Tukin haudontalämpötilan, viilun kosteuspitoisuuden ja kuumapuristuslämpötilan ja -ajan vaikutus sorvatun koivuviilun itseliimautuvuuteen

摘要

Self-bonding of wood refers to a technique where pieces of wood are bonded by activating wood constituents with heat and pressure without any added adhesive, and it is enabled by chemical and physical changes within wood. The aim of this thesis was to study the self-bonding ability of birch (Betula pendula) veneer with Automated Bonding Evaluation System (ABES). The effect of moisture content of veneer and log soaking temperature on tensile shear strength of bond line was examined with different hot-pressing parameters, and also the effect of humidity on bonded veneers was assessed. Furthermore, the results from ABES tests were scaled up to a laboratory level plywood testing.The results showed that log soaking temperature and moisture content of veneer significantly influenced the self-bonding ability of birch veneer. Especially, log soaking temperature of 20 °C evidently contributed to bond formation compared to soaking at 70 °C. Moreover, joint effect of lower log soaking temperature and approximately 6 % moisture content provided the greatest shear strength values. Self-bonded birch veneer joint also resisted moisture moderately when relative humidity is elevated from 35 % to 65 %, although signs of weak-ening of the bond was noted. Based on the results in this thesis the effect of hot-pressing temperature and hot-pressing time on self-bonding was substantial. Formation of a proper bond required at least 220 °C of hot-pressing temperature. Alternatively, higher pressing temperature enabled the use of a shorter hot-pressing time. Although the results gained with ABES considering pressing parameters appears to be unambiguous, the application of the results to plywood manufacture requires further research.