• Specifi c heat capacity is defi ned as the amount of heat that a kilogram of a given substance is required to absorb in order to (1967.) (DIP), Wood Handbooku (1999.) (WH) i radu Deliiskog (2012.) (DEL).Ključne riječi: specifi čni toplinski kapacitet, drvo, sadržaj vode, temperatura

Activation spectra of wood under natural irradiation were investigated in detail in this work. The main purpose was to study colour changes on the wood surface over time and into the depth during natural light exposure and thus to further contribute to the optimization of surface-protecting treatments. In a natural weathering test, three 80-lm-thick strips of fir wood forming the surface layer of a wood composite were exposed to light under a series of glass cut-off filters. Samples were withdrawn at intervals and tested for colour changes. Identification of the most detrimental wavebands of light causing photodegradation was performed based on recorded colour changes. With chronological development of exposure, the colour changes shifted ever deeper into the surface and further into the visible region of the spectrum. A relatively narrow waveband from 360 to 435 nm was identified in the activation spectra to be the most active band, causing the greatest proportion of recorded colour changes. However, also visible light of wavelengths up to 515 nm significantly contributed to colour changes of the surface layers.

A review paper was designed as a lab-scale start-up guideline for general pelletizing process and technologies for biomass feedstock. The main body consists of summarized published research on the topic of all main parts of the biomass pelletizing process and technology, including machinery and their parts, optimal feedstock conditions as well as pellet forming processes and principles. This paper is more focused on the specific parameters necessary to obtain optimal pelletizing process that results in desired pellet quality, and less on feedstock preparation, final product post-treatment (e.g. cooling), handling (storage, transportation) or exact quality specifications. A summary of the suggested feedstock, technological and other parameters for the purpose of easier lab-scale start-up of biomass pellets production, which is based on the cited literature throughout this paper, is given in the last section.

Woodworkers' exposure to airborne particles is measured with different sampling techniques throughout the world. Due to a great number of exposure data obtained with different samplers, European countries have aimed over the last ten years to find a conversion factor for mass concentrations that would render these measurements comparable. Following the accepted EU standards and regulations, we replaced a 25 mm open-faced (OF) filter holder with an IOM head to determine woodworkers' exposure to inhalable dust and establish an IOM/OF sampler ratio that might serve as a reliable factor for converting the existing OF data to IOM dust mass concentration in the industrial environment. For this side-by-side sampling we used personal 25 mm OF (N=29) and IOM (N=29) sampling heads over eight working hours. The obtained IOM/OF ratios ranged between 0.7 and 2.3. However, mass concentrations obtained by IOM and OF samplers did not significantly differ. Our findings suggest that there is no need for conversion of the existing OF data for workers exposed to wood dust, provided that dust mass concentrations in the working environment range between 1 mg m-3 and 7 mg m-3. Future side-by-side measurements should also involve environments with low wood dust mass concentrations.

Welding temperature is an important factor of rotary welding and affects the strength of the joint or the embedded force. This research focused on the parameters that affect the welding temperature and the effect of welding temperature on the embedded force of the dowel. Welding temperature was measured using measuring probes that were moved away from the dowel being welded. The results indicate that the speed of the dowel feed (duration of the welding process) influenced the welding temperature; the embedded force was then determined. With increased rotation frequency with the same duration of the welding process, there was a slight increase in the welding temperature. The influence of the rotational frequency on the extraction force was not unambiguously determined, because the rotational frequency is related to the duration of the welding process. As the welding temperature increased, the embedded force decreased. To avoid difficulties in contact measurement of welding temperature, it is necessary to develop a mathematical model of heat transfer to more accurately determine the welding temperature.