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3K\VLFDODQGPHFKDQLFDOSURSHUWLHVHVWLPDWLRQ Test samples were made from the manufactured boards with a rectangular shape for four-point bending, internal bonding, vertical density profile measurement, and samples for water uptake with thickness swelling. Before the mechanical properties measurement, the test specimens were air-conditioned at 65% RH and a temperature of 20 °C. Strength tests (Fig. 2) were performed on a TIRA test 2850 (TIRA GmbH, Schalkau, Germany) universal testing machine. The maximum force, ) max , was always recorded with 1% accuracy. The maximum load was always achieved within 60 s ± 30 s. Before loading, the test specimens were placed in an air-conditioned chamber at 65% RH and a temperature of 20 °C. The basis of the bending test was to place the test specimen (50 mm × 300 mm) flat on two parallel cylindrical supports ( G = 30 mm). Another two supports ( G = 30 mm) had a constant loading force, ) , cantered above the axis of the board and the maximum force, ) max , derived by the machine was measured. The total bending strength was calculated as the arithmetic mean of the values of the following equation for each group of specimens, ୫ ሺ כ ି ଶ ሻൌ ଷ כ ౣ ౮ כ ୪ౣ ଶ כ ୠౣ כ ୲ౣ మ , (1) where O m is the length (mm), E m is the width (mm), and W m is the thickness (mm) of the test specimen for four-point bending. Tests were not performed according to EN 798 (2004) because no characteristic values of board properties were determined. Using this measuring method, it is possible to compare measured strength values with previously obtained data from the authors’ research. The internal bonding of boards was estimated according to EN 319 (1993) on samples with dimensions of 50 mm × 50 mm.
Fig. 2. Diagram of mechanical properties testing According to Eq. 2, dimensional changes at different air-conditioning stages were determined for water uptake and thickness swelling. The test specimens were first dried to 0% board moisture at 103 °C (air-conditioning stage 0). The samples were then air- conditioned at 20 °C and 65% RH (air-conditioning stage 1) and then at 85% RH (air- conditioning stage 2).
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Hýsek et al . (2018). “Cold plasma & straw board,” B io R esources 13(3), 5065-5079.
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