Fundamental investigations on the laser-melting of lignocellulosic fibres

This publication presents the results of the fundamental research on the interaction of laser radiation and lignocellulosic fibres with respect to the melting of the fibre main components cellulose, hemicellulose and lignin. In the first part, hand sheets made of different lignocellulosic fibres were irradiated with laser radiation from a carbon monoxide laser. Fluence-dependent interaction regimes, the dynamics of flash pyrolysis and chemical changes due to irradiation are discussed. Using a high-speed camera, an intermediate liquid state could be observed as a result of the irradiation. This is decomposed into gaseous reaction products by a highly dynamic boiling process. In addition to the time-resolved investigations, extensive FTIR studies were carried out. The second part is intended to further investigate former work on melting of cellulose. The basic idea is to combine laser radiation and mechanical pressure by compressing the sample between two steel bolts and simultaneously irradiating the joint. The processed samples show some visual indications of intermediate melting, such as increased transparency or flow behaviour. However, these can be traced back to effects that do not require a melting state.