Ding et al. J Wood Sci
(2020) 66:55
Page 5 of 9
Fig. 4 Non-wood components in MDF sanding dust sample. a Crystal-shaped particle; b brick-shaped particle
P240 sandpaper according to Welling et al. [7]. In gen- eral, sub-micrometer is the domain of fumes and smokes, and mechanical processing of solid materials seldom pro- duces particles less than 1 μm, which might be attributed to the volatile compounds in the MDF resin [7]. It can therefore be suggested that the existence of the resin in MDF not only influences the physiochemical properties of MDF sanding dust, but also extends the lowest limit of particle size. The PSD obtained by IA also showed the dominance of inhalable particles in MDF sanding dust with 99.6% of the sample particles smaller than 100 μm (Fig. 5). What’s more, of all the particles, around one-third was smaller than 10 μm and termed PM 10 , which can penetrate into the lower region of human respiratory tract. A small quantity (1.5%) with the size lower than 2.5 μm termed PM 2.5 was also detected, which are fine inhalable parti- cles to have the greatest health risks to humans [29]. The shape analysis showed that the MDF sanding dust samples had a pretty low aspect ratio as a whole, and the mean AR value was 0.32, almost the same as the median value of 0.31 (Table 1), which indicated that the width of at least 50% of the particles was comparable to the length. This coincided with the visual observation of SEM pic- tures (Fig. 3b). But elongated or fibrous particles also existed. Around 10% of the particles had length-to-width
indicated the presence of components other than wood in the MDF sanding dust, which should be derived from chemical components in the MDF panel like UF resin or the combination of wood fibers and chemical additives. In small quantities as they presented, the physiochemi- cal properties of MDF sanding dust could be significantly changed to cause environmental impacts. For example, the burning and pyrolysis of UF-containing wood wastes can release environmentally harmful gases, which results in a restriction of their energy utilization [32]. Morphological characteristics determined by flatbed scanning image analysis The IA provided much detailed statistical results on particle morphology. According to Table 1, the median size (50th percentile value) of MDF sanding dust was 12.90 μm, and the mean value was a little bit higher (17.28 μm), which might be due to the existence of rela- tively large particles with the size up to 192.70 μm. The RS of particle size was 2.20, which is wider than some other bio-based particles [33], indicating the heterogene- ity of MDF sanding dust size. Sub-micrometer particles as small as 0.66 μm were also detected, showing the presence of ultrafine particles in MDF sanding dust. Similarly, particles smaller than 0.1 μm was detected when sanding MDF panels with
Table 1 Size and shape distributions of MDF sanding dust determined by flatbed scanning image analysis Mean Min P2 P10 P25 P50 P75 P90 P98 Max RS
D in (μm)
17.28
0.66 0.00 0.03
3.08 0.06 0.65
4.83 0.14 0.74
7.93 0.22 0.84
12.90
20.47
33.15
59.41
192.70
2.20 1.26 0.26
AR
0.32 0.89
0.31 0.93
0.42 0.96
0.53 0.98
0.63 0.99
0.86 1.00
Solidity
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