Some surface energy effects in the strength of moist polymer agglomerates

The crushing strengths of agglomerates made by tumbling cellulose acetate and cellulose acetate butyrate powders wetted by water-methanol solutions of various concentrations were measured. After normalization for the effects of variable pore saturation and porosity, agglomerate strength factors exhibited minima as methanol concentration was increased. These minima also corresponded approximately to maximum pore saturation by the wetting liquid. It is proposed that these experimental maxima and minima correspond to a condition under which surface tensions of the liquid and solid phases are just matched, so that maximum capillary suction and zero van der Waals attraction exist in the wetted particle systems. It is concluded that reliable solids surface tension data can thus be generated from compressive strength measurements on agglomerates of low energy particulate solids.