Effect of Humidity on the Microstructures of Electrospun Polystyrene Nanofibers

Abstract

In recent years, many researchers have been studied and developed the nanofibers which have a large specific surface area and a small pore size. The polymer nanofibers are being used or finding uses in filtration, biomedical applications including wound dressings as structural elements in artificial organs, and reinforced composites. Thus these special needs have stimulated recent studies and renewed interest in the process, quantitative technical and scientific information regarding process and product characterization are extremely limited. The electrospinning can allow producing and encouraging the utilization of nanofibers. The surface morphology of e-spun fiber is affected by many variables that involve polymer concentration, applied voltage, spinning distance, air friction, gravity and ambient parameters. This study shows the effect of relative humidity on the microstructures of the e-spun Polystyrene (PS) fiber.A PS solution is prepared from PS pellet (Aldrich, molecular weight 170,000 g/mol) which is dissolved with Tetrahydrofuran and Dimethylformamide (Junsei Co.) in the ultrasonicator. The concentration of the PS solution was 7 weight%. The Spinning occurs from the droplet of solution protruding from the 0.7 mm internal diameter of the tip. A positive electric potential is applied to the polymer blend solution by attaching the lead to the variable high voltage power supply (Chungpa EMT Inc.). It was directly connected to the copper wire located in the inside of the solution. A drum collector covered with aluminum foil is placed 10 cm vertically from the tip of the syringe as a grounded collector. The relative humidity was changed with four steps from 10 to 70%. All experiments were performed at the constant temperature-humidity chamber. The surface morphology and the diameter of the e-spun fiber were investigated by the Scanning Electron Microscope (AMRAY model 1400), Atomic force Microscope (PSIA XE-100) and the image processor (GAIA Blue).The relative humidity has shown a great influence on the fiber diameter in terms of the analysis of SEM and measurement of fiber diameter which are given in FIG. 1 and TABLE 1. When the relative humidity was 10%, e-spun fibers have the average diameter of 130 nm (FIG. 1-a), but as the relative humidity increased to 70%, the fiber diameter gradually thickened to 380 nm (FIG. 1-d). The higher relative humidity makes thicker fiber because the higher electrostatic charge on the fiber surface has the opportunity to split the fibers more. Thus it results in producing thinner fibers in the travel of the fibers towards the target. In other words, the higher moisture can produce thicker fiber due to more discharge of electrostatics on the surface of the polymer solution.

Electrospinning of poly(l-lactide-co -dl-lactide) copolymers: Effect of chemical structures and spinning conditions

“…This agrees with a recent study that the change in RH condition can change the nanofiber thickness, depending on the chemical nature of the polymer, polymer‐solvent interaction, which leads to different evaporation rates . The increase in RH typically causes an increase in fiber size and formation of surface features of spun fibers derived from nonaqueous solvent, for example, poly(acrylonitrile)/DMF, polysulfone/DMF , and polystyrene/THF . The interplay between crystallization and discharging rate of the solution jets was proposed as the origin of this behavior.…”

“…During the spinning, the applied surface charge on solution jets is interfered with and captured by moisture droplets in the surroundings, as water has higher conductivity than air. This lowers the opportunity to split the solution jets to become thinner fiber, leading to formation of larger fibers, for semicrystalline copolymers . In addition, it was reported that RH conditions affected fiber properties differently, depending on the polymer structure and interactions, due to complex interactions between the nonsolvent (water), the hygroscopic solvent, and the polymer.…”

Effects of Polarity on Electrospinning Process

“…It was determined that while the surface tension of polymer solution had linear correlation with the critical voltage of process initiation, throughput was dependent on electric conductivity [10]. Additionally, when relative humidity, which is an ambient condition, is increased, mean fiber diameters on the web are increased [11].…”

Nano Fibres by Electro spinning: Properties and Applications

“…The increase in humidity resulted in formation of circular pores in smaller quantities and a further increase resulted in non uniform pores. Kim et al 90 observed that when the relative humidity is increased, mean fibre diameter is also increased. Polyamide-6 was electrospun at temperatures ranging from 25 to 60˚C and it was found that at higher temperatures the fibre diameter decreased which was attributed to the decrease in viscosity of the solution at higher temperatures.…”