Modified Standard Polylactic Acid (PLA) for Extrusion Foaming

摘要

Polymeric foams are used in disposable packaging because of their low density, high impact resistance and the low material consumption. Nowadays they are often made of petroleum-based extruded polystyrene foam (XPS). The use of biodegradable and biobased polymers in short-living packaging could be an ecological benefit. One of PLA's shortcomings is its poor melt viscosity and poor melt stiffness. To foam a standard, cost effective man-produced PLA, it must be modified to increase its low melt strength. In the presented work the effects of grafting, crosslinking and chain extension on the melt strength were investigated. The addition of different modifiers and the performance of the reaction were performed by means of reactive extrusion on a twin screw extruder. The rheological properties in shear and elongation deformation, the foam densities, the cell sizes and the morphology were examined. The melt viscosity was increased and could be correlated to a higher molecular weight and broader molecular weight distribution. Foams with fine and closed-cell structure with relatively thin cell walls and bars were made in batchfoaming experiments. Here, the densities of the modified PLAs could be reduced to one third as compared to the unmodified PLA. The aim to generate bio-foams with standard and cost effective PLA was achieved.