Fabrication of PMMA/phosphogypsum non-fired ceramic composites with improved mechanical and waterproof properties

Previously, a way to process phosphogypsum (PG) into non-fired ceramic tile by an intermittent loading hydration process was proposed; however, its mechanical strength and especially waterproof property are unsatisfactory. Herein, PG non-fired ceramic with a porosity reduced was prepared and used as a matrix, which was then impregnated with MMA together with azobisisobutyronitrile (AIBN) and benzoyl peroxide (BPO) as initiators. After polymerization, a novel 3-3 type PMMA/PG non-fired ceramic composite with highly improved mechanical and waterproof properties was obtained. The bending strength, softening coefficient, and contact angle of the PMMA/PG composite are 21.5 MPa, 0.78, and 75.1°, which are 1.43, 1.77, and 1.68 times those of the matrix, respectively. It is found that PMMA completely covers the matrix surface and well fills the interparticle pores of dihydrate gypsum crystals inside the matrix, forming an interpenetrating and dense composite structure. This work can guide not only the utilization of waste PG but also the development of polymer/gypsum composite product. Graphical abstract We designed a facile process to prepare a novel 3-3 type PMMA/PG non-fired ceramic composite with highly improved mechanical and waterproof properties. The bending strength, softening coefficient, and contact angle of the final PMMA/PG composite are 21.5 MPa, 0.78, and 75.1°, which are 1.43, 1.77, and 1.68 times those of the matrix, respectively. The improvements originate from the delicate structure that PMMA completely covers the outside surface of the PG matrix and well fills the pores inside the PG matrix. PMMA tightly combines with dihydrate gypsum crystals and forms a relatively dense 3-3 type three-dimensional composite.