Assembly of odour adsorbent nanofilters by incorporating cyclodextrin molecules into electrospun cellulose acetate webs

Behrouz Ghorani*1, Rassoul Kadkhodaee1, Ghadir Rajabzadeh1& Nick Tucker2

Emails: b.ghorani@rifst.ac.ir, r.kadkhodaee@rifst.ac.ir, gh.rajabzadeh@rifst.ac.ir, NTucker@lincoln.ac.uk

1 Department of Food Nanotechnology, Research Institute of Food Science and Technology (RIFST), Km. 12-Mashhad/Quchan Highway, P.O.Box: 91895/157/356, Mashhad, Iran

2 University of Lincoln, School of Engineering, Brayford Pool, Lincoln, LN6 7TS, United Kingdom (UK)

Corresponding author: Dr.Behrouz Ghorani, Department of Food Nanotechnology

Research Institute of Food Science & Technology (RIFST), km 12 Mashhad-Quchan Highway, Khorasan Razavi, Mashhad ,IRAN- P.O.Box : 91895/157/356 ,E-mail: b.ghorani@rifst.ac.ir ;

Phone : +98-513-5425386 ;Fax : +98-513-5425406

Abstract

A significant problem in ventilating domestic or commercial kitchens is the removal and separation of volatile compounds which we perceive as strong smells of the sort particularly emitted whilst frying food. In this research, the feasibility of preparing enriched electrospun cellulose acetate (CA)-based nanofibres containing cone-shaped molecules of beta-cyclodextrin (β-CD) for the adsorption of the very strong and sharp aldehyde odour of hexanal, which is a marker for oil and fat oxidation was investigated. A binary solvent system using acetone: DMF (2:1) was shown to be suitable for solution blending of CA with β-CD. Nanofibrous webs were continuously produced and found to be substantially free of defects such as beading, producing fibres with the average diameters of 773±50 nm in the range: 250–1.5μm. Colorimetry was used to show the entrapment of β-CD in the CA structure. The encapsulation efficiency of β-CD in the fibre structures was typically 85%. FTIR of the electrospun nanofibres examining the fingerprint region of CA indicating no structural changes in the CA during processing. Our results show that electrospun CA fibres embedded with β-CD molecules demonstrate enhanced direct adsorption of model odour material hexanal (up to 80%) indicating feasibility for use in filtration.

Keywords: electrospinning; inclusion compound; β-cyclodextrin; cellulose acetate; odour adsorption

1*Corresponding email : b.ghorani@rifst.ac.ir

1-Introduction

A widely used method for the commercial production of nanoscale materials is

electrospinning, a process producing long fibres with diameters that are commonly less

than 1µm [1]. The electrospinning process was first developed in the late nineteenth

century, attempts were made to scale up and commercialise in the early nineteen

hundreds. Successful commercialisation was not achieved until the 1930s when Soviet

scientists made ultrafine fibres for application in non-woven filtration media; this is still

the commonest commercial application of electrospinning [2]. As is widely reported, in

the electrospinning process, a polymer solution is drawn from a droplet at the end of a

spinneret towards an earthed collector by an externally applied electric field. During the

flight from the spinneret to the collector, the droplet is first deformed into the structure

known as a Taylor cone [3]. When the surface tension forming the droplet is overcome

by electrostatic forces within, a charged liquid stream of polymer solution is ejected

from the apex of the Taylor cone [4]. The jet is initially stretched into a linear strand,

but the flight path deviates into an expanding helix (sometime called the “whipping

instability”) during passage from the spinneret to the collector [5]. The interplay of

surface tension, electrostatic, and viscoelastic forces, electrostatic forces, viscous drag,

and gravity, all effect the properties of the jet as it stretches, and dries out into solid

fibre. Thinning of the polymer jet continues even after the solvent is evaporated and the

jet impacts on the grounded collector as a solid fibre [5]. Submicron and nanofibre

electrospun materials find specific technical application because of their high specific

surface area, small (in the nano-scale) pore size, resulting in unique physical and

mechanical properties and a consequent design flexibility for chemical or physical

surface functionalisation [6].

Cellulose acetate (CA) membranes and nanofibrous webs are of particular importance

infiltration processes because of their high specific surface area and the ability to

modify the bulk properties of filter medium when introduced as part of a multilayer

fibrous assembly [7]. CA is a polymer obtained by substituting some of the hydroxyl

groups in cellulose [8]. CA has acceptable chemical resistance, excellent mechanical

strength, and a high level of stability as well as widespread linearity and

biodegradability [9]. CA is an acetyl derivative of cellulose which can be described as

cellulose with 92% acetylation of the hydroxyl groups [8]. Previous studies concerned

with the electrospinning of CA have focused on solvent choice and the influence of

electrospinning process conditions on fibre dimensions [10-12],immobilization of

bioactive substances [13], cell culture and tissue engineering [14], nutraceutical and

drug deliverysuch as vitamins A and E [15], curcumin [16], gallic acid [17], gingerol

[18], naproxen [19],tetracycline hydrochloride [20], l-tryptophan [21], anti-

counterfeiting and pH sensitive material [22], optical device and biosensor application

[23], photocatalytic self-cleaning material [24], temperature-adaptable fabrics [25] and

purification membranes [26]. CA demonstrably possesses all the unique characteristics

of the cellulosic raw material and in addition exhibits high solubility in most organic

solvents coupled with membrane-forming capacity which gives the material clear

potential for both air and liquid filtration [7].

Currently electrospun CA webs are typically used in membrane separation technologies

based on hybrid systems. In such hybrid systems, the nanofibre web is placed either on

a support (commercial air filters of the Petryanov type), “sandwiched” between

different layers, or merged together with micro-fibres [27].

A significant problem in ventilating domestic or commercial kitchens is the removal

and separation of volatile compounds which we perceive as strong smells of the sort

emitted particularly during the frying of foods. This issue poses a difficulty in indoor

public environments that are not well externally ventilated, such as shopping malls.

High efficiency particulate air (HEPA) filters or nonwoven fabrics are widely used in

modern hospital environments [28]. However, the majority of existing air purification-

filtration systems only claim efficiencies of 70% to 80% for particulate and aerosol

adsorption– a level that does not match the efficiency of the human nose to detect

unpleasant odours. For this reason, current commercial practice is not remove

unpleasant odours, but to mask them using so-called “air fresheners” which are strongly

aromatic scents released from surfaces or combined with activated carbon elements

[29]. In other words, non-woven fabrics are not currently capable of dealing with odours

by removing them. The aim of this paper is to show the feasibility of designing and

producing CA electrospun carrier membranes using surface active molecules

incorporated on the CA fibres to efficiently trap and adsorb volatile molecules and thus

remove unpleasant odours.

Cyclodextrins (CD) are cyclic oligosaccharides consisting of α-(1,4)-linked

glucopyranose units having a truncated cone-shaped molecular structure. The three

major CDs are - α-CD with six glucose units, followed by β-CD with seven glucose

units and γ-CD with eight glucose units [30, 31]. Due to this unique molecular structure,

CD can form a variety of supramolecular assemblies by forming non-covalent host-

guest inclusion complexes with a variety of small and macro-scale molecules [32].

Inclusion complexation involves the capture of a guest molecule, totally or partially, by

a host molecule by physical forces, not by covalent bonding [33]. CDs are appropriate

host molecules owing to their structure and geometry which allow the formation of

inclusion complexes with chemicals possessing one or more benzene rings, or even

bigger compounds with side chains of a compatible size. Thus CDs have potential to be

used for filtration and separation of harmful gases and detrimental chemical/physical

species [34, 35]. An electrospun CD can potentially increase the efficiency of filters by

facilitating formation of complexes with organic compounds by exploiting the very high

specific surface area of the fibres [36]. It is possible to electrospin fibres directly from

non-polymeric systems such as CDs [37]. Electrospun derivatives of hydroxypropyl-β-

CD, hydroxypropyl-γ-CD, and methyl-β-CD have also been made [32, 37, 38]. CDs

have the ability to form inclusion complexes with functional food substances such as

antioxidants, anti-bacterials, flavours, and aromas [39]. It has been shown that the

complexation with CD enhances stability, solubility, reactivity and sustained release of

bioactive encapsulates [40]. Inclusion of complexes of vanilla, menthol and eugenol

flavour compounds, and CDs (α-CD, β-CD, γ-CD) makes the preparation more stable at

high temperatures and increases shelf life if they are electrospun into PVA nanofibres

[40]. Dry CD pellets (typically 12mm diameter) are used for odour control in cosmetic

products [41]. However, to the best of our knowledge, the incorporation of a CD into

electrospun fibres to exploit their potential for removal of unpleasant odours has not

been yet demonstrated, perhaps because of the high solubility of fibres made entirely

from CD. Recently it was shown that the formation of electrospun poly(ε‐caprolactone)

(PCL)/β‐CD functional nanofibres using binary solvent systems of chloroform/N,N‐dimethylformamide (DMF) in the ratio of 60:40, can effectively remove wound odours

[42]. The efficiency of wound odour absorbance by these electrospun composites was

examined using a simulated wound odour solution, consisting of butyric and propionic

acids in ethanol. Immersion tests indicated that even in suboptimal test conditions, the

nanofibres containing β‐CDs were very efficient in removing the odour [42]. In the

present study we produce β-CD functionalised electrospun CA functional fibrous

structures and we have shown that these CA/β-CD functionalised webs have the

potential to be used as molecular filters.

2-Materials and Methods

2.1 Materials

Cellulose acetate (acetyl content: 39.8% (w/w), Mw 30,000 Da) and beta-cyclodextrin

(β-CD) (purity>97%, Mw: 1134.98 Da) were sourced from Sigma-Aldrich (Australia).

Acetone (HPLC grade, ≥99.8%), ethanol (absolute, HPLC grade, ≥99.8%), N,N-

dimethylacetamide (DMAc) and dimethylformamide (DMF) (Aldrich 99 %,) were all

purchased from Sigma-Aldrich and used without any further purification. For detection

of β-CD in the CA structures phenolphthalein solution (PhP) (1%) (Mw 318.33 g/mol)

in ethanol was prepared using materials purchased from Merck (Germany). The

detection and characterization of β-CD also required a basic pH10 buffer which was

prepared using sodium hydroxide (NaOH) and disodium hydrogen phosphate

(Na2HPO4). Sodium hydroxide having a molecular weight of 40.00g/mol and

purity>99% was purchased in the form of pure anhydrous pellets from Merck

(Germany). Disodium hydrogen phosphate, anhydrous Na2HPO4 having molecular

weight of 137.99g/mol and purity>98% was also purchased from Merck (Germany). To

evaluate the feasibility of nanofibres in terms of odour adsorption, a hexanal aqueous

solution (CH3 (CH2)4CHO, Mw 100.16g/mol, ≥97%) was also sourced from Sigma-

Aldrich and used as received.

2.2 Preparation of polymer solution

To prepare spinning solutions of CA/β-CD, single and binary solvent systems were

evaluated as follows:

(1) Neat DMAc and neat DMF

(2) Acetone:DMAc (2:1),

(3) Acetone:DMF (2:1),

(4) DMAc:acetone (2:1),

(5) DMF:acetone (2:1).

The solvent systems and ratios were selected based on previously published examples

[43, 44] of the most suitable binary solvents systems for co-electrospinning of CA/β-

CD. Solutions were prepared by constant stirring at room temperature (25±5ºC). The

CA concentration in the spinning solutions was first fixed at a concentration of 16%

(w/v) to consistently evaluate the single and binary solvent systems. To optimise the

electrospinning process, the CA concentration was then varied between 12-24% (w/v)

in the selected solvent system. The β-CD content was fixed at 5% (w/v) for all the

solvent systems as the optimal solubility of β-CD. These concentrations were selected

based on previous studies to establish the most suitable condition for electrospinning

[21, 36].The suitability of each solution was assessed in terms of the freedom from gel

formation (an indication of too high a solution viscosity) during preparation of the

spinning solution and the spinnability of the resulting polymer solution. Spinnability in

this context was assessed in terms of lack of blocked spinnerets, consistent fibre

morphology, and the absence of bead and spindle defects in the web [12].

2.3 Viscosity of Polymer Solutions

The viscosities of all the prepared solutions were measured using a digital viscometer

(Brookfield DVIII Ultra, Brookfield Engineering Laboratories, Stoughton, MA, USA),

at a constant shear rate and temperature (20°C). Flow curves were acquired at shear

rates of 10–300s−1 and all solutions were assumed to be non-Newtonian. 10ml of sample

solutions were placed in a beaker (the same beaker was used for all measurements), into

which an SC4-27 spindle was immersed and rotated. Measurements were made at

constant spindle rotation speeds to evaluate the dynamic viscosities of the

electrospinning solutions [45]. All measurements were performed in triplicate and the

results presented are the average of these three readings.

2.4 Electrospinning

Electrospinning of the CA/β-CD polymer solutions was performed in horizontal

alignment with the polymer solution loaded into a 10 ml syringe connected to a blunt-

ended Luer Lock metal needle (18- Sigma-Aldrich) with an inner diameter of 0.838mm

The syringe was then mounted into a triple-head syringe pump that was connected to a

high voltage power supply (ES-Lab RN/X, ANSTCO, Iran). On the basis of previous

experimental work, the process was carried out for one hour at a constant flow rate of

1.5 ml/min at a voltage of 25kV and a tip-to-collector distance of 150mm under ambient

conditions (25±5ºC) with a relative humidity (RH) of 50%. A grounded copper plate

wrapped in aluminium foil (10cm×10cm) and mounted on two polypropylene blocks

was used as the target for the collection of specimen webs. All the parameters were

accurately controlled using a touch screen panel through the process [22]. The fibres

collected on aluminium foil were dried at 40ºC under vacuum for 24 hours to remove

the residual solvent [36].

2.5 Scanning electron microscopy (SEM) and image analysis

The morphology of electrospun fibres was observed by scanning electron microscopy

(SEM) (VEGA II, TESCAN, Czech Republic) applying an accelerating voltage of 5kV.

Prior to SEM imaging, the samples were coated with gold using a sputter coater

(POLARON E5200C) under vacuum (2mbar) for 5 minutes. The diameters of the

electrospun fibres were measured using Image-J 1.46r (USA) image visualisation

software. Average fibre diameters for the samples were determined by measuring about

50 random fibres from the SEM images [46].

The web porosity (P) was determined from binary SEM images (BMP format) that were

prepared using the technique of image thresholding and measuring the mean intensity of

the image:

(1)

Where, n is the number of white pixels and N is the total number of pixels in the binary

image.[47, 48].

2.6 Pore Size

Pore size characterisation of the as-spun webs was undertaken by capillary flow

porometry (PMI model App122 AE). The characteristic features of the pore structure

such as pore size at the bubble point and pore size distribution were calculated from =

differential pressures measured at various gas flow rates. In dry samples, the flow rate

increasing pressure increase the flow rate. With a wet sample that has been saturated

with a known surface tension liquid (in this case Galwick liquid: surface tension

P = (1−nN ) × 100

=0.015Nm-1), because all the pores are filled with the liquid, there is initially no flow.

At a certain pressure the nitrogen gas penetrates the largest pores (the Bubble point)

starting measurable gas flow through the wet sample. Increasing the pressure

progressively empties smaller and smaller pores and the flow rate consequently

increases until all the pores are empty and the flow rate through the wet sample equals

that measured through the dry sample [49].

2.7 Fourier-transform infrared (FTIR) spectroscopy

The FTIR spectrum was used to detect the β-CD in the fibre structures and to analyse

the interaction between CA and β-CD in the nanofibres. Electrospun samples were

mixed with KBr and pressed into pellets. Scanning was conducted from 4000 to

400cm−1 with a resolution of 4cm−1 and a scanning interval of 2cm−1 taking an average of

64 scans per sample using a FTIR spectrometer (Bruker Alpha FTIR, US) [12].

2.8 Inclusion complexation of β-CD with Phenolphthalein (PhP)

PhP is used as a standard to examine for CD inclusion complexation due to its high

affinity for the CD cavity [50]. This method was previously used to show the trapping

ability of β-CD functionalized electrospun fibres [36]. When the PhP solution is added

to the β-CD solution, it immediately loses its colour [50]. Therefore, for the detection of

β-CD in CA/β-CD nanofibrous structures, the inclusion complex formation of β-CD

with PhP was used to confirm the presence of β-CD in the fibre structures. Both the CA

only control sample fibres and CA/β-CD fibres were immersed into a PhP solution and

the change in absorbance of PhP was recorded as a function of time by UV–vis

spectrometry. Briefly, the CA and CA/β-CD fibres (100mg each) were carefully

removed from the aluminium foil and immersed into50ml of deionised (DI) water. The

beakers were placed in an orbital shaker (Benchmark Scientific, USA) for 240min and

shaken at 120rpm and ambient temperature (25±5ºC). The fibre samples were then removed

from the beakers; the solutions were passed through syringe filters (0.45μm) and used for

further experiments. A 1% solution of PhP in ethanol was prepared and added dropwise

(to a total of about 5ml) into 100ml of the pH10 phosphate buffer solution, producing a

pH10 alkaline PhP solution which was used as the test chemical for inclusion complexation

with the two sample solutions of CA and β-CD. 20ml of alkaline PhP solution was added

dropwise to each of the sample solutions and the corresponding change in colour was

visually observed, and analysed in the UV-Vis spectrophotometer (Chromtech-CT

5700,India) in the visible region of 400-700nm [36].

2.9 β-CD Encapsulation Efficiency

The decolourisation of the PhP solution results from host-guest complexation by β-CD

and can be used to form a calibration curve (based on the PhP absorption at

λmax=552nm) to quantify and further characterize the amount of β-CD in the electrospun

CA nanofibres.

To determine the concentration of β-CD loaded in nanofibres (mfibre), a specific weight of

each electrospun sample was suspended in 50ml of DI water (pH6.2) and then shaken in

a water bath at room temperature (25±5ºC); alkaline solution of PhP (1%) was added

dropwise to the filtered solutions and the resulting solution was analysed by UV at

552nm in triplicate and the concentration determined from calibration graphs.

Encapsulation efficiency (EE) was calculated using equation 2

where mformulation is the concentration of β-CD loaded into the initial formulation use to

produce the nanofibres [21].

2.10 Evaluation of odour adsorption by electrospun fibres

Deep-fat frying is one of the oldest and most popular food preparation methods. Fried

foods have desirable flavours, colours, and a crispy texture, which make deep-fat fried

foods very popular. Frying is a process of immersing food in hot oil engendering

contact between the oil, air, and food at temperatures in the range of 150ºC to 190ºC.

Heat transfer is facilitated through the medium of the hot cooking oil, contributing to

the both the texture and flavour of fried product [51]. Hydrolysis, oxidation, and

polymerization of the cooking oil are common chemical reactions in frying and result in

both volatile and non-volatile compounds. Most of volatile compounds boil into the

atmosphere with the team steam and those volatile compounds that remain undergo

further chemical reactions or are absorbed into the food product [51]. During cooking

by frying, such compounds as saturated and unsaturated aldehydes (such as hexanal –

EE (% )=100mfibre

mformulation

(2)

our model odour material), ketones, hydrocarbons, lactones, alcohols, acids and esters

are formed by oxidative reactions involving the formation and decomposition of

hydroperoxides [52-54]. Sulfur compounds and pyrazine derivatives may develop in the

food itself or from the interactions between the food and oil [54]. It has been reported

that certain aldehydes, ketones and other compounds could be markers for oil and fat

oxidation, and that hexanal could be an alternative marker for lipid oxidation [55].

Hexanal is a volatile compound that has been associated with the development of

undesirable flavours (very strong and sharp aldehyde odours). Hexanal is easily

detected because of its low odour threshold and is chemically related to oxidative off-

flavours [56].

To evaluate the feasibility of electrospun fibres in terms of odour adsorption, a hexanal

aqueous solution (CH3(CH2)4CHO) at a concentration of 4.6ppm was prepared in DI

water in a fume cupboard due to the high volatility of hexanal. The solution was then

poured into a vacuum glass filter (EMD Millipore™ XX1504700) equipped with an

aluminium clamp and a Hamilton syringe. The electrospun CA mats (control sample)

and CA containing β-CD molecules were accurately cut into circular discs with outside

diameter of 50mm and weight of 100mg, and then carefully inserted in the filter section

of the Millipore funnel. Note that all the air outlets were completely covered with

plastic bungs and aluminium foil so that no extraneous air could enter or leave the

system (shown in supplementary).

The experimental system was then placed inside a water bath equipped with a heating

circulator (Julabo/EH-19, USA) at a temperature of 30°C. The temperature of the

chamber was then slowly increased up to 125±5ºC, and held in this condition for 30min

until droplets of vapour were observed on the internal surface of the container. The

hexanal vapour was passed through the filters and was collected at the top of the

chamber. A Hamilton syringe (10ml volume) was carefully inserted into the air

collector chamber and held in the chamber for 15minutes, then very slowly filled with

the filtered air and immediately discharged into a gas chromatography (GC-MS) vial.

All the experiments related to the GC-MS were performed in triplicate and rapid

succession.

2.11 Molecular Analysis

The amount of hexanal in the filtered air which was passed through both the control

sample CA fibres, and β-CD functionalised electrospun CA nanofibres were analysed

using a gas chromatograph system (GC-MS) (Agilent technologies -7890A, USA)

equipped with DB-5Ms EVDX columns (30m×0.25mm i.d and 0.25μm film thickness).

The operating conditions were optimised as follows: the GC temperature program was

held at 40ºC for 5min, then increased at 10ºC/min from 40ºC to 80ºC; held at 80ºC for 1

min, then increased from 80ºC to 220ºC at 5ºC/min, and held at 220ºC for 3 min.

Helium was used as carrier gas ata flow rate of 3 ml/min; the injector temperature was

150ºC; the sample injection volume was 1μl and the split ratio was 20:1[55, 57]. The

individual compounds were identified using the library data supplied with the GC/MS

system (Wiley2001 data software) and cited literature. The expected retention time of

hexanal was 6.56min [58]. Five different concentrations: 0.2, 0.4, 0.6, 0.8, 1ppm and a

blank were prepared and linear calibration curves of hexanal plotted.

2.12 Statistical analysis

The statistical analysis of the data was performed using SPSS statistical software v. 11.5

(IBM SPSS, New York, USA). One-way ANOVA in a completely randomized design

followed by the Duncan’s multiple range test (DMRT) was used to compare any

significant differences among means at the level of p<0.05.

3. Results and Discussion

3.1 Electrospinning of CA/β-CD in single and binary solvent systems

The solubility characteristics of the polymer are of fundamental importance and are a

crucial factor in selecting suitable solvent systems for electrospinning [59]. The

selection of solvents was informed by previous studies of the solubility of CA and β-CD

[21, 60, 61] and by the Hansen theory of solubility [62, 63]. The solubility parameter (δ)

is a number that relates to the relative solvating behaviour of a specific solvent.

Hildebrand postulated that the square root of the cohesive energy density (CED) of the

material and that solubility is thus related to the internal energy of solvents. Hansen

extended the concept with a total cohesive term and hence a total solubility parameter

(δt) of the total Hildebrand value are divided into the dispersion component (δd), polar

component (δp) and hydrogen bonding component (δh) as follows[63]:

δ t=√δd2+δ p

2 +δh2 (3)

The SI unit for all Hansen parameters is MPa½. Values of δd, δp, and δh at room

temperature for a variety of CA solvents are presented in Table.1.

Table 1. Total solubility parameters (δt) of various solvents and cellulose acetate (CA) [12, 62, 64]

From Hansen, an approximately spherical zone of solubility can be constructed using a

three-dimensional coordinate system of δd, δp, and δh. The radius of that sphere, 12.40

MPa½, for CA, known as the interaction radius (R) (Table.1). For a particular solvent, a

polymer will be soluble if the distance between the solvent and the centre of the

polymer solubility sphere (D(s-p)) is less than the radius of interaction for the polymer

(D(s-p)< R) [63]. Accordingly, acetone, DMAc, DMF and perhaps methanol would be

expected to dissolve CA, because the distance (D(s-p)) is less than the radius of

interaction (R) of CA (Table.1).

β-CD is highly soluble in dimethyl sulfoxide (DMSO),DMF,DMAc, and has varying

solubility in water from 25ºC to 60ºC, but is mostly insoluble in alcoholic solvents [65].

However, based on Hansen theory, DMSO and water should not be solvents for CA

(Table.1). The Hansen sphere (D (𝑠−𝑝)) of water and DMSO are 32.47 and 13.31 MPa1/2

respectively, which is not within a credible range for the dissolution of CA.

Other important considerations are the boiling temperature (°C), viscosity (η), and

surface tension (γ) which also affect the selection of a solvent because they also

influence the possibility of continuous electrospinning of uniform ultra-fine CA fibres.

Table 2 summarises the boiling points, viscosity, surface tension, and Hildebrand and

Flory-Huggins parameters for each solvent type [66-68]. The Hildebrand solubility

parameter (δ) indicates the degree of interaction between materials, and is a particularly

good solubility predictor solubility for non-polar polymer materials [66]. The

Hildebrand solubility parameter (δ) is based on the cohesive energy density of the

solvent, which in turn is obtained from the heat of vaporisation [69].

Table 2.Physical Properties of Solvents [66-68, 70, 71]

CA is soluble when the Hildebrand solubility parameters (δ) lie between 9.5 and 12.5

(cal cm-3)½ [66]. The Hildebrand solubility parameters of water, DMSO and methanol

are 23.5, 13,14.3 (cal cm-3)1/2 respectively which are not within an appropriate range for

the dissolution of CA.Incorporation of water also decreases the overall evaporation rate

during electrospinning [12]. Significantly, it was previously reported that the use of a

DMSO based system led to the formation of a product with a high proportion of

interconnected CA fibres (considered to be a poor-performance morphology), mainly

due to the lower volatility of DMSO in comparison with the other solvents (Table.2)

[62]. Therefore, DMAc and DMF, which both are proper solvents for β-CD, were

selected as a component in the preparation of CA binary solvent systems.

The Hansen sphere (D(𝑠−𝑝)) of acetone, DMAc and DMF are 5.39,5.88 and 8.28 MPa1/2,

respectively, which indicates that acetone is a better solvent for the dissolution of CA

than other solvents (Table.1). Furthermore, compared to other solvents (acetone and

DMAc) the distance (D(s-p)) of DMF to the radius of interaction (R) of CA was not too

high, in other words, DMF, itself was not able to dissolve CA properly. This was

confirmed in preliminary results (shown elsewhere).As a result, binary solvent systems

of acetone:DMAc (2:1), acetone:DMF (2:1), DMAc:acetone (2:1), and DMF:acetone

(2:1) were also evaluated to improve the electrospinnability of CA enriched with β-CD.

The solvent system suitability was determined in terms of the absence of precipitation

during spinning solution preparation and the final spinnability of the polymer solution.

Spinnability in this context was assessed in terms of freedom from needle blockages,

consistency of fibre morphology and freedom from bead and spindle defects in the web.

Fibrous webs could not be obtained using a CA concentration of less than 12% (w/v).

Similarly, spinnability issues were encountered due to high viscosity at polymer

concentrations greater than 18-20% (w/v) using single solvent systems. Therefore, the

CA concentration in the spinning solutions was fixed at a concentration of 16% (w/v).

The β-CD content was also fixed at the most possible solubility of β-CD at 5% (w/v)

with respect to the polymer [21, 36].

Satisfactory spinning conditions could not be established for single solvent system of

DMAc or DMF at a constant flow rate of 1.5ml/min with a voltage of 25kV and a tip-

to-collector distance of 150mm under ambient conditions (25±5ºC). The poor

performance of single solvent systems of DMAc and DMF may be explained in terms

of the Flory-Huggins (χ) parameters (Table.2). The Flory-Huggins parameter (χ)

characterises the polymer-solvent interaction wherein a smaller value of χ indicates a

more thermodynamically compatible interaction between the solvent and the polymer

[66]. Therefore, among the solvents examined, DMF and DMAc were expected to be

the most thermodynamically compatible solvent for CA, followed by acetone, DMSO,

water and methanol. Strong hydrogen bonding between CA and solvents (DMF/

DMAc) [72] and also the high boiling point of the solvents (Table. 2) resulted in poor

evaporation of solvents during electrospinning. Evidence of insufficient solvent

evaporation (wet-surface) and bead formation is shown in Figure 1 (A-B).

Figure 1. SEM micrographs showing the effect of individual and binary solvent systems on resulting CA/β-CD electrospun fibre morphology and web structure at CA

concentration of 16 (%w/v). Mag. (10 µm)-3500X. (A)DMF;(B) DMAc;(C) DMF:acetone (2:1); (D) DMAc:acetone (2:1);(E) acetone:DMF (2:1);(F)

acetone:DMAc (2:1). The operating voltage was 25 kV, flow rate 1.5 ml/hr and tip-to-collector distance 150 mm.

Table 2 demonstrates that DMAc, DMF and acetone possess the two extremes of

solvent properties. To achieve intermediate surface tensions and viscosities, CA was

dissolved in a binary solvent system of DMAc and acetone, with DMF in ratios of 2:1

or 1:2. Electrospinning of CA in DMAc:acetone (2:1) and DMF:acetone (2:1) at any

concentration generated beads rather than fibres (Fig.1, C-D), similar to the use of

single solvent system. The presence of the many large beads on their surface can be

attributed to the high surface tension of solvents [66]. However, increasing the fraction

of acetone to solvents (2:1) improved spinning stability and produced substantiality

fibres with small beads (Fig.1, E-F).

Electrospun CA/β-CD fibres of 339±50nm and 578±50nm were produced in the binary

solvent systems of acetone:DMAc (2:1) and acetone:DMF (2:1) respectively with a

polymer concentration of CA 16% (w/v). A binary solvent system of acetone:DMAc

(2:1) was previously found to be the most suitable solvent system for continuous

electrospinning of CA fibres [12, 73], however due to the higher solubility of β-CD in

DMF and the importance of obtaining a suitable morphology of ribbon-like fibre

structures, as good as the solvent system of acetone:DMAc(2:1) is, (Fig.1), the

optimisation of the electrospinning process was mainly focused on the binary solvent

system of acetone:DMF (2:1) for assembly of β-CD webs.

The suitability of a 2:1 acetone:DMF system for assembly of β-CD was assessed by the

absence of precipitation whilst preparing the spinning solution and the solution

spinnability. Spinnability means the absence of blocked spinnerets, the presence of

consistent fibre morphology and absence of bead and spindle defects in the product.

Therefore for the binary system of 2:1 acetone:DMF, the CA concentration was varied

from 12-24% (w/v) and the β-CD content was precisely fixed at 5% (w/v) in all

solutions (Table.3).

Table 3. Fibre morphology of CA/β-CD webs produced from binary solvent system of acetone: DMF (2:1)

No fibres or large beads were obtained at a concentration of 12% (w/v) due to a lack of

molecular cohesion - indicated by the low solution viscosity (figures shown elsewhere).

Dumbbell-shaped beads were observed for CA/β-CD electrospun webs produced at CA

concentrations of16-18 % (w/v) in acetone:DMF (2:1) solution (Fig.2,A-B). The

morphology of the electrospun webs improved with CA concentration up to 20% (w/v)

(Fig.2C). As expected, as CA concentration increased from 16% (w/v) to 22% (w/v),

electrospun mean fibre diameter increased from 578nm to 1.12μm (Table.3).

Figure 2. SEM micrographs of CA/β-CD webs produced from binary solvent system of acetone:DMF (2:1) at CA concentrations of 16-22 (%w/v).The operating voltage was 25

kV, flow rate 1.5 ml/hr and tip-to-collector distance 150 mm.

A minimum polymer concentration is required for fibre formation during

electrospinning. Chain entanglement in polymer solutions results from physical polymer

chain interlocking - a direct consequence of chains overlapping [74]. Below this critical

level of overlap, charging the solution results in electrospraying and bead formation.

These defects are attributed to capillary wave break-up, commonly known as Rayleigh

instability. As the polymer concentration increases, a mixture of beads and fibres are

obtained. At higher polymer concentrations continuous fibres will form [5]. However

there is an upper limit to the polymer concentration because although it is seldom

reported, electrospinning is prevented if the solution viscosity is too high [74]

(Table.3).

The porosity of the webs produced from different concentrations of CA was 55% to

65% (Table.3). The pore structure plays an important role in the filtration behaviour of

the web. The mean pore size increase with increasing fibre diameter [49]. The largest

pore observed, with a diameter of 16.28μm was produced from CA concentration of

22% (w/v), with the average diameters of CA/β-CD fibres 1.12± 0.5μm, range: 500nm-

2.5μm (Table.3). This comparatively large pore size is attributed to the fibre diameter

of electrospun fibres which potentially affects mean pore size of the sample [49].

The filtration process is routinely optimised by controlling the pore diameter and

its pore distribution within the filter media. The average pore diameter and pore

size distribution in an electrospun membrane both have a significant impact on

pressure drop and filtration properties of the membrane [75, 76]. The general

trend within pore sizes is that larger pores have a lower excess adsorption density

than the smaller ones [76]. Park and Park (2005) studied the factors affecting the

nanofibre morphology and concluded that the difference between the filtration

efficiency in electrospun webs produced under different voltages is mainly due to

variation in fibre diameter [77]. Zhang et al. (2010) investigated filtration

performance of the sandwiched multilayer nanofibrous media. They revealed that

better thickness uniformity in the multilayer nanofibre structure due to stacking

compensation and smaller fibre diameters are two reasons for the improvement of

the filter quality [78]. Maze et al [79] reported through simulation data that the

filtration efficiency of the electrospun nanofibres for nanoparticles can be

improved by decreasing the fibre diameter and increasing the flow temperature of

the air. Consequently, the collection efficiency of aerosol particles increases by

decreasing fibre diameter and pore size. However, it should be noted that

optimisation of this type operational efficiency is strongly related to the design of

the complete filtration apparatus, and therefore more appropriately done in the

latter development phase.

Figure 3 reveals the influence of polymer concentration on viscosity. The rheological

behaviour of CA/β-CD in the binary solvent system of acetone:DMF (2:1) could be

characterised as shear-thinning (pseudo-plastic) and non-Newtonian at almost all

concentrations (Fig.3A). The viscosity measurements of solutions were carried out at

25°C (Table.3). It is clear that the increase in CA concentration from 12% to 24% (w/v)

leads to a dramatic increase in solution viscosity from 198 to 2748cP (Fig.3B).

Figure 3. (A).Viscosity changes of polymer solutions produced from the binary solvent system of acetone: DMF (2:1) vs. shear rate. (B).Concentration vs. viscosity graph of

polymer solutions.

Sigmoidal fitting of the experimental results establishes correlation between the

variations of the viscosity with solution concentration. Equation 3 is suggested where X

is the concentration of solution (w/v%) and Y refers to the viscosity. All other

parameters in this application of the Gompertz equation are constant (K=0.5, Xc=16.74,

a=2329.6, R2=0.92).

y=ae−e(−k ( x−xc) ) (4)

Morphologically, more uniform ribbon-like CA/β-CD fibres, free of bead defects were

obtained at the highest CA concentration of 22% (w/v) with mean fibre diameter of

1.12±0.5μm (Fig.2D), however in CA concentration of 20% (w/v) the mean fibre

diameter of the electrospun webs was 773±50nm, range: 250nm-1.5μm and essentially

more smooth fibres (Fig.2C) with an acceptable pore size of 5.92μm were observed in

all the webs (Table.3). Therefore, the optimum conditions for the production of CA/β-

CD webs was identified as a CA polymer concentration of 20% (w/v) containing 5%

(w/v) of β-CD in the binary solvent system of acetone: DMF (2:1) made at an operating

voltage of 25kV, flow rate of 1.5ml/hr and a tip-to-collector distance of 150mm. To

accurately evaluate and isolate the effect of β-CD on the adsorption of hexanal,

other physical parameters such as pore size (5.92µm), porosity (59.05%) and

thickness (150µm) of the electrospun fibres were controlled and kept constant.

3.2 FTIR Analysis

The FTIR spectrum of the CA web is shown in figure 4. The broad absorption band

seen at 3455.91cm−1 is attributed to O–H stretching. The absorption band at 2700-

2900cm-1 is attributed to -CH2 groups (CH stretching). The characteristics bands at

1068.30cm-1 for C-O-C (ether linkage) from glycosidic units [80]. The band at

1730.51cm−1 is associated with the overlapped ester carbonyls in CA. This peak is a

characteristic peak or fingerprint region for CA, as other bands may also occur in other

various cellulosic polymers [12].

Figure 4.FTIR spectra of the cellulose acetate (CA), β-Cyclodextrin (β-CD) and electrospun CA fibres containing β-CD

The spectra of β-CD are characterised by intense bands at 3300-3500cm-1 due to O-H

stretching vibration, while the asymmetric stretching vibration of the –CH and -CH2-

groups appears in the 2800-3000cm-1 region. The asymmetric stretching vibrations of

C–O appeared at 1648.60cm-1 [81]. The stretching vibration of C-O-C bond has been

identified at 1417.36cm-1 and 1080cm-1 which are evidence for glucose linkages in β-CD

structure [82]. The other frequencies for β-CD are observed as 1156.94cm-1, and

1028.25cm−1 which correspond to the stretching of C–C and bending vibration of O–H

respectively [83].

The spectrum of electrospun nanofibres shows the characteristic peak of CA at

1732.71cm-1 which indicate no structural changes in the CA polymer after the spinning

process. Many of the characteristic peaks of CA and β-CD are situated between

common regions of 3500-2500cm-1 and specifically 1650-1000cm-1 which makes it quite

difficult to distinguish them by comparing the spectra of the electrospun fibres. In fact,

due to the high CA concentration and predominance of overlapping regions, β-CD

peaks in the spectrum do mask or interfere with each other. Therefore, another method

was suggested and applied to demonstrate the entrapment of β-CD in the CA structure

[84].

3.3 Colorimetric determination of β-CD

The colorimetric determination of CDs in the web structures was possible due to the

host-guest complex formation of β-CD and PhP. PhP changes from colourless to purple

when the neutral solution becomes alkaline. However, PhP included in the β-CD cavity

exhibits no absorbance even at pH10.5 in the visible region. The decolourisation of the

indicator in alkaline solutions is probably due to the destruction of the planar conjugated

structure of the PhP molecule [84].

Figure5 shows the absorption spectrum of alkaline solution of PhP in aqueous solutions

of β-CD at λ Max=552nm. The results indicate that the colour absorption of PhP has an

inverse relationship with the increase of β-CD in the solution, so that its colour strength

was significantly reduced [Fig.5A]. In other words, by loading different concentrations

of β-CD, the absorption value decreased from 0.76912nm (control sample) to

0.02562nm containing 0.5mg/l β-CD (Table. 4).

Figure 5. (A).The absorption spectrum of alkaline solution of phenolphthalein (PhP) in aqueous solutions of β-CD. (B) Schematic diagram of the hydrogen bonds between the β-CD molecule and the phenolphthalein (PhP) dianion.(C) Showing the UV-Vis graph for detection of β-CD. (D) Comparison of colour changes (decolourisation) resulted from the addition of alkaline solution of phenolphthalein to the washed aqueous solutions of control sample (CA) (A), CA/β-CD (B) and PhP solution with a red-purple colour (R)

Table 4. Absorbance values of phenolphthalein (PhP)-β-CD solutions as a function of

β-CD concentration

When the PhP solution is added to the β-CD solution, the cone-shaped of the β-CD

molecule forms a host-guest complex with the guest molecule PhP, due to a

combination of van der Waals interactions and formation of three hydrogen bonds with

the β-CD molecules (Fig 5.B) [65]. These intermolecular interactions cause the PhP

molecule to twist more strongly around the central carbon atom. Delocalization of the

conjugated п-electron is consequently impaired, so that the colour disappears [50, 85].

The control sample of electrospun pure CA fibres and optimised CA/β-CD fibres were

immersed into a PhP solution and the change in absorbance of PhP was recorded as a

function of time by UV–vis spectrometry in the visible region of 400-700nm (Fig5.C).

The CA control sample is expected to contain only water since CA is completely

insoluble in water. However, CA/β-CD contains 5% (w/v) of β-CD which is fairly

soluble in water and is thus expected to release β-CD molecules into aqueous solution.

As can been seen in figure5.C, the absorption peak of CA solution was significantly

reduced in comparison with the washed aqueous solution of CA/β-CD. This change

confirms the presence of β-CD in the structure of the electrospun nanofibres and

provides reasonable evidence in substantiating the detection of β-CD. Visual changes

were also assessed and are shown in Figure5.D. After the removal of the nanofibre

webs from water, a specified amount of alkaline PhP solution was added to both

solutions. The CA solution, which was essentially DI water, turned pink due to the

colour of the alkaline PhP solution whereas the solution containing β-CD extracted from

the CA/β-CD nanofibrous webs completely decolourised (Fig 5.D) [85]. To substantiate

the fact that the decolourisation of the magenta-coloured alkaline PhP solution by CA/β-

CD solution was not because of change in pH but due to the inclusion complexation

with β-CD, the pH of both solutions was measured and recorded giving a reading of

pH10 for both solutions. The encapsulation efficiency of β-CD in the fibre structures

was also measured as about 85% which clearly confirmed the capability of this process

for the production of a cyclodextrin carrier system [37, 86].

3.4 The potential for odour adsorption by electrospun CA containing β-CD

molecules

Molecular filters based on CD functionalised electrospun nanofibre with potential

applications in separation of organic molecules from complex solutions, water

purification, waste treatment and absorbing hazardous chemicals have previously

reported [87, 88]. The filtration performance of electrospun nanofibres can clearly be

enhanced by fibre functionalisation with CD [86]. There are also a number of patents

detailing cyclodextrin-containing products for the absorption of odour associated with

personal hygiene, such as feminine sanitary protection [89]. However, to the best of our

knowledge, the ability of odour-adsorption via electrospun nanofibres containing β-CD

for frying oils has not yet been reported.

To evaluate the odour adsorbent of electrospun nanofibres, the electrospun mats were

produced at optimised CA concentration of 20% (w/v) containing 5%(w/v) of β-CD in

the binary solvent system of acetone:DMF (2:1) using an operating voltage of

25kV,flow rate 1.5ml/hr and tip-to-collector distance 150mm. CA electrospun mats

were also prepared as a control sample exactly by the same procedure in the absence of

β-CD and evaluated by adsorbing our model odour material, hexanal. The electrospun

samples were accurately cut into disc shaped mats and then carefully inserted in the

filter base of a Millipore funnel to follow the experimental procedure described in

sections 2.10 and 2.11. The mean fibre diameter in the both collected webs was

700±50nm.

Table 5 shows the final results of GC-MS analysis of filtered air for the blank sample,

control sample and electrospun CA containing β-CD mats. The amount of measured

hexanal when no filter used is the blank sample. The retention time of hexanal was

6.56min for all samples [55].

Table 5. The final results of GC-MS data analysed by software for blank, control

sample and electrospun CA mats containing β-CD

The highest peak area was shown for the blank sample when no filter used (Table.5).

The amount of measured hexanal for blank sample was about 0.41ppm. As expected,

the electrospun fibres embedded with β-CD molecules showed the lowest peak area

(Table.5). The amount of hexanal measured in the β-CD free control sample was

0.18ppm, and this amount was significantly decreased by the presence of β-CD to

0.09ppm, clearly indicating the ability of β-CD molecules to entrap odours such as

hexanal (up to 80% adsorption of hexanal molecules in the air compared to the blank

sample) (Table.5).

The mechanism through which the odour is absorbed by the CD molecule is the familiar

host-guest physicochemical interaction process typically seen with cyclic molecules,

such as CD [30]. Complex formation is achieved by a dimensional fit between the host

cavity and the guest molecule. The lipophilic cavity of CD molecules provides a micro-

environment into which non-polar moieties of appropriate size can form inclusion

complexes. No covalent bonds are formed or broken during the creation of the

inclusion complexes [30, 90]. Binding of guest molecules within the host CD is in

dynamic equilibrium. The strength of binding depends on the quality of the ‘host–

guest’ complex fit and in turn, on specific local interactions between surface atoms.

Inclusion in the CD host exerts a significant effect on physicochemical properties of the

guest molecules as they are temporarily enmeshed in the host cavity allowing potential

beneficial modifications to the guest molecules, more effective than other current

methods of masking off-flavours or unpleasant odours [30].

Our results both confirm and build on previous research showing the potential of CD for

adsorbing adventitious odours. Recently, a research group has developed a charcoal-

based odour-absorbing dressing for direct wound contact using CD. They showed that

the smaller cavity of the α-CD was a more effective absorber than the β-CD, while the

δ-CD cavity was too large to effectively immobilize the butyric acid [89]. Similarly, the

absorption of a model wound odour solution consisting of butyric and propionic acids

by neat and functionalised poly (ε-caprolactone) (PCL) nanofibres containing β-CD was

examined [42]. It was shown that functionalised nanofibres absorbed and retained much

higher amounts of odour compounds, with the possibility of taking up even more, if

provided with a higher residence time [42]. Aqueous solutions of CD were also shown

to be efficient to trap volatile organic compounds (VOCs). It was reported that β-CD

presented the highest adsorption capacity among other forms of CD [91]. Temperature,

concentration of the waste gas and CD concentration have an influence on the

absorption capacities of the absorbent [91].

4- Conclusion

A binary solvent system consisting of acetone: DMF (2:1) has been demonstrated to

permit solution blending of CA with β-CD. Nanofibre webs substantially free of

structural defects such as beads were continuously produced, comprising fibres with

average diameters of 773±50nm in the range of 250–1.5μm. The morphology, diameter

of fibres, pore size and solution viscosity were influenced by the concentration of CA

spinning solution. Optimal CA concentration was 20% (w/v) as judged by the ability to

produce bead-free fibres using the binary solvent system. CA/β-CD fibres were readily

produced at a high rate of production when the CA concentration was 20% (w/v) -

containing 5%(w/v) of β-CD with an operating voltage of 25kV, flow rate of 1.5ml/hr

and a tip-to-collector distance of 150mm. The FTIR spectrum of the electrospun

nanofibres showed the fingerprint region of CA indicating no structural changes in the

CA polymer structure during processing, however, due to overlapping regions between

CA and β-CD molecules, the colorimetric method used to quantitatively demonstrate

the entrapment of β-CD in the CA structure. When the PhP solution was inserted to the

β-CD solution, the cone-shaped of β-CD forms a host-guest complex with the guest

molecule PhP, due to van der Waals interactions and formation of three hydrogen bonds

to the β-CD molecules. Consequently, the colour absorption of PhP has an inverse

relationship with the increase of β-CD in the solution. The presence of β-CD in the CA/β-

CD nanofibres was successfully detected and substantiated by the means of UV-Vis

spectroscopy (in the UV region) and by inclusion complexation using alkaline PhP as

the test organic molecule (giving a colour response in the visible region). The CA

solution which was essentially DI water, turned into pink due to the colour of the

alkaline PhP solution whereas solution containing β-CD extracted from the CA/β-CD

nanofibrous webs completely decolourised. The encapsulation efficiency of β-CD in the

fibre structures was measured up to 85% which is a highly acceptable level. Our results

illustrated that electrospun CA fibres embedded with β-CD molecules demonstrate

enhanced adsorption of hexanal, which is desirable for filtration applications. The

authors believe that the next steps in progress towards development of these kinds

of filters will be based on optimising the filter fibre morphology in terms of pore

size, porosity and alignment of the electrospun part of the structure – this phase of

work is clearly dependant on the design of the future industrial plant. This will

require further interaction between the academic and the industrial communities

commencing with a critical assessment this research with a view to industrial scale

up. In preliminary discussions with development partners, the prospect of a design

that will obviate the need for desorption from the CA/β-CD nanofibres has been

adumbrated.

5- Acknowledgments

The first author would like to express his deeply gratitude to Iran National Science

Foundation (INSF) for supporting this research under grant number 91003845.This

work would not have been possible without the financial support of the INSF.I am also

very thankful to Dr.Masoud Najaf Najafi for providing the opportunity to visit the

industrial units. In addition, I must also express my gratitude to Ms. Fatemeh Tadarokat,

my excellent research assistant who unfortunately passed away a few months before the

successful accomplishment of this project.

6- Funding

This work was supported by the Iran National Science Foundation (INSF) [grant

number 91003845].

7-Data Availability statement

The raw/processed data required to reproduce these findings cannot be shared at this

time and would remain confidential as the project was financially supported by the Iran

National Science Foundation (INSF) and it has not yet been authorised to

shared/published.

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Figure captions

Figure 1. SEM micrographs showing the effect of individual and binary solvent systems on resulting CA/β-CD electrospun fibre morphology and web structure at CA concentration of 16 (%w/v). Mag. (10 µm)-3500X. (A)DMF;(B) DMAc;(C) DMF:acetone (2:1); (D) DMAc:acetone (2:1);(E) acetone:DMF (2:1);(F) acetone:DMAc (2:1). The operating voltage was 25 kV, flow rate 1.5 ml/hr and tip-to-collector distance 150 mm.

Figure 2. SEM micrographs of CA/β-CD webs produced from binary solvent system of acetone:DMF (2:1) at CA concentrations of 16-22 (%w/v).The operating voltage was 25 kV, flow rate 1.5 ml/hr and tip-to-collector distance 150 mm.

Figure 3. (A).Viscosity changes of polymer solutions produced from the binary solvent system of acetone: DMF (2:1) vs. shear rate. (B).Concentration vs. viscosity graph of polymer solutions.

Figure 4.FTIR spectra of the cellulose acetate (CA), β-Cyclodextrin (β-CD) and electrospun CA fibres containing β-CD.

Figure 5. (A).The absorption spectrum of alkaline solution of phenolphthalein (PhP) in aqueous solutions of β-CD. (B) Schematic diagram of the hydrogen bonds between the β-CD molecule and the phenolphthalein (PhP) dianion. (C) Showing the UV-Vis graph for detection of β-CD. (D) Comparison of colour changes (decolourisation) resulted from the addition of alkaline solution of phenolphthalein to the washed aqueous solutions of control sample (CA) (A), CA/β-CD (B) and PhP solution with a red-purple colour (R)

Figures

Figure 1. SEM micrographs showing the effect of

individual and binary solvent systems on resulting CA/β-CD electrospun fibre morphology and web structure at CA concentration of 16 (%w/v). Mag. (10 µm)-3500X. (A)DMF;(B) DMAc;(C) DMF:acetone (2:1); (D) DMAc:acetone (2:1);(E)

acetone:DMF (2:1);(F) acetone:DMAc (2:1). The operating voltage was 25 kV, flow rate 1.5 ml/hr and tip-to-collector distance 150 mm.

A-DMF B-DMAc

D-DMAc: acetone (2:1) E-acetone:DMF (2:1)

Figure 2. SEM micrographs of CA/β-CD webs produced from binary solvent system of acetone:DMF (2:1) at CA concentrations of 16-22 (%w/v).The operating

voltage was 25 kV, flow rate 1.5 ml/hr and tip-to-collector distance 150 mm.

Figure 3. (A).Viscosity changes of polymer solutions produced from the binary solvent system of acetone: DMF (2:1) vs. shear rate. (B).Concentration vs. viscosity

graph of polymer solutions.

0 10 20 30 40 50 60

0100020003000400050006000700080009000

1000011000120001300014000

16 w/v% 18 w/v% 20 w/v% 22 w/v%

Visc

osity

(cP)

Shear Rate (1/S)

(A) (B)

Figure 4.FTIR spectra of the cellulose acetate (CA), β-Cyclodextrin (β-CD) and electrospun CA fibres containing β-CD

4000 3500 3000 2500 2000 1500 1000 500

50

100

150

200

250

300

% T

rans

mitt

ance

Wavenumber(cm-1)

Cellulose acetate (CA) Beta-Cyclodextrin Electrospun Nanofibres

3455.912958.69

1730.511068.301237.60

3373.64

2926.011648.60

1028.251080.01

3481.862945.98

2643.10

2641.57

1732.711067.53

1254.28

1599.97

Figure 5. (A).The absorption spectrum of alkaline solution of phenolphthalein (PhP) in aqueous solutions of β-CD. (B) Schematic diagram of the hydrogen bonds between the β-CD molecule and the phenolphthalein (PhP) dianion. (C) Showing the UV-Vis graph

for detection of β-CD. (D) Comparison of colour changes (decolourisation) resulted from the addition of alkaline solution of phenolphthalein to the washed aqueous

solutions of control sample (CA) (A), CA/β-CD (B) and PhP solution with a red-purple colour (R)

400 450 500 550 600 650 700

0.04

0.05

0.06

0.07

0.08

0.09

CA-CD CA

Abso

rban

ce

Wavelength (nm)

(C)

(B)

(A)

(D)

R A B

Tables

Table 1.Total solubility parameters (δt) of various solvents and cellulose acetate (CA)

Solvent Solubility Parameter

(MPa1/2)δt δd δp δh D(s-p)* R

Acetone 19.93 15.50 10.40 7.00 5.39

Dimethylacetamide (DMAc)

22.77 16.80 11.50 10.20 5.88

Dimethylformamide(DMF)

24.8 17.40 13.70 11.30 8.28

Methanol 29.60 15.10 12.30 22.30 12.35

Dimethyl sulfoxide(DMSO)

13 9 8 5 13.31

Water 47.83 15.60 16.0 42.3 32.47

Cellulose Acetate (CA)

19.89 14.90 7.10 11.10 - 12.40

* D(s-p) = [4(δdS-δdP)2 + (δpS-δpP)2 + (δhS-δhP)2]1/2

δxs= Hansen component parameter for the solvent.

δxp= Hansen component parameter for the polymer.

Table2. Physical Properties of Solvents

Table 3. Fibre morphology of CA/β-CD webs produced from binary solvent system of acetone: DMF (2:1)

Solvent Boiling Temperature

(°C)

Viscosity (η) cP at

20 °C

Flory-Huggins

parameter(χ) at 25 °C

Hildebrand Solubility Parameter

( δ) (cal/cm3)1/2

Surface Tension (γ) (dyne

cm-1) at 20 °C

Water 100 1 1.4 23.5 72.8

Acetone 56.29 0.36 0.48 9.77 23.32

DMAc 164 2.14 0.28 11.1 32.43

DMF 153 0.802 0.2 12.14 36.42

DMSO 189 2.0 0.53 13.0 43.53

Methanol 65 0.59 1.87 14.3 22

Means not followed by the same letters are significantly different (p < 0.05)

Sample No.

Concentration of CA

electrospinning solution

(%w/v) contain β-CD

Fibre diameter

(nm)

Solution viscosity

(cP)

Porosity (%)

Pore size (μm)

Morphological observation of CA/β- CD web

structure

1 12 - 198a - - No Fibre formation

(Large Beads)

2 16 578.21a 367b 62.94a 3.78a Beads- Fibres

3 18 614.91b 1664c 60.59b 4.12b Small beads-

Fibres

4 20 772.67c 1907d 59.05b 5.92c Smooth Fibres

5 22 1120d 2329e 57.52b 16.28d Fibres

6 24 - 2748f - - No Fibre production due to gel formation

Table 4. Absorbance values of phenolphthalein (PhP)-β-CD solutions as a function of

β-CD concentration

Sample No. β-CD concentration (mg/l) Absorbance

(λmax=552 nm)

1 0 0.76912

2 0.1 0.20386

3 0.2 0.09402

4 0.3 0.05954

5 0.4 0.03911

6 0.5 0.02526

Table 5.The final results of GC-MS data analysed by software for blank, control sample

and electrospun CA mats containing β-CD

Means not follow

ed by the same letters are significantly different (p < 0.05)

Sample Retention Time(min)

Peak Height

Area % of Total

Hexanal concentration

(ppm)

Blank 6.56a 12290a 824929a 49.89a 0.41a

Electrospun CA mats

6.56a 3198b 392479b 44.8b 0.18b

Electrospun CA mats

containing β-CD

6.56a 2574c 201358c 27.55c 0.09c