Welding of amorphous and semicrystalline PLA Bead Foams (EPLA)

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The welding of bead foams is usually done with hot steam in a so called steam chest mold. Depending on the thermal properties of the polymer of the bead foam (amorphous/semi crystalline) different mechanisms occur during the welding with hot steam in a volume around the bead interfaces (the later weld line). In EPS (expanded polystyrene) as an example for amorphous polymers only interdiffusion and entanglements of polymer chains can be observed while in semi-crystalline EPP (expanded polypropylene) different crystal structures show an influence. Furthermore, the properties of the welded parts strongly depend from the welding quality. Here the weldability is influenced by softening/melting behavior of the single beads and the processing parameters of the steam chest mold (steam temperature, -pressure, -time).Aim of the project is the systematic investigation of PLA bead foams as a model substance to uncover relationships of the thermal properties of the used polymers, the morphology in the welded parts and in the weld line with the mechanical properties of the welded parts.Due to process conditions and/or modifications PLA bead foams can be amorphous or semi-crystalline which is unique compared to other polymers that are used for bead foams (e. g. PP and PS) which makes it interesting for fundamental research focusing on correlations of thermal behavior, welding mechanisms and mechanical performance.Additionally, PLA owes a high potential to be an environmental friendly pendant to EPS because of its similar property profile. Thus, EPS will be the benchmark system in this project. Although, in the past 10 years some patents in the field of EPLA were done it is yet not well established. With this project a scientifically contribution regarding welding mechanisms in bead foams will be made.