Effect of Polymer Modifier on the Mor­pho­logical and Separation Properties of Asymmetric Microfiltration Membranes

Abstract

Modifying membranes is a common approach to improve their separation ability. In this work, a series of the membranes, which reject colloidal particles of a wide diapason of their size, was obtained by modifying acetylcellulose microfiltration membranes with such rigid polymer as polymetylmetacrilate. Modifying was carried out by precipitation of the polymer in the membrane pores, the depo­sition occurred from the solutions of different concentrations. Other way was multistage modifying membranes with a solution of the same concentration. Depending on the modifying conditions, the content of polymetylmetacrilate in the membrane was 12–44 %. Morphology of the composite membranes was investigated by optical and scanning electron microscopy. Water test was also performed at 0.5–2 bar. The membranes obey Darcy law in this pressure diapason: thus, the pore radius can be approximately estimated from the Hagen – Poiseuille equation (18–63 nm). Moreover, the modifier minimizes the membrane compression: a decrease of the permeate flux is 19 % (pristine membrane) and 8% for membranes containing high amount of the modifier. Colloidal solutions of water-soluble linear polymer, vegetable protein and sol of hydrated iron oxide were also used for the membrane testing. The selectivity of composite membranes enhances in the row: polyvinylpyrollidone < iron oxide < albumin. In the case of vegetable protein, the membrane selectivity is 30–91% depending on the modifier content. The membrane with highest separation ability was used for clarification of goiaba juice: the selectivity towards total solids was found to reach 33–73%. The permeate can be used for the production of beverages, the concentrate is recommended for confectionery industry. Polymethylmetacrylate can be recommended for the membrane modifying as a binding component in the composite containing also hydrophilic agent.