A renewable, environmentally friendly alternative is desired to replace petroleum based polymers. Polylactide (PLA) is one commercially available bio-based, compostable polymer. One drawback of PLA is its brittleness, but this can be improved through compatibilized blending. Vegetable oils can be used to toughen PLA, but are not very compatible due to the large differences in viscosity and molecular weight. Vegetable oils can be polymerized to create a plasticizer or polymer/oligomer that is potentially more compatible. PLA is blended with polymerized castor oil (polyCO) to toughen PLA. Castor oil is polymerized via free radical polymerization in a supercritical carbon dioxide (scCO2) medium to varying molecular weights and its effectiveness as a toughening agent for PLA is investigated.
The polymerization of castor oil is carried out in a custom-built, batch scCO2 reaction system. The molecular weight distribution of the polymers is determined by gel permeation chromatography. The molecular structure is analyzed by nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. The viscosity of the products is determined. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) is used to analyze the thermal properties.
The thermodynamic interactions of the polymer blends can be described by the Flory-Huggins interaction parameter which is determined for the blends of PLA with the polyCO. The polyCO is melt blended with PLA using a twin screw extruder. Thermal properties of the samples are determined using TGA and DSC. The morphology of the blends is analyzed using a scanning electron microscope. The mechanical properties of blended samples are determined by tensile and impact testing as well as dynamic mechanical analysis. The effectiveness of the hydroxyl groups in the polyCO on compatiblizing the blends will be determined.