A new polyurethane binder providing high green strength of dry-pressed alumina

The effect of a new polyurethane binder on the green strength of dry-pressed alumina bodies was studied. The alumina compacts showed exceptionally high green strength. Depending on binder concentration (1-5 wt%) the tensile and flexural strength were 1.6-7.0 MPa and 2.0-12.7 MPa, respectively. The high green strength was controlled by polymer-ceramics interactions, as shown by IR study. The glass transition temperature of the polymer influenced the binder behaviour in ceramic processing. Some residual moisture was needed to achieve high green density, but then the samples had to be dried to obtain high green strength. The binder burnout was characterised by TGA and DTA in air and nitrogen. The polyurethane binder had a gradual burnout with a low char residue in both types of atmosphere. The thermal decomposition in air was caused by oxidation reactions while, in nitrogen, the polyurethane binder underwent a depolymerisation process. 18 refs.