Pine Bark Particle Separation Improves as Moisture Content Decreases at Time of Screening

Bark particle screening is a critical secondary processing stage when engineering bark-based horticultural substrates. There are several factors that can influence bark screening efficiency; however, the bark moisture content immediately before screening may have the largest impact. The objectives of this study were to determine the effect bark moisture content has on bark particle separation across two commonly used screen apertures and the subsequent static physical properties of the screened bark. The moisture contents examined herein ranged from 50%, 55%, 60%, 65%, and 70% and were gravimetrically determined. The screen apertures used were 6.3 mm and 9.5 mm. The results showed that moisture content has a considerable effect on both screening yield and the physical properties. Generally, as moisture content increased, bark yield (i.e., bark processed through the aperture) decreased. Moreover, as moisture content increased, the proportions of fine bark particles adhered to coarse bark increased, shifting the air-filled porosity: water-holding capacity of the substrate. In summation, the drier moisture content had the greatest (i.e., most equal) separation, regardless of screen aperture. Future research should identify the interaction between feed rate and moisture content.