Synergistic activities of binary accelerators in presence of magnesium oxide as a cure activator in the vulcanization of natural rubber

We describe the synergistic activities of binary vulcanizing accelerators in presence of magnesium oxide as cure activator in the vulcanization of natural rubber. Thiuram type tetramethyl thiuram disulfide (TMTD) and thiocarbamate type zinc dimethyl dithiocarbamate (ZDMC) accelerators in combination with dibenzothiazyl disulfide (MBTS) were investigated for the vulcanization of rubber. The cure, mechanical, and thermal properties of rubber vulcanizates were studied with magnesium oxide-based cure activator. Notable synergism in the delta torque, cross-link density, and mechanical properties was found when using binary accelerators with magnesium oxide. The zinc-containing thiocarbamate accelerator, ZDMC, showed better synergistic activity in presence of magnesium oxide than the non-zinc-based thiuram accelerator, TMTD. To find out the possibility of making a zinc-oxide-free natural rubber compound, a control compound was prepared with 5 phr of zinc oxide as a cure activator with the best evaluated binary accelerators system with magnesium oxide (3:6 millimolar ratio of ZDMC to MBTS). We also compared the curing and mechanical properties of carbon black-reinforced rubber with zinc oxide and magnesium oxide separately with this binary accelerators system. The results indicated that a completely zinc-oxide-free natural rubber compound was possible with comparable values in the mechanical properties, thermal properties and a higher rate of vulcanization.

EXPLORING THE SUITABILITY OF SOL-GEL–SYNTHESIZED NANO ZnO AS A CURE ACTIVATOR IN CARBON BLACK– AND SILICA-FILLED NR COMPOSITES

ABSTRACT Sol-gel–synthesized nano zinc oxide (ZnO) is introduced as a cure activator in carbon black (CB)– and silica-filled natural rubber (NR) composites. The performance of sol-gel–synthesized nano ZnO was systematically compared with conventional ZnO for various filled NR composites in terms of cure, mechanical, aging, and thermal properties. At a filler loading level of 40 parts per hundred parts of rubber (phr), only 1 phr nano ZnO provided a better cure rate index and tensile strength as compared with 5 phr conventional ZnO in CB-filled NR composites. On the other hand, at a 40 phr filler loading level, the cure and mechanical properties of the 1 phr nano ZnO cured NR/silica composite were comparable with the properties of the 5 phr conventional ZnO cured NR/silica composite. At the same filler loading level, both 1 phr nano ZnO and 5 phr conventional ZnO had a similar effect on the thermal stability of NR/CB and NR/silica composites. As a whole, 1 phr sol-gel–based nano ZnO could be used as an efficient cure activator instead of 5 phr conventional ZnO in CB- and silica-filled NR composites with successive reduction of ZnO level.

Influência do Primer e Sistema Adesivo Sobre a Resistência de União do Cimento Resinoso Quimicamente Ativado à Liga Dental Co-Cr

O objetivo foi avaliar os efeitos de primers e sistemas adesivos sobre a resistência de união ao microcisalhamento do cimento resinoso quimicamente ativado à liga de Co-Cr. Setenta e dois blocos retangulares de liga metálica Co-Cr foram fabricados e pré-tratados com partículas de dióxido de alumínio (50 µm) por 15 segundos. Aplicaram-se os primers (Alloy Primer - AP ou Clearfil Ceramic Primer - CP), adesivos (Adper Scotchbond Multi-Purpose Adhesive ativado por Adper Scotchbond Multi-Purpose Adhesive Catalyst - SASC ou Primer & Bond 2.1 ativado pelo Self Cure Activator - PBCA) e subsequentemente divididos em seis grupos (SASC AP / SASC CP / SASC PBCAAP / PBCA CP / PBCA), n 12. Em seguida, foi aplicado o cimento de resina (Enforce). Os dados para os valores resistência de união foram estatisticamente avaliados por análise de variância e teste de Tukey. A resistência de união ao microcisalhamento (MPa) foi menor (p<0,001) em grupos com sistema adesivo somente (SASC- 5,02 e PBCA- 13,38) em comparação com os grupos com adição de primers Alloy Primer (AP / SASC- 15,81 e AP / PBCA- 15,36) e Ceramic Primer (CP / SASC- 16,92 e CP / PBCA- 16,30). A aplicação de primers melhora a resistência à união do cimento resinoso à liga de metal Co-Cr.Palavras-chave: Resistência ao Cisalhamento. Cimentos de Resina. Cimentação.

Thermal Conductivity and Mechanical Properties of the Rubber Stopper Filled with ZnO Nanograins

ZnO nanograins (nZnO) were synthesized by a precipitation method. The nZnO exhibited the average grain size of ~30 nm and the specific surface area of 28.24 m2 g-1. Then, it was incorporated into the ethylene propylene diene monomer (EPDM) rubber and produced to be a rubber stopper. This work studied the effect of nZnO and conventional ZnO (cZnO) as a cure activator on the thermal conductivity and mechanical properties of the rubber stopper. As the content of nZnO increased, the thermal conductivity and mechanical properties are also increased. The obtained results could be reduced successfully from 5 to 2 parts per hundred parts of rubber (phr) compared with a cZnO because nZnO provides a satisfactory thermal conductivity and mechanical properties. Moreover, it also gives uniform completely vulcanized for thick rubber product due to swelling value (Q) between outer and inner portion of rubber stopper is less difference. In this work is concluded that the dosage, grain sizes and grain boundary of ZnO are effective parameter in the thermal conductivity and mechanical properties of the rubber stopper.

PRECIPITATED NANO ZINC HYDROXIDE ON THE SILICA SURFACE AS AN ALTERNATIVE CURE ACTIVATOR IN THE VULCANIZATION OF NATURAL RUBBER

ABSTRACT We synthesized precipitated zinc hydroxide on the surface of precipitated silica via a conventional precipitation method. The zinc hydroxide is characterized by Fourier transform infrared spectroscope, X-ray diffraction, and field-emission scanning electron microscope measurements. The synthesized zinc hydroxide is a platelike structure with an average nano dimension of 40 nm in crystalline depth. The aim of the present study is to reduce the cure activator level of conventional environment pollutant zinc oxide in the vulcanization of natural rubber. To study the effects of the synthesized zinc hydroxide on the vulcanization of natural rubber curing, mechanical and thermal properties were determined and compared with the vulcanized properties of conventional 5 phr (per hundred grams of rubber) zinc oxide cured rubber vulcanizate. A strong enhancement in the cross-link density and mechanical properties (namely, modulus, tensile strength, and hardness) with only 2 phr of synthesized zinc hydroxide cured rubber system compared with 5 phr of conventional zinc oxide cured rubber system was found. A slightly higher thermal stability of 2 phr zinc hydroxide cured vulcanizate was observed because of better cross-link density than conventional 5 phr zinc oxide cured rubber vulcanizate. Thus, by this novel method, a greater than 60% reduction of the conventional cure activator level can be possible with improved physical properties in the vulcanization of natural rubber.