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

Cardanol, a naturally occurring C₁₅ alkyl chain substituted phenol obtained from cashew nut shell liquid (CNSL), is used as a dispersant and plasticizer 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 m²/g occurs at a cardanol concentration 2 wt.% of the powder at which the cardanol molecules form a monolayer on the particles with an end-on-adsorbed configuration through phenolic hydroxyl anchored on the surface. Cardanol added in excess of the dispersing agent acts as a plasticizer for PMMA, as revealed by significant decrease in the T_g of the polymer, reduction in the slurry viscosity and increase in the tape flexibility. Green tapes with good flexibility (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 binder 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 (97% TD) of the tapes sintered at 1500°C.