Showing papers in "Macromolecular Materials and Engineering in 2012"
TL;DR: The properties, structure, and processing of carbon fibers are reviewed in this paper, with PAN being the dominating precursor in the market, and the essential processes for carbon fiber production are similar, different precursors require different processing conditions in order to achieve improved performance.
Abstract: The properties, structure, and processing of carbon fibers are reviewed. Carbon fibers are made from several precursors, with PAN being the dominating precursor in the market. Carbon fibers have high tensile strength, high modulus (up to the theoretical limit of around 1000 GPa), and low density, depending on the structure and processing in very limited combinations. Both the structure and composition of the precursor affect the properties of the resulting carbon fibers significantly. Although the essential processes for carbon fiber production are similar, different precursors require different processing conditions in order to achieve improved performance. Future developments are discussed.
328 citations
TL;DR: In this article, in situ compatibilization using DCP as a free-radical grafting initiator was used to improve the tensile strength, impact toughness, and elongation at break of injection-molded PHB(homopolymer)/PBS blends.
Abstract: PHB/PBS and PHBV/PBS blends are prepared via in situ compatibilization using DCP as a free-radical grafting initiator. A considerable reduction in PBS particle size and a significant increase in the interfacial adhesion between the PHB(V) and PBS phases are observed after the compatibilization. The elongation at break of the PHBV/PBS blends was considerably increased. The local deformation mechanism indicates that matrix yielding together with dilatation, deformation, and fibrillation of the PBS particles are responsible for the improved tensile toughness of the compatibilized PHBV/PBS blends. The tensile strength, impact toughness, and elongation at break of injection-molded PHB(homopolymer)/PBS blends are also increased after in situ compatibilization.
135 citations
TL;DR: In this article, Gentamicin-loaded clay nanotubes were used to improve the tensile strength of orthopedic-grade PMMA bone cement, which is used in hip and knee replacement surgery.
Abstract: Orthopedic-grade PMMA bone cement, admixed with prophylactic antibiotics, is widely used in hip and knee replacement surgery. There is a critical need to improve its structural integrity and to control antibiotic release. In this study, clay nanotubes are loaded with the antibiotic gentamicin sulfate and the cement is doped with 5–8 wt% nanotubes. The halloysite nanotubes isolate the drug from the cement monomers and serve as nanocontainers for sustained release of the antibiotic. Gentamicin-loaded clay nanotubes admixed in PMMA cement provide sustained release up to 300– 400 h and with enhanced release at cement cracks. The PMMA/halloysite/gentamicin composite tensile strength does not deteriorate as compared with pure cement and its adhesion to bone is significantly increased.
132 citations
TL;DR: A thiol-ene/acrylate shape memory polymer is utilized to create 3D softening substrates for stimulation electrodes and a nerve cuff electrode that coils around the vagus nerve in a rat and that drives neural activity is demonstrated.
Abstract: Planar electronics processing methods have enabled neural interfaces to become more precise and deliver more information. However, this processing paradigm is inherently 2D and rigid. The resulting mechanical and geometrical mismatch at the biotic-abiotic interface can elicit an immune response that prevents effective stimulation. In this work, a thiol-ene/acrylate shape memory polymer is utilized to create 3D softening substrates for stimulation electrodes. This substrate system is shown to soften in vivo from more than 600 to 6 MPa. A nerve cuff electrode that coils around the vagus nerve in a rat and that drives neural activity is demonstrated.
117 citations
TL;DR: In this article, the electrical conductivity of UHMWPE/GNS composites is shown to be almost four orders of magnitude lower than that of MWCNT composites.
Abstract: UHMWPE/MWCNT and UHMWPE/GNS composites with a segregated network are prepared. TEM and SEM images indicate that the conducting fillers are distributed on the UHMWPE surface and form a segregated conducting network. The percolation threshold of UHMWPE/GNS composites is ≈0.25 wt% and that of UHMWPE/MWCNT composites is 0.20 wt%. The electrical conductivity of UHMWPE/GNS composites is almost four orders of magnitude lower than that of the UHMWPE/MWCNT composites. For equivalent concentrations of GNS and MWCNT, the composites with hybrid fillers exhibit a lower percolation threshold and a higher conductivity than that with GNS or MWCNT alone. Due to the high strength of the fillers and the segregated network structure, the mechanical properties of the composites first increase and then decrease with increasing filler content.
114 citations
TL;DR: In this paper, the formation of an integral asymmetric membrane composed of a cylinder-forming polystyrene-block-poly(2-vinylpyridine) on a nonwoven by using solvent casting followed by solvent/nonsolvent exchange (phase inversion) is reported for the first time.
Abstract: The formation of an integral asymmetric membrane composed of a cylinder-forming polystyrene-block-poly(2-vinylpyridine) on a nonwoven by using solvent casting followed by solvent/nonsolvent exchange (phase inversion) is reported for the first time. The influence of parameters such as solvent composition, evaporation time of the solution-cast block copolymer film before phase inversion, and immersion bath temperature is demonstrated. The optimized membranes are characterized in terms of stimuli-responsive water flux properties. The morphologies of the membranes as well as of the bulk of the block copolymer are imaged by scanning force microscopy, scanning electron microscopy, and transmission electron microscopy.
98 citations
TL;DR: In this paper, a 3D arrangement of polymer brushes covalently attach to the inner wall of the micro-capillary where the spiropyran moiety has the freedom to open and close in response to light (ultraviolet, white light).
Abstract: Spiropyrans are one of the most popular classes of photocromic compounds as they are particularly interesting targets for the development of new multifunctional materials that take advantage of their photo-reversible interconversion between two thermodynamically stable states: a spiropyran (SP) form, and a merocyanine (MC) form, which have dramatically different charge, polarity and molecular conformations.
In this work, polymer brushes based on spiropyran were synthesised on the interior of micro-capillaries to study the influence of these brushes on solvent flow through a confined space and to determine their sensing capabilities. We demonstrate that using “grafting from” approach we obtain a 3D arrangement of polymer brushes covalently attach to the inner wall of the micro-capillary where the spiropyran moiety has the freedom to open and close in response to light (ultraviolet, white light).
This type of manipulation of capillary surface properties using light as the controlled external stimulus holds promise as a means for developing new modes of controlling liquid transport in micro-fluidic devices as well as novel micro-fluidic integrated optical sensors.
92 citations
TL;DR: In vitro biocompatibility studies with human fibroblasts reveal good cytocomp compatibility, making PHBV/PLA bicomponent fibers promising candidates for medical therapeutic approaches.
Abstract: PHBV is produced by bacteria as intracellular carbon storage. It is advantageous concerning biocompatibility and biodegradability, but its low crystallization rate hinders the melt-processing of fibers. This problem can be overcome by combining PHBV with PLA in a core/sheath configuration and introducing a new spin pack concept. The resulting PHBV/PLA bicomponent fibers show an ultimate tensile stress of up to 0.34 GPa and an E-modulus of up to 7.1 GPa. XRD reveals that PLA alone is responsible for tensile strength. In vitro biocompatibility studies with human fibroblasts reveal good cytocompatibility, making these fibers promising candidates for medical therapeutic approaches.
80 citations
TL;DR: In this article, the authors proposed a new material-processing route for the production of advanced high-performance structures for different applications, such as aerospace and other high-temperature applications, which should be produced by cost-efficient processes.
Abstract: Newmaterialsandprocessingroutesprovideopportunitiesfortheproductionofadvancedhighperformancestructuresfor different applications. Ceramic matrix composites(CMCs)areoneofthesepromisingmaterials.Bycombiningdifferent ceramic matrix materials with special suitablefibers, new properties can be created and tailored forinteresting technical fields. The demand for lightweight,high modulus, and high-temperature-resistant materialsforaerospaceandotherhightemperatureapplicationsgaverise to the development of CMCs. These materials exhibitmost of the positive properties of monolithic ceramics,however, are less brittle. The further optimization of thesematerials is closely connected to the development of highperformance ceramic fibers, which should be producedby cost-efficient processes.
78 citations
77 citations
TL;DR: In this paper, the effect of polyol on the final chemical structures, morphologies and properties of bio-based TPUs is evaluated by different analytical techniques and it is observed that the percentage of hard segment (HS) distributed in organised and unorganised phases is a key factor to control the materials properties.
Abstract: Bio-based TPUs from dimer acid-based polyols are synthesised by using a two-step prepolymer process including reactive processing. The effect of the polyol on the final chemical structures, morphologiesand properties ofbio-based TPUs is evaluatedby different analytical techniques. It is observed that the percentage of hard segment (HS) distributed in organised and unorganised phases is a key factor to control the materials properties. DSC reveals that the percentages of HS dispersed in the soft domains are high at low experimental HS contents. Multiscale microscopies show better defined organised structures with increasing HS content in TPUs, highlighting the importance of the distribution between hard and soft segments in the material structure.
TL;DR: The application of computationally inexpensive modeling methods for a predictive study of powder mixing is discussed and low-order statisticalmodels, including responsesurfacemethods, kriging, and high-dimensional model representations are presented.
Abstract: The application of computationally inexpensive modeling methods for a predictive study of powder mixing is discussed. A multidimensional population balance model is formulated to track the evolution of the distribution of a mixture of particle populations with respect to position and time. Integrating knowledge derived from a discrete element model, this method can be used to predict residence time distribution, mean and relative standard deviation of the API concentration in a continuous mixer. Low-order statisticalmodels, including responsesurfacemethods, kriging, and high-dimensional model representations are also presented. Their efficiency for design optimization and process design space identification with respect to operating and design variables is illustrated.
TL;DR: In this paper, the effects of MWNT content and aspect ratio on the properties of epoxy-based nanocomposites are investigated using nanoindentation and nanoscratch methods.
Abstract: nanocomposites DTU Orbit (09/12/2018) Nano-/microscale investigation of tribological and mechanical properties of epoxy/MWNT nanocomposites The effects of MWNT content and aspect ratio on the properties of epoxy-based nanocomposites are investigated using nanoindentation and nanoscratch methods. The Halpin-Tsai model for predicting the elastic modulus and hardness is modified to include the effective aspect ratio factor. The modified model predicts the experimental results more accurately. The frictional behavior is investigated and a new equation is proposed that correlates the ploughing friction with the plasticity index. The dispersion state of MWNTs and the surface features of residual grooves are investigated using scanning electron micrographs and AFM profiles. The mechanisms of improvements in the properties are also discussed.
TL;DR: In this paper, the preparation of cellulose/polymer blend fibers in textile fabrics is described and the rheology of spinning dopes, structural parameters, and physical textile properties of the prepared fibers are determined.
Abstract: Combinations of cellulosic fibers (cotton, viscose) with man-made chemical fibers (polyesters, polyamides, or polyacrylonitrile) are common as composites in textile fabrics. In this work the preparation of cellulose/polymer blend fibers in ILs is described. Cellulose is solved in ILs with other fiber polymers such as polyamides or PAN and processed to fiber blends by wet spinning. The rheology of spinning dopes, structural parameters, and physical textile properties of the prepared fibers are determined. TGA indicates a significant increase of carbon yield of the cellulose fibers blended with m-aramide and PAN, respectively.
TL;DR: In this article, the authors used coaxial electrospinning with surfactants as sheath fluid for preparing high-quality polymer nanofibers, and demonstrated that the Triton X-100 solution has a significant influence on the quality of the nanofiber.
Abstract: Coaxial electrospinning using surfactants as sheath fluid for preparing high-quality polymer nanofibers is studied. PAN nanofibers are fabricated using this process with Triton X-100 solutions in DMF. FESEM demonstrates that the Triton X-100 solution has a significant influence on the quality of the nanofibers. The nanofiber diameters can be controlled by adjusting the concentration of Triton X-100 in the sheath fluids with a scaling law D = 640 C -0.32 . The mechanism of the influence of Triton X-100 solutions on the formation of PAN fibers is discussed and it is demonstrated that coaxial electrospinning with surfactant solution is a facile method for achieving high-quality polymer nanofibers.
TL;DR: In this article, a new flame retardant based on an ammonium phosphonate is studied with respect to its thermal decomposition and its mode of action in wood-plastic composites.
Abstract: A new flame retardant based on an ammonium phosphonate is studied with respect to its thermal decomposition and its mode of action in wood-plastic composites (WPCs). The measurements are carried out by means of fire tests (cone calorimeter) and pyrolysis investigations (thermogravimetry, infrared spectroscopy). The flame retardant acts mainly in the condensed phase by increasing the amount of residue formed by the wood part in the WPC. Additional flame dilution is achieved by the release of water, ammonia and carbon dioxide during the decomposition of the flame retardant.
TL;DR: In this paper, a biomimetic micropatterning of surfaces for tuning of wetting and adhesion properties of polymeric materials is reported, where a thin film-terminated structure can help overcome this problem and increase adhesion.
Abstract: Progress in using biomimetic micropatterning of surfaces for tuning of wetting and adhesion properties of polymeric materials is reported. Surface patterning with low aspect ratios and low surface energy leads to superhydrophobicity and low adhesion while surface patterning with high aspect ratios leads to high adhesion. The condition of high aspect ratio and/or high number density creates the risk of fibril bundling owing to the adhesion between fibrils. A thin film-terminated structure can help overcome this problem and increase adhesion. In contrast to the spatular contacts, the conformal adhesion at interface can be enhanced significantly by creating micropatterns; the enhancement monotonically increases with the aspect ratios, where the side-wall friction plays an important role.
TL;DR: In this article, a high degree of exfoliation of MMT in NR is achieved by using the so-called "propping-open approach" in which a stepwise expansion of the interlayer spacing takes place.
Abstract: A high degree of exfoliation of MMT in NR is achieved by using the so-called “propping-open approach” in which a stepwise expansion of the interlayer spacing of MMT takes place. The nanostructure is characterized by WAXD and TEM which indicate different extents of clay dispersion depending on the fatty-acid chain length. Curing kinetics of different nanocomposites is studied and interestingly low activation energies of the vulcanization process are observed in the case of NR/EMMT nanocomposites. The incorporation of EMMT dramatically affects composite properties whereas DMA indicates significant reduction of tan δ peak height and the tensile strength approximately doubles from 14 to 30 MPa with only 5 phr EMMT.
TL;DR: In this article, the authors present a review of the problem of solvent costs, environmental hazards, and presence of traces of solvent impurities for polymer scaffolds, and the drawbacks of current methods, and future challenges.
Abstract: Electrospinning of polymer scaffolds is mostly carried out using organic solvents, but the drawbacks are: solvent costs, environmental hazards, and presence of traces of solvent impurities. The use of water-soluble polymers (WSPs), water or aqueous solutions as an electrospinning medium (green processing) is a very attractive method to avoid such issues. However, a few WSP such as polyelectrolytes are not spinnable as such, but have been electrospun by addition of WSPs, additives, and salts. This paper covers solution properties, polyelectrolyte nanofibrous scaffolds (polysaccharides, biopolymers, etc.), fabrication through green processing, and their regenerative medical applications such as wound dressing, drug delivery, and tissue engineering. This is the first review to cover the above issues, the drawbacks of current methods, and future challenges.
TL;DR: Hybrid polymeric inlays, patterned by nanoimprint lithography, are used to rapidly mass replicate pillar-like nanostructures by injection molding.
Abstract: Hybrid polymeric inlays, patterned by nanoimprint lithography, are used to rapidly mass replicate pillar-like nanostructures by injection moulding. This is difficult to achieve with traditional nickel inlays due to the rapid heat transfer of the metal, which results in premature cooling of the molten polymer and improper filling of nanoscale features. Using hybrid inlays, nanopillars can reliably be stretched by up to 40% of their designed height by adjusting moulding parameters. Hybrid inlays display longevity of more than 2000 cycles and can rapidly be fabricated to firmly establish injection moulding as an exceptionally useful tool for the high volume prototyping and production of nanopatterned polymeric devices.
TL;DR: In this article, a systematic and up-to-date account of a carbon nanopaper enabled shape memory polymers (SMPs) composite from electrical actuation to multifunctionalization is presented.
Abstract: Shape memory polymers (SMPs) are fascinating materials, with promising potential in a range of applications as actively moving polymers, which can undergo significant macroscopic deformation in a predefined manner between/among shapes in the presence of an appropriate stimulus. This work aims to present a systematic and up-to-date account of a carbon nanopaper enabled SMP composite from electrical actuation to multifunctionalization. Studies exploring nanopaper enabled SMP composites in various design principles in manufacturing, characterization, improvement, and development were included, especially for those induced by electricity and rendered multifunctional; making the article a comprehensive account of and systemic progress in SMP composite incorporated with carbon nanopaper.