Preparation And Properties Of PU/PVDF Blend Films

Polyurethane(PU),as a membrane material,has been widely used in leather,clothing,industrial filtration and other fields.The traditional wet PU films are limited in application because it’s easy to form dense surface layer and large pores in the film-forming process,and the PU films have poor air permeability and moisture permeability.In this paper,we studied the compatibility of PU and PVDF.The PU/PVDF blend films were prepared by wet film formation method and improve the properties of PU films by adding PVDF.Ultrasonic atomization method is used to change the shape of the coagulation bath,and the liquid water is changed into a dispersed water mist.The contact area and exchange speed of the solvent and the non-solvent are changed,so the micro pore morphology and performance of the blend films were improved.The research results are as follows:(1)According to the polymer blending compatibility mechanism,the compatibility of PU and PVDF blends was predicted by solubility parameter method,and the polymer compatibility was determined by absolute viscosity method and cloud point phase diagram method.According to the solubility parameter prediction,the PU/PVDF blend system should be a partially compatible system.The viscosity curve of PU/PVDF blend system is non-S and non-linear by viscosity method.It shows that PU/PVDF blend system belongs to partial compatibility system,which is consistent with the prediction of solubility parameters.By plotting the cloud point phase diagrams of different ratios of PU/PVDF blends,it was found that when PU/PVDF=80/20,the amount of non solvent used was the least and the compatibility of the blends was the best.(2)The PU/PVDF blend films were prepared by wet film formation method.It was found that the microporous structure of the blend films changed significantly compared with the pure PU membrane after adding PVDF.The number of micropores is obviously increased,the irregular macropores are reduced,and the"sponge-like"micropores are increased.The microporous structure which can connect with each other was formed,and the permeability and mechanical properties of the blend films were improved.The contact angle of blend films increased with the increase of PVDF content,which enhanced the waterproof and anti pollution performance of films.When PU/PVDF=80/20,the air permeability of the blend film is 7.945mm/s,which is 227.50%higher than that of the pure PU films.The moisture permeability is 1502.43g/m~2·24h,which is11.13%higher than that of the pure PU films.The porosity is 80.1%,which is 16.92%higher than that of the pure PU films.The breaking strength is 1.72MPa,which is 81.05%higher than that of the pure PU films.The elongation at break is 501%,which is 11.13%higher than that of the pure PU films.(3)Compared with the traditional wet blend films,the pore structure of the blend films prepared by ultrasonic atomization technology was obviously improved.The permeability of UA-PU/PVDF blend films was tested,and it was found that the permeability of the blend films was increased by 128.03%,97.56%,54.51%,192.85%and 228.77%with PVDF content from 0%to 40%,and the highest permeability was 12.276mm/s.The moisture permeability of UA-PU/PVDF increased by 96.15%、84.68%、102.88%、98.90%and 90.84%with PVDF content from 0%to 40%.we analyzed the moisture permeability mechanism of the blend films and the effect of interfacial micropores on the moisture permeability of the blend films.The mechanical properties of UA-PU/PVDF blend membranes were tested.It was found that the fracture strength and elongation at break were significantly improved compared with the traditional wet method.It shows that the improvement of microporous structure enhances its mechanical properties.By observing the DSC curve of UA-PU/PVDF blend film,it is found that the melting enthalpy is increased compared with the traditional wet method,indicating that the ultrasonic atomization method is helpful to the formation of PVDF crystals.