| In recent years,with the development of high-temperature fields such as automobile,petroleum,nuclear power and aerospace,piezoelectric materials,as the core component of nondestructive testing and sustainable self-powered equipment used in these extreme environment,have become the hotspot of research.Working in such an extreme environment,materials were not only owning excellent high temperature stability,but also high piezoelectric and flexibility,In order to realize precision operation,wearable health detection and other applications of equipment.At present,the development of this kind of piezoelectric materials or films with high softness resistance and high-temperature stability have been reported,however,due to the complex preparation process,strict matching conditions and difficult coordination between piezoelectricity and high temperature stability,most researches only stalled at the experimental stage.Therefore,it is urgent to develop a flexible polymer with intrinsic high temperature stability and high piezoelectricity,realizing the excellent piezoelectric high temperature stability of devices made of this material through a simple preparation process.Up to now,there were no reports on the piezoelectric research of PBI,but its high dipole moment of 6.12 D and high glass transition temperature of 420 ℃ made PBI become the most promising piezoelectric polymer with high-temperature stability and high piezoelectric.In this paper,PBI nanofiber membranes with different electrospinning parameters and different heat treatment temperature were prepared by electrospinning.The research contents and conclusions are as follows:Firstly,by comparing the piezoelectric outputs of PBI and PVDF in different states,the piezoelectric thermal stability potential of PBI was confirmed.And then,the conformation and molecular polarity of PBI films in different states were studied by FTIR,XRD and dipole moments theoretical calculation.The results showed that,with the strengthening of the drafting degree of PBI,from powder to scratch film and then to electrospun film,There were non coplanar 0-0 linked units in PBI molecules,which changed to more coplanar 0-0 linked units through small groups rotation.With the improvement of the regularity of 0-0 linked units in the chain conformation or the coplanarity of groups,the piezoelectric properties and dipole moment of the material also increased.It was confirmed that PBI owned the potential to improve piezoelectric properties by drafting.Secondly,PBI nanofiber films were prepared by electrospinning.The effects of spinning solution concentration,rotate speed and spinning voltage on the piezoelectric,molecular conformation and thermal properties of PBI were studied,analyzed and tested by FTIR,XRD,DSC and TG.The results showed that under the electrospinning parameters of 30 wt%/900 rpm/31 kv,PBI obtained the optimal piezoelectric output and thermal stability,which all results from the formation of 0-0linked conformation with higher regularity.These phenomena confirmed that the improvement of group coplanarity in 0-0 linked conformation promoted the piezoelectric and thermal stability of materials.Finally,the piezoelectric and thermal properties of PBI electrospun films after fixed length heat treatment at different temperatures were studied.Through FTIR,XRD,DSC,TG and piezoelectric tests,it was found that the PBI films after heat treatment at 250 ℃ realized the transformation from the low-energy conformation with molecular chain cyclotron arrangement to the high-energy conformation with nearly coplanar arrangement,so that the PBI materials owned piezoelectric and thermal stability at 200 ℃,The output electric energy can directly light the commercial led and charge the capacitor.The results show that PBI has intrinsic high temperature stability and high piezoelectricity,and also has the development potential to greatly improve the piezoelectric and thermal properties through drafting and heat treatment. |
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