Alexandria Engineering Journal (2016) 55, 2975–2984

HO ST E D BY

Alexandria University

Alexandria Engineering Journal

www.elsevier.com/locate/aejwww.sciencedirect.com

ORIGINAL ARTICLE

Effect of polymer concentration on the morphology

and mechanical characteristics of electrospun

cellulose acetate and poly (vinyl chloride) nanofiber

mats

* Corresponding author at: Textile Engineering Dept., Faculty of Engineering, Alexandria University, 21544, Egypt. Tel.: +20 1225343

E-mail addresses: bethweltarus@gmail.com (B. Tarus), nermin.fadel@yahoo.com (N. Fadel), affafaloufy@yahoo.com (A. A

mmessiry@yahoo.com (M. El-Messiry).

Peer review under responsibility of Faculty of Engineering, Alexandria University.

http://dx.doi.org/10.1016/j.aej.2016.04.0251110-0168 � 2016 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Bethwel Tarus a,b, Nermin Fadel a,*, Affaf Al-Oufy c, Magdi El-Messiry d

aTextile Engineering Dept., Faculty of Engineering, Alexandria University, Alexandria, EgyptbSchool of Engineering, Moi University, Eldoret, KenyacNew Advanced Materials & Nanotechnology Lab, Textile Eng Dept., Faculty of Engineering, Alexandria University, 21544, Egyptd International Innovation & Technology Transfer Expert, Textile Engineering Department, Faculty of Engineering,

Alexandria University, Egypt

Received 20 March 2016; accepted 7 April 2016Available online 3 August 2016

KEYWORDS

Electrospinning;

Cellulose acetate (CA);

Poly (Vinyl Chloride) (PVC);

Mechanical properties;

Morphology

Abstract Cellulose Acetate (CA) and Poly (Vinyl Chloride) (PVC) nanofiber mats were

electrospun into nanofibers. The morphology and mechanical properties of nanofiber mats

were evaluated versus different solution concentrations. Solutions were prepared in mixed

solvent systems of 2:1 (w/w) Acetone/N,N-Dimethylacetamide (DMAc) and 3:2 (w/w) Acetone/

N,N-Dimethylformamide (DMF) for CA and 1:1 (w/w) Tetrahydrofuran/DMF for PVC. Scanning

electron microscopy (SEM) images revealed that a beaded fibrous structure could be electrospun

beginning at 10% CA in both Acetone/DMAc and Acetone/DMF solvent systems. The experimen-

tal results showed that smooth fibers were achievable at 14% CA in Acetone/DMAc and at 16%

CA in Acetone/DMF solvent systems. For PVC, beaded fibers were formed at 12% PVC and

smooth fibers were formed beginning at 14% PVC. Tensile strength tests showed that mechanical

properties of the nonaligned nanofiber mats were influenced by solution concentration. With

increasing solution concentration, the tensile strengths, break strains and initial moduli of the

CA nanofiber mats increased. The effect of solution concentration on the tensile strengths of nano-

fiber mats was quite significant while it did not have any considerable effect on the tensile properties

of the cast films.� 2016 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an

open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

368.

l-Oufy),

2976 B. Tarus et al.

1. Introduction

The manufacture of ultrafine fibers in the nanometer to sub-micrometer range has opened up new applications in which

fibrous materials can be used [1–4]. Many techniques for ultra-fine fiber production exist, from which one technique popu-larly known, as electrospinning has been outstanding. With

electrospinning, one can easily fabricate highly functionalnanofibrous mats with high surface area to volume ratio, highporosity and uniform morphology [5]. Materials fabricatedthrough electrospinning have found their way into numerous

applications, including food packaging, tissue engineering,wound dressing, protective clothing, high efficiency filtration,and many more [6–10]. The process is quite simple and eco-

nomical, thus has become the preferred method of choice formany in nanofiber fabrication. Electrospinning involves a highvoltage being applied on a contained polymer solution to cre-

ate electrically charged jets of solution that get acceleratedthrough a spinneret toward a grounded target that acts as acollector. These jets dry, as they approach the target forming

beads or nanofibers [11].The mechanical integrity of nanofibers, which is of main inter-

est in this study, plays an important role in the applicability ofnanofibers in many promising fields [12–14]. For electrospun

nanofiber mats, the chosen solution and process parameters[15,16], such as the gap distance between the capillary tip andthe collector, applied voltage, and hydrostatic pressure in the solu-

tion container are accompanied by a certain level of mechanicaland morphological properties. Effective control of these parame-ters would enable one to achieve optimal nanofiber mats [15–18].

Cellulose acetate (CA) is a bio-plastic prepared from natu-ral purified cellulose. The mode of processing of cellulose acet-ate greatly influences the way it can be used, for example in

films, membranes or fibers. CA in its primary form has beenreported to be easily processed by spinning or casting in solu-tion form [19]. Cellulose-based materials are currently beingused widely because of their advantages of edibility, biocom-

patibility, barrier properties, attractive appearance, low toxic-ity, low cost and environment friendliness [20]. Studiesregarding electrospinning of CA using different solvents e.g.

acetone, acetic acid, DMAc, pyridine, etc., and some of theirmixtures have been done with various results [21–24]. Tung-prapa et al. [21] studied the effects of different single and bin-

ary solvent systems on electrospun CA. It was found thatsolution concentration and the type of solvent used strongly

Figure 1 Typical electros

affected the electrospinning process and the electrospinnabilityof CA solutions. A mixed solvent system of 2:1 Acetone–DMAc has been reported to be the most versatile mixing ratio

as it allows continuous electrospinning of CA solutionsbetween 12.5% and 20% [22].

Poly Vinyl Chloride (PVC) is the third-most widely produced

synthetic plastic polymer after Polyethylene and Polypropylene[25]. The applications of PVC vary widely from food packagingto construction and plumbing. A major disadvantage in the man-

ufacture and use of PVC is its low thermal stability [26]. At hightemperatures well below its decomposition temperature, PVCloses hydrogen chloride and becomes mottled. This causes dete-rioration of some of the useful properties of the polymer [27].

Electrospinning or solvent casting can therefore be used so asto preserve these properties. A popular solvent system for electro-spinning PVC is 1:1 THF–DMF mixture [28].

In this study, PVC dissolved in 1:1 THF–DMF and CA dis-solved in 2:1 acetone–DMAc and in 3:2 acetone–DMF were elec-trospun at various solution concentrations and their morphology

and mechanical properties evaluated. The objectives were todetermine the effects of solution concentration and the solventused on the morphology and mechanical properties of the elec-

trospun nanofibrous mats. Experimental investigations were car-ried out to determine and correlate the tensile properties of theelectrospun nanofiber mats and solvent cast films of the samematerials. A potential application of the nanofiber mats would

be in food packaging where polymer films currently dominate.

2. Material and methods

2.1. Materials

Cellulose acetate (CA), with molecular weight (Mw) of 30,000and Polyvinyl Chloride (PVC), with Mw of 80,000 from Sigma

Aldrich (USA) were purchased. The used Solvents were acetone,

N,N-dimethylacetamide (DMAc) andN,N-dimethylformamide(DMF) and Tetrahydrofuran (THF). All chemicals were usedwithout further purification.

2.2. Preparation of solutions and fabrication of nanofibrous mats

and cast films

A vertical electrospinning configuration with a stationary col-

lector as illustrated in Fig. 1 was used in this study.

pinning process setup.

Effect of polymer concentration 2977

Solutions for electrospinning and film casting were pre-pared in mixed solvent systems at room temperature. Two setsof 7, 10, 12, 14 and 16 wt.% CA solutions were prepared in 2:1

(w/w) Acetone/DMAc and in 3:2 (w/w) Acetone/DMF solventsystems. PVC solutions of 12, 14 and 16 wt.% PVC concentra-tions were prepared in 1:1 (w/w) DMF/THF solvent systems.

A magnetic stirrer was used in order to achieve homogenoussolutions. The electrospinning equipment, as shown in Fig. 1,

Table 1 SEM micrographs of electrospun CA nanofibers.

Conc. 10% 12%

CA in acetone–DMAc solvent

CA in acetone–DMF solvent

PVC in THF–DMF solvent

Cardboaframe (sam

Test

Sam

ple

(a)

40 m

m

60m

m

10m

m

Figure 2 Preparation of tensile test samples; (a) test sample attached

cutting the sample holder sides.

consists of a capillary tube with a needle of small diameter, ametallic collector, and a high voltage supply. Electrospinningwas carried out at 20 kV and 20 cm vertical collection distance.

Cast films were prepared from the same solution concentra-tions as those prepared for electrospinning. Casting was doneby applying and uniformly pressing the solutions between two

glass plates and then gently and uniformly sliding the glassplates in opposite directions, eventually separating them to

14% 16%

Test

Sam

ple

rd ple

Machine Clamp

(b)

to the sample holder, (b) sample clamped onto the machine and

CA

3:2 Acetone:DMF solvent system

2:1 Acetone:DMAc solvent system

CA Nanofiber

CA Film CA Nanofiber

CA Film

Tests

- Specific tensile stress

- Initial Modulus - Work of rupture - Fiber diameter - Fiber diameter

CV%

Tests

- Specific tensile stress

- Initial Modulus

Tests

- Specific tensile stress - Initial Modulus - Work of rupture - Fiber diameter - Fiber diameter CV%

Tests

- Specific tensile stress

- Initial Modulus

7%

14%

10%

16%

12% 7%

14%

10%

16%

12%

Figure 3 Experimental design chart of CA.

2978 B. Tarus et al.

achieve uniform films on the surfaces of the glass plates. Thefilms were left for 24 h to allow the solvents to evaporate

before peeling them off from the glass surfaces.

PVC

1:1 THF:DMF solvent system

PVC Nanofiber PVC Film

Tests

- Specific tensile stress - Initial Modulus - Work of rupture - Fiber diameter - Fiber diameter CV%

Tests

- Specific tensile stress - Initial Modulus

12% PVC 14% PVC 16% PVC

Figure 4 Experimental design chart of PVC.

2.3. Nanofibers characterization

2.3.1. Morphology

Geometric properties such as fiber orientation, fiber morphol-ogy and fiber diameter were characterized using scanning elec-tron microscope (SEM) (JEOL JSM – 5300 SEM). The fiber

diameters of the beaded and smooth fibers were measureddirectly from selected SEM images and their means and coef-ficients of variation were determined.

2.3.2. Tensile tests

Tensile strength tests were done on the produced nanofibermats and cast films using a MesdanLab strength tester with

a load cell of 100 N, clamp speed of 50 mm/min and 40 mmgauge length. Five rectangular samples measuring 60 mm �10 mm were prepared for each concentration. Each test samplewas secured between two cardboard frames of a sample holder

before being clamped for testing. The sample holder was thencut at the sides by the scissors as indicated in Fig. 2.

2.4. Experimental design

Solution concentration was taken to be the principle factor tobe investigated in this study. Fiber mean diameter, nanofibrous

mat tensile strength and the initial modulus were taken as theresponse variables. Five CA solution concentrations in twosolvent systems and three PVC solution concentrations were

used. Regression analysis was used to determine the correla-tions between solution concentration and the response

variables chosen. Analysis of variance (ANOVA) was usedto determine variations between the tensile strengths of the

nanofiber mats and cast films. To account for any variabilityin fiber distribution of the different electrospun mats or bulkvariation in the cast films, Eq. (1) was used to calculate specific

tensile strengths and Young’s moduli of the samples to give theresults in Newtons/Tex (N/Tex).

Stress ðN=TexÞ ¼ Force ðNÞArea density ðg=m2Þ � width ðmmÞ ð1Þ

10% CA I

25 30 35 40 45 50 55 60 65 70 75 80 85 90 95Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

27%

31%

Freq

uenc

y (%

)

14% CA I

70 80 90 100 110 120 130 140 150 160

Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

27%

31%

35%

39%

43%

Freq

uenc

y (%

)

Figure 5 Fiber diameter distribution for CA nanofibe

Table 3 PVC nanofiber diameter.

Polymer

concentration (%)

Mean fiber diameter

(nm)

CV% of fiber

diameter

12 121 14.58

14 253 12.79

16 275 11.55

Table 2 CA nanofibers mean diameters (nm).

Polymer

concentration

(%)

CA in

acetone–

DMAc

mean fiber

diameter

(nm)

CV% of

fiber

diameter

CA in

acetone–

DMF mean

fiber

diameter

(nm)

CV% of

fiber

diameter

10 60 22.24 – –

12 99 15.99 56 17.19

14 113 16.41 73 14.80

16 122 10.3 104 12.05

Effect of polymer concentration 2979

3. Results and discussion

3.1. Effect of solution concentration and solvent used onnanofiber morphology and diameter

From the SEM micrographs, solution concentration had con-

siderable influence on the morphology of the nanofibers. Themorphology images are illustrated in Table 1. It can also beobserved that there is difference in the surface appearances

of CA nano fibers in the two solvent systems: Acetone/(DMAC) and Acetone/(DMF) (see Figs. 3 and 4).

For cellulose Acetate nanofiber mat, only discrete beadswere formed at 7% CA for both the two solvent systems. At

10% CA, beads that were connected by very fine strings wereformed. Acetone–DMAc solvent system resulted in beadedfibers at 12% CA and smooth fibers at 14% and 16% CA.

Acetone/DMF solvent system resulted in beaded fibersat 14% CA and fairly smooth fibers at 16% CA. The diame-ters of the nanofibers and their uniformity were found to

increase with the increase in solution concentration as shownin Table 2. The average diameter of electrospun smooth fiberswas found to be above 100 nm for CA in Acetone–DMAcwhich is consistent with what has been previously reported

[22] (see Table 3).Figs. 5–7 gives the diameter distribution of the nanofiber

mats.

12% CA I

70 75 80 85 90 95 100 105 110 115 120 125 130

Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

27%

Freq

uenc

y (%

)

16% CA I

95 100 105 110 115 120 125 130 135 140

Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

27%

31%

35%

Freq

uenc

y (%

)

rs electrospun from acetone–DMAc solvent system.

12% CA II

25 30 35 40 45 50 55 60 65 70 75

Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

28%

Freq

uenc

y (%

)

14% CA II

50 55 60 65 70 75 80 85 90 95

Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

Freq

uenc

y (%

)

16% CA II

70 75 80 85 90 95 100 105 110 115 120 125 130 135

Fiber diameter (nm)

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

Freq

uenc

y (%

)

Figure 6 Fiber diameter distribution for CA nanofibers electrospun from Acetone–DMF solvent system.

2980 B. Tarus et al.

For PVC Nanofiber, beaded fibers were obtained at 12%PVC while smooth fibers were achieved at 14% and 16%PVC. The diameters of the nanofibers were found to increasewith the increase in solution concentration as shown in

Table 3.The effect of solution concentration on fiber diameter is

shown in Fig. 8.

The diameter CV % for all the electrospun nanofibersdecreased with the increase in polymer concentration as shownin Fig. 9. This implies an improvement in diameter uniformity

as the concentration was increased.The formation of beads at lower polymer concentrations

and the increase in fiber diameter with increase in solution con-centration for both polymers was attributed to the changes in

viscosity of the solution. Solution viscosity is related to theextent of polymer chain molecules entanglement within a solu-tion [29]. Increase in polymer chain entanglement due to the

increase in number of polymer molecules results in an increasein its viscosity [21]. During electrospinning, a solution with lowviscosity possesses a low viscoelastic force, which is not able to

match the electrostatic, and columbic repulsion forces thatstretch the electrospinning jet. This causes the jet to partiallybreak up. Under the effect of surface tension, the high num-

bers of free solvent molecules in the solution come togetherinto a spherical shape causing formation of beads. When

solution concentration is increased, an increase in viscosityoccurs, causing an improvement in the viscoelastic force.Hence, partial breakup of the jet is prevented. The increasedpolymer chain entanglement with increase in solution concen-

tration also enables the solvent molecules to be distributedover the entangled polymer molecules leading to formationof smooth fibers and improved fiber uniformity [17].

The increase in fiber diameter and diameter uniformity withthe increase in solution concentration, other factors constant,is then as a result of the gradually increasing viscoelastic force

that limits the stretching effect of the electrostatic and colum-bic repulsion forces. The surface tension of the solvents alsoplays an important role such that, the solution concentrationat which smooth fibers can be achieved for one solvent with

a lower surface tension, may be higher for another solvent,that has a higher surface tension [11,14,30].

From regression analysis, equations relating solution con-

centration to fiber diameter at the electrospinning used condi-tions were generated. These equations were generated frombest-fit curves of solution concentration against the diameter.

Eqs. (2) and (3) give these relationships for CA in Acetone–DMAc and CA in Acetone–DMF respectively.

Diameter ðnmÞ ¼ �17; 331 � ðsoln: conc:Þ2 þ 5505:3

� ðsoln: conc:Þ � 321:13 ð2Þ

12% PVC

95 100 105 110 115 120 125 130 135 140 145

Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

28%Fr

eque

ncy

(%)

14% PVC

190 200 210 220 230 240 250 260 270 280 290 300 310 320

Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

27%

Freq

uenc

y (%

)

16% PVC

180 200 220 240 260 280 300 320 340 360

Fiber diameter (nm)

0%

4%

8%

12%

16%

20%

24%

28%

32%

Freq

uenc

y (%

)

Figure 7 Fiber diameter distribution for PVC nanofibers.

Effect of polymer concentration 2981

Diameter ðnmÞ ¼ 162:39 � lnðsoln: conc:Þ þ 393:85 ð3Þ

3.2. Effect of polymer concentration and solvent used onnanofibers mechanical properties

Many of the applications for nanofibrous mats require adequatemechanical strength [13]. Tensile strength tests were performed

on PVC and CA nanofiber mats; electrospun from solutions inAcetone–DMAc and Acetone–DMF solvent system, at differentconcentrations. These samples could be handled and prepared

for test with minimal damage on the structure of the mats.12% CA nanofiber mat in acetone–DMF was quite weak andgot damaged very easily when handled.

Mechanical failure of nonaligned nanofiber mats occurswhen the fibers get rotated and eventually break at junctionsand cohesion points between fibers. This is because the individ-ual fibers in a nonaligned nanofiber mat are all at different

angles in relation to the direction of loading [14]. Therefore,the mats have low tensile strength values and quite high strainsat break since individual fibers do not necessarily break when

the mats fail. For aligned nanofiber mats, their tensilestrengths would be higher and comparable to those of solventcast films of the same material because individual fibers would

contribute in load carrying. A study that was done on alignednanofibers and solvent cast films from chitosan found no

significant difference between their tensile properties [31](see Fig. 10).

3.2.1. Tensile strength

The breakage mechanism and fiber morphology of nanofibermats are the main reasons for the increase in tensile strength

with increase in polymer concentration.The presence of beads in the nanofiber mats at low concen-

tration causes fewer fiber to fiber interactions and increased

weakness of individual fibers resulting in generally low tensilestrength values. Beads act as defects on a fiber. Hence, fromthe present study it has been observed that the weak points

increase with the increased beads of nano fibers. As the con-centration is increased, smoother fibers with improved diame-ter uniformity are formed. This results in increased fibercohesion points, accordingly, increasing the tensile strength

as shown in Fig. 11.Eqs. (4) and (5) give the best-fit relations between the nano-

fiber mats tensile stress and solution concentration for PVC

and CA.

PVC Tensile strength ¼ 0:0248 � lnðsoln: conc:Þþ 0:0557 ð4Þ

CA Tensile strength ¼ 0:0105 � lnðsoln: conc:Þ þ 0:0254 ð5Þ

0

0.002

0.004

0.006

0.008

0 5 10 15 20

Stre

ss (N

/tex)

Strain (%)

12% CA14% CA16% CA

(a)

0

0.002

0.004

0.006

0.008

0.01

Stre

ss (N

/tex)

14% CA16% CA

050

100150200250300350

8% 10% 12% 14% 16%

Fibe

r mea

n di

amet

er (n

m)

Solution concentration (%)

CA in acetone-DMAc CA in acetone-DMF PVC

Figure 8 Fiber diameter (nm) vs. solution concentration (%).

2982 B. Tarus et al.

From the stress–strain curves, the initial difference in tensilestrength values between the CA nanofibers from the two sol-

vent systems could be attributed to the presence of a highernumber of beads on the fibers produced from Acetone–DMFsolvent system, leading to lesser fiber cohesion points. At these

low concentrations, the solution properties of CA in Acetone–DMAc favored production of fibers with less beads.

At 16% CA, the smaller diameters of the fairly smooth

nanofibers produced from Acetone–DMF solvent system cou-pled with improved diameter uniformity, meant that there washigher fiber to fiber interaction points, hence, the slightly

higher tensile strength and break strain values than the nano-fiber mat from 16% CA in Acetone–DMAc.

Therefore, the choice of solvent used for electrospinninghas an impact on the mechanical properties of the resultant

mat. Solvent properties, such as volatility, dielectric effect,conductivity, etc. dictate the solution properties at any givenconcentration, thereby, influencing nanofiber morphology,

which in turn affects the mechanical properties [17].It is expected that as solution concentration is further

increased, an optimum point would ultimately be reached

where further concentration increase would lead to diminishtensile properties. This would be due to the increasing diametercausing reduced fiber surface area to volume ratio, hence,

decreased fiber interaction points. Researchers focusing onlyon smooth nanofibers have reported a decrease in tensile prop-erties with increase in solution concentration [12].

8

13

18

23

8% 10% 12% 14% 16%

CV

(%)

Polymer Concentration (%)

CA in Acetone-DMAc CA in Acetone-DMF PVC

Figure 9 Fiber diameter CV% versus polymer concentration.

3.2.2. The initial modulus

The Young’s modulus of the nanofibrous mats increased withthe increase in polymer concentration as shown in Fig. 12. Thisrelationship can be attributed to the effect of increasing fiber

diameter, which caused the nanofibrous mats to become stiffer.Best fit equations, relating polymer solution concentration to

0 5 10 15 20 25Strain (%)

(b)

0

0.004

0.008

0.012

0.016

0 20 40 60 80

Stre

ss (N

/tex)

Strain (%)

12% PVC14% PVC16% PVC

(c)

Figure 10 Nanofiber mats stress–strain curves; (a) CA in

acetone–DMAc solvent system, (b) CA in acetone–DMF solvent

system and (c) PVC in THF–DMF solvent system.

Figure 14 Work of rupture (J/tex) vs. polymer

0

0.002

0.004

0.006

0.008

0.01

12% 14% 16%

Tens

ile S

treng

th (N

/tex)

Concentration (%)

CA in acetone-DMF CA in acetone-DMAc PVC

Figure 11 Tensile strength (N/Tex) vs. polymer concentration

(%) of electrospun nanofiber mats.

0

0.05

0.1

0.15

0.2

0.25

12% 14% 16%

Initi

al M

odul

us (N

/tex)

Concentration (%)

CA in acetone-DMAc

CA in acetone-DMFsolvent system

PVC

Figure 12 Young’s modulus (N/Tex) vs. polymer concentration

(%) for PVC and CA nanofibers.

0

0.000015

0.00003

0.000045

0.00006

10% 12% 14% 16%

Wor

k of

rupt

ure

(J/te

x)

Concentration (%)

CA in Acetone-DMAc CA in Acetone-DMF

Figure 13 Work of rupture (J/tex) vs. polymer concentration

(%) for CA nanofiber mats.

Effect of polymer concentration 2983

its Young’s modulus were generated for CA in acetone–DMAcsolvent system and PVC in THF–DMF solvent system.

CA initial Modulus ¼ 0:4488 � lnðsoln: conc:Þ þ 1:0173 ð6Þ

PVC initial Modulus ¼ 0:2245 � lnðsoln: conc:Þ þ 0:5046 ð7Þ

3.2.3. Work of rupture

From the load–extension curves, the work of rupture was cal-culated for each of the electrospun mats. The work of rupture

is important in determining the ability of a material to with-stand sudden shocks of a given energy [32]. It is determinedby the integral of the load–extension curve from zero to break.

Work of rupture ¼Z break

0

F � dl ðJÞ ð8Þ

For comparison, the specific works of rupture for the differ-ent samples were calculated.

Specific work of rupture ¼ Work of rupture

g=m2 � width ðmmÞ ðJ=texÞ ð9Þ

From the plots in Figs. 13 and 14, the work of rupture forthe electrospun nanofiber mats was seen to increase withincrease in polymer concentration. From the expression in

Eq. (8), work of rupture is directly dependent upon thestrength and elongation of the sample. As the strength andelongation of the nanofiber mats increased with increase in

the solution concentration, the work needed to cause the mate-rial to fail also increased.

4. Conclusions

The morphology and tensile properties of electrospun CA andPVC were evaluated against solution concentration. CA was

dissolved in acetone–DMAc and in acetone–DMF solvent sys-tems while PVC was dissolved in THF:DMF. Solvent castfilms of PVC and CA had their mechanical properties com-

pared to those of the electrospun nanofiber mats.As solution concentration was increased, the nanofiber

diameter, tensile strength and work of rupture increased. Thevariation in the morphology of the nanofibers was attributed

to the effect of the properties of the solution on the electrospin-ning process. Smooth and more uniform fibers obtained athigher solution concentration had better mechanical properties

concentration (%) for PVC nanofiber mats.

2984 B. Tarus et al.

compared to beaded nanofiber mats obtained at lower concen-trations. Due to the increase in tensile strength and breakingelongation with increase in solution concentration, nanofiber

mats with higher work of rupture are obtained from high poly-mer concentration solutions.

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