High-Elongation Fiber Mats by Electrospinning of Polyoxymethylene

Abstract

Electrospinning is a recently explored simple and versatile fabrication technique for producing nano-to microscale fibers. The electrospun fiber mats possess a number of characteristics such as high specific surface area, high aspect ratio, and high porosity as a result of random deposition of the fibers, which allow a wide range of potential applications such as optoelectronics, sensor technology, catalysis, filtration, and medicine. 1,2 The mechanical properties of the electrospun fibers or mats are usually different from those of the corresponding bulk materials. Sometimes, the difference is enormous and surprising. [3][4][5] For example, Gu et al. 4 reported a Young's modulus of 50 GPa for polyacrylonitrile single nanofibers, which is much greater than that of the corresponding cast film (1.2 GPa). Kim et al. 5 observed the phenomenon of "necking" with poly(methyl methacrylate) (PMMA)/montmorillonite nanocomposite electrospun single fibers, whereas PMMA is known as a brittle plastic.Polyoxymethylene (POM) is a versatile engineering plastic. 6,7 It is widely used in automobile and electronic industries due to good properties such as good strength, stiffness, abrasion, and chemical resistance. 8,9 Although almost 100 polymer solutions or melts have been electrospun into fibers, 4 to the best of our knowledge, electrospinning of POM has not yet been reported due to presumably poor solubility in common solvents. However, POM is soluble in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which is frequently used in electrospinning of natural biopolymers such as collagen and chitin. [10][11][12][13] In this work, electrospinning of POM solutions in HFIP is investigated, and to our surprise, a very high elongation to break was observed with the POM electrospun fiber mats. Figure 1 shows the morphology of the electrospun POM mat obtained from a 5 wt % solution at 30°C with a relative humidity of 40%. The average diameter is 940 nm, and microporous structure was observed with an average pore size of 150 nm. It is well-known that microporous structure is frequently obtained when volatile solvents are used for electrospinning, 14,15 and that high relative humidity also favors formation of pores. 1,16 HFIP is a volatile solvent with a boiling point of 58°C. The formation of microporous structure in the current case is understandable, although the electrospun fibers of biopolymers reported so far have no obvious pores. [10][11][12][13] The mechanical properties of the nonwoven POM electrospun mats were measured by tensile tests after thorough drying at 40°C under vacuum, and a typical load-elongation curve is shown in Figure 2a. Elongation of 460% was observed. For comparison, the elongation at break of bulk POM such as a tensile bar obtained from injection molding is known to be 40-50%, 9 and that of the thin film cast from the same solution used for electrospinning is only 1%. Therefore, the elongation at break of the electrospun nonwoven mat is about 10-fold of that of the bulk tensile bar and about 460-fold of that of the...

Nanoplastics in the Aquatic Environment. Critical Review

“…A second speculated source is fragmentation of microplastic to smaller-sized particles eventually reaching the nanoscale (Andrady 2011). Electrospinning of engineered plastics is used to produce mats with nanoscale fibres, which when applied in products might degrade further to the nanoscale (Lu et al 2008). Polymers consist of a mixture of polymer chains of various lengths.…”

Biodegradable polyesters reinforced with triclosan loaded polylactide micro/nanofibers: Properties, release and biocompatibility

“…ANOVA and Tukey tests were performed as statistical analysis at a confidence level of 95% (p < 0.05). Fiber coated disks were fixed in 2.5% glutaraldehyde-PBS overnight at 4ºC, dehydrated by washing in an alcohol battery (30,50,70,90,95 and 100º) at 4ºC for 30 min per wash, and finally dyed with Giemsa 1% for observation in the optical microscope.…”

“…Another advantage of smaller fiber diameters is that they should lead to higher tensile strengths since the fiber surface becomes dominant over the core region with bulk-like properties, and segmental motion is more constrained when dimensions approach the polymer radius of gyration [27,29]. Finally, it must be pointed out that oriented and stretched polymer chains in electrospun samples lead to a decrease in the tensile deformation with respect to the bulk polymer [27,30]. Representative fracture surfaces of samples after mechanical testing show micro/nanofiber pullout ( Figure 6) as well as good dispersion of fibers inside the matrix.…”

X-ray Tomographic Imaging of Tensile Deformation Modes of Electrospun Biodegradable Polyester Fibers

“…Magnified images in Figures 2H-J show that before any deformation the fibers are randomly oriented within the fiber mat ( Figure 2H); however, once deformation starts, the fibers begin to reorient and align in the direction parallel to the applied force (Figures 2I,J). Rotation and realignment of fibers along direction of the strain has previously been shown in the literature (Lee et al, 2002;Pedicini and Farris, 2003;Kim et al, 2004;Lu et al, 2008;Cheng et al, 2011;Zundel et al, 2017). Closer investigation of P(3HB-co-4HB) fibers shows that majority of fiber reorientation is complete by strain of 100% and this is then followed by fiber thinning to accommodate the large strain the material displays.…”

“…Literature on the failure mechanisms of whole fiber mats is sparse. It is known that in the case of non-woven fiber mats the fibers first reorientate to the direction of the applied force, and this is then followed by fiber thinning and failure of individual fibers and hence the network (Lee et al, 2002;Pedicini and Farris, 2003;Kim et al, 2004;Lu et al, 2008;Cheng et al, 2011). The complex micro and macro-structures formed by electrospinning makes it a difficult task to explain failure mechanisms of entire fiber mats and then to compare it to individual fibers and bulk materials.…”