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

该项目的总体目标是开发用于选择性激光烧结（SLS）的新型半结晶聚合物粉末，通过液-液相分离（LLPS）和随后的结晶，用于聚对苯二甲酸乙二醇酯（PET），聚对苯二甲酸丁二酯（PBT），聚甲醛（POM）和聚偏氟乙烯（PVDF）。通过基于Hildebrand和Hansen溶解度参数的迭代筛选方法，推导出LLPS合适溶剂的选择标准。原位模型LLPS实验采用动态光散射，光学显微镜和阻抗谱-由非原位电子显微镜支持-将允许更深入地了解相分离和颗粒形成机制。详细了解LLPS的基本机制，即成核，液滴聚结和生长，并阐明它们对系统组成，时间-温度历史的依赖关系。LLPS将在小型工厂规模上实施，其中工艺参数（例如搅拌，冷却制度的影响）对所获得的聚合物颗粒的材料和大块固体性能的影响将被系统地研究。此外，将研究纳米颗粒助流剂的原位功能化和热稳定剂（抗氧化剂）的添加剂增强，推导出放大标准，并生产适用于SLS加工行为研究的粉末量（从100克到千克）。将使用动态扫描量热法、x射线衍射法、振动光谱法（IR、拉曼光谱法）和电子显微镜对所获得的SLS颗粒的结晶度、多态性、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来评估。对加工最重要的散装固体特性，如产品粒度分布和粉末流动性，将分别通过激光衍射粒度测定、剪切试验和粉末应用模型实验来表征。合作伙伴提供的对结构-性能关系的理解和SLS可加工性的信息将用于进一步的LLPS工艺优化，以定制新型SLS粉末的所需性能。新型SLS粉末的材料性能将得到改善，即耐化学性（PET、PBT、PVDF）、耐冲击性（PBT）、高刚度、尺寸稳定性（PET、PBT、POM），从而拓宽SLS制造零件的应用领域。

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.