Adsorption Equilibrium Moisture Contents of Flax Straw, Hemp Stalks and Reed Canary Grass

The quality of fibres obtained from flax, hemp and reed canary grass is dependent on the moisture characteristics of the crops. In this study, the adsorption equilibrium moisture contents of un-retted and dew-retted flax straw, un-retted and frost-retted hemp stalks and spring-harvested reed canary grass were determined using the dynamic gravimetric method at different temperatures (5, 15, 25 °C) for relative humidities in the range 35-95%. Non-linear regression was used to fit five commonly used three-parameter isotherm models [the modified Henderson model, the modified Chung-Pfost model, the modified Halsey model, the modified Oswin model and the modified Guggenheim-Anderson-de Boer (GAB) model] to the data obtained. The goodness-of-fit of the models was compared using the mean relative percentage deviation, the standard error of estimate and residual plots. The modified Halsey model was considered the best for predicting the equilibrium moisture content of un-retted flax and spring-harvested reed canary grass, and the modified Oswin model for predicting the equilibrium moisture content of dew-retted flax and un-retted hemp, while the Chung-Pfost model was the best for predicting the equilibrium moisture content of frost-retted hemp. For flax and hemp, there were statistically significant differences between un-retted and retted plant materials, whereas the differences between varieties were small.