Preparation of nonwoven mats of electrospun poly(lactic acid)/polyaniline blend nanofibers: A new approach

The preparation of nonwoven mats of electrospun poly(lactic acid)/polyaniline (PANI) blend nanofibers faces some critical challenges that will be addressed in the present work. The challenges are in achieving high and adjustable content of PANI while keeping the spinnable solution nonagglomerated with no need to further filtration that might lead to wrong estimation of PANI content in the mat. We report an unprecedented content of 40% wt of PANI that is achieved using a new two‐step procedure. It is based on: (1) the preparation of the spinnable solution from a friable nonagglomerated and readily dispersible PANI: ‐TSA powder and (2) the use of an optimized mixture of ‐cresol/dichloromethane. The obtained nanofiber mats are characterized by FTIR and UV–vis spectroscopy. The morphology and the thermal stability of the nanofibers are investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The amorphous structure of the nanofibers is verified using XRD measurements. The DC‐conductivity of these blend nanofibers is found to be far larger than the published DC‐conductivity values for blend nanofibers of PANI with PLLA or with other polymers. This is attributed to the high content of PANI in the blend and to the role played by ‐cresol as a secondary dopant. The investigation of the aging effect on the DC‐conductivity reveals an exponential decrease with a characteristic time of weeks. The electrical impedance spectroscopy (EIS) shows a pure ohmic behavior of the blend mat. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43687.     

Comparison of the Effects of an Ionic Liquid and Triethylbenzylammonium Chloride on the Properties of Electrospun Fibers, 1 – Poly(lactic acid)

Improving the conductivity of electrospinning solutions is often achieved by adding small amounts of conductive additives. HMIMCl, a room temperature ionic liquid, and TEBAC, a quaternary ammonium salt, were added to polylactic acid in chloroform and their effects on solution properties, electrospinning, and fiber properties were investigated. Both additives increased the conductivity which decreased the fiber diameter, but differences were observed on the fiber dispersity and fiber morphology. The conductive solutions caused fiber backbuilding with aggregation and fiber fusion. Reasons for the differences in fiber diameter and fiber morphology are discussed.

     

Thermal,Mechanical and Rheological Properties of Polypropylene/Poly(ethylene-co-methyl acrylate) Blends

Isotactic polypropylene (PP) has been blended with poly(ethylene-co-methyl acrylate) (EMA) (75/25 wt/wt%) in a single-screw extruder. The compatibilizing effect of polypropylene grafted with maleic anhydride (PP-g-MAH) has been examined. The nonisothermal crystallization of the developed blends has been investigated using differential scanning calorimetry (DSC) and analyzed using Avrami, Tobin and Liu models. The thermal stability of the blends was assessed through thermogravimetric analysis (TGA). The tensile and impact properties, as well as the melt viscosity, have also been determined. The presence of rubber accelerates the crystallization of PP. The thermal stabilities of the blends are intermediate between those of their constituents. Tensile strength and modulus are reduced upon incorporation of EMA into PP, but ultimate elongation and impact strength are improved. The melt viscosity variation with shear rate for all the systems was typical of shear-thinning behavior. The compatibilizing agent has a pronounced effect on enhancing the thermal and mechanical properties of the blend.     

Electrospun poly(hydroxybutyrate)/chitosan blend fibrous scaffolds for cartilage tissue engineering

In this study, polyhydroxybutyrate (PHB) was blended with chitosan (CTS), and electrospun in order to produce more hydrophilic fibrous scaffolds with higher mass loss rates for cartilage tissue engineering application. First, the effects of diverse factors on the average and distribution of fiber's diameter of PHB scaffolds were systematically evaluated by experimental design. Then, PHB 9 wt % solutions were blended with various ratios of CTS (5%, 10%, 15%, and 20%) using trifluoroacetic acid as a co‐solvent, and electrospun. The addition of CTS could decrease both water droplet contact angle from ～74° to ～67° and tensile strength from, ～87 MPa to ～31 MPa. According to the results, the scaffolds containing 15% and 20% CTS were selected as optimized scaffolds for further investigations. Mass loss percentage of these scaffolds was directly proportional to the amount of CTS. Chondrocytes attached well to the surfaces of these scaffolds. The findings suggested that PHB/CTS blend fibrous scaffolds have tremendous potentials for further investigations for the intended application. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44171.     

Electrospun Polyvinyl Borate/Poly(Methyl Methacrylate) (PVB/PMMA) Blend Nanofibers

The aim of this study was to prepare polyvinyl borate (PVB)/poly(methyl methacrylate) (PMMA) blend nanofibers by electrospinning process. Polyvinyl borate was synthesized by the condensation reaction of polyvinyl alcohol and boric acid. FTIR analyses showed that boron atoms were found to be integrated into the polymer network. Blending PMMA with PVB decreased the fiber diameter and enhanced the surface roughness of PVB/PMMA blend nanofiber mats. The water wetting property of the nanofiber mats was influenced by the surface roughness. The blend composition with the highest polyvinyl borate content was found to be suitable for thermally stable nanofiber formation.     

聚乳酸／PBAT共混物的制备及其性能研究

用熔融挤出法制备了聚乳酸饼苯二甲酸-己二酸-1，4-丁二醇三元共聚酯（PLA／PBAT）共混物，研究了聚乳酸／PBAT共混物的力学性能、热性能以及相容性。结果表明：共混物的冲击强度及断裂伸长率随着PRAT含量的增加而增大，在PBAT含量为30％时，断裂伸长率最大，达到9％，PBAT的加入降低了共混物的拉伸、弯曲性能，但在添加量较少的情况下（如5％和10％），拉伸、弯曲性能下降不大。退火处理极大的提高了材料的维卡软化温度。当PBAT含量较高时，共混物的断面可以明显的观察到不相容的两相结构。     

Electrical and Optical Properties of Conducting Poly(3-hexylthiophene)/Multi-walled Carbon Nanotube System

Polymer multi-wall carbon nanotube (MWNT) composites were prepared and characterized as part of an effort to develop polymeric materials with improved combinations of properties for potential use in solar cell applications. Multi-walled carbon nanotube (MWNT) poly(3-hexylthiophene) nanocomposites were synthesized by in situ polymerization of monomers in the presence of different amounts of MWNTs. A process is reported to efficiently disperse multi-walled carbon nanotube (MWNT) bundles in a semiconducting polymer matrix. A uniform dispersion of the nanotubes in the polymer matrix was obtained. Characterization of the nanocomposites and the effects of MWNT concentration and dispersion on the structural, optical and electrical properties were discussed. FTIR and Raman spectroscopic investigations of nanocomposites indicate that the polymer is wrapped on the nanotubes, taking up a rigid orientation through π-π stacking. The Hall voltage measurement is followed to monitor carrier concentrations and mobilities, instead of the device fabrication and hole mobility measurements.     

Effect of Blend Preparation on Electrical,Dielectric, and Dynamical‐Mechanical Properties of Conducting Polymer Blend: SBS Triblock Copolymer/Polyaniline

Conducting polymer blends based on styrene–butadiene–styrene (SBS) triblock copolymer and polyaniline doped with dodecylbenzene sulfonic acid (Pani.DBSA) were prepared by different procedures: mechanical mixing (MM) and ‘in situ’ polymerization (ISP) methods. The ISP blends exhibited higher levels of electrical conductivity, as compared to MM blends. The scanning electron micrographs of the ISP blend were characterized by the presence of microtubules, which favored the formation of the conducting pathways inside the SBS matrix. From dynamic mechanical and dielectric analysis, it was possible to suggest a higher interaction degree of the polyaniline with the polystyrene phase of the block copolymer. Blends prepared by ISP method displayed also higher dielectric constant and higher dielectric loss factor than blends prepared by MM method.

     

Mechanical,Thermal, and Electrical Properties of Epoxy Matrix Composites Reinforced With Polyamide-Grafted-MWCNT/poly(azo-pyridine-benzophenone-imide)/Polyaniline Nanofibers

Friedel-Crafts acylation and in situ polymerization were adopted to graft polyamide on multi-walled carbon nanotube (MWCNT) surface to form MWCNT-PA using γ-Phenyl-?-caprolactone. Via electrospinning, MWCNT-PA/PAPBI and MWCNT-PA/PAPBI/PANI nanofibers were prepared using MWCNT-PA, poly(azo-pyridine-benzophenone-imide) (PAPBI) and polyaniline (PANI) and DGEBA as matrix. Compared with 3 wt% MWCNT-PA/PAPBI nanofibers (20.2 GPa), tensile modulus for film reinforced with 3 wt% MWCNT-PA/PAPBI/PANI nanofibers (27.6 GPa) was considerably increased. Thermal stability of MWCNT-PA/PAPBI/PANI nanofibers reinforced epoxy was higher with T₁₀ 633–654°C and T_g 283–291°C relative to DGEBAMWCNT-PA/PAPBI system. The filler loading also increased the electrical conductivity of DGEBA/MWCNT-PA/PAPBI/PANI from 3.44 to 6.01 S cm^?1.     

Comparison of the Effects of an Ionic Liquid and Other Salts on the Properties of Electrospun Fibers, 2 – Poly(vinyl alcohol)

Understanding the effect of conductivity in electrospinning solutions is crucial in order to improve or control the electrospinning process. In this paper the effect of adding small amounts (0.039–0.259 mol · kg^?1) of three different conductive additives to aqueous solutions of polyvinyl alcohol has been investigated. The salts were HMICl (a room temperature ionic liquid), TEBAC (a quaternary ammonium salt) and KCl. Addition of these salts caused a steady increase in the solution conductivity but the fiber diameter was typically greater than that of PVA alone, and exhibited an oscillatory trend. The oscillatory trend on the fiber diameter is attributed to fiber backbuilding and fusion that occurs prior to deposition on the collector.

     

A Comparative Study on the Mechanical, Thermal and Morphological Characterization of Poly(lactic acid)/Epoxidized Palm Oil Blend

In this work, poly(lactic acid) (PLA) a fully biodegradable thermoplastic polymer matrix was melt blended with three different epoxidized palm oil (EPO). The aim of this research was to enhance the flexibility, mechanical and thermal properties of PLA. The blends were prepared at various EPO contents of 1, 2, 3, 4 and 5 wt% and characterized. The SEM analysis evidenced successful modification on the neat PLA brittle morphology. Tensile tests indicate that the addition of 1 wt% EPO is sufficient to improve the strength and flexibility compared to neat PLA. Additionally, the flexural and impact properties were also enhanced. Further, DSC analysis showed that the addition of EPO results in a decrease in T(g), which implies an increase in the PLA chain mobility. In the presence of 1 wt% EPO, TGA results revealed significant increase in the thermal stability by 27%. Among the three EPOs used, EPO(3) showed the best mechanical and thermal properties compared to the other EPO's, with an optimum loading of 1 wt%. Conclusively, EPO showed a promising outcome to overcome the brittleness and improve the overall properties of neat PLA, thus can be considered as a potential plasticizer.     

Mechanical and Rheological Properties of Poly(ethylene terephthalate)/ Polypropylene Blends

Poly(ethylene terephthalate) and polypropylene (PET/PP) were compounded and pelletized with a single-screw extruder. Standard ASTM tensile test specimens were made by injection moulding. The blends are stronger and stiffer than the plain PP specimens. The addition of a compatibilizer, EPOLENE E-43, is found to improve the strength and stiffness of the blends at loadings of 50% and 70% PET. At 10% PET loading, E-43 has the opposite effect of slightly reducing the tensile properties. All the blends are more brittle relative to either plain PET or PP. The addition of E-43 results in negligible improvement in the elongation at break. E-43 is also found to be an effective lubricant in improving the processability of the blends. The blends with E-43 added have lower viscosities and less shear-thinning characteristics than those without E-43. © 1997 SCI.     

Effect of Blending Procedure on Tensile and Degradation Properties of Toughened Biodegradable Poly(lactic acid) Blend with Poly(trimethylene terephthalate) and Reactive Compatibilizer

This research focuses on brittleness improvement of biodegradable poly(lactic acid) (PLA) by reactive melt blending with poly(trimethylene terephthalate) (PTT). First, PLA is simultaneously blended with PTT and a reactive compatibilizer, poly(ethylene‐co‐glycidyl methacrylate) (PEGMA), (one‐step blending procedure). In the PLA/PTT/PEGMA blend, PEGMA mainly disperses in the PLA matrix phase, and the blend shows unimproved tensile properties. To increase the reaction between PTT and PEGMA, PEGMA is sequentially blended with PTT then PLA (two‐step blending procedure). This procedure is effective in drastically enhancing elongation at break of the blend. The strain at break of the blend formed by two‐step blending is significantly improved because the blending procedure affects the blend morphology. PLA‐g‐PEGMA‐g‐PTT graft copolymer is formed at the interface between PLA and PTT during reactive melt blending with PEGMA when the two‐step blending procedure is employed as a blending method which is confirmed by Fourier transform infrared spectroscopy and viscosity measurement. Such features bring about craze formation during tensile test and this is the reason why the toughening is achieved by the two‐step blending procedure.     

Thermal property,morphology, and hydrolysis ability of poly(lactic acid)/chitosan nanocomposites using polyethylene oxide

Poly(lactic acid) (PLA) and chitosan (CS) are two natural resource polymers, which have been applied widely into different fields. Polymer composites based on PLA and CS have some advantages such as good adhesion, biodegradability, biocompatibility, and high stability. They can be prepared by different methods including the solution, emulsion, and electrospinning methods. In this work, the PLA/chitosan nanocomposites were prepared by solution method using poly(ethylene oxide) (PEO) as a compatibilizer in order to improve interaction and dispersion between PLA and CS phases. The characterization and morphology of the above nanocomposites were determined by Fourier Transform Infrared Spectroscopy (FTIR), thermograviety analysis, differential scanning calorimetry, and scanning electron microscopy. Hydrolysis ability of PLA/CS nanocomposites with and without PEO was also investigated in acid and phosphate buffer solutions. The obtained results showed the compatibility between PLA and CS phases in the PLA/CS nanocomposites using PEO was improved clearly and weight loss of PLA/CS/PEO nanocomposites in the above environments lower than that of PLA/CS nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41690.     

Hierarchical Self‐Assembly of Poly(Urethane)/Poly(Vinylidene Fluoride‐co‐Hexafluoropropylene) Blends into Highly Hydrophobic Electrospun Fibers with Reduced Protein Adsorption Profiles

Electrospinning of blend systems, combining two or more polymers, has gained increasing interest for the fabrication of fibers that combine properties of the individual polymers. Here, a versatile method to produce hydrophobic fibers composed of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDFhfp) and polyurethane (PUR) is presented. PVDFhfp containing fibers are expected to reduce protein adsorption. In a one‐step process, blend solutions are electrospun into homogeneous nonwoven membranes with fiber diameters in the range of 0.6 ± 0.2 to 1.4 ± 0.7 µm. Surface fluorine concentrations measured by X‐ray photospectroscopy show an asymptotic dependency in function of the PVDFhfp to PUR ratio, reaching values close to pure PVDFhfp at a weight per weight ratio of 10% PVDFhfp to 90% PUR. This fluorine enrichment on the surface suggests a gradient structure along the fiber cross‐section. At increased surface fluorine concentration, the contact angle changes from 121 ± 3° (PUR) to 141 ± 4° (PUR/PVDFhfp). Furthermore, these highly hydrophobic fibers present significantly reduced fibrinogen or albumin adsorption compared to PUR membranes.     

Fabrication and Thermal Dissipation Properties of Carbon Nanofibers Derived from Electrospun Poly(Amic Acid) Carboxylate Salt Nanofibers

Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI‐based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp² bonding between carbon atoms.     

聚乳酸/聚癸二酸丙三醇酯共混物的形态及结晶性能

用SEM、DSC、光学解偏振光、POM及WAXD研究聚乳酸/聚癸二酸丙三醇酯(PLA/PGS)共混物的形态和等温结晶性能.结果表明:PLA与PGS发生了相分离,PLA分子链之间存在部分PGS.当<110℃等温结晶时PLA/PGS共混物的半结晶时间(t1/2)随PGS含量的增加而降低,其晶体尺寸较纯PLA大;当≥110℃等温结晶时,PLA/PGS共混物的t1/2随PGS含量的增加而变大,共混物的晶体尺寸明显增大,形成球晶.但当PGS的含量为20%并于120℃等温结晶时,晶体产生暗斑.PLA及PLA/PGS共混物的晶形都为α形.     

Synthesis and Substrate-Aided Alignment of Porphyrinated Poly(ethylene oxide) (PEO) Electrospun Nanofibers

Aligned and unaligned vanadium (IV) oxide meso-tetraphenyl porphine (VMP)/polyethylene oxide (PEO) hybrid nanofibers have been successfully synthesized by electrospinning technique. The nanofibers were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), optical microscopy and scanning electron microscopy (SEM). The SEM and AFM analyses of the morphology showed that the nanofibers are cylindrical with diameters ranging from 400–700 nm. The AFM analysis also confirmed that the aligned nanofibers deposited on a small metallic spring are smoother than the unaligned ones deposited on FTO. FTIR analysis showed that the polar environment provided by the phenyl groups of VMP molecules modified the chemical configuration of PEO molecules, and XRD studies indicated that the VMP molecules were homogeneously distributed within the PEO matrix.     

Thermal Characterization of Polyhydroxyalkanoates and Poly(lactic acid) Blends Obtained by Injection Molding

In this work we present the thermal characterization of the full scope of polyhydroxyalcanoate and poly(lactic acid) blends obtain by injection molding. Blends of polyhydroxyalcanoate and poly(lactic acid) (PHA/PLA) were prepared in different compositions ranging from 0–100% in steps of 10%. The blends were injection molded and then characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). The increment of PHA fraction increased the degree of crystallinity of the blend and the miscibility of the base polymers as verified by the Fox model. The WAXD analysis indicates that the presence of PHA hindered the PLA crystallization. The crystallization evolution trough PHA weight fraction (wf) shows a phase inversion around 50-60%. SEM analyses confirmed that the miscibility of PHA/PLA blends increased with the incorporation of PHA and became total for values of PHA higher that 50%.