Uimonen EFFECT OF HORNIFICATION ON THE PROPERTIES OF THERMALLY MODIFIED SCOTS PINE UNDER SATURATED STEAM

The aim of this thesis was to investigate the effect of hornification on the properties of Scots pine thermally modified under saturated steam. Experiment was carried out to never-dried Scots pine samples at temperatures of 160 °C and 170 °C under saturated steam for 3 hours. After the modification, samples were dried at 75 °C at five different RH: 0%, 25%, 50%, 75% and 95%. EMC at 20 °C and RH 65%, impact strength, MOE and MOR, swelling and ASE were then tested and compared. Addition to those, hornification was measured using deuterium exchange method in DVS apparatus. The method for DVS was developed, and resulted to the adding of re-wetting step to the process and using of 12 hours impregnation time for deuterium oxide. Finally, HPAEC and GC-MS were used to analyse condensation water and the acetone soluble compounds from modified and unmodified samples. Based on the results, EMC differed at 160 °C treatment but not at 170 °C treatment. Accessibility of hydroxyl groups was measured with DVS from the 160 °C samples dried at 50% and 95%, and was found to have significant differences. Therefore, it was concluded that a difference in hornification is possible due to the initial drying. Mechanical tests and swelling test had no statistical difference between the different assumed states of hornification in this experiment. Chemical analysis revealed that condensation water contained many sugars from hemicelluloses, mostly mannose and xylose. Great quantities of different degradation compounds and extractives were also found from the condensed water as well as from the modified wood sample. Based on the chemical analyses, modified samples should be extracted before performing any tests since those compounds may vary the results. Even though this experiment showed that the presumed hornification had no significant impact on the properties of thermally modified Scots pine under saturated steam, hornification is a phenomenon that should be understood better in the field of solid wood. There was at least indication that hornification might influence the EMC in thermally modified wood, which is essential also for some other properties that were not measured in this thesis, such as biological resistance. Therefore, additional tests should be performed concerning the effect of hornification.

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