Study On The Preparation And Properties Of Polyurethane-Based Functional Materials For Oil/Water Separation

In the development of modern industry,large and small oil spills and the treatment of industrial oily wastewater are one of the problems that people have to face.Traditional oil/water separation methods are inefficient and energy intensive,and people have to study better oil/water separation methods.Based on the in-depth study of the superhydrophilic and superhydrophobic phenomena of natural organisms and the theory of solid interface wetting,a series of oil/water separation materials with superhydrophobic and superlipophilic properties or superhydrophilic and superoleophobic properties were prepared.However,the real application situation is extremely complicated,which greatly limits the application of these materials.Separation of oil and water under different environments(such as varied pH,temperature,pressure,oils,etc.)may cause damage to the surface structure of the two types of oil/water separation materials,resulting in poor or even loss of oil/water separation performance.In addition,these two types of materials can only act on the oil phase or the water phase alone,and can not selectively act on different phases as needed to achieve oil/water separation,so their application has certain limitation.In response to these problems,this study aims to design functional materials with controlled switchable hydrophilicity and hydrophobicity,which can achieve the conversion between hydrophilicity and hydrophobicity under the stimulation of different environment conditions,so that it can be applied to oil/water separation process in complex environments.In this study,polyurethane(PU)sponges with low density,high porosity,and excellent mechanical properties was used as substrate,and materials with different chemical properties were grafted onto the surface of the substrate,and then designed and prepared modified PU sponges with superhydrophobic and superlipophilic surface properties or temperature sensitivity.The chemical composition,morphology of modified PU sponges surface were characterized by Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS)and field emission scanning electron microscopy(FE-SEM).The surface wettability of modified PU sponges under different environments and its controlled switchable hydrophilicity and hydrophobicity characteristics were measured by contact angle measuring instrument.On this basis,the oil/water separation performance of the modified PU sponges under different environmental conditions were tested and evaluated by properly designed oil/water separation tests.The main contents and results of the study are as follows:(1)First,PU sponges were used as substrate,and surface of PU sponges were etched by chromic acid solution,forming rough structure on the surface and introducing hydrophilic groups.Then,chloropropyltrichlorosilane(CPTS)was used to react hydrolysis polycondensation reaction on the surface of the etched sponges,and a series of coupling agent modified PU sponges(PU-CPTS)were prepared under different reaction conditions.The surface wettability and oil/water separation performance of PU-CPTS were investigated,and the influence of the reaction conditions on the surface wettability were analyzed.The results show that CPTS effectively improves the surface hydrophobicity of modified PU sponges.In the range of CPTS concentration of 0.5 ~ 2 vol %,with the increase of CPTS concentration,the water contact angle of PU-CPTS surface decreases;in the range of time of 10 ~ 50 min,with the increase of hydrolysis polycondensation time,the water contact angle of the PU-CPTS surface increases first and then decreases,when the hydrolysis polycondensation time is 30 min,the water contact angle of the PU-CPTS surface is the largest.When the CPTS concentration is 0.5 vol % and hydrolysis polycondensation time is 30 min,the surface hydrophobicity of PU-CPTS is the best,and the water contact angle is 151.7°,which achieved superhydrophobicity.Oil absorption tests show that PU-CPTS can adsorb organic oils with 11 ~ 30 times of their own weight for the first time.When it is recycled to the fifth time,they can still absorb organic oils with 2 ~ 5 times of their own weight.(2)First,PU sponge was used as substrate,and surface of the PU sponge was hydrolyzed and polycondensed by the coupling agent vinyl trichlorosilane(ViTS)to obtain modified PU sponges(PU-ViTS)with reactive carbon-carbon double bonds C=C on the surface.Then,thermosensitive polymer poly N-isopropylacrylamide(PNIPAAm)were grafted onto the PU-ViTS surface by thermal initiated polymerization to obtain poly N-isopropylacrylamide modified PU sponge(PU-PNIPAAm).The results show that PNIPAAm is grafted onto PUViTS after free radical polymerization.Under the action of cross-linking agent MethyleneBis-Acrylamide(MBA),PNIPAAm hydrogel formed a three-dimensional cross-linked network structure wrapped around the sponge surface and distributed between the pores of the sponge.At 25 ?,PU-PNIPAAm has superhydrophilicity in air and superoleophobicity under water;at 45 ?,PU-PNIPAAm has high hydrophobicity in air and superlipophilicity under water.When the temperature cyclically varies between 25 ? and 45 ?,the water wettability in air and oil wettability underwater of PU-PNIPAAm also cyclically change and exhibit stable reversible state.At 45 ?,PU-PNIPAAm absorbes oil under water,when it is under water at 25 ?,the oil automatically release from the sponge without mechanical extrusion,thus achieving temperature-controlled oil/water separation.PU-PNIPAAm has a certain selection specificity for the absorption of different oils.PU-PNIPAAm has good oil absorption and oil discharge capacity for 1,2-dichloroethane and 1,2-dibromoethane during the circulating process of oil/water separation.The oil absorption at 45 ? is 7.62 ~ 13.02 times of its own weight,at 25 ° C the oil discharge is 5.49 ~ 13.46 times its own weight,and the recovery efficiency is over 70%.PU-PNIPAAm has an LCST of 31.65 ? and excellent thermal stability.The stress-strain curves show that PU-PNIPAAm could recover the original state well after extrusion,with less plastic deformation and better mechanical properties.(3)On the basis of the second part,a series of PU-PNIPAAm-x(x is the mass ratio of MBA to NIPAAm)was prepared by changing the amount of MBA.The effects of different MBA dosages on the performance of PU-PNIPAAm-x were investigated.The results show that with the increase of MBA dosage,the network structure of PU-PNIPAAm-x hydrogel became dense with the increase of cross-linking points between molecules,and the pore size of the mesh also indicate a trend of miniaturization.When the temperature is higher than LCST,the water contact angle of PU-PNIPAAm-x in air increase with the increase of MBA dosage;when the temperature is lower than LCST,the change of MBA dosage have no effect on the underwater oleophobic state of PU-PNIPAAm-x.The wettability of PUPNIPAAm-x has a good reversible stable state when the temperature cyclically varies between 45 ? and 25 ?.At 45 ?,with the increase of the number of cycles,the oil absorption ratio of PU-PNIPAAm-x to 1,2-dichloroethane and 1,2-dibromoethane shows a downward trend.With the increase of MBA dosage,the oil absorption ratio of PU-PNIPAAm-x also shows a downward trend.During the five cycles,the average oil absorption ratio of PU-PNIPAAm-x to 1,2-dichloroethane and 1,2-dibromoethane at 45 ? shows a decreasing trend with the increase of MBA dosage.The average recycling efficiency of the product shows an increasing trend with the increase of MBA dosage.The change in MBA dosage has little effect on the temperature sensitivity of PU-PNIPAAm-x.