Abstract
In this study, the feasibility of co-grinding and the subsequent thermal rounding to produce spherical polymer blend particles for selective laser sintering (SLS) is demonstrated for polybutylene terephthalate (PBT) and polycarbonate (PC). The polymers are jointly comminuted in a planetary ball mill, and the obtained product particles are rounded in a heated downer reactor. The size distribution of PBT–PC composite particles is characterized with laser diffraction particle sizing, while the shape and morphology are investigated via scanning electron microscopy (SEM). A thorough investigation and characterization of the polymer intermixing in single particles is achieved via staining techniques and Raman microscopy. Furthermore, polarized light microscopy on thin film cuts enables the visualization of polymer mixing inside the particles. Trans-esterification between PBT and PC during the process steps is investigated via vibrational spectroscopy and differential scanning calorimetry (DSC). In this way, a new process route for the production of novel polymer blend particle systems for SLS is developed and carefully analyzed.
Highlights
Polymer-based additive manufacturing (AM) techniques allow for the building of highly customized parts that are not accessible with conventional subtractive manufacturing [1]
The temporal evolution of the volume averaged mean product particle size, x50,3, during the co-comminution of a polybutylene terephthalate (PBT)–PC mixture with and without the addition of a magnesium oxide (MgO) trans-esterification catalyst is illustrated in Figure 2
These findings are complementary to the scanning electron microscopy (SEM) observations of stained spherical particles, where the identification of PBT and PC domains in single particles was possible
Summary
Polymer-based additive manufacturing (AM) techniques allow for the building of highly customized parts that are not accessible with conventional subtractive manufacturing [1]. Technologies like fused filament fabrication (FFF), stereolithography (SLA), and binder jetting offer the manufacturing of a wide variety of rigid to flexible parts. Most of these parts, do not provide the toughness and stability needed for parts subjected to mechanical loads [2]. Selective laser sintering (SLS), a technology employing polymer powders, which are applied layer-by-layer and selectively sintered with a laser, yields dense parts with a high mechanical strength [3]. The most frequently used material is polyamide 12 (PA12), but polyamide 11 (PA11), polyamide 6 (PA6), polystyrene (PS), poly(methyl methacrylate) (PMMA), polypropylene (PP), thermoplastic elastomers (TPE), high-density polyethylene (HDPE), and polyaryletherketones (PAEKs) are available, but not yet optimized for SLS processing [2]. Several approaches to provide SLS one-component powders from other polymers are reported in the literature (e.g., a process chain [8] employing wet grinding of polymers [9] followed by rounding the comminution product in a heated downer reactor [10], a melt emulsification process [11], spray agglomeration [12], spray drying [13], and precipitation-based processes [14,15])
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