New powder reuse schema in laser-based powder bed fusion of polymers.

The laser-based powder bed fusion of polymers (PBF-LB/P) process often utilizes a blend of powders with varying degrees of degradation. Specifically, for polyamide 12, the traditional reuse schema involves mixing post-processed powder with virgin powder at a predetermined ratio before reintroducing it to the process. Given that only about 15% of the powder is utilized in part production, and powders are refreshed in equal proportions, there arises a challenge with the incremental accumulation of material across build cycles. To mitigate the consumption of fresh powder relative to the actual material usage, this study introduces the incorporation of recycled material into the PBF-LB/P process. This new powder reuse schema is presented for the first time, focusing on the laser sintering process. The characteristics of the recycled powder were evaluated through scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, particle size distribution, and dynamic powder flowability assessments. The findings reveal that waste powders can be effectively reused in PBF-LB/P to produce components with satisfactory mechanical properties, porosity levels, dimensional accuracy, and surface quality.

Influence of bioactive metal fillers on antimicrobial properties of PA12 composites produced by laser-based powder bed fusion of polymers.

Purpose: This study investigated the influence of three types of metallic microfillers, spherical silver and spherical, and dendritic copper, on the ability of polyamide 12 (PA12) to inhibit microorganism growth on the surfaces of samples produced using laser-based powder bed fusion of polymers (PBF-LB/P). The aim of this study was to initially characterize these materials regarding their potential applicability for parts dedicated to use in the hospitals, where surfaces are periodically disinfected using chemical and/or physical measures. Methods: Composite powders with filler concentrations of 0.5, 1, 2 and 5% by weight were prepared using the mechanical mixing method and processed using PBF-LB/P. Three common hospital pathogens responsible for healthcare-associated infections: Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans were tested. Additionally, the safety of the composites was assessed through in vitro tests using human cell lines: keratinocytes and fibroblasts. Results: The research reveals that addition of copper or silver causes decrease in bacterial colony viability compared to the material without a filler, but an insignificant effect on antifungal properties. There was no significant impact within the tested range of filler's content on the antibacterial properties. Furthermore, a strong effect of the microfillers on tested material's toxicity is observed. Conclusions: The addition of metallic microfillers enhances the antibacterial response of polymeric materials processed with PBF-LB/P. Nevertheless, the observed varying levels of cytotoxicity toward eukaryotic cell lines underscore the need for further studies on the analysed materials to unequivocally determine their potential applicability as materials for short-term contact with human skin in a hospital setting.

Influence of Thermal Annealing on the Sinterability of Different Grades of Polylactide Microspheres Dedicated for Laser Sintering.

We present a comparison of the influence of the conditioning temperature of microspheres made of medical grade poly(L-lactide) (PLLA) and polylactide with 4 wt % of D-lactide content (PLA) on the thermal and structural properties. The microspheres were fabricated using the solid-in-oil-in-water method for applications in additive manufacturing. The microspheres were annealed below the glass transition temperature (Tg), above Tg but below the onset of cold crystallization, and at two temperatures selected from the range of cold crystallization corresponding to the crystallization of the α' and α form of poly(L-lactide), i.e., at 40, 70, 90, and 120 °C, in order to verify the influence of the conditioning temperature on the sinterability of the microspheres set as the sintering window (SW). Based on differential scanning calorimetry measurements, the SWs of the microspheres were evaluated with consideration of the existence of cold crystallization and reorganization of crystal polymorphs. The results indicated that the conditioning temperature influenced the availability and range of the SWs depending on the D-lactide presence. We postulate the need for an individual approach for polylactide powders in determining the SW as a temperature range free of any thermal events. We also characterized other core powder characteristics, such as the residual solvent content, morphology, particle size distribution, powder flowability, and thermal conductivity, as key properties for successful laser sintering. The microspheres were close to spheres, and the size of the microspheres was below 100 µm. The residual solvent content decreased with the increase of the annealing temperature. The thermal conductivities were 0.073 and 0.064 W/mK for PLA and PLLA microspheres, respectively, and this depended on the spherical shape of the microspheres. The wide angle X-ray diffraction (WAXD) studies proved that an increase in the conditioning temperature caused a slight increase in the crystallinity degree for PLLA microspheres and a clear increase in crystallization for the PLA microspheres.