Mechanical,chemical and bacterial resistance of modified polyvinylidene fluoride membranes suitable for ultrafiltration of oily emulsions

The ultrafiltration membranes prepared at the Institute of Industrial Chemistry of the University of Genoa and, at the present time, developed in a tubular form by ANIC S.p.A. for ultrafiltration of oily emulsions, are made from modified polyvinylidene fluoride. The base polymer shows very good resistance to chemical and bacterial attack and the membranes prepared from it should presumably have the same properties. In order to verify the above assumption, the membranes were stored for one year in the presence of the following agents: water, wool scouring waste water, acids, alkali, calcium chloride sodium hypochlorite and sodium bisulfite at concentrations ranging from a few grams to more than one hundred grams per liter. Every month the membranes were washed and tested. The results show that, in most cases, after an initial decline of about 30% during the first three months of storage, the permeate flux for these membranes becomes constant with values corresponding to more than 7000 liters per square meter per day. Among the chemicals used, only concentrated solutions of sodium hydroxide and sodium hypochlorite affect the performance of the membranes. The membranes were also submitted to bacterial attack tests in order to check their suitability for processes involving ultrafiltration of organic media such as wool scouring wastes or sewage. The bursting strength of the membranes was also checked as a function of their storage in the presence of all the above agents. No change was noticed except for those immersed in sodium hydroxide solutions. It can therefore be inferred that the membranes exhibit substantially the same resistance properties as the parent polyvinylidene fluoride.