We studied the electrospinning process of the blend of polylactic acid (PLA) and polybutylene succinate (PBS). The blend PLA/PBS ratio 95/5, 90/10, 85/15 and 80/20 wt% were prepared by dissolved in mixture of solvent between dichloromethane (DCM) and N, N-dimethylformamide (DMF) at ratio 3/1. The suitable condition for electrospun of the blend was 17% wt concentration, 16 kV and 18 cm projection distance. The round fiber with pore on the surface was observed. Increasing content of PBS in the blend impact to the diameter of fibril decreased from 1350, 1290, 1210 and 1170 nm, respectively; while the pore on the surface changes from circle to oval shape. Regarding the thermal properties, blending of PBS increases the glass transition temperature (T g) of PLA without affect to the melting temperature (T m) of the electrospun nanofibers. The best tensile properties of PLA/PBS nanofibers were achieved at blend ratio of 95/5, and Young’s modulus is increased comparing to those of the pure electrospun fibers.
Recently, it has been increasing interested in method to produce polymer fiber using electrostatic spinning technique or electrospinning, which produces fibers diameter in the range of sub-micro meter down to nanometer. The electrospinning technique is a simple and versatile method which utilizes a high voltage source to inject charge of a certain polarity into a polymer solution or melt and then accelerated toward a collector of opposite polarity. It’s capable to produce fiber in biological size scale, and created a new interested in electrospinning for drug delivery application. The fibers exhibit several interesting characteristics, for example, a high surface area to mass or volume ratio, high density of pores in sub-micrometer length scale, vast possibilities for surface functionalization [
Both synthetic and natural polymer nanofibers were produced from electrospinning such as aliphatic polyester, polyvinyl alcohol and polyamide. Among the various aliphatic degradable polyesters, polylactic acid (PLA) has been considered as one of the most interesting and promising biodegradable materials and has been the material of choice to be used in various medical applications, such as surgical sutures [
In order to improve the properties and explore the applications of the material, several approaches have been developed to modify it. Blending with aliphatic polyester was found to be an effective method due to containing the same functionality. The blending with flexible polymers would enhance PLA flexibility [
In this work, electrospinning was applied to fabricate ultrafine fibers from pure PLA, PBS and their blends. Chemical structure of PLA and PBS were showed in
properties of the as-spun PLA/PBS blend nanofiber mats were also investigated.
Polylactic acid, PLA (MW = 5.0594 × 104) was supplied by Nature Work. Polybutylene succinate, PBS (MW = 5.8207 × 104) was supplied by Mitsubishi Chemical Corporation (AZ91TN). Dichloromethane, DCM (analytical grade) was supplied by RCI Labscan Limited, Thailand. N, N-dimethyl formamide, DMF (analytical grade) was supplied by Lab scan Asia Co., Ltd., Thailand. All of the above chemicals were used as received.
To prepare as-spun PLA/PBS blend nanofiber mats, solutions of PBS and PLA were prepared separately with concentration of 17% (w/v) by using DCM and DMF with ratio 3/1 as the solvent. The solutions of PLA/PBS blends were weight ratios of 100/0, 95/5, 90/10, 85/5, 80/20 and 0/100, respectively. The polymer blend solution was fabricated into nanofibers using an electrospinning apparatus at 25˚C with applied electrostatic field strength at 16 kV/18 cm of projection distance.
Solution rotational viscosity of the as-prepared PLA/PBS blend solutions were measured using a rotational viscometer (VISCO STAR Plus L) with carried out at room condition.
Morphology of the blend as-spun nanofiber mats was evaluated by scanning electron microscopy (SEM). The samples were coated with gold under vacuum and then observed by SEM (JEOL JSM 6610LV).
Crystal structures of PLA, PBS and the blend as-spun nanofiber mats were investigated with an X-ray diffraction (XRD) technique with a diffractometer (D8-Discover model from Bruker AXS). The XRD data were collected at 2 theta from 5 to 35 in a step of 0.02˚.
Glass transition temperature (Tg), melting temperature (Tm) values, crystallization temperature (Tc) and enthalpy of melting of blend as-spun nanofiber mats were investigated using DSC (Perkin Elmer DSC7). The samples were first heated and cooled over a temperature range of −60˚C to 230˚C at a rate of 10˚C/min to set a standard thermal history, and heated again at a heating rate of 10˚C/min over a temperature range of −60˚C to 230˚C under nitrogen atmosphere.
The blend as-spun nanofiber mats were cut into a rectangle sheet (2.5 × 10 cm2) according to ASTM D882-02 standard. The thickness of the as-spun mat was about 0.25 mm. Tensile testing was performed on the PLA/PBS blend as-spun mat along with electro-spinning direction using a Texture analyzer (Stable Micro System TA. XT plus) at a crosshead speed of 20 mm/min. The average data value and the standard deviation value from five samples were calculated and recorded.
The rotational viscosity of the as-prepared PLA/PBS blend solutions at different weight ratios in DCM/DMF:3/1 solution is listed in
Scanning electron micrographs of the as-spun PLA/PBS fibres that prepared using a various blend ratio were shown in
Obviously, the as-spun PLA fibers (100/0) appeared as circular in their cross-section and pore-like structure appeared at the surface of fibers, which is in good agreement to the previous report [
PLA/PBS blend ratio | Rotational viscosity (cP) | Fiber diameter (nm) | Fiber content (count/ 100 µm2) |
---|---|---|---|
100/0 | 56.4 ± 2.4 | 1360 ± 570 | 25 |
95/5 | 54.4 ± 2.0 | 1350 ± 680 | 19 |
90/10 | 53.7 ± 2.0 | 1290 ± 520 | 21 |
85/15 | 50.2 ± 1.3 | 1210 ± 360 | 20 |
80/20 | 43.5 ± 0.8 | 1170 ± 330 | 21 |
0/100 | 54.6 ± 0.7 | 550 ± 200 | 68 |
The applied electrostatic field strength was 16 kV/18cm.
surface of the fibers is postulated to be a result of the high volatility of the solvents and the microscopic phase separation of the solutions at the surface of the ejected, charged jet that occurred very rapidly during electrospinning. With the latter notion in mind, the solvent-rich phase readily transformed into the pore-like structure. On the other hand, the as-spun PBS fibers (0/100) appeared to be circular in their cross-section and the smooth surface. Interestingly, even the same concentration and same range of solution viscosity, as-spun PBS fibers were found to lower average diameter as compared to as-spun PLA fiber.
When PLA blends with PBS were electrospun, it was found that the presence of PBS does not affect substantially the morphology of the PLA matrix phase.
The as-spun blend fibers were still circular in cross-section with pore-like structure. It is interesting that as increasing PBS content, diameter of pore-like structure increased. This might be the effect of lowering viscosity of polymer blend solution as increasing PBS content, and lead to easy expansion of solvent-rich phase during electrospinning.
However, their diameters were found to decrease with increasing amount of added PBS solution (see
For the as-spun PLA/PBS fibers, the obtained diffraction patterns apparently exhibited only one broad diffraction peak centering at about the same 2θ value of the pure as-spun PLA fibers. The intensity of the XRD peak at 2θ of about 16.5˚ and 17.9˚ were decreased at the present of PBS in the blend. This suggests that the percentage crystallinity of the PLA phase decreased with increasing PBS content.
It is obvious that present small amount of PBS in the blend could enhance the crystallinity of the PLA, and it is in a good agreement with the hypothesis of the PBS could interpenetrate into the PLA during solution blending, and consequence in modification the crystallinity of the PLA, which could be observed in
the XRD results.
The DSC thermograms of the as-spun PLA, PBS and PLA/PBS fibers were shown in
As-spun PBS fibers possess a glass transition temperature (Tg) at −31.2˚C, cold crystallization temperature (Tcc) at ca. 75.5˚C, melting temperature (Tm) at ca 104.9˚C, which has percentage of crystallization at 41.3%. It has very high crystallinity comparing to those of ultrafine fibers of common polymers [
PLA/PBS blend ratio | PLA phase | PBS phase | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Tg (˚C) | Tm (˚C) | Tcc (˚C) | Hm (J/g) | Xc (%) | Tg (˚C) | Tm (˚C) | Tcc (˚C) | Hm (J/g) | Xc (%) | |
100/0 | 76.4 | 160.7 | 114.9 | 17.0 | 18.1 | - | - | - | - | - |
95/5 | 70.3 | 160.4 | 108.9 | 22.3 | 23.8 | - | - | - | - | - |
90/10 | 62.4 | 160.3 | 108.2 | 21.4 | 22.8 | - | - | - | - | - |
85/15 | 61.7 | 160.2 | 108.1 | 20.3 | 21.7 | - | 101.2 | 72.4 | 11.3 | 5.7 |
80/20 | 73.4 | 160.6 | 106.7 | 19.0 | 20.3 | −30.1 | 104.9 | 73.8 | 12.1 | 6.1 |
0/100 | - | - | - | - | - | −31.2 | 104.9 | 75.5 | 82.5 | 41.3 |
was reported that the crystallization of electrospun polymer was retarded because the rapid solidification of fiber prohibits crystallinity of polymer. Although the crystallization of the as-spun PBS fibers was retarded, the PBS fibers showed high crystallinity due to its high crystallization rate [
While as-spun PLA fibers possess a glass transition temperature (Tg) at 76.4˚C, cold crystallization temperature (Tc) at ca. 115˚C, melting temperature (Tm) at ca. 161˚C, which has percentage of crystallization at 17%. This result was in accordance to others study in thermal behavior of PLA-based electrospun fibers [
For the as-spun PLA/PBS fibres, DSC thermograms show only thermal characteristic of PLA phase when the PBS content in the range of 5% - 10%. When increasing PBS content to 15% - 20%, DSC thermograms show both thermal characteristic of PLA and PBS phase.
The Tg of as-spun blend fibers were shifted to low temperature when increased PBS content. Except 20% concentration of PBS, the Tg was increased again up to almost the same Tg value of PLA. However, Tg of as-spun blend fibers was still higher than as-spun PBS fibers. At “low” PBS contents (i.e. 15 wt%), decreasing Tg of the blend products from pure PLA could be a result from miscibility between PLA and PBS molecules in the amorphous phase. Further increasing PBS content, phase separation between PLA and PBS molecules takes place as observing of two Tg values in thermogram. This result was in a good agreement to the previous report [
Crystallinity of PLA and PBS electrospun fiber were 18.1% and 41.3%, respectively. It is interesting that percentage crystallinity of PLA phase in as-spun blend fibers was increasing ca. 5% as comparing to pure PLA fibers, especially at PLA/PBS blending ratio 95/5. It’s possible that PBS in the blend function as nuclei for PLA crystallization [
Effect of PLA/PBS blending ratio to tensile strength, elongation at break and Young’s modulus were shown in
Tensile strength of electrospun PBS mat was higher than electrospun of PLA mat, and the blend giving significantly increased in tensile strength comparing to neat electrospun of both materials. However, PBS content was not significantly affected to tensile strength. This result was difference from work of E. Hassan and coworker [
Elongational at break (
blend ratio of 80/20 was immiscible blend. As increase PBS content, phase separation between PLA and PBS was dominated and finally completely immiscible blend. From work of Yokohara and Yamaguchi [
Young’s modulus (
The electronspun of PLA/PBS blend nanofibers show good tensile properties, which is suitable to be used in some application. Electrospun PLA/PBS blend nanofiber at ratio of 95/5, having maximum modulus, was perfected for high load application such as bulletproof vest. Meanwhile electrospun PLA/PBS blend nanofiber at ratio of 80/20, giving maximum elongation and smallest diameter, is perfect to apply in filtration application or using as tissue scaffold in bio-engineering.
Porous electrospun nanofiber from biomass-based polyester blends of PLA and PBS was successfully prepared by an electrospinning process under various blend composition. The blend PLA/PBS ratios 95/5, 90/10, 85/15 and 80/20 wt% were studied. Diameter of the electrospun fiber decreased with an increase of PBS content. The round fiber with pore on the surface was observed. It is PLA fiber characteristic when prepared by electrospinning process. Shape of the pore changes from circle to oval as increasing PBS content. Miscibility of electrospun PLA/PBS blend nanofibers was found from PBS content not more than 15 wt% which is detected by single Tg of PLA phase. However, blending of PBS increases Tg and crystallinity of PLA without affect to Tm of as-spun blend fiber. Increasing of PBS content, elongation at break of the electrospun fiber mat was increased due to flexibility of PBS molecule but tensile strength was not significantly affected. PLA/PBS nanofibers at blend ratio of 95/5 showed highest Young’s modulus (in range of investigation). In conclusion, electrospun PLA/PBS blend nanofibers were found to be a promising material to apply in many applications.
This work has been supported by Department of Tool and Materials Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi.
The authors declare no conflicts of interest regarding the publication of this paper.
Phiriyawirut, M., Sarapat, K., Sirima, S. and Prasertchol, A. (2019) Porous Electrospun Nanofiber from Biomass-Based Polyester Blends of Polylactic Acid and Polybutylene Succinate. Open Journal of Polymer Chemistry, 9, 1-15. https://doi.org/10.4236/ojpchem.2019.91001