Effect of Mannanase and Lipase on the properties of colloidal wood extractives and their interaction with mechanical pulp fines

• The effects of enzymatic treatments of dissolved and colloidal substances (DCS) released from thermomechanical pulp (TMP) have been investigated. A model dispersion of DCS was made by leaching several portions of TMP in distilled water and separating the fibrous material. Some samples were enriched in colloidal particles by removing dissolved substances using ultra-filtration. The DCS, which had been subjected to different enzymatic treatments, were added in a fixed quantity to TMP fines that had been made cationic, and were subsequently used to form handsheets. All DCS additions increased the content of lipophilic extractives in the sheets. Lipase gave a complete hydrolysation of triglycerides into free fatty acids. The untreated DCS gave no significant decrease in tensile strength, because of the relatively small addition. A treatment of the DCS with Lipase gave a higher extractives content and a tensile strength on the same level as the reference. A Mannanase treatment gave a decrease in strength compared with the reference at the same amount of extractives in the sheet. A combined treatment with Mannanase and Lipase gave a more pronounced decrease in tensile strength. Two possible reasons for the differences in strength at a given amount of extractives were suggested: (i) the destabilisation of the colloidal wood extractives due to the Mannanase could affect the distribution of the colloid in the sheet, making it more detrimental to sheet strength compared with the stable colloid. This would account for the observation that Lipase did not affect sheet strength as such, but the combination with Mannanase gave the lowest tensile strength; (ii) the decomposition of galactoglucomannans in aqueous solution would diminish their positive effect on tensile strength and/or affect the adsorption of the colloid. A reflectometry technique was used to quantify the adsorption of the differently treated DCS onto a model surface of the cationic fines. Colloidal wood extractives were identified on the surfaces after adsorption using staining and light microscopy. No variations in adsorbed amounts were found that could explain the differences in sheet strength, which indirectly suggests that the distribution of the colloid over the surface was affecting the ability of a strong bonded joint to be formed between two such surfaces.

Nyckelord

adsorption

dissolved and colloidal substances

enzymes

mechanical pulps

reflectometry

retention

tensile strength

wood resin

adsorption

reflectometry

quality

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