Insights into the Development of a Short-fiber Reinforced Polypropylene for Laser Sintering

Selective laser sintering (SLS) is a powder based additive manufacturing technology, and currently one of the most promising technologies in use for the manufacturing of medium sized series of functional parts. However, the availability of suitable materials is still very limited. Recently, a number of polypropylene materials has come onto the market as an addition to the SLS materials portfolio. The current study focuses on the improvement of mechanical properties of one of these materials by fiber reinforcement, a method well known in traditional polymer processing. Various amounts of wollastonite and glass fibers of different lengths (50 - 150 mu m) were dry blended with two varieties of bonding agents and the polypropylene powder. The processability on an SLS machine of the produced blends was assessed, and the mechanical properties of produced parts were determined via tensile tests. Additionally, the nature of fracture was investigated with SEM. Through simple dry blending, homogeneous distributions of fibers could be achieved. It was found that both fiber length and amount play a critical role with respect to powder flowability, and therewith processability. The addition of the shortest glass fibers available with a length of 50 um, led to the biggest improvement of tensile modulus. Addition of small quantities of longer glass fibers hinted towards even larger improvements, however processability issues prohibited these from being used in larger fractions.