EVOH in situ fibrillation and its effect of strengthening, toughening and hydrophilic modification on PVDF hollow fiber microfiltration membrane via TIPS process

In order to enhance the strength and overcome the poor antifouling capacity of poly(vinylidene fluoride) (PVDF) membrane used in water treatment, herein, poly(ethylene-co-vinyl alcohol) (EVOH) was selected and the PVDF/EVOH blend hollow fiber microfiltration membrane was prepared via the thermally induced phase separation (TIPS) technique. The morphology for the pristine and blend membrane was compared, and the distribution of EVOH on outer surface and within matrix was explored. The fibrous-shaped EVOH enhanced the breaking strength of the membrane markedly (up to 13.63 MPa) due to the in situ fibrillation; especially, when the blend membrane was immersed into water, the internal plasticization of water molecular enhanced the toughness of the membrane and the elongation at break increased up to 86.39% compared with 27.63% for the corresponding dry membrane and 36.62% for the pristine membrane, respectively. The addition of EVOH introduced hydroxyl group into the bulk and thus endowed the membrane with a better hydrophilicity (the contact angle is as low as 43°) and higher pure water flux (up to 449.11 L m⁻² h⁻¹) compared with pristine PVDF membrane. Moreover, the blend membrane showed a better rejection of carbonic particle (nearly 100%) and higher flux recovery rate (up to 87.30%). The present investigation offers an effective and simple pattern to regulate microstructure and enhance mechanical strength, flux and hydrophilicity of the polymeric microfiltration membrane via the TIPS process for water treatment.