EFFECTS OF POLY(VINYL ALCOHOLS) MODIFIED WITH COPOLYMERIZATION AS A BINDER ON GREEN STRENGTH OF PRESSED COMPACTS OF ALUMINA POWDER

Effects of poly (vinyl alcohol) (PVA) as a binder on pressed compacts of alumina powder were investigated from the viewpoints of bending str engths, bending moduli and densities of green bodies. With increasing water contents in granules at press molding, the strengths and moduli increased. This shows the importance of the decrease in glass transiti on temperature (T(g)) of PVA owing to absorbed water to a temperature below the press molding temperature. PVA should be plasticized well at press molding, but should not contain a lot of plasticizer after mold ing to enhance the strengths. Several PVAs modified with comonomers we re studied as a binder. PVA copolymerized with a small amounts of VeoV a (vinyl ester of C-10 carboxylic acid) and itaconic acid was found to be a good binder showing the marked increase in the green strength an d density. Effects of the contents of the two comonomers were investig ated in more detail. The PVA system with the most suitable composition revealed 3 times stronger in bending strength and 4 times larger in t oughness compared with the ordinary PVA system. This is thought to ari se from the lubricating effect of long parafinic chains in the comonom er moiety to afford the deformation and compaction of the granules.