Morphology and hydroscopic properties of acrylic/thermoplastic polyurethane core–shell electrospun micro/nano fibrous mats with tunable porosity

Abstract

A coaxial electrospinning set up was developed in an electrospinning machine to produce core–shell nanofibers of hydrophobic thermoplastic polyurethane (TPU) and acrylic (textile grade, hydrophilic polyacrylonitrile – PAN). The TEM images showed the average diameter of PAN/TPU to be 107 nm with a core of 65 nm while TPU/PAN core–shell nanofibers have 156 nm average diameter with 82 nm core. FTIR data confirms the presence of TPU and PAN on core–shell electrospun micro/nano fibrous mats. The PAN/TPU core–shell electrospun mat exhibited better mechanical properties compared to TPU/PAN core–shell fibrous mats. Water contact angle results indicate that the shell polymer's hydroscopic (hydrophilic/hydrophobic) property influences the surface properties of electrospun mats. The water retention value tests were also performed for all electrospun fibers. The swelling thickness and porosity change in water were studied for pure TPU and PAN/TPU core–shell electrospun mats at two different temperatures (28 °C and 45 °C) for 20 min. The PAN/TPU core–shell mat showed an increase in swelled fiber diameter and a decrease in overall porosity with time which is more prominent at higher temperature (45 °C) due to the increase in vapor pressure from the hydrophilic core to its hydrophobic shell. The average porosity was found to be decreased from 62% to 48% at 45 °C while it was decreased from 61% to 52% at 28 °C, with immersion time of 20 min. Such an effect is not observed for pure TPU mat. Porosity increases at higher temperature as this elastomer shrinks. This property of PAN/TPU core–shell electrospun membrane makes it a good candidate for smart waterproof membranes.