Paper, Wool and Paint … but not as we know it

 

Imagine the following: inkjet printers that produce perfectly crisp, clean printed images on low cost paper; packaging that keeps its contents as cool or hot as required for long periods of time without electricity; walls that store heat from the sun during the day and release it at night; powder that soaks up phosphate from streams and recycles it as fertiliser; and clothing that can’t fade.

Sounds impossibly futuristic? Not if Jim Johnston, a Professor of Chemistry at Victoria University, and a Principal Investigator of the MacDiarmid Institute, has anything to do with it.

Professor Johnston’s research centres around the development and applications of new nano-materials – substances which contain very smallscale structures, giving them unique and interesting new properties. On their own, or combined with traditional New Zealand products such as paper, wool, or paint, nano-materials have enormous potential to address a wide range of everyday issues, and add significant value to many commodity products.

A 20-year relationship

One such material is a new ‘designer’ form of nano-structured calcium silicate which, along with its precursor, geothermal silica, has been the subject of Professor Johnston’s longest-running research project, spanning some 20 years. The new calcium silicate material is shaped like a giant sponge, made up of a network of millions of tiny pores, giving it two essential qualities which make it useful for an enormous range of applications – a great capacity to absorb liquids, and a very large surface area on which different functional chemical groups can be attached for specific applications. One gram of the material can absorb six times its weight in liquid, and has the same surface area as a six metre wide strip down a football field.

One of the uses that Professor Johnston and his team are exploring is to make new paper that dramatically improves the print quality of inkjet printed images, at a much lower cost than presently available photographic paper. Ink bleeds and soaks through regular paper, producing fuzzy print and ‘shadows’ on the back of the sheet. When calcium silicate is mixed in with the paper fibre, or used as a surface coating, its ability to absorb liquid signifi cantly reduces both  these problems, giving clean, sharp, contained print. The team is currently working with a large international paper company to develop and make the paper available commercially.

Another use for calcium silicate is to make thermally responsive paint, wallboard, and paper that absorb heat from the sun during the day, and release it at night. The secret behind this is to use a ‘phase change’ material – a substance that absorbs heat energy as it melts, and releases it as it solidifies. Phase change materials have been available for some time but, Professor Johnston explained, “the big problem is that when they melt, they become liquid. If you had wallboard, for example, that had phase change material in it, when the sun came up, it would leak out. Not everybody wants that!” The sponge-like action of calcium silicate is used to permanently capture the phase change material, meaning it can not seep away, even in its liquid phase. The particles can then be put into paint or wallboard, to make energy efficient building materials.

A related use is in ‘smart packaging’, which keeps its contents at a stable temperature, regardless of what is happening outside. “The purpose here is to address the problem of when we send produce, for example, live shellfish, to high value markets in the northern hemisphere,” said Professor Johnston. “They can only tolerate a certain temperature range – if they’re too cold they freeze, if they’re too hot then they die. If they sit on a forklift or pallet out in the sun, then the damage is done.” Using a combination of calcium silicate and phase change material, together with specially developed insulation, the team has developed packaging that buffers produce from external temperature changes. 

The calcium silicate sponge has a multitude of other potential uses, depending on the functional chemical groups that are added to the large surface area of the material. Some uses that are being explored include antimicrobial agents, absorption or release of aromas, anticorrosive coatings, and electricallyconducting plastics. The material’s simple capacity for absorbing liquid is also very useful, and this could have a variety of environmental applications. Currently, team member Dr Thomas Borrmann is investigating absorption of heavy metals such as copper, nickel, and zinc from industrial and mine waters, and has shown that a suitably-functionalised material can even be used to absorb radioactive elements such as those produced in nuclear power generation, or for absorbing phosphate from streams and lakes, which could then be recovered and re-used as a fertilizer. “We have a large number of interactions with international industry,” said Professor Johnston.

Good combinations

As well as his work with nanostructured calcium silicate, Professor Johnston is involved in the development of a range of other new substances, including ‘hybrid materials’, which combine the inherent properties of fibres of paper or wool with new nano-materials. The MacDiarmid Institute has funded two students and postdoctoral fellows for this research, including postdoctoral fellow Dr Michael Richardson, current PhD student Aaron Small, and Masters student John Moraes. Dr Thomas Borrmann is also an Associate Investigator on this project. 

One example of a hybrid material that the team is exploring consists of paper fi bres coated with a conducting polymer – a plastic that conducts electricity and exhibits interesting chemical properties. “One of the problems with conducting polymers is they’re very difficult to use in products, because they’re crumbly,” explained Professor Johnston. “The idea is to produce a material that has the electrical properties of the conducting polymer, but also has the flexibility and the fabrication ability of paper.” When mixed together, the conducting polymer wraps around each individual paper fibre, completely encapsulating it. The result is a very stable, electrically conducting and chemically responsive paper, which could be useful for many applications, such as antistatic coatings, or to replace heavy, bulky metal in microwave shielding. This work is being carried out in collaboration with the Polymer Electronics group in the University of Auckland.

Another, intriguing example of a hybrid material that the team are working on consists of wool fibres mixed with gold nano-particles. In bulk quantities, the metal has its characteristic gold colour. Reduce the particles to nano-size however, and gold is no longer gold in colour – instead, it takes on shades of red, green, or blue. “This principle has long been recognised,” said Professor Johnston, “a lot of the early European churches have stained glass windows, and the red colour in these is actually due to gold nano-particles in the glass.” When used to dye wool, gold nanoparticles produce a colour which is not only attractive, but is also stable to UV light, and extremely colourfast. The aim now is to introduce this material into the high fashion industry. This work is being carried out in collaboration with Canesis Network Ltd.

At centre:  Aaron Small, Jim Johnston and Thomas Borrmann