The influence of beech bark concentrations as filler in urea-formaldehyde (UF) adhesives was investigated relative to the composite forming process and selected properties of final 5-layer beech plywood. Beech bark was used as filler to lower the wood processing waste production and decrease formaldehyde emissions. A combination of UF adhesives filled with different beech bark concentrations as the adhesive was used. Three different concentrations of beech bark, 15 wt.%, 20 wt.%, and 25 wt.% were used in the experiment. Urea-formaldehyde adhesive filled with 20 wt.% technical flour was used as a reference sample. The effect of the filler was studied via its temperature profile during pressing, mechanical properties in bending, water absorption, thickness swelling, and formaldehyde emissions after pressing. The time needed to reach the temperature between the beech veneers, at least 105 °C, which was equal to the final temperature filler-adhesive-wood matrix cross-linking, was also investigated during the pressing process. The measurements of the free formaldehyde emissions showed that for samples with non-zero bark concentrations there was a decrease of formaldehyde emissions by at least 46%.
During production, thermally modified wood is processed using the same machining operations as unmodified wood. Machining wood is always accompanied with the creation of dust particles. The smaller they become, the more hazardous they are. Employees are exposed to a greater health hazard when machining thermally modified wood because a considerable amount of fine dust is produced under the same processing conditions than in the case of unmodified wood. The International Agency for Research on Cancer (IARC) states that wood dust causes cancer of the nasal cavity and paranasal sinuses and of the nasopharynx. Wood dust is also associated with toxic effects, irritation of the eyes, nose and throat, dermatitis, and respiratory system effects which include decreased lung capacity, chronic obstructive pulmonary disease, asthma and allergic reactions. In our research, granular composition of particles resulting from the process of longitudinal milling of heat-treated oak and spruce wood under variable conditions (i.e., the temperature of modification of 160, 180, 200 and 220 °C and feed rate of 6, 10 and 15 m.min−1) are presented in the paper. Sieve analysis was used to determine the granular composition of particles. An increase in fine particle fraction when the temperature of modification rises was confirmed by the research. This can be due to the lower strength of thermally modified wood. Moreover, a different effect of the temperature modification on granularity due to the tree species was observed. In the case of oak wood, changes occurred at a temperature of 160 °C and in the case of spruce wood, changes occurred at the temperatures of 200 and 220 °C. At the temperatures of modification of 200 and 220 °C, the dust fraction (i.e., that occurred in the mesh sieves, particles with the size ≤ 0.08 mm) ranged from 2.99% (oak wood, feed rate of 10 m.min−1) to 8.07% (spruce wood, feed rate of 6 m.min−1). Such particles might have a harmful effect on employee health in wood-processing facilities.
The effects of wear on the performance of sanding belts were determined for European beech (Fagus sylvatica L.) and English oak (Quercus robur). These measurements are presented as a function of the defined sanding time of 480 min on a manual sanding belt machine. Sanding belt pressure on the piece surface (6600, 10400, 14700, and 18600 Pa), sanding direction (cutting speed vector with reference to wood fibers equal to 0°, 60° and 90°), wood hydrothermal treatment, and sanding belts from various manufacturers were the variables. The sanding belt wear was monitored by means of specific wood removal rate (g/cm 2 .min) in 20-min intervals by the means of reference samples with size of 50 x 50 x 50 mm, which were sanded for 1 min. The resulting curves for the sanding belts, as well as the statistical models of the wood removal rate, decreased as a function of the sanding time, described by the function y = a + b.e -ct . This work also describes the impact of wood species, optimum pressure, and grinding time on the characteristics to abrasion.
The article presents results of the granulometric composition of chip particles when sanding wood (beech) and wood-based materials (particleboard and semi-hardboard) using different types of sanders – wide belt sander, narrow belt sander, and hand sander. On the basis of the carried out sieve analyses, the proportion of produced particles, which can be marked as dust with the particle size of ≤ 80 μm, is high at the interval from 89.21% - 96.29 %. The highest percentage of dust particles was reached at dust from the hand disk sander. At the end of the article we point to possible technical safety measures – additional dust exhausting, suction, to possibly reduce the dust getting to the working environment.
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