Preparation Of Microporous Ethylene-Vinyl Alcohol Copolymer (EVOH) And The Investigation Of Its Fouling Behaviour

Based on the good hydrophilic properties of ethylene-vinyl alcohol copolymer(EVOH),this paper studies the method of preparing EVOH microporous membrane by immersion precipitation phase inversion method,systematically investigated the temperature of gel bath and the conditions of casting solution to EVOH microporous membrane The characteristics of the performance are affected,and the anti-pollution performance of the typical pore structure EVOH microporous membrane is investigated.turn out:(1)The temperature of the gel bath is the dominant parameter to control the performance of the EVOH microporous membrane: with dissolved pure EVOH as the film casting liquid system,when the gel bath temperature is 0-20 ℃,asymmetric finger pore EVOH micropores are formed The membrane,that is,the membrane surface forms a dense skin layer,and the membrane cross-section presents a typical finger-like pore structure.With the increase of temperature,the development of the finger pore structure decreases.～ 800 ± 50 L · m-2 · h-1,the mechanical properties of the corresponding microporous membrane are poor;on the contrary,when the gel bath temperature reaches40 ℃,a typical spongy symmetric membrane is formed,and a large number of micropores are formed on the surface,And a typical sponge-like structure is formed on the cross section,the membrane permeation flux increases sharply to 2500 ± 50 L · m-2 · h-1,but its mechanical properties begin to improve;when the temperature of the gel bath continues to increase to 60 ℃ The spongy structure of EVOH membrane cross section is further aggravated.The above phenomenon shows that the preparation of two typical membrane pore structure EVOH microporous membranes can be achieved within the gel bath temperature range of 0-60 ℃.The gel bath temperature is a key factor for controlling the pore structure and performance of EVOH microporous membranes.(2)Under the conditions of gel bath at 20 ℃ and 40 ℃,the single-factor control variable method was used to investigate the conditions of the casting solution(polymer concentration,casting solution solvent type and casting solution temperature)on EVOH micropores.The effect of the membrane performance,the results found that under the conditions of the two gel bath temperatures,with the increase in the content of EVOH,the pore morphology of the membrane cross section did not change,but the pore density decreased,and the mechanical properties improved,the penetration and Hydrophilic properties become worse;in addition,the type of EVOH solvent is another key factor affecting the performance of the microporous membrane structure.Different solvents lead to completely different membrane pore structure and performance;The effect of membrane pore structure and performance is not obvious.The effect of comprehensive gel bath temperature on the performance of EVOH microporous membrane is obtained.When the temperature of the gel bath is 20 ℃,the concentration of EVOH is 20%,and the solvent is DMAc,the asymmetric finger pore structure with better comprehensive performance can be prepared EVOH microporous membrane;when the gel bath temperature is 40 ℃,the EVOH concentration is 20%,and the solvent is DMAc,an EVOH microporous membrane with good overall performance and symmetrical sponge structure can be prepared.(3)For the two structures of EVOH microporous membranes,the membrane fouling behavior of typical dissolved organic substances humic acid(HA)and bovine serum albumin(BSA)was investigated,and it was found that no matter what pollutants were targeted,the same operation Within a period of time,the interaction force between the pollutants and the sponge-like EVOH microporous membrane is strong,and the accumulation rate of the pollutants on the surface of the pollutant is relatively fast,resulting in the attenuation rate of the sponge-like EVOH microporous membrane flux and Irreversible pollution is more serious,and the EVOH microporous membrane with finger pore structure has better anti-pollution performance.At the same time,it was found that compared with humic pollutants,protein pollutants had a lower pollutant rate and irreversible pollution on EVOH microporous membranes,indicating that EVOH has a stronger ability to resist protein organic pollutants.This is not the same as traditional PVDF membranes.For PVDF membranes,BSA can adsorb and accumulate on the membrane surface in a large amount of time,which is a typical dominant pollutant that can cause PVDF membrane pollution.