Optimization of the Methylation Conditions of Kraft Cellulose Pulp for Its Use As a Thickener Agent in Biodegradable Lubricating Greases

This work evaluates the influence of the operating conditions used in the derivatization of commercial Kraft cellulose pulp (mercerization time (1−3 h) methylation process temperature (30−60 °C), methylation process time (1−4 h), (initial pulp)/(final wet alkali pulp) ratio (S/S) (1/7−1/12), and pulp/acetone ratio (S/L) concentration (1/3−1/12)) on the obtained methylcellulose pulp characteristics such as degree of polymerization of cellulose, substitution degree, water solubility, and viscosity of the resulting pulps in order to determine the best process conditions of this pulp for its use as a thickener agent in biodegradable lubricating grease formulations. Efficient use of the raw material (i.e., obtaining a degree of polymerization with suitable substitution degree) entailed using a 2.5 h methylation time and a 45 °C methylation temperature. The substitution degree (DS) and consistency index thus obtained are only 14.5% and 36.3% respectively lower than the optimum value, and an increment of 28.6% could be obtained for the degree of polymerization. Some methylcellulose-based oleogels display rheological properties very similar to those found in traditional lubricating greases. Methylcellulose with DS values of around 0.4 produces oleogels with better mechanical properties than highly derivatized cellulose and much better than the original Kraft cellulose pulp.