The kinetics of oil absorption into cotton-phenolic ball-bearing retainer material was determined. The results fit a model of two-step absorption in which the first step can be described by capillary rise and the second step by diffusion of oil from the capillaries into the bulk phenolic resin. The capillaries are associated with the cotton threads and are on the order of several micrometers or less in radius. The model successfully describes data for two cotton-phenolics with different cloth weaves, and five nonpolar liquids (four lubricating oils and heptane) with viscosities that vary over 3 orders of magnitude. The total amount of oil absorbed at the completion of the first step (1.5 to 3.4% v/v in this work) is proportional to the volume of the sample, not its surface area, suggesting that the entire volume of the material stores oil and not just the surface region. If the material is not completely dry when submerged in oil, the capillaries are blocked and only surface absorption of oil can take place. The saturation amount of oil in the resin after diffusion is complete at about 2 to 3% v/v (not including the amount of oil stored in the capillaries). The diffusion coefficient calculated using our model is 3 x 10(-12) cm2/s, which is reasonable when compared with available literature data on large and small molecules diffusing into polymers.
