Nanoscience and nanotechnology has revitalised material science and led to the development and evolution of a range of new and improved materials through nanostructuring

These could have critical importance for the paper industry in the future.

Materials in the nanometre size range exhibit fundamentally new behaviour, as their size falls below the critical length associated with any given property. Intervention in the properties of materials at the nanoscale permits the creation of materials and devices with performance characteristics and functionality not previously thought possible.

Such organised nanostructures as exhibited by coatings, powders,

dispersions and composites will help revolutionise a number of industry

sectors through products such as:

l    Functional coatings and paints;

l    Corrosion protection;

l    Environmental remediation;

l    Conductive adhesives and polymers;

l    Drug and active ingredients delivery;

l    Biocompatible materials;

l    Functional barriers;

l    Self-cleaning smart surfaces;

l    ‘Functional’ printing;

l    Optical communications;

l    E-ink and e-paper;

l    Portable energy;

l    Water purification.

Nanomaterials include:

l    Clusters of atoms (quantum dots,

nanodots, inorganic macromolecules);

l    Grains that are less than 100nm in size (nanocrystalline, nanophase, nanostructured materials);

l    Fibres that are less than 100nm in diameter (nanorods, nanoplatelets, nanotubes, nanofibrils, quantum wires);

l    Films that are less than 100nm

in thickness;

l    Nanoholes;

l    Composites.

The composition can be any combination of naturally occurring elements, with the more important compositions being:

l    Silicates;

l    Carbides;

l    Nitrides;

l    Oxides;

l    Borides;

l    Selenides;

l    Tellurides;

l    Sulphides;

l    Halides;

l    Alloys;

l    Intermetallics;

l    Metals;

l    Organic polymers.

Nanoparticles

Nanoparticles and nanoparticle technology has the potential to influence – and is already influencing – a number of products and services, including the paper industry. Developments have already led to reductions in the amount of material needed to make products, for example, and also to improvements in fuel efficiency for cars and aeroplanes. Control of structure on the nanoscale has been used to improve the performance of magnetic materials, and this progress in turn will contribute to improvements in performance of electric motors and generators. Other types of materials, particularly those being used in

batteries and fuel cells, are also being improved in the same way and the results in terms of lighter and more

efficient portable power sources are being seen in mobile phones, laptop computers, etc. In the control of surface properties in textiles, paints and

coatings, improved materials are being developed with properties such as breathability of waterproof fabrics and stain resistance in clothes and carpets.

Nanoparticles are highly effective

catalysts due to the increased surface area at such a small scale and are being tested for use in plastics manufacturing to improve the properties and versatility of the resulting materials. Nanoparticles are also used in colloids, which in turn find application in sunscreens, printer inks and paints.

Pigments for inks

Recent developments in nanotechnology are beginning to offer novel opportunities and are increasingly being considered by ink manufacturers and customers, to enable inks to be developed with

superior performance properties.

BASF, for example, estimates that nanotechnology products of this type already make up ten per cent of their sales. Amongst its leading products in the area are nanoscale pigments. These include titanium dioxide for inks, which have a high capacity for light absorption.

They are currently working on making nanomaterials to provide colours without the use of dyes or conventional pigments. The colours are generated by dispersions of uniformly sized nanoparticles

in the same way that colour is created

by the ordered, textured surface of

butterfly wings.

They are also developing hyperbranched polymers from polyurethanes that they believe will solve the problem for printers of having to use different ink systems for printing on polar polymer packaging like polyester and polyamide and on non-polar plastic such as

polyethylene and polypropylene. The large number of functional groups on the hyperbranched polymer will provide enough anchor groups to allow the ink to dock on to adhesion points on the plastic surface when the print is applied.

Inkjet inks are another area where nanoparticle technology is being utilised. Degussa, for example, has applied its nanoparticle technology to develop a range of ultra small-size

pigments that will work effectively

with printheads and achieve sufficient

stability on the substrate.

NanoProducts in the US has recently announced that it has added additional product lines derived from PüreNano™ nanoparticles as dispersions and inks. Examples of inks and dispersions

available include doped and undoped dielectrics, conductive and magnetic compositions, pigments and coating materials.

Retention and drainage

systems in papermaking

The paper industry has been using the principles of nanoscience and nanotechnology for many years, particularly in the area of wet end chemistry for the development of retention and drainage systems. The original nanoparticle

system, which is still applied today, combines an anionic nanoparticle

(colloidal silica sol) and cationic starch. The next generation introduced in 1992 includes specially designed, structured silica sols, which were developed for use in combination with synthetic cationic polyacrylamide (C-PAM). These highly structured nanoparticles were found to react significantly better with C-PAM: silica spheres in the structured nanoparticle form strong covalent siloxane bonds that cannot be broken by shear on the paper machine. As effective as these chemistries have been for ‘cleaner’ fine paper and board grades, their effectiveness has been of minimal value in grades that have high conductivity at the wet end and a high level of stickies.

In 2000 Eka Chemicals introduced Compozil Select. This is a nanoparticle system based on sixth generation anionic colloidal silica sol molecules and cationic polymer components such as guar gum, polyacrylamides, cationic starches and proprietary anionic trash catchers (ATC). The extremely small size molecules provide a highly active surface area and high charge density. These key characteristics lead to enhanced flocculation and improvements in retention and drainage.

An alternative retention system

developed by Buckman Laboratories Inc. uses a synthetic hectorite nano-

particle. The evaluation of its use with a cationic polyacylamide and coagulant in a newsprint mill operating a twin wire

former with a thermomechanical and deinked pulp furnish has been promising. The machine has been able to operate at sustained speeds of up to 4,500 feet per minute with very few signs of water handling issues.

Coatings

Coatings are an important nano material. Such coatings are applicable in many ways from scratch resistant coatings for glass to self-cleaning services. One such example is a nanoceramic composite coating made from alumina and titania, which Inframat Corp. – a privately held nanotechnology company founded in 1996 and based in Farmington, Connecticut – now manufactures under the trade name Nanox 2613.

This alumina/titania nanoceramic exhibits a four- to six-fold improvement in wear, and a two-fold improvement in factor toughness and bond strength when compared to the conventional ceramic alternative. It is expensive at between US$30-50 per pound however its use has saved money. For example, the US Navy is already using the nanostructured

coating for a number of applications including air intake and exhaust valves in submarines which have been coated, saving US$400,000 per ship – or an

estimated US$20 million over the next ten years. Coating propulsion shafts on mine sweepers will result in a US$1

million annual savings per ship.

Nanox is being evaluated as a

potential coating for ballast tanks, periscope shafts, valves and a variety of machinery components submersed in marine environments.

One mining company that leaches nickel and cobalt from low-grade ore has been testing Nanox coated ball valves. Such valves have to withstand a

high-pressure slurry of crushed rock in an extremely acidic environment. Conventional valves last a few hours between refurbishings, but coated valves can survive for a couple of days.

In the automotive industry, Nanox is being tested for potential application to exhaust systems and manifolds. Oil and gas companies are also evaluating it for use on screw pump rotors in commercial gas turbines and fuel feed pumps. Other applications that have been suggested include the printing, pulp and paper industries.

Nanocomposite based coatings are regarded as the potentially ideal solution for plastic beer bottles, since previous attempts to use plastic for this application have resulted in spoilage and flavour problems. A Japanese company, Nano Material Inc., developed a microgravure process for coating plastic films such as PET with a nanocompsite

barrier material.

Case Study –

Nano Tech Coatings GmbH

Nano Tech Coatings make high-tech coatings that bond well with dry layers of only a few micrometers thick on

various bases. These bases can include metal, glass, ceramic and plastic, for example. A key area is the development and production of non-corrosive layers for light alloys such as aluminium and magnesium, i.e. materials which are gaining in importance in the area of technological development all over

the world.

The manufacturing of inorganic-organic hybrids by the sol-gel process is the basis for most of these nano-technological materials for protecting surfaces. The features of such materials include:

l    No chromating required;

l    Very good adhesive qualities on light alloys;

l    Transparent and pigmented;

l    Thin layers (3–5µm transparent,

10–15µm pigmented);

l    Excellent protection against corrosion;

l    Resistant to mechanical stress;

l    Resistant to organic solvents;

l    Resistant to high temperatures

(currently to 700°C);

l    Very good diffusion barrier effect on heavy metals, aromas and various gases;

l    Water- and oil-repellent;

l    Transparent or pigmented: a wide variety of colours is possible using nano-technological surfaces.

Mineral based coatings for paper and board have always employed the

variations in mineral particles to develop specific surface properties for the coated substrate. Such developments will continue and embrace the nanostructured mineral particles to engineer filler surfaces. Research is also being undertaken to assess the potential for polymer encapsulated nanoclay hybrids and their application in paper coating.

The properties of polyamide based nanocomposites in paper coating have been investigated by Bayer in extrusion coating experiments. They used a layer structure composed of:

l    Paper;

l    Polyethylene – 5gsm;

l    Adhesive – 5gsm;

l    Polyamide nanocomposite 5–40gsm;

l    Adhesive – 5gsm;

l    Polyethylene – 10gsm.

Improvements in barrier properties were achieved. On average oxygen

transmission rates of the nanocomposite based film were at least 30 per cent lower than the oxygen transmission rates of a standard grade film.

Fibres

Smart textiles are also being developed, from stain and crease resistant fabric to a material that is responsive to its environment. For example, Toray Industries Inc. has focused on the development of fibres utilising nanotechnology, and achieved hygroscopic properties better than those of cotton through the use of extremely fine nylon measuring several tens of nanometers, this being one-

hundredth the size of traditional fibres.

Driven by defence requirements, research at the Massachusetts Institute of Technology in the US is seeking to create a 21st century battlesuit. This has led into research that is investigating smart materials that are responsive to the conditions of the environment,

sensors able to detect chemical or

biological warfare agents and lightweight bullet proof materials. There are also attempts to incorporate wound detection and treatment systems

within uniforms.

While polyester is a textile with very poor water absorption, Kanebo Ltd has increased its hygroscopic properties by

a factor of 30 by coating it with a special film tens of nanometers thick. Furthermore, technology developed in the US can control the molecules of

textile auxiliaries on the level of several tens of nanometers, producing natural and synthetic fibres that repel water.

Nanotechnology has been used to combine the soft handle of cotton with durability and strength of synthetic fibres. Nano-Tex, a US-based advanced materials company, have developed the idea by grafting a cotton-like coating around a synthetic fibre core and created a product that has the key characteristic of both fibre types.

Polymeric nanofibres can be made using the electrospinning process. This process uses an electric field to draw a polymer melt or polymer solution from the tip of a capillary to a collector. A voltage is applied to the polymer, which causes a jet of the solution to be drawn towards a grounded collector.

The fine jets dry to form polymeric fibres, which can be collected on a web. By choosing a suitable polymer and solvent system and controlling parameters of the electrospinning allows the generation of nanofibre webs with different filtration characteristics. Typically, nanofibres with diameters in the range of 40–2000nm can be made.

Many nanofibre web composites have been used for air filtration applications where they provide an improvement in filter efficiency, without a substantial increase in pressure drop. Many of these air filters are made from webs of a nanofibre filter media in widths exceeding 610mm. A commercial facility manufacturing polyamide nanofibre web composites currently has production volumes in excess of 10,000 square metres per day.

As the nanofibre webs cannot be handled on normal web handling equipment without additional support, they have to be used in a composite structure with some other nonwoven material as a

support. With the increasing availability of commercial quantities of nanofibre web products, their incorporation into a range of products e.g. barrier fabrics, wipes and medical and pharmaceutical products will increase.

The Korean company NanoTechniques Inc. has developed a mass production technology for nanofibres based on the blackout radiation method. Ultrathin fibres are produced through the formation of electromagnetism around an ion in the liquid of the macromolecule, with segmentation of the liquid by electric power. The method can be used to mass produce nanofibres from a range of

synthetic or biological macromolecules, all with uniform diameters. The web density is also easily adjustable. The company can currently produce 40 tonnes per year of Nylon 6 and Nylon 66 nanofibres.

Carbon based nanofibres have also been produced by NanoTechniques. When produced as a paper, the carbon nanofibre papers have been found

to exhibit excellent electrical

conductibility and air permeability.

Such products can be used in filtration applications and as shielding for

electromagnetic radiation.

Research is also being undertaken in Finland to determine the potential for nanostructuring of the cell wall of

wood for better paper properties and

to produce cellulose fibre/mineral

filler blends.