Influence of Eucalyptus globulus Kraft Pulping Severity on the Rheological Properties of Gel-like Cellulose Pulp Dispersions in Castor Oil

Abstract

The development of some cellulose pulp gel-like dispersions in castor oil with application as biodegradable lubricants was explored in this work by analyzing the effect that Kraft cellulosic pulp cooking conditions exerts on the rheological properties and mechanical stability of these formulations. With this aim, Eucalyptus globulus cellulosic pulps were obtained by increasing the pulping time at the maximum temperature, yielding H factors ranging from 150 to 500. Gel-like dispersions of cellulosic pulps in castor oil were prepared and characterized from a rheological point of view. Small-amplitude oscillatory shear (SAOS) measurements and some standard mechanical tests, usually performed on commercial lubricating greases, were carried out in order to evaluate the lubricant performance of these dispersions. In general, the values of linear viscoelastic functions increase with the H factor. Cellulose pulps submitted to lower H factors provides gel-like dispersions with SAOS functions values more similar to those found in traditional lubricating greases. Results were explained attending to a balance between the cellulose polymerization degree and lignin and α-cellulose contents, all of them affected by the H factor applied. An empirical correlation between these variables and both the plateau modulus and the loss of consistency has been proposed to predict the rheological behavior and mechanical stability of gel-like cellulose pulp dispersions in castor oil.