ABSTRACT
The main steps in paper making are to separate the fibres from the plant tissue, to bleach them and to rearrange them to form a paper sheet. The fibres are separated either mechanically by stone-grinding whole logs or by disc-refining wood chips. Both processes are extremely energy consuming. In mechanical pulping processes the wood tissues break apart mainly at the middle lamella or at the interface of the middle lamella and the wood cell wall. In chemi-thermo-mechanical pulping (CTMP) the refining process is assisted by chemicals and high temperature. As mechanical pulps still contain most of the lignin, their yield is very high (88-96 per cent). They lead to an opaque paper, mainly used for newsprint, books and magazines. Besides the high energy consumption, mechanical pulps suffer from low strength and low brightness (Biermann, 1993).
