Authors:Z. Cibulková, P. Šimon, P. Lehocký and J. Balko
Summary The antioxidant activity of selected N,N'-substituted p-phenylenediamines derived from 6PPD in polyisoprene matrix has been studied by differential scanning calorimetry (DSC) under non-isothermal conditions. The kinetic parameters describing temperature dependence of induction period have been obtained. Protection factors and antioxidant effectiveness have been calculated to characterize the stabilizing effect of the antioxidants under study. Using both criteria, the highest antioxidant activity has been observed in the case of Dusantox L, which is a mixture of 6PPD and its p-kumyl derivative. Its high antioxidant efficiency can be explained by the synergistic effect of 6PPD and its p-kumyl derivative. The lowest antioxidant efficiency of o-kumylderivative of 6PPD is probably caused by the sterical effect of the bulky kumyl group.
Authors:T. Sopcak, L. Medvecky, T. Zagyva, M. Dzupon, J. Balko, K. Balázsi and C. Balázsi
The current study was initiated in order to evaluate the adhesion strength of thin and porous hydroxyapatite (Hap) coatings on titanium (Ti) substrates deposited by the low temperature electrospraying method. The nanocrystalline hydroxyapatite powder was synthesized by coprecipitation method using eggshell biowaste as a nontoxic and natural source of the calcium precursor. Five hydroxyapatite coatings were electrosprayed onto Ti substrates by varying the concentration (0.05 and 0.1 wt%) of polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) polymers in Hap suspensions. It has been shown that the adhesion strength of composite polymer–Hap coatings increased with increasing polymer concentration and the highest value (8.75 ± 0.75 MPa) was measured for the sample containing 0.1 wt% of PVP. The reason for the change in bonding strength was ascribed owing to microstructural changes caused by polymer addition whereas on one hand lower adhesion strength in Hap–0.1PEG was caused by the presence of separated polymer contained islands, and hence, weaker adhesion to substrate was found in this sample. On the other hand, more uniform, homogeneous, and denser microstructure resulted in an increasing cohesive strength inside the Hap–0.1PVP layer which lead to stronger mechanical bonding at the coating–substrate interface.