Laser sealing of PLA-based compostable coffee capsules

The aim of the present work is to examine the possibility of using laser technology to make welded joints to hermetically seal bioplastic containers with aluminum or bioplastic foils. Specifically, the focus is on the laser sealing process of compostable coffee capsules with toplids in aluminum and in paper coated with compostable plastic (mainly based on polylactic acid, PLA). The aluminum toplid does not allow obtaining a compostable package, but represents the currently most used standard on the coffee capsule market. The welded joints made with laser technology were characterized by peel-off tests to evaluate the adhesion strength of the toplid to the capsule with the laser operational parameters, namely processing and pre-heating laser power, scanning speed of the laser beam. The results of the peel-off test allowed optimizing the choice of the operational parameters of the laser sealing process for the various scenarios examined. Based on the experimental findings, 3D process maps have therefore been built in which the adhesion strength between the toplid and the capsule has been plotted by varying the laser operational parameters process, making it possible to identify the optimal processing windows.