Use of enzymes for modification of dissolved and colloidal substances in process waters of mechanical pulping

During mechanical pulp production and bleaching wood components, such as extractives, carbohydrates and lignin are dissolved and dispersed into the process waters. These components are called dissolved and colloidal substances (DCS). DCS can accumulate during water circulation and can in turn affect paper machine runnability and also the strength and optical properties of the paper. In this work DCS fraction originating from TMP process were treated with enzymes acting on triglycerides, glucomannans, and lignin and the effect of enzymatic treatments on the water composition as well as sheet properties were evaluated. Lipases were found to modify the chemical structure of the extractives resulting in more hydrophilic fibre surface and subsequent improvement in the sheet strength properties. Mannanase treatment, on the other hand, destabilized pitch. As a result, aggregation of pitch to the fibres was observed. which in turn resulted in impaired strength properties. Laccase could effectively polymerize lignans and the reaction products seemed to be sorbed onto the fibres.