Leander Verbelen

Flow-induced crystallization studied in the RheoDSC device : quantifying the importance of edge effects

Flow-induced crystallization is investigated through short-term shear flow experiments on poly(1-butene) in the RheoDSC device. We demonstrate that the DSC signal shows contributions from spherulitic morphology in the center of the sample and oriented structures at the edge of the sample, the latter being induced by edge effects at the free surface. It is shown that, although small in terms of volume, the crystallization at the edge has a dominating influence on the measured rheology. We show how these kinds of effects can be recognized in stand-alone rheometric studies of flow-induced crystallization.

Influence of temperature on the flowability of polymer powders in laser sintering

Powder flowability is a determining factor in many industrial applications. Multiple techniques exist for assessing whether a powder flows adequately or not. However, most of these techniques occur at ambient conditions, rather than the actual processing temperature. Especially for laser sintering (LS), in which polymer powders are spread at a strongly elevated temperature, thermal effects cannot be ignored. This work expands an existing set-up, the powder spreader, which is designed for analysing LS powder flowability, to include temperature control. The focus in this paper lies on the additions made to the set-up. Tests on the standard PA12 2200 of EOS illustrate the use of this expanded technique, as well as the level of temperature control attained.

Selective laser sintering of polystyrene: a single-layer approach

ABSTRACT Selective laser sintering (SLS) is a powder bed-based additive manufacturing technique to produce complex three-dimensional parts. Although every thermoplastic polymer theoretically can be processed via this technique, variable material behaviour complicates the optimisation of the processing parameters. This study investigates the processability of polystyrene by SLS by evaluating bed temperatures and laser parameters. The morphology of single-layer parts is examined through scanning electron microscopy and roughness measurements to find an indication for the optimal processing parameters. Additionally, the effect of carbon black (CB) (as a colouring additive) on the processability of polystyrene is studied. It is found that polystyrene without CB is processable at a bed temperature just below the glass transition temperature. The addition of CB reduces the consolidation of single layers. The single-layer investigation is extended to, and shown to correlate with, a preliminary investigation of the relative density of multilayer parts.