| Due to the rapid development of society and economy,a large amount of industrial wastewater and domestic sewage has caused great pollution and waste to water resources and the environment,films separation technology provides a highly efficient solution for water treatment.Along with the continuous expansion of films technology applications,compound semi-permeable films applications such as microfiltration,nanofiltration,forward and reverse osmosis have emerged,but most of these semi-permeable films have high raw material costs,complex preparation processes,and secondary pollution to the environment after disposal,so the preparation of low-cost,simple and environmentally friendly semi-permeable film is of great research significance.Polyvinyl alcohol（PVA）is an environmentally friendly film material that is safe,non-toxic,widely available and inexpensive.Because it swells or dissolves easily in water and has poor stability,it is decided that PVA film cannot be directly used for water treatment,so it needs to be modified to improve comprehensive performance.In this paper,to address the shortcomings of PVA which is extremely easy to swell in water,chemical crosslinking and inorganic modification were used to regulate the swelling of PVA,and the performance of preparing PVA semi-permeable film was investigated.The main research contents of this project are as follows:（1）Preparation and performance of PVA chemical crosslinking semi-permeable films.Using PVA as raw material,three crosslinking agents of ethylene glycol（EG）,glutaraldehyde（GA）and citric acid（CA）were selected to crosslink and modify the PVA semi-permeable films.Three crosslinkers and PVA were prepared with different proportions of PVA semi-permeable films,and the microscopic morphology,molecular structure,hydrophobicity,water resistance,permeability and thermal stability of the films were studied.Combined with infrared data analysis,the results show that the crosslinking reaction between the crosslinking agent and the PVA occurs,which makes the PVA films form a crosslinked network structure,the structure of the film is denser,and the thermal stability is improved to a certain extent.From the contact angle and swelling rate data,it is known that the contact angle of pure PVA is about 45°,the swelling rate is as high as 1024%,and after several crosslinker modifications,the hydrophilicity of the film has decreased,and the swelling rate is controlled within 600%,which plays a certain control role in the swelling of the films.Among them,when ethylene glycol is a crosslinker,the performance of E0.09P semi-permeable film is the best;when glutaraldehyde is a crosslinker,the performance of G0.05P semi-permeable film is the best;when citric acid is a crosslinker,C0.07P semi-permeable film performance is the best.（2）Preparation and performance of organically modified PVA crosslinked semi-permeable films.To improve the water resistance of PVA and control its swelling degree,the optimal proportion of crosslinker is used,and the polyurethane（PU）and polyvinyl alcohol with excellent mechanical properties and good water resistance are introduced for organic blending,and the amount of PVA added is changed for composite semi-permeable film preparation.Its microscopic morphology,molecular structure,hydrophobicity,water resistance,permeability and thermal stability have been studied.The analysis found that the addition of organic PU had a certain impact on the swelling rate and transmission performance of PVA,the overall swelling rate decreased,and the on-time of water molecules on the film was prolonged.The semi-permeable film Polyvinyl alcohol（PVA）is a new generation of semi-permeable film,PVA material is safe and non-toxic,excellent film-forming and wide range of sources,the fly in the ointment is that it is very easy to swell or dissolve in water,the stability is poor,so it is of great significance to modify the preparation of low cost,simple process,swelling controllable PVA-based composite semi-permeable film.In this paper,because of the defect that PVA is extremely easy to swell in water,the chemical crosslinking and organic-inorganic blending methods are used to modify PVA,and regulate the swelling degree of PVA,and study the performance of the preparation of PVA semi-permeable films.the film screened out is also different,combined with all the data analysis,it can be seen the performance of EP0.11P,GP0.13P,CP0.11P composite semi-permeable film is the best.（3）Preparation and performance of inorganic-organic composite modified PVA crosslinked semi-permeable films.Nano-silica（Si O2）was used to in chemical crosslinking modification of PVA,and different proportions of SP semi-permeable films were prepared by adding nano-silica sol to PVA,and 7%was further optimized and determined to be the optimal Si O2addition ratio,at this time,the contact angle of the films was 63.8°,the swelling rate was 833.33%,and the time required for water molecules to conduct the films was 60 s.Based on the optimal Si O2 ratio,PU was added for inorganic and organic compounding,SPP composite semi-permeable films with different PVA ratios were prepared,and the swelling rate and transmittance of the films were studied.The results show that the performance of the SP0.09P composite semi-permeable film is the best,the contact angle of the film is 62.15°,the swelling rate is50.00%,and the time required for water molecules to conduct the film is 150 s.The addition of PU effectively reduces the swelling of the film,nano silica sol is a good dispersant,and the thermogravimetric curve shows that Si O2,PVA and PU synergistic effect can significantly improve the thermal stability of PVA semi-permeable film.（4）Application study of PVA semi-permeable films.The prepared EP0.11P semi-permeable films had a good interception effect on salty wastewater,the reception rate is 88.36%.And by studying the relationship between the conductivity and concentration of the electrolyte,the concentration of the diffusion solution can be known according to the measured conductivity,and the pore size after the expansion of the semi-permeable films can be inferred according to the conductivity of the solution through different films at the same time;At the same time,in order to verify the practicability of the modified films,the semi-permeable films and copper electrodes prepared by different types of optimal formulations were assembled into thin-films thick difference batteries,and the discharge performance of the samples under the same experimental conditions was investigated,and the discharge differences of different formulations of semi-permeable films in the battery were explored,of which EP0.11P semi-permeable film was the best application in the battery;different proportions of Si O2/PVA/PU composite semi-permeable films were selected to treat organic wastewater,The results show that the absorbance of the solution intercepted by Si O2/PVA/PU composite semi-permeable film is significantly lower than that of the original methylene blue solution,and the composite membrane can block most of the macromolecular organic pollutants and play a good role in wastewater treatment.In summary,the chemical crosslinking and inorganic modification of PVA can obtain a semi-permeable film material with excellent performance and swell control,which lays a theoretical foundation for the application of PVA semi-permeable films in seawater desalination and sewage reuse industries.Figure[59]table[31]reference[114]... |
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