THERMAL AGING STUDY OF BIODEGRADABLE POLYMER MATERIALS BY DIELECTRIC THERMAL ANALYSIS

Two different studies of the thermal aging of polyesters based on lactic and glycolic acids were compared. Thermal degradation of poly(L-lactic acid) (PLLA), poly(L-lactic acid-co-glycolic acid) (PLLGA) and poly(DL-lactic acid-co-glycolic acid) (PDLGA) was studied by the dielectric thermal analysis (DETA). The aging was performed at 37 0C in vacuum oven. The dielectric features i.e., dielectric permittivity,, dielectric losses,, and phase lag, tg , were determined by PL-DETA containing a parallel plate capacitance cell, from the room temperature to 80 0, 150 0, and 180 0 C, at the heating rates of 2 and 3 0 Cmin-1 . Dielectric scans were obtained at a frequency of 1 kHz and a.c. signal of 200 mV. Different behavior of PLLA, PLLGA, and PDLGA during degradation was observed. As the aging of PDLGA proceeds, dielectric losses shift to the lower temperatures, indicating existence of lower molecular weights. - T, and tg - T dependences of PLLGA, as well as those for PLLA show two simultaneous processes occurring, crystallization and degradation

THE DEVELOPMENT OF MODERN LOW TEMPERATURE FUEL CELLS

Classification of fuel cells is presented. Progress in low temperature fuel cells fueled by hydrogen, methanol and formic acid is discussed and the possible future use of fuel cells is indicated. Ethanol is a special fuel because it is available from renewable environmentally friendly sources and its oxidation product (CO2) can be transformed by photosynthesis to ethanol. The design of the anode catalyst for electrochemical ethanol oxidation in the Direct Ethanol Fuel Cell (DEFC) is described in some detail

The effects of concentration and salinity on polymer adsorption isotherm at sandstone rock surface

Adsorption of hydrolyzed polyacrylamide (HPAM) polymers on sandstone rock surface was studied by static adsorption experiments. Total of 10 Runs of static experiments were conducted in test tubes by mixing the desired solution with crushed rock sample, at temperature of 25 °C, and salinity range from 0-4 wt%. The results are in conformity with Langmuir's isotherm. Ten different isotherms were generated at each Run. The initial polymer concentration was varied from 0.3-2.1 g/l. The effects of salinity have been studied by observation on Langmuir adsorption coefficients (Y and K). The results show that the adsorption coefficient (Y) was found to have linear relationship with salinity. The adsorption coefficient (K) was found to be related to salinity by a quadratic relationship

PET PACKAGING CHARACTERIZATION BY MEANS OF DIELECTRIC THERMAL ANALYSIS AND IMPEDANCE SPECTROSCOPY

Chemical inertness and physical properties like adequate gas barrier, transparency, light weight and good recyclability, have made poly(ethylene therephtalate) (PET) particularly suitable in food packaging applications, especially in beverages and drinking water. However, several studies have shown the presence of compounds not expected a priori in packed food or bottled water and other beverages. One of the possible sources of these substances is a migration of constituents like monomers, catalysts, additives, degradation products, impurities in starting substances etc, from PET packaging. Therefore, migration of possible contaminants from PET, in normal and extreme conditions, is extensively studied and huge amount of data are reported elsewhere. As the migration process from plastics is closely related to the structure and physical properties of the packaging material, the aim of this work was to study structural changes of PET packaging in different media and under different conditions, and to correlate the data with the possibilities for migration of possible contaminants into the food in contact. It was shown that both techniques, especially DETA, could indicate structural changes into the polymer material, under certain conditions related with packaging applications, which could promote migration process