Abstract This paper investigated the formation of crosslinks in natural rubber compounds in the vulcanization systems: conventional (CV), semi-efficient (SEV), and efficient (EV), processed with three types of accelerators: MBTS (dibenzothiazole disulfide), TMTD (tetramethylthiuram disulfide) and CBS (n-cyclohexyl 2-benzothiazole sulfenamide). The cross-linked densities were determined by organic solvent swelling, dynamic mechanical analysis (DMA), stress vs strain, and low-field nuclear magnetic resonance, the latter being the reference technique for comparison with the other results. It was found that the choice of accelerator type influences the processing time and the cross-linked density of the vulcanizate. The four techniques showed close values of cross-linked density for natural rubber compounds, demonstrating that the analytical techniques studied can be applied to determine cross-linked density.

In this study, we obtained and characterized a piezoelectric composite with 1-3 connectivity from castor oil polyurethane (PUR) and lead zirconate titanate (PZT) rods. Two samples were obtained, one with 15% PZT volume and the other with 34% PZT volume. The ac electrical properties of the 1-3 piezoelectric composite samples demonstrated the frequency-dependence behavior of disordered solids. The piezoelectric coefficient (d33) was greatly influenced by the number of PZT rods and the matrix curing process. The sample with 34% PZT volume showed a higher d33 value, (246 pC/N measured after 30 d of polarization). The composites were evaluated for use in acoustic emission wave sensors for application in structural health monitoring.

The third generation (G-3) poly(propyleneimine)hexadecaamine dendrimer (DAB-Am-16) was grafted onto the chloropropylsilica gel surface (DPPIPS). The modified silica (DPPIPS) was characterized by Electronic (Uv-Vis), vibrational and Electron Paramagnetic Resonance (EPR), spectrocopies, surface area (331.07 m².g-1) and porosity analyses (pore diameter of 41.9 nm) and cyclic voltammetry technique. The copper adsorption studies were performed using a batchwise process and the DPPIPS showed adsorption capacities of 16.3, 47.8 and 659.5 mol.g-1 in aqueous, ethanol and acetone medium, respectively, with recoveries close to 100% after percolation with HCl 1.0 mol.L-1. The results suggest that the sorption of copper ions on DPPIPS occurs mainly by surface complexation and a Langmuir model allowed describing the sorption of the metal ions on DPPIPS. As an application of this chemically modified material, copper was determined in real samples of distilled spirits and fuel alcohol.