Material extrusion 3D printing of leakproof capsules: Experimental study on phase change material macroencapsulation

This article provides insight into an extensive experimental study on applying a material extrusion 3D printing process, commonly referred to as fused deposition modelling (FDM), to the manufacturing of leakproof capsules for macroencapsulating phase change materials (PCM). It aims at providing a solution to the lack of systematic and reliable production of custom PCM macrocapsules. This study presents an experimental research which tested and compared the impact of multiple 3D printing parameters, geometries and materials in the leakproofness of the capsules when submitted to multiple thermal cycles in a climatic chamber. The challenge of encapsulating materials that cycle between liquid and solid state with varying densities and thus cyclical inner pressure oscillations and mechanical fatigue is overcome. Promising results are shown regarding the encapsulation of organic and inorganic PCMs with both PETG (polyethylene terephthalate glycol) and TPU (thermoplastic polyurethane) polymers, whose capsules withstood 35 melting and freezing cycles. Initial PETG capsules lost close to 50 % of their inner PCM content. With the successive improvements made in each iteration, concerning parameter adjustment, the final cylindrical PETG capsules achieved 0 % PCM mass losses. TPU cylindrical capsules surpassed expectations, achieving 100 % retained PCM at first try, proving that the principles behind the leakproofness of the capsules are transversal across polymers. Layer height, extrusion factor and multiplier, cooling intensity, capsule geometry and polymer material have shown to be the most impactful parameters in the leakproofness of the macrocapsules. Parameters such as the PCM infill percentage managed to reduce leakage up to 94 %, and changes in design (rectangular vs cylindrical capsules) had a reduction in leakage of 44 %.