Wood extractives: Is colloid thermal stability a suitable measure of pitch deposition potential?

摘要

The stability of colloidal suspensions in pulp and paper process waters is a key factor in determining whether or not the extractives present will agglomerate and deposit to form troublesome pitch deposits. An instrument that uses thermally induced changes in colloid properties has been evaluated to test the claim that pitch deposition propensity and stickiness can be estimated by spectroscopic measurements. It has been well established that dissolved hydrophilic carbohydrates are capable of stabilising hydrophobic extractives and therefore reducing the tendency for extractives to deposit as pitch. Pinus raditata thermo-mechanical pulp (TMP) was used to prepare aqueous mixtures of colloidal extractives and dissolved carbohydrates in varying ratios in order to simulate suspensions of varying colloidal stability. Manipulation of both the electrostatic charge (by addition of electrolyte) and the concentration of hydrophilic substances (by the addition of dissolved carbohydrates) demonstrated that the colloidal suspension displayed the expected behaviour as measured by changes in turbidity. The colloidal suspensions became more stable, and therefore less likely to deposit, as the concentration of dissolved substances increased. These colloidal suspensions were than analysed in a UV/Vis Spectrophotometer equipped with the Aquantix Aqueous Colloid Thermal Spectroscopic Analyser (ACTSA) software. Two variables determined by the ACTSA technique, Pitch Deposition Propensity and Stickiness, did not correlate with the responses measured by changes in turbidity induced by addition of electrolyte and dissolved substances.