Polyamide-6 surface cracked forms nanobers: A novel way for increasing the surface roughness, and porosity

Here away used to reduce the porosity of the nanobers, which is removing PVA nanobers from PVA/PA6 nanobers by water treatment. Measuring the porosity of the electrospun web before and after treatment by the BET method proved this. The specic surface area of the web was 60 % reduced after water treatment. Surface roughness and pore volume have reduced after water treatment. Also, I introduced BET as the method for measuring the diameters of mesopores (or lower than 100nm). I used BET to prove that the cracks can make mesopores on the nanobers. The tension applied to the jet was high and resulted in higher surface roughness. I used etching PVA with water treating to reduce the porosity of the nanobers.


Introduction
There are many methods for forming porous nano bers, which are presented in Table 1 [1]. Here, I used two methods: 1)high tension applied to the jet which could not tolerate it, and cracks made on the nano bers, and 2)removing one part. Reducing porosity by solving PVA or PEO [2][3][4] is used to reduce the porosity of the PVA/non-hydrophobic nanoweb, but here reducing the porosity for a web of PVA/ hydrophilic nano bers happened differently. It happened due to the different hydrophilicity of the rst part of the web. This product can use for applications in which we need lower porosity than usual [5]. The porosity measurements did by BET (measuring surface area and pore sizes). Cracks reduced a lot after water treatment. Also, using a hydrophilic polymer as the rst part gave the same results compared to previous works [4]. Both reducing cracks and removing the PVA resulted in porosity reduction.

Morphology of the nano bers
There is a bit difference between average diameters before and after the water etching (according to table 1) [6]. With higher resolution, the pores on the nano bers were seen. In the electrospinning process because of applying, high tension to nano bers [7][8], the cracks made on the nano bers are like mesopores but after water treatment, they are reduced. So, cracks are the new way of making mesopores. From the FESEM results, it is clear that the porosity and the pore size have reduced after removing the PVA [4]. Unfortunately, the nano bers did not get more porous after removing PVA.
Porosity and pore size measurement The porosity of the web was measured by BET [5,9], and results showed that the porosity was reduced by solving one part (according to table 2). Image processing shows the surface porosity, and BET shows the total porosity (only for mesopores which are not made usually in nano bers webs). BET adsorption and deadsorption curves showed that the pores of the nanowebs are slit-like (table 3). BET showed that the nanoweb is not porous because it is for mesopores. The cracks increased the surface roughness of the nanoweb compared to my previous work [4] so, it is a new way for increasing the surface roughness. After water treatment, the cracks changed, and the removal of PVA resulted in lower porosity. Overall, the porosity reduced after water treatment. So, this work gave a new way for making higher surface roughness on the nano bers and showed that compared to previous works using a hydrophilic polymer for hybrid nano webs or co-solution results in lower porosity. Comparing to my previous article, the speci c surface area is lower, and it is for higher nano bers diameters of this work. In p/p0 >0.6, the curves of adsorption and deadsorption are almost on each other, so the pores are open, but in my previous article was vice versa, and that means that the pores are near to micropores (<2nm) [4].
Measuring surface roughness and pore volume by Matlab By using Matlab, surface roughness [10], and pore volume were measured. They decreased according to the results ( Table 5). As you see in table 5, the threshold images show that the roughness of the nano bers decreased after water treatment. Reduction in the surface roughness is for reducing the cracks.
Measuring the orientation of the nano ber web By using Matlab the orientation of the nanowebs measured, which the results are reported below (table   6). Water treatment had not any special effect on orientation degree, but same in other works, it has been more isotropy than before etching [6]. It happened because water replaces the nano bers.

Results
From the results, electrospinning of this co-solution and solving PVA in water resulted in lower porosity. The application of this nanoweb is in applications that need lower porosity than usual. This method increased the porosity and pore size without changing the average nano ber diameter [3]. Surface roughness and pore volume reduced too. Overall, BET measures speci c surface area, and pore size diameters and gives the average diameter of the pores, which are the most, but it is not the real average, but it is only for mesopores. FESEM images are appropriate for measuring surface porosity and pore sizes. The density method is an appropriate method for investigating the overall porosity of the nanowebs, but it does not give any information about pore sizes. It was proved that using a hydrophilic polymer cannot result in increasing the porosity. My previous suggestion for reducing the porosity was 10% more successful than this work. Here cracked nano bers are interesting.

Declarations
The author declares no competing interests.