Effect of Segregation of a Polyacrylic Acid (PAA) Binder on the Green Strength of Dry‐Pressed Alumina Compacts

Abstract

A polyacrylic acid (PAA) binder with both binder and disperser properties was applied to prepare alumina granules with and without a segregated binder layer (SBL) to investigate an SBL's effects on the mechanical properties of dry‐pressed alumina green compacts. The formation of SBLs in granules was based on the production of free, unadsorbed PAA ionic molecules in the liquid phase. The green strength of the alumina compact showed a significant increase as SBLs formed. Adequate forming conditions lead to squeezing out of the binder and redistribution of SBLs to bind granules together, thus enhancing the green strength of the compact and successfully eliminating intergranular pores and granule relics.

Cold compression of ceramic spray-dried granules: Role of the spatial distribution of the binder

“…For acrylic latex, the threshold pressure is smaller by about 20% when a segregated layer is present. A similar feature was reported during the compaction of alumina with a polyacrylic acid binder [5]. However, in the present experiments, the differences of behaviour of the samples in which the binder distribution has been tuned remain very close to the ones of the reference samples in which segregation layers are present.…”

“…Evidences for that layer have been provided [3,4] and it has been shown to form with binders that do not (or only poorly) adsorb onto the surfaces of the ceramic colloidal particle before spray drying. Segregated layers are suspected to have a role on green strength by enhancing the adhesion between granules [1,5]. However, they can be also detrimental to the quality of the final ceramics: their removal leaving coarse defects, segregated layers have been found to be at the origin of defaults in the final sintered ceramics [6].…”

Influence of particles packing in granules on the particles orientation in compacts

“…Dimpled granules are harder due to dense particle arrangement and formation of thick shell of particles during drying. 17,18 Dense granules D2 show high resistance against deformation and have the highest strength. It is also interesting to note the difference in number of point of gradient transition between loose and dense granule.…”

Improved green strength of ceramic bodies through extrusion using hydroxypropyl methylcellulose as binder

“…Because the starch used is insoluble in water at room temperature, whereas the HPMC also dissolves at an extremely slow rate under current conditions (room temperature and inadequate water in formulation), these two binders therefore exist mainly as solid in the green bodies. Therefore, free, unadsorbed binder molecules are hardly produced within the liquid phase, and the segregation of binder, a kind of common phenomenon reported during spray drying (usually used prior to dry pressing) is effectively eliminated in our study . It should be mentioned that although in the form of solid, starch, and HPMC containing a large amount of hydrogen bonds possess strong hydrophilic character, which can hinder the movement of water and obtain a cohesive paste …”