engleski

THE NON-ISOTHERMAL DEGRADATION OF POLY(3-HYDROXYBUTYRATE)/ORGANOCLAY NANOCOMPOSITES

Using biodegradable polymers instead of traditional plastics is one of the ultimate solutions to the environmental problems caused by disposal of plastic waste. Poly(3-hydroxybutyrate) (PHB) is made by micro organisms from renewable biological origin and is fully biodegradable at the end of its life. However, there is no large commercial production of PHB products because of its high cost, pronounced brittleness and very low resistance to thermal degradation at processing temperatures. Recently developed nanocomposites consisting of a polymer and only a few percent of layered silicates as environmentally friendly nanofillers, often exhibit remarkably improved mechanical, thermal and other properties when compared to pure polymers and conventional composites. Furthermore, nanocomposites of some biodegradable polymers and layered silicates show improved biodegradability compared to pure polymers. The current investigation is focused on the preparation of nanocomposites of PHB with organically modified montmorillonite (OMMT), the effects of OMMT loading on the thermal stability of PHB and the determination of kinetic parameters and mechanism of the non-isothermal degradation of PHB/OMMT nanocomposites. PHB/OMMT nanocomposites with compositions 100/0, 100/1, 100/3, 100/5, 100/7 and 100/10 by weight were prepared by solution intercalation method. The non-isothermal TG analysis of PHB/OMMT nanocomposites was carried out over the temperature range 50-500°C at four heating rates (2, 5 ; 5 ; 10 and 20°C/min) in the nitrogen atmosphere. The onset decomposition temperatures (T°) and the temperatures at the maximal degradation rate (Tmax) of PHB/OMMT samples are significantly shifted towards higher values when compared to pure PHB and therefore the thermal stability is improved. For PHB/OMMT 100/5 sample the highest values of T° and Tmax were observed. The invariant kinetic parameters method (IKP) as well as the isoconversional methods (Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Friedman) was used to determine the kinetic parameters, i.e. the activation energy (E) and the pre-exponential factor (A). The E values obtained from IKP method are in a good agreement with the values obtained by isoconversional methods. In the conversion range 0, 10≤ alpha≥ 0, 90 E values obtained are practically constant and therefore the investigated process is simple and can be described by a unique kinetic triplet, i.e. E, A and the conversion function, f(alpha). The values of E and A obtained by IKP method were used for numeric evaluation of f(alpha). The dependence of f(alpha) vs. alpha can not be fitted precisely by any ideal kinetic model but its shape suggests the true f(alpha) characteristic. Finally, the kinetic triplets for the non-isothermal degradation of each PHB/OMMT nanocomposite were obtained.

kinetic analysis; non-isothermal degradation; PHB/OMMT nanocomposites; thermal stability

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