Abstract:

Layer-by-layer（LbL） self-assembly of lignosulfonates（LS） and Cu ^2＋ was applied to the hydrophobic modification of pulp fiber surface.The modified fiber surface was then characterized by means of X-ray photoelectron spectroscopy,atomic force microscopy（AFM） and dynamic contact-angle measurement.The results show that  the contents of S and Cu on fiber surface both increase with the alternate assembly of LS and Cu ²⁺ ,which veri-fies the feasibility of the LbL self-assembly of lignosulfonates on fiber surface ； the microfibrils on fiber surface are gradually and compactly covered by granular lignin particles during the process of self-assembly  the ave-rage phase of AFM phase images increases with the content of lignin on fiber surface,which suggests the improvement of the hydrophobicity of fiber surface  with the increase of self-assembly layers,the initial contact angle of fiber surface increases and the decline rate of contact angle decreases in a period of 0.08s;and  the initial contact angle increases from 0° to 104.8° after the fiber surface has been modified with five self-assembly layers,and then decreases to 78.9° after 0.08s,which means that the excessively hydrophilic fiber surface is modified to a hydrophobic one in a certain degree.It is thus concluded that the hydrophobic modification of fiber surface can successfully be implemented by controlling the number of assembled layers.

Key words: lignosulfonate, layer-by-layer self-assembly, surface modification, hydrophobicity, hydrophilicity