A straightforward method, which is termed novel handspinning, is reported for producing uniaxially aligned sPP nanofibers. As demonstrated by SEM analysis, the morphologies of handspun sPP nanofibers are strongly dependent upon the processing conditions such as spinning method and solvent system. Compared to the normal electrospun sPP nanofibers, the handspun sPP nanofibers show smoother morphologies. FT‐IR analysis demonstrates a significant difference in polymer chain conformation between the handspun and electrospun sPP nanofibers. Moreover, interestingly, the handspun sPP single nanofibers show higher Young's modulus and tensile strength than electrospun sPP single nanofibers.
We study the effect of the gap size on the molecular orientation and crystalline structure of uniaxially well‐aligned nylon‐6 nanofibers produced in the gap between negatively charged metal plates. The relative intensities of several absorbance bands are found to be different in the parallel‐ and perpendicularly polarized FTIR spectra. X‐ray analysis indicates that the metastable γ‐form is predominant in as‐spun nylon‐6 nanofibers, and is transformed into the thermodynamically stable α‐form by increasing the gap size. The polymer chains are thought to be oriented perpendicular to the fiber direction, and the molecular orientation to the fiber axis is enhanced on increasing the gap size.
The inherent properties of poly(lactide), a biocompatible and biodegradable polymer, are concurrently improved by the incorporation of a small amount of surface functionalized carbon nanotubes. A new method has been used to functionalize the CNTs' outer surface with hexadecylamine. A composite of PLA with functionalized CNTs has been prepared by melt‐extrusion. FT‐IR spectroscopy, Raman spectroscopy, DSC, and optical microscopy are used to investigate the thermal and mechanical property improvement mechanism in f‐CNTs containing PLA composite.
MA is grafted onto both PLLA and starch in an internal mixer in the presence of DCP in a one‐step reactive compatibilization process. The effect of maleation of MA on the physical and mechanical properties and morphology of the blends was assessed. The onset decomposition temperature of the PLLA/starch blends decreased as the starch content increases due to the lower thermal stability of starch and the low effect of the maleation reaction on the thermal stability of the blends. PLLA/starch blends without grafted MA showed higher crystallinity as the starch content increased. Reactive compatibilized blends with less than 20 wt% starch had higher storage modulus, indicating that the compatibility between the two phases was improved.
A novel method to produce uniaxially aligned nanofibers is described, in which a pair of parallel auxiliary electrodes at a positive potential is placed between the needle and the collector electrodes. Charged nanofibers ejecting from the polymer solution are pre‐aligned by the electrostatic repulsion originating from the auxiliary electrodes and deposited on the collector electrodes, forming a narrow mat with the fiber segments strongly curved. By adjusting the conductivity and shape profile of the collector, the curved segments can be straightened longitudinally. A seamless tube composed of longitudinally aligned nanofibers can be obtained. Such seamless tubes may be useful as biomaterials in tissue engineering.
In this work, polyacrylonitrile (PAN) and carbon nanofibers with controllable nanoporous structures were successfully prepared via electrospinning technique. For the preparation of porous PAN nanofibers, two kinds of polymers of PAN and polyvinylpyrrolidone (PVP) were used as electrospun precursor materials, and then the bicomponent nanofibers of PAN and PVP were extracted with water to remove the PVP in the composite polymer nanofibers. By altering the ratio of PAN/PVP in the precursor, the pore size and pore distribution of porous PAN nanofibers could be easily controlled. By using the porous PAN nanofibers as structures directing template and through heat treatment, carbon nanofibers with nanoporous structures were obtained. The porous nanofibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), differential thermal analyses (DTA), Brunauer–Emmett–Teller (BET) nitrogen adsorption, X‐ray diffraction (XRD), and Raman spectra.
The effects of nucleobases, especially uracil, on the nonisothermal and isothermal crystallization, melting behavior, spherulite morphology, and crystalline structure of bio‐based and biodegradable PLLA are studied. The melt‐ and cold‐crystallization rates of PLLA increase with increasing uracil loading. The melting behavior of nonisothermally melt‐ and cold‐crystallized PLLAs depends on the uracil content. The isothermal crystallization kinetics is analyzed based on an Avrami model. The incorporation of uracil changes the t1/2/Tc profile of PLLA due to the more distinct heterogeneous nucleation effects at small supercooling. The crystalline structure of PLLA is not affected by uracil presence. The nucleation density increases and the spherulite size decreases by uracil incorporation.
Poly(lactic acid) (PLA) toughening is often associated with significant modulus and/or strength losses making it unsuitable for many consumer and biomedical applications. The major objective of this research was to toughen PLA without significant loss in modulus and strength and to introduce reactive acid groups using reactive blending of PLA with a combination of polymers. PLA was reactive blended with poly(acrylic acid) (PAA) followed by physical blending with poly(ethylene glycol) (PEG) in solution. The modified PLA was extruded into films using a co‐rotating twin‐screw extruder and characterized using tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical analyses (DMA). This technology resulted in films with a ten‐fold increase in toughness compared to neat PLA with little or no decrease in strength and modulus.
A variety of polymer parts used in microsystems technology is produced by injection molding. For dimensioning and design of these products, both the material properties and changes during the life cycle have to be taken into account. The aging behavior of parts with decreasing dimensions or of parts processed under different cooling conditions is discussed in terms of their morphological and mechanical long‐term properties. The results indicate that a decreasing part size leads to higher post‐crystallization and higher thermo‐oxidative degradation. This leads to size‐dependent changes in mechanical properties. Adjusted process conditions by application of thermal low‐conductive mold materials can favor the process‐related properties and thus the long term properties can be improved.
With their high‐surface‐to‐volume ratio, nanofibers have been postulated to increase interactions between nanofibrous materials and targeted substrates, which are helpful to overcome many obstacles and enhance the efficiency in a diverse number of applications. Over the past decade, many studies have been published on the fabrication of nanofibers and their applications in various fields. In this review, novel biological, chemical, and electrical characteristics of nanofibers as well as their recent status and achievements in medicine, chemistry, and electronics are analyzed. It is found that nanofibers can induce fast regeneration of many tissues/organs in medical applications and improve the efficiency of many chemical and electronics applications.
In this study, the use of PLA‐g‐MA is investigated as a potential method for improving interfacial adhesion between agricultural residues and PLA, with the goal of enhancing mechanical properties. Compatibilization was achieved by using PLA‐g‐MA prepared via reactive extrusion. Green renewable and compatibilized PLA/wheat straw composites were extruded and injection‐molded. Addition of 3 and 5 phr PLA‐g‐MA to the composites resulted in significant improvements in tensile strength (20%) and flexural strength (14%) of the composites, matching that of the neat polymer. The observed improvement in strength was attributed to the good interfacial adhesion between the fiber and matrix.
A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.
HPLC is applied and assessed as an effective tool to investigate both the production of PLA by polycondensation and its corresponding degradation. A new HPLC calibration procedure, through which it is possible to fully characterize LMW PLA samples by determining the concentration of each individual oligomer, is developed. A comparison between HPLC, 1H NMR spectroscopy and non‐aqueous solution titration is also reported in order to confirm the reliability of the proposed method. Finally, the proposed analytical technique is applied to monitor the development of a polycondensation reaction performed at 150 °C and 133.3 mbar for 12 h.
Highly‐aligned luminescent electrospun nanofibers were successfully prepared from two binary blends of PFO/PMMA and PF+/PMMA. The PFO/PMMA aligned electrospun fibers showed a core/shell structure but the PF+/PMMA fibers exhibited periodic aggregate domains in the fibers. The aligned fibers had polarized steady‐state luminescence with a polarized ratio as high as 4, much higher than the non‐woven electrospun fibers or spin‐coated film. Besides, the PF+/PMMA aligned electrospun fibers showed an enhanced sensitivity to plasmid DNA. Such aligned electrospun fibers could have potential applications in optoelectronic or sensory devices.
In recent years TPS has attracted more and more research interest as a promising replacement for commodity polymers in some applications. In this paper, a novel manufacturing technology to produce PLA fiber reinforced biodegradable TPS composite, and the microstructure and tensile properties of the composite, were first reported. PLA micro/sub‐micro fibers were generated in situ by elongational flow during die extrusion and subsequent hot stretching. The addition of 10% PLA significantly increased the drawability of TPS. Compared to direct extrusion, hot stretching tripled the tensile strength of the composite to 34 MPa. Extensive PLA fibrillation was evident in the composite. The generated PLA fibers measured ca. 400 nm in diameter with a large L/D ratio.
A new, nickel‐coated graphite resistance‐change‐based method for gel‐point determination for epoxy‐based thermoset resins is presented and compared with DSC and rheological methods. Gelation times determined by this new method are in very good agreement with conventional techniques; this new method is potentially simpler and less time consuming than existing ones.
PLA/PBAT blends and PLA/PBAT/MWNT nanocomposite systems were prepared via a melt mixing process to examine their thermal and rheological properties. To compare the polymer blend/MWNT nanocomposite with a pure polymer/MWNT nanocomposite, PLA/MWNT, PBAT/MWNT, and PLA/PBAT/MWNT nanocomposite systems were prepared. TEM and SEM were used to observe that one phase has better affinity with the MWNT, while the MWNT was found to increase both the thermal properties of the PLA/PBAT blends and rheological properties of the PLA/PBAT/MWNT nanocomposite with distinct shear‐thinning behavior due to the addition of the MWNT. An increase in the storage (G′) and loss (G″) moduli for the PLA/PBT/MWNT nanocomposite was also observed.
Novel fluoroalkyl end‐capped oligomer/hydroxyapatite nanocomposites have been easily prepared by the reaction of disodium hydrogenphosphate and calcium chloride in the presence of self‐assembled molecular aggregates formed by fluoroalkyl end‐capped oligomers in aqueous media. The fluorinated hydroxyapatite nanocomposites thus obtained were found to exhibit a good dispersibility in a variety of media, and were applied to the surface modification of glass.
A new way of producing rigid or semi‐rigid foams from vital wheat gluten using a freeze‐drying process is reported. Water/gluten‐based mixtures were frozen and freeze‐dried. Different foam structures were obtained by varying the mixing process and wheat gluten concentration, or by adding glycerol or bacterial cellulose nanofibers. MIP revealed that the foams had mainly an open porosity peaking at 93%. The average pore diameter ranged between 20 and 73 µm; the sample with the highest wheat gluten concentration and no plasticizer had the smallest pores. Immersion tests with limonene revealed that the foams rapidly soaked up the liquid. An especially interesting feature of the low‐wheat‐concentration foams was the “in situ” created soft‐top‐rigid‐bottom foams.
The influence of melt and mold temperature on the solidification behavior of HDPE during the GAIM process is studied using a transient‐heat‐transfer model of the enthalpy transformation approach. An in situ measurement of temperature decay in the mold cavity was carried out to verify the simulated results experimentally, and reasonable agreement was observed. The comparison of the HDPE solidification behavior under various cooling conditions reveals that the rapid cooling rate (due to thin wall‐thickness) is the main reason for the shortening of molding cycles, and that the mold temperature shows greater influence on the controlling of cooling rates than melt temperature during GAIM process.
