bioresources. com
PEER-REVIEWED ARTICLE
Fig. 3. Results of the particle size analysis 3ODVPDDSSOLFDWLRQDQGVXUIDFHWHQVLRQFKDQJHV
Due to the designed enclosed mixer, it was possible to modify the particle mixture homogeneously using plasma. Two modification degrees of lower (26.9V/6.9A) and maximum power (28.6 V/8.7 A) were used to treat the straw. Despite the fact that cold plasma was used, the maximum average vessel temperature reached 81 °C at lower power, while at maximum power it increased up to 86 °C. As a result, most likely a small effect of thermal treatment has to be taken in consideration in addition to the plasma treatment of the wheat straw. This effect led to a pre-drying of the particles. After plasma treatment, test inks on the outer sides of the straw determined a change in the surface energy of the modified particles, which were compared with the reference particles without modification. The surface tension on the outside of the reference straw covered range values from 24 mN/m to 28 mN/m. Wheat straw with a lower degree of plasma treatment (A) ranged from 28 mN/m to 30 mN/m, and at a higher degree of modification (B), the surface tension was from 30 mN/m to 32 mN/m. The variability of the unmodified particles was thus higher than that of the plasma-treated particles. Therefore, the testing inks confirmed that both degrees of cold plasma treatment increased the surface wettability and changed the surface energy. However, these results could be affected by the different moisture of particles. Plasma-treated particles in the missing agent were partly dried and then immediately examined by test inks. The treated particles were not conditioned because the effect of cold air plasma on the physical properties of modified material decreases with time after the plasma application (Klímek HWDO 2016). 'HQVLW\DQGYHUWLFDOGHQVLW\SURILOH The average density of the reference boards was 540.0 kg/m 3 . Boards with a lower degree of modification reached 524.9 kg/m 3 and boards with a higher degree of modification had an average density of 545.7 kg/m 3 . Due to manual layering, the density also exhibited considerable variability (Table 3). Further, it was noticed that the boards manufactured from the reference particles had the steepest density profile (Fig. 4a). The different average density, the variability of the density, and the shape of the density profile have to be taken into consideration while interpreting the physical and mechanical properties measured. Figure 4b shows a cross-sectional cut of the board showing individual particles of winter wheat stalk.
5071
Hýsek et al . (2018). “Cold plasma & straw board,” B io R esources 13(3), 5065-5079.
Made with FlippingBook Ebook Creator