HEMA and PPG Enable Simultaneous Control of Overcuring and Debinding Defects in Photopolymerizable β-Tricalcium Phosphate Ceramic Printing Slurries

Abstract

Abstract Ceramic parts fabricated by vat photopolymerization often suffer from pores, delamination, and cracks, which greatly limit their development, mainly due to poor slurry flowability, high polymerization shrinkage stress of the resin, and insufficient removal of organics. To address the above challenges, this study investigates the effects of introducing a monofunctional resin monomer, 2-hydroxyethyl methacrylate (HEMA) and a non-reactive diluent, polypropylene glycol (PPG-400), on the rheological properties, photopolymerization behavior, and debinding process of β-tricalcium phosphate ceramic printing slurries. When the volume ratio of monofunctional resin to multifunctional resin is 1:9 (H2 experimental group), the slurry viscosity decreases significantly to 2.33 Pa·s (at a shear rate of 50 s−1). The improved flowability of the slurry facilitates the spreading of fresh material during printing. Furthermore, the introduction of HEMA enhances the photocuring performance of the slurry, achieving a curing depth of 262 ± 3 μm (at a laser exposure energy of 32 mJ/cm2), which helps to prevent delamination defects. Meanwhile, HEMA effectively buffers the polymerization shrinkage stress within the multifunctional resin network, thereby increasing the green body flexural strength by a factor of 2. When HEMA and PPG act synergistically, the overcuring width is as low as 115 ± 7 μm (at a laser exposure energy of 30 mJ/cm2), and the actual formed profile is closer to the designed dimensions, thus improving the curing accuracy and mitigating the overcuring phenomenon. Furthermore, PPG crosslinks with P-HEMA during the early stage of debinding, which inhibits its premature pyrolysis and prevents defect formation. The sintered part achieves a flexural strength of up to 38 ± 1 MPa, and internal CT characterization reveals fewer defects than the control group. This study provides insights for the design of high-precision, low-defect β-tricalcium phosphate ceramic slurries for vat photopolymerization.