Abstract
Because of the growing utilization of renewable raw materials, the technical use of lignocellulosic fibres from wood and other annual plant materials is becoming increasingly important. The conventional production process of fibreboards is characterized by high‐energy consumption and use of ecologically insecure synthetic lesins. Approximately 40 to 45% of the total energy expenditure are used for the thermo‐mechanical pulping. Because of high plastication temperatures, an inactive lignin crust on the fibre surface is formed. For that reason, for glueing of the fibres, urea formaldehyde and melamin resins are usually used. The costs for the resin amount to approximately 50% of the entire material costs. In addition, environmental problems are caused. The aim of our investigation is the reduction of energy and resin consumption by enzymatic modification of wood chips and the enzymatic activation of the inherent bonding strength of the material. The first industrial use of fungi for the modification of wood was in the production of “Myco wood”. Pleurothus ostreatus and Trametes versicolor were applied for nonsterile delignification of beech wood. The present investigation of the authors deals with the mycological pre‐treatment of wood chips in order to reduce the energy consumption during wood pulping. The screening results favour the brown rotter Gleophyllum trabeum for pinewood (Pinus silvestris) and the white rotter Trametes hirsuta for beech (Fagus silvatica). Both species show resistance against mould fungi. The use of submerged inoculum of these fungi has the advantage over wheat inoculum that the lag phase is less than 12 hours and that the addition of nutrients or fungicides is not necessary. Short‐time wood chip incubation results in a 40% decrease of energy consumption during thermo‐mechanical pulping and in improved fibreboard properties. Lignin reduction could not be determined by gravimetrical and x‐ray microanalysis.
Comparative investigations of fibre incubation using laccase, a submerged culture of Trametes versicolor and rape straw fibres show a high increase in bending and tensile strength and an improvement in the hygroscopic properties of glue‐free fibre boards for the last two incubation kinds. Similar effects have been obtained incubating pine wood fibres for the production of fibre sheets with enzyme medium of Trichoderma reseei.