Enhancement of strength and water resistance of macro-defect free （MDF） gypsum modified by pregelatinized starch and hydrogen silicone oil

Gypsum, as a building material with renewable and environmentally friendly characteristics, is severely limited due to its poor mechanical properties and water resistance. Here, this paper investigates pregelatinized starch and hydrogen silicon oil modified macro-defect free (MDF) gypsum composite prepared by pressing. The compressive strength, water absorption, and softening coefficients of foamed MDF gypsum composite were subjected to strict testing. The hydration products, microtopography and pore structure was characterized using XRD, FTIR, SEM and LF-NMR. The result shows that that the compressive strength of MDF gypsum composite with 5 % pregelatinized starch was 82.4 MPa, a 44.5% increase compared to the dry blank group, whilst water absorption also rose by 7.8%. Additionally, the compressive strength of MDF gypsum composite with 5 % pregelatinized starch and 1% hydrogen silicon oil was 123.9 MPa, 225.2% higher than that of the dry blank group. The water absorption rate decreases to less than 1.2%. Pregelatinized starch and hydrogen silicone oil assist in the accumulation and arrangement of crystals, while also reducing the space between them. The enhancement mechanism of compressive strength and water resistance of MDF gypsum involves pore filling by pregelatinized starch, as well as crystal contact point modification including stronger adhesion by the pregelatinized starch and hydrophobic properties of hydrogen silicon oil.