Cardanol as a dispersant plasticizer for an alumina/toluene tape casting slip

Cardanol, a naturally occurring C-15 alkyl chain substituted phenol obtaine d from cashew nut shell liquid (CNSL), is used as a dispersant and plastici zer for PMMA binder based alumina tape casting slips in toluene medium. The best dispersion of an alumina powder with BET surface area of 10.4 m(2)/g occurs at a cardanol concentration 2 wt.% of the powder at which the cardan ol molecules form a monolayer on the particles with an end-on-adsorbed conf iguration through phenolic hydroxyl anchored on the surface. Cardanol added in excess of the dispersing agent acts as a plasticizer for PMMA, as revea led by significant decrease in the T-g of the polymer, reduction in the slu rry viscosity and increase in the tape flexibility. Green tapes with good f lexibility (failure strain, 10-20%) and strength (5.7-7 MPa) were obtained using a binder content 12 wt.% of alumina and employing a plasticizer to bi nder ratio in the range 0.66-0.82 by weight. The green tapes were thermally debinded with or without extraction of the plasticizer with methanol. The solvent extraction of the plasticizer prior to thermal debinding. however, did not show any effect on the density (similar to 97% TD) of the tapes sin tered at 1500 degreesC. (C) 2001 Elsevier Science Ltd. All rights reserved.