Welding of amorphous and semicrystalline PLA Bead Foams (EPLA)

泡沫头的焊接通常在所谓的蒸汽箱模具中用热蒸汽进行。根据泡沫焊头（非晶/半晶）聚合物的热性能不同，在焊接过程中，泡沫焊头界面（后焊缝）周围的热蒸汽会产生不同的机制。以膨胀聚苯乙烯（EPS）为例，非晶聚合物中只观察到聚合物链的相互扩散和缠结，而在半结晶的EPP（膨胀聚丙烯）中，不同的晶体结构表现出影响。此外，焊接件的性能在很大程度上取决于焊接质量。这里的可焊性受单珠的软化/熔化行为和蒸汽箱模具的加工参数（蒸汽温度、压力、时间）的影响。该项目的目的是系统地研究PLA泡沫珠作为模型物质，以揭示所用聚合物的热性能、焊接部件和焊缝中的形态与焊接部件的机械性能之间的关系。由于工艺条件和/或改性，PLA泡沫珠可以是无定形或半结晶的，这与用于泡沫珠的其他聚合物（例如PP和PS）相比是独一无二的，这使得它对热行为，焊接机制和机械性能相关性的基础研究很感兴趣。此外，PLA由于其相似的性能特征，因此具有成为EPS环保型挂件的高潜力。因此，EPS将作为本项目的标杆体系。虽然在过去的10年里，在EPLA领域取得了一些专利，但还没有很好地建立。本项目将对泡沫珠的焊接机理做出科学贡献。

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.