Features Research & Innovation
Papermaking On A Nano Scale

What if fibre content in paper could be replaced with significantly less costly minerals, and quality went up? What if this substitution saved energy, as well? What if paper could win out over not-in-kind materials, because of innovative changes in formulations that produce a “greener”, more dynamic sheet? For Canadian papermakers, these what-ifs are not as far-fetched as some might think.

“There are some nano applications in papermaking that have been around for a long time, such as retention/dewatering aids and some coating formulations. We are also seeing new concepts in coating pigments, binders, and starch which look promising,” notes Dean Benjamin, director of research for NewPage Corporation.

“Nano is the buzzword these days, even for materials we would have looked at anyway, but nonetheless, it’s important on a practical basis.”

Professor Art Ragaustus, of the School of Chemistry and Biochemistry — Institute of Paper Science and Technology at Georgia Institute of Technology, believes now is the right time for paper scientists to re-invent paper, employing knowledge on a nano level to achieve big results.

“Composite materials are the way of the future,” he states. “This includes nano-composites — composed of fibre, minerals, silica sols, starches, resins, and more — designed to achieve desired results in a more efficient way. Some innovations will require radical change, and others will require modest adjustments for very big results. So what are we waiting for?”

According to Tony Lyons, director of research, Imerys Pigments for Paper Business Group, “Nano-engineering is becoming as important as, or maybe even more important than, the use of nano-materials. Structuring paper on the nano-scale to optimize its properties, at as low a cost as possible, without new capital investments, is the way to go in today’s new world.”

Downstream benefits are numerous

Benjamin confirms that many NewPage mills have employed silica and bentonite nanoparticle or microparticle systems for retention, drainage, and formation of the sheet for more than fifteen years. He says that the efficiencies achieved would not have been possible with standard polymers.

“Some of the mechanics and chemistry of forming a paper web happen on a very small scale approaching the nanometer dimension. So, naturally we need materials that can function in that size range.

“Anything that enhances formation will improve the uniformity of the sheet,” he continues. “For example, our printers will see better-looking prints because the sheet is more uniform in appearance. Strength is also more uniform, which leads to better runnability on our paper machines and in our customer’s pressroom. Better uniformity also allows lighter basis weights of paper, which create savings in postage costs for our customers.”

On the papermaking side, “better drainage leads to a higher solids web, which translates to energy savings because of a reduction of the drying energy demand.”

Retention breakthrough: fourth generation silica sols

Mark Zempel characterizes Eka Chemicals’ fourth generation structured silica nanoparticle technology as the first major breakthrough in retention/drainage systems since the early 1990s. Zempel is market manager-retention for Eka Chemicals in North America.

“Dramatic efficiency and performance gains have been regularly achieved at lower active nanoparticle dosage rates. These results have been achieved in commercial applications while maintaining and often improving fines and filler retention levels,” he explains.

Zempel notes that the first pioneering U. S. customer using this technology, called Eka NP 2180, has documented an 8% average machine speed increase, which, along with improved additive efficiencies, has resulted in considerable cost benefits.

According to Zempel, the basis for these efficiency and performance improvements is the nano-scale engineering of the colloidal silica particles themselves. “Manufacturing and formulation innovations have allowed careful control of particle size, degree and type of aggregation, and surface modification. The resulting improvements in these important product dimensions have lead to the ability to provide paper and board makers with more dewatering and retention than were previously possible.”

Joakim Carln, Eka’s paper chemistry research and development manager, who led this initiative, puts it in perspective. “This advance in particle design represents a step change from any previous nanoparticle design.”

Carln says the new nanoparticles are even more like a strand of pearls than before, with particles only 2.5 nanometers in size. “Just as the most desirable sea pearls have perfection in size and shape, it’s the same for our nanoparticles. Smaller particles in extended structure with perfect roundness are better.”

Give Printers An Edge

A wide range of white top liner producers have employed advanced micro and nanoparticle systems for years, gaining smoothness of the sheet for better printability. Smurfit Kappa Facture in France, Eurocan of Spain, Kemiart of Finland, and Simpson Tacoma are notable examples of producers adding value for their customers through dynamic graphics on packaged goods.

According to Zempel, as the knowledge continues to grow about the application of retention and drainage chemistries, the additional value delivered by nanoparticle technologies increasingly impacts the properties of the final paper and board. “We hear about even better results at the printers and converters, on fast modern printing presses and other machinery.”

Embracing nature’s nanoparticles

Nanoparticles have applications in other areas of papermaking as well. Nanoclays are emerging in the coatings field, with nano innovations in binders on the horizon as well.

NewPage’s Benjamin explains that nano-sized, in reference to clays, primarily refers to the thinness of clay platelets. This equates to many more plates for a given volume or mass of clay.

What makes nano-sized clay particles even more interesting, as Benjamin sees it, is how they open doors to other nanosized additives. “Now, we can look at latex and starch binders, which are smaller and smaller. The end result will be thinner coats of equal or higher effectiveness, adding new dimensions to coating with less raw material content.”

He continues: “Anytime you can be just as effective, or better, but use less raw material you are ahead. We are always looking for better ways to control the physical and optical properties of coated paper, and nanomaterials might make this possible.”

Imerys’ Lyons adds, “Nano-thin and large aspect ratio clay products are already revolutionizing the way in which coatings are being formulated. This new dimension opens up new avenues of creativity to meet the needs of the end user.”

Lyons is particularly enthusiastic about nanomaterials found in nature. “What is especially motivating is naturally occurring materials like oyster shells, made of stabilized calcium carbonates plates of nano-dimension in their thickness that can achieve incredible stiffness and optical properties. You win for the mill, your print customers, and for the environment. What nature has been able to design, by building up the right sized binder and pigment morphology, is impressive, compared with man’s best efforts. The ability to mimic natural systems is of great interest.”

Translating knowledge of nanomaterials to papermaking presents opportunities for unique optical properties and strength, says Lyons. “Stiffness is very important for paper if you are reducing weight. Nano options offer incredible stiffness, brightness, colour, opacity, and unique optical properties. Opacity gains could be very valuable.”

With research continuing at both the industrial and academic level, papermakers, converters, and printers are sure to feel the effects of these very small particles in a big way.< /p>

PPC

Martin Koepenick of Innova has written about the paper industry and innovations in technology for more than 25 years. He can be reached at mkoepen@earthlink.net.