Various biotic and abiotic agents are affecting the performance of wood and wood based products. Chemicals, thermal energy, radiation, as well as different organisms have the potential to alter the optical, haptic and finally functional performance of wood. Many of these effects come along with a change of the structural integrity of wood, which in turn affects its strength properties. Therefore a test was developed to determine the structural integrity of wood in terms of its resistance to impact milling. A High-energy multiple impact (HEMI) – test has been designed using steel balls in a heavy vibratory mill for crushing wood samples. Thousands of single events are captured by analyzing the resulting fragments. Based on the degree of integrity and the percentage of fine fragments (< 1mm) an indicator has been defined to detect structural changes on cell wall level with high sensitivity.
This paper gives an overview about the effects on the structural integrity of wood that can be detected by HEMI tests. In first instance the reduction of structural integrity through thermal cell wall modification was examined and found to be quantitatively detectable with high precision. Negative effects of different chemical modification treatments were detectable as well. In contrary, the impregnation with wax and oil, but also with water led to an increased structural integrity.
Further studies showed the negative effect of gamma radiation, which is frequently used for sterilizing wood samples. Hence the results of durability tests are likely influenced by pre-damage through radiation as well. Decay by fungi and bacteria had a significant effect: The impact of brown and white rot on the structural integrity of wood was remarkably, but different, partly even on species level. Structural damages occurred far before mass loss was detected. In contrast to the wide range of agents that can be easily detected, the resistance to impact milling (RIM) as measure of the structural integrity was found to be unaffected by wood density and weathering effects such as cracking.
In a recent study the interrelationship between structural integrity and standard impact bending strength were investigated. Preliminary results are presented in this paper.
Keywords: Ball milling, crushing, High-energy multi impact (HEMI) test
Authors
Brischke C.
Leibniz University Hannover, Faculty of Architecture and Landscape Sciences, Institute of Vocational Sciences in the Building Trade, Hannover, Germany
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