PAPER CHEMISTRY LABORATORY, INC. December Newsletter 2004
Machine Implementation of Nanotechnology
(A brief excerpt, Chapter 3, from the book - Papermaking Nanotechnology, Volume I, Chemistry
published by PAPER CHEMISTRY LABORATORY, INC.; author John G. Penniman)
John Penniman
The fundamental purpose of papermaking nanotechnology is to maximize intermolecular proximity, because the influence of van der Waals force can increase strength to the 6th power as a function of intermolecular contact.
Effective execution results in counter-intuitive results. For example, ash level can increase by about 10%, accompanied by increased sheet strength. Investigators in Sweden and Russia have used stoichiometric quantities of cationic and anionic polyelectrolytes to achieve comparable results, such as doubling sheet strength.
A North American colleague was mentored by the Russians, following which he did lab development work that resulted in the issuance of US Patents. He is now increasing his investment in Zeta Datatm on-line zeta potential measurement technology, for three reasons. The stoichiometric balance of cationic and anionic polyelectrolytes is not appropriate to the variability of papermaking processes, nor is their raw material cost. Closed loop control offers additional benefit, to be discussed later.
Our first on-machine task is to increase thoroughness of mixing to attain homogeneity. Otherwise nanoscience cannot play a role. We must also switch from macroflocculation (see cover picture) to nanoflocculation, the key contribution of polyelectrolyte stoichiometry.
High speed machines producing products as disparate as alkaline fine paper, coated free sheet, coated board and recycle coated board operate in a range of about 4-5mV zeta potential standard deviation, often accompanied by a large number of breaks that result from web heterogeneity. This contrasts with a 0.2mV standard deviation lab measurement. Modern machines fail by a large margin to meet an appropriate thoroughness of mixing criterion, such as 6 sigma zeta potential standard deviation.
The issue is beginning to be addressed. TrumpJet www.wetend.com has introduced technology that won a Finnish 2003 prize for innovation, as has POM Technology Oy Ab, Helsinki, info@pom.fi Both Metso and Voith have followed suit.
Unless chemicals and stock are mixed to homogeneity, or at least to a quality level of 6 sigma zeta potential standard deviation, intermolecular contact is simply out of the question. Functional surface quality across the machine is heterogeneous and variable. End use performance results are unpredictable and break frequency increases.
The 6 sigma mixing performance criterion applies twice: once after addition of the cationic charge-neutralizing component, and again after addition of the nanoparticle.
We need to use the most cost-effective chemicals that maximize nano-flocculation, and to eliminate all residual surface charge prior to web formation. Current industry practice creates macroflocculation that has a huge adverse impact on both aesthetics and performance.
The most cost-effective methodology lies in addition of an efficient charge neutralizing component, such as cationic starch, followed by mixing to homogeneity. The highly anionic nanoparticle, such as colloidal silica, is then added and mixed until homogeneous. Feed rates of both chemicals are under closed loop control, and the final surface charge is maintained at zero prior to web formation.
Water removal rate is measured and optimized on-line, coupled with computer control of chemical feed rates. The flow of cationic and anionic components is adjusted in tandem to increase or decrease drainage while maintaining a final surface charge of zero. Productivity is maximized at the highest level of retention, formation and quality.
The author has introduced internal size by first blending it with a low surface tension liquid, and then spraying it on the web. In previously unpublished research, alkaline size usage was decreased by 2 orders of magnitude, as opposed to mechanical mixing, or from 3# per ton to .03#.
Application of the principles of nanoscience can be effective in continuously optimizing quality and maximizing the cost efficiency of papermaking.
Nanotechnology potential is so great that its dimensions remain undefined.
| John G. Penniman |
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