Nanostructures of Cellulose Acetate Phthalate Obtained by

Dec 12, 2012 - ‡“Al. I. Cuza” University, Bd. Carol I 11, Iasi 700506, Romania. ABSTRACT: Cellulose acetate phthalate (CAP) is well-known and largely ...
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Nanostructures of Cellulose Acetate Phthalate Obtained by Electrospinning from 2‑Methoxyethanol-Containing Solvent Systems: Morphological Aspects, Thermal Behavior, and Antimicrobial Activity Niculae Olaru,*,† Liliana Olaru,† Nita Tudorachi,† Simona Dunca,‡ and Manuela Pintilie† †

“Petru Poni” Institute of Macromolecular Chemistry, Aleea Gr. Ghica-Voda 41 A, Iasi 700487, Romania “Al. I. Cuza” University, Bd. Carol I 11, Iasi 700506, Romania

‡

ABSTRACT: Cellulose acetate phthalate (CAP) is well-known and largely used as a pharmaceutical excipient for enteric coating of tablets and capsules. Recent literature has proved that this polymer exhibits antimicrobial and antiviral properties when it is used as a micronized powder. Nanostructures of CAP are also prepared, and their potential for antimicrobial and technological applications is recently reported. In the present work, we are focused on synthesis and characterization of CAP nanofibers and powders by electrospinning/electrospraying from solutions in solvent mixtures containing 2-methoxyethanol. The morphologies of the obtained nanostructures are investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses and discussed in comparison with those previously reported for products obtained in 2-methoxyethanol alone. Thermal properties of CAP nanostructured as powders and fibers are studied in comparison with those of CAP films using thermogravimetric (TG), Fourier transform infrared (FTIR), and mass spectrometry. TG analysis reveals that CAP nanoproducts exhibit an apparent lower stability than CAP films. Further investigations of both residual polymer and the evolved degradation gas products evidence the presence of phthalic anhydride as a main degradation product in the initial stage of the process. In the case of nanostructures of CAP, due to their high porosity and very high specific surface areas, this degradation product is easier and continuously eliminated during the thermal treatment. This behavior explains their apparent lower thermal stability as compared with that of the films where the diffusion of phthalic anhydride proceeds slowly and therefore the weight loss of the sample is delayed. The paper also reports preliminary results of antimicrobial activities of the investigated products against Escherichia coli and Staphylococcus aureus. and fibers of CAP with sizes in the submicrometer range and different morphologies can be easily obtained using a simple electrospinning laboratory setup. It has also been observed that the morphology of the electrospun CAP changes as a function of the solution characteristics like viscosity, surface tension, and conductivity. When using only 2-methoxyethanol as the electrospinning solvent, polymer concentrations higher than 25% (w/v) were necessary to obtain smooth filaments without beads, whereas at a polymer concentration as low as 12.5% (w/ v), only micro/nanoparticles that look like void hemispheres have been obtained. When a ternary system 2-methoxyethanol−acetone−water 50/42.5/7.5 (v/v/v) was used as the electrospinning solvent system for CAP, smooth filaments without beads and fiber diameters of about 600 nm could be produced at concentrations of 25% (w/v). The potential use of electrospun CAP fibers as a tool to prevent HIV transmission has been very recently discussed by Huang et al.24 By taking into account the observation that the electrospinnability of CAP from 2-methoxyethanol-containing solvents was better than that from acetone−water mixtures,23 in

1. INTRODUCTION Cellulosic polymers have gathered great interest in recent years in the field of nanoproducts useful for high-value applications. The biodegradability, biocompatibility, and versatility of these natural polymers are the reasons for those approaches regarding the possibilities to transform them in nanostructured materials with large applications especially in biomedicine, for tissue engineering scaffolds, wound dressing, controlled release, and technology purposes such as filtration, catalysis, sensors, affinity membranes, etc.1−15 One of the most interesting cellulose derivative from this point of view is cellulose acetate phthalate (CAP), a mixed ester with acetic and o-phthalic acids. CAP has been known for several decades as a pharmaceutical excipient used for enteric coating of tablets and capsules. Recently, it has been shown that CAP formulated as a micronized powder exhibits activity against the human immunodeficiency virus type I (HIV-I), several herpes viruses (herpes simplex viruses I and II), and many nonviral sexually transmitted disease pathogens.16−22 In a previous paper,23 we have studied the possibility to obtain micro/nanostructured CAP with high specific surface areas via the electrospinning procedure. Several solvent systems (2-methoxyethanol, acetone−water mixture 85/15 (v/v), and 2-methoxyethanol−acetone−water mixture 50/42.5/7.5 (v/v/ v)) were investigated, and it has been found that by variation of the solvent system and the polymer concentration, powders © 2012 American Chemical Society

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May 17, 2012 December 12, 2012 December 12, 2012 December 12, 2012 dx.doi.org/10.1021/ie301299d | Ind. Eng. Chem. Res. 2013, 52, 696−705

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The particle size distribution curves for CAP powders were obtained by means of a system Mastersizer 2000 version 5.31, Malvern Instruments. The electrical conductivity of polymer solutions was measured using a CDM 210 (Radiometer, Copenhagen) Conductometer. Viscosity of CAP solutions was determined by means of a Brookfield SYNCHRO-LECTRIC Viscometer, model LVF. 2.5. Thermal Treatment. Thermal analysis was performed by simultaneous TG, MS, and FTIR determinations using the following equipment: TG-DSC model STA 449F1 Jupiter (Netzsch−Germania), QMS 403C Aëolos (Netzsch−Germania), and FTIR spectrophotometer model Vertex-70 (Bruker) with an accessory for ATR (attenuated total reflectance) type Golden Gate. The experiments were carried out in the following conditions: heating rate 10 K min−1; gas purge He; reference material Al2O3; temperature range 30−600 °C. 2.6. Antimicrobial Tests. The in vitro antimicrobial activity was assessed using the disk-diffusion method KirbyBauer30 on two strains of bacteria: Staphylococcus aureus ATCC 25923 (S. aureus) and Escherichia coli ATCC 25922 (E. coli). CAP samples obtained from solutions in 2-methoxyethanol and 2-methoxyethanol−water 85/15 (v/v) at 10% (w/v) polymer concentration were used for these tests. The bacterial inoculum obtained from bacterial cultures preincubated for 18 h at 37 °C was standardized according to McFarland scale and a number of 107−108 CFU/mL was obtained. The culture medium (LB-Lysogeny broth) was seeded with the inoculum thus obtained and then microdisks of 1 cm diameter impregnated with CAP powders (0.01 g/ microdisk) were placed on the surface of the medium. Three determinations were carried out for each sample, and the average values obtained for the diameters of the inhibition zones are shown in Table 1.

the present paper we further investigate the electrospinning of CAP from 2-methoxyethanol and 2-methoxyethanol−water systems with different compositions. A detailed characterization of CAP has been reported by Roxin et al.25 including data about its thermal behavior when treated in oxygen and inert atmospheres. Glass transition temperatures of CAP samples were also determined. Earlier26 we demonstrated that by treating CAP films at temperatures between 120 and 220 °C for various times of exposure, one of the principal degradation products is the phthalic anhydride, which is partially evolved during the process. Having in mind the possibility to change drastically the polymer properties by transforming it into nanostructured materials and also taking into account the importance of the thermal behavior of these materials from an applicative point of view, in the present paper we are concerned with a study on thermal properties of micro/nanopowders and fibers of CAP in comparison with those of the usual films obtained from the same polymer. TG-DTG analysis, FTIR, ATR, and mass spectrometry were used to investigate thermal stability of nanostructured CAP. On the basis of literature reports, we expect that the obtained nanostructures of CAP could enhance its potential as antimicrobial agent. Therefore, in this paper, preliminary tests on the antimicrobial activity of the electrospun CAP products are also reported in relation to their morphology.

2. MATERIALS AND METHODS 2.1. Materials. The chemicals were of reagent grade and were used as received, without further purification. 2.2. Synthesis and Characterization of CAP. Cellulose acetate phthalate investigated in this work had a degree of phthaloylation of 0.70 and a degree of acetylation of 1.73 and was synthesized by phthaloylation of cellulose acetate (CA) with degree of acetylation of 1.77 and degree of polymerization of 185. Both cellulose derivatives were prepared in our laboratory, as described in our previous papers.23,27 Characterization of CAP and CA with respect to their degrees of modification was performed by means of the known methods: refs 28 and 29, respectively. 2.3. Electrospinning and Electrospraying Experiments. The experiments for obtaining of both fibers and powders of CAP were carried out using the same typical laboratory setup, consisting of a high voltage source, a pump and a syringe for polymer solution and a rotary collector disk. Solutions of CAP were prepared in 2-methoxyethanol and mixtures of 2-methoxyethanol−water of three compositions: 95/5 (v/v), 90/10 (v/v), and 85/15 (v/v). On the basis of previous results,23 the concentration of polymer solutions was chosen to be 10% and 30% (w/v) so as to obtain powders and fibers, respectively, with sizes in the submicrometer range. The same parameters were chosen for both electrospinning and electrospraying experiments, as follows: voltage potential, 15−20 kV; tip-to- collector distance, about 15 cm; flow rate of the solution through the syringe, 1.5 mL h−1. The processes were carried out in air at room temperature. 2.4. Characterization of CAP Micro/nanoproducts. The morphology of CAP ultrafine fibers and powders was characterized by scanning electron microscopy (SEM; VEGA II SBH TESCAN) and transmission electron microscopy (TEM; TESLA BS 513A).

Table 1. Antimicrobial Activity Expressed by the Diameter of the Inhibition Zone (mm) of CAP Nanopowders Obtained from Solution in 2-Methoxyethanol for P1 and Solution in 2Methoxyethanol−Water 85/15 (v/v) for P2 at 10% (w/v) Polymer Concentration microorganism test sample

Staphylococcus aureus ATCC 25923

Escherichia coli ATCC 25922

P1 P2

12 16

11 14

Samples of CAP nanofibers were placed directly on the surface of the culture medium. The plates were then incubated at 37 °C for 24 h, and the antibacterial activity was evidenced by the occurrence of an inhibition zone around the sample area.

3. RESULTS AND DISCUSSION 3.1. Morphological Aspects of Nanostructured CAPs. 3.1.1. Ultrafine CAP Powders. The morphology of CAP micro/ nanoparticles obtained from 2-methoxyethanol−water systems, as revealed by SEM images for 10% (w/v) polymer concentration in the electrospun solution (Figure 1), does not differ from that reported for similar products obtained from 2-methoxyethanol solvent. The shape of void hemispheres for CAP micro/nanoparticles is preserved when water is present in the electrospinning solvent. 697

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Figure 1. SEM micrographs of CAP micro/nanoparticles obtained from 2-methoxyethanol (a) and 2-methoxyethanol−water 85/15 (v/v) (b) at 10% (w/v) polymer concentration.

Figure 2. TEM images of CAP micro/nanoparticles obtained from 2-methoxyethanol (a) and 2-methoxyethanol−water mixtures 95/5 (v/v) (b), 90/10 (v/v) (c), and 85/15 (v/v) (d) at 10% (w/v) polymer concentration.

system containing water, which can influence the polarity of the solvated polymer molecules, but the lower viscosity of the system may be also involved. As compared with particles obtained from 2-methoxyethanol at 12.5% (w/v) polymer concentration,23 those obtained from the same solvent at 10% (w/v) polymer concentration as well as those obtained from 2-methoxyethanol−water mixture 85/ 15 (v/v) at 10% (w/v) polymer concentration seem to have lower width of their walls (Figure 1) and also lower diameters as revealed by the particle size distribution data. Thus,

As in the case of the particles obtained at 12.5% (w/v) polymer concentration,23 most of the particles obtained in the present work appear to have the same orientation, with the bowl directed to the positive electrode, probably as a consequence of the orientation in the electric field of the solvated polymer molecules. However, TEM images suggest a slight deformation of the spherical part of the bowl (that part oriented to the collector plate) when adding water and increasing the proportion of water in the solvent (Figure 2a− d). This may be due to the increased polarity of the solvent 698

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Figure 3. Particle size distribution of CAP micro/nanoparticles obtained from 2-methoxyethanol (a) and 2-methoxyethanol−water mixture 85/15 (v/v) (b) at 10% (w/v) polymer concentration.

Figure 4. SEM micrographs of CAP nanofiber mats obtained from 2-methoxyethanol (a) and 2-methoxyethanol−water mixture 85/15 (v/v) (b) at 30% (w/v) polymer concentration.

methoxyethanol−water 85/15 (v/v) gave smaller particles with specific surface area higher than of those produced from 2methoxyethanol solution (Figure 3). The presence of water in the electrospinning solution may be responsible for such effect, due to the higher electrical conductivity of the polymer solution containing water (19.0 μS/cm as compared with 4.82 μS/cm

distribution curves in Figure 3 clearly show that 10% polymer concentration in the electrospun solutions for both solvent systems investigated in this paper gave 50% of the obtained particles with diameters lower than 5 μm as compared with 10 μm previously reported for higher polymer concentrations.23 At the same time, the polymer solution in the solvent mixture 2699

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Figure 5. TEM images of CAP nanofibers obtained from 2-methoxyethanol (a) and 2-methoxyethanol−water mixture 85/15 (v/v) (b) at 30% (w/ v) polymer concentration.

for the solution free of water), on one hand. On the other hand, the presence of water may contribute to the disruption of some macromolecular associations linked together by strong hydrogen bonding between the carboxyl groups of the polymer. One consequence of this effect is the lower viscosity of the polymer solution containing water which also favors formation of smaller particles. Thus, solvent systems based on 2-methoxyethanol containing small proportions of water (until 15% (v/ v) and low polymer concentration (10%, w/v) can be more efficient for obtaining membranes with higher porosity and higher specific surface areas. The electrospinning of cellulose acetate phthalate from 2methoxyethanol−water mixtures proceeded without interruption and the polymer jet was as uniform as in the case of 2methoxyethanol alone, previously described.23 No variation was observed from the electrospinnability point of view depending on the polymer concentration and on the proportion of water in the mixture. 3.1.2. Ultrafine CAP Fibers. As it has been already shown for 2-methoxyethanol solutions,23 higher polymer concentrations (up to 35%, w/v) provided smooth nanofiber mats and the morphology of the nanosized material gradually changed from particles to beaded nanofiber and finally to nanofiber mats. The same behavior was observed in the case of electrospinning of CAP from 2-methoxyethanol−water mixtures. SEM micrographs in Figure 4 reveal that nanofiber mats obtained from 2methoxyethanol−water mixture 85/15 (v/v) at 30% (w/v) polymer concentration appear more uniform in terms of entanglement and fibers diameters. Besides, TEM images (Figure 5) suggest that fibers diameters produced from solvent mixture could be lower than those obtained from 2-methoxyethanol solvent. This fact is expected because of the presence of water which determines higher conductivity for the solution in this mixture (19.66 μS/cm) as compared with the solution in 2-methoxyethanol (5.52 μS/ cm), as well as lower viscosity for water-containing solution: 17 800 cP comparatively with 28 000 cP in the absence of water. 3.2. Thermal Behavior of Nanostructured CAPs. During preliminary experiments, we have observed that the composition of the solvent used for electrospinning experiments did not produce significant differences between the obtained CAP nanoproducts from the point of view of their thermal behavior. For this reason, in this section we discuss the results obtained during thermal treatment of CAP nanofibers and powders obtained from polymer solutions in 2-methox-

yethanol−water mixture 85/15 (v/v) in comparison with the behavior of CAP film. It is established that, irrespective of the solvent used for electrospinning process, the two CAP nanostructures obtained in this work have specific surface areas of the same size order and much higher than those of CAP films which have a thickness of about 10 μm. This can be an important parameter for the behavior of these different CAP morphologies when they are subjected to thermal treatment in dynamic conditions. Thermograms of nanofibers and powder of CAP are quite similar (Figure 6), and it can be seen that both nanostructures are apparently less stable to thermal treatment up to 600 °C as compared with the film.

Figure 6. TG and DTG curves obtained at 10 °C/min for CAP: (*) film; (○) fibers; (▲) powder.

Three degradation stages could be detected on TG-DTG curves for all the samples (Figure 6), but the amount of the solid residue after the thermal treatment represents 16.45 wt % from the initial sample for the film while it is reduced to only 8.00 and 7.50 wt % in the case of the fibers and powder, respectively. Differences between the nanostructured products and the film with respect to the rate of weight loss are more pronounced in the initial stages of the process: 10 wt % of the film sample is removed at 201 °C while the corresponding temperature is considerably lower for the fibers (164 °C) and the powder (170 °C). This is no more the case at higher temperatures of exposure when 50 wt % of the initial sample is 700

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Figure 7. 3D FTIR spectra of gaseous products evolved during thermal degradation of CAP film (a), fibers (b), and powder (c).

A comparative analysis of FTIR spectra of the film on one hand and of the powder and fibers on the other hand clearly evidence some peculiarities of nanostructured CAPs with respect to the thermal behavior. In Figure 8, the bands characteristic to the anhydride groups as detected in gaseous products evolved at 172 °C are clearly more pronounced for fibers and powders of CAP than for the film because the highly porous micro/nanostructures present a much higher specific surface than in the case of the more compact product (the film), and this feature allows a much easier diffusion of the degradation product. At higher temperatures, the amount of the gases evolved from the film is considerably increased and the bands specific to anhydride also increase. The initial characteristic gas phase CO2 peak at 2360 cm−1 is attributable to air flow fluctuation found within the air vent inside the IR beam chamber (due to the presence of CO2 content in the laboratory atmosphere), but it is possible that this CO2 could be adsorbed for a while on the very high surface of nanoparticles and nanofibers and subsequently evolved gradually when flowing the helium inside the chamber. This could explain the decrease of this peak with increasing the temperature and time of exposure just for nanopowder and nanofibers, not in the case of the film (see Figure 8b and c comparatively with a). The wide absorption band at 3200 cm−1 is characteristic to the MCT detector of the TGA-IR external module, but this could be overlapped with the absorption band of acetic acid. The spectral characteristics of gaseous products as discussed above for anhydride groups region are confirmed by FTIR

degraded at about the same temperature (about 325 °C) for all the three materials. In order to find an explanation for this thermal behavior we have further examined the information provided by FTIR and mass spectrometry analyses. Thus, Figure 7 emphasizes 3D FTIR spectra of gaseous products evolved during the degradation process of the three investigated products for all the studied temperature range. For a more detailed examination, in Figure 8 are presented FTIR spectra recorded for the gaseous product evolved at temperatures corresponding to maxima on DTG curves and in Figure 9 are presented FTIR spectra for the solid residue at 175 °C as both transmission (Figure 9a) and ATR (Figure 9b). In our previous paper on thermal stability of CAP,26 we found out that when treating films of CAP at temperatures between 120 and 220 °C one of the main degradation products as detected by HPLC is the phthalic anhydride which is partially evolved during the process. Thus, new bands of absorption specific to the anhydride groups could be detected on IR spectra in the vicinity of 1860−1780 cm−1 (usually assigned to the carbonyl stretching vibration), at 910 cm−1 (assigned to the anhydride cycle) and 715 cm−1.26 Figure 8 in this paper shows evidence of the presence of all these anhydride peaks in the gases evolved during thermal degradation of the three samples at various temperatures. Besides, another strong IR band specific to cyclic anhydrides at about 1260 cm−1 appears in the spectrum of gaseous products, but it cannot be identified on the solid residue spectrum (Figure 9) because of the superposition over the acetyl band in this region. 701

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Figure 8. FTIR spectra of gaseous products evolved during thermal degradation of CAP film (a), fibers (b), and powder (c) at temperatures corresponding to maxima on DTG curves.

anhydride evolved during degradation of CAP fibers (a), powder (b), and film (c) as a function of temperature. It is observed that phthalic anhydride can be detected in degradation products at lower temperatures in the case of the fibers and powder (about 170 °C) than for the film (above 200 °C). This behavior is due to the higher specific surface of nanostructured CAP products as it is also confirmed by FTIR analysis discussed above. MS spectra also evidence the presence of other compounds like acetic acid, formic acid, phthalic acid, water, and carbon dioxide beside phthalic anhydride.

analysis (transmission spectra) of the solid residue at 175 °C (Figure 9a) where the most pronounced band specific to anhydride groups at 1870 cm−1 appears in the case of the film. It should be further noted that ATR spectra do not emphasize any trace of anhydride on the surface of any of the three investigated products (Figure 9b) which is also consistent with the above explanation. Mass spectrometry used to identify the degradation products proved that one of the main gaseous products evolved was phthalic anhydride as we have shown previously using HPLC method.26 Figure 10 presents the amounts of phthalic 702

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Figure 9. FTIR spectra for the solid residue of CAP at 175 °C as (a) transmission and (b) ATR. Figure 10. MS analysis of phthalic anhydride produced by thermal degradation of CAP fibers (a), powder (b), and film (c) as a function of temperature.

3.3. Antimicrobial Activity of Nanostructured CAPs. The antimicrobial tests show evidence of the susceptibility of the two investigated microorganisms over the nanofiber samples and nanopowders of CAP as it is illustrated in Figures 11 and 12 by the occurrence of an inhibition zone around the sample. For CAP powders, in Table 1 the antimicrobial activity is expressed by the diameter of the inhibition zone, as in the case of CAP films previously reported.31 Both nanopowders of CAP exhibit antibacterial activity, but this is slightly more pronounced in the case of powder obtained from solution in 2-methoxyethanol−water mixture 85/15 (v/v) (P2 sample),

probably because of the lower particle size resulted in these conditions. In the case of CAP nanofibers, the samples were soaked on the surface of the culture medium and the inhibition zone in this case may be associated with the area occupied by the sample and around it. The dark color of the sample area and the halo around it suggest the inhibition of microorganism growth within these areas. 703

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Figure 11. Antimicrobial tests for CAP nanopowders obtained from solutions in 2-methoxyethanol (P1) and in 2-methoxyethanol−water mixture 85/15 (v/v) (P2) at 10% (w/v) polymer concentration, against S. aureus (a) and E. coli (b).

Figure 12. Antimicrobial tests for CAP nanofibers obtained from solutions in 2-methoxyethanol (F1) and in 2-methoxyethanol−water mixture 85/15 (v/v) (F2) at 10% (w/v) polymer concentration, against S. aureus (a) and E. coli (b).

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CONCLUSIONS Cellulose acetate phthalate (CAP) micro/nanoparticles obtained from 2-methoxyethanol at 10% (w/v) polymer concentration and those obtained from 2-methoxyethanol− water mixture 85/15 (v/v) at 10% (w/v) polymer concentration exhibit lower width of their walls and lower diameters than particles obtained from 2-methoxyethanol at 12.5% (w/v) polymer concentration previously reported. Also, polymer solution in the solvent mixture 2-methoxyethanol−water 85/ 15 (v/v) gives smaller particles with specific surface area higher than of those produced from 2-methoxyethanol solution. CAP nanofiber mats obtained from 2-methoxyethanol−water mixture 85/15 (v/v) at 30% (w/v) polymer concentration appear more uniform and fibers diameters produced from solvent mixture are lower than those obtained from 2methoxyethanol solvent. TG analysis reveals that CAP nanoproducts exhibit an apparent lower stability than CAP films. Although TG/DTG curves show a lower temperature of weight loss for the first stage of degradation for nanostructured products as compared with the film, FTIR investigations of the residual polymer and the evolved degradation gas products as well as mass spectrometry evidence the presence of phthalic anhydride as a main degradation product for all CAP samples. The higher porosity and specific surface areas of nanostructured CAPs allow a better diffusion of this degradation product which is easier and continuously eliminated from these samples during the thermal treatment.

Nanostructured CAPs exhibit antimicrobial activity on both Staphylococcus aureus and Escherichia coli.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Fang, J.; Niu, H. T.; Lin, T.; Wang, X. G. Applications of electrospun nanofibers. Chin. Sci. Bull. 2008, 53, 2265. (2) Subbiah, T.; Bhat, G. S.; Tock, R. W.; Parameswaran, S.; Ramkumar, S. S. Electrospinning of nanofibers. J. Appl. Polym. Sci. 2005, 96, 557. (3) Liu, H.; Hsieh, Y.-L. Ultrafine fibrous cellulose membranes from electrospinning of cellulose acetate. J. Polym. Sci., Part B: Polym. Phys. 2002, 40, 2119. (4) Liu, H.; Tang, C. Electrospinning of Cellulose Acetate in Solvent Mixture N,N-Dimethylacetamide (DMAc)/Acetone. Polym. J. 2007, 39, 65. (5) Han, D.; Gouma, P. I. Electrospun bioscaffolds that mimic the topology of extracellular matrix. Nanomed.: NBM 2006, 2, 37. (6) Chen, L.; Bromberg, L.; Alan Hatton, T.; Rutledge, G. C. Electrospun cellulose acetate fibers containing chlorhexidine as a bactericide. Polymer 2008, 49, 1266. (7) Son, W. K.; Youk, J. H.; Lee, T. S.; Park, W. H. Electrospinning of ultrafine cellulose acetate fibers: Studies of a new solvent system and acetylation of ultrafine cellulose acetate fibers. J. Polym. Sci., Part B: Polym. Phys. 2004, 42, 5.

704

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Methods in Carbohydrate Chemistry; Whistler, R. L., Ed.; Academic Press: New York, London, 1963; Vol. 3, 201−203. (30) Wistreich, G. A. Microbiology Laboratory; Prentice Hall: Upper Saddle River, NJ, 2000. (31) Necula, A. M.; Dunca, S.; Stoica, I.; Olaru, N.; Olaru, L.; Ioan, S. Morphological properties and antibacterial activity of nano-silver containing cellulose acetate phthalate films. Int. J. Polym. Anal. Charact. 2010, 15, 341.

(8) Zuwei, M.; Kotaki, M.; Ramakrishna, S. Electrospun cellulose nanofiber as affinity membrane. J. Membr. Sci. 2005, 265, 115. (9) Wu, X.; Wang, L.; Yu, H.; Huang, Y. Effect of solvent on morphology of electrospinning ethyl cellulose fibers. J. Appl. Polym. Sci. 2005, 97, 1292. (10) Park, J. Y.; Han, S. W.; Lee, I. H. Preparation of Electrospun Porous Ethyl Cellulose Fiber by THF/DMAc Binary Solvent System. J. Ind. Eng. Chem. 2007, 13, 1002. (11) Jeun, J.-P.; Lim, Y.-M.; Choi, J.-H.; La, H.-S.; Kang, P.-H.; Nho, Y.-C. Preparation of Ethyl-Cellulose Nanofibers via An Electrospinning. Solid State Phenom. 2007, 119, 255. (12) Frenot, A.; Walenius Henriksson, M.; Walkenstrom, P. Electrospinning of cellulose-based nanofibers. J. Appl. Polym. Sci. 2007, 103, 1473. (13) Sui, X.; Yuan, J.; Yuan, W.; Zhou, M. Preparation of Cellulose Nanofibers/Nanoparticles via Electrospray. Chem. Lett. 2008, 37, 114. (14) Kim, C.-W.; Frey, M. W.; Marquez, M.; Joo, Y. L. Preparation of submicron-scale, electrospun cellulose fibers via direct dissolution. J. Polym. Sci., Part B: Polym. Phys. 2005, 43, 1673. (15) Kulpinski, P. Cellulose nanofibers prepared by the Nmethylmorpholine-N-oxide method. J. Appl. Polym. Sci. 2005, 98, 1855. (16) Gyotoku, T.; Aurelian, L.; Neurath, A. R. Cellulose acetate phthalate (CAP): an ‘inactive’ pharmaceutical excipient with antiviral activity in the mouse model of genital herpesvirus infection. Antiviral. Chem. Chemother. 1999, 10, 327. (17) Neurath, A. R.; Strick, N.; Li, Y. Y.; Debnath, A. K. Cellulose acetate phthalate, a common pharmaceutical excipient, inactivates HIV-1 and blocks the coreceptor binding site on the virus envelope glycoprotein gp 120. BMC Infect. Dis. 2001, 1, 17 ; http://www. biomedcentral.com/1471-2334/1/17. (18) Duncan, R. The dawning era of polymer therapeutics. Nat. Rev. Drug Discovery 2003, 2, 347. (19) Neurath, A. R.; Strick, N.; Li, Y. Y. Water dispersible microbicidal cellulose acetate phthalate film. BMC Infect. Dis. 2003, 3, 27 ; http://www.biomedcentral.com/1471-2334/3/27. (20) Neurath, A. R.; Strick, N.; Jiang, S.; Li, Y. Y.; Debnath, A. K. Anti-HIV-1 activity of cellulose acetate phthalate: Synergy with soluble CD4 and induction of “dead-end” gp41 six-helix bundles. BMC Infect. Dis. 2002, 2, 6 ; http://www.biomedcentral.com/1471-2334/2/6. (21) Manson, K. H.; Wyand, M. S.; Miller, C.; Neurath, A. R. Effect of a Cellulose Acetate Phthalate Topical Cream on Vaginal Transmission of Simian Immunodeficiency Virus in Rhesus Monkeys. Antimicrob. Agents Chemother. 2000, 44, 3199. (22) Neurath, A. R.; Strick, N.; Li, Y. Y. Anti-HIV-1 activity of anionic polymers: a comparative study of candidate microbicides. BMC Infect. Dis. 2002, 2, 27. (23) Olaru, N.; Olaru, L. Electrospinning of cellulose acetate phthalate from different solvent systems. Ind. Eng. Chem. Res. 2010, 49, 1953. (24) Huang, C.; Soenen, S. J.; Van Gulck, E.; Vanham, G.; Rejman, J.; Van Calenbergh, S.; Vervaet, C.; Coenye, T.; Verstraelen, H.; Temmerman, M.; Demeester, J.; De Smedt, S. C. Electrospun cellulose acetate phthalate fibers for semen induced anti-HIV vaginal drug delivery. Biomaterials 2012, 33, 962. (25) Roxin, P.; Karlsson, A.; Singh, S. K. Characterization of Cellulose Acetate Phthalate (CAP). Drug Dev. Ind. Pharm. 1998, 24, 1025. (26) Olaru, N.; Olaru, L.; Leanca, M. On Thermal Degradation of Cellulose Acetate Phthalate. Cellul. Chem. Technol. 1995, 29, 253. (27) Olaru, N.; Olaru, L.; Andriescu, A.; Tudorachi, N. Partial Hydrolysis of cellulose acetate in toluene/acetic acid/water system. Angew. Makromol. Chem. 1996, 241, 67. (28) Malm, C. J.; Genung, L. B.; Kuchmy, W. Analysis of Phthalic Acid Esters of Cellulose and of Polyvinyl Alcohol. Anal. Chem. 1953, 25, 245. (29) Tanghe, L. J.; Genung, L. B.; Mench, J. W. ; Determination of Acetyl Content and Degree of Substitution of Cellulose Acetate. In 705

dx.doi.org/10.1021/ie301299d | Ind. Eng. Chem. Res. 2013, 52, 696−705