electrical applications. Aluminum hydroxide, known for its characteristics of flame retardancy, is a semi-reinforcing filler and, in this sense, it is unable to impart the reinforcement level necessary to several applications. Thus, to have in the same artifact the non-flammability properties together with a high mechanical performance, carbon black, the most widely used reinforcing filler, has also been used. The choice of EPDM can be justified by the availability of this polymer in the brazilian market, allied to its characteristics to accept large amounts of filler and its apolar chemical character, which is a basic requirement for application in electrical insulation. To meet the Brazilian Technical Standards - ABNT, mechanical and flammability tests were carried out in order to find out the relative amounts of the two fillers which would give the best balance of properties. Amounts as high as 160 phr of aluminum hydroxide are required to achieve good flame resistance.

Misturas NR/SBR: modos de preparação e propriedades

Abstract: Frequently a set of properties required for a given application cannot be accomplished by only one elastomer and, thus, mixtures of two or more polymers must be employed. In these cases, the other ingredients normally added are dispersed differently, depending on their affinity to each polymer. The degree of dispersion each additive experiences in each elastomeric phase will influence the rate and the degree of vulcanization and will certainly have consequences on the performance of the final product. In this work, natural rubber (NR) was mixed to butadiene-styrene elastomer (SBR) in a 50:50 w/w ratio. The compositions were prepared in a two-roll mill, according to ASTM D3182, introducing the additives in four different modes. After vulcanization, the mixes were investigated as for their mechanical (stress and tear strengths and hardness), dynamic mechanical thermal and morphological analysis. Mechanical properties were evaluated according to ASTM procedures, specific for each test. The results show that, although having been prepared following the same formulation, the properties of these mixtures are influenced by the preparation mode, which could be detected by mechanical and morphological analysis and evidenced through more sensitive methods as DMTA. For NR/SBR blends, the best properties are achieved when one favours the vulcanization of the rubber with inferior properties, that is, SBR.

EPDM formulations for electric wires and cables

Abstract: EPDM formulations were developed with both carbon black and aluminum hydroxide as fillers. Mechanical and electrical properties were evaluated with the purpose to find out those compositions which would meet the Brazilian Association for Technical Standards, ABNT, requirements as for their use in wires and cables. As expected carbon black has a negative effect and its presence should be restricted to less than 22 phr if these materials are to be used in the range of medium voltages (up to 15 kV).

Rice husk ash in polysiloxane compounds - Physico-mechanical, processability and morphological aspects

Abstract: Rice husk ash (RHA) is an agricultural residue abundant in many countries. However, the number of applications involving this residue is not high enough to deplete the amounts generated. Thus, in this work, RHA was used in polysiloxane compounds, in order to investigate its potential as filler. The results show that, depending on the content of RHA in the formulation, apart from superior processability one can achieve comparable values of some mechanical properties.

Propriedades mecânicas e resistência à chama de composições SBR/negro de fumo/hidróxido de alumínio

Abstract: Vulcanizable SBR (butadiene-styrene copolymer) formulations were developed with the objective to obtain high mechanical performance materials with flame resistance and low cost. Aluminum hydroxide (ATH) was used as anti-flame and smoke suppressor agent in addition to the conventional additives used in diene elastomers like zinc oxide, stearic acid, sulfur, carbon black (NF) and TBBS (N-t-butyl-2-benzothiazole sulfenamide) accelerator. To reach the proposed goal, different amounts of ATH/NF ratio were used in these formulations. The resulting composites were characterized by the following tests: tensile strength, tear resistance, hardness, compression set, flame resistance and limiting oxygen index (LOI). Based upon the results obtained with the formulations used for SBR, it was possible to conclude that carbon black in the range of 25-50 phr and aluminum hydroxide in amounts higher than 125 phr, characterize the final composites as having high mechanical performance, flame resistance and low cost, as a consequence of the large quantity of incorporated filler.

Avaliação do processo de cura da borracha nitrílica (NBR) pela resina fenólica através do cálculo da constante de cura

Abstract: The cure process involves reactions with multiple mechanisms and its investigation can be followed by using different techniques. This work compares two methods in which rheometric parameters are used to calculate the cure rate constant (k), related to the cure of nitrile rubber with phenolic resin and having polychloroprene and zinc oxide as the activators. A complete factorial (23 + central point) experimental design was used as base to prepare the formulations and to analyse the results. The results obtained identified the influence of the temperature, the amount of each component in the formulation and the suitability of the evaluation methods for the cure process of nitrile rubber with phenolic resin.

Effect of cnsl resin on the crystallinity of polypropylene in pp/nbr mixtures

Abstract: Blends of polypropylene (PP) and acrylonitrile rubber (NBR) were prepared in a Haake 9000 Rheocord System. Two different phenolic resins were introduced into these blends and the effect of this third component on the mechanical properties was evaluated, as well as the relationship between the crystallization of the polypropylene matrix and the properties analysed.