Welding of amorphous and semicrystalline PLA Bead Foams (EPLA)

珠状泡沫的焊接通常在所谓的蒸汽箱模具中用热蒸汽进行。取决于珠粒泡沫的聚合物的热性质（无定形/半结晶），在焊接期间，在珠粒界面周围的体积中使用热蒸汽（后一焊接线）发生不同的机制。在EPS（发泡聚苯乙烯）中，作为无定形聚合物的一个例子，只能观察到聚合物链的相互扩散和缠结，而在半结晶EPP（发泡聚丙烯）中，不同的晶体结构显示出影响。此外，焊接件的性能在很大程度上取决于焊接质量。焊接性受单个焊道的软化/熔化行为和蒸汽室模具的工艺参数的影响（蒸汽温度，压力，时间）。该项目的目的是系统地研究PLA珠泡沫作为模型物质，以揭示所用聚合物的热性能之间的关系，由于工艺条件和/或改性，PLA珠状泡沫可以是无定形的或半无定形的。结晶的，其与用于珠粒泡沫的其它聚合物相比是独特的（例如，G.聚乳酸（PLA）与聚苯乙烯（EPS）具有相似的性能特征，因此PLA与EPS的热性能、焊接机理和力学性能的相关性成为基础研究的热点。因此，EPS将是本项目的基准系统。虽然在过去的10年里，EPLA领域的一些专利已经完成，但尚未得到很好的确立。通过这个项目，将对珠状泡沫塑料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.