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The thermal decomposition of some polyhydroxyalkanoates (PHA) has been investigated by means of thermogravimetry and differential thermogravimetry. The thermal stability of the studied polyesters decreases slightly with increasing hydroxyvalerate (HV) comonomer. This result is different from those reported in the literature. Other results agree with reaction mechanisms proposed in the literature. The data from dynamic thermogravimetric experiments are consistent with a first order reaction, as would be expected from the reaction mechanism. Infrared spectra of the thermally degraded and undegraded copolymers are evidence of the cis‐elimination mechanism. © 1999 Society of Chemical Industry

Poly(ethyleneimine)-TiO 2 -anthocyanin modified cellulose fiber sheets were prepared as a support material for dye-sensitized solar cells. The study is focused on the effects of different anthocyanins on the photo-induced changes and contact relaxation of the surface AC-conductivity of the papers. The anthocyanins were extracted from purple cabbage, beet-root, plum peel, red vine and red currant juice. The results showed that there were pronounced contact relaxation effects at the interfaces between alumina electrode and the papers, which were further affected by the presence of anthocyanins. The electrode effects are mainly manifested by a decrease in conductance, which falls by about 30 % from its initial value about 400 min after the beginning of the experiment carried out in the dark. The illumination of the samples induces an increase in the magnitude of the observed changes in conductance but does not affect the nature of the relaxation processes. By estimating the temperature coefficients of conductivity of the papers and the changes in temperature during the illumination of the samples, we succeeded to separate the effects of heating from the total effects of illumination on the conductance and susceptance of the papers.

ABSTRACT:The use of polyhydroxyalkanoates as a biodegradable semicrystalline polymer is currently increasing. The prediction of crystallinity profiles produced in part with this polymer requires the knowledge of the kinetic expression. In the present article, a kinetic expression of the isothermal melt crystallization of poly(3-hydroxybutyrate)-11%poly(3-hydroxyvalerate) [P(HB-co-11%HV)] was studied in two temperature ranges, close to the melting point and close to the glass transition. Melting behavior and molecular mobility of the amorphous phase were analyzed as a function of crystallization temperatures by performing calorimetric experiments. The Avrami equation was used and the activation energy of the crystal nucleation and growth were obtained.

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