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Preview: Die Angewandte Makromolekulare Chemie

Macromolecular Materials and Engineering



Wiley Online Library : Macromolecular Materials and Engineering



Published: 2017-11-01T00:00:00-05:00

 



Semicrystalline Shape-Memory Elastomers: Effects of Molecular Weight, Architecture, and Thermomechanical Path

2017-11-14T12:36:20.58947-05:00

Poly(caprolactone) networks are well-studied shape-memory polymers owing to their high fixity and recovery, their ability to store large amounts of elastic energy, and their tunable shape-triggering temperature. To elucidate the influence of network structure on shape-memory features, poly(caprolactone) networks are prepared by reacting different molecular weight diacrylate prepolymers with trifunctional (trimethylolpropane tris(3-mercaptopropionate), 3T) or tetrafunctional (pentaerythritol tetrakis(3-mercaptopropionate), 4T) crosslinkers. Networks from 4T crosslinkers generally exhibit higher gel fractions, more elastically active strands, and superior shape-memory properties compared with networks from 3T. Melted elastomers exhibit stress–strain behavior well described by the neo-Hookean model. How the state of crystallization during the cold-drawing process has a large effect on the draw stress, the network's shape fixity, and its elastic storage capacity is shown. Finally, the working strain range of networks is evaluated. Cured elastomers prepared from prepolymers with different molecular weights can store and release large amounts of elastic energy (>2 MJ m−3), over different ranges of tensile strain. The effect of architecture and molecular weight on shape-memory performance is examined for a series of poly(caprolactone) networks prepared using thiol–ene click chemistry. A sample's thermomechanical history, especially cold drawing, is shown to have a significant impact on shape-memory fixity and the amount of recoverable elastic energy.



Effect of Draw Ratio on Physical, Release, and Antibacterial Properties of Poly(ε-caprolactone) Loaded with Lysozyme

2017-11-14T12:30:37.172312-05:00

In this work, some films of poly(ε-caprolactone) (PCL) containing lysozyme at 5% by weight are obtained. Lysozyme is a natural antimicrobial molecule. The films are submitted to cold drawing process at three different draw ratios, λ = 3, 4, and 5, where λ is the ratio between final and initial length. Morphology, physical and barrier properties of the drawn samples are studied and correlated to the release of lysozyme. Tests against Bacillus sp are performed and correlated to the material texture. The molecular orientation of uniaxially drawn lysozyme doped PCL films is demonstrated to be a significant parameter for controlled release monitoring of the active molecule and the antimicrobial activity. Poly(ε-caprolactone) and lysozyme are submitted to draw processing at different draw ratios. The release of lysozyme is studied and found dependent on the draw ratio. The relationship between release rate and antimicrobial activity is also investigated. The macromolecular chain orientation is demonstrated to be an interesting and easy tool for the achievement of desired controlled release systems.



Raising Nanofiber Output: The Progress, Mechanisms, Challenges, and Reasons for the Pursuit

2017-11-14T04:12:48.042161-05:00

The paper discusses the extent to the scale of the electrospun fiber membrane. Literatures show that two distinct methods of raising electrospun nanofiber production can be employed via spinning from a setup of multiple nozzles arranged side by side or from an expanse of polymer solution (needleless electrospinning). Both of these methods are thoroughly explored by considering the variations available within either of their respective productivities. Their mechanisms are duly dealt with by looking at principles and parameters behind the process performances and an analysis of the strategies devised to deal with the shortcomings and ensure process feasibility is given. It has to be noted that most of the available work on electrospinning and their applications is achieved via single needle electrospinning. In this review, a projection is taken to be accomplished whether the nanofiber production can be consistently raised to commercial levels at the exceptional application routes so far produced by the conventional electrospinning means. This review discusses the extent to the scale of the electrospun fiber membrane. A projection is taken to be accomplished whether the nanofiber production can be consistently raised to commercial levels at the exceptional application routes so far produced by the conventional electrospinning means.



Resolving Inclusion Structure and Deformation Mechanisms in Polylactide Plasticized by Reactive Extrusion

2017-11-14T04:12:03.613673-05:00

A multiscale characterization approach is developed to resolve the structure of inclusions in polylactide (PLA) plasticized with acrylated poly(ethylene glycol) (acrylPEG) by reactive extrusion. Scanning transmission X-ray microscopy (STXM) coupled with near-edge X-ray absorption fine structure (NEXAFS) nanospectroscopy demonstrates that these inclusions have a core–shell morphology. This technique also proves that the inclusions consist of polymerized acrylPEG (poly(acrylPEG)), which is also confirmed by elastic modulus measurement using an atomic force microscope. The shell consists of poly(acrylPEG)-rich domains, while the core is less rich in the polymerized plasticizer. Upon drawing, the density of the inclusion's core and shell markedly decreases as shown by microcomputed X-ray tomography measurements, and no inclusion–matrix debonding is observed. At the same time, sub-micrometer cracks are noted between inclusions by STXM/NEXAFS imaging, which may result from the presence of crosslinking points restricting the local chain mobility. Novel knowledge about the reactive extrusion-induced PLA structure is released. The reactive plasticization of polylactide with acrylated poly(ethylene glycol) (acrylPEG) forms grafted inclusions inside the matrix. The inclusions exhibit a core–shell structure, where the core consisted of less dense poly(acrylPEG) than the shell. Upon drawing, the inclusions are stretched, while their density decreases at the shell and core regions. At the same time, sub-micrometer cracks form between inclusions.



Gel Electrolytes of Covalent Network Polybenzimidazole and Phosphoric Acid by Direct Casting

2017-11-13T02:31:15.476175-05:00

Polybenzimidazole membranes imbibed with phosphoric acid can support high proton conductivity at 120–200 °C, and have therefore emerged as the state-of-the-art electrolytes for fuel cells operating in this temperature range. This work presents a novel and operationally simple methodology for preparing mechanically robust covalent network polybenzimidazole membranes containing up to 95 wt% phosphoric acid. Diamino-terminal pre-polymers of different chain lengths are first prepared, followed by addition of a trifunctional carboxylic acid. The crude solutions are cast and subsequently heat treated at up to 230 °C, yielding free-standing membranes of networked polybenzimidazole with high proton conductivity at up to 180 °C and encouraging fuel cell performance. Covalent network polybenzimidazole membranes are obtained via a novel sequential direct casting procedure. Free-standing and mechanically robust gel electrolytes are obtained with phosphoric acid contents of up to 95 wt%. It supports high proton conductivity at temperatures well above 100 °C as ultimately manifested by low internal resistance in fuel cells operating at 180 °C.



Influence of the Hydrophobic–Hydrophilic Nature of Biomedical Polymers and Nanocomposites on In Vitro Biological Development

2017-11-10T10:17:22.375-05:00

In this work, cell viability, proliferation, and morphology are studied on two pairs of polymers used in the biomedical field that have similar chemical natures but differ in hydrophobicity. On the one hand, hydrophobic polyester poly(ε-caprolactone), is modified by blending with poly(lactic acid). On the other hand, the hydrophilic acrylate poly(2-hydroxyethyl methacrylate) (PHEMA), is copolymerized with ethyl methacrylate (EMA) at a ratio of 50/50 wt.% P(HEMA-co-EMA). These two polymers are used as neat resins or combined with hydroxyapatite (HA) nanoparticles and halloysite nanotubes (HNTs) to enhance cell attachment and mechanical properties. Cell proliferation is greater on moderately hydrophobic materials at the initial stage, with cells showing a round shape and aggregating in clusters. However, over longer culture periods, cell proliferation is more advanced on more hydrophilic surfaces, where cells spread out with a flatter shape. Improvement of cell viability is observed with the addition of HA and HNTs. Studying the biological development and compatibility, this original research shows, as at the initial stage, the cell proliferation is greater on hydrophobic materials (poly(ε-caprolactone)-poly(lactic acid)), but over longer stage, cell proliferation is greater on hydrophilic materials (poly(2-hydroxyethyl methacrylate)-ethyl methacrylate). This effect is improved with the creation of composites using hydroxyapatite and halloysite nanotubes.



Inkjet Printing Based Layer-by-Layer Assembly Capable of Composite Patterning of Multilayered Nanofilms

2017-11-10T10:16:40.432121-05:00

Surface modification involves developing a versatile thin film by combining the physical, chemical, or biological characteristics of the functional materials and can facilitate controlling material for desirable aims. Layer-by-layer (LbL) assembly can be used to create materials with controlled thicknesses and morphologies, diverse functionalities, and unique structures on any surface. However, despite the advantages of the LbL fabrication technique, there are limits to its application because it is a time-consuming process and has difficulty controlling the shape of nanofilms. In addition, controlling the lateral organization is difficult because the preparation methods are based on one-pot self-assembly. In this study, a multilayered fabrication system is developed for the high-throughput LbL assembly of nanofilms through inkjet printing. With various types of materials from synthetic polymer to graphene oxide to natural polymer and protein, the approach can tune the preparation of nanoscale multilayers with desired structures and shapes for specific applications on various substrates, including a silicon wafer, quartz glass, and cellulose-based paper. Multilayered nanofilms with various functional materials (synthetic and natural polymer, protein, and graphene) are fabricated by integrating layer-by-layer assembly and inkjet printing. Thickness, roughness, combinations, structures, and shapes of the nanofilms are desirably controllable. In addition, the printed nanofilms are deposited on several substrates ranging from silicon wafer to paper.



Mechanical and Rheological Behavior of Hybrid Cross-Linked Polyacrylamide/Cationic Micelle Hydrogels

2017-11-10T10:16:21.53895-05:00

In this work, a hybrid cross-linked polyacrylamide (PAM)/cationic micelle hydrogel is fabricated by introducing the cationic micelles into the chemically cross-linked PAM network. The cationic micelles act as the physical cross-linking points through the strong electrostatic interaction with anionic initiator potassium persulfate. Thereafter, in situ free radical polymerization is initiated thermally from the cationic micelle surface to form the hybrid cross-linked network. The synergistic effect between chemical and physical cross-link endows the hydrogel with excellent mechanical and recoverable properties. The resulting hydrogel exhibits tensile stress of 481 kPa and fracture toughness of 1.65 MJ m−3. It is found that the chemical cross-linking can inhibit the hysteresis of the hybrid hydrogel, exhibiting good elasticity in the tensile loading–unloading test. Moreover, dynamic rheological measurements show that the hybrid hydrogels possess fewer defects of network and exhibit excellent self-recovery behavior. Thus, this investigation provides a different view for the design of new high elastic and tough hydrogels containing hybrid physical and chemical cross-linking networks. A hybrid cross-linked polyacrylamide/cationic micelle hydrogel is fabricated by in situ free radical polymerization, and cationic micelles act as physical cross-linking points in the chemically cross-linked polyacrylamide. The introduction of cationic micelles can consummate effectively the network structure, contributing to the excellent mechanical properties of the hybrid hydrogels. This provides a different view for the design of high elastic and tough hydrogels.



Relaxation Dynamics and Strain Persistency of Azobenzene-Functionalized Polymers and Actuators

2017-10-23T07:56:32.461994-05:00

The accumulation of photoinduced deformation in azobenzene functionalized polymers has received a significant amount of attention in recent years. Critically, the induced photomechanical deformation in these systems experiences varying degrees of relaxation. Control over the persistence of photomechanical strains is vital to the broader utility of these materials in shape programmable systems including soft robotics and engineered origami. Furthermore, investigations of relaxation in light responsive polymer systems triggered by UV light are more prominent than those triggered by blue-green light. In this study, the impact of chain mobility and initially induced photostrain on the relaxation dynamics of azobenzene-functionalized polyimides after irradiation with blue light is examined. A modeling effort coupling chromophore population dynamics to material strain is carried out to further explore the relationship between material structure, relaxation dynamics, and macroscopic deformation. The implications for controlling strain persistence are highlighted by simulating one example of a photoprimed bistable actuator. Understanding the relaxation dynamics and strain persistency in photomechanical polymers is crucial to the development of these materials for functional devices. The relaxation of five azobenzene functionalized polyimides after irradiation with blue light is studied. A finite element model coupling chromophore population dynamics to material strain is used to clarify the material behavior and to explore a bistable actuator concept.



Preparation of Hollow Fiber Membranes by Nonsolvent Induced Phase Separation along with Hydrogen Gas Formation Using a Single Orifice Spinneret

2017-10-23T07:50:43.522282-05:00

Traditional nonsolvent induced phase separation (NIPS) process for fabrication of hollow fiber membranes (HFMs) faces challenges, like design and manufacture of spinneret with two concentric orifices to provide parallel and continuous feed of polymer solution and bore fluid at specific rates. These factors limit the use of traditional technique to produce HFMs. Here, a new direct spinning method for fabricating HFMs by feeding a polymer solution, containing a gas producing agent using single orifice spinneret is reported. Polysulfone-dimethylacetamide solution containing NaBH4 is extruded through a stainless-steel needle (single orifice spinneret) into HCl aqueous solution (coagulation bath) at specific rates. Effects of polysulfone concentration, temperature, and pH of coagulant bath on structure and performance of the HFMs are investigated. Synergy between hydrogen from NaBH4 hydrolysis and NIPS process benefits fabrication of HFMs with good hollow bore structure and high porous wall. The prepared HFMs show good dye separation. A direct spinning method is reported for fabricating hollow fiber membranes through feeding a polymer solution containing gas producing agent with a single orifice spinneret. Effects of concentration of polysulfone dope, temperature, and pH of coagulant bath on structure and performance of the hollow fiber membranes (HFMs) are investigated. The prepared HFMs show promising application for dyes separation.



Soybean-Oil-Based Thermosetting Resins with Methacrylated Vanillyl Alcohol as Bio-Based, Low-Viscosity Comonomer

2017-10-23T03:22:13.42551-05:00

A novel, bio-based, aromatic monomer (methacrylated vanillyl alcohol, MVA) is synthesized using vanillyl alcohol and methacrylic anhydride in the absence of solvents. The resulting MVA is used as a sustainable comonomer to replace styrene in a maleinated acrylated epoxidized soybean-oil (MAESO) resin to produce novel thermosets via free radical polymerization. The influence of MVA loading on the viscosity, gelation time, curing extent, thermomechanical properties, and tensile properties of the MAESO–MVA thermoset is investigated. The synthesized MVA exhibits very low volatility, which is beneficial for the development of construction material with low or zero emission. The viscosity of the MAESO–MVA system can be tailored to meet the commercial requirements. Increasing the MVA content accelerates the crosslinking reaction rate and improves thermal and mechanical properties of the MAESO–MVA system. The glass transition temperature increases with increasing MVA content. Soxhlet extraction experiments show that more than 90% of the components are incorporated into the crosslinking network. Overall, the developed MVA monomer shows promising properties to be used as an effective, green comonomer to replace styrene. Methacrylated vanillyl alcohol (MVA) monomer shows promising results as a bio-based comonomer to replace styrene for maleinated acrylated epoxidized soybean-oil (MAESO) resins and exhibits advantages in terms of low volatility, sustainability, environmental friendliness, good processability, and improved glass transition temperature. Moreover, both methacrylated vanillyl alcohol and MAESO resin are derived from bio-based renewable resource.



Key Production Parameters to Obtain Transparent Nanocellular PMMA

2017-10-17T01:21:08.552049-05:00

Transparent nanocellular polymethylmethacrylate (PMMA) with relative density around 0.4 is produced for the first time by using the gas dissolution foaming technique. The processing conditions and the typical characteristics of the cellular structure needed to manufacture this novel material are discovered. It is proved that low saturation temperatures (−32 °C) combined with high saturation pressures (6, 10, 20 MPa) allow increasing the solubility of PMMA up to values not reached before. In particular, the highest CO2 uptake ever reported for PMMA, (i.e., 48 wt%) is found for a saturation pressure of 20 MPa and a saturation temperature of −32 °C. Due to these processing conditions, cell nucleation densities of 1016 nuclei cm−3 and cell sizes clearly below 50 nm are achieved. The nanocellular polymers obtained, with cell sizes ten times smaller than the wavelength of visible light and very homogeneous cellular structures, show a significant transparency. Transparent nanocellular polymethylmethacrylate (PMMA) is produced for the first time. The key parameters needed for its production are low saturation temperatures (−32 °C) combined with high saturation pressures (6–20 MPa). The materials obtained by using this method present high homogeneous cellular structure, with cell nucleation densities higher than 1016 nuclei cm−3 and cell sizes clearly below 50 nm.



Electrothermal Actuator on Graphene Bilayer Film

2017-10-17T01:15:47.022755-05:00

Electrodriven bilayer actuator is designed and fabricated by spin-coating a reduced graphene oxide solution onto a polymer substrate. The bonded interface properties, electrical and thermal conductivities are characterized through scanning electron microscopy and X-ray diffraction. The bilayer actuator exhibits fast and large bending response when a direct current voltage is applied to the graphene layer. Whereas it exhibits oscillation when an alternating current voltage is applied to the bilayer actuator. The effects of the layer structure and the electro-operation methods on the bending motions are studied. Two new actuation modes are explored to broaden the applications of electrodriven bilayer actuator, which are achieved by the actuator structure design and the driven current control. Electrically responsive graphene bilayer soft actuator provides the potential applications in the fields of thin-film electronics, sensors, and energy conversion. Electric current generated Joule heating on a graphene bilayer film subsequently results in the expansion and bending of the bilayer film, which achieves electrical-to-mechanical energy transition of a smart actuator. Various actuation modes are demonstrated by the bilayer structure design and the electric current controlling.



Carboxylated Lignin as an Effective Cohardener for Enhancing Strength and Toughness of Epoxy

2017-10-12T01:15:55.168985-05:00

It is demonstrated that pristine or functionalized lignin can be used in epoxy as a cohardener or comonomer; however either unsatisfactory mechanical properties or low lignin content remains a challenge in utilizing the sustainable biomass to replace petrochemical product. In this study, carboxylic acid-modified kraft lignin (lignin–COOH) is synthesized and used as a cohardener for epoxy with loading content of up to 10.0 wt%. With incorporation of 10.0 wt% of lignin–COOH, the resulting composite exhibits increments of 16%, 13%, 20%, and 95% on tensile modulus, flexural modulus, tensile strength, and toughness respectively, in contrast to neat epoxy. The good dispersion of lignin–COOH in epoxy, rigid aromatic structure of lignin, and the reduced crosslink density in the composite can simultaneously contribute to the high mechanical performance, which is verified by the thermal and mechanical analysis results. It suggests that lignin can be converted to effective alternative curing agents for epoxy thermosets. Cured epoxy incorporated with carboxylic acid–modified kraft lignin as a cohardener at moderate loading contents exhibits simultaneous enhancement of tensile modulus, flexural modulus, tensile strength, and toughness, which can promote the utilization of this sustainable biomass as an alternative feedstock in practical thermosetting applications in terms of substituting petrochemical product.



Surface Modification of Carbon Fibers by Free Radical Graft-Polymerization of 2-Hydroxyethyl Methacrylate for High Mechanical Strength Fiber–Matrix Composites

2017-10-12T01:06:08.600148-05:00

Free radical polymerization of vinylic monomers in the presence of carbon fibers results in the grafting of polymers onto the carbon fiber surface. Graft polymers cannot be removed by intense washing with good polymer solvents. The density and size of these structures are successfully controlled by reaction conditions. Grafting of the carbon fiber surface with hydroxyethyl methacrylate allows for introducing functional groups suitable for the reaction with an epoxy-based resin. The resulting fiber-reinforced composites show enhanced mechanical properties compared to samples prepared from carbon fibers equipped with a standard sizing for epoxy resins. Thus, tensile strength increases by 10%, while interlaminar shear strength improves by 20%. Free radical graft polymerization of vinylic monomers to carbon fibers is described. Grafting with hydroxyethyl methacrylate allows for the introduction of polar groups suitable for the reaction with an epoxy-based resin. The corresponding composites show improved mechanical properties compared to composites prepared from carbon fibers equipped with standard sizing: tensile strength increases by 10%, interlaminar shear strength improves by 20%.



Initiated-Chemical Vapor Deposition of Polymer Thin Films: Unexpected Two-Regime Growth

2017-10-11T03:30:38.113498-05:00

Initiated-chemical vapor deposition (iCVD) is a very promising technique which has demonstrated the ability to deposit a large variety of polymers that can be integrated in micro-nanotechnology applications. However, studies on the underlying growth mechanisms responsible for the formation of these thin films remain scarce in the literature. This work shows that the iCVD growth follows surprisingly two regimes: in the first stage of the growth, the deposition rate is relatively slow then increases with the deposition time until a linear growth is reached. The presence of these two growth regimes can be interpreted by taking into account, as the iCVD growth progresses, that the synthesized polymer chains help the monomer adsorption on the substrate which locally increases the concentration of monomers available for the polymerization and thus the growth rate. This increase of the local concentration of monomer consistently correlates with the formation of polymer chains with higher molar mass. The initiated chemical vapor deposition of poly(meth)acrylate-based thin films follows surprisingly a two-regime growth. This paper provides an explanation based on a combination of an experimental study of the polymer thin films properties as a function of deposition time and film thickness and a simple model taking into account the local increase of the concentration of monomers available for the polymerization.



House of Cards Nanostructuring of Graphene Oxide and Montmorillonite Clay for Oil–Water Separation

2017-09-28T11:34:05.831466-05:00

Noncovalent interactions are ubiquitous in our daily living. Nature employs hydrophobic effects, π–π interactions, hydrogen bonding, van der Waals forces, and electrostatic interactions in many biological processes such as protein folding. In the same manner, scientists exploit this plethora of inherently reversible noncovalent interactions as dials to design robust and smart materials. Electrostatic interaction is particularly interesting due to the simplicity of its concept, i.e., opposite charges attract. However, to our knowledge, the electrostatic interaction between two different 2D nanomaterials has not been investigated in literature. A myriad of natural and synthetic 2D nanomaterials should be explored for what may be an exciting cocktail of synergistic and tunable properties brought about by their charges and physical properties. This contribution highlights an interesting phenomena when organic, negatively charged graphene oxide and inorganic, positively charged montmorillonite (MMT) clay edges are brought into contact. A house-of-cards structure is proposed for two different 2D nanomaterials (graphene oxide and montmorillonite) interacting electrostatically. Such behavior is manifested by a dramatic change in viscosity leading to the formation of a hydrogel, which is later used as a precursor for the fabrication of aerogels. The materials are promising for oil–spill cleanup and oil–water separation.



Amorphous Electrically Actuating Submicron Fiber Waveguides

2017-09-21T01:31:21.802114-05:00

Amorphous electrically actuating submicron fiber waveguides are promising building blocks for creating novel opto-electromechanical devices. In this study, waveguiding and electrically actuating properties of the waveguides composed of racemic poly(lactic acid) and a dye are investigated. The fibers have mean diameters of <0.4 µm, and each fiber demonstrates subwavelength waveguiding with a loss coefficient of 1.5 × 10−4–8.3 × 10−4 µm−1 at 0.63 µm wavelength. Light propagates with a near-light speed group velocity between wavelengths of 0.59 and 0.63 µm, where the fraction of power inside the core is 0.13–0.28. The fiber mat thicknesses change in response to both the polarity and the magnitude of an applied voltage, similar to the inverse-piezoelectric effect. The estimated values for both the apparent piezoelectric constant (29 000 × 10−12 m V−1) and Young's modulus (1.5 kPa) indicate a high degree of electricity actuation and a soft mat. Extremely small, soft, and electrically actuating waveguides can produce novel opto-electromechanical devices. The properties of novel electrically actuating and waveguiding amorphous polymer submicron fibers are investigated in detail. These fibers guide light at subwavelength diameters with a group velocity greater than 0.71c0. The fiber mat also demonstrates electrical actuation with a high apparent piezoelectric constant of ≈29 000 × 10−12 m V−1. Extremely small and functional waveguides can be used to produce novel opto-electromechanical devices.



Ionic Liquid Approach Toward Manufacture and Full Recycling of All-Cellulose Composites

2017-09-06T11:15:23.803735-05:00

All-cellulose composites (ACCs) are prepared from high-strength rayon fibers and cellulose pulp. The procedure comprises the use of a pulp cellulose solution in the ionic liquid (IL) 1-ethyl-3-methyl imidazolium acetate ([EMIM][OAc]) as a precursor for the matrix component. High-strength rayon fibers/fabrics are embedded in this solution of cellulose in the IL followed by removal of the IL. Different concentrations of cellulose in the IL are investigated and the mechanical properties of the final ACCs are determined via tensile, bending, and impact testing. ACCs prepared in this study show mechanical properties comparable to thermoplastic glass fiber-reinforced plastics. Apart from being bio-based, they possess several advantages such as biodegradability and full recyclability. The recycling of ACCs is successfully demonstrated in several cycles by using the recycled cellulose for subsequent matrix preparation. The manufacture of all-cellulose composites (ACCs) reinforced with high-strength rayon fibers is reported. Solutions of cellulose in the ionic liquid 1-ethyl-3-methyl imidazolium acetate are used as matrix precursors. Full recycling of these ACCs is successfully demonstrated in several cycles by using the recycled material for subsequent matrix preparation without any significant loss in mechanic performance.



High-Impact Polyamide Composites with Linear Ethylene–Norbornene Anhydride Copolymers from Insertion Polymerization

2017-08-23T12:18:11.558467-05:00

Toughening of polyamide 66 with novel linear norbornene anhydride functionalized polyethylenes leads to an impact performance in the Charpy-notch impact testing at 23 °C and −30 °C as high as aCN = 18.0 ± 1.0 and 13.7 ± 0.8 kJ m−2, respectively, which compares favorably to a state of the art functional low density polyethylene (LDPE) from high-pressure copolymerization with a Charpy-notch impact strength of aCN = 16.8 ± 0.0 and 13.8 ± 2.1 kJ m−2 at 23 and −30 °C, respectively. The linear copolymers are obtained by insertion polymerization at mild ethylene pressures of 5 to 15 bars with phosphinesulfonato Pd (II) catalysts, to yield linear copolymers with norbornene anhydride incorporations as high as 4.8 mol% along with a polymer molecular weight of >105 g mol−1. Furthermore, the norbornene anhydride functionality serves as a reaction site for postpolymerization functionalization with alcohols to obtain the respective half- and diesters of the anhydride functionality. Notably, the impact performance is improved with the increase of the alkyl chain length and degree of branching of the ester functionality in the order methanol < n-butanol < 2-ethyl hexanol from 10.0 to 13.8 kJ m−2. Norbornene-anhydride-functionalized linear polyethylenes from catalytic insertion copolymerization under mild conditions provide a high impact resistance to nylon-6,6 that compares favorably to existing impact modifiers, at ambient and low temperatures. Morphologies of the blends underline a strong binding between the microphases.



Tailoring the Morphology of Responsive Bioinspired Bicomponent Fibers

2017-07-25T01:37:09.38309-05:00

Nature is an intriguing inspiration for designing a myriad of functional materials. However, artificial mimicking of bioinspired structures usually requires different specialized procedures and setups. In this study, a new upscalable concept is presented that allows to produce two bioinspired, bicomponent fiber morphologies (side-by-side and coaxial bead-on-string) using the same electrospinning setup, just by changing the employed spinning solvent. The generated fiber morphologies are highly attractive for thermoresponsive actuation and water harvesting. Another challenge solved in this work is the compositional characterization of complex fiber morphologies. Raman imaging and atomic force microscopy is introduced as a powerful method for the unambiguous characterization of complex bicomponent fiber morphologies. The work opens the way for the construction of heterostructured fiber morphologies based on different polymers combinations, offering high potential for applications as actuators, smart textiles, water management, drug release, and catalysis. Tailoring of bioinspired bicomponent fiber structures in a simple way and unambiguous characterization of complex fiber structures by combination of Raman imaging with atomic force microscopy, giving access to promising applications as actuators or for water harvesting, is highlighted.



Tough and Enzyme-Degradable Hydrogels

2017-07-24T07:45:33.356192-05:00

Mechanically robust hydrogels that degrade only via cell action have potential as scaffolds for the generation of load-bearing soft connective tissue. This study demonstrates that terminally acrylated 4-arm-poly(ethylene glycol)-block-oligo(trimethylene carbonate) (4a-PEG-(TMC)n) can be readily reacted with a collagenase-degradable bis-cysteine peptide to form hydrogels. The inclusion of the TMC blocks renders the hydrogels mechanically tough when tested under compression, with modulus and toughness values within the range of those of articular cartilage. Moreover, the hydrogels formed are resistant to degradation by hydrolysis in the absence of collagenase but degrade via surface erosion in the presence of collagenase. The strategy employed to form these hydrogels is readily tailored to create a variety of tough, enzyme-degradable hydrogels of varying mechanical and degradation properties. This paper describes a means of creating an enzyme-degradable hydrogel with mechanical properties approximating those of soft connective tissues such as the articular cartilage and meniscus. These properties are achieved through Michael-type addition crosslinking of a bis-cysteine peptide with a terminally acrylated 4-arm-poly(ethylene glycol) (4a-PEG)-block-oligo(trimethylene carbonate).



Macromol. Mater. Eng. 11/2017

2017-11-17T09:23:22.142379-05:00

Front Cover: Cucurbit[7]uril-based conjugated polyrotaxanes are synthesized and co-crystallized with sugar-based matrices such as sucrose and trehalose to obtain highly efficient color-converting solids with remarkably high QYs (>50%) which are suitable for solid-state lighting. This is reported by Talha Erdem, Muazzam Idris, Hilmi Volkan Demir and Dönüs Tuncel, in article number 1700290.



Masthead: Macromol. Mater. Eng. 11/2017

2017-11-17T09:23:23.080394-05:00




Contents: Macromol. Mater. Eng. 11/2017

2017-11-17T09:23:24.366761-05:00




Surface Modification of Polyhydroxyalkanoates toward Enhancing Cell Compatibility and Antibacterial Activity

2017-08-18T01:56:23.454313-05:00

Biomaterials for in vivo application should induce positive interaction with various histocytes and inhibit bacteria inflection as well. Cells and/or bacteria response to the extracellular environment is therefore the basic principle to design the biomaterials surface in order to induce the specific biomaterial–biological interaction. Polyhydroxyalkanoate (PHAs) are of growing interests because of their natural origin, biodegradability, biocompatibility, and thermoplasticity; however, quite inert and intrinsic hydrophobic characteristics have hindered their extensive usage in medical applications. Surface modification of PHAs tailors the chemistry, wettability, and topography without altering the bulk properties, and introduces specific proteins/peptides and/or antibacterial agents to mediate cell–matrix interactions. This review describes the recent developments on the surface modification of PHAs to construct cell compatible and antibacterial surfaces. Inert and hydrophobic characteristics of polyhydroxyalkanoates (PHAs) have limited in vivo biomedical applications. Surface modifications to introduce reactive functional groups add valuable attributes to PHAs, which can further immobilize specific proteins/peptides and/or antibacterial agents to mediate cell–matrix interactions. This review describes the recent developments on the surface modification of PHAs to tailor the interactions with cells or bacteria in vivo.



Pore Size Distribution and Blend Composition Affect In Vitro Prevascularized Bone Matrix Formation on Poly(Vinyl Alcohol)/Gelatin Sponges

2017-09-12T00:46:52.74263-05:00

This study aims at identifying compositional and architectural (pore size and distribution) parameters of biocompatible scaffolds, which can be best suitable for both osteoblasts and endothelial cells to produce optimized 3D cocultured constructs. Spongy scaffolds are prepared using poly(vinyl alcohol) (PVA) and gelatin (G) at different weight compositions (PVA/G range: 100/0–50/50, w/w) via emulsion and freeze-drying. The higher the gelatin content, the larger is the volume occupied by higher size pores. Human umbilical vein endothelial cells and human mesenchymal stromal cells are independently differentiated on the scaffolds to select the best candidate for the coculture. The results of metabolic activity and histology on single platforms show both cell- and material-type dependent outcomes. PVA/G 80/20 scaffolds are finally selected and allow the formation of mineralized matrix containing organized endothelial-like structures. This study highlights the need for systematic investigations on multifactorial parameters of scaffolds to improve vascularized bone substitutes. Poly(vinyl alcohol) (PVA)/gelatin scaffolds are produced via emulsion and freeze-drying from 100/0 to 50/50 (w/w) compositions. Changing composition affects pore size distribution and biological response of endothelial cells and mesenchymal stromal cells, including metabolic activity and differentiation. PVA/gelatin 80/20 scaffolds allow the formation of mineralized matrix containing organized endothelial-like structures. Systematic investigations on physicochemical and architectural features can improve vascularized bone substitutes.



Novel Macromolecular Emulsifiers as Coatings with Water-Tolerant Antifogging Properties Based on Coumarin-Containing Copolymeric Micelles

2017-08-28T05:30:51.05224-05:00

An efficient macromolecular emulsifier as water-tolerant antifogging coating based on coumarin-containing copolymeric micelles is reported. Compared to the previous work using poly(methyl methacrylate-co-2-(dimethylamino)ethyl methacrylate), coumarin unit in copolymer-based coating can be photo-crosslinked under UV light to form an interchain network, successfully avoiding the use of chemical crosslinking agents. Coumarin unit in the amphiphilic copolymer can be photo-crosslinked under UV light irradiation to form an interchain network, effectively avoiding the use of chemical crosslinking agents. A possible antifogging mechanism is that the water molecules are absorbed into the hydrophilic chains of the coatings and droplets are not attached to the surface.



3D Printing of BaTiO3/PVDF Composites with Electric In Situ Poling for Pressure Sensor Applications

2017-08-23T12:17:33.664791-05:00

This paper presents 3D printing of piezoelectric sensors using BaTiO3 (BTO) filler in a poly(vinylidene) fluoride (PVDF) matrix through electric in situ poling during the 3D printing process. Several conventional methods require complicated and time-consuming procedures. Recently developed electric poling-assisted additive manufacturing (EPAM) process paves the way for printing of piezoelectric filaments by incorporating polarizing processes that include mechanical stretching, heat press, and electric field poling simultaneously. However, this process is limited to fabrication of a single PVDF layer and quantitative material characterizations such as piezoelectric coefficient and β-phase percentage are not investigated. In this paper, an enhanced EPAM process is proposed that applies a higher electric field during 3D printing. To further increase piezoelectric response, BTO ceramic filler is used in the PVDF matrix. It is found that a 55.91% PVDF β-phase content is nucleated at 15 wt% of BTO. The output current and β-phase content gradually increase as the BTO weight percentage increases. Scanning electron microscopy analysis demonstrates that larger agglomerates are formulated as the increase of BTO filler contents and results in increase of toughness and decrease of tensile strength. The highest fatigue strength is observed at 3 wt% BTO and the fatigue strength gradually decreases as the BTO filler contents increases. The fabrication of piezoelectric pressure sensors with BaTiO3 (BTO) nanoparticles in a poly(vinylidene) fluoride (PVDF) matrix through electric in situ poling during the FDM 3D printing process is presented. The enhanced electric poling-assisted additive manufacturing process enables to polarize dipoles of PVDF and BTO to longitudinal direction.



Highly Luminescent CB[7]-Based Conjugated Polyrotaxanes Embedded into Crystalline Matrices

2017-09-12T00:46:31.138535-05:00

π-Conjugated polymers suffer from low quantum yields (QYs) due to chain–chain interactions. Furthermore, their emission in solid films is significantly quenched due to aggregation leading further decrease in QY. These are the two main issues of these materials hampering their widespread use in optoelectronic devices. To address these issues, here the backbone of poly(9,9′-bis(6″-(N,N,N-trimethylammonium)hexyl)fluorene-alt-co-thiophenelene) is isolated by threading with cucurbit[7]uril (CB7). Subsequently, the conjugated polyrotaxanes are incorporated into organic crystalline matrices to obtain highly efficient color-converting solids suitable for solid-state lighting. Upon threading the polymer backbone with CB7s, although the QY of the resulting polyrotaxane in solution state increases, the quenching problem in their solid state is not completely tackled. To solve this problem, these conjugated polyrotaxanes are embedded into various crystalline matrices and their remarkably high QYs (>50%) in the solution are successfully maintained in the solid state. To demonstrate the suitability of these aforementioned materials for solid-state lighting, a proof-of-concept light-emitting diode is constructed by employing their powders as color converters. Conjugated polyrotaxanes are incorporated into organic crystalline matrices to obtain highly efficient color converting solids suitable for solid-state lighting.



Ionically Crosslinked Thermoresponsive Chitosan Hydrogels formed In Situ: A Conceptual Basis for Deeper Understanding

2017-09-20T03:17:46.24949-05:00

In situ formation and the performance of ionically crosslinked thermosensitive chitosan-based hydrogels are presented. Experimental analyses, together with mechanistic descriptions of the events during hydrolysis, are employed to uncover the role of urea and isobutanol as chemical modifiers by comparing three classes of hydrogels formed in chitosan/β-glycerolphosphate (β-GP) solutions. Rheological measurements demonstrate that urea caused an increase in gelation time and temperature of chitosan/β-GP systems, while isobutanol has an inverse effect. Interpretations based on increase in pH and chemical bonding of components in chitosan solutions provide further insight into hydrogel network formation. Urea can hinder the hydrophobic characteristics of chitosan-based hydrogels, whereas isobutanol has the opposite effect. The shape retaining strategy applied here helps in simulation and interpretation of performance of thermosensitive hydrogels for biomedical purposes. This study uncovers the role of urea and isobutanol as chemical modifiers by comparing three classes of hydrogels. An increased or a decreased pH affects gelation, where the best conditions for gelation would be achievable in the case of neutral medium. Either a rise or a fall in pH value upsets the balance between electrostatic interactions and crosslinking, the driving forces behind gelation.



Hydroquinone Based Sulfonated Copolytriazoles with Enhanced Proton Conductivity

2017-08-01T01:01:05.718956-05:00

A series of new fluorinated sulfonated copolytriazoles (PTHQSH-XX) with ion exchange capacity (IECw) values ranging from 1.66 to 2.82 meq g−1 are prepared via cuprous ion catalyzed azide-alkyne click polymerization reaction between 1,4-bis(prop-2-ynyloxy)benzene, 4,4′-diazido-2,2′-stilbene disulfonic acid disodium salt (SA), and 4,4-bis[3′-trifluoromethyl-4′(4-azidobenzoxy) benzyl] biphenyl (QAZ). The degree of sulfonation of the copolytriazoles is adjusted between 60% and 90% by varying the molar ratio of sulfonated monomer (SA) to the nonsulfonated monomer (QAZ). The structure of the copolytriazoles is characterized by Fourier transform infrared and NMR spectroscopy. The solution-cast membranes of these copolymers exhibit high thermal, mechanical, oxidative and hydrolytic stability, and high proton conductivity (19–142 mS cm−1 at 80 °C and 22–157 mS cm−1 at 90 °C). Transmission electron microscopy confirms the formation of good phase separated morphology with ionic clusters in the range of 15–145 nm. A series of fluorinated sulfonated copolytriazoles with high ion exchange capacity are prepared by Cu (I) catalyzed azide-alkyne click polymerization. The membranes prepared from these copolymers exhibit high thermal, mechanical, oxidative and hydrolytic stability, and proton conductivity as high as 142 mS cm−1 at 80 °C.



Selective Laser Sintering 3D Printing: A Way to Construct 3D Electrically Conductive Segregated Network in Polymer Matrix

2017-08-01T01:03:00.077311-05:00

Selective laser sintering (SLS), which can directly turn 3D models into real objects, is employed to prepare the flexible thermoplastic polyurethane (TPU) conductor using self-made carbon nanotubes (CNTs) wrapped TPU powders. The SLS printing, as a shear-free and free-flowing processing without compacting, provides a unique approach to construct conductive segregated networks of CNTs in the polymer matrix. The electrical conductivity for the SLS processed TPU/CNTs composite has a lower percolation threshold of 0.2 wt% and reaches ≈10−1 S m−1 at 1 wt% CNTs content, which is seven orders of magnitude higher than that of conventional injection-molded TPU/CNTs composites at the same CNTs content. The 3D printed TPU/CNTs specimen can maintain good flexibility and durability, even after repeated bending for 1000 cycles, the electrical resistance can keep at a nearly constant value. The flexible conductive TPU/CNTs composite with complicated structures and shapes like porous piezoresistors can be easily obtained by this approach. A stretchable and bendable, and electrically conductive polymer nanocomposite with segregated network and designed geometric structure, which is prepared by selective laser sintering, may have potential application in 3D printing of flexible circuit, wearable devices, implantable devices, electronic skin, and dielectric elastomer actuators, etc.



Cocoa Shell Waste Biofilaments for 3D Printing Applications

2017-08-17T07:46:59.27212-05:00

In this study, biofilaments based on cocoa shell waste, a by-product of the chocolate industry, and biodegradable poly(ε-caprolactone), PCL, have been prepared using a single-screw extruder. Micronized cocoa shell waste is compounded in the polymer up to 50% by weight without significant alteration of its crystalline structure. Resultant elastic (Young's) modulus of biofilaments remains close to that of pure PCL. Scanning electron microscopy results indicate that micronized cocoa shell waste is homogeneously dispersed in the polymer during the extrusion process. Detailed thermal characterization measurements on the extruded filaments allow tuning of the fused deposition modeling 3D printing parameters. 3D printed items display a well-defined structure with good adhesion between deposition layers and fine resolution. Hence, with this simple and solvent-free fabrication technique, uniformly structured cocoa shell waste biofilaments can be produced in a very reproducible manner and can be used in 3D printing of diverse objects with potential household and biomedical applications. Direct valorization of cocoa shell waste, a by-product of the chocolate industry, for the fabrication of low-cost biofilaments for 3D printing application at lower 3D printing temperatures compared to standard filaments and highly reproducible process is reported.



Microfluidic Fabrication of Physically Assembled Nanogels and Micrometric Fibers by Using a Hyaluronic Acid Derivative

2017-08-18T01:51:15.863017-05:00

The employ of a hyaluronic acid (HA) derivative, bearing octadecyl (C18) and ethylenediamine (EDA) groups, for microfluidic fabrication of nanogels and microfibers is reported in this study. Two HA-EDA-C18 derivatives (125 and 320 kDa) having ionic strength sensitive properties are synthesized and characterized. The control of the rheological properties of HA-EDA-C18 aqueous dispersions by formation of inclusion complexes with hydroxypropyl-β-cyclodextrins (HPCD) is described. Reversibility of C18/HPCD complexation and physical crosslinking is detected in media with different ionic strength through oscillation frequency tests. HA-EDA-C18 125 kDa is employed for nanogel fabrication. Control over nanogel dimension by flow ratio regulation is demonstrated. HA-EDA-C18 320 kDa with HPCD is employed for fabrication of both microfibers and microchannels. Dimension of fibers is controlled by modulating flow ratios. Suitability for biological functionalization is assayed introducing cell adhesive peptides. Adhesion and encapsulation of human umbilical vein endothelial cells is evaluated. Microfluidic fabrication of biomaterials by using ionic strength sensitive hyaluronic acid derivatives is described. Rheological characterization demonstrates the salt sensitive coacervation of hyaluronic acid derivatives depending of media ionic strength. Hydroxypropyl-β-cyclodextrins are employed to control fluidity of polymer dispersion without affecting crosslinking properties. Biomaterials fabrication is performed by using very mild conditions suitable for a safe cell encapsulation.



Novel Core–Shell PS-co-PBA@SiO2 Nanoparticles Coated on PP Separator as “Thermal Shutdown Switch” for High Safety Lithium-Ion Batteries

2017-08-18T01:51:38.182667-05:00

Thermal runaway is a hazardous behavior of lithium-ion batteries under extreme conditions and is mainly cause for restraint of its commercial applications in development of high-power and high-rate lithium-ion batteries. In this paper, a new dual-functions coating layer fabricated from polystyrene-poly(butyl acrylate) copolymer encapsulated silica nanoparticles as “thermal shutdown switch” with a reasonable shutdown temperature of ≈80 °C is designed and coated on polypropylene separator. The shell polymer owing to its self-adhesion upon glass transition temperature (Tg) can retard off the Li+ conduction between the electrodes, thus prevents cell from thermal runaway, the core nanoparticles protect the separator from significantly thermal shrinkage when the cell temperature keeps going up. Moreover, the coated separator has no negative affection on the normal electrochemical performance of the batteries, thereby implying that this coating layer provides a simple and effective approach to control the safety of commercial lithium-ion batteries by internal self-protecting. Polystyrene-poly(butyl acrylate) copolymer (PS-co-PBA) encapsulating (3-(methacryloxy)propyl) trimethoxysilane-treated SiO2 is prepared by free radical polymerization and coated on polypropylene separator. The coating layer through glass transition can retard off ion transport to protect Li-ion batteries at risk temperature.



Balancing Block Copolymer Thickness over Template Density in Graphoepitaxy Approach

2017-09-12T00:46:16.588964-05:00

Directed self-assembly (DSA) of block copolymers (BCP) is one of the most promising patterning solutions for sub-10 nm nodes. While significant achievements are demonstrated in pattern fidelity for various applications (contact shrink, line patterning), some challenges are still needed to be overcome especially regarding the defect density reduction, in order to ensure DSA insertion in high-volume manufacturing. In particular, in the case of the graphoepitaxy approach, a remaining challenge is to solve the pattern-densities-related defect issue due to BCP film thickness variation inside the guiding template. In order to address this issue, a new DSA process flow called “DSA planarization” is employed for contact-hole patterning, and consists in overfilling the guiding pattern cavities with a thick BCP film, followed by a plasma etch-back step. This new approach ensures a uniform control of the final thickness of the BCP inside guiding cavities of different densities, as demonstrated herein by AFM measurement. Thus, defect-free isolated and dense patterns for both contact shrink and multiplication are simultaneously resolved. Furthermore, the simulation results of BCP self-assembly overfilling the templates demonstrate that BCP domains are well-directed in vertical cylinders ordering inside guiding cavities, which confirms the experimental results and the viability of this approach. Uniform block copolymer (BCP) thickness over template density is achieved using a new and simple graphoepitaxy process flow called “directed self-assembly (DSA) planarization.” Simulations and SEM characterizations of BCP self-assembly overfilling the guiding patterns confirm the viability of this approach. Experimental results demonstrate the enhancement of DSA performances when using the DSA planarization flow.



Enhanced Piezoelectric Performance of Electrospun Polyvinylidene Fluoride Doped with Inorganic Salts

2017-09-13T13:30:53.02638-05:00

A novel approach to preparing electrospun polyvinylidene fluoride (PVDF) nanofibers is proposed, with high piezoelectric performance. PVDF nanofibers are doped with inorganic salts without the use of any postpolarization treatment. Twenty-six salts are doped into the nanofibers and their piezoelectric properties are studied. The salts are classified into three groups based on their differing piezoelectric enhancement effects. A piezoelectric nanogenerator fabricated with an optimized electrospun PVDF nanofiber mat shows a piezovoltage seven times greater than that of a device based on undoped nanofibers. The simple and low-cost approach to fabricate these piezoelectric nanofiber mats may broaden the range of industrial applications of these materials in energy-harvesting devices and portable sensors. The piezoelectric performance of electrospun polyvinylidene fluoride nanofiber piezoelectric nanogenerators is increased obviously by doping inorganic salts. This simple and low-cost approach may open the way for new applications of miniature energy-harvesting devices.



Biodegradable Inorganic–Organic POSS–PEG Hybrid Hydrogels as Scaffolds for Tissue Engineering

2017-09-20T03:16:09.516814-05:00

Biodegradable hydrogels have attracted much attention in tissue engineering due to their good biocompatibility and elastomeric behavior. In this work, a series of inorganic–organic polyhedral oligomeric silsequioxanes–poly(ethylene glycol) (POSS–PEG) hybrid hydrogels are prepared by covalently grafting POSS into PEG and further cross-linked by matrix metalloproteinase (MMP) degradable peptide via Michael-type addition polymerization. All the POSS–PEG hybrid hydrogels have a porous structure and high hydrophilic ability, and the grafted hydrophobic POSS macromers result in a higher mechanical properties and lower equilibrium swelling ratio. Additionally, the hydrogels can be biodegraded by MMP-2 solution and the POSS loading level can influence the degradation rate. It is worth mentioning that POSS-containing hybrid hydrogels can be prepared in water and be used for 3D cell culture. In vitro cell viability study on human umbilical vein endothelial cells for 3D cell culture indicates POSS–PEG hydrogels have good compatibility. All of these results suggest that these POSS–PEG hybrid hydrogels exhibit the potential for tissue engineering scaffolds. A series of inorganic–organic polyhedral oligomeric silsequioxanes–poly(ethylene glycol) (POSS–PEG) hybrid hydrogels are prepared in water by covalently grafting POSS into PEG and further cross-linked by matrix metalloproteinase degradable peptide via Michael-type addition. All POSS–PEG hybrid hydrogels have a porous structure, high mechanical properties and hydrophilic ability, good biodegradability and biocompatibility.



Surface Modification of Electrospun TPU Nanofiber Scaffold with CNF Particles by Ultrasound-Assisted Technique for Tissue Engineering

2017-09-13T13:29:41.210776-05:00

A straightforward, fast, and versatile technique is developed to fabricate nanofibrous scaffold with excellent hydrophilicity, mechanical properties, and biocompatibility for tissue engineering. The thermoplastic polyurethane (TPU) nanofiber is fabricated by utilizing electrospinning, and then its surface is modified through simply immersing it into cellulose nanofibrils (CNF) dispersion and subjecting to ultrasonication. The results show that the CNF particles are successfully absorbed on the surface of TPU nanofiber. By introducing CNF particles on the surface of TPU nanofiber, the hydrophilicity, mechanical properties of fabricated CNF-absorbed TPU scaffold are significantly increased. Additionally, the adhesion and proliferation of human umbilical vein endothelial cells cultured on CNF-absorbed TPU scaffold are prominently enhanced in comparison with those of cultured on TPU scaffold. These findings suggest that the ultrasound-assisted technique opens up a new way to simply and effectively modify the surface of various scaffolds and the modified scaffold could be shown a great potential in tissue engineering. A novel method is developed to modify the surface of thermoplastic polyurethane (TPU) nanofiber with cellulose nanofibril (CNF) particles. CNF particles are successfully used as a modifier to improve the hydrophilicity, water retention ratio, mechanical property and biocompatibility of TPU scaffold. These finding suggest that the ultrasound-assisted technique opens up a new way to simply modify the scaffold surface.



Epoxy-Based Azopolymers with Enhanced Photoresponsive Properties Obtained by Cationic Homopolymerization

2017-09-22T01:00:29.251378-05:00

Azopolymers are highly versatile materials due to their unique photoresponsive properties. In this contribution, a novel azo-modified epoxy network is synthesized by cationic homopolymerization with boron trifluoride monoethylamine (BF3.MEA) complex as initiator. The effect of the addition of a fixed content of amino-functionalized azo chromophore, Disperse Orange 3, into the polymer matrix is studied in detail. First of all, the thermal curing cycle is optimized by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) measurements. Then, the resulting bulk azo-modified epoxy networks are characterized by means of thermogravimetric analysis (TGA), FTIR, DSC, UV–vis spectroscopy, and rheological measurements. Finally, the optical response of thin films of these materials is determined. The results evidence that azo-modified epoxy networks obtained by cationic polymerization with optimized curing cycle display high Tg values, high maximum photoinduced birefringence, fast writing speed, and exceptionally high remnant anisotropy. Therefore, this material is a promising candidate to be used for optical storage applications. A new type of azo-modified epoxy network has been prepared by the way of cationic homopolymerization with boron trifluoride monoethylamine (BF3·MEA) complex as initiator. The resulting networks are promising materials for optical storage applications.



A Novel NIR Laser Switched Nanocomposite Hydrogel as Remote Stimuli Smart Valve

2017-09-22T01:08:06.975761-05:00

Thermosensitive nanocomposite (NC) hydrogels are considered as a significant kind of intelligent material to be utilized as sensor, biomaterial, drug carrier, etc. Recently, preparation of remotely controlled NC hydrogel with high-performance attracts more and more concern. To produce facile remote-stimuli thermosensitive NC hydrogel, a novel near-infrared (NIR) laser switched CuS/clay/poly(OEGMA-co-MEO2MA) hydrogel is demonstrated, which can be precisely remote-stimulated by NIR irradiation based on the excellent NIR photothermal conversion property of CuS nanoparticle. The temperature change of hydrogel is related to the NIR intensity, CuS content, and crosslinking density. Moreover, the influences on dimensional variation of hydrogel on macroscale are systematically studied, and the hydrogel as smart liquid valve is further utilized which can be remotely controlled by NIR switch on/off successfully. Cyclic test illustrates that this novel CuS/clay/poly(OEGMA-co-MEO2MA) hydrogel exhibits stable cyclic volume transition property which has promising applications in the areas of sensors, valves, and intelligent switches. To produce facile remote-stimuli thermosensitive nanocomposite hydrogel, a novel near-infrared (NIR) laser switched CuS/clay/poly(OEGMA-co-MEO2MA) hydrogel is fabricated. The temperature change and dimensional variation of hydrogel are related to the NIR intensity, CuS content, and crosslinking density. The hydrogel can be utilized as smart liquid valve, which can be remotely controlled by NIR switch on/off successfully.



Influence of Annealing on Mechanical αc-Relaxation of Isotactic Polypropylene: A Study from the Intermediate Phase Perspective

2017-09-05T12:00:49.478877-05:00

The influence of annealing on mechanical αc-relaxation of isotactic polypropylene (iPP) is investigated. In the sample without annealing, polymer chains in the intermediate phase are constrained by crystallites with a broad size distribution, leading to one αc-relaxation peak with activation energy (Ea) of 53.39 kJ mol−1. With an annealing temperature between 60 and 105 °C imperfect lamellae melting releases a part of the constraining force. Consequently, two αc-relaxation peaks can be observed (αc1- and αc2-relaxation in the order of increasing temperature). Both relaxation peaks shift to higher temperatures as annealing temperature increases. Ea of αc1-relaxation decreases from 38.43 to 35.55 kJ mol−1 as the intermediate phase thickness increases from 2.0 to 2.2 nm. With an annealing temperature higher than 105 °C, a new crystalline phase is formed, which enhances the constraining force on the polymer chains. So the αc1-relaxation peak is broadened and its position shifts to a higher temperature. Moreover, the polymer chains between the initial and the newly formed crystalline phase are strongly confined. Therefore, the αc2-relaxation is undetectable. Ea of αc1-relaxation decreases from 23.58 to 13.68 kJ mol−1 as the intermediate phase thickness increases from 2.3 to 3.0 nm. Mechanical αc-relaxation of isotactic polypropylene can be greatly influenced by the constraint force on polymer chains in the intermediate phase. Imperfect lamellae melting caused by annealing leads to a nonhomogeneous intermediate phase, giving rise to two mechanical αc-relaxation. Lamellae thickening enhance the constraint force on polymer chains in the intermediate phase, resulting in an increase of the mechanical αc-relaxation temperature.



Oil–Water Separation Using Superhydrophobic PET Membranes Fabricated Via Simple Dip-Coating Of PDMS–SiO2 Nanoparticles

2017-08-17T07:37:11.110984-05:00

The surfaces of commercially available polyester (PET) and polypropylene (PP) are superhydrophobically modified via the deposition of polydimethylsiloxane (PDMS)-coated SiO2 nanoparticles (P-SiO2) and PDMS binder. The adhesion of P-SiO2 is stronger on PET than on PP due to a stronger chemical interaction between PET and PDMS, which is attributed to the higher surface energy of PET than PP. The waterproof ability and oil separation rate of the P-SiO2-coated PET (dip-PET) membranes are studied as a function of membrane thickness, and the influence of oil viscosity on the oil separation efficiency is investigated. Optimal membrane thickness should be selected in a given environment for the facile oil–water separation and the dip-PET membrane is chemically stable and can be used repetitively for oil–water separation. Finally, an automated prototype instrument is introduced for the dip-coating process. It is suggested that our dip-PET is a promising solution for oil–water separation in real-world oil-spill applications. Superhydrophobically modified polyester (dip-PET) via the deposition of polydimethylsiloxane (PDMS)-coated SiO2 nanoparticles (P-SiO2) using a simple dip-coating method is reported. The equipment consisting of the dip-PET membrane for selective oil-capturing from the water–oil mixture is displayed and an automated prototype instrument for the hydrophobic dip-coating of the fabric samples is demonstrated.



Flexible Polysaccharide Hydrogel with pH-Regulated Recovery of Self-Healing and Mechanical Properties

2017-08-01T01:01:59.290697-05:00

A self-healable hydrogel with recoverable self-healing and mechanical properties is reported. The hydrogel (coded as ACSH) crosslinked by Schiff base linkage contains two polysaccharides of acrylamide-modified chitosan (AMCS) and oxidized alginate (ADA). Self-healing and mechanical properties are heavily influenced by the crosslinking time. The hydrogel crosslinked for 2 h possesses better mechanical and self-healing properties than hydrogel crosslinked for 24 h. Macroscopic test shows that hydrogel without self-healing ability can recover the self-repair and mechanical properties by adjusting the pHs. The recovery of self-healing and mechanical properties relies on the pH sensitivity of the Schiff base linkage. Adjusting the pH to acid, the Schiff base linkage becomes unstable and breaks. Regulating the pH to neutral, reconstruction of Schiff base linkage leads to recovery of the self-repair and mechanical properties. The recoverable self-healing property can be cycled once breakage and reconstruction of the Schiff base linkage can be conducted. In addition, this study demonstrates that the hydrogel can be remodeled into different shapes based on self-healing property of the hydrogel. It is anticipated that this self-healable hydrogel with recoverable self-healing and mechanical properties may open a new way to investigate self-healing hydrogel and find potential applications in different biomedical fields. A flexible biopolymeric hydrogel with recoverable self-healing and mechanical properties is developed. The hydrogel crosslinked by Schiff base linkage contains two polysaccharides of acrylamide-modified chitosan and oxidized alginate. Circular recovery of self-healing and mechanical properties can be realized by adjusting the pHs.