Regenerated Cellulose Fibers

Keywords

Cellulose • Chitosan • Blend • Cellulose dissolution

The NaOH/urea/thiourea systems have been further modified to enable dissolution of wood cellulose and high DP cellulose and obtain stable spinning solutions [13Zha]. Up to 87 % solubility was obtained for wood cellulose with a DP of 648 using NaOH/acetamide/tetraethylammonium chloride [13Zha]. Morphology and thermal stability of the fibers obtained using the multicomponent system were studied, but the tensile properties were not reported.

NMMO process was used to produce regenerated blend fibers from bacterial cellulose and hydroxypropyl chitosan [13Lu]. The addition of chitosan improved strength and modulus but decreased elongation substantially. Blend fibers also had higher antibacterial activity compared to fibers produced from bacterial cellulose alone.

References

[13Lu] Lu, X., Tang, S., Huang, B., Shen, X., Hong, F.: Fibers Polym. 14(6), 935 (2013) [13Zha] Zhao, D., Liu, M., Ren, H., Li, H., Fu, L., Ren, P.: Fibers Polym. 14(8), 1261 (2013)

Regenerated Protein Fibers

Keywords

Silk • Fibroin • Dissolution • Silk regeneration • Primary structure • Secondary structure • Drawing • Tensile properties • Artificial biospinning

Bombyx mori silk fibroin was regenerated into fibers, and the structural differences between the native and regenerated fibers were investigated [98Tra]. To produce fibers, degummed natural silk fibers were dissolved (17 %) in 9.3 M LiBr and dialyzed for 72 h. The aqueous fibroin solution obtained was cast into films. Later, the films were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and spun into fibers using a methanol coagulation bath. During the coagulation of the fibers in methanol, the predominant a-helix form found in fibroin converts to the insoluble crystalline p-sheet. Fibers obtained after drawing had an average diameter of 88 pm and were composed of 56 % p-sheet, 13 % a-helix, 23 % p-turn, and 11 % undefined component similar to that seen in natural silk [98Tra]. Table 48.1 provides a comparison of the secondary structure in the natural and drawn and undrawn regenerated fibers.

A microfabricated wet spinning apparatus was developed to produce regenerated silk fibers using low quantities (10 mg) of silk proteins [99Jel]. In this approach, silk was dissolved in a good solvent such as hexafluoroisopropanol and extruded into a bad solvent such as methanol. Molecular alignment and p-sheet formation occur as the fibers are extruded through the aperture and the fibers are further drawn to improve the properties. Impressively, fibers produced using B. mori proteins had tensile properties similar to that of the native fibers. In another study, silk fibroin from B. mori was dissolved (13 %) in N-methylmorpholine-N-oxide (NMMO) and regenerated into fibers, and the structure and properties of the fibers were studied [05Mar]. Fibroin solution was extruded through spinnerets with 100, 200, or 300 pm orifice at an extrusion rate of 4 m/min into an ethanol coagulation bath and was later drawn in air. Morphologically, the diameter of the fibers was dependent on the draw ratio, and the finest fibers obtained had a diameter of

Table 48.1 Secondary structural compositions of natural fibroin and regenerated fibroin fibers [98Tra] B. mori fiber Orientation a-Helix (%) Disordered helix (%) P-Sheet (%) P-Tum (%) Undefined (%) Natural fibroin X 8.4 10.2 48.6 20.9 10.2 У 5.5 7.0 58.1 23.6 11.1 Pseudoisotropic 5.6 7.0 56.5 23.1 10.9 Regenerated fibroin X 5.7 7.1 56.4 23.2 10.9 Undrawn Y 6.0 7.3 56.0 23.2 11.0 Pseudoisotropic 5.9 7.3 56.2 23.2 11.0 Regenerated fibroin X 6.5 8.3 53.3 21.7 10.4 3.5 x drawn Y 1.4 3.6 64.2 23.0 10.5 Pseudoisotropic 2.9 4.8 60.7 22.8 10.5

19 pm. Undrawn fibers showed ridges on the surface due to protein aggregation but disappeared in the drawn fibers as seen in Fig. 48.1. Fibers were predominantly of the fibroin II (P-sheet) structure and had good thermal stability. The p-sheet formation is shown to occur during coagulation due to the realignment of the intra — and intermolecular forces and leads to substantial improvement in properties [03Li]. Concentration of the protein solution and temperature determine the extent of a — and p-sheets and the crystallization in the fibers [00Mag]. Random coil conformation was obtained when dilute silk fibroin solutions were dried between 0 and 50 °C, whereas a — and p-crystals were obtained by casting concentrated

fibroin solutions [00Mag]. From differential scanning calorimetry (DSC) data, it was found that the exothermic peaks at 65 °C were caused due to the formation of P-sheets in Antheraea pernyi silks. The tensile properties were also dependent on the draw ratio, and some of the properties of the fibers are listed in Table 48.2. As seen from the table, the best regenerated fibers obtained have considerably lower tensile properties compared to native silk fibers. Although most regenerated protein fibers from silk fibroin have been produced using ionic solvents, it has been shown that the fibroin directly extracted from silk glands can be dissolved in 1 % (w/w) sodium dodecyl sulfate and used to develop fibers, films, and other protein-based biomaterials [08Man].

Similar to developing regenerated fibers using B. mori silk, the wild silk pro­duced by A. perni silkworm was regenerated using calcium nitrate solution, and the properties of the regenerated fibroin were studied [01Kwe]. Concentration of calcium nitrate and temperature were found to influence the protein dissolution to a large extent. Solubility increased from 0 to 100 % as the concentration was increased from 4 to 7 M. Similarly, 100 % dissolution was achieved when the temperature was between 100 and 130 °C after 3 h with a calcium nitrate concen­tration of 7 M. Dissolution was suggested to change the conformation of the proteins to а-form and random coil form compared to the predominant p-sheets found in the natural silk. However, other studies have shown that the extent of a — or P-sheet formation in regenerated A. perni fibroin can be controlled during coagula­tion [03Li]. In another study, A. perni silk fibroin was dissolved in lithium thiocya­nate and wet spun into films [09Zuo]. Regenerated protein fibers had a diameter of 0.369 mm with irregular cross section. Proteins were mainly in the p-sheet config­uration and showed typical diffraction peaks, but a-helices and random coils were also present. Tensile properties of the fibers obtained were not reported [09Zuo].

Although strictly not a process of regeneration, an artificial method of biospinning silk fiber matrices was adopted, and the fibers and matrices were used as substrates for tissue engineering. Wild silkworms (A. mylitta) in their fifth instar were collected, and fibers were manually (forcefully) drawn from the silk­worm onto glass slides as shown in Fig. 48.2. Fibers obtained were aligned in

Steps in artificial biospinning of regenerated protein fiber matrices from A. mittrei silk

various fashions to develop matrices for tissue engineering. Alternatively, the silkworms were allowed to naturally spin silk onto Teflon-coated glass plates, and the matrices formed (Fig. 48.2) were collected. Fibers and matrices were degummed and later characterized for their properties, and the potential of using the fibers as substrates for tissue engineering was studied [10Man]. Fibers obtained by forceful extrusion and drawing were circular and had diameters of 12-15 ^m compared to 30-35 ^m for naturally extruded silk. Similarly, the biospun fibers had a tensile strength of 4.1 ± 1.4 g/den, similar to that of B. mori and much higher than that of the natural fibers from A. mylitta. The fibers and matrices developed had enhanced stability to degradation by proteases and found to have good compatibil­ity and supported the attachment and proliferation of fibroblasts [10Man].

References

[98Tra] Trabbic, K. A., Yager, P.: Macromolecules 31, 462 (1998)

[99Jel] Jelinski, L. W., Blye, A., Liivak, O., Michal, C., Verde, G., Seidel, A., Shah, N., Yang, Z.: Int. J. Biol. Macromol. 24, 197 (1999)

[00Mag] Magoshi, J., Magoshi, Y., Becker, M. A., Kato, M., Han, Z., Tanaka, T., Inoue, S., Nakamura, T.: Thermochim. Acta 352-353, 165 (2000)

[01Kwe] Kweon, H., Park, Y. H.: J. Appl. Polym. Sci. 82, 750 (2001)

[03Li] Li, M., Tao, W., Kuga, S., Nishiyama, Y.: Polym. Adv. Technol. 14, 694 (2003)

[05Mar] Marsano, E., Corsini, P., Arosio, C., Boschi, A., Mormino, M., Freddi, G.: Int. J. Biol.

Macromol. 37, 179 (2005)

[08Man] Mandal, B. B., Kundu, S. C.: Biotechnol. Bioeng. 100(6), 1237 (2008)

[09Zuo] Zuo, B., Liu, L., Zhang, F.: J. Appl. Polym. Sci. 113, 2160 (2009)

[10Man] Mandal, B. B., Kundu, S. C.: Acta Biomater. 6(2), 360 (2010)

Biothermoplastics from Renewable Resources

Keywords

PTT • Renewable resource • Biopolymer • Propanediol • Drawing • Annealing • Fiber properties • Orientation • Crystallinity • PTT dyeing • Solid state polymer­ization • Hybrid yarn

PTT is one of the more recently manufactured synthetic fiber that is derived from renewable resource. Companies such as Shell chemical company and Dupont are manufacturing PTT on a commercial scale and are selling the fibers under the trade names of Corterra and Sorona, respectively [03Duh]. PTT is said to have excellent resiliency and softness and also chemical stability and stain resistance which makes them particularly suitable for carpet applications. PTT is produced in a two-step process, similar to the common polyester (polyethylene terephthalate). In the first step, terephthalic acid (TPA) is esterified using 1,3-propanediol or transesterified using dimethyl terephthalate. The second step involves polycondensation of the esterified or transesterified product to remove the polycondensation byproducts until the desired molecular weight is reached. It is the use of 1,3-propanediol that is derived from an renewable resource that makes PTT fibers eco-friendly. Two distinguishing features of producing PTT compared to PET are the use of a titanium catalyst instead of the antimony catalyst and a considerably lower polycondensation temperature. Due to the use of low polycondensation temperatures, the cost of producing PTT is considerably higher than that of PET. In addition, PTT has a melting temperature 20-30 °C lower than that of PET and a low initial modulus that provides high flexibility to the fibers [01Lyo]. The high extensibility of PTT fibers is attributed to the arrangement and orientation of the polymers in the chain. The chemical structure of PTT is shown in Fig. 64.1, PTT fibers have — O-(CH2)3-O bond conformation with a concentration of the repeating units and opposite incli­nation of successive phenylene groups along the chain which force the molecular chain to assume a extended zigzag configuration. The helical structure of PTT with an angle of 60 ° provides an opportunity to extend the PTT chain by drawing during

fiber production (zone-drawing) and improve the tensile properties of the fibers [01Lyo].

Although the chemical composition of PTT is similar to that of PET, the structure of PTT is considerably different. PTT has odd number of methylene units between the terephthalates compared to PET which has three methylene units [01Kim]. In PTT, the propylene glycol segment assumes the trans — gauchegauche-trans conformation in the crystalline phase with two monomers forming a 2/1 helix compared to the all-trans conformation seen in PET. The phenyl groups in the PTT chain are inclined in opposite directions with an angle of 52° between the terephthaloyl residues [04Fri]. Such a structural arrangement provides unique properties to PTT, for instance, outstanding resiliency and chemi­cal resistance. The morphology of PTT fibers was found to evolve in three distinct stages. First, an oriented noncrystalline region is formed leading to an increase in density. This is followed by an increase in the order in the oriented noncrystalline phase which causes crystallization. Finally, an increase in the oriented and non-oriented region occurs with decrease in the amorphous regions.

The influence of take-up speeds (winding speeds) during fiber spinning on the structure and properties of PTT fibers was investigated. Initial modulus of the PTT fibers did not change with increasing speeds whereas the fiber crystallinity, density, and heat of fusion increased [ 11 Kim]. T able 64.1 provides the changes in some of the properties of the PTT fibers with increasing speed. Increase in density and % crystallinity with increasing take-up speed was reported to be due to stress-induced crystallization. At high take-up speeds, small rigid crystallites are formed along the fiber axis leading to decreased birefringence. Substantial decrease in boil-off shrink­age with increasing take-up speed is due to the increased crystallinity and orientation. In a similar study, Wu et al. have studied the effect of take-up velocities between 0.5 and 8 km/min on the structure and properties of the fibers [02Wu]. Fibers processed below 4 km/min were found to have a predominantly amorphous structure whereas those processed above 4 km/min were crystalline. As seen in Fig. 64.2 increasing take-up speeds increased the orientation and crystallinity as evident from the

diffraction arcs becoming sharper and brighter. In addition, cold crystallization decreased substantially at higher take-up speeds whereas the melting temperature remained relatively stable. Similarly, tensile strength was found to increase with increasing take-up speed whereas elongation remained decreased and modulus was constant [02Wu]. Fibers obtained had strength up to 3.4 g/den and initial modulus was 20 g/den [02Wu]. Studies on in situ crystallization of PTT have shown that crystallization occurs in stages and lamellar tips grow in the edge-on and flat-on configurations [08Iva]. As seen in Fig. 64.3 crystal growth was not uniform and large regions of amorphous materials were observed. Based on measurement of birefrin­gence, it was found that a sudden increase in crystalline fraction occurred when the take-up speed was between 4 and 5 km/min [08Kim].

PTT with two different viscosities and molecular weight was blended and melt extruded to form crimp fibers [06Oh]. One of the PTT components had a molecular weight of 30,100 and viscosity of 1.02 compared to molecular weight of 26,967 and viscosity of 0.92. By changing the draw ratio, fibers having fineness between 1.3

and 1.4 denier with various crimp levels were obtained. As seen in Fig. 64.4, fibers had a circular cross-section and crimped to various extents before and after treating in boiling water [06Oh]. Various cross-sectional shapes of the fibers varying from round, peanut, dog bone, and pear-shaped were obtained by changing the crimping conditions [09Luo]. Various shapes of PTT/PET fiber cross-section were detected, such as round, peanut, dog bone, and pear-like shapes, as shown in Fig. 64.5, which were obtained by varying the crimping conditions [09Luo].

Dyeing behavior of PTT fibers was compared with PET fibers at constant and changing temperatures. Several dyeing kinetic parameters and isotherms were reported as given in Table 64.2. It was found that the dyeing rate was controlled by the rate of diffusion of the dye and that smaller dye molecules had higher dyeing rate [02Yan]. The % dye exhaustion for PTT was similar to that of PET fibers even though the dyeing temperature was 100 °C for PTT compared to 130 °C for PET. It was suggested that 100 °C was most suitable for dyeing PTT and that the tempera­ture should be well controlled above 70 °C to obtain uniform dyeing [02Yan].

To improve the dyeability of PTT, a dye fixing additive was introduced into the polymer before extrusion [06Hsi, 07Shu, 09Wan] that enables dyeing of PTT using

acid dyes. Ability to dye the fibers with acid dyes will reduce the cost of dyeing, provide wide range of colors and bright shades, and possibility of dyeing PTT along with wool and nylon. In one such attempt to improve dyeability of PTT, copolyamides were synthesized and blended and later co-extruded into fibers in the presence of an compatibilizer (Surlyn) [09Wan]. Mechanical properties of the

fibers did not show any major change when the additive in the blend was less than 0.1 % but decreased substantially at higher concentrations of the additives as seen in Table 64.3. Tensile strength of the fibers obtained was considerably low compared to the strength of normal PTT and the remarkable decrease in tensile properties at higher concentration of the additives was suggested to be due to the morphological and/or thermodynamic immiscibility. As seen in Table 64.4, substantial improve­ment in dye uptake was observed with the inclusion of the additive due to the presence of polar groups and also due to the reduction in % crystallinity and increase in accessibility of the fibers to dyes and chemicals.

In a similar approach, PTT and cationic dyeable PTT (CD-PTT) were blended and extruded at a temperature of 265 °C in a capillary rheometer [06Hsi]. After extrusion, a portion of the fibers were drawn three times to produce fully drawn yarns. Table 64.5 provides information of some of the properties of the PTT and CD-PTT used to produce the blend fibers. DSC studies indicated that the PTT and CD-PTT components were miscible and the melting temperature decreased with

increase in the content of 5-SSDMI. However, the crystallinities decreased with increase in the proportion of CD-PTT in the blend. Similarly, the tenacities of the PTT/CD-PTT blend fibers also decreased as the 5-SSDMI increased as shown in Fig. 64.6. Similar results were also obtained by [07Shu].

Increasing drawing speed was found to increase the total degree of molecular orientation in both the crystalline and amorphous regions. Contrarily, increasing drawing speed decreased the crystallization temperature but increased crystal size. A continual increase in strength and modulus of the fibers was observed with increase in take-up velocity and draw ratio at all drawing temperatures studied [01Lyo].

To overcome the limitation of PTT production through melt-polymerization, a combination of melt and solid state polymerization (SSP) was proposed [03Duh]. It was reported that PTT does not pose the stickiness problem during SSP and the rate of polymerization of SSP was more than twice that of PET as seen in Table 64.6. Continuous SSP of PTT could be done at 225 °C and it was therefore suggested that a combination of melt and SSP could provide economical fiber grade PTT. The crystallization kinetics of PTT were studied by Chuah and they reported that PTT had a crystallization rate between that of PET and poly(butylene terepthalate) (PBT). Although PTT had odd number of methylene units in it structure, it did not follow the previous understanding that odd numbered polyesters were difficult to crystallize [01Chu]. Polarized optical microscope images show the presence of spherulitic PTT as seen in Fig. 64.7.

Hybrid PTT fibers were prepared by mixing two types of organoclay (IMD-MMT and C12PPh-MMT) with 1,3-propanediol (PDO) and heating the mixture up to 265 °C. Crude solid obtained was washed with water, dried, and later extruded into fibers at 250 °C in a capillary rheometer [06Cha]. Fibers were drawn to various extents and the effect of drawing on the mechanical properties and thermal stability was studied. Table 64.7 provides a comparison of the thermal behavior of the pure and hybrid PTT fibers. The organoclay showed intercalated and partially exfoliated features and had well-dispersed individual clay layers. As seen in Table 64.8, inclusion of the organoclay increased the strength and modulus for the IMD-MMT clay but decreased for the C12PPh-MMT clay due to debonding between the organoclay and the matrix polymer and due to the presence of many nano-sized voids caused by excessive stretching of the fibers. Drawing of the fibers at slow speed resulted in glass transition followed by cold crystallization, and the extent of cold crystallization was in turn dependent on initial crystallinity [01Gre].

Blends of polypropylene (PP), PTT, and nanoclay were prepared and the properties of the fibers were studied [12Hez]. In addition to virgin PP, maleic anhydride grated PP was also blended to improve biocompatibility. SEM images (Fig. 64.7) showed that the PTT and PP were immiscible and PTT appeared as a disperse phase with irregular shapes. Addition of nanoclay decreased the interpar­ticle distance and the size of the dispersed PTT phase. Thermal analysis and X-ray diffraction also showed that the two polymers were not compatible. Table 64.9 provides a comparison of the thermal and crystalline parameters of the PP, PTT, and their blends. Addition of nanoclay and compatibilizer provided improved mechanical properties.

PTT was blended with poly(ether esteramide) (PEEA) with the addition of various amounts of ionomers such as lithium-neutralized poly(ethylene-co- methacrylic acid) copolymer (EMAA-li) and sodium neutralized poly(ethylene- co-methacrylic acid) copolymer (EMAA-Na) [11Kob]. Different effects were

Table 64.7 Comparison of the thermal properties of pure and hybrid PTT fibers containing different extents of clay and at varying draw ratios [06Cha] IMD-MMT C12PPh-MMT % Draw Intrinsic Tm Td Intrinsic 7m Td Clay ratio viscosity (°С) (°С) Residue, 600 °С (%) viscosity (°С) (°С) Residue, 600 °С (%) 0 1 0.84 228 362 1 0.84 228 362 1 1 1 0.81 232 367 8 — — — — 2 1 0.80 232 370 10 0.86 227 371 10 3 1 0.85 232 372 11 0.83 228 370 11 3 — 233 371 11 — — — — 7 — 232 372 10 — — — — 9 — 232 371 10 — — 4 1 — — — — 0.81 227 371 12 3 — — — — — 228 370 12 7 — — — — — 227 370 13 9 — — — — 228 371 13

observed with the different ionomers. Table 64.10 provides a comparison of the changes in thermal properties of the PTT/PEEA blends with various levels of ionomers.

Several researchers have attempted to produce PTT blend fibers with an attempt to improve quality and performance of the fibers. Padee et al., have blended PTT

Table 64.10 Thermal properties of various blends of PTT/PEEA with and without ionomers [1 IKob] Heating Cooling Te TCc А Ясс Tm Tc ДЯ ATc Tc. for PEEA Degree of crystallinity Sample (°С) (°С) (J/g) (°С) (°С) (J/g) (°С) (°С) {%) PTT 45.9 72.4 36.5 229.1 172.6 45.4 17.2 — 31.2 PTT/25 % PEEA 44.2 69.6 29.1 228.1 153.7 32.7 32.0 108.9 29.9 PTT/10 % E/MAA-Li 44.6 68.3 35.6 227.5 171.5 47.9 18.7 — 36.5 PTT/10 % E MAa-Na 44.4 69.2 1.5 227.3 198.1 50.9 5.0 — 38.8 PTT/25 % PEEA/10 % E/MAA-li 44..4 70.3 20.3 227.0 173.5 35.2 18.1 126.3 37.2 PTT/25 %/PEEA/20%E-MAA — li 43.5 69.0 19.6 226.9 175.7 26.3 17.7 137.9 32.8 PTT/25 % PEEA/10 % E MAA-Na 45.5 — 0 227.6 200.3 37.5 5.7 123.3 39.6 PTT/25 % PEEA/20 % E/MAA-Na 44.6 — 0 227.6 199.0 30.3 5.2 125.3 37.8

with PET in various ratios but found that the two polymers were not compatible and it was difficult to produce fibers. Contrarily, Liang et al. have reported that PTT and PET were completely miscible and formed homogenous blends [08Lia]. Various blends of the PTT and PET fibers were found to have a single glass transition temperature and cold crystallization temperature. In addition, polymer-polymer interaction parameter, melt crystallization temperature, and homogeneity of the fracture surfaces observed using scanning electron microscopes were provided as evidence of the miscibility of PTT and PET [08Lia]. Although fibers could not be produced from higher ratios of PET and PTT, fibers were produced from a blend of 10 % PTT and 90 % PET by extruding at a temperature of 250 °C [13Pad]. Melting temperature of both PTT and PET decreased when either fraction was increased and was attributed to the decrease in crystal size. However, crystallization temperature increased with increasing ratio of one polymer in another. Some of the thermal and crystallinity parameters of the pure and blend fibers are shown in Table 64.11. DSC and polarized light microscope suggested significant nucleation and crystallization rate enhancement for PTT by the addition of EMAA-Na. However, addition of lithium ionomer did not enhance PTT nucleation and crystallization [11Kob]. Morphologically, the PEEA was found to segregate into domains of EMAA-Li and EMAA-Na and the ionomer domains were partially or completely covered by PEEA. Such a distribution of the polymers resulted in core-shell morphology that provided synergistic static decay.

The tensile modulus and strength showed a moderate increase with increasing levels of PTT but the 50/50 blend fibers had considerably lower strength than that of PTT fibers. In addition to the ratio of the two polymers in the blend, it has been shown that the type of weave and crimp configuration also affect the properties of the fabrics made from PTT/PET blends [10Luo]. Woven fabrics made from PTT/PET blends were highly elastic and the elasticity could be controlled by varying the fiber production conditions [10Luo].

Instead of blending two synthetic polymers, Wang and Sun developed blends of PTT and cellulose acetate butyrate (CAB) that would make the fibers more environmentally friendly [11Wan]. PTT was reactive melt mixed with maleic anhydride (MA) and blends were later prepared with various ratios of PTT/CAB

and PTT/CAB/PTT-g-MA. Fibers were extruded from a Brabender twin screw extruder at a temperature of 240 °C and screw speed of 100 rpm. SEM studies of the fracture surface of the blend fibers showed that the CAB was evenly distributed in the PTT matrix but PTT and CAB were thermodynamically immiscible. Thermal studies showed that the blend fibers have better thermal stability than the individual neat polymers. To improve properties of the fibers, grafting of MA onto PTT was done and in addition, several compatibilizers were added to enhance the interfacial adhesion. Tensile properties in Table 64.12 show that blends had inferior properties than the neat polymers and addition of compatibilizers significantly increased the tensile strength. To develop PTT nanofibers, PTT was blended with cellulose acetate butyrate and in situ fibrillation was achieved during melt processing [12Li]. In this approach, two immiscible polymer blends were mixed together and melt extruded. Later, the matrix polymer (cellulose acetate) was removed. PTT fibers with average diameter of 145 nm were obtained using this approach. The extruded fibers formed bundles similar to yarns as seen in Fig. 64.8. It was suggested that the nanofibers could be assembled into fabrics for various uses [12Li].

An investigation on the dyeing behavior of PTT fibers showed that unlike PET, PTT could be dyed at 100 °C under atmospheric conditions using disperse dyes. However, higher temperatures (110-120 °C) produced deeper shades. Table 64.13 shows the K/S values of PTT and PET dyed at different temperatures using three different disperse dyes. As seen in the table, PTT fibers have considerably higher shade depth at any given temperature for all the three dyes studied [03Mad]. Dyed fibers showed good fastness to washing, crocking, and light. In a similar study, poly (trimethyelene-co-butylene-terephthalate) copolymer filaments were found to have better dyeability and could be dyed at room temperature [09Zou]. The kinetics of dyeing PTT with an azo disperse dye (C. I. Disperse Red 82) was studied by Ovejero et al. [07Ove]. Dyeing rate was found to increase with temperature and acceptable exhaustions were not obtained even above dyeing temperature above 80 °C. How­ever, a dye exhaustion rate of 90 % was obtained when the dyeing was done at 90 ° C [07Ove].

Polyblend fibers of poly(trimethylene terephthalate) and cationic dyeable poly (trimethylene terephthalate) were produced in various ratios and the dyeing behav­ior was studied. Unlike PTT, CD-PTT contains 5-sodium sulfonate dimethyl

H-foKHjhOOC-O-COtaOH + 2NaOH — и-г<ХСН2)3оос-0-со-}-пои + NaOOC—(3^COONa + HO(CH2)3OH

isophthalate (5-SSDMI) that contains the sulfonate (SO3Na) groups and therefore can be easily dyed. The polymer blends could be considered to be miscible but the addition of 5-SSDMI decreased the tensile properties and crystallinity of the fibers [06Hsi].

Since PTT is a thermoplastic polymer, it would be feasible to reprocess and use thermoplastic products from PTT. To understand the potential of converting PTT waste into successful products, the effects of reaction media, composition, temper­ature, and rate of depolymerization of PTT were studied [01Kim]. Figure 64.9 shows the mechanism of alkaline hydrolysis of PTT. As seen from the figure, the products obtained after depolymerization of PTT are ethylene glycol and disodium terephthalate. It was found that the depolymerization occurs in two stages believed to be due to the twisted and crumpled configuration of the polymers. Some of the depolymerization parameters that were obtained during the study are given in Table 64.14.

In a similar study, the surface alkaline hydrolysis of PTT filaments at high spinning speeds was investigated with an aim to obtain more porous and hydro­philic fiber surface [04Kot]. Increasing spinning and hydrolysis time had a direct effect on the weight loss of the fibers which varied from 5 to 30 %. A more predominant effect on weight loss was observed when the spinning speed was increased at heat setting temperatures between 100 and 180 °C. Substantial weight loss of up to 70 % was observed when the heat setting temperature was 180 °C and the spinning speed was about 2,000 m/min. However, the weight loss decreased to about 50 % when the spinning speed was 6,000 m/min [04Kot]. Changes in the

morphology of the fibers after hydrolysis at 86 °C for 90 min at various spinning speeds and heat setting at 180 °C are shown in Fig. 64.10. As seen from the figure the fibers have considerable number of pores and under these conditions, the pore size varied from 1 to 1.2 pm [04Kot].

PTT is preferable for carpet applications due to its high resiliency. However, PTT is mostly made in the staple form whereas bulk continuous filaments (BCF) are preferred for carpets [04Chu]. PTT has also been made into BCF by extruding the polymer at a melt temperature of 250-265 °C into multiple filaments that are cooled by air, drawn between two hot air rollers, and texturized into BCF. It was found that PTT BCF bulk development during heat treatment is a function of the DUO II yarn preheating temperature and the texturing air temperature.

The high surface reflectance of polyesters including PTT and PET poses problems in obtaining dark shades on the fibers. Several approaches have been used to modify the surface of PET and decrease the surface reflectance. In one such approach, PTT-PET blend fabrics were UV irradiated to create micro and nanoscale roughness through photoxidation [06Jan]. SEM images in Fig. 64.11 clearly show the increase in roughness (58 nm to 122 nm at a UV dose of 9.5 J/cm2) of the fibers after the UV treatment. When dyed with Disperse Red 60 and C. I. Disperse Blue 56, both the UV irradiated PET and PTT fabrics showed no deterioration in dyeability and similar shade depth (K/S) values [06Jan]. However, lightness

decreased due to irradiation before and after treatment when dyed with black disperse dyes [06Jan]. The dyed fabrics also showed excellent colorfastness to laundering and rubbing.

References

[01Chu] Chuah, H. H.: Polym. Eng. Sci. 41(2), 308 (2001)

[01Gre] Grebowicz, J. S., Brown, H., Chuah, H., Olvera, J. M., Wasiak, A., Sajkiewicz, P., Ziabicki, A.: Polymer 42, 7153 (2001)

[01Kim] Kim, J. H., Lee, J. J., Yoon, J. Y., Lyoo, W. S., Kotek, R.: J. Appl. Polym. Sci. 82, 99 (2001)

[01Lyo] Lyoo, W. S., Lee, H. S., Ji, B. C., Han, S. S., Koo, K., Kim, A. S., Kim, J. H., Lee, J., Son, T. W., Yoon, W. S.: J. Appl. Polym. Sci. 81, 3471 (2001)

[02Wu] Wu, G., Li, H., Wu, Y., Cuculo, J. A.: Polymer 43, 4915 (2002)

[02Yan] Yang, Y., Brown, H., Li, S.: J. Appl. Polym. Sci. 86, 223 (2002)

[03Duh] Duh, B.: J. Appl. Polym. Sci. 89, 3188 (2003)

[03Mad] Madhavamoorthi, P., Premalatha, C.: Synthetic Fibers 32, 4 (2003)

[04Chu] Chuah, H. H.: J. Appl. Polym. Sci. 92, 1011 (2004)

[04Fri] Frisk, S., Ikeda, R. M., Chase, D. B., Kennedy, A., Rabolt, J. F.: Macromolecules 37, 6027 (2004)

[04Kot] Kotek, R., Jung, D., Kim, J., Smith, B., Guzman, P., Schmidt, B.: J. Appl. Polym. Sci. 92, 1724 (2004)

[06Cha] Chang, J., Mun, M. K., Kim, J.: J. Appl. Polym. Sci. 102, 4535 (2006)

[06Hsi] Hsiao, K. J., Lee, S. P., Kong, D. C., Chen, F. L.: J. Appl. Polym. Sci. 102, 1008 (2006) [06Jan] Jang, J., Jeong, Y.: Dyes Pigments 69, 137 (2006) [06Oh] Oh, T. H.: J. Appl. Polym. Sci. 102, 1322 (2006)

[07Ove] Ovejero, R. G., Sanchez, J. R., Ovejero, J. B., Valldeperas, J., Lis, M. J.: Text. Res. J. 77, 804 (2007)

[07Shu] Shu, Y. C., Hsiao, K. J.: J. Appl. Polym. Sci. 106, 644 (2007)

[08Iva] Ivanov, D. A., Bar, G., Dosiere, M., Koch, M. H.J.: Macromolecules 41(23), 9224 (2008)

[08Kim] Kim, K. H., Cho, H. H., Ito, H., Kikutani, T.: J. Polym. Sci. B Polym. Phys. 46(9), 847 (2008)

[08Lia] Liang, H., Xie, F., Chen, B., Guo, F., Jin, Z., Luo, F.: J. Appl. Polym. Sci. 107, 431 (2008)

[09Luo] Luo, J., Xu, G., Wang, F.: Fibers Polym. 10(4), 508 (2009)

[09Wan] Wang, L., Hu, Z.: Text. Res. J. 79, 1135 (2009)

[09Zou] Zou, H., Yi, C., Wang, L., Xu, W.: Mater. Lett. 63, 1580 (2009)

[10Chi] Chiu, H.: Polym. Eng. Sci; 50, 2236 (2010)

[10Luo] Luo, J., Wang, F., Li, D., Xu, B.: Text. Res. J. 81(8), 865 (2010)

[11Kim] Kim, J. H., Yang, S. S., Hudson, S. M.: Fibers Polym. 12(6), 771 (2011)

[11Kob] Kobayashi, T., Wood, B. A., Takemura, A.: J. Appl. Polym. Sci. 119, 2714 (2011) [11Wan] Wang, D., Sun, G.: J. Appl. Polym. Sci. 119, 2302 (2011)

[12Hez] Hezavehi, E., Bigdeli, A., Zolgharnein, P.: Mater. Sci. Poland 30(2), 82 (2012)

[12Li] Li, M., Xiao, R., Sun, G.: J. Appl. Polym. Sci. 124, 28 (2012)

[13Pad] Padee, S., Thumsorn, S., On, J. W., Surin, P., Apawet, C., Chaichalermwong, T., Kaabbuathong, N., O-Charoen, N., Srisawat, N.: Energy Procedia 34, 534 (2013)

Natural Cellulose Fibers from Renewable Resources

Keywords

Sorghum stalk • Sorghum leave • Fiber extraction • Fiber properties • Single fiber

Unlike corn stover where only the husks and stalks have been used for fiber production, fibers have been produced from both the leaves and stalks of sorghum plants [07Red]. As seen in Table 4.1, fibers obtained from sorghum stalks and leaves have similar properties. Tensile properties of the sorghum fibers were similar to that of jute, but the elongation was lower than that of linen or cotton fibers. About 20 % fibers were obtained from both the stems and leaves, and the fibers had relatively shorter lengths compared to fibers obtained from cornhusks.

Reference

[07Red] Reddy, N., Yang, Y.: J. Agric. Food Chem. 55, 5569 (2007)

Chitin, Chitosan, and Alginate Fibers

Keywords

Metal sorption • Catalysis support • Tubular scaffold • Nerve tissue engineering

Hollow chitosan fibers (Fig. 27.1) were fabricated by removing unprecipitated chitosan through air and water flow [01Vin, 08Ara]. These hollow fibers have been used for various applications. For instance, hollow chitosan fibers were used to extract Cr(VI) with aliquot 336 by assembling the hollow fibers into a module and circulating the metal ion solution and extract inside the hollow lumen. It was observed that Cr(VI) ions were sorbed on the fiber and also by solvent which flowed through the fiber. Reacetylation of the fiber maintained the efficiency of extraction and also increased the mechanical and chemical resistance [01Vin]. Hollow chitosan fibers supported with palladium were also used to degrade nitrophenol found in industrial waste waters [04Vin]. A sodium formate system and a hydrogen system were used, and the former was found to be more efficient. Experimental parameters such as residence time, recycling, and concentration of the chemicals were reported to determine the efficiency of degradation. Similarly, palladium — supported chitosan fibers were also used as a catalytic system for hydrogenation of nitrotoluene [08Blo]. The diffusion of biological agents such as tryptophan, chlor­amphenicol, amoxicillin, and vitamin B12 through hollow chitosan fibers was investigated to understand the potential of using the fibers as nerve guide channels [08Pei]. pH of the permeant was found to have the most significant impact on permeability with the permeability coefficient decreasing with the molecular weight of the permeant. These fibers were considered suitable for catalysis and support for biological molecules or enzymes or for controlled drug release and enzyme immobilization [08Pei]. Hollow chitosan/cellulose acetate fibers were produced by wet spinning for use as absorptive membranes for affinity-based separations [05Liu]. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) studies showed interactions between cellulose acetate and chitosan. Blend fibers had good tensile properties and showed high surface absorption for copper

ions and bovine serum albumin [05Liu]. Absorption of copper up to 30 mg/g of chitosan and 8 mg/g of bovine serum albumin was obtained.

Porous chitosan tubular scaffolds for nerve tissue engineering were developed by knitting and lyophilizing. Chitosan fibers were knitted into tubes into which mandrels (acupuncture needles) were inserted, and the assembly was later dipped in a chitosan solution and lyophilized. The freeze-dried samples were immersed in NaOH solution and then neutralized with acetic acid, and the mandrels were then removed to obtain the hollow structures [06Wan]. Figure 27.2 shows a digital image of the hollow tubular scaffolds produced, and Fig. 27.3 shows the SEM image of the highly porous matrix with axially oriented microchannels. Scaffolds developed had an average porosity of 68.8 %, and the total pores were 0.031 m2/g. It was also found that the inner surface of the scaffold was about 30 times higher than that of the hollow tubes. Neuro-2a cells cocultured on the scaffolds showed confluent cell growth, 5 days after incubation. Extensive growth of the cells oriented along the scaffold in the channel and bridging between the cells was observed as seen in Fig. 27.3. In a continuation of this work, porous fiber-reinforced nerve conduits were fabricated from chitosan yarns using braiding, casting, and lyophilization. Conduits developed were permeable to glucose (180 Da) and to bovine serum albumin (66,200 Da) and had tensile strength of about 3.4 MPa

(0.03 g/den). In vitro and in vivo studies showed that the conduits were compatible with the tissues and suitable for medical applications [07Wan].

Composite fibers composed of chitosan (2 x 105 Mw; 76 % deacetylation), and carbon nanotubes were developed via wet spinning. CNTs (0.7-1.3 nm in diameter and several micrometers in length) dispersed in chitosan solution were extruded into an ethanol-NaOH coagulation bath. Fibers obtained were cross-linked with 25 % glutaraldehyde to improve performance properties [06Spi]. Fibers obtained after centrifuging did not show any aggregation of the CNTs and resulted in fibers with smooth surfaces. CNT-reinforced fibers had considerably low elongation of 10-14 % compared to 24 % for the neat chitosan fibers. However, the CNT-containing fibers had a modulus of 77 g/den compared to 32 g/den for the neat chitosan fibers. In the swollen state, the CNT-reinforced fibers showed higher elongation but lower strength compared to their properties in the dry state. The swollen microfiber gel was reported to have strength of 0.4 g/den similar to that of the pure chitosan fibers.

References

[01Vin] Vincent, T., Guibal, A.: Ind. Eng. Chem. Res. 40(5), 1406-1411 (2001)

[04Vin] Vincent, T., Guibal, A.: Environ. Sci. Technol. 38, 4233-4240 (2004)

[05Liu] Liu, C., Bai, R.: J. Membr. Sci. 267, 68 (2005)

[06Spi] Spinks, G. M., Shin, S. R., Wallace, G. G., Whitten, P. G., Kim, S. I., Kim, S. J.: Sensor Actuator B 115, 678 (2006)

[06Wan] Wang, A., Ao, Q., Cao, W., Yu, M., He, Q., Kong, L., Zhang, L., Gong, Y., Zhang, X.: J. Biomed. Mater. Res. 79A, 36-46 (2006)

[07Wan] Wang, A., Ao, Q., Wei, Y., Gong, K., Liu, X., Zhao, N., Gong, Y., Zhang, X.: Biotechnol. Lett. 29(11), 1697 (2007)

[08Ara] Araiza, R. N.R., Rochas, C., David, L., Domard, A.: Macromol. Symp. 266, 1-5 (2008)

[08Blo] Blondet, F. P., Vincent, T., Guibal, E.: Int. J. Biol. Macromol. 43, 69 (2008)

[08Pei] Peirano, F., Vincent, T., Guibal, E.: J. Appl. Polym. Sci. 107, 3568 (2008)

Although chitin has limited solubility in common solvents, chitin and chitin derivatives have been electrospun into fibers for various applications. To produce electrospun fibers, chitin was first depolymerized using irradiation and then dissolved using 1,1,1,3,3,3-hexafluoro 2-propanol and fibers with average diameters of 110 nm were obtained [04Min]. After electrospinning, the chitin mats were deacetylated using 40 % aqueous NaOH solution at 60-100 °C to achieve about 85 % deacetylation and form chitosan fibers. SEM images and some of the properties of the chitin and chitosan fibers obtained after deacetylation of the spun chitin membranes are shown in Fig. 58.1. Minimal changes were observed in the diameters of the fibers before and after deacetylation.

Chitin has been chemically modified to facilitate dissolution and obtain electrospun fibers [09Du]. Chitin was acylated to obtain dibutyryl chitin that was soluble in electrospinnable solvents such as acetone, dimethyl formamide, dimethyl acetate, ethanol, and acetic acid. Modified chitin was electrospun into fibers in 100 % form and also as blends with cellulose acetate. Electrospun fibers were later treated with NaOH to convert the chitin into chitosan and cellulose acetate into cellulose. Fibers obtained had diameters from 200 to 550 nm depending on the ratio of chitin and cellulose acetate. It was suggested that the combined one-step

Diameter (nm)

Fig. 58.1 SEM images and physical properties of fibers obtained from chitin and chitosan hydrolysis of chitin and cellulose acetate would be beneficial to develop nanofiber membranes for various applications [09Du].

To improve dissolvability in HFIP, chitin (Mw 920,000; 8 % degree of deacetylation) was irradiated with gamma rays to reduce the Mw to 91,000. Electrospun chitin nanofibers had diameters of 163 nm and electrospun chitin microfibers had an average diameter of 8.8 pm. After being in PBS solution containing lysozyme for 15 days, the chitin nanofibers had about 20 % weight loss indicating that they were considerably stable.

58.1 Electrospun Chitosan Fibers

Miscellaneous Applications of Biofibers from Renewable Resource

Keywords

Biofiber • Renewable resource • Chitin • Nanofibril • Catalytic support • Extrusion

Recyclable green catalyst supports were prepared using catalytically active hybrid cellulose fibers in nanochitin hydrogels [12Das]. Hydrogels containing chitin nanofibrils of 9 nm diameter and several micrometers in length were wet spun into macrofibers by extrusion. Figure 73.1 shows SEM images of the surface of the fibers. The extruded microfibers had a large plastic region of 12 % and work to fracture of 10 MJ/m3. In addition, Nobel metal nanoparticles were added onto the surface of the chitin macrofibers via the amine functional groups. Developed organic-inorganic supports were considered to be suitable for fast catalytic reductions of model compounds.

Reference

[12Das] Das, P., Heuser, T., Wolf, A., Zhu, B., Demco, D. E., Ifuku, S.: Biomacromolecules 13, 4205 (2012)

Natural Cellulose Fibers from Renewable Resources

Keywords

Unconventional cellulose • Unconventional cellulose properties • Unconven­tional cellulose availability

In addition to the by-products from the major food crops, several other nontradi­tional lignocellulosic sources have been studied as sources for fibers. Examples of such plants used for fiber production include bamboo [07Rao], Wrightia tinctoria [05Sub], piassava [06Alm], blue agave [13Kes], stinging nettle [08Bod], sponge gourd [09Gui], Luffa cylindrica [10Siq], and others. Most of these sources are available in small quantities or need to be exclusively grown (bamboo) and do not have highly distinguishable properties. We have therefore not covered these fibers in this chapter.

References

[05Sub] Subramanian, K., Kumar, P. S., Jeyapal, P., Venkatesh, N.: Eur. Polym. J. 41(4), 853 (2005)

[06Alm] Almeida, J. R.M., Aquino, R. C.M. P., Monteiro, S. N.: Compos. Part A 37, 1473 (2006) [07Rao] Rao, M. M.K., Rao, M. K.: J. Compos. Struct. 77, 288 (2007)

[08Bod] Bodros, E., Baley, C.: Mater. Lett. 62(14), 2143 (2008)

[09Gui] Guimares, J. L., Frollini, E., Silva, C. G.D., Wyoch, F., Satyanarayan, K. G.: Ind. Crop. Prod. 30(3), 407 (2009)

[10Siq] Siqueira, G., Bras, J., Dufresne, A.: Bioresources 5(2), 727 (2010)

[13Kes] Kestur, S. G., Fores-Sahagun, T. H.S., Santos, L. O.D., Santos, J. D., Mazzaro, I., Mikowski, A.: Compos. Part A 45, 153-161 (2013)

Natural Protein Fibers

Keywords

Silk • Biospinning • Artificial biospinning • Matrix

To obtain fibers with better properties, an artificial method of biospinning silk fiber matrices was adopted, and the fibers and matrices were used as substrates for tissue engineering. Wild silk worms (Antheraea mylitta) in their fifth instar were col­lected, and fibers were manually (forcefully) drawn from the silkworm onto glass slides as shown in Fig. 38.1a. Fibers obtained were aligned in various fashions to develop matrices for tissue engineering. Alternatively, the silk worms were allowed to naturally spin silk onto Teflon-coated glass plates, and the matrices formed (Fig. 38.1b) were collected. Fibers and matrices were degummed and later characterized for their properties, and the potential of using the fibers as substrates for tissue engineering was studied [10Man]. Fibers obtained by forceful extrusion and drawing were circular and had diameters of 12-15 pm compared to 30-35 pm for naturally extruded silk. Similarly, the biospun fibers had tensile strength of

4.1 ± 1.4 g/den, much higher than that of Bombyx mori or the natural fibers obtained from A. mylitta. The fibers and matrices developed had enhanced stability to degradation by proteases and found to have good compatibility and supported the attachment and proliferation of fibroblasts [10Man].

Reference [10Man] Mandal, B. B., Kundu, S. C.: Acta Biomater. 6, 360 (2010)

Electrospun Fibers from Biopolymers

Keywords

Electrospinning • Polylactic acid • Polyethylene glycol • Polytrimethylene terephthalate • Artificial wool • PHBV • Implant

Synthetic biopolymers such as PLA, PEG, and PHBV that are considered to be suitable for medical applications have been made into electrospun structures. Unique crimped and bicomponent nanofibers were produced from high shrinkage polyethylene terephthalate (PET) and polytrimethylene terephthalate (PTT). The polymers were separately dissolved and electrospun into the same collector from different sources and with opposite charges. Such an arrangement led to the attraction between the oppositely charged polymers and formation of twisted fibers. Such twisted fibers were also produced from polyurethane and polyacrylonitrile and termed as artificial wool [12Li]. Figure 60.1a-d shows SEM images of the twisted fibers obtained with an average diameter of about 800 nm [12Li].

Poly(D, L-lactide-co-glycolide) (PLGA) was electrospun into fibers with diameters ranging from 500 to 800 nm and the scaffold was found to have favorable cell-matrix interactions [02Li]. Scaffolds obtained had strength of 19-23 MPa, elongation of 20-120 %, and modulus of 130-323 MPa, similar to that of skin. Composite nanofibers consisting of poly(ethylene oxide), hydrated iron, and sodium alginate were prepared for multifunctional applications

[12Moo]. Matrices containing fibers with diameters ranging from 159 to 475 nm had ultimate tensile strength of about 32 MPa. Addition of hydrated ion provided the scaffolds ability for bacterial decontamination, and the presence of sodium alginate provided antimicrobial properties [12Moo].

Similar to PLA, PHBV is a synthetic biopolymer considered to be biocompatible and suitable for medical and other applications. Considerable attempts have been made to develop electrospun structures from PHBV. Electrospun fibers from PHBV with coral-like surface microstructure were developed by Yang

et al. [13Yan]. PHBV with a molecular weight of 1,000,000 was dissolved in

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N. Reddy, Y. Yang, Innovative Biofibers from Renewable Resources,

DOI 10.1007/978-3-662-45136-6_60

chloroform (4-16 wt%) and fibers were electrospun by varying the voltage, dis­tance between collector and needle, and extrusion rates. SEM images in Fig. 60.2 depict the beaded and coral-like surface of the fibers. Increasing the temperature decreased the number of beads as seen in Fig. 60.2. Cytotoxicity assays showed that the fibers were biocompatible and promoted cell attachment and proliferation [13Yan]. Defect-free electrospun PHBV fibers were developed for tissue engineer­ing using dichloromethane and dimethylformamide as the solvents [11Kup]. Fibers developed had average diameter of 724 ± 91 nm and used as substrates to culture human skin fibroblast cells. Proliferation of cells on the PHBV fibers was similar to that of polystyrene control whereas gene expression of collagen I and elastin was significantly upregulated and collagen II was downregulated on PHBV fibers after 14 days of culture. The addition of angiogenis factor (R-Spondin 1) to the PHBV

fibers considerably increased wound contracture as seen in Fig. 60.3. As seen in the figure, significantly higher wound healing was obtained after 7 days for the PHBV fibers with and without R. spondin, but the difference was insignificant after 14 days of culture.

PHBV was grafted with poly(N-vinylpyrrolidone) groups and electrospun into fibers for potential drug delivery applications [12Wan]. Grafted PHBV was dissolved (4 %) in chloroform and electrospun into fibers. Later, drugs were loaded onto the fibers and the release behavior was studied. SEM pictures revealed bead — free fibers with surface morphology that did not change after the drugs were released from the fibers. The percentage of drug released from the fibers was found to increase with increasing graft %. Some of the properties of the electrospun fibers obtained are given in Table 60.1.

Blends of PHBV (Mw of 680,000) were also made with poly(e-caprolactone) (Mw of 80,000) and electrospun into matrices for culturing bone cells [11Kha]. The polymers were dissolved in a mixture of chloroform/dimethylformamide and the solution electrospun at various conditions. Among the various conditions studied, a l0 % solution of PHBV/PCL provided smooth fibers that promoted the attachment, proliferation, and differentiation of preosteoblastic cells. Some of the properties of the fibers are given in Table 60.2.

PHBV was also blended with poly(ethylene oxide) and the microstructural, mechanical, and thermal properties of the electrospun fibers were studied [13Bia]. Fibers obtained had diameters between 0.5 and 2.6 pm and were heavily dependent on the ratio of the blend. In terms of structure, separate crystalline phases with interdispersed amorphous phases were seen and the mechanical properties of the blend fibers (Table 60.3) were in between that of the two neat polymers [l3Bia]. In a similar study, PHB and PHB blends with PEO were electrospun into fibers with various amounts of chlorhexidine, an antimicrobial agent, and the potential of using the matrices for controlled release applications was investigated [l4Fer]. Inclusion of l % chlorhexidine resulted in high antimicrobial activity with 100 and 99.69 % reduction in colony-forming units for Escherichia coli and Staphylococcus aureus, respectively. Figure 60.4 shows the zones of inhibition of

Table 60.2 Properties of PHBV and PCL blend fibers at various ratios of PCL in the blend Sample Fiber diameter (pm) Thickness (pm) Water contact angle (°) Strength (MPa) Modulus (MPa) Elongation (%) 4 % PCL/PHBV 0.44 ± 0.09 93 ±7 121 ±2 0.98 ± 0.06 162.1 ±4.6 1.4 ±0.2 6 % PCL/PHBV 0.51 ±0.03 98 ±3 117 ± 1 1.21 ±0.38 145.6 ±3.7 2.3 ±0.6 8 % PCL/PHBV 0.58 ±0.02 109 ±4 106 ±3 1.58 ± 0.17 139.2 ±3.8 2.8 ±0.4 10 % PCL/PHBV 0.77 ± 0.02 117 ± 5 85 ±2 1.84 ±0.09 112.3 ±1.9 4.3 ±0.7 12 % PCL/PHBV 1.08 ±0.06 113 ± 6 90 ±1 1.87 ±0.11 108.8 ±2.2 4.5 ±0.5 14 % PCL/PHBV 1.79 ±0.05 110 ± 5 99 ±1 1.95 ±0.26 102.7 ±2.6 4.9 ±0.2 12 % PCL 0.96 ± 0.04 121 ±2 103 ±1 2.41 ±0.36 82.4 ±5.6 5.7 ±0.8 14 % PHBV 2.19 ±0.07 92 ±4 115 ± 3 1.79 ±0.13 126.7 ±7.1 3.8 ±0.3

Fig. 60.4 Digital images showing the zone of inhibition of the PHB/PEO blend membranes against E. coli (a) and S. aureus (b) at three different levels of the antimicrobial agent [14Fer]

the blend membranes against E. coli and S. aureus at three different concentrations of chlorhexidine. Mechanical properties of the fiber matrices showed considerable increase in strength and modulus but decrease in elongation after the addition of the antimicrobial agent as seen in Table 60.4. It was supposed that chlorhexidine acted as filler and had excellent interfacial adhesion resulting in increased mechanical properties [14Fer].

References

[02Li] Li, W., Laurencin, C. T., Caterson, E. J., Tuan, R. S., Ko, F. K.: J. Biomed. Mater. Res. 60, 613 (2002)

[11Kha] Khasuwan, P., Pavasant, P., Supaphol, P.: Langmuir 27, 10938 (2011)

[11Kup] Kuppan, P., Vasanthan, K. S., Sundaramurthi, D., Krishna, U. M., Sethuraman, S.: Biomacromolecules 12, 3156 (2011)

[12Li] Li, C., Wang, J., Zhang, B.: J. Appl. Polym. Sci. 123, 2992 (2012)

[12Moo] Moon, S., Lee, J.: Polym. Eng. Sci. 53, 1321 (2012)

[12Wan] Wang, W., Cao, J., Lan, P., Wu, W.: J. Appl. Polym. Sci. 124, 1919 (2012)

[13Bia] Bianco, A., Calderone, M., Cacciotti, I.: Mater. Sci. Eng. C 33, 1067 (2013)

[13Yan] Yang, D., Zhang, J., Xue, J., Nie, J., Zhang, Z.: J. Appl. Polym. Sci. 127, 2867 (2013)

[14Fer] Fernandez, J. G., Correia, D. M., Botelho, G., Padrao, J., Dourado, F., Ribeiro, C.,

Lanceros-Mendez, S., Sencadas, V.: Polym. Test. 34, 64 (2014)

Part VII

Fibers from Biotechnology