Direct relationship between crystalline structure and part deformation of polypropylene copolymer parts fabricated by material extrusion additive manufacturing

Abstract

The high crystallinity and fast crystallization rate of polypropylene (PP) often result in severe warpage of final parts prepared by means of material extrusion additive manufacturing (MEAM). In this work, the effect of bed temperature (Tb) and nozzle temperature (Tn) on the dimensional accuracy and mechanical property of MEAM-printed PP copolymer parts was investigated. It is found that raising Tb and Tn could significantly reduce the warpage of PP parts by regulating the crystallization behavior of PP. Specially, the amount of γ-crystal grows obviously while the total crystallinity remains unchanged, as Tb or Tn increases. Moreover, the more the content of γ-crystal, the lower the warpage height of PP samples is. Hence, a close correlation between the content of γ-crystal and part deformation of MEAM-printed PP parts is successfully established. This is mainly related to the large rigidity of γ-crystal, which significantly reduces the volume shrinkage of PP during MEAM process. Besides, the raise of Tb or Tn also enhances the tensile strength, modulus and the elongation at break of PP parts. This wok provides an effective and convenient method for the manufacture of PP parts with good dimensional accuracy and excellent mechanical properties by means of MEAM techniques.