Flexible and semi-flexible packaging encompasses a large share of food packaging items that must be disposed of immediately after their usage. There is a growing interest in developing alternative materials that are compostable and/or recyclable. Semi-flexible packaging can be manufactured by cast extrusion of plastic foils and, subsequently, by thermoforming of the resulting foils. Thermal stability is often required as packaging items after being thermoformed can come into contact with hot food/beverage, especially during hot filling operations. The present study deals with the design and manufacturing of plastic containers by thermoforming that are, at the same time, compostable and suitable for high temperature applications (&gt; 100°C). First, cast extrusion of several grades of Poly Lactic (Acid) (PLA)/Poly Butylene Succinate (PBS) blends was performed. In particular, the effect on the material properties of different types of nucleating agents was investigated. Combinations of micro-lamellar talc, Ethylene-Bis(Stearamide) (EBS) and Poly-D- Lactic(Acid) (PDLA) were studied. The experimental findings show that the formulations involving EBS boast the highest crystallinity of the plastic foils and the fastest onset of the crystalline phase. Conversely, the formulations involving PDLA feature the lowest degree of crystallinity and the slowest onset of the crystalline phase. Talc exhibits an intermediate behavior. Second, thermoforming of the plastic foils was performed. The experimental findings show an opposite trend, with the crystallization in the final packaging items being the highest for the formulations involving talc and PDLA, the lowest for the ones containing EBS. The previous results can be ascribed to the role of EBS that promotes the onset of crystallization during cast extrusion, acting as nucleating agent. EBS features a peculiar macromolecular structure characterized by big steric hindrance (i.e., the long aliphatic C-shaped chains on both sides of the amidic groups). This hinders the rearrangement in crystalline domains of the plastic material during thermoforming, leading to lower crystallinity and thermal stability of the polymer. In conclusion, PLA/PBS blends are suitable for the manufacturing of compostable and thermo-stable packaging items by cast extrusion and thermoforming. Final crystallization of the material and resulting thermal stability can be fine-tuned by modulating type and amount of nucleating agents in the formulations.

Cast extrusion and thermoforming of PLA/PBS blends: Effect of nucleating agents on crystallization

256th National Meeting (2018)

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