Superabsorbent hydrogel nanocomposites (SHN) with semi‐interpenetrating polymer network (semi‐IPN) are synthesized by the polymerization of acrylamide monomer in a polyethylene glycol aqueous solution in the presence of the octadecylamine (ODA)‐modified graphene oxide (GO‐ODA) nanosheets. The hydrogel composites are characterized by Fourier transform infrared spectroscopy, thermal gravity analysis, and scanning electron microscopy. The water absorbency of the resulting SHN in distilled water and saline solutions are measured. The results show that doping GO‐ODA nanosheets into hydrogel semi‐IPN would enhance both their salt resistance and water retention. Using a simple freezing‐dry method, porous SHN with macroscopically interconnected pores is prepared, which exhibits excellent separation ability for removal of trace water from oils. Based on their better water absorbency, salt resistance, and excellent oil/water separation ability, the resulting SHN has great potentials in a wide range of applications, for example, oil dehydration, absorption, and separation.
Silicone materials are widely used in many fields such as electrical or food industries and their consumption is constantly growing. They are generally cured by vulcanization reaction for long time at high temperatures which requires high energy consumption. The possibility to achieve the polymerization of silicone rubbers by UV‐activation promotes the reduction of both time and temperature leading to an impressive energy saving. Indeed, this process is more than 30 times faster than the thermal one. Moreover, the properties of the two resulting materials are comparable, indicating that the low time of UV‐activated hydrosilation reaction is suitable for the formation of crosslinked silicone polymers.
Graphene has resulted in significant research effort to generate polymer nanocomposites with improved mechanical, thermal as electrical properties as compared to pure polymers. A large number of studies have been undertaken using different graphene derivatives, filler loadings, synthesis methods, and so on to obtain optimum filler dispersion as well as filler–matrix interactions, which are crucial for achieving significant enhancement in the properties, especially at low filler fraction. This review summarizes the mechanical and thermal properties of numerous studies carried out for the property enhancements of commercially relevant thermosetting materials such as epoxy, polyurethane, natural rubber, melamine formaldehyde, phenol formaldehyde, silicones, vinyl ester, cyanate ester, and unsaturated polyester resin.
Preparation of novel nanocomposite hydrogels opens up new avenues to next generation of biocompatible materials to be used in bioengineering and drug delivery. Toward this goal, chitosan nanocomposite hydrogels using click chemistry inspired cross‐linking are prepared. To enable this, Diels–Alder reaction of furan‐containing chitosan and maleimide‐coated gold nanoparticles is employed. The viscoelastic properties of the obtained nanocomposites as well as the effect of the nanoparticles as cross‐linkers are studied, indicating that they play significant role in hydrogel formation and stability. Nanoparticle‐enriched hydrogels are also found to demonstrate pH‐sensitivity therefore showing their potential for future biosensing applications.
This study describes novel and simple conditions for the fabrication of collagen microfibers with specific physical and mechanical properties, which can then be potentially applied as cell‐based matrices. The microfibers are fabricated from collagen hydrogels, using various concentrations of ethanol, in ethanol–water solvents. At higher ethanol concentration, fibers exhibited increased uniformity of surface morphology, decreased diameter, and increased tensile strength. The morphology of cells on microfibers varies due to the surface morphology of microfibers but the microfibers fabricated under all conditions investigated show similar number of attached cells on the surface of fibers, and cells sustain their viability for 90 h.
The fabrication of asymmetric polymer membranes via vapor phase deposition is demonstrated. In this solventless process, the dense layer is deposited first and then the porous layer is subsequently deposited onto the dense layer. A variety of functional polymer membranes can be produced by varying the precursor molecules. The functionality of the dense and porous layers can be independently tailored to be either hydrophobic or hydrophilic, resulting in membranes that are fully hydrophilic, fully hydrophobic, or asymmetric in both structure and chemical functionality. The thickness of both the porous and dense layers can be separately tuned by controlling the deposition time.
Five new urethane groups containing monomers 1 – 5 , acetylated glycerol dimethacrylate (AGDMA), and glycerol trimethacrylate (GTMA) are synthesized as alternative diluents to triethylene glycol dimethacrylate (TEGDMA) for dental resins or composites. The synthesized monomers are characterized by means of 1H NMR, 13C NMR, and IR spectroscopy. The secondary acrylamide group containing hybrid monomers 1 and 2 are solids. However, the monomers 3 – 5 , AGDMA and GTMA are colorless and relatively low‐viscosity liquids. They are not mutagenic in the Ames test and show a lower cytotoxicity and a lower polymerization shrinkage compared to TEGDMA. The tertiary amide group containing crosslinker 3 shows a significantly higher photopolymerization rate compared to that of TEGDMA in the presence of the monomolecular Ge‐based photoinitiator Ivocerin. The synthesized diluents are evaluated in experimental dental formulations for resins, cements, and direct filling composites using a conventional binary camphorquinone/amine photoinitiator.
Detection methods for heavy metals are important and highly required due to their toxicity to the health of humans and the environment. Hence, using a polydiacetylene (PDA)‐based sensoring bead, the presence of barium ions is exclusively detected for the first time. The sensoring platform has been designed as a PDA vesicle functionalized with a succinoglycan octasaccharide subunit serving as a metal coordination ligand. First, the succinoglycan octasaccahride subunit is isolated from Sinorhizobium meliloti, successfully conjugated to pentacosa‐10,12‐diynoic acid via reductive amination, and the functionalized vesicle system is investigated for color and fluorescence changes targeting nine different metal ions. To further improve the long‐term storage stability and convenient handling of the vesicle detection system, the sensory vesicle is immobilized on millimeter‐sized alginate beads through the ionotropic gelation method. This study provides an opportunity to design and develop various carbohydrate‐based sensor materials.
The mechanical properties and microstructure of injection molded isotactic polypropylene parts with high orientation before and after annealing are analyzed. The mechanical properties of the annealed samples are improved effectively. Through thorough analysis of various structural characterizations, a microstructural model based on the fact that the total length of long period kept constant to analyze the variation of mechanical properties is proposed. It is suggested that the increase of overall crystallinity, the recombination of crystalline phase, and the increase of amorphous phase, respectively, are beneficial for the improvements of the strength, stiffness, and toughness of annealed samples.
A novel route to lignin epoxy composites is developed through covalent incorporation of depolymerized lignin epoxide into amine‐cured epoxy matrix. The partially depolymerized lignin is first epoxidized with epichlorohydrin and the resultant depolymerized lignin epoxide shows decreased solubility in common organic solvents. When dispersed in epoxy matrix and cured, the depolymerized lignin epoxide is integrated into epoxy networks in the form of submicron aggregates. The resulting lignin epoxy composites show improved mechanical properties compared with neat epoxy. At a loading content of 1.0 wt% of degraded lignin epoxide, the Young's modulus and the critical stress intensity factor (KIC) of the composite increase by 10% and 25%, respectively, in comparison with those of neat epoxy, while the glass transition temperature is little changed. This method presents a promising way to convert wasteful lignin to an alternative epoxy monomer and effective additive in epoxy composites.
Most insect eyes use microvillar photoreceptors, where the visual pigment rhodopsin is aligned within tubular microvilli, endowing the insects with amazing navigation ability through detecting the polarization of illuminating light in the sky. Herein, polydiacetylene‐polystyrene (PDA‐PS) hybrid microfibers are fabricated by electrospinning method and it is demonstrated that PDA‐PS hybrid microfibers exhibit interesting polarized waveguiding properties, which is found to be dependent on the ordered alignment of PDA chains, but not on the propagating distance or the wavelength of the excitation light. Moreover, three PDA‐PS microfibers with different polarized waveguiding behavior can be assembled together as polarization sensitive photoreceptors to mimic the natural rhabdome arrays in insect eyes, since the physical dimensions, structure, and function of single PDA‐PS microfiber are comparable to that of natural rhabdomere.
In the present study, the covalent bonding of electroconductive cross‐linked hydrogel networks with both electro‐properties and hydrogel characteristics to titanium surfaces via a UV‐initiated radical thiol‐ene click reaction is investigated. The electroconductive hydrogel layers are formed by the electropolymerization of pyrrole within the titanium implant‐supported gelatin methacrylate hydrogel. Characterization of the surface morphology of the layers reveals a unique rough macroporous structure. The hydrogel coating layer on the titanium surfaces possesses the desired characteristics of high electrochemical activity and high mechanical stability due to the effects of the chemical functionalization. Bone mesenchymal stem cells cultured on the hydrogel substrates exhibit high cell viability. This study is the first to demonstrate the potential of an electroconductive hydrogel as a surface coating on titanium implants for cell growth and provides a foundation for the development of new implantable bioelectronic devices.
Pollution control has become increasingly important in recent years. Heavy metal ions, proteins, and dyes are frequently found in wastewater because of their extensive industrial applications. In this study, pH, temperature, and magnetic triple‐responsive poly(N‐isopropylacrylamide‐co‐methacrylic acid) porous microspheres doped with magnetite nanoparticles as a new type of smart adsorbents are used to remove the aforementioned pollutants. The pH‐ and temperature‐responsiveness of these microspheres realizes tunable adsorption toward Cu(II). Simultaneously, the microspheres exhibit good adsorption capability to lysozyme and basic fuchsine. Microsphere‐adsorbing pollutants are easlily separated from wastewater by applying an external magnetic field to reuse the microspheres.
Different carbon‐based fillers such as carbon nanotubes (CNTs), graphite, and thermally reduced graphene oxide (TrGO) are melt mixed with an isotactic poly(propylene) (iPP) and the mechanical properties of the resulting composites in the solid and melt state are analyzed. The Young's modulus of composites is increased around 25% relative to the neat iPP at concentrations above 10 wt% of CNTs or graphite whereas composites with TrGO are increased around 40% at similar concentrations. These results are compared with theoretical models showing that the filler agglomeration and surface area are key parameters. The rheological results of the composites under oscillatory shear conditions at the melt state show that the viscous raw polymer melt experiences a solid‐like transition at a threshold concentration that strongly depends on the filler used. This transition appears at 10 wt% for CNTs, 8 wt% for TrGO, and 40 wt% for graphite. The viscosity of iPP/TrGO composites is further increased by adding CNTs particles, although the Young's modulus does not increase.
Electrospinning of sulfur‐free softwood lignin (SFSL) in N,N‐dimethylformamide (DMF) is reported as is and with poly(ethylene oxide) (PEO). SFSL macromolecules behave as rigid spheres, instead of free draining macromolecules in DMF. Hence they are investigated as colloids. Colloidal SFSL generates uniform fibers only at the volume fraction of 0.63. It is due to the sufficiently high longest mean relaxation time at the volume fraction of 0.63. Colloidal SFSL below the volume fraction of 0.63 does not exhibit any measurable viscoelasticity and also does not generate any uniform fibers. Bead‐free fibers are generated at volume fractions below 0.63 only by adding PEO. PEO presence brings elasticity to colloidal SFSL and produces bead‐free fibers only above the entanglement concentration of PEO in DMF. The presence of SFSL macromolecules does not cause any interactions with PEO molecules, except it reduces the available of free volume for PEO chains in DMF.
A simple method of preparing stimuli‐responsive polystyrene (PS)/polycaprolactone (PCL) nanolayered films with by growing poly(N‐isopropylacrylamide) (PNIPAM) brush on the surface by surface‐initiated polymerization is reported. Atom transfer radical polymerization (ATRP) initiator with a benzophenone moiety is attached onto the surface by UV irradiation. After ATRP polymerization, PNIPAM brush films with varying thicknesses are produced. X‐ray photoelectron spectroscopy (XPS) confirms the successful deposition of initiator and grafting of the polymer. Moreover, the behavior of the brush film as a function of temperature is demonstrated by contact angle experiments. Photopatterning is also achieved by using a photomask and is confirmed by Fourier Transform Infrared (FTIR) imaging.
Porous polymer materials prepared from biodegradable polymers have received considerable attention due to their potential as cell culture scaffolds for tissue engineering. Porous materials are generally sterilized by autoclaving prior to use as cell culture scaffolds to avoid unexpected biological infection. However, the melting point of biodegradable polymers is typically lower than the temperature used in autoclave sterilization. Here, the preparation of honeycomb films comprising a poly(L‐lactic acid) (PLLA) and poly(D‐lactic acid) (PDLA) stereo complex is described and their thermal stabilities are evaluated. The hierarchic photochemical patterning of PLLA/PDLA stereo complex honeycomb‐patterned films by UV‐O3 treatment is also demonstrated.
In this study, polyamide 6/polystyrene in situ microfibrillar blends are prepared via anionic polymerization of ε‐caprolactam in a twin screw extruder. Scanning electron microscope analysis reveals that microfibrillated PA6 dispersed phase, which is continuous and preferentially oriented parallel to the extrusion direction, is in situ formed within polystyrene (PS) matrix during reactive extrusion at the content PS equal to 30 and 40 wt%. Mechanical properties analysis shows that the yield strength and elongation at break of PA6/PS (70/30 and 60/40) microfibrillar blends are remarkably increased with respect to those of pure PS. Also, the in situ fibrillation mechanisms are investigated by the analysis of morphological evolution. This work demonstrates a facile and efficient route to fabricate the microfibrillar blends with relatively high contents of polymer microfibrils.
Suitable membranes for blood‐contacting medical applications need to be resistant in confrontation with blood proteins and cells, while possessing high blood compatibility and permeability at the same time. Herein, an overview of the recent advances and strategies that have been used to enhance the hemocompatibility of polymeric membranes is provided. The review focuses on two modification strategies: (i) physical modifications and (ii) chemical modifications. It also highlights the current progress in the design of hemocompatible‐functionalized membranes for biomedical applications. Subsequently, the commonly applied biocompatibility tests are also discussed and finally the future perspectives of the application of polymeric membranes in the biomedical field are presented.
A 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO)‐triazine based anhydride (2,4,6‐tris‐(DOPO‐methylformatephthalic anhydride‐phenoxy)‐1,3,5‐triazine (TDA)) is synthesized and used as a halogen‐free flame retardant co‐curing agent for diglycidyl ether of bisphenol A/methylhexahydrophthalic anhydride (DGEBA/MHHPA) system. The conjugation of anhydride group is increased by the utilization of TDA, leading to the reduction in the curing activation energy. The cured epoxy resin passes V‐0 rating of UL 94 test with the limiting oxygen index of 32.7 vol% when the phosphorus content is only 1.5 wt%. The flame‐retarding action of triazine ring and DOPO moiety is investigated by the residue analysis and the characterization of pyrolysis gas. Due to the presence of bulky aromatic subunits in the molecular structure of TDA, the flame‐retarded epoxy resins maintain the high glass transition temperature of DGEBA/MHHPA. Besides, the moisture absorption is diminished following the usage of TDA.
下载免费PDF全文 