Revista de ciencias e ingeniería de materiales

3D plotting of micro-extruded filaments is a promising method for the additive manufacturing of porous scaffolds (for tissue engineering) in thermoplastic polymers. A much investigated polymer for degradable scaffolds is poly-ε- caprolactone (PCL). One of the remaining issues with the material is its inherent hydrophilicity, which leads to nonspecific protein adsorption. Specifically for cardiovascular applications, it has also been found that PCL is insufficiently flexible to mimic the mechanic-elastic behavior of the natural tissue. Earlier research has shown that blending with low molecular weight poly-ethylene-oxide (PEO) may offer an improvement in terms of both hydrophilicity and flexibility. Until now, solution-based blending has been used as a manufacturing method for these blends, since PCL and PEO are largely immiscible in the melt. This, however, is tedious work which yields only a few grams of material at a time. Therefore, in the current research, a method has been developed for the bulk compounding of PCL-PEO blends, using a twin-screw extruder. The manufactured blends were evaluated for composition, dispersion of the PEO and crystalline morphology. It was found that by re-compounding the blends after the first extrusion step, a good dispersion of the PEO within the PCL matrix was achieved.

Reliable performance of a Zinc Oxide surge arrester is highly dependent on its energy absorption capability. This paper presents two simple but promising approaches for enhancement of this property: one with an alternative sintering orientation and the other with the changed geometry of arrester discs to provide higher surface to volume (S/V) ratio. Several sintering orientations including the control (or conventional) process were tried and assessed. Some of these attempts have demonstrated quite superior results which might be linked to lower level of contamination during sintering. Study conducted to observe the effect of the higher surface to volume (S/V) ratio through geometrical modification of the discs from cylindrical to hexagonal shape has also demonstrated improved outcome. Average energy absorption capability for the hexagonal discs was found to increase markedly which might be attributable to faster heat dissipation aided by higher S/V ratio preventing the discs from premature failure. Thus by combining the appropriate sintering orientation and the change in geometrical shape for higher (S/V) ratio, substantial enhancement of the arrester block capability is achievable which would be eventually helpful for improved protection of electrical system.

Positron lifetime spectroscopy (PAL), Doppler broadening (DB) as well as coincidence Doppler broadening (CDB) spectroscopy of a new variety of Folic acid (FA) capped zinc oxide nano-particle samples has been performed at room temperature. The results show interesting patterns of observation, hither-to unobserved in ZnO wurtzite crystalline samples, such as predominance of positronium formation, as reflected in the (PAL) analysis, phase transition in the nano crystalline samples at ~0.8-1.0 % FA concentration as depicted from DB results. Also, the chemical environment of the samples has been analysed from the ratio curves of CDB studies. Beside these, other independent results from X-ray diffraction (XRD) data and Debye- Scherrer method, Transmission electron microscopic (TEM) observations and as well as Fourier transformed infrared spectroscopic (FT-IR) analysis are reported for comparison.