Spring-Summer 2009 Newsletter    Papermaking Nanotechnology Is a Game Changer	John Penniman
Preface Following technically productive careers in coatings, and then polymers, the author turned to paper in the early 1970s.  This soon led to a position as Contributing Editor, Chemistry, at Paper Trade Journal, the principal industry publication until TAPPI started the TAPPI JOURNAL. My driving ambition was to learn how best to fully optimize the papermaking process.  In the course of doing this I helped to invent five different means of measuring electrostatic charge on particulates, culminating in the on-line Zeta Data which uses the streaming potential principle to measure zeta potential, and also measures conductance and specific filtration resistance, a parameter fundamental to drainage. Oddly enough, the most productive line of investigation turned out to be the apparent anomalies to normal systemic behavior.  Some of them took years and were very costly to explore, but the total picture slowly emerged. The fundamental technical rationale to wet end chemistry is nanotechnology, which is the application of nanoscience principles to nanoparticles, those on the order of a billionth of a meter in size. Nanotechnology is a game changer that will enable great improvements in the cost and quality of papermaking:  90% reduction in chemical cost; 40-60% reduction in energy usage for water removal; minimum raw material cost, maximum productivity, unsurpassed quality and sustainability. The process consists essentially of a series of well established unit engineering processes, conducted under computer control in the most efficient way.  The only serious functional uncertainty is that of scaling each process to an existing or (much less expensive) new machine or re-build. The following process description is not submitted as definitive; it is simply intended to connect all the principal dots, and provide a coherent explanation for those interested in licensing on exceptionally attractive terms.   Introduction Paper was made on a continuous wire for a century and a half prior to the introduction of synthetic organic chemicals on the wet end.  The use of “retention and drainage aids” was so revolutionary that machine management delegated supervision to their chemical supplier.  No analogy exists in modern industry.  One could think in terms of a bakery in which recipes for the breads, cakes and other pastries are assembled and prepared by one chef, then baked by another.  Such a division of duties is so inappropriate to the task, it inevitably leads to dysfunction. Our research over decades has led to the definition of papermaking as a nanotechnology.  A brief review of the defining differences between the ‘conventional wisdom’, as practiced by the specialty chemical suppliers, and papermaking nanotechnology reveals the gross inefficiencies that have developed because of the cultural split between physics and chemistry.   Mixing to Homogeneity In the ‘conventional wisdom’ process, a decrease in positive charge with time is observed, characterized as “cationic decay.” On the other hand, papermaking nanotechnology first reduces the interfacial by about two-thirds.  It then exposes the stock to vigorous agitation, such as ultrasonication.  The bundles of chemicals are dispersed on a molecular scale, creating a homogeneous stock. Not only does “cationic decay” disappear, but chemical efficiency increases by one to two orders of magnitude, resulting in chemical cost savings in the range of 90-99%.   Macroflocculation vs. Nanoflocculation In the ‘conventional process’ a “retention aid” polymer is used to flocculate the fillers, fines and fibers so they are retained in the web of stock on the rapidly moving mesh surface.  The resultant macroflocculation is effective in retention, but imposes a cost of major loss in smoothness and strength.   In the nanoflocculation process, mono-functional chemicals rather than polymers are used, with the result that flocculation is on a nanoscale.  The result is a smoother, thinner, stronger sheet. Computer Control of Zeta Potential The electrostatic charge is conventionally measured by an off-line assessment of cationic demand, using a charge analyzer with a Teflon tube that adsorbs colloidal particles and is exceptionally difficult to clean. There are two decisive problems with this methodology:  it is not reproducible, with a low correlation coefficient of 0.17 vs. zeta potential; and it is not the most appropriate measurement to begin with.  The most desirable parameter would be zero zeta potential; it bears a correlation coefficient of 0.72 with sizing. The nanoflocculation process ideally uses no polymeric retention aid and achieves a zeta potential of zero millivolts.  This form of electrostatic flocculation is sensitive to agitation.  It requires a homogeneous state entering the headbox and quiescence thereafter, to support aggregation. Zeta potential is measured by the online assessment of streaming potential, sampling from the downstream recirculation leg of the headbox, and continuously returning the measured stream to the white water system. Zeta potential is controlled by a computer which serves to adjust chemical feed rates to maintain a headbox zeta potential of 0 mV, using a chemical balance that maximizes productivity at minimum raw materials cost.  The result is unparalleled quality and uniformity, at minimum raw materials cost.  Software provides the actual cost of each roll, to the penny.   Increased Water Removal and Energy Savings Process chemicals include an anionic nanoparticle, such as colloidal silica; and a mono-functional cationic chemical such as cationic starch.  Under zeta potential control they yield the best possible balance between retention and formation, and result in a structure that maximizes water removal on the wire, press section and in the dryer. Our nanotechnology process employs a water immiscible hydrocarbon catalyst which, at low concentrations, reduces interfacial tension; and at higher levels can azeotrope with water, greatly reducing the amount of energy required for water removal.  It is easily re-cycled, using standard engineering unit processes.  The hydrocarbon is innocuous, and approved for use in food packaging.  It is fully retained within the process; none exits with the product. Sophisticated techniques have been used to explore the dimensions of water removal, including differential scanning calorimetry, thermogravimetric analysis, variable and fixed speed pilot plants, and azeotropic efficiency.  Some of the physical parameters we measure are interdependent and some are concentration dependent.  Quantitative analysis is complex indeed.  It is important to understand that the faster the machine, the greater the water removal in the press section; the hydrodynamics and reduced interfacial tension reduces water rewetting; and also recognize that increased press section consistency has a multiplier effect on dryer efficiency. Finally, one must realize the large effect of reduced interfacial tension in reducing the hydrogen bonding of liquid water, and thereby saving energyOur best conservative estimates of energy saving are 20% in a high speed press section; and 20-40% in the dryer, or a total range of 40-60%.  John G. Penniman www.papermaking-chemistry.com Return to Home Page