Search

The aim of the present study was to investigate the effect of moisture content and temperature on the fracture behaviour of thermally modified Norway spruce ( Picea abies [L.] Karst.) in the transverse plane. Spruce was thermally modified at two heat treatment temperatures, 190 and 210 °C. Mode I fracture tests were carried out at temperatures of 22 and 50 °C on air-dried and fully water-saturated (>fibre saturation point) material. Small CT specimens were used, and load-CMOD curves were recorded. Characteristic fracture parameters were calculated. The fracture surfaces were subsequently examined using optical microscopy. Thermal modification altered all the calculated fracture parameter values and the changes increased as the severity of heat treatment increased. The parameters were altered more in the radial-tangential (RT) than in tangential-radial (TR) orientation. The failure mode changed due to heat treatment in the TR orientation but in the RT orientation the failure mode of unmodified and heat treated material differs only at high moisture content and elevated temperature. [ABSTRACT FROM AUTHOR]

This work investigated the impact that the processing of hemp (C. sativa L.) fibre has on the mechanical properties of unidirectional fibre-reinforced epoxy resin composites loaded in axial tension, and particleboard reinforced with aligned fibre bundles applied to one surface of the panel. For this purpose, mechanically processed (decorticated) and un-processed hemp fibre bundles, obtained from retted and un-retted hemp stems, were utilised. The results clearly show the impact of fibre reinforcement in both materials. Epoxy composites reinforced with processed hemp exhibited 3.3 times greater tensile strength when compared to the un-reinforced polymer, while for the particleboards, the bending strength obtained in those reinforced with processed hemp was 1.7 times greater than the un-reinforced particleboards. Moreover, whether the fibre bundles were processed or un-processed also affected the mechanical performance, especially in the epoxy composites. For example, the un-processed fibre-reinforced epoxy composites exhibited 49% greater work of fracture than the composites reinforced with processed hemp. In the wood-based particleboards, however, the difference was not significant. Additionally, observations of the fracture zone of the specimens showed different failure characteristics depending on whether the composites were reinforced with processed or un-processed hemp. Both epoxy composites and wood-based particleboards reinforced with un-processed hemp exhibited fibre reinforcement apparently able to retain structural integrity after the composite's failure. On the other hand, when processed hemp was used as reinforcement, fibre bundles showed a clear cut across the specimen, with the fibre-reinforcement mainly failing at the composite's fracture zone. [ABSTRACT FROM AUTHOR]

The sorption behaviour of extracted and un-extracted Scots pine ( Pinus sylvestris L.) heartwood was analysed using dynamic vapour sorption apparatus. In addition to the sorption isotherm and hysteresis, the moisture increments and decrements were determined as well as the rate of sorption. Parallel exponential kinetics model was used for further analysis. The effect of cyclic humidity loading on the sorption characteristics was studied by exposing samples to ten repeated sorption cycles and by determining the amount of accessible hydroxyl (OH) groups before and after the cyclic humidity loading. Removal of extractives led to an increase in EMC both in adsorption and in desorption. Hysteresis decreased due to the removal of extractives. Cyclic humidity loading reduced the sorptive capacity of wood material for both extracted and un-extracted wood, but was more pronounced in un-extracted wood. However, despite the decrease in the sorptive capacity, the amount of accessible OH groups increased after ten repeated dry-humid cycles. [ABSTRACT FROM AUTHOR]