Effect of Lanthanum Cerium Cysteine on Cure Characteristics, Mechanical Properties, and Thermooxidative Aging for Natural Rubber

In this work, a novel additive lanthanum cerium cysteine (LC-Cys), with the molecular formula La0.35Ce0.65(Cys)3Cl3·3H2O, was successfully synthesized through complex decomposition reaction of L-Cysteine and chlorinated rare earths. The effects of additive LC-Cys on cure characteristics, mechanical properties, and thermooxidative aging were investigated. LC-Cys as a multifunctional additive was applied to increase the curing rate and reduce the content of zinc oxide in the presence of the sulfur vulcanization system. It was found that the vulcanizates filled with (5ZnO/2LC-Cys) exhibited the highest modulus, which indirectly indicated the high crosslink and stiffness of the vulcanizates. Moreover, the vulcanizates with LC-Cys showed excellent mechanical properties and resistance to thermooxidative aging. Compared to NR composites filled with normal ZnO, LC-Cys even enhanced the mechanical strength and thermooxidative aging properties with 40% lower ZnO addition.

Zinc Complexes with 1,3-Diketones as Activators for Sulfur Vulcanization of Styrene-Butadiene Elastomer Filled with Carbon Black

Zinc oxide nanoparticles (N-ZnO) and zinc complexes with 1,3-diketones of different structures were applied instead of microsized zinc oxide (M-ZnO) to activate the sulfur vulcanization of styrene-butadiene rubber (SBR). The influence of vulcanization activators on the cure characteristics of rubber compounds, as well as crosslink density and functional properties of SBR vulcanizates, such as tensile properties, hardness, damping behavior, thermal stability and resistance to thermo-oxidative aging was explored. Applying N-ZnO allowed to reduce the content of zinc by 40% compared to M-ZnO without detrimental influence on the cure characteristic and performance of SBR composites. The activity of zinc complexes in vulcanization seems to strongly depend on their structure, i.e., availability of zinc to react with curatives. The lower the steric hindrance of the substituents and thus the better the availability of zinc ions, the greater was the activity of the zinc complex and consequently the higher the crosslink density of the vulcanizates. Zinc complexes had no detrimental effect on the time and temperature of SBR vulcanization. Despite lower crosslink density, most vulcanizates with zinc complexes demonstrated similar or improved functional properties in comparison with SBR containing M-ZnO. Most importantly, zinc complexes allowed the content of zinc in SBR compounds to be reduced by approximately 90% compared to M-ZnO.

Identification of volatiles from six marine Celeribacter strains

The volatiles emitted from six marine Rhodobacteraceae species of the genus Celeribacter were investigated by GC–MS. Besides several known compounds including dimethyl trisulfide and S-methyl methanethiosulfonate, the sulfur-containing compounds ethyl (E)-3-(methylsulfanyl)acrylate and 2-(methyldisulfanyl)benzothiazole were identified and their structures were verified by synthesis. Feeding experiments with [methyl-2H3]methionine, [methyl-13C]methionine and [34S]-3-(dimethylsulfonio)propanoate (DMSP) resulted in the high incorporation into dimethyl trisulfide and S-methyl methanethiosulfonate, and revealed the origin of the methylsulfanyl group of 2-(methyldisulfanyl)benzothiazole from methionine or DMSP, while the biosynthetic origin of the benzothiazol-2-ylsulfanyl portion could not be traced. The heterocyclic moiety of this compound is likely of anthropogenic origin, because 2-mercaptobenzothiazole is used in the sulfur vulcanization of rubber. Also in none of the feeding experiments incorporation into ethyl (E)-3-(methylsulfanyl)acrylate could be observed, questioning its bacterial origin. Our results demonstrate that the Celeribacter strains are capable of methionine and DMSP degradation to widespread sulfur volatiles, but the analysis of trace compounds in natural samples must be taken with care.

Effect of Carbon Synthesized from Durian Bark on Properties of Natural Rubber Composite Foam

Natural rubber foam is used in industries as a gasket and insulation product. Dimensional expansion of specimen is the crucial problem of rubber foam specimen, especially in the automotive parts assembly. This work aims to understand the behavior of natural rubber foam (NRF)/carbon composites on microstructure and properties of NRF before being used. Carbon was synthesized from durian bark which was the agricultural waste that had the potential for using as reinforcing filler. The result showed the fast sulfur vulcanization rate with small bubble size at high amount of carbon. In addition, the young modulus of NRF/carbon composites increased with increasing carbon content.

Study on sulfur vulcanized natural rubber formulated with nitrosamine safe diisopropyl xanthogen polysulfide/tertiary butyl benzothiazole sulphenamide binary accelerator system

An outstanding interest on elimination of nitrosamine generation in traditional sulfur vulcanization systems has led to introduce nitrosamine safe accelerator/s to produce safe natural rubber (NR) vulcanizates. It is an effective way to prevent formation of carcinogenic N-nitroso compounds during manufacture of rubber products. In the present study, behavior of nitrosamine safe binary accelerator system consisting of diisopropyl xanthogen polysulfide (DIXP) with commonly used non-regulated accelerator N-tert-butyl-2-benzothiazole sulfenamide (TBBS) was investigated in efficient sulfur vulcanization of NR. Cure characteristics, physico-mechanical properties and crosslink density of vulcanizates prepared with different combinations of the accelerator system were evaluated and compared with those of individual accelerators. The study reveals that moduli and strength properties of the vulcanizate prepared with DIXP accelerator are inferior to those of the vulcanizate prepared with TBBS accelerator. Nevertheless, optimum cure time of the DIXP compounds is lower in comparison to TBBS compounds. Moreover, progressive replacement of DIXP with TBBS in the accelerator system showed a synergistic effect in regard to cure characteristics and physico-mechanical properties.