Abstract:

The aim was to illustrate the effect of straw fiber size on drying and water absorption rate of vacuum dehydrated seeding mats. In this paper, rice seedling mats were prepared by vacuum dehydration using three fiber processing techniques including coarse crushing fermentation grinding (A), fine crushing fermentation grinding (B) and fine crushing fermentation (C). According to the fiber size frequency distribution, fiber and water binding energy in the seedling mats, combined with the changes of porosity degree, drying and water absorption rate of different seedling mats, we simulated the drying and moisture absorption model of seedling mats, respectively. The results showed that the fiber diameter and length were reduced by defibrination and grinding respectively. The fiber length-to-width ratio of seedling mat A was up to 19.5, and the water-holding porosity degree and total porosity degree reached 85.66% and 93.48%, respectively. The binding energy of fiber and water (X_A=0.11kg water/kg DS) was significantly better than those of other fiber treatments. The Logarithmic model of drying kinetics might fit the water loss rate of seedling mats optimally. The seedling mat C with the smallest fiber length-to-width ratio had the fastest moisture drying rate of 0.29 kg/(kg·h), the highest water diffusion coefficient was 1.962×10^-5 m²/s, and the shortest time for matrix seedling mat C to reach the saturated water content was 61.5 min. However, the saturation moisture content was the lowest to 531.06%. In summary, the seedling mat by fine crushing fermentation with smaller fiber aspect ratio has the better drying efficiency and water absorption rate.

Key words: straw seedling mats, aspect ratio, porosity degree, drying kinetics, water diffusion coefficient