Thermal Stabilization of Surface Layers of Composite Ultrafiltration Membranes

To increase the stability of the dynamic layer of a membrane that consists of the polystyrene(PS) microparticles, a nylon-PS membrane was heat treated at temperatures from 50 to 100 °C within 10 minutes. Increasing the temperature from 50 to 100 °С leads to a decrease of the weight up to 0.86%.Temperature impacts on a surface of the dynamic membrane was investigated by the scanning electronic microscopy and the measurement of a wetting contact angle of the studied samples of membranes. The heat treatment of nylon-PS membranes at temperature of 50° С during 10 minutes lead to a decrease of their wetting contact angle from 136° to 129°. Increasing hydrophily of membranes is associated with a decrease of roughness of a blanket and the formation of the open areas acting sites consisting of hydrophilic "nylon 66". Besides, the molten sites were formed on the surface of a membrane. In addition, the intensities of IR spectra were reduced. However, after heat treatment at a temperature of 70 °C, the intensities of IR spectra increased. The specific capacity of the dynamic membrane is reduced by 1.5 times after heat treatment at a temperature of 50 °C, but at higher temperatures, the membrane permeability increased up to 4.5 times. A decrease of the specific capacity of the membrane is related to the compaction and connection of PS particles under the action of temperature. Heat treatment at temperatures above 50 °C leads to an increase in stiffness and brittleness of the dynamic layer of PS, as a result the cracks are formed on the surface of the layer and the membrane permeability increases. The stability of the dynamic layer is achieved by processing for 10 minutes at a temperature of 50 °C, it  is increased by 4 times, while the mass of the membrane after backwash with anionic surfactants solution did not decrease when the initial nylon–PS membranes mass decreased by 0.84 %.The rate of separation of the water-oil emulsion increases from 97% to 99 % as a result of thermal stabilization of the dynamic layer of the membrane.