Production of syndiotactic polystyrene powder for part manufacturing through SLS

Selective laser sintering (SLS) is a well-established additive manufacturing (AM) process. While AM originally found its use as rapid prototyping technique, it is nowadays more and more considered for the production of actual end-use parts. A widely acknowledged hindrance in the evolution of this technology is the limited range of materials available for processing with SLS, making the application window rather small. Introducing new materials with the correct morphology and thermal requirements for SLS could broaden this window and give rise to new products. This research aims at identifying such promising materials, considering the relevant requirements for selecting and processing a new material. Considered foremost within this manuscript is the processability of syndiotactic polystyrene from pellet form into spherical particles of 50-90 μm without significantly changing their properties. Regarding processing methods, the focus of this work is on solution based techniques (single phase precipitation, emulsion precipitation) instead of more conventional mechanical processing methods (ball milling) as these are believed to be more accessible and more suitable as a precursor step for a wide range of processing technique

Effect of matrix and graphite filler on thermal conductivity of industrially feasible injection molded thermoplastic composites

To understand how the thermal conductivity (TC) of virgin commercial polymers and their composites with low graphite filler amounts can be improved, the effect of material choice, annealing and moisture content is investigated, all with feasible industrial applicability in mind focusing on injection molding. Comparison of commercial HDPE, PP, PLA, ABS, PS, and PA6 based composites under conditions minimizing the effect of the skin-core layer (measurement at half the sample thickness) allows to deduce that at 20 m% of filler, both the (overall) in- and through-plane TC can be significantly improved. The most promising results are for HDPE and PA6 (through/in-plane TC near 0.7/4.3 W·m−1K−1 for HDPE and 0.47/4.3 W·m−1K−1 for PA6 or an increase of 50/825% and 45/1200% respectively, compared to the virgin polymer). Testing with annealed and nucleated PA6 and PLA samples shows that further increasing the crystallinity has a limited effect. A variation of the average molar mass and moisture content is also almost without impact. Intriguingly, the variation of the measuring depth allows to control the relative importance of the TC of the core and skin layer. An increased measurement depth, hence, a higher core-to-skin ratio measurement specifically indicates a clear increase in the through-plane TC (e.g., factor 2). Therefore, for basic shapes, the removal of the skin layer is recommendable to increase the T

Microstructural contributions of different polyolefins to the deformation mechanisms of their binary blends

The mixing of polymers, even structurally similar polyolefins, inevitably leads to blend systems with a phase-separated morphology. Fundamentally understanding the changes in mechanical properties and occurring deformation mechanisms of these immiscible polymer blends, is important with respect to potential mechanical recycling. This work focuses on the behavior of binary blends of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) under tensile deformation and their related changes in crystallinity and morphology. All of these polymers plastically deform by shear yielding. When unmixed, the high crystalline polyolefins HDPE and PP both exhibit a progressive necking phenomenon. LDPE initiates a local neck before material failure, while LLDPE is characterized by a uniform deformation as well as clear strain hardening. LLDPE/LDPE and LLDPE/PP combinations both exhibit a clear-cut matrix switchover. Polymer blends LLDPE/LDPE, LDPE/HDPE, and LDPE/PP show transition forms with features of composing materials. Combining PP in an HDPE matrix causes a radical switch to brittle behavior