Plasma surface modification of polymer powders in a fluidized bed reactor

Abstract

To modify the surface properties of fine powders, polymer powders have been oxidized and fluorinated by the active species in a glow discharge. A plasma surface modification of polymer powders has been carried out in a fluidized bed reactor. The optimum reaction conditions for oxidation and fluorination of polymer powders in a fluidized bed reactor have been determined under the several different plasma conditions. The chemistry of the oxygen and fluorine reactions with polymer powders in the plasma is also elucidated. The chemical and physical properties of the modified surfaces have been determined by using electron spectroscopy for chemical analysis (ESCA), Fourier transform infra-red spectroscopy (FTIR), contact angle measurements, differential scanning calorimeter (DSC) and scanning electron microscopy (SEM). The plasma surface modification of powders were carried out in a Pyrex glass fluidized bed reactor (34 mm-ID $\times$ 0.8 m-high). High density polyethylene (HDPE) powders were fluidized by gas. An inductively coupled electrode (4.8 mm-OD copper tube, 6 turns) for glow discharge at 13.56 MHz (rf) frequency was placed at 90 mm from the gas distributor and connected to an auto matching network and an rf power generator. For oxygen plasma treatment, the HDPE powders (mean diameter 231 $\mu m$ ; density 956 kg/$m^3$) were treated by plasma in the fluidized bed reactor at rf power of 50 to 200 W, oxygen flow rate of 15.2 to 28.4 sccm, and treatment time of 1 to 13 h at a pressure of 133 Pa. The surface property of HDPE powders were changed from hydrophobic to hydrophilic by the oxygen plasma treatment in a fluidized bed reactor without change of bulk property. The formation of oxygen functionalities and hydrophilicity of HDPE powders increase with the plasma treatment time and rf power. The degree of surface oxygen content and hydrophilicity decrease with increasing flow rate of oxygen. The contacting angle or hydrophobic property decreases down to about 6...