Effect of clay treatment on the thermal degradation of PHB based nanocomposites

A detailed understanding of the thermal degradation processes taking place during the melt processing of bio-nanocomposites is crucial in order to increase the processing window of these materials. In this work, the influence of the content of neat clay and modified-clay on the thermal degradation of a biodegradable bacterial poly(3-hydroxybutyrate) (PHB) matrix, was studied. The modified clay consisted in a multi-treated organo-bentonite, which was first acid-activated, then silylated and further modified by cationic exchange treatment. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) tests were carried out to investigate the thermal behavior of the different nanocomposites as a function of temperature, whereas size exclusion chromatography (SEC) runs were performed to analyze the changes on the molecular weight distribution of the PHB. The obtained results reveal that the organic modifiers of the muti-treated clay promote the thermal degradation process leading to a dramatic decrease in the molecular weight of PHB. It was demonstrated that the degradation mechanism of PHB was not modified by the incorporation of neat clay or modified-clay, and that the process can be well described by the Avrami-Erofeev random nucleation model (m = 4), in which the reaction is controlled by initial random nucleation followed by overlapping growth.