Mechanical,thermal, morphological,and curing properties of geopolymer filled natural rubber composites

The main objective of this work was to investigate influence of natural rubber (NR) types on mechanical, thermal, morphological, and curing properties together with relaxation behavior of geopolymer filled NR composites with and without bis(triethoxysilylpropyl) tetrasulfide (TESPT) silane coupling agent. Three alternative types of NR: unmodified NR, and epoxidized NR with 25 (ENR-25) or 50 mol % epoxide (ENR-50) were exploited. Rubber compounds filled with GP particles were prepared in an internal mixer at 60 °C and 130–150 °C for the ones with and without TESPT, respectively. It was found that incorporation of GP significantly affected cure characteristics and mechanical properties of the rubber composites. That is, decreasing cure time was observed from 11.6, 3.2, and 7.0 min in gum NR, ENR-25, and ENR-50 to 6.9, 2.1, and 5.0 min in NR/GP, ENR-25/GP, and ENR-50/GP compounds, respectively. Furthermore, the ENR-25/GP and ENR-50/GP composites showed finely dispersed GP particles which indicate high filler–rubber interactions. The in situ silanization with TESPT in rubber composites enhanced the mechanical properties of NR/GP and ENR-25/GP composites but no such enhancement was found in the ENR-50/GP composite. This matched the observations of Payne effect, maximum tan δ, and stress relaxation properties of the composites. We found that the ENR-25/GP composites exhibited the best overall properties. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47346.     

Dielectric properties and temperature profile of fly ash-based geopolymer mortar

In this paper, the fresh properties, dielectric properties and temperature profile of fly ash-based geopolymer mortars are investigated to observe the effect of mixture proportions and time after mixing. Sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) were used as the activators. The results of fresh properties revealed that the added water could improve the workability of geopolymer mortar. It is also found that the initial and final setting times of all the geopolymer mortars are less than those of cement mortars. For the dielectric properties and surface temperature, mortars were measured during a 24-hours geopolymerisation period at room temperature. The obtained results show that dielectric properties and surface temperature of geopolymer mortars tended to decrease with increasing time after mixing. And the geopolymer mortars had the highest value of dielectric properties and surface temperature at right after mixing. In addition, the dielectric properties (ε_r' and ε_r″) of the specimens with more liquid constituents were also higher. In particular, this work shows that it is possible to cure the fly ash-based geopolymer mortars with microwave energy depending on the mixture proportion and time after mixing.