Search

Properties of poly(L-lactide) (PLLA) were modifi ed using olive stone fl our (OSF) and citrate plasticizers such as tributyl citrate (TBC) and acetyltributyl citrate (TBAC). The properties of blends and composites prepared by applying different processing procedures were investigated. The results of differential scanning calorimetry (DSC) indicate that thermal properties of the samples were greatly affected by processing procedure, without any difference among the chosen plasticizers. Thus, the research has been continued with acetyltributyl citrate. OSF slightly affects thermal properties of PLLA; the greatest infl uence is on the crystallization of PLLA. Plasticizer lowers the value of thermal transition temperatures, but increases the crystallinity of PLLA. Non-isothermal thermogravimetric analysis (TGA) showed that addition of OSF deteriorates the thermal stability of PLLA while TBAC improves it. Scanning electron microscope (SEM) images confi rmed weak interactions between PLLA and OSF and no infl uence of TBAC on it. According to Fourier transform infrared spectroscopy (FT-IR) spectrums in plasticized composites only hydrogen bonds were formed. OSF reduces the fl exibility and the strength of PLLA while TBAC increases the fl exibility and signifi cantly reduces the strength of PLLA. Thermal properties of the investigated blends and composites, especially the process of crystallization and melting of PLLA crystals have been affected by ageing. Biodegradation of prepared PLLA samples in the soil was increased substantially by addition of OSF and TBAC, but TBAC has a lower infl uence. The migration of plasticizer at elevated temperatures increases with time exposure to given temperatures. In such conditions OSF facilitates migration of TBAC from the investigated composites. Migration of plasticizer from samples immersed in food-simulating solvents increases with time exposure to food-simulating solvents. Therefore, thermal properties of the investigated samples have been changed. [ABSTRACT FROM AUTHOR]

The infl uence of repeated extrusions of polypropylene (PP) on its thermal properties is investigated by differential scanning calorimetry and non-isothermal thermogravimetric analysis. PP is extruded six times on a laboratory extruder at a temperature of 190 °C and screw speed of 120 min-1. Extruded samples show a slight reduction of the melting point and the crystallization degree compared to the original PP. The non-isothermal degradation of all samples occurs through one degradation step and the extruded samples show a slightly lower thermal stability compared to the original PP. Kinetics analysis of the non-isothermal degradation of all samples was performed by isoconversional Flynn-Wall-Ozawa method. All extruded samples show higher values of activation energy compared to the original PP. Activation energy is constant in a wide range of conversion for all samples what also indicates that the non-isothermal degradation of PP occurs through one degradation step, without change of the reaction mechanism due to extrusion. Therefore, repeated extrusions under these conditions slightly worsen the thermal properties of PP and can be used for recycling its waste. [ABSTRACT FROM AUTHOR]