These results are very promising; locust bean gum can be used as a binder for wood adhesives and can be applied both at room temperature and at elevated temperatures. The bonding performance and water resistance are comparable to the commercial wood adhesive Cascol and it shows superior heat resistance compared with Cascol. The dry solids content, the adhesive material, is also much lower in the locust bean gum dispersion compared to Cascol.
This work will be continued by investigating corresponding polysaccharides from other species. The possibility to crosslink polysaccharides to improve the adhesion strength and durability will be investigated.
4. Conclusions
Locust bean gum, guar gum, xanthan gum and tamarind gum have successfully been dispersed and evaluated as wood adhesives. Even though the molar mass of the gums is very high, it was possible to prepare dispersions. However, the viscosity of the dispersions is very high and therefore only dispersions with a low dry solids content could be prepared. The contact angles against water for the films are higher and more stable than the corresponding results for Cascol. The film prepared of locust bean gum dispersed in brown liquor shows lower contact angles and a poor water resistance. The dispersions show good bonding performance and the majority fulfills the criteria of D1 and WATT 91. Locust bean gum show by far the best bonding performance of the gum dispersions. By hot pressing, the adhesive fulfills the D2 and WATT 91 criteria. By pressing at room temperature it was surprisingly observed that it fulfills the D2 and WATT 91 criteria even then. This bonding performance, water resistance and heat resistance are remarkable properties since the dry solids content is very low.
Acknowledgements
Wobama, WoodWisdom – Net ERA-NET/Formas are acknowledged for financial support. SP Technical Research Institute of Sweden is thanked for providing the ABES equipment and Magdalena Sterley at SP Technical Research Institute of Sweden is thanked for valuable discussion.