pps proceeding - Abstract Preview
pps proceeding
Symposium: Natural Based & Biodegradable Polymers
Keynote Presentation
 
 

Influence of blending, annealing and reprocessing on morphology and properties of polylactide

Radusch Hans-Joachim (1)*, Wutzler André (2), Anton Werner (1)

(1) University Halle-Wittenberg - Sachsen-Anhalt - Germany, (2) Polymer Service GmbH Merseburg - Sachsen-Anhalt - Germany

The typical but disadvantageous brittleness as well as the rather slow crystallization behavior of polylactide (PLA) leading to insufficient mechanical properties and limited application profile can be influenced by different procedures like blending with other polymers, addition of nucleation agents as well as annealing during or after processing. Because PLA shows a very slow crystallization behavior especially under high cooling rates - like usual in injection molding - it tends to solidify in the amorphous state that is resulting e.g. in the insufficient heat resistance. It could be shown that blending of PLA with poly (ethylene-co-vinylacetate) (EVA) is a promising way that leads to PLA blends with improved impact strength. EVA was melt-mixed with PLA using a laboratory 25D twin-screw extruder with compounding screw geometry. Using an EVA with 14 wt.-% vinyl acetate, only low amounts of the copolymer are sufficiently to improve the impact strength markedly. Because of the general thermodynamic incompatibility of PLA and EVA a heterogeneous phase morphology appears. Introducing higher amounts of EVA the application of a compatibilizer is indicated to finely disperse the EVA in the PLA matrix. Using a maleic anhydride grafted EVA as compatibilizer the impact strength of the blends could be further improved. As shown in previous work the control of crystallization behavior of PLA by annealing procedures leads to an increase of crystallinity and thermal-mechanical properties, especially modulus of elasticity, tensile strength and thermal resistance, that corresponds to the increased content of crystalline phase. Also the EVA-modified PLA showed a comparable behavior, while the application of the flexible compatibilizer amplified the annealing effect that is caused in the improved molecular mobility during structure formation.