Production of SLS particles via liquid-liquid phase separation and precipitation

该项目的总体目标是开发新型半结晶聚合物粉末，用于聚对苯二甲酸乙二酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚甲醛(POM)和聚偏氟乙烯(PVDF)的液液相分离(LLP)和后续结晶。基于希尔德布兰德和汉森溶解度参数的迭代筛选方法将推导出适合LLP的溶剂的选择标准。利用动态光散射、光学显微镜和阻抗谱的原位模型LLP实验--由非原位电子显微镜支持--将使人们能够更深入地了解相分离和颗粒形成机制。将从机理上详细了解LLP的基本机制，即成核、液滴合并和生长，并阐明它们对系统组成、时间-温度历史的依赖关系。LLP将在小型工厂规模上实施，在那里将系统地研究工艺参数(如搅拌、冷却制度的影响)对所获得的聚合物颗粒的材料和块体固体性质的影响。此外，还将研究纳米颗粒流动助剂的原位功能化和热稳定剂(抗氧剂)的添加剂增强，推导放大标准，并生产适用于SLS加工行为研究的粉末数量(100克到千克)。利用动态扫描量热仪、X射线衍射仪、振动光谱(IR、拉曼光谱)和电子显微镜等手段，将对所获得的SLS颗粒的结晶度、晶型、热特性和形貌进行详细的结构表征。工艺参数对聚合物摩尔质量分布和熔体粘度的影响将通过凝胶渗透色谱和熔体流变学进行评估。激光衍射仪、剪切试验机和粉末应用模型实验将分别表征对加工最为重要的产品粒度分布和粉末流动性等块体固体特性。对结构-性能关系的了解和合作伙伴提供的关于SLS加工性的信息将被用于进一步的LLP工艺优化，以定制新型SLS粉末所需的性能。提高材料性能(如耐化学性(PET、PBT、PVDF)、抗冲击性(PBT)、高硬度、尺寸稳定性(PET、PBT、POM))的新型SLS粉末将被开发，以扩大SLS制件的应用领域。

The overall aim of this project is the development of novel semi-crystalline polymer powders for selective laser sintering (SLS) via a liquid-liquid phase separation (LLPS) and subsequent crystallization for polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyoxymethylene (POM) and polyvinylidene fluoride (PVDF). Selection criteria for appropriate solvents for LLPS will be deduced by an iterative screening method based on Hildebrand and Hansen solubility parameters. In-situ model LLPS experiments employing dynamic light scattering, optical microscopy and impedance spectroscopy –supported by ex-situ electron microscopy- will allow for deeper insights into the phase separation and particle formation mechanisms. A detailed mechanistic understanding of the underlying mechanism of LLPS, i.e. nucleation, droplet coalescence and growth and elucidation of their dependencies on system composition, time-temperature history will be achieved. LLPS will be implemented on the mini plant scale, where the effect of process parameters (e.g. influence of stirring, cooling regime) on material and bulk solid properties of the obtained polymer particles will be systematically studied. Moreover, in-situ functionalization of the particles with nanoparticulate flowing aids and additive enhancement with thermal stabilizers (antioxidants) will be studied, scale-up criteria will be deduced and powder amounts applicable for studies on SLS processing behavior (several 100 grams to the kilogram scale) will be produced. A detailed structural characterization of the obtained SLS particles with respect to crystallinity, polymorphism, thermal characteristics and morphology will be performed employing amongst others dynamic scanning calorimetry, X-ray diffraction, vibrational spectroscopy (IR, Raman) and electron microscopy. The effect of process parameters on molar mass distributions of the polymer and melt viscosity will be assessed by gel permeation chromatography and melt rheology. Bulk solid characteristics such as the product particle size distribution and the powder flowability which are seen to be most important for processing will be characterized by laser diffraction particle sizing, respectively shear testers and powder application model experiments. The gained understanding of the structure-property relationships and the information on SLS processability provided by the cooperation partners will be utilized for further LLPS process optimization to tailor the desired properties of the novel SLS powders. Novel SLS powders with improved material behavior, i.e. chemical resistance (PET, PBT, PVDF), impact resistance (PBT), high stiffness, excellent dimensional stability (PET, PBT, POM) shall be developed widening the field of application of SLS-manufactured parts.