Electrospun HBPPO₈/PVA Composite Nanfibers With High Environmental Humidity Sensing Properties

Environmental humidity is one of the most important facts in many areas such as industry, agriculture, military, environmental protection as well as daily life. Humidity sensitive materials with a high property are essential for developing humidity sensor to analyze the humidity in environment. In this study, HBPPO8/PVA composite nanofibers were fabricated via electrospinnig technology using amphiphilic hyperbranched polyphenylphosphonate (HBPPPO8) as a raw material and PVA as a template. The HBPPO8 and PVA were dissolved in distilled water to get a homogeneous solution prior to the electrospinning. The morphology and the structure of the electrospun HBPPO8/PVA composite nanofibers were adjusted by controlling electrospinning parameters. The as-electrospun HBPPO8/PVA composite nanofibers mat was then cross-linked with glutaraldehyde(GA) vapor at room temperature to prevent the melting or dissolving of composite fibers when contact with water. The water absorption capacity, the water retention performance, the humidity sensitive characteristics, and the nonlinear hysteresis characteristic etc., were investigated respectively. The details are described as follows:1. The effects of electrospinning conditions including voltage, concentration of HBPPO8/PVA solution, ejection rate on the morphology and fiber structure of the electrospun HBPPO8/PVA composite nanofibers. The result shows that the HBPPO8/PVA composite nanofibers can be successfully fabricated from the HBPPO8/PVA (mass ratio 3/7) solution under the electrospinning conditions as follows:the high voltage of 21 kV, the solidified distance of 15 cm, the ejection rate of 0.4 mL·h-1, the metal needle diameter of 1.0 mm, and the temperature of 35℃. The prepared HBPPO8/PVA composite nanofibers show an excellent morphology with a diameter range of 40～140 nm.2. Crosslinking of the electrospun HBPPO8/PVA composite nanofibers was carried out in the presence of GA vapors. HCl was employed as a catalyst in the process. The influence of the crosslinking conditions on the fiber structure, fiber shape stability and mechanical properties of the electrospun HBPPO8/PVA composite nanofibers were discussed. It is clear that the cross-linked HBPPO8/PVA composite nanofibers possess an excellent morphology with high mechanical properties. Increasing cross-linking reaction time results in improving the stability and mechanical properties of the fibers. The resultant composite fibers show a good silk shape when soaked in water.The cross-linked HBPPO8/PVA composite nanofibers were employed to investigated the water adsorption capacity, the water retention performance, the humidity sensitive characteristics and the nonlinear hysteresis characteristic respectively. The results show that the cross-linked composite nanofibers possess high water vapor sensitivity, small hysteresis, wide sensing range, and high water adsorption-desorption capabilities. The prepared materials also show a good regeneration property, suggesting that the composite fibers are promising materials applied on humidity sensitive and adsrorptive materials.