Laser sealing of compostable packaging solutions: experimental approach and adhesion mechanisms

This work aims to demonstrate the possibility of using laser technology to seal compostable coffee capsules in engineered, poly(lactic acid) (PLA) based, bioplastic material with thermoplastic starch (TPS) toplids. The welded joints were characterized by peel-off tests to evaluate the adhesion energy of the toplid to the capsule body as the laser process parameters vary, i.e. the power of the laser beam and scan speed. The results of the peel-off test made it possible to optimize the choice of laser process parameters for the various scenarios under investigation. 3D process maps were then constructed in which the adhesion index between toplid and capsule body was reported as the laser process parameters changed, allowing to identify the intervals of greatest practical relevance. In particular, the procedure allowed to define an adhesion index, a measure of the total adhesion energy between capsule body and toplid. Adhesion between conventional aluminum toplids and compostable capsules were also studied for comparative purposes. Based on the experimental findings, mechanisms of adhesion varying the material used for the toplid and capsule body were also discussed.