Dynamic and Isothermal Thermogravimetric Degradation of Poly(vinyl Chloride)/Chlorinated Poly(ethylene) Blends

The thermal degradation of poly(vinyl chloride)/chlorinated poly(ethylene) (PVC/CPE) blends of different compositions was investigated by means of dynamic and isothermal thermogravimetric analysis in flowing atmosphere of nitrogen. Kinetic parameters (the apparent activation energy E, and pre-exponential factor Z) were calculated after Flynn-Wall-Ozawa method for the first stage of dynamic degradation of PVC/CPE blends, and after Flynn method for the isothermal degradation. In both cases, there is the compensation dependence between the values E and logZ. The values of compensation ratios as well as the characteristics of TG and DTG curves, confirm the stabilizing effect of CPE on PVC dehydrochlorination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spectral methods for growth curve clustering

Central European Journal of Operations Research - The growth curve clustering problem is analyzed and its connection with the spectral relaxation method is described. For a given set of growth...     

On the Jensen-Steffensen inequality for generalized convex functions

Jensen-Steffensen type inequalities for P-convex functions and functions with nondecreasing increments are presented. The obtained results are used to prove a generalization of ?eby?ev’s inequality and several variants of Hölder’s inequality with weights satisfying the conditions as in the Jensen-Steffensen inequality. A few well-known inequalities for quasi-arithmetic means are generalized.     

Converse Jensen–Steffensen inequality

In this paper we prove a converse to the Jensen–Steffensen inequality. We also present two inequalities complementary to the Jensen–Steffensen inequality. The equality case conditions are thoroughly investigated.     

Generalizations of the Jensen-Steffensen and related inequalities

We present a couple of general inequalities related to the Jensen-Steffensen inequality in its discrete and integral form. The Jensen-Steffensen inequality, Slater’s inequality and a generalization of the counterpart to the Jensen-Steffensen inequality are deduced as special cases from these general inequalities.     

Thermal degradation of poly(vinyl chloride)/poly(ethylene oxide) blends: Thermogravimetric analysis

Thermal stability of poly(vinyl chloride)/poly(ethylene oxide) (PVC/PEO) blends has been investigated by thermogravimetric analysis (TGA) in dynamic and isothermal heating regime. PVC/PEO blends were prepared by hot-melt extrusion (HME). According to TG analysis, PEO decomposes in one stage, while PVC and PVC/PEO blends in two degradation stages. In order to evaluate the effect of PEO content on the thermal stability of PVC/PEO blends, different criteria were used. It was found that thermal stability of PVC/PEO blends depends on the blend composition. The interactions of blends components with their degradation products were confirmed. By using multiple heating rate kinetics the activation energies of the PVC/PEO blends thermal degradation were calculated by isoconversional integral Flynn–Wall–Ozawa and differential Friedman method. According to dependence of activation energy on degree of conversion the complexity of degradation processes was determined.     

Kinetics of isothermal thermogravimetrical degradation of PVC/ABS blends

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.     

Thermooxidative degradation of poly(vinyl chloride) and chlorinated polyethylene with different Ca/Zn carboxylates

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. This revised version was published online in August 2006 with corrections to the Cover Date.