The thermooxidative degradation of poly(vinyl chloride) (PVC), chlorinated polyethylene (CPE) and PVC/CPE blend 50/50 was
investigated by means of dynamic and isothermal thermogravimetric analysis in the flowing atmosphere of air. To estimate the
thermooxidative stability of the samples the characteristics of thermogravimetric (TG) curves were used. Kinetic parameters
(the apparent activation energy E and preexponential factor Z) were calculated after isoconversional method for the first
stage of dynamic degradation where dehydrochlorination (DHCl) of PVC and/or CPE is the main degradation reaction. Despite
the chemical resemblance, the degradation mechanisms of CPE and PVC are different, as a consequence of differences in microregularity
of the corresponding polymer chains. The addition of Ca/Zn carboxylates as well as the ratio of Ca and Zn carboxylates have
considerably different influence on the investigated polymers.
The PVC/ABS blends were degradated by means of isothermal thermogravimetry at temperatures at 210...240°C in nitrogen. Applying
the stationary point method to the data obtained from thermogravimetric curves, apparent activation energy, preexponential
factor and compensation parameter for each blend were calculated. The constancy of compensation parameters points to an unchanged
mechanism of poly (vinyl-chloride) (PVC) thermal degradation in the presence of acrylonitrile butadiene-styrene (ABS). Upon
increasing the fraction of ABS in the blend up to 50% only the kinetics of the process is changed.
Authors:J. Bošnir, D. Puntarić, V. Novosel, I. Klarić, and M. Miškulin
The aim of this study was to determine the residue levels of the organochlorine pesticides in cows’ milk from Karlovac County, Croatia. The study included 48 pooled milk samples: 40 pooled samples of non-processed (raw) milk and 8 pooled samples of processed milk collected in the Karlovac County from May 2003 until April 2004. Organochlorine pesticides DDT and derivates, HCH, lindane, heptachlor and endosulfan were determined using the GC-ECD method. The detection limit was 0.01 μg kg
. The determined amounts of organochlorine pesticides were predominantly and significantly below the Maximum Residue Limit (MRL) set by the European Union and which Croatia has also recently adopted as its standard. The study has confirmed pesticide persistence in milk samples from our country despite the fact that some of them have been banned some thirty years ago, which indicates a high degree of dispersion of this substances in the environment. Taking into account that milk is a foodstuff of high biological value consumed frequently and in large quantities by vulnerable groups of population (children, pregnant women, elderly people), the continued monitoring and control of organochlorine pesticides in milk is therefore of great importance for public health.