Flexibility of Diels-Alder reversible covalent bonds in fused deposition modeling 3D printing: Bonding and de-bonding

Abstract

A novel 3D printing process (Diels-Alder reversible thermoset process), which exhibit thermoset properties at room temperature, low melt viscosity at print temperature was investigated in this paper. Based on the Diels-Alder (D-A) reversible reaction mechanism, furanized PLA (prepared by grafting with maleic anhydride (MAH) and furfurylamine, named PLA-Fu) and bismaleimide (BMI) were introduced into the matrix of polylactic acid (PLA)/poly (adipic acid-butyl terephthalate) (PBAT) blend with compatibilizer to construct a reversible dynamic covalent bonding. When the printing wire passed through the high temperature nozzle, the D-A bonds broke to ensure the material excellent fluidity; after printing, the temperature of product dropped, and the D-A bonds combined to improve the interlayer binding force of 3D printing products as well as end-to-end joint bonding of bi-material printing. The combination and break of reversible dynamic covalent bonds can be observed in the thermal performance test. With increase of D-A bonds, the tensile strength and interlayer bonding of samples pronouncedly rose, and the morphology of 3D printing products became smoother and evener, and the holes in the interphase disappeared. More importantly, the introduction of D-A reversible covalent bonds significantly improved the binding force of end-to-end joint of bi-material printing, of which the tensile strength was increased by 408%. So, introducing chemical bonding based on physical welding to improve the performance of 3D printing products made it possible to fabricate robust complex bi-material products. More findings that 3D printing products did not collapse in shape memory cycles due to the strong interlayer bonding resulted by D-A reaction assumed more intelligent applications.