Forcespinning technique for the production of poly(d,l-lactic acid) submicrometer fibers: Process–morphology–properties relationship

This work addresses a systematic study for the process development and optimization of poly(d,l-lactic acid) (PDLLA) submicrometer fibers utilizing the centrifugal spinning technique known as Forcespinning. This study analyzes the effect of polymer concentration (8, 10, and 12 wt %) and angular speed on the fiber morphology, diameter distribution, and fiber yield. The increase in polymer concentration and angular speed favored the formation of continuous and homogeneous submicrometer fibers with an absence of bead formation and higher output. The optimal conditions were established considering the morphological characteristics that exhibit a greater surface area (homogeneous and submicrometer fibers); and they were achieved at a polymer concentration of 10 wt % at an angular speed ranging from 8000 to 10 000 rpm. Optimization of PDLLA submicrometer fiber fabrication lays the groundwork for scaling up the process and serves as a platform to further develop promising applications of PDLLA nonwoven mats, particularly in the biomedical area such as in scaffolds for tissue engineering

Color tunable aerogels/sponge-like structures developed from fine fiber membranes

The development of macroscopic aerogels from 1D systems, such as nanofibers, has resulted in a novel pathway to obtain porous and lightweight architectures. In this work, bright green, red, and tunable color emitting aerogels were obtained with luminescent nanofibers as the precursor system. A simple, low cost, and environmentally friendly process is followed where luminescent fillers are encapsulated within fibers which were subsequently freeze-dried to form 3D aerogels and sponge-like structures. Moreover, the aerogels/sponge-like structures show higher photoluminescence intensity than the fiber mats due to an increase of porosity which provides higher and direct interaction with the fillers and therefore an efficient light absorption resulting in higher luminescence. Manganese doped zinc germanate (Mn: Zn2GeO4) nanorods and chromium doped zinc gallate (Cr: ZnGa2O4) nanoparticles were used as the source of green and red emissions respectively. By precisely adjusting the stoichiometric ratios of nanorods and nanoparticles within the nanofibers, a broad spectrum output is obtained from the final aerogels. We foresee that these types of photoluminescent aerogels have promising potential applications in a variety of fields such as display devices, solid-state lighting, sensors, etc

Centrifugally spun mats based on biopolyesters/hydroxyapatite and their potential as bone scaffolds

This work studied the potential of centrifugal spinning for the production of fibrous materials based on poly(D,L-lactic acid) (PDLLA) and poly(3-hydroxybutyrate) (PHB) with hydroxyapatite nanoparticles (n-Hap). The influence of n-Hap concentration (5, 10, and 15 wt.%) and spinneret angular speed on the final fiber morphology were analyzed. Further experimental evaluations were implemented to determine the effect of n-Hap on the thermal and mechanical performance. The optimum parameters that show a balance among high yield production of homogeneous fibers with the smallest fiber average diameter were found to be at 5 wt.% of n-Hap processed at 7000 rpm for PDLLA, and 5, 10, and 15 wt.% of n-Hap at 6000 rpm for PHB. The thermal stability, for both systems, was not significantly affected. The mechanical performance of PHB systems was improved with the addition of n-Hap. Osteoblast cell viability tests depicted a favorable cell response on the PDLLA systems

On the thermogravimetric analysis of polymers: Polyethylene oxide powder and nanofibers

Thermogravimetric analysis of polyethylene oxide (powder and nanofibers obtained by force spinning water or chloroform solutions of polyethylene oxide) was studied using different theoretical models such as Friedman and Flynn-Wall-Ozawa. A semiempirical approach for estimating the “sigmoid activation energy” from the thermal degradation was suggested and confirmed by the experimental data on PEO powder and nanofibers\u27 mats. The equation allowed for calculating a “sigmoid activation energy” from a single thermogram using a single heating rate without requiring any model for the actual complex set of chemical reactions involved in the thermal degradation process. For PEO (powder and nanofibers obtained from water solutions), the “sigmoid activation energy” increased as the heating rate was increased. The sigmoid activation energy for PEO mats obtained from chloroform solutions exhibited a small decrease as the heating rate was increased. Thermograms\u27 derivatives were fitted to determine the coordinates of the inflection points. The “sigmoid activation energy” was compared to the activation energy determined from the Flynn-Wall-Ozawa model. Similarities between the thermal degradation of polyethylene oxide powder and of the nanofibers obtained from water solutions were discussed. Significant differences between the sigmoid activation energies of the mats obtained from water and chloroform solutions were reported

Processing-structure-property relationships of biopolyester/zinc oxide fibrous scaffolds engineered by centrifugal spinning

This study addresses the processing of nonwoven fibrous materials obtained by centrifugal spinning method, namely Forcespinning; a high yield and low production cost technique little explored in this field. Poly(D, L-lactic acid) (PDLLA) and poly(3-hydroxybutyrate) (PHB) were used as matrices and reinforced with zinc oxide nanoparticles (n-ZnO). The morphology, mechanical, and thermal performance of the developed composites were analyzed as well as the antibacterial effect of n-ZnO. Fibrous materials with n-ZnO concentrations of 1, 3, and 5 wt. % for PDLLA and 1 and 3 wt. % for PHB were evaluated. The results showed that the incorporation of n-ZnO produces an increase in the viscosity of the precursor solutions for both polymeric systems, which caused an increase in the average fiber diameter, though the morphology was not affected, obtaining mostly long, continuous, and homogenous fibers. In addition, a decrease in thermal stability was observed to a greater extent in PDLLA systems. Regarding the mechanical performance, optimal properties were obtained at a concentration of 3 and 1 wt. % of n-ZnO for PDLLA and PHB, respectively. Antibacterial studies showed that PHB with 1 and 3 wt. % of n-ZnO effectively combat strains of E. coli and S. aureus, presenting 100% of strain growth inhibition. In the case of PDLLA, a higher n-ZnO concentration (5 wt. %) was required to reach a strain growth inhibition above 97%. Finally, cell viability tests demonstrated that the designed fibrous mats support cell proliferation, indicating their potential for use as scaffolds in bone tissue regeneration

Halloysite Reinforced Natural Esters for Energy Applications

Recently, environmentally friendly and sustainable materials are being developed, searching for biocompatible and efficient materials which could be incorporated into diverse industries and fields. Natural esters are investigated and have emerged as eco-friendly high-performance alternatives to mineral fluids. This research shows the evaluations on thermal transport and tribological properties of halloysite nanotubular structures (HNS) reinforcing natural ester lubricant at various filler fractions (0.01, 0.05, and 0.10 wt.%). Nanolubricant tribotestings were evaluated under two configurations, block-on-ring, and 4-balls, to obtain the coefficient of friction (COF) and wear scar diameter (WSD), respectively. Results indicated improvements, even at merely 0.01 wt.% HNS concentration, where COF and WSD were reduced by ~66% and 8%, respectively, when compared to pure natural ester. The maximum significant improvement was observed for the 0.05 wt.% concentration, which resulted in a reduction of 87% in COF and 37% in WSD. Thermal conductivity was analyzed under a temperature scan from room temperature up to 70 °C (343 K). Results indicate that thermal conductivity is improved as the HNS concentration and testing temperature are increased. Results revealed improvements for the nanolubricants in the range of 8–16% at 50 °C (323 K) and reached a maximum of 30% at 70 °C (343 K). Therefore, this research suggests that natural ester/HNS lubricants might be used in industrial applications as green lubricants

Halloysite Reinforced Natural Esters for Energy Applications

Recently, environmentally friendly and sustainable materials are being developed, searching for biocompatible and efficient materials which could be incorporated into diverse industries and fields. Natural esters are investigated and have emerged as eco-friendly high-performance alternatives to mineral fluids. This research shows the evaluations on thermal transport and tribological properties of halloysite nanotubular structures (HNS) reinforcing natural ester lubricant at various filler fractions (0.01, 0.05, and 0.10 wt.%). Nanolubricant tribotestings were evaluated under two configurations, block-on-ring, and 4-balls, to obtain the coefficient of friction (COF) and wear scar diameter (WSD), respectively. Results indicated improvements, even at merely 0.01 wt.% HNS concentration, where COF and WSD were reduced by ~66% and 8%, respectively, when compared to pure natural ester. The maximum significant improvement was observed for the 0.05 wt.% concentration, which resulted in a reduction of 87% in COF and 37% in WSD. Thermal conductivity was analyzed under a temperature scan from room temperature up to 70 °C (343 K). Results indicate that thermal conductivity is improved as the HNS concentration and testing temperature are increased. Results revealed improvements for the nanolubricants in the range of 8–16% at 50 °C (323 K) and reached a maximum of 30% at 70 °C (343 K). Therefore, this research suggests that natural ester/HNS lubricants might be used in industrial applications as green lubricants

Processing-structure–property relationships of oleanolic acid loaded PLGA fiber membranes

Oleanolic acid (OA) loaded poly(lactic-co-glycolic) acid fiber membranes were developed utilizing the Forcespinning technology. OA is a natural pentacyclic triterpenoid compound available in fruits and vegetables and known for its plethora of biological activities. The incorporation of OA into polymeric fine fiber membranes opens promising potential applications for biomedical applications, such as a system for transdermal delivery of bioactive agents. In this study, nonwoven fiber membranes were developed with different concentrations of OA, and morphological, thermo-physical, and biological studies were conducted. Results show a high yield of fiber membranes with average fiber diameters ranging from 541 to 630 nm, depending on the concentration of OA. Developed membranes are composed of long and continuous fibers showing rough surfaces with stability in aqueous media. Thermo-physical analysis showed miscibility of the components and negligible effects of processing conditions on the structure and stability of the components. High drug loading efficiency (\u3e 80%) was observed, and cellular studies indicated that the developed fiber membranes were not toxic to fibroblast cells. The structural and thermal stability and non-cytotoxic behavior of these membranes make them a promising potential vehicle for drug delivery applications

Study on thermal transport behavior of magnesium oxide (MgO) nanostructures as lubricant additives in vegetable oils

Due to harmful impact of petroleum-based fluids and lubricants on the environment and Mankind, vegetable oil-based fluids with incorporation of eco-friendly nanostructures have a great potential to be an alternative lubricant if it possesses proper thermal transport and physico-chemical characteristics. In this study, thermal conductivity, and viscosity performance of vegetable nanolubricants, developed from soybean oil and sunflower oil, modified with homogeneous dispersion of magnesium oxide (MgO) nanostructures were evaluated at various filler fractions (0.01, 0.05, 0.10 and 0.25 wt%) over diversetemperatures. For thermal conductivity evaluation, a transient hot wire (THW) methodology was employed. It is observed that for MgO nanolubricants, thermal conductivity increased as a filler fraction and temperature were increased, reaching a maximum of 22% improvement at 0.25 wt% reinforcement at 50 °C. On the other hand, the viscosity showed a consistent behavior as a function of nanostructures filler fraction and decreased significantly in response to increased evaluating temperature

Photocatalytic degradation of methylene blue using PMMA/TiO2 nanoparticles composites fibers obtained through centrifugal spinning

In this research work, using the Forcespinning® technique, composites based on poly(methyl methacrylate) with TiO2 nanoparticles (PMMA/NPsTiO2) with different morphologies, spherical (NPs0D) and one-dimensional (NPs1D) were prepared. The compounds obtained were characterized through various analytical techniques, in order to evaluate their physicochemical, thermal, mechanical, surface, and structural properties. Likewise, the photocatalytic efficiency in the degradation of methylene blue (MB) of both composites was evaluated and compared. There were no representative changes in the viscosity of the systems due to the incorporation of the NPsTiO2 resulting in fibers with average diameters without significant variation concerning the reference fibers. The incorporation of NPsTiO2 produced an increase in the thermal stability of the materials, showing a more pronounced effect at a concentration of 3% NPs1D. The higher tensile strength (3.5 ± 1.9 MPa) and Young’s modulus (302.6 ± 152.6 MPa) did not present a significant change in the presence of NPs0D but they decreased with the incorporation of the NPs1D as a consequence of fiber morphology and NPs distribution. MB photocatalytic degradation yield of 28.8% was obtained with the PMMA-based composites with NPs0D (PMMA/NPs0D) and 18.3% with the PMMA-based composite with NPs1D (PMMA/NPs1D), at a concentration of 5% by weight of NPs in both cases, at 4 h of irradiation