RESUMO
Natural rubber with 50 mol % epoxidation (ENR-50) was filled with carbon nanotubes (CNTs) and conductive carbon black (CCB) hybrid fillers with various CCB loadings of 2.5, 5.0, 7.0, 10.0 and 15.0 phr, and the compounds were mixed with ferric ion (Fe3+) as a crosslinking agent. The ENRs filled exclusively with CNTs, and CNT-CCB hybrid fillers exhibited typical curing curves at different CCB loadings, i.e., increasing torque with time and thus crosslinked networks. Furthermore, the incorporation of CNT-CCB hybrid fillers and increasing CCB loadings caused an enhancement of tensile properties (modulus and tensile strength) and crosslink densities, which are indicated by the increasing torque difference and the crosslink densities. The crosslink densities are determined by swelling and temperature scanning stress relaxation (TSSR). Increasing CCB loadings also caused a significant improvement in bound rubber content, filler-rubber interactions, thermal resistance, glass transition temperature (Tg) and electrical conductivity. A combination of 7 phr CNT and CCB with loading higher than 2.5 phr gave superior properties to ENR vulcanizates. Furthermore, the secondary CCB filler contributes to the improvement of CNT dispersion in the ENR matrix by networking the CNT capsules and forming CNT-CCB-CNT pathways and thus strong CNT-CCB networks, indicating the improvement in the tensile properties, bound rubber content and dynamic properties of the ENR composites. Moreover, higher electrical conductivity with a comparatively low percolation threshold of the hybrid composites was found as compared to the ENR filled with CNTs without CCB composite. The superior mechanical and other properties are due to the finer dispersion and even distribution of CNT-CCB hybrid fillers in the ENR matrix.
RESUMO
In this work, studies are carried out to understand the crosslinking reaction of epoxidized natural rubber (50 mol% epoxy, ENR-50) by metal ion namely ferric ion (Fe3+, FeCl3, ferric chloride). It is found that a small amount of FeCl3 can cure ENR to a considerable extent. A direct interaction of the ferric ion with the epoxy group as well as internal polymerization enable the ENR to be cured in an efficient manner. It was also found that with the increased concentration of FeCl3, the crosslinking density of the matrix increased and therefore, the ENR offers higher mechanical properties (i.e., modulus and tensile strength). In addition, the glass transition temperature (tg) of ENR vulcanizate is increased with increasing concentration of FeCl3. Moreover, the thermal degradation temperature (Td) of the ENR-FeCl3 compound was shifted toward higher temperature as increasing concentration FeCl3.
RESUMO
Geopolymer (GP) based on fly ash waste from electric power generating plants has been applied in natural rubber composites as a sustainable solution to deal with this industrial solid waste. This alternative type of rubber filler can reduce hazards and environmental impacts of that waste. Novel elastomer composites based on geopolymer (GP) filled epoxidized natural rubber (ENR) were prepared with various GP loadings. Cure characteristics, mechanical, dynamic, thermal, and morphological properties of the ENR/GP composites were characterized. It was found that incorporating GP significantly affected cure characteristics of ENR compounds, decreasing scorch and cure times by accelerating the cure rate via the excessive metal oxides in GP. Furthermore, the ENR/GP composites with 15â¯phr GP showed the highest tensile strength due to maximal chemical linkages of hydroxyl groups and metal oxides on GP surfaces and epoxide groups in ENR. This was confirmed by a new FTIR peak for SiOH bending vibrations at the wavenumber 970â¯cm-1. Furthermore, the Payne effect in ENR/GP composites was assessed from the relationship of shear modulus and strain amplitude at a fixed oscillation frequency. It was found that the Payne effect, or the level of filler-filler interactions, increased with GP loading. In addition, it was also found that the glass transition temperature (Tg) of ENR/GP composites increased with GP loading. Furthermore, TGA and TSSR results suggest that the metal oxide in GP activated degradation of the rubber network at elevated temperatures.
