Preparation,Structure Control And Application Of Graphene Oxide Modified Waterborne Polyurethane Membrane

Waterborne polyurethane(WPU)showed the advantage of soft-hard segment structure adjustable,which enables WPU to be promising functional materials through the different molecular structure design.The free movement of soft segments can provide the dissolution-diffusion pathway of the organic solution,while the hard segment provides a support point for the pervaporation membrane to resist the pressure of pervaporation separation systems.Inspired by the principles of biology and separation science,the microphase composition adjustment strategy was applied to modify pervaporation pathways of WU.Two-dimensional graphene oxides as a channel-regulating material was used to investigate the bridging effect between modifier and WPU,as well as the GO dispersion property.1)Aliphatic isophorone diisocyanate(IPDI)and aromatic 2,4-toluene diisocyanate(TDI)were used for hard segment raw materials,and polyethylene glycol adipate diol(PEA)and polybutylene adipate diol(PBA)with different-CH2 lenth polyester polyols,polytetrahydrofuran ether glycol(PTMG)and polypropylene glycol(PPG)as different chain type polyether polyols were used for soft segment raw materials.Three isomers of P-phenylenediamine(PPD),M-phenylenediamine(MPD),O-phenylene-diamine(OPD)were used as post-chain extenders to prepare WPU respectively.It showed that,hydrogen bonding between hard-hard segments of the WPU prepared from aliphatic IPDI was stronger than that from the aromatic TDI,resulting in better microphase separation structure,enhanced thermal stability at low temperature,and increased pervaporation performance by 71%.Also attributed to the hard segment hydrogen bonding and linear soft segment stacking order of the polyether soft segment,rather than the polyester soft segment,the WPU-IPDI-PTMG has the better microphase separation structure,stronger thermal stability,and larger pervaporation fluxes.Compared with the other two kinds of chain extenders,more dense structures were formed in WPU-PPD membrane,due to their geometric orientation of phenylenediamine chain extenders.WPU-PPD showed more thermal stability and lower glass transition temperature,better solvent resistance and optimum selectivity to benzene when-NH2:-NCO is 1.25:1.2)A kind of polyether waterborne polyurethane membrane was modified by Graphene oxide(GO/WPU)through a facile approach at low temperature,in water phase and without surface modifier.The mechanical property,thermal stability and the impact of PV performance were studied.GO was embedded in the WPU matrix and exhibited a high orientation at high GO contents.When the GO/WPU content was 2.0 wt%,the tensile modulus of the GO-WPU film increased by 193%compared with the pure WPU,and the TG thermal stability was 30? higher than that of the WPU.In order to further regulate the permeation channel of the WU membrane,the reduction of graphene oxide were carried out by using diamine modifiers such as PPD,MPD,OPD and ethylenediamine(EDA)to control the inter-layer pathway of GO in WPU.Results indicated that the mild reduction of OPD was more conducive to expanding the GO layers.GO-OPD/WPU showed the best pervaporation performance,the separation factor was 2.27,the flux was 5.1667 kg·m-2·h-1),higher than GO-WPU(3.5344 kg·M-2·h-1).Specially,the GO-OPD/WPU membanes's flux was 2.6 times of the unmodified WPU membrane's and still maintained good stability.3)Furthermore,based on the preparation of GO/WPU,?-cyclodextrin modified graphene oxide suface structure(?CD@GO)was designed,and then the OCD@GO/WPU membrane were fabricated using the "soft-cutting" technique.The enhanced dispersibility and interfacial adhesion of GO could be gained by bridging ?-cyclodextrin.Results indicated that the oxygen-containing group on the surface of the graphene oxide were reduced,some PCD adsorbed on the surface of GO,which promoted the exfoliation of graphene layer.Then,the unique hydrophilic structure of cyclodextrin made ?CD@GO to exhibit more dispersible and higher thermal stability.The prepared ?CD@GO-WPU membrane material also has uniform cross-section.However,?CD@GO is mainly hydrogen-bonded with WPU,which restricted the movement of the segment,leading to failure in improving separation factor,but increase the flux slightly.We also prepared a ?CD@GO-PEG/WPU membrane containing a sacrificial bond by introducing a small molecule polyethylene glycol(PEG)into the interlayers.The presence of small molecular polyos improves the stress compatibility between GO and WPU,making ?CD@GO-PEG/WPU higher strength and better ductility.