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Researchers of the LGP2 (EFPG, INPG, CNRS, CTP)
(November 2006)
Documents taken from the
"Scientific Report of the Laboratory of Pulp and Paper Science and Graphic Arts - UMR 5518
Grenoble - France
January 2002-November 2005"

III - Paper physics

III - 4 - Wet end chemistry

Elisa Zeno, Jérôme Da Silva Mourao, Bruno Carré, Evelyne Mauret

The investigation conducted by the department in this area deals with the use of additives at the wet end on the paper machine, i.e. the chemicals added to the pulp at its different stages of processing.
These chemical additives can be divided into two main categories:

Nevertheless, a high degree of water system closure allied to the use of certain pulps lead to an increase in the amount of dissolved and colloidal substances. For instance, deinked pulps and associated disturbing substances negatively impact the efficiency of the wet end additives. The aim of this project, realized in the framework of a partnership (CIFRE) with the CTP, is to study the effect of the use of deinked pulps on the efficiency of conventional retention and drainage systems and internal sizing agents.

Characterization of pulps, papers and released substances: effect of deinking process

The main origin of DIP processing problems is its associated contamination which depends on the deinked process stage and raw materials used. The effects of repulping conditions (neutral or alkaline) and bleaching processes (hydrogen peroxide or sodium hydrosulphite bleaching) are investigated for a wood-free (kraft) pulp, a wood-containing (thermo-mechanical) pulp and different types of papers. The release of the dissolved and colloidal substances – DCS – by pulps or papers is increased by alkaline pulping, but the bleaching treatments give generally the highest release, with a more aggressive action of the oxidative treatment. Kraft pulp is a negligible source of DCS compared to TMP. Papers followed the same tendency : woodcontaining grades induce the highest release that is sharply increased after printing or coating. The most relevant result is that surface active substances are released in the liquid phase and their amount greatly depends on the paper grade [Figure1].

Dynamic surface tension, water phase, kraft pulp, uncoated and coated papers, repulping, bleaching
Figure 1 - Dynamic surface tension of the water phase for a kraft pulp
and uncoated and coated papers after repulping and bleaching

Effect of contaminants on conventional retention/dewatering systems

By adding calcium ions and two main classes of surface active substances (anionic fatty acids and non ionic surfactants) to model virgin pulps (kraft and thermo-mechanical pulps), the influence of interfering substances is investigated for polyethylene oxide, cationic polyacrylamide and cationic starch based systems. The study of the interactions between contaminants and the systems allows a better understanding of the involved phenomena.
For instance, the complexation between cationic amylopectine – which is the major component of cationic starch – and sodium oleate is pointed out by surface tension measurements of a solution of fatty acids [Figure 2]. Measurements of starch adsorption by microcrystalline cellulose with and without sodium oleate lead to the conclusion that the interaction with fatty acids is competitive to the adsorption of starch.
In this case, the addition of a third component (polyaluminium chlorure) helps to suppress or limit the detrimental effect of ionic surfactants.

Surface tension decrease of a solution of sodium oleate
Figure 2 - Surface tension decrease of a solution of sodium oleate
as a function of sodium oleate (NaOl) concentration, in the absence
and in the presence of cationic amylopectine(CA) at two concentrations
(0,008 and 0,02%) for a given degree of substitution (DS)..

Effect of contaminants on internal sizing

The DIP contamination has also a negative impact on sizing obtained from AKD (alkyl ketene dimer). Measurements of contact angles show that paper wetting occurs in the presence of fatty acids even for high dosage of the sizing agent [Figure 3].
Further investigations allow concluding that the level of size retained in the handsheet is not affected. On the opposite, reacted size dramatically drops. Here again, the addition of PAC results in maintaining a good level of sizing, by neutralizing the fatty acids.
This work is continuing with another PhD thesis. The objective is to investigate more deeply the effect of the use of certain pulps (DIP, TMP…) on the internal sizing level of papers.

Contact angle versus time for papers sized by AKD
Figure 3 - Contact angle versus time for papers sized by AKD
(at 3 dosages: 0.75, 1.5 and 3.75 kg/ton) with and without addition
 of sodium oleate (10-4M) – [Ca2+] = 150 mg/L.
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