Ageing of polyvinylidene fluoride hollow fiber membranes in sodium hypochlorite solutions

Abstract

International audienceIn order to study the effect of cleaning operations on polyvinylidene fluoride (PVDF) hollow fiber membrane stability, ageing of two PVDF based membranes (one is additive free, the other contains hydrophilic additives) in contact with sodium hypochlorite solutions with various pH values has been studied. The aim of this experimental study was to identify the degradation mechanisms and to gain a better understanding of the effect of the (macro)molecular structure changes on the mechanical and functional properties of the membranes. In both membranes, double bond formation, chain scission and crosslinking are observed and all these processes (except crosslinking) are faster in acidified solutions than in natural NaOCl solutions (pH 11.5). It can be deduced that if ionic processes such as dehydrofluorination occur, radical processes resulting from the presence of hypochlorous acid and perhaps its coexistence with the ClO− ion, predominate in acidified solutions. The presence of non-fluorinated aliphatic or cycloaliphatic additives, which are highly reactive with bleach, accelerates chain scission at the expense of crosslinking. In the chosen conditions (135 days in 4000 ppm bleach solutions at 40 °C), PVDF chains are degraded but not enough to induce polymer embrittlement. While in the additive free membrane no significant change of the use properties has been observed, the polymeric additives of the other membrane are completely destroyed, leading to a decrease of the membrane hydrophilicity, but their destruction improves the membrane selectivity by a decrease of the average porosity

Influence of Sodium Hypochlorite Treatment on Pore Size Distribution of Polysulfone/Polyvinylpyrrolidone Membranes

“…In the work [ 32 ], dialysis membranes of PSf were treated with hypochlorite solution with an active chlorine concentration of 4% for 1 h. Based on the dextrans retention data, it was calculated that such treatment increased the effective pore size from 0.76 to 1.58 nm. Similar tendencies were observed for other polymeric membranes containing PVP as an additive, namely for polyethersulfone [ 28 , 34 , 35 , 36 , 37 ], polyvinylidene fluoride [ 38 , 39 ], cellulose acetate [ 40 ] and polyacrylonitrile [ 41 ]. Thus, it should be taken into consideration that exposure to sodium hypochlorite solution can modify PSf/PVP membrane properties.…”

Effects of Chemical Cleaning on the Ageing of Polyvinylidene Fluoride Microfiltration and Ultrafiltration Membranes Fouled with Organic and Inorganic Matter

“…Subsequently, the contact angle increased significantly after a soaking time of 2 weeks, indicating that prolonged exposure to NaOH changed the chemical structure of the membrane. Caustic cleaning agents have been reported to lead to dehydrofluorination phenomena, in which C=C bonds are formed when the H-F units are eliminated from the polymer [8,19]. Absorbance (a.u.)…”

“…Hollow-fiber membranes are usually pressurized in a housing or immerged in a basin and are mainly made of polyvinylidene fluoride (PVDF) or polyethersulfone (PES) [ 7 ]. PVDF is widely used as a polymeric membrane material due to its outstanding properties: i.e., high mechanical strength, flexibility, thermal stability, and chemical resistance [ 8 ].…”

Effect of concentration on virus removal for ultrafiltration membrane in drinking water production

“…Studies already observed different results depending on membrane modifications and retention compounds. Ravereau et al showed an increase in MS2 phages retention after membrane exposition to chlorine because of the increase in hydrophobicity of membrane surface [40]. Studies about retentions of bovine serum albumin (BSA) concluded on the enhancement of BSA retention with increase of membrane hydrophilicity, or BSA retention reduction with increase in membrane hydrophobicity [30,34,35].…”

“…Retention evolution with membrane ageing has already been assessed according to various compounds. Studies about organic compounds [37], E.coli and total bacteria [33,40], and bovine serum albumin (BSA) [30,34,35] retentions after chlorine exposure have given different results. Moreover, Ravereau et al observed MS2 retention and showed an increasing retention on aged membranes [40], when other studies at industrial scale observed a loss of 1 log in MS2 phage retention for 6 years-old membranes [19,25].…”