Views: 55 Author: Site Editor Publish Time: 2022-11-14 Origin: Site
The hydroxyl groups on the PVA molecular chain have good hydrophilic properties, but while increasing the water flux, the membrane is easily swelled or even dissolved in water. It is necessary to consume some hydroxyl groups through cross-linking to form stable functional groups to improve the water resistance of PVA films.
Here is the content list:
l Add crosslinker
l Solution blending
Aldehydes and carboxylic acids can undergo acetalization and esterification reactions with PVA molecules to achieve permanent modification. PVA composite membrane with a glutaraldehyde cross-linking agent and focused on exploring the effect of different cross-linking degrees on the performance of the composite membrane as a fluid loss agent. The cross-linked PVA composite film formed a complex network structure, and the reduction of hydroxyl groups resulted in a corresponding reduction in easily broken hydrogen bonds, and at the same time, the movement of free water was reduced, and the film had good water resistance. The effect of formic acid on the water resistance of PVA cross-linked films was explored. Formic acid was used as a cross-linking agent to cross-link with PVA molecules to form a nanofiber network structure. The pore size of this structure is extremely small, the structure is stable, and it has good water resistance. perfluorosulfonic acid (PFSA) is also a commonly used cross-linking agent. The prepared PVA-ethyl orthosilicate (TEOS)-PFSA/polyacrylonitrile (PAN) composite membranes swelled with the increase of TEOS content. The degree of water is reduced and the water resistance is improved. This is attributed to the addition of ethyl orthosilicate, which is cross-linked with PVA and PFSA to form a stable network macromolecular structure after hydrolysis, which makes the composite membrane stably exist in water. In the process of PVA solution film formation, the added cross-linking agent will chemically cross-link with PVA molecules to form a network structure, which can improve the stability of the film; a large number of hydroxyl groups are consumed in the reaction, which greatly improves the performance of the PVA film. Swell ability in the water, thereby improving its water resistance.
The same modification purpose can also be achieved by blending the film-forming matrix with chemical groups and PVA to obtain the casting liquid, which is the same as adding a cross-linking agent. The chemical cross-linking reaction is used to improve the water resistance of the PVA film. The sulfonated polystyrene (SPS) with a sulfonation degree of 75% was blended with PVA to make a membrane. Due to the strong water absorption of the sulfonic acid group itself, the sulfonic acid group of SPS and the hydroxyl group of PVA formed sulfonic acid after heat treatment. The ester bond improves the water resistance of the SPS-PVA cross-linked film. The NCC-RGO material was prepared with nanocrystalline cellulose (NCC) modified graphene, and the PVA composite membrane was prepared by blending with the PVA solution. Due to the good hydrophilic properties of NCC itself, the water absorption rate of the PVA composite membrane was higher than that of PVA. Membranes are greatly improved. The PVA-sodium alginate (SA) composite membrane was also prepared, and the water absorption rate of the composite membrane could reach 551%. The results showed that adding SA significantly improved the water resistance of the PVA composite membrane.
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