Abstract: The process of using pre-mixed α-hemihydrate gypsum slurry material for 3D printing has the advantages of high product strength and short printing cycle. However, there are problems such as short initial setting time of the gypsum and insufficient buildability of the slurry. On this basis, the effects of plant protein retarder and polyphosphate retarder on the compressive strength, fluidity and printable time of the material were studied. And the effect of the hydroxypropyl methylcellulose ether (HPMC) on the rheological properties of the slurry and the volume stability of 3D printed components was also studied. The results show that the two kinds of retarders have different mechanisms for retarding gypsum hydration. Plant protein retarders can extend the stable period of fluidity, while polyphosphate retarders cannot increase the printable time well. The slurry with polyphosphate retarder has lost its fluidity before the initial setting 8 min to 12 min. The addition of HPMC significantly increases the apparent viscosity and yield stress of the slurry material and eliminates the bleeding caused by the retarder, but it has little effect on the plastic viscosity and it reduces the compressive strength of the material. The α-hemihydrate gypsum 3D printed component with high HPMC content has good volume stability, and the volume deformation rate of the 3D printing component with 0.020% (mass fraction) plant protein retarder and 0.60% (mass fraction) HPMC is 0.09.

Key words: α-hemihydrate gypsum, 3D printing material, retarder, plasticizer, fluidity, rheological property