Tailoring the crystalline structures and mechanical properties of polyamide 1012 specimens by material extrusion-based additive manufacturing

Abstract

In this work, the evolution of the crystalline structures of MEAM-printed polyamide1012 (PA1012) parts with the nozzle temperatures (Tn) and thermal annealing temperatures (Ta) was investigated. It is found that Tn plays an important role in determining the crystalline structure of PA1012 parts. The freshly-printed PA1012 parts crystalize as γ crystals at Tn lower than 230 °C. With Tn increasing to above 230 °C, a small amount of α phase coexists with γ phase in the PA1012 parts. Also, the thermal annealing treatment can tailor the crystalline structure of the MEAM-printed PA1012 parts. Specifically, the crystalline structure exhibits a transformation from γ phase to α crystal, after annealing the PA1012 parts at a Ta higher than 90 °C for 10 min. Due to the presence of a high content of γ phase, the Brill transition occurs at a low temperature for the MEAM-printed PA1012 parts, implying a close relationship between the H-bond sheet structures and the formation of γ phase. Moreover, the crystalline structure exerts a significant influence on the mechanical properties of the PA1012 parts. The samples with only γ phase exhibit much higher tensile strength and Young's modulus, but much lower ductility, compared to those containing only α crystal. Hence, this work provides effective pathways for regulating crystalline structures as well as mechanical properties of MEAM-printed long-chain polyamide materials.