Abstract
AbstractUltralight highly porous sponges made of short electrospun polymer fibers have gained significant attention for a variety of applications. According to the established procedures, short electrospun fibers are obtained by cutting or homogenization of electrospun fibers in suspension, which yield fibers with inhomogeneous fiber length. The role of the fiber length distribution and the fiber length in the mechanical compressibility of the sponges is unknown. Therefore, as a model study, sponges made from suspensions of short electrospun poly(acrylonitrile) (PAN) fibers with controlled fiber length distribution are investigated, and the role of the fiber length distribution in the compressibility of the sponges is analyzed quantitatively. These sponges are also compared to the ones prepared by established procedure as a benchmark. It is found that the compression stress and modulus of ultralight sponges with monodisperse short fibers are respectively 32% and 45% higher than that made with polydisperse short fibers. The study also shows that sponges made from longer fibers have higher modulus in comparison to the sponges made from shorter fibers.
Highlights
As a model study, sponges made from suspensions of short electrospun poly(acrylonitrile) (PAN) fibers with controlled fiber length distribution are investigated, and the role of the fiber length distribution in the compressibility of the sponges is analyzed quantitatively
Ultralight porous 3D materials, with unique integral proper- the short fibers obtained by using mechanical cutting devices, ties of ultralow density,[1,2] low thermal conductivity,[3,4,5] high such as homogenizer, mixer, blender, grinder, exhibit uncontrolporosity,[6,7] and good mechanical properties,[8,9] exhibit a large lable length and broad length distribution represented by the high range of applications as absorption materials, in thermal insula- coefficient of variation (CV),[3,24,25,26] which is defined as the ratio of tion, electronic equipment, as scaffolds for tissue engineering, the standard deviation to the mean length
Electrospun PAN yarns consisting of about 3000 unaligned individual fibers were obtained by continuous yarn electrospinning, followed by roll-to-roll heat stretching at 160 °C and alignment of the fibers
Summary
PAN (Mn 120 000, co-polymer with 6 wt% methyl acrylate, Dolan), polyurethane (PU) synthesized in the authors’ group according to the previous report (sample no. 8 in Lit.,[37] Mn of 50 000), dimethylformamide (DMF; Fisher Chemical, 99.99%), dimethylsulfoxide (DMSO; Fisher Chemical, 99.99%), dioxane (technical grade), ethanol (technical grade), and acetone (technical grade) were used as received. The whole electrospun yarn process was operated under the light of an infrared lamp (250 W) at about 45 °C and with about 10–15% of humidity. The subsequent stretching processes were performed by a homemade roll-to-roll heat-stretching instrument consisting of three parts: a tubular furnace with one heat position zone (Heraeus, D6450 Hanau, Typ: RE 1.1, 400 mm in length, Germany), two rollers with electronic motors, and a laptop with “LV2016” controlling software for controlling the velocities of the motors. By adjusting the velocities of the two rollers by the LV2016 software, the yarn could be stretched continuously. The stretch ratio (SR) was calculated by the equation: SR = vf/vs, where vf and vs represent the velocities of fast roller and slow roller, respectively
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