# Improving the Physical Properties of Nanofibers Prepared by Electrospinning from Polyvinyl Chloride and Polyacrylonitrile at Low Concentrations

Authors: Salih Abbas Habeeb; Baseem Ali Nadhim; Ban Jawad Kadhim; Mohammed Salam Ktab; Ali Jawad Kadhim; Farqad Saleem Murad
Journal: Advances in Polymer Technology
 (2023)

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## Abstract

In this study, both polyvinyl chloride (PVC) and polyacrylonitrile (PAN) were dissolved in dimethyl formaldehyde (DMF) with 8 wt. % concentrations at 25 : 75, 50 : 50, and 75 : 25 of PVC: PAN blending. For the investigation of the homogeneity and compatibility of mixture polymer solutions, it is examined by rheological properties such as viscosity, shear stress, shear rate, and calculation of the flow behavior index, while the investigation of the stability and high density of nanofibers without beads used field-emission scanning electron microscopy (FE-SEM), Fourier transform near-infrared spectroscopy (FT-NIR), X-ray diffraction (XRD), and differential scanning calorimetry-thermogravimetric analysis (DSC-TGA). The results show that blending of PAN with PVC leads to improving of the electro spun ability of PVC with more stability, and the mean nanofiber diameter was90.873±40.82nm at 25 : 75 PVC: PAN. Moreover, mechanical properties are ultimate tensile strength and modulus of elasticity decreasing with decreasing the blending ration from pure PVC to 75 : 25 PVC: PAN nanofibers by 71% and 83%, respectively, while the elongation at break increases by 79%, and decomposition temperatures decreased from 451.96 to 345.38°C when changing the PVC content from pure PVC to 25 : 75 PVC: PAN. On the other hand, changing of the nanofiber behavior from hydrophobicity to hydrophilic increased the PAN content in PVC: PAN blends. Furthermore, the low interaction between the chains of polymers and the crystallinity (%) and crystalline size (nm) of blend nanofibers slightly decreased compared to the pure polymers. According to all tests, the 25: 75 PVC: PAN was the best blending ratio, which gave a more stable nanofiber produced at low concentrations and more compatible between the PVC and PAN.


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## Body

## 1. Introduction

Each polymer has special properties or advantages that differ from the other polymer properties, for improving the performance of the polymer and enabling it to obtain new properties. It can be blended with another polymer to obtain a blending that combines the new properties with the properties of the original polymer [1, 2]. The importance of blending polymers has increased in recent times to improve the performance or reduce the products cost of polymers due to the biomedical [3, 4] and increase in engineering applications [5, 6]. Viscosity is an important parameter that directly affects the productivity and uniformity of nanofibers produced from polymeric mixtures using the electrospinning technique, which has a low surface area, if the viscosity is high [7, 8]. Therefore, the value of the electric applied voltage must be sufficient to exceed the surface tension of the polymeric solution and form a jet of fibers [8, 9]. In addition, the properties of the fibers produced from polymeric mixtures such as the morphological properties represented by the diameter of the fibers and the formation of beads with the fibers deposited on the collector are related to the properties of the solvent and the concentration of the polymer [10]. PVC nanofibers are among the most important polymeric nanofibers suitable for applications such as air purification systems, sensors, reinforcement compound, tissue engineering, energy storage systems, optical, drug delivery, catalyst, and water treatment due to the cheap and easily accessible polymer in the market [11].Polyvinyl chloride is one of the polymers that possesses high mechanical properties due to in addition of this polymer that is a stiffener [12] and poor hydrophilicity [13]; therefore, Alnaqbi et al. blended polystyrene and polyvinyl chloride to obtain more felsitic properties [14]. Moreover, it is blended with a lot of polymers such as ethylene vinyl acetate (EVA), polyvinylidene fluoride (PVDF), and chlorinated polyvinyl chloride (CPVC) to improve the performance of PVC membrane for many engineering applications [12, 15]. Solvents play an important role in controlling the surface tension, conductivity, and dielectric constant and make polymeric solutions suitable for electrospinning [16]. Many researchers have used a mixture of solvents such as tetrahydrofuran (THF) and dimethylformamide (DMF) for dissolving high concentrations of polymer PVC mixtures in different ratios, for example, Chiscan et al. used THF: DMF 4 : 1 v/v [17], and Zhong et al. used THF: DMF 7 : 3 w/w [18]. THF solvent has a low boiling point, which leads to rapid evaporation of the solvent and an increase in the solidification rate of the fibers, which leads to unstable jet [19, 20], while DMF has high boiling point [16]; also, the diameters of nanofibers decrease with increasing boiling point and solvent density [21]. The production of nanofibers from polymers with low concentrations leads to the production of unstable fibers accompanied by the formation of beads on the surface of the fibers because of the decrease in the surface tension of the solution and the breaking of the liquid into droplets instead of pulling it into uniform fibers [22]. On the other hand, Lee et al. studied the effect of solvents on the morphological properties of PVC nanofibers by dissolving them in different proportions of a mixture of tetrahydrofuran (THF) and N,N-dimethylformamide (DMF). The researchers found that the average diameter of the fibers produced from dissolving polymer in DMF is 200 nm while the average diameter of the fiber produced in the presence of THF is 500 nm to 6 m in addition to the high porosity [23].On the other hand, mechanical properties of PVC nanofibers depend on the morphological properties, the most important of which is the diameter of the nanofiber and the speed of the spinner deposition collector. When the diameter of the nanofiber is decreased by 27% and the speed of the rotor is increased from 500 to 2500 rpm, the tensile stress and modulus of elasticity increase by 76% and 83%, respectively, and this result enhances the thermal properties of PVC nanofibers [24].Polyacrylonitrile nanofibers have good thermal stability, high surface area, and high physical properties, especially when strengthened with nanoparticles such asγ-Fe2O3, such as the ability to attract heavy metal ions from aqueous solutions or remove pollutants, and such as chemical oxygen demand, total suspended solid, and cyanide or kill bacteria from wastewater [25]. The mechanical properties of PAN nanofibers depend on the diameter of the nanofibers. Reducing the diameter of the fiber by 93% leads to an increase in tensile strength, elastic modulus, and toughness by 97%, 94%, and 40%, respectively. The crystalline properties depend on the role of inorganic nanofilters in strengthening the PAN nanofibers, which increases the engineering and medical applications [26]. The compatibility between polymer solutions greatly affects the formation of improved properties according to different compositions. The mixture of PVC/PAN is thermodynamically incompatible, but what distinguishes PAN is the ionic conductivity of the solid PAN-based polymer electrolytes, which depends on the ion mobility and not segmental motion of the polymer, in addition to the difficult obtaining thin and strong polymeric films except by mixing PVC with PAN [27]. On the other hand, the researchers, Rabiee et al., found that the blending ratio of 70/30 (PVC/PAN) represents the best concentration for the fabrication of nanofiber membranes for water purification and gives the best flux recovery ratio [28], which shows that 20-80% of the PAN in the mixture lead to improvement of the miscibility between the two polymers [29]. Therefore, the blending of the PVC with PAN is essential because PAN nanofibers are more hydrophilic than PVC nanofibers, and PAN solution produces continuous fibers when the applied voltage force exceeds the surface tension force of the solution [30, 31]. In this study, both polyvinyl chloride and polyacrylonitrile were dissolved in dimethyl formaldehyde with 8 wt. % concentrations at different blending ratios, in addition to studying the effect of polyacrylonitrile ratios on the rheological, morphological, crystalline, and thermal properties of nanofibers.


## 2. Experimental Work

### 2.1. Materials

The Sigma-Aldrich, Germany supplied commercial PAN powder with a molecular weight of 150000 g/mol. N, N-dimethylformamide (DMF, 99.7%) was purchased from ALPHA CHEMIKA, India. Poly (vinyl chloride) with chemical formula (CH2CHCl)n and average molecular weight~233,000 g/mole was supplied by Sigma-Aldrich, Germany.


### 2.2. Preparation of Solutions and Method

Dissolving polyacrylonitrile and polyvinyl chloride powders with dimethyl formaldehyde solution at a concentration 8 wt. % for each polymer using a magnetic stirrer and a temperature not exceeding 40°C and until homogeneity of the solution occurs for 45 minutes in PAN: DMF solution, while continuous mixing of the PVC: DMF solution under a temperature of 60°C until the homogeneous solution. Blending of PVC: PAN solutions with different ratios (25 : 75, 50 : 50, 75 : 25) % PVC: PAN [18]. Homogeneous solutions are prepared according to the above blending ratios for the electrospinning technique to produce nanofibers, where the solution is pumped at a flow rate 0.5 mL/h by MS-2200-Daiwha syringe infusion pump; the applying voltage, rotational speed of the collector, and the distance between the needle and the collector were 20 Kv, 600 rpm, and 20 cm, respectively.


### 2.3. Characterizations

The morphology (size, shape, and diameter) of the PVC: PAN nanofiber was evaluated using field-emission scanning electron microscopy (FE-SEM) (MIRA3, TESCAN FRANCE). Using the digitizer image analysis software application, the average diameter with standard deviation (SD) was estimated, and the frequency histograms of the diameter distribution of the nanofibers were plotted using QI Macros (SPC Software for Excel, Six Sigma Software). Mountans9 software is used to estimate the texture direction for PVC: PAN nanofibers. The viscosity of the solutions was measured by using Brookfield DV-III Ultra Rheometer United Kingdom in cP units with a shear rate range of (0.00-200) s-1. A contact angle system was used to test the wettability of the nanofiber samples by using SL200B Optical Dynamic/Static Contact Angle Meter Cambodia. Fourier transform near-infrared spectroscopy (Spectrum Two N™ FT-NIR, PerkinElmer, Inc.,USA) was used to characterize the electrospun within the sample range of 400–4,000 cm-1.The crystal structures of the samples were investigated by the X-ray diffraction (Philips PANalytical–X’Pert High Score Plus, Almelo, The Netherlands) at room temperature and used the X-ray tube: Cu (Kα=1.54060 Å), generator settings: 30 mA, at 40 kV, and 2θ=9.9250°-80.0750°, and step size (°2Theta): 0.0500). The thermal analysis as DSC-TGA of electro spun nanofibers used SDT Q600 V20.9 Build 20-USA, thermal gravimetric Universal V4.5A, TA Instruments, New Castle, DE, USA. The tensile properties of the nanofibrous structures were obtained using the Hi-Zwick model 1446-60-Germany of the universal testing machine (UTM). The samples were prepared according to the ASTM D-638-14 standard (2.0 cm in length, mounted on the clamps to be tested at the speed of 5 mm/min until the sample broke) with three samples for each composition.


## 2.1. Materials

The Sigma-Aldrich, Germany supplied commercial PAN powder with a molecular weight of 150000 g/mol. N, N-dimethylformamide (DMF, 99.7%) was purchased from ALPHA CHEMIKA, India. Poly (vinyl chloride) with chemical formula (CH2CHCl)n and average molecular weight~233,000 g/mole was supplied by Sigma-Aldrich, Germany.


## 2.2. Preparation of Solutions and Method

Dissolving polyacrylonitrile and polyvinyl chloride powders with dimethyl formaldehyde solution at a concentration 8 wt. % for each polymer using a magnetic stirrer and a temperature not exceeding 40°C and until homogeneity of the solution occurs for 45 minutes in PAN: DMF solution, while continuous mixing of the PVC: DMF solution under a temperature of 60°C until the homogeneous solution. Blending of PVC: PAN solutions with different ratios (25 : 75, 50 : 50, 75 : 25) % PVC: PAN [18]. Homogeneous solutions are prepared according to the above blending ratios for the electrospinning technique to produce nanofibers, where the solution is pumped at a flow rate 0.5 mL/h by MS-2200-Daiwha syringe infusion pump; the applying voltage, rotational speed of the collector, and the distance between the needle and the collector were 20 Kv, 600 rpm, and 20 cm, respectively.


## 2.3. Characterizations

The morphology (size, shape, and diameter) of the PVC: PAN nanofiber was evaluated using field-emission scanning electron microscopy (FE-SEM) (MIRA3, TESCAN FRANCE). Using the digitizer image analysis software application, the average diameter with standard deviation (SD) was estimated, and the frequency histograms of the diameter distribution of the nanofibers were plotted using QI Macros (SPC Software for Excel, Six Sigma Software). Mountans9 software is used to estimate the texture direction for PVC: PAN nanofibers. The viscosity of the solutions was measured by using Brookfield DV-III Ultra Rheometer United Kingdom in cP units with a shear rate range of (0.00-200) s-1. A contact angle system was used to test the wettability of the nanofiber samples by using SL200B Optical Dynamic/Static Contact Angle Meter Cambodia. Fourier transform near-infrared spectroscopy (Spectrum Two N™ FT-NIR, PerkinElmer, Inc.,USA) was used to characterize the electrospun within the sample range of 400–4,000 cm-1.The crystal structures of the samples were investigated by the X-ray diffraction (Philips PANalytical–X’Pert High Score Plus, Almelo, The Netherlands) at room temperature and used the X-ray tube: Cu (Kα=1.54060 Å), generator settings: 30 mA, at 40 kV, and 2θ=9.9250°-80.0750°, and step size (°2Theta): 0.0500). The thermal analysis as DSC-TGA of electro spun nanofibers used SDT Q600 V20.9 Build 20-USA, thermal gravimetric Universal V4.5A, TA Instruments, New Castle, DE, USA. The tensile properties of the nanofibrous structures were obtained using the Hi-Zwick model 1446-60-Germany of the universal testing machine (UTM). The samples were prepared according to the ASTM D-638-14 standard (2.0 cm in length, mounted on the clamps to be tested at the speed of 5 mm/min until the sample broke) with three samples for each composition.


## 3. Results and Discussion

### 3.1. Rheological Properties

Ionic conductivity is one of the important properties of the polymer, which directly relates to viscosity, and polymeric solutions with low viscosity produce high ionic conductivity due to the presence of more voids in the polymer matrix. Therefore, all viscoelastic materials depend on the deformation schedule. Polymeric fluids can be classified as non-Newtonian fluids because of the decreased viscosity with increased shear rates and is considered a power law model, and the Carreau-Yasuda model is common laws for determining the flow behavior index of polymeric solutions. The Carreau-Yasuda model is the best models for determining the behavior flow index of dilute polymeric solutions, while the power law is used for limited range of shear rates [32]. The description of the behavior of polymeric solutions of PVC: PAN based on viscosity and according to the:
(1)μ=μ∞μ∘+1−μ∞μ∘1+λγan−1a,where μ∘ and μ∞ are the zero-shear-rate and infinite-shear-rate viscosities, μ is nondimensional and normalized with respect to μ∘, γ is a shear rate, a describes the transition between the zero-shear-rate viscosity and the infinite-shear-rate viscosity and a=2 for polymeric solutions, and λ is the material time constant. Carreau model is reduced to the power law model according to Equation (2) [33]:
(2)μ=Kγn−1,where K is the consistency factor, for determining the flow index (n) according to Carreau model that must be plotted to the logarithmic viscosity (μ) against logarithmic of the shear rate (γ), the interception represented by log K and slope represented by n−1. On the other hand, the flow index of polymeric solution index (n) and the consistency coefficient (K) can be determined by using the power law model according to the following equations [34]:
(3)δ=Kγn,(4)Logδ=LogK+Logγ,where (δ) shear stress, shear rate (γ), and flow behavior index (n) represent the slope, and logK represents the consistency coefficient. The study of flow technique and deformation characteristics is known as the study of rheological properties represented by the relationship of shear viscosity with the shear rate of mixing polymer solution (PVC: PAN) in different ratios. Figures 1(a) and 1(b) show a decrease in shear viscosity with an increase in shear rate by using two models, while increasing the shear stress of pure polymers and PVC: PAN blends solution with the increased shear rates as shown in Figure 2 as a result of the inhomogeneity of PVC on PAN where it represents a large deformation at 75-90% PVC [35] while a little deformation of the viscosity is observed when the ratio is (25% PVC) at low shear rate (6-96 s-1). On the other hand, the deformation or decrease in viscosity is stable at high shear rates (126-200 s-1). The ratio (25 : 75 PVC: PAN in blend solution) represents the best mixing ratio between polyvinyl chloride and polyacrylonitrile, discussed by Namsaeng et al. [36]. Figures 1(a) and 1(b) represent the relationship of shear stress with the shear rate according to power law and Carreau models for pure and PVC blends, where the shear stress increases with the increase in shear rate, indicating that the behavior of PVC blends is non-Newtonian, and the behavior of the shear stress-shear rate curves follows the power law system. Table 1 shows the results of flow index (n) according to Carreau and power law models for pure polymers and PVC: PAN blends. We noticed that all values of the flow index (n) at two models were lower than unity, but at Carreau model, there were lower values campried with flow index values at power law which indicates the best described rheological behavior of dilute polymeric solution. A more pseudoplastic or shear-thinning behavior of PVC blends with the decrease inflow index (n) values, which lead to more homogeneous and contain cross-links. 25 : 75 PVC: PAN represents the best homogeneity between PVC and PAN, and the increase in the correlation coefficients (R2) in both models indicates the homogeneity of the solutions, and we note a large variation in the values of the correlation coefficients (R2) in the power law model, while the values of the correlation coefficients (R2) in the Carreau model are consistent and regular [34, 37]. The result of (n) flow index for pure PVC at 8 wt. % is much closed to the flow index (n) of 7 wt. % of pure PVC at previous study [38].Figure 1
(a) The viscosity-shear rate curves and (b) log viscosity-log shear rate curves according to Carreau model of pure PVC, pure PAN, and PVC: PAN blending ratio solutions.
(a)(b)Figure 2
Shear stress-shear rate curves for pure polymers and different PVC: PAN blending ratio solutions.Table 1
Results of flow index (n) according to Carreau and power law models for pure polymers and PVC: PAN blends according to Equations (2) and (4) respectively.
PVC: PAN solution concentrations (wt. %)Carreau modelPower law modelFlow index (n)Correlation coefficients (R2)Flow index (n)Correlation coefficients (R2)PAN0.330.86550.72850.953625 : 750.2780.81000.78950.888750 : 500.2230.81810.789530.739775 : 250.2010.81530.856850.8166PVC0.4740.81730.718040.7886


### 3.2. Water Contact Angle

PAN is one of the important and commercially available polymers due to its ability to absorb water and is thermally stable, while PVC has a low water absorption capacity, so PVC has been mixed with PAN to improve the performance of PVC nanofibers [16]. Figure 3 shows the decrease in the water contact angle from 110.33±6.49° to 33.588±1.176° when the PVC % decreases from 100% to 25%, and thus, the behavior of the nanofibers changes from hydrophobicity to hydrophilic, which indicates that PAN nanofibers had a good hydrophilicity, discussed by Yang and Liu [39]. The addition of PAN to PVC increases the flow of pure water and improves the porosity of the membrane, when used in water treatment and formation of an interface due to the lack of mixing of PVC with PAN [29, 40].Figure 3
Changing of the water contact angles on the surface of PVC: PAN nanofibers dependent on increased of the PVC wt. % content in PVC: PAN blends.


### 3.3. Morphological Properties

One of the important factors affecting on the morphological properties of nanofibers produced from the blending of PVC with PAN is the type of solvent used such as DMF, which has a good relative vitality, high polarity, and high dielectric constant, and these properties lead to formation of low fiber diameter and low bead formation. Moreover, the high density of nanofibers is deposed on the collector [12, 41], compared with the diameters of the nanofibers produced from PVC: PAN blends by using a mixture of solvents as THF: DMF, where the diameters were at twice the size from 407 to 567 nm [36]. In this study, only DMF solvent was used to dissolve PVC and PAN at different ratios. Figure 4 and Table 2 show the effecting of PAN on morphological properties such as the size, number of bead formation, stability, and density of the nanofibers. In addition to the decrease in the average diameter (AD) with standard deviation (Stdv) and range of nanofiber diameters from 136.508±68.33nm at pure PAN nanofibers to 59.127±40.82nm at 50 : 50 PVC: PAN blend and range of nanofiber diameters from 47.62 to 309.524 nm at pure nanofiber to11.90-142.85 nm at 50 : 50 PVC: PAN blend, respectively, decreasing in the density and stability of the nanofibers when the PVC: PAN ratio blends increases (from 75 : 25 PVC: PAN to pure PVC), which is an indication of the heterogeneity of polymeric mixtures in the presence of PVC for more than 75 : 25 PVC: PAN. In addition, we noted that the pure PVC nanofibers had average nanofiber diameter 187.02±85.85nm with high bead formation, and this result agrees with the previous study [23]; also, blending the PVC with PAN produced low density of nanofibers with more bead formation at high blend ratios of PVC: PAN discussed by Mei et al. [2].Figure 4
FE-SEM images and diameter distribution histograms for (a) pure PAN, (b) 25 : 75, (c) 50 : 50, (d) 75 : 25 PVC: PAN, and (e) pure PVC nanofibers.Table 2
The results of ranges of nanofiber diameters and morphological properties of pure and blended nanofibers.
PVC: PAN ratio (%)Ranges (nm)Nanofiber morphologyPAN47.62–357.143High density of nanofibers, low beads25 : 7523.809–214.28High density of nanofibers, low beads50 : 5011.90–142.85Good density of nanofibers, high beads75 : 2535.71–190.47Low density of nanofibers, high beads, and aggregationsPVC47.62–440.48Low density of nanofibers, bigger beads


### 3.4. Fourier Transform Near-Infrared Analysis

FT-NIR spectroscopy is used to detect the interactions between polymer chains, especially when the polymeric blends are homogeneous and compatible. Figure5 represents the FT-NIR spectroscopy of the nanofibers of pure PAN, pure PVC, and 25 : 75 PVC: PAN. The spectroscopy of pure PAN indicates a strong absorption peak at 2244 cm-1 which represented stretching vibration of C≡N. In addition, a strong absorption peak at 2933 and 3418 cm-1 was found, which was indicated to C-H alkane and O-H alcohol, respectively, while the 1237, 1452, 1667, and 1738 cm-1 were indicated to vibration bands [42, 43]. Pure PVC nanofiber FT-NIR spectrum was characterized by strong peak at 1430 and 2851 cm-1 for vibration band of deformation of CH2, CH stretching vibration, and stretching C-H of CH2, respectively. Also, the stretching C-Cl at 618 and 689 cm-1 was found, while the absorption peak at 1540 was indicated for C-N amide II band. Moreover, the peaks 2330, 2358, 1730, 3300, and 3368-3797 cm-1 represented the C=C conjugated and C≡C, C=O stretch, (N-H) amines, and (O-H) alcohol, respectively [29, 44].Figure 5
FT-R-IR spectra for pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers.The FT-IR spectrum of 25 : 75 PVC: PAN nanofibers was shifted of some absorption peaks of pure PAN and PVC nanofibers; the strong peak at 2244 cm-1 for C=N nitrile group of PAN was shifted from blending polymers to 2348 cm-1, while the absorption peak at 618 and 689 cm-1 of PVC was shifted to 665 cm-1 for blend polymers. Furthermore, the some functional groups as (O-H) alcohol and (N-H) amine were found in blending of nanofibers, the result indication for molecular interactions between polymers [12].


### 3.5. X-Ray Diffraction Analysis

Figure6 shows the XRD spectra of pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers. The XRD analysis of many calculated structural parameters such as crystallinity (%), crystalline size (nm), FWHM, reflection intensity, interplanar distance (nm), and peak position (2θ) is summarized in Table 3 according to different peaks. The XRD peaks at 2θ=18.32° and 2θ=24.101° were found in the PVC [45]. It was noted that the value of 2θ at 17.8°, 19.32°, 21.16°, 21.43°, 25°, and 26.2° corresponds to pure PAN, respectively [46], while the peaks at 17.4°, 20°, 20.985°, and 21.112° correspond to 25 : 75 PVC: PAN blend. It was noted that both PNA and PVC had an amorphous behavior, and there is a poor interaction between their molecules at blending [2]. On the other hand, d-spacing was found to be slightly increased at blending of polymers, which indicated the low interaction between the PAN and PVC chains, in addition of the slightly decrease in crystallinity (%) and crystalline size (nm) at 25 : 75 PVC: PAN blend.Figure 6
XRD spectra of pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers.Table 3
Results of XRD analysis of many calculated structural parameters such as crystallinity (%), crystalline size (nm), FWHM, reflection intensity, d-spacing (d), and peak position (2θ) of pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers.
Samples2θd (nm)Rel. int. (%)FWHMCrystalline size (nm)Crystallinity (%) in (100) rel. int.Pure PAN17.7880.4982234.80.962861.219.3240.45896501.065721.160.419521001.883421.4320.4142543.30.8249250.3558946.51.127726.20.3398511.70.39921Pure PVC18.320.4838880.50.4161963.4424.1010.368961000.5761425 : 75 PVC: PAN17.40.5092436.11.426560.00200.4435984.81.252620.9850.4229884.61.299621.1120.420461001.3825Rel. int.: reflection intensity, d: d-spacing, and2θ: peak position.


### 3.6. Mechanical Properties

Both polymers have good mechanical properties, but PVC has hydrophobic properties which limit the applications of PVC nanofibers, so the blending of the PVC with PAN is essential because PAN nanofibers are more hydrophilic than PVC nanofibers, and PAN solution continuously produces fibers when the applied voltage force exceeds the surface tension force of the solution. Figure7 shows the stress-strain behavior for pure PVC, pure PAN, and blending series as 25 : 75, 50 : 50, and 75 : 25 PVC: PAN nanofibers, and Table 4 shows the tensile test results for the nonwoven pure and blend mats of PVC: PAN with many blending ratios. The results show that the mechanical properties as ultimate strength and modulus of elasticity decreases with decreasing the blending ration from pure PVC to 75 : 25 PVC: PAN nanofibers by 71% and 83%, respectively, while the elongation at break increases by 79%. On the other hand, a decrease in ultimate strength and modulus of elasticity by 38% and 51% is beside an increase in elongation at break 26% at 25 : 75 PVC: PAN, as the homogeneity is better at low mixing ratios of PVC with PAN with an improvement in these properties compared with the mechanical properties of PAN alone. In order for the good compatibility of PVC with PAN to occur the percentage of PAN in the polymer mixture should be (>20 wt%), these results are in agreement with the results in the previous study [40]. Generally, the results indicate an increase in elongation at break with less tensile strength that occurs when the PAN content increases at PVC: PAN nanofibers [29, 47].Figure 7
Stress-strain relation for the nonwoven blend mats of PVC: PAN with many blending ratios.Table 4
Tensile test results for the nonwoven blend mats of PVC: PAN with many blending ratios (n=3).
PVC: PAN (%)Ultimate strength (MPa)Elongation at break (%)Modulus (MPa)Pure PVC17.13±0.84012.41±0.61138.034±2.3375 : 255.04±0.45822.203±1.49222.70±0.76950 : 506.93±0.70719.502±1.16435.535±2.15125 : 7510.636 ±0.97415.63±1.35568.05±1.591Pure PAN8.58±0.89912.4±1.13869.20±2.848


### 3.7. Thermal Analysis

Depending on the results of the viscosity test, we found that 75% for PAN or 25% for PVC is the best percentage in which both polymers are homogeneous. The thermal properties as DSC-TGA analysis of electro spun nanofibers of pure PVC, 25 : 75 PVC: PAN, and pure PAN were summarized in Figure8, whereas the decomposition temperatures of pure PVC, 25 : 75 PVC: PAN, and pure PAN were 451.96, 345.38, and 328.56°C accompanied by thermal energy of decomposition 2110, 103.3, and 204.8 J/g, respectively.Figure 8
TGA-DSC analysis curves for pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers.These results indicate an increase in thermal decomposition in the presence of PAN. The results of thermal analysis showed that 25 : 75 PVC: PAN is the best blending ratio for PVC/PAN because the two compounds are miscible in a greater proportion to the rest of the ratios, and this blend is not compatible even in strong solvents such as DMF and increased the compatibility between the two.Polymers are at high percentages of PAN [39]. On the other hand, the thermal degradation contentious stable until 328.94°C, then the degradation with mass lost at two stages of degradations, the first stage dehydrochlorination and second stage are decomposition. Table 5 shows the results of thermal properties of thermogravimetric analysis data under pure nitrogen for pure PVC, pure PAN, and 25 : 75 PVC: PAN nanofibers, and the results indicated to the initial decomposition temperature Tinitial were 308, 300, and 288°C, respectively. Decreasing the initial decomposition temperature at 25 : 75 PVC: PAN and pure PAN is accompanied by the decreased of the mass lost in the first stage, where the 65% of mass loss at pure PVC while 24, 22% at pure PAN, and 25 : 75 PVC: PAN.Table 5
Results of thermal properties of thermogravimetric analysis data under pure nitrogen for pure PVC, pure PAN, and 25 : 75 PVC: PAN nanofibers.
SamplesTinitial (°C)First stageSecond stageTemperature range (%)Mass loss (%)Temperature range (%)Mass loss (%)Pure PVC308308–38565385–60016Pure PAN288288–41024410–600825 : 75 PVC: PAN300300–38022380–60017In addition, we found that all samples experience a higher mass loss in the first stage than in the second stage [48].


## 3.1. Rheological Properties

Ionic conductivity is one of the important properties of the polymer, which directly relates to viscosity, and polymeric solutions with low viscosity produce high ionic conductivity due to the presence of more voids in the polymer matrix. Therefore, all viscoelastic materials depend on the deformation schedule. Polymeric fluids can be classified as non-Newtonian fluids because of the decreased viscosity with increased shear rates and is considered a power law model, and the Carreau-Yasuda model is common laws for determining the flow behavior index of polymeric solutions. The Carreau-Yasuda model is the best models for determining the behavior flow index of dilute polymeric solutions, while the power law is used for limited range of shear rates [32]. The description of the behavior of polymeric solutions of PVC: PAN based on viscosity and according to the:
(1)μ=μ∞μ∘+1−μ∞μ∘1+λγan−1a,where μ∘ and μ∞ are the zero-shear-rate and infinite-shear-rate viscosities, μ is nondimensional and normalized with respect to μ∘, γ is a shear rate, a describes the transition between the zero-shear-rate viscosity and the infinite-shear-rate viscosity and a=2 for polymeric solutions, and λ is the material time constant. Carreau model is reduced to the power law model according to Equation (2) [33]:
(2)μ=Kγn−1,where K is the consistency factor, for determining the flow index (n) according to Carreau model that must be plotted to the logarithmic viscosity (μ) against logarithmic of the shear rate (γ), the interception represented by log K and slope represented by n−1. On the other hand, the flow index of polymeric solution index (n) and the consistency coefficient (K) can be determined by using the power law model according to the following equations [34]:
(3)δ=Kγn,(4)Logδ=LogK+Logγ,where (δ) shear stress, shear rate (γ), and flow behavior index (n) represent the slope, and logK represents the consistency coefficient. The study of flow technique and deformation characteristics is known as the study of rheological properties represented by the relationship of shear viscosity with the shear rate of mixing polymer solution (PVC: PAN) in different ratios. Figures 1(a) and 1(b) show a decrease in shear viscosity with an increase in shear rate by using two models, while increasing the shear stress of pure polymers and PVC: PAN blends solution with the increased shear rates as shown in Figure 2 as a result of the inhomogeneity of PVC on PAN where it represents a large deformation at 75-90% PVC [35] while a little deformation of the viscosity is observed when the ratio is (25% PVC) at low shear rate (6-96 s-1). On the other hand, the deformation or decrease in viscosity is stable at high shear rates (126-200 s-1). The ratio (25 : 75 PVC: PAN in blend solution) represents the best mixing ratio between polyvinyl chloride and polyacrylonitrile, discussed by Namsaeng et al. [36]. Figures 1(a) and 1(b) represent the relationship of shear stress with the shear rate according to power law and Carreau models for pure and PVC blends, where the shear stress increases with the increase in shear rate, indicating that the behavior of PVC blends is non-Newtonian, and the behavior of the shear stress-shear rate curves follows the power law system. Table 1 shows the results of flow index (n) according to Carreau and power law models for pure polymers and PVC: PAN blends. We noticed that all values of the flow index (n) at two models were lower than unity, but at Carreau model, there were lower values campried with flow index values at power law which indicates the best described rheological behavior of dilute polymeric solution. A more pseudoplastic or shear-thinning behavior of PVC blends with the decrease inflow index (n) values, which lead to more homogeneous and contain cross-links. 25 : 75 PVC: PAN represents the best homogeneity between PVC and PAN, and the increase in the correlation coefficients (R2) in both models indicates the homogeneity of the solutions, and we note a large variation in the values of the correlation coefficients (R2) in the power law model, while the values of the correlation coefficients (R2) in the Carreau model are consistent and regular [34, 37]. The result of (n) flow index for pure PVC at 8 wt. % is much closed to the flow index (n) of 7 wt. % of pure PVC at previous study [38].Figure 1
(a) The viscosity-shear rate curves and (b) log viscosity-log shear rate curves according to Carreau model of pure PVC, pure PAN, and PVC: PAN blending ratio solutions.
(a)(b)Figure 2
Shear stress-shear rate curves for pure polymers and different PVC: PAN blending ratio solutions.Table 1
Results of flow index (n) according to Carreau and power law models for pure polymers and PVC: PAN blends according to Equations (2) and (4) respectively.
PVC: PAN solution concentrations (wt. %)Carreau modelPower law modelFlow index (n)Correlation coefficients (R2)Flow index (n)Correlation coefficients (R2)PAN0.330.86550.72850.953625 : 750.2780.81000.78950.888750 : 500.2230.81810.789530.739775 : 250.2010.81530.856850.8166PVC0.4740.81730.718040.7886


## 3.2. Water Contact Angle

PAN is one of the important and commercially available polymers due to its ability to absorb water and is thermally stable, while PVC has a low water absorption capacity, so PVC has been mixed with PAN to improve the performance of PVC nanofibers [16]. Figure 3 shows the decrease in the water contact angle from 110.33±6.49° to 33.588±1.176° when the PVC % decreases from 100% to 25%, and thus, the behavior of the nanofibers changes from hydrophobicity to hydrophilic, which indicates that PAN nanofibers had a good hydrophilicity, discussed by Yang and Liu [39]. The addition of PAN to PVC increases the flow of pure water and improves the porosity of the membrane, when used in water treatment and formation of an interface due to the lack of mixing of PVC with PAN [29, 40].Figure 3
Changing of the water contact angles on the surface of PVC: PAN nanofibers dependent on increased of the PVC wt. % content in PVC: PAN blends.


## 3.3. Morphological Properties

One of the important factors affecting on the morphological properties of nanofibers produced from the blending of PVC with PAN is the type of solvent used such as DMF, which has a good relative vitality, high polarity, and high dielectric constant, and these properties lead to formation of low fiber diameter and low bead formation. Moreover, the high density of nanofibers is deposed on the collector [12, 41], compared with the diameters of the nanofibers produced from PVC: PAN blends by using a mixture of solvents as THF: DMF, where the diameters were at twice the size from 407 to 567 nm [36]. In this study, only DMF solvent was used to dissolve PVC and PAN at different ratios. Figure 4 and Table 2 show the effecting of PAN on morphological properties such as the size, number of bead formation, stability, and density of the nanofibers. In addition to the decrease in the average diameter (AD) with standard deviation (Stdv) and range of nanofiber diameters from 136.508±68.33nm at pure PAN nanofibers to 59.127±40.82nm at 50 : 50 PVC: PAN blend and range of nanofiber diameters from 47.62 to 309.524 nm at pure nanofiber to11.90-142.85 nm at 50 : 50 PVC: PAN blend, respectively, decreasing in the density and stability of the nanofibers when the PVC: PAN ratio blends increases (from 75 : 25 PVC: PAN to pure PVC), which is an indication of the heterogeneity of polymeric mixtures in the presence of PVC for more than 75 : 25 PVC: PAN. In addition, we noted that the pure PVC nanofibers had average nanofiber diameter 187.02±85.85nm with high bead formation, and this result agrees with the previous study [23]; also, blending the PVC with PAN produced low density of nanofibers with more bead formation at high blend ratios of PVC: PAN discussed by Mei et al. [2].Figure 4
FE-SEM images and diameter distribution histograms for (a) pure PAN, (b) 25 : 75, (c) 50 : 50, (d) 75 : 25 PVC: PAN, and (e) pure PVC nanofibers.Table 2
The results of ranges of nanofiber diameters and morphological properties of pure and blended nanofibers.
PVC: PAN ratio (%)Ranges (nm)Nanofiber morphologyPAN47.62–357.143High density of nanofibers, low beads25 : 7523.809–214.28High density of nanofibers, low beads50 : 5011.90–142.85Good density of nanofibers, high beads75 : 2535.71–190.47Low density of nanofibers, high beads, and aggregationsPVC47.62–440.48Low density of nanofibers, bigger beads


## 3.4. Fourier Transform Near-Infrared Analysis

FT-NIR spectroscopy is used to detect the interactions between polymer chains, especially when the polymeric blends are homogeneous and compatible. Figure5 represents the FT-NIR spectroscopy of the nanofibers of pure PAN, pure PVC, and 25 : 75 PVC: PAN. The spectroscopy of pure PAN indicates a strong absorption peak at 2244 cm-1 which represented stretching vibration of C≡N. In addition, a strong absorption peak at 2933 and 3418 cm-1 was found, which was indicated to C-H alkane and O-H alcohol, respectively, while the 1237, 1452, 1667, and 1738 cm-1 were indicated to vibration bands [42, 43]. Pure PVC nanofiber FT-NIR spectrum was characterized by strong peak at 1430 and 2851 cm-1 for vibration band of deformation of CH2, CH stretching vibration, and stretching C-H of CH2, respectively. Also, the stretching C-Cl at 618 and 689 cm-1 was found, while the absorption peak at 1540 was indicated for C-N amide II band. Moreover, the peaks 2330, 2358, 1730, 3300, and 3368-3797 cm-1 represented the C=C conjugated and C≡C, C=O stretch, (N-H) amines, and (O-H) alcohol, respectively [29, 44].Figure 5
FT-R-IR spectra for pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers.The FT-IR spectrum of 25 : 75 PVC: PAN nanofibers was shifted of some absorption peaks of pure PAN and PVC nanofibers; the strong peak at 2244 cm-1 for C=N nitrile group of PAN was shifted from blending polymers to 2348 cm-1, while the absorption peak at 618 and 689 cm-1 of PVC was shifted to 665 cm-1 for blend polymers. Furthermore, the some functional groups as (O-H) alcohol and (N-H) amine were found in blending of nanofibers, the result indication for molecular interactions between polymers [12].


## 3.5. X-Ray Diffraction Analysis

Figure6 shows the XRD spectra of pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers. The XRD analysis of many calculated structural parameters such as crystallinity (%), crystalline size (nm), FWHM, reflection intensity, interplanar distance (nm), and peak position (2θ) is summarized in Table 3 according to different peaks. The XRD peaks at 2θ=18.32° and 2θ=24.101° were found in the PVC [45]. It was noted that the value of 2θ at 17.8°, 19.32°, 21.16°, 21.43°, 25°, and 26.2° corresponds to pure PAN, respectively [46], while the peaks at 17.4°, 20°, 20.985°, and 21.112° correspond to 25 : 75 PVC: PAN blend. It was noted that both PNA and PVC had an amorphous behavior, and there is a poor interaction between their molecules at blending [2]. On the other hand, d-spacing was found to be slightly increased at blending of polymers, which indicated the low interaction between the PAN and PVC chains, in addition of the slightly decrease in crystallinity (%) and crystalline size (nm) at 25 : 75 PVC: PAN blend.Figure 6
XRD spectra of pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers.Table 3
Results of XRD analysis of many calculated structural parameters such as crystallinity (%), crystalline size (nm), FWHM, reflection intensity, d-spacing (d), and peak position (2θ) of pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers.
Samples2θd (nm)Rel. int. (%)FWHMCrystalline size (nm)Crystallinity (%) in (100) rel. int.Pure PAN17.7880.4982234.80.962861.219.3240.45896501.065721.160.419521001.883421.4320.4142543.30.8249250.3558946.51.127726.20.3398511.70.39921Pure PVC18.320.4838880.50.4161963.4424.1010.368961000.5761425 : 75 PVC: PAN17.40.5092436.11.426560.00200.4435984.81.252620.9850.4229884.61.299621.1120.420461001.3825Rel. int.: reflection intensity, d: d-spacing, and2θ: peak position.


## 3.6. Mechanical Properties

Both polymers have good mechanical properties, but PVC has hydrophobic properties which limit the applications of PVC nanofibers, so the blending of the PVC with PAN is essential because PAN nanofibers are more hydrophilic than PVC nanofibers, and PAN solution continuously produces fibers when the applied voltage force exceeds the surface tension force of the solution. Figure7 shows the stress-strain behavior for pure PVC, pure PAN, and blending series as 25 : 75, 50 : 50, and 75 : 25 PVC: PAN nanofibers, and Table 4 shows the tensile test results for the nonwoven pure and blend mats of PVC: PAN with many blending ratios. The results show that the mechanical properties as ultimate strength and modulus of elasticity decreases with decreasing the blending ration from pure PVC to 75 : 25 PVC: PAN nanofibers by 71% and 83%, respectively, while the elongation at break increases by 79%. On the other hand, a decrease in ultimate strength and modulus of elasticity by 38% and 51% is beside an increase in elongation at break 26% at 25 : 75 PVC: PAN, as the homogeneity is better at low mixing ratios of PVC with PAN with an improvement in these properties compared with the mechanical properties of PAN alone. In order for the good compatibility of PVC with PAN to occur the percentage of PAN in the polymer mixture should be (>20 wt%), these results are in agreement with the results in the previous study [40]. Generally, the results indicate an increase in elongation at break with less tensile strength that occurs when the PAN content increases at PVC: PAN nanofibers [29, 47].Figure 7
Stress-strain relation for the nonwoven blend mats of PVC: PAN with many blending ratios.Table 4
Tensile test results for the nonwoven blend mats of PVC: PAN with many blending ratios (n=3).
PVC: PAN (%)Ultimate strength (MPa)Elongation at break (%)Modulus (MPa)Pure PVC17.13±0.84012.41±0.61138.034±2.3375 : 255.04±0.45822.203±1.49222.70±0.76950 : 506.93±0.70719.502±1.16435.535±2.15125 : 7510.636 ±0.97415.63±1.35568.05±1.591Pure PAN8.58±0.89912.4±1.13869.20±2.848


## 3.7. Thermal Analysis

Depending on the results of the viscosity test, we found that 75% for PAN or 25% for PVC is the best percentage in which both polymers are homogeneous. The thermal properties as DSC-TGA analysis of electro spun nanofibers of pure PVC, 25 : 75 PVC: PAN, and pure PAN were summarized in Figure8, whereas the decomposition temperatures of pure PVC, 25 : 75 PVC: PAN, and pure PAN were 451.96, 345.38, and 328.56°C accompanied by thermal energy of decomposition 2110, 103.3, and 204.8 J/g, respectively.Figure 8
TGA-DSC analysis curves for pure PAN, pure PVC, and 25 : 75 PVC: PAN nanofibers.These results indicate an increase in thermal decomposition in the presence of PAN. The results of thermal analysis showed that 25 : 75 PVC: PAN is the best blending ratio for PVC/PAN because the two compounds are miscible in a greater proportion to the rest of the ratios, and this blend is not compatible even in strong solvents such as DMF and increased the compatibility between the two.Polymers are at high percentages of PAN [39]. On the other hand, the thermal degradation contentious stable until 328.94°C, then the degradation with mass lost at two stages of degradations, the first stage dehydrochlorination and second stage are decomposition. Table 5 shows the results of thermal properties of thermogravimetric analysis data under pure nitrogen for pure PVC, pure PAN, and 25 : 75 PVC: PAN nanofibers, and the results indicated to the initial decomposition temperature Tinitial were 308, 300, and 288°C, respectively. Decreasing the initial decomposition temperature at 25 : 75 PVC: PAN and pure PAN is accompanied by the decreased of the mass lost in the first stage, where the 65% of mass loss at pure PVC while 24, 22% at pure PAN, and 25 : 75 PVC: PAN.Table 5
Results of thermal properties of thermogravimetric analysis data under pure nitrogen for pure PVC, pure PAN, and 25 : 75 PVC: PAN nanofibers.
SamplesTinitial (°C)First stageSecond stageTemperature range (%)Mass loss (%)Temperature range (%)Mass loss (%)Pure PVC308308–38565385–60016Pure PAN288288–41024410–600825 : 75 PVC: PAN300300–38022380–60017In addition, we found that all samples experience a higher mass loss in the first stage than in the second stage [48].


## 4. Conclusion

PVC is a thermoplastic material with low thermal stability, stiffness, and brittle. These properties limit the application of the polymer compared with PAN, which has good thermal stability and good polarity. The results of the rheological properties proved that PVC: PAN blends showed incompatibility and homogeneity at high ratios of PVC, indicating that the behavior of PVC blends was non-Newtonian and more pseudoplastic or shear-thinning behavior of PVC:PAN blends. Morphological properties proved that an increase in the ratio of PAN leads to an increase in the density of nanofibers with improved stability and a decline in the formation of beads; also, the diameters of the nanofibers of the blends were less than the diameters of the nanofibers of pure polymers. On the other hand, PVC increases the water contact angle, while PAN decreased the thermal stability of PVC: PAN blends and thermal degradation contentious stable until 328.94°C. The results of FT-IR and XRD analysis proved that the bonding between PVC and PAN chains was weak, but there is good homogeneity at low ratios as 25 : 75 PVC: PAN. Moreover, the crystalline properties such as crystallinity (%) and crystalline size of the blends are lower than in pure polymers. The ultimate tensile strength and modulus of elasticity are decreasing with decreasing the PVC content in PVC: PAN blending.



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*Source: 1811577-2023-03-11.xml*