Controllable Preparation And Properties Of Humidifying Fibrous Membrane For Air Conditioning

Air relative humidity is an essential factor for the indoor air quality,which is important for people's comfort,health,and industrial production.Low relative humidity could damage the human body's skin,aggravate the growth of harmful bacteria,cause respiratory diseases,and even damage electronic equipment.Therefore,humidification is necessary for a low humidity environment.However,the humidification capacity of the commercial nonwoven humidifying membranes is insufficient to realize controllable air humidity regulation.In this paper,viscose/PET spunbonded nonwoven(NW)was used as the substrate,and the highly aligned NW/PAN micro-/nanofibrous composite membrane was successfully prepared by the moisture-assisted electrostatic spinning technology.Moreover,the hydrophilic SiO₂ nanoparticles(SiO₂NPs)were introduced to construct nanoscaled roughness on the surface of highly aligned nanofibers,further improving its water transport and evaporation performance to achieve efficient indoor humidification.The main work of our research contains the following contents:(1)The highly aligned NW/PAN micro-/nanofibrous composite membranes were successfully prepared by the moisture-assisted electrostatic spinning technology with tailoring spinning parameters.We have studied the effects of polymer content and relative humidity on the morphology and structure of nanofibers,the degree of fiber orientation,and humidification performance,and confirmed the optimal conditions.The results indicated that a stable spinning process with uniform nanofibers can be achieved by the optimized 10 wt%polymer concentration.The degree of fiber orientation was greatly improved at an ambient relative humidity of 85%,which enhanced water transport and evaporation performance,and reduced the air pressure drop.In addition,the forming mechanism of highly aligned fibrous structure was investigated.It was found that the high relative humidity-induced charge loss led to an increased degree of fiber alignment.Subsequently,the mechanisms of vertical capillary wicking and horizontal water spreading were investigated.Theoretical analysis showed that the synergistic effect between highly aligned fibrous structure and surface wettability could enhance capillary force to drive rapid water transport and evaporation,which is beneficial to the humidification performance.(2)In order to further increase the wettability of the highly aligned composite membrane,highly aligned NW/PAN-SiO₂ micro-/nanofibrous composite membranes were prepared by introducing SiO₂ NPs into PAN nanofibers.The structure,surface chemical composition,average surface roughness,and wettability of nanofibrous membranes were analyzed in detail.The results exhibited that with the increase of SiO₂ NPs content,the surface tension and conductivity of the corresponding spinning solution decreased and the viscosity increased,which led to thicker fiber diameter and larger inter-fiber pores.After introducing nanoparticles,the surface of nanofiber exhibited nanoscaled roughness feature,and its surface wettability was improved.It only takes 0.35 s for water to wet entirely.However,when the particle content further increased to 30 wt%,the particle agglomeration blocked the capillary channels,leading to decreased wettability.(3)The humidification performance of highly aligned NW/PAN-SiO₂ micro-/nanofibrous composite membrane was comprehensively evaluated.The thickness of the composite membrane was adjusted to achieve the maximum humidification capacity.The results indicated that the composite membrane had outstanding comprehensive humidification performance with a wicking height of 19.5 cm,a water absorption rate of 497.7%,a water evaporation rate of0.34 m L h^-1,and an air pressure drop of 14.4 Pa.Meanwhile,the nonwoven substrate had a certain stiffness,which could meet the demands of mechanical properties in practical humidification applications.Moreover,the increase of thickness in a certain range was beneficial to the humidification capacity,but the excessive thickness led to the increase of wind resistance and the decrease of humidification.When the thickness was 580±10?m,a maximum humidification capacity of 514 m L h^-1 was achieved,obviously better than those of commercial nonwoven humidification membranes.