Making wood fibres water-resistant and conductive
An environmentally friendly method for introducing moisture repellancy and electrical conductivity to wood fibres has been developed by researchers at VTT Technical Research Centre of Finland, based in Espoo. This could find use in packaging, composite and paper applications.
Lignocellulosic fibres are hydrophilic by nature, meaning products such as wooden packaging often require special thin-films or plastic sheets to avoid moisture damage.
The enhanced properties created by the VTT team result from a chemo-enzymatic modification process that involves two stages – activation of the lignin-containing fibres and then bonding of a functional chemical to the fibres. ‘Both stages can be carried out by enzymes, chemicals or chemo-enzymatically, and are based on oxidative reactions,’ explains Dr Anna Suurnäkki, Senior Research Scientist at VTT.
The chemicals, such as dodecyl gallate, can be mixed in with the fibre material or simply applied to the surface during its final stage of formulation, depending on the application.
Dodecyl gallate is a hydrophobic chemical that adds water repellancy, while polyanilin, an electrically conductive polymer, can be trigger-bonded to the fibre to make it conductive. This could be useful for creating anti-static filter paper.
But what makes this system environmentally friendly compared to traditional chemical modification is its use of enzymes, which are non-toxic proteins that are used in small quantities to catalyse reactions under mild conditions. They are also surface specific, meaning the reactions will focus on the outer layer of the fibres. ‘Combining enzymes with non-toxic functional chemicals, when available, is the aim,’ says Suurnäkki.
‘The functional chemicals need to have a structure that can be activated by enzymatic reaction. For example, a phenolic structure can be activated by a laccase enzyme.’
These reactions can take from minutes to one-to-two hours. However, the team claims the chemicals should not add any extra time when incorporated into existing manufacturing and finishing processes of fibres, and they do not require curing.
John Dye, President of the UK Timber Packaging and Pallet Confederation, based in Thurmaston, says an improved system for water repellancy would be of great use to the industry.
‘Our pharmaceutical customers are putting powerful oxides onto pallets and they have to be of a certain moisture content [down to 18-22% for some applications], so moisture getting into the boxes is something we’re very aware of.’ He says drying out the pallets, or adding plastic film or lining, can increase costs by up to £10-15/m3 of wood, ‘so an alternative is welcome’.