Mémoire
| Résumé : | Tannin is one promising organic substitute to the currently used copper-based wood preservatives due to its anti-fungal performance and sustainable raw material base. Cellulose nanofibrils (CNFs) are currently studied as potential fixing agents to solve the leaching problem of tannin and other preservatives. However, the competitiveness of using tannins as anti-fungal agents highly depends on the operational performance and corresponding environmental load that has remained unknown. Life cycle assessment (LCA) is acknowledged to be a standardized method to assess environmental performance and useful tool to support product development at the early stage.This thesis presents an LCA study of tannin-CNF impregnated wood from cradle to grave in Finnish context. In addition, an inventory model was developed for tannin extraction using pressure hot water extraction (PHWE) and purification through ultrafiltration with comparisons of few different scenarios. Four extraction scenarios combine the methods of adding one step of cold water-extraction before single process or multiple processes of extraction. Purification scenarios are evaporation, spray drying and ultrafiltration. The study is based on assumption that retention rates of preservative in wood are 5% of tannin and 0.5 % of CNF. The results show that extraction scenarios of adding one step of cold water extraction or multiple extractions would lead to higher environmental burdens. Using evaporation to required concentration or spray drying after evaporation has significantly higher impacts than ultrafiltration. Raw material production is the main contributor to most of the environmental impacts of product and saw log production is the major factor instead of tannin and CNF production if tannin is purified through ultrafiltration. Preservation and waste disposal process also has noticeable impacts. The overall environmental impacts of a functional unit of tannin-CNF impregnated wood are lower than copper-based impregnated wood for similar usage. However, the results are sensitive to the effectiveness (or service lifetime) of this novel preservative. |
