Effect of Low pH on Forming Process of Desulfurization Gypsum Composite Boards Strengthened by Melamine-formaldehyde Resin

Through exploring the effects of low pH on the composite system of desulfurization gypsum (DG) enhanced by melamine-formaldehyde resin (MF), it is found that the inducing of sulfate-ion, in contrast to chloride and oxalate ions, favors the longitudinal growth of the crystalline form of the hydration product, which was relatively simple and had the highest length to width (L/D) ratio. At the same time, MF can also improve L/D ratio of gypsum hydration products, which favors the formation of hydrated whiskers. Finally, in a composite system composed of hemihydrate gypsum, MF, and glass fibers, when dilute sulfuric acid was used to regulate pH=3–4, the tight binding formed among the components of the composite system compared to pH=5–6. The hydration product of gypsum adheres tightly to glass fiber surface and produces a good cross-linking and binding effect with MF. The flexural strength, compressive strength, elastic modulus, and water absorption of the desulphurized gypsum composite board is 22.7 MPa, 39.8 MPa, 5 608 MPa, and 1.8%, respectively.