Processing and characterization of polymeric materials to spherical powders as candidate build material for fusion based additive manufacturing

Selective Laser Sintering (SLS) is a process which builds 3D objects by selectively sintering successive layers of powdered material with a laser. Brought to life in 1987 by the hands of Carl Deckard at the University of Texas, the technique was used mainly for rapid prototyping purposes. It quickly gained interest because of its capability to print more complex geometric structures than possible with other Additive Manufacturing (AM) techniques without the need for support structures or tooling. Slowly, one began to understand its true potential by trying to produce functional prototypes and actual end-use parts. This shift from modelling products to actual end-use parts also caused a shift in interest towards the properties of the material itself. Emphasis on the mechanical, thermal and chemical properties is now more prominent depending on the application at hand. Since many materials show limited processability, the applications remain restricted to the properties of the available materials for SLS. Despite of the commercial interest in SLS, the variety of polymers available for processing remains rather scarce. With the growing number and variety of applications that require components that can withstand high mechanical loads, have high density, be chemically resistant to solvents, caustic or acidic solutions or be thermally resistant for high temperature applications, new materials have to be sought. This research project focusses on two main ways of doing so. The first viable way of adding to the range of materials available for SLS is by making use of the large amount of material grades available for the traditional manufacturing processes like injection molding. In addition adding to this one can also contribute to expanding the application window by improving the mechanical or physical properties of polymeric materials by reinforcing them with micron- to nanoscale sized inorganic filers. In this research, the nanoclay Montmorillonite is incorporated in a polysulfone matrix in order to create a nanocomposite with unique properties. In order to achieve this goal, the nanoclays were organically modified to improve compatibility with the matrix. Next, there does not exist a general production method to produce the polymer material in the right size and morphology that can be readily processed using SLS. Hence, as most commercially available materials are not produced directly in powder form, a suitable processing method has to be found in order to convert these materials to the powder form of correct size and morphology. Both a mechanical method and physicochemical method were optimized in order to overcome this stumbling block. Characterization of the produced powders via the optimized processing methods as a result makes up an important part of this thesis in order to see if the produced samples fit with the ideal powder characteristics for SLS and have not changed dramatically in their intrinsic properties. Finally, the finished products were tested on their sinterability at the University of Leuven.