RESEARCH Fabrication of PMMA/phosphogypsum non-fired ceramic composites with improved mechanical and waterproof properties Yu Zhao 1 & Jun Zhou 1,2 & Zhu Shu 1,2 & Yanxin Wang 3 & Yahaya Yakubu 4 & Yi Zhang 1 & Xiaoqian Li 1 Received: 26 September 2019 /Revised: 24 July 2020 /Accepted: 20 August 2020 # Australian Ceramic Society 2020 Abstract 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. Keywords Composite . Non-fired ceramic . Phosphogypsum . Methyl methacrylate . Impregnation polymerization Introduction Phosphogypsum (PG) is a solid waste generated from the production of phosphoric acid and phosphate fertilizer [1]. The main constituent of PG is CaSO 4 ·2H 2 O, and it also con- tains some impurities such as P 2 O 5 and fluorides [2]. The annual worldwide production of PG is estimated to be 100– 280 million tons [3]. At present, there have been several ap- proaches for utilizing PG to resources especially in building material field, for example, preparing plasterboard [4], cement retards [5], and non-fired bricks [6]. But even with that, ap- proximately 85% of PG is not efficiently utilized and still piled up outside, which occupies a large amount of land and contaminates the surrounding soil and water [5, 7]. Thus, the massive and efficient utilization of PG is still of great impor- tance and urgency. On the other hand, non-fired ceramic and its composite are a type of green ceramic materials processed without high- temperature sintering [8, 9]. Due to sintering-free, the produc- tion of non-fired ceramics can effectively improve the short- ages of serious pollution and high energy consumption in conventional ceramic industry. Nevertheless, in order to re- place the sintering procedure, certain treatments, such as adding adhesives [ 9 ], alkali-activation [ 10 ], mechanochemical-treatment [11], and cold-sintering [12], are needed to bind and solidify the loose raw material particles into bulk non-fired ceramics. It is important to note that the production of adhesives themselves usually involves high en- ergy usage and environmental pollution problems. Complex Highlights • A non-fired ceramic-based composite was prepared from waste phos- phogypsum (PG). • The highest proportion of PG in the polymer/gypsum composite mate- rials with polymer well-filled inside gypsum matrix can reach 94.2%, and it is beneficial to recycle PG. • The composite has favorable mechanical strength and waterproof prop- erties. • This composite may be an alternative to conventional building ceramics as a decorative material. * Jun Zhou zhoujun@cug.edu.cn 1 Engineering Research Center of Nano-Geomaterials of Ministry of Education, Faculty of Materials Science and Chemistry, China University of Geosciences, 388 Lumo Road, Wuhan 430074, China 2 Zhejiang Institute, China University of Geosciences, Hangzhou 311305, China 3 School of Environmental Studies, China University of Geosciences, Wuhan 430074, China 4 Zoomlion Ghana Limited, PMB 117, Madina, Accra, Ghana Journal of the Australian Ceramic Society https://doi.org/10.1007/s41779-020-00510-z