Waste office paper comes to a sticky end

A process for generating aluminium–aluminium bonding adhesives from waste office paper could give a purpose to paper than can no longer be recycled into more paper.

Paper can typically only be recycled as a new paper product 3–4 times, after this the fibres become too short to be used in new paper or cardboard. Finding alternative ways of reusing this readily available resource is crucial.

‘We look at the where there’s large volumes of under or poorly used resource and then apply innovative chemical technologies to elicit functional molecules, which can then be turned into products and applications,’ explains Avtar Matharu from the University of York, UK, who led the study.

Metal adhesives are used widely within the automotive industry. They provide continuous joints with more uniform stress and strain distributions than other joining techniques, which results in such structures lasting for longer.

Matharu’s process uses low temperature (<200 ^oC) microwave-assisted pyrolysis  – thermal decomposition of biomass in the absence of oxygen – to convert milled waste office paper to bio-oil. The resulting bio-oils were tested as metal-to-metal bonding adhesives and the organic phase bio-oil bonded, with satisfactory strength, two aluminium plates. By looking at the effects of different curing times and temperatures, they found that the tensile strength increased with curing time and the highest tensile strengths (2300N) were achieved when cured at 160°C for 8 hours. ‘The mechanism for bonding is intriguing as it involves subtle interplay between acidic- and aldehydic-components with sugars all of which emanate from low-temperature microwave pyrolysis of waste paper,’ comments Matharu.

Alistair King, whose research at the University of Helsinki in Finland involves lignocellulosic processing, says this is a valuable example for green chemists. ‘Recycling lignocellulosics, including papers, packaging, textiles and construction materials, is becoming increasingly important due to the relatively high cost of processed wood and pulp.’

The group are now looking to expand their research in this area, by looking at converting all grades of paper into adhesive oils.