Investigation of Poly(lactic acid) Crystallization in Additive Manufacturing through Alternating the Flow Area: Flow Induced Crystallization

H. Noor, K. Alqosaibi, A. Duhuh, J. Coulter
Lehigh University,
United States

Keywords: additive manufacturing, PLA, crystallinity, flow induced crystallization

Summary:

The crystallization of poly(lactic acid) (PLA) under different shear conditions in additive manufacturing is investigated. A novel patent pending extrusion based additive manufacturing technique is examined in the Manufacturing Science Laboratory at Lehigh University with the purpose of enabling the dynamic control of shear rate during the printing process. Shear rate is controlled through precise control of flow area of the polymer melt, thus, altering its rheology, which affects the evolution of morphology. Therefore, control over the local evolution of crystallinity is achieved. As a result, precise control over mechanical and optical properties can be obtained during the additive manufacturing process. This research experimentally validates a previous analytical investigation done by the group. The crystallinity of the printed PLA rod is shown to be affected by shear rate applied. The application of high shear rate through decreasing the flow area on the polymer melt resulted in an increase of crystallinity in the printed samples, which is proved by the characterization of the samples using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). This study attempts to understand the influence of polymer melt rheology in 3D printing on the final properties of printed parts to allow precise customization of properties and to minimize post processing steps.