Alex S. Sirqueira

The effect of mercapto- and thioacetate-modified EPDM on the curing parameters and mechanical properties of natural rubber/EPDM blends

Abstract The vulcanization characteristics of natural rubber (NR)/ethylene–propylene–ethylidenenorbornene (EPDM) rubber blends were studied in the presence of thioacetate-(EPDMTA) or mercapto-modified EPDM (EPDMSH), using oscillating disk rheometer. The effect of both functionalized EPDMs was investigated in unaccelerated-sulfur curing system and accelerated-sulfur curing systems containing 0.4 and 0.8 phr of MBTS. Both EPDMTA and EPDMSH act as accelerator agent in the curing process, as indicated by the higher values of cure rate index and lower values of activation energy of vulcanization. A substantial increase of the crosslink density has been also observed in EPDMSH-modified blends. Both EPDMTA and EPDMSH resulted in an increase in tensile strength, but the best performance has been achieved with EPDMSH, probably because of the increase of crosslink density associated to the reactive compatibilization promoted by the reaction between mercapto groups and rubber matrix. The best ageing resistance has been observed in EPDMTA-modified blends.

Compatibilization of Natural Rubber/EPDM Blends by Anhydride‐ and Mercapto‐functionalized Copolymers

The compatibilization of natural rubber (NR)/ethylene‐propylene‐ethylidenenorbornene (EPDM) rubber blends was performed by using anhydride‐ and mercapto‐functionalized copolymers. EPDM functionalized with mercapto (EPDMSH) and anhydride groups (EPDM‐g‐MA), as well as ethylene‐vinyl acetate copolymer (EVA) functionalized with mercapto (EVASH) and anhydride groups (EVA‐g‐MA) were employed in small proportion in NR/EPDM (70:30 wt.%) blends. All functionalized copolymers resulted in an improvement of ultimate tensile strength, but the best results were achieved with the addition of 2.5 phr of EVA‐g‐MA. The rheological experiments performed on a rheological processing analyzer (RPA) revealed that the addition of small amount of EVASH resulted in a substantial increase of elastic modulus of non‐vulcanized blends, indicating effective interaction between the blend components. The solvent uptake experiments suggest a co‐vulcanization process in blends compatibilized with functionalized EVA.

Desenvolvimento de elastômeros termoplásticos vulcanizados (TPV) a base de polipropileno com resíduo de pneu: I - Planejamento fatorial de experimentos

The use of waste tire in blends with thermoplastics enables the formation of new materials. In this paper the use of waste tire was characterized with a complete 23 factorial design with central point, in blends with polypropylene (PP), in the development of new thermoplastic elastomers vulcanized dynamically (TPVs) and containing recycled material. The factors used in this study were: waste tire, dicumylperoxide and bismaleimides in three levels, one being the central point. The factorial design was built to evaluate the effects of the factors (and their interaction) in the responses of tensile, elongation and oil swelling. The results showed that the level of waste tire is predominant to improve the performance of TPV. The swelling resistance is approximately 150% higher in some formulations.

O efeito de EPDM modificado com grupos mercapto ou tioacetato na cinética de vulcanização de misturas NR/EPDM

Vulcanization kinetics for natural rubber (NR)/ ethylene-propylene-diene rubber (EPDM) blends was studied as a function of the compatibilization, by using an oscillatory disk rheometer. For this study, 2.5 phr of thioacetate- (EPDMTA) or mercapto-modified EPDM (EPDMSH) were employed in blends vulcanized with sulfur/CBS curing system. Both functionalized copolymers increased the curing velocity of the blends, but the higher overall rate was achieved with EPDMSH-modified systems, using the Chough and Chang model. However, when using the Coran model, we observed that they act in distinct vulcanization steps: EPDMSH acts preferentially at the beginning of the curing process whereas EPDMTA increases the rate of the crosslink formation. In addition, EPDMTA decreased the tendency for crosslink decomposition, as indicated by the lower value of reversion degree.

Rheological behavior of acrylic paint blends based on polyaniline

The rheological properties of acrylic paints and polyaniline (PAni) blends, with different contents of PAni doped by dodecyl benzene sulphonic acid (DBSA) and, dispersed by mechanical stirrer and ultrasonic, were investigated by controlled shear rate testing ramps. The results showed that the commercial acrylic paint had tended to deliver the required stability on the blends, in order to avoid sedimentation process. All samples exhibited non-Newtonian flow behavior (shear thinning), increasing PAni content the flow behavior index (n) decreased (0.41 to 0.11) and power law model were used to fitted the experimental curves. The results showed that the addition of PAni-DBSA affects the viscoelastic behavior of the mixtures due to the interactions between the components in the mixture. The best properties were obtained for samples 90/10 wt % dispersed by ultrasonic, indicating the feasibility of the usage as a conducting paint.

Nitrigreen a borracha ecológica

New vegetable oil pre-plasticized rubbers (Nitrigreen) with 33% of acrilonitrile were especially developed by Nitriflex to supply the rubber market necessities. Nitrigreen complies with European regulation 2005/84/EC as it uses a plasticizer from renewable source. This rubber has superior effect in the Mooney viscosity reduction compared with usual plasticizer such as phthalates. In addition to the ease of processing, Nitigreen is compatible with vulcanization additives and may be used in low hardness products, including toys, cylinders and technical parts. This new pre-plasticized nitrile rubber with 50 phr of plasticizer has excellent processability, low consumption of energy, and facilitates incorporation of additives, especially reinforcing loadings such as carbon black. The mechanical properties of this rubber are slightly superior to those of a rubber containing DOP.

CINÉTICA DE RETICULAÇÃO DE BORRACHA NITRÍLICA CARBOXILADA

Este trabalho teve como objetivo estudar diferentes sistemas de vulcanizacao, a base de enxofre e oxido de zinco, em composicoes de borracha nitrilica carboxilada. A borracha nitrilica carboxilada destaca-se por sua otima resistencia a abrasao e capacidade de reticulacao por oxidos metalicos formando uma rede de ligacoes ionicas. As propriedades mecânicas dos compostos vulcanizados foram avaliadas por ensaios de tracao, modulo, envelhecimento em ar e deformacao permanente a compressao. A analise do sistema oxido de zinco/enxofre/MBTS por reometria de disco oscilatorio apresentou duas inflexoes, indicando uma cinetica de cura de natureza de segunda ordem. A partir dos resultados obtidos nos ensaios mecânicos, conclui-se que o sistema oxido de zinco/enxofre/MBTS possui o melhor desempenho mecânico.