Study on Wheat Straw Surface Free Energy and Its Polar and Non Polar Part

The contact angles for calculating free energy of wheat straw surface pretreated with different methods were chosen by continuous monitoring the response of contact angles to time.The surface free energies and its polar and non polar part were studied,based on Young equation and methods suggested by Owens-Wendt-Kaelble.The results reveal that both free energy of out and inner surfaces untreated are 37.20 mJ/m2 and 51.54 mJ/m2,wherein the non polar part of out and inner surfaces accounts for 84.11% and 50.50%,respectively.After pretreated with 1% NaOH solution at 95 ℃ and 85 ℃,51.72 mJ/m2 and 44.21 mJ/m2 out surface free energy are achieved,wherein the polar part increases 377.58% and 229.13%,respectively.Pretreated at 180 ℃ and 160 ℃,the out surface free energy changes a little,but its polar part elevats significantly,its non polar part decreases significantly.