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  • Author or Editor: J. Budinski-Simendić x
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Abstract  

It is well known that the free radical bulk polymerization of lower n-alkyl methacrylates is characterized by autoacceleration after definite conversions of the monomers. The conversion vs.time curves of polymerization have a typical 'S' shape. There are several characteristic points in these curves: the onset of autoacceleration (point M), the maximum in the polymerization rate (point S) and the end of the polymerization (point K). We have observed points P and R (maximum and minimum of autoacceleration) as inflection points in the derived polymerization rate vs. time curve. In this work, the free radical bulk polymerizations of methyl, ethyl and butyl methacrylates were investigated by differential scanning calorimetry. The effects of the polymerization temperature and the alkyl group length in the esters on the monomer conversions at the points M, P, S, R and K were studied. By regression analysis of the experimental results, relations were developed with which it is possible to predict the positions of the characteristic points, depending on the polymerization temperature and the alkyl group length.

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Abstract  

An alkyd/melamine resin mixtures are mainly used in industrial baking enamels. The aim of this work was to study the curing behaviour of alkyds based on dehydrated castor oil and soybean oil with melamine resin by differential scanning calorimetry (DSC). The kinetic parameters obtained by the transformation of dynamic DSC results into isothermal data through Ozawa kinetic model are in good agreement with those determined by the isothermal DSC experiments. The apparent degree of curing, determined by DSC measurements and sol/gel method, has a pronounced effect on the hardness of the resultant coating film.

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Abstract  

The free radical polymerizations of higher n-alkyl methacrylates were not investigated in detail until now. In this work, the courses of the isothermal free radical bulk polymerization of dodecyl, quatrodecyl and hexadecyl methacrylates were investigated by differential scanning calorimetry. The effects of the polymerization temperature and the alkyl group length in the esters on the monomer conversions during polymerization were studied. It was found that the polymerization rate vs. time curves have two maxima. The free radical polymerizations of above-mentioned monomers proceed with slightly expressed gel effect at the temperatures below 90°C, at initiator concentration 1 mass% in monomer.

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The etheric oil components in garlic are proven to have numerous positive effects on human health, and powdered garlic has long been widely used in both the food industry and private households. In order to prolong the stability of etheric oil components, different combinations of packaging materials are used for the storage of powdered garlic. Since the quality of dehydrated powder depends on the packaging used, the investigation was aimed to determine the effects of packaging material types on etheric oil content in industrially powdered garlic over the storage period. Powdered samples were analysed immediately after production and during long periods of storage (after 30, 90, 120, 180 and 270 days). The investigations were focused on the correlation between packaging materials performances (light, water vapour and air permeability), and the changes of etheric oil and moisture content in powdered garlic. In order to describe the changes in etheric oil content during time, as well as to predict changes in packed powdered garlic, a statistical procedure was applied for all examined packaging materials and curve fitting data were estimated (the least square approach).

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